A comparison of the fracture resistance of three machinable ceramics after thermal and mechanical fatigue.

PubMed

Yang, Rui; Arola, Dwayne; Han, Zhihui; Zhang, Xiuyin

2014-10-01

Mechanical and thermal fatigue may affect ceramic restorations in the oral environment. The purpose of this study was to determine the influence of thermal and mechanical cycling on the fracture load and fracture patterns of 3 machinable ceramics. Seventy-two human third molar teeth were prepared for bonding ceramic specimens of Sirona CEREC Blocs, IPS e.maxCAD, or inCoris ZI meso blocks. The 24 specimens of each ceramic were divided into 4 groups (n=6), which underwent no preloading (control), thermocycling (5°C-55°C, 2000 cycles), mechanical cycling (10(5) cycles, 100 N), and thermocycling (5°C-55°C, 2000 cycles) plus mechanical cycling (10(5) cycles, 100 N). The specimens were subsequently loaded to failure, and both stereomicroscopy and scanning electron microscopy were used to investigate the fracture patterns. The data were analyzed with 2-way ANOVA and the Fisher exact probability test (α=.05). Mechanical and thermal cycling had a significant influence on the critical load to failure of the 3 ceramics. No significant difference was found between mechanical cycling for 10(5) times and thermocycling for 2000 times within the same ceramic. The specimens of inCoris ZI experienced significantly higher fracture loads for all the groups. The fracture patterns of the 3 machinable ceramics showed that failure mainly occurred at the cement-dentin interface. The effects of combined thermal and mechanical cycling on the fracture load of ceramics were more significant than any individual mode of cyclic fatigue. Overall, the inCoris ZI resisted thermal and mechanical fatigue better than the Sirona CEREC and IPS e.maxCAD. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Fractured rock stress-permeability relationships from in situ data and effects of temperature and chemical-mechanical couplings

DOE PAGES

Rutqvist, J.

2014-09-19

The purpose of this paper is to (i) review field data on stress-induced permeability changes in fractured rock; (ii) describe estimation of fractured rock stress-permeability relationships through model calibration against such field data; and (iii) discuss observations of temperature and chemically mediated fracture closure and its effect on fractured rock permeability. The field data that are reviewed include in situ block experiments, excavation-induced changes in permeability around tunnels, borehole injection experiments, depth (and stress) dependent permeability, and permeability changes associated with a large-scale rock-mass heating experiment. Data show how the stress-permeability relationship of fractured rock very much depends on localmore » in situ conditions, such as fracture shear offset and fracture infilling by mineral precipitation. Field and laboratory experiments involving temperature have shown significant temperature-driven fracture closure even under constant stress. Such temperature-driven fracture closure has been described as thermal overclosure and relates to better fitting of opposing fracture surfaces at high temperatures, or is attributed to chemically mediated fracture closure related to pressure solution (and compaction) of stressed fracture surface asperities. Back-calculated stress-permeability relationships from field data may implicitly account for such effects, but the relative contribution of purely thermal-mechanical and chemically mediated changes is difficult to isolate. Therefore, it is concluded that further laboratory and in situ experiments are needed to increase the knowledge of the true mechanisms behind thermally driven fracture closure, and to further assess the importance of chemical-mechanical coupling for the long-term evolution of fractured rock permeability.« less

Fractured rock stress-permeability relationships from in situ data and effects of temperature and chemical-mechanical couplings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rutqvist, J.

The purpose of this paper is to (i) review field data on stress-induced permeability changes in fractured rock; (ii) describe estimation of fractured rock stress-permeability relationships through model calibration against such field data; and (iii) discuss observations of temperature and chemically mediated fracture closure and its effect on fractured rock permeability. The field data that are reviewed include in situ block experiments, excavation-induced changes in permeability around tunnels, borehole injection experiments, depth (and stress) dependent permeability, and permeability changes associated with a large-scale rock-mass heating experiment. Data show how the stress-permeability relationship of fractured rock very much depends on localmore » in situ conditions, such as fracture shear offset and fracture infilling by mineral precipitation. Field and laboratory experiments involving temperature have shown significant temperature-driven fracture closure even under constant stress. Such temperature-driven fracture closure has been described as thermal overclosure and relates to better fitting of opposing fracture surfaces at high temperatures, or is attributed to chemically mediated fracture closure related to pressure solution (and compaction) of stressed fracture surface asperities. Back-calculated stress-permeability relationships from field data may implicitly account for such effects, but the relative contribution of purely thermal-mechanical and chemically mediated changes is difficult to isolate. Therefore, it is concluded that further laboratory and in situ experiments are needed to increase the knowledge of the true mechanisms behind thermally driven fracture closure, and to further assess the importance of chemical-mechanical coupling for the long-term evolution of fractured rock permeability.« less

Numerical modeling of thermal conductive heating in fractured bedrock.

PubMed

Baston, Daniel P; Falta, Ronald W; Kueper, Bernard H

2010-01-01

Numerical modeling was employed to study the performance of thermal conductive heating (TCH) in fractured shale under a variety of hydrogeological conditions. Model results show that groundwater flow in fractures does not significantly affect the minimum treatment zone temperature, except near the beginning of heating or when groundwater influx is high. However, fracture and rock matrix properties can significantly influence the time necessary to remove all liquid water (i.e., reach superheated steam conditions) in the treatment area. Low matrix permeability, high matrix porosity, and wide fracture spacing can contribute to boiling point elevation in the rock matrix. Consequently, knowledge of these properties is important for the estimation of treatment times. Because of the variability in boiling point throughout a fractured rock treatment zone and the absence of a well-defined constant temperature boiling plateau in the rock matrix, it may be difficult to monitor the progress of thermal treatment using temperature measurements alone. Copyright © 2010 The Author(s). Journal compilation © 2010 National Ground Water Association.

Thermal shock resistance of ceramic matrix composites

NASA Technical Reports Server (NTRS)

Carper, D. M.; Nied, H. F.

1993-01-01

The experimental and analytical investigation of the thermal shock phenomena in ceramic matrix composites is detailed. The composite systems examined were oxide-based, consisting of an aluminosilicate matrix with either polycrystalline aluminosilicate or single crystal alumina fiber reinforcement. The program was divided into three technical tasks; baseline mechanical properties, thermal shock modeling, and thermal shock testing. The analytical investigation focused on the development of simple expressions for transient thermal stresses induced during thermal shock. The effect of various material parameters, including thermal conductivity, elastic modulus, and thermal expansion, were examined analytically for their effect on thermal shock performance. Using a simple maximum stress criteria for each constituent, it was observed that fiber fracture would occur only at the most extreme thermal shock conditions and that matrix fracture, splitting parallel to the reinforcing fiber, was to be expected for most practical cases. Thermal shock resistance for the two material systems was determined experimentally by subjecting plates to sudden changes in temperature on one surface while maintaining the opposite surface at a constant temperature. This temperature change was varied in severity (magnitude) and in number of shocks applied to a given sample. The results showed that for the most severe conditions examined that only surface matrix fracture was present with no observable fiber fracture. The impact of this damage on material performance was limited to the matrix dominated properties only. Specifically, compression strength was observed to decrease by as much as 50 percent from the measured baseline.

Recovery Act. Development and Validation of an Advanced Stimulation Prediction Model for Enhanced Geothermal System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gutierrez, Marte

The research project aims to develop and validate an advanced computer model that can be used in the planning and design of stimulation techniques to create engineered reservoirs for Enhanced Geothermal Systems. The specific objectives of the proposal are to: 1) Develop a true three-dimensional hydro-thermal fracturing simulator that is particularly suited for EGS reservoir creation. 2) Perform laboratory scale model tests of hydraulic fracturing and proppant flow/transport using a polyaxial loading device, and use the laboratory results to test and validate the 3D simulator. 3) Perform discrete element/particulate modeling of proppant transport in hydraulic fractures, and use the resultsmore » to improve understand of proppant flow and transport. 4) Test and validate the 3D hydro-thermal fracturing simulator against case histories of EGS energy production. 5) Develop a plan to commercialize the 3D fracturing and proppant flow/transport simulator. The project is expected to yield several specific results and benefits. Major technical products from the proposal include: 1) A true-3D hydro-thermal fracturing computer code that is particularly suited to EGS, 2) Documented results of scale model tests on hydro-thermal fracturing and fracture propping in an analogue crystalline rock, 3) Documented procedures and results of discrete element/particulate modeling of flow and transport of proppants for EGS applications, and 4) Database of monitoring data, with focus of Acoustic Emissions (AE) from lab scale modeling and field case histories of EGS reservoir creation.« less

Recovery Act. Development and Validation of an Advanced Stimulation Prediction Model for Enhanced Geothermal Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gutierrez, Marte

2013-12-31

This research project aims to develop and validate an advanced computer model that can be used in the planning and design of stimulation techniques to create engineered reservoirs for Enhanced Geothermal Systems. The specific objectives of the proposal are to; Develop a true three-dimensional hydro-thermal fracturing simulator that is particularly suited for EGS reservoir creation; Perform laboratory scale model tests of hydraulic fracturing and proppant flow/transport using a polyaxial loading device, and use the laboratory results to test and validate the 3D simulator; Perform discrete element/particulate modeling of proppant transport in hydraulic fractures, and use the results to improve understandmore » of proppant flow and transport; Test and validate the 3D hydro-thermal fracturing simulator against case histories of EGS energy production; and Develop a plan to commercialize the 3D fracturing and proppant flow/transport simulator. The project is expected to yield several specific results and benefits. Major technical products from the proposal include; A true-3D hydro-thermal fracturing computer code that is particularly suited to EGS; Documented results of scale model tests on hydro-thermal fracturing and fracture propping in an analogue crystalline rock; Documented procedures and results of discrete element/particulate modeling of flow and transport of proppants for EGS applications; and Database of monitoring data, with focus of Acoustic Emissions (AE) from lab scale modeling and field case histories of EGS reservoir creation.« less

Probabilistic thermal-shock strength testing using infrared imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wereszczak, A.A.; Scheidt, R.A.; Ferber, M.K.

1999-12-01

A thermal-shock strength-testing technique has been developed that uses a high-resolution, high-temperature infrared camera to capture a specimen's surface temperature distribution at fracture. Aluminum nitride (AlN) substrates are thermally shocked to fracture to demonstrate the technique. The surface temperature distribution for each test and AlN's thermal expansion are used as input in a finite-element model to determine the thermal-shock strength for each specimen. An uncensored thermal-shock strength Weibull distribution is then determined. The test and analysis algorithm show promise as a means to characterize thermal shock strength of ceramic materials.

Thermally induced fracture for core-veneered dental ceramic structures.

PubMed

Zhang, Zhongpu; Guazzato, Massimiliano; Sornsuwan, Tanapon; Scherrer, Susanne S; Rungsiyakull, Chaiy; Li, Wei; Swain, Michael V; Li, Qing

2013-09-01

Effective and reliable clinical uses of dental ceramics necessitate an insightful analysis of the fracture behaviour under critical conditions. To better understand failure characteristics of porcelain veneered to zirconia core ceramic structures, thermally induced cracking during the cooling phase of fabrication is studied here by using the extended finite element method (XFEM). In this study, a transient thermal analysis of cooling is conducted first to determine the temperature distributions. The time-dependent temperature field is then imported to the XFEM model for viscoelastic thermomechanical analysis, which predicts thermally induced damage and cracking at different time steps. Temperature-dependent material properties are used in both transient thermal and thermomechanical analyses. Three typical ceramic structures are considered in this paper, namely bi-layered spheres, squat cylinders and dental crowns with thickness ratios of either 1:2 or 1:1. The XFEM fracture patterns exhibit good agreement with clinical observation and the in vitro experimental results obtained from scanning electron microscopy characterization. The study reveals that fast cooling can lead to thermal fracture of these different bi-layered ceramic structures, and cooling rate (in terms of heat transfer coefficient) plays a critical role in crack initiation and propagation. By exploring different cooling rates, the heat transfer coefficient thresholds of fracture are determined for different structures, which are of clear clinical implication. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Natural thermal convection in fractured porous media

NASA Astrophysics Data System (ADS)

Adler, P. M.; Mezon, C.; Mourzenko, V.; Thovert, J. F.; Antoine, R.; Finizola, A.

2015-12-01

In the crust, fractures/faults can provide preferential pathways for fluid flow or act as barriers preventing the flow across these structures. In hydrothermal systems (usually found in fractured rock masses), these discontinuities may play a critical role at various scales, controlling fluid flows and heat transfer. The thermal convection is numerically computed in 3D fluid satured fractured porous media. Fractures are inserted as discrete objects, randomly distributed over a damaged volume, which is a fraction of the total volume. The fluid is assumed to satisfy Darcy's law in the fractures and in the porous medium with exchanges between them. All simulations were made for Rayleigh numbers (Ra) < 150 (hence, the fluid is in thermal equilibrium with the medium), cubic boxes and closed-top conditions. Checks were performed on an unfractured porous medium and the convection cells do start for the theoretical value of Ra, namely 4p². 2D convection was verified up to Ra=800. The influence of parameters such as fracture aperture (or fracture transmissivity), fracture density and fracture length is studied. Moreover, these models are compared to porous media with the same macroscopic permeability. Preliminary results show that the non-uniqueness associated with initial conditions which makes possible either 2D or 3D convection in porous media (Schubert & Straus 1979) is no longer true for fractured porous media (at least for 50

Fracture Toughness of Z3CN20.09M Cast Stainless Steel with Long-Term Thermal Aging

NASA Astrophysics Data System (ADS)

Yu, Weiwei; Yu, Dunji; Gao, Hongbo; Xue, Fei; Chen, Xu

2017-09-01

Accelerated thermal aging tests were performed at 400 °C for nearly 18,000 h on Z3CN20.09M cast stainless steel which was used for primary coolant pipes of nuclear power plants. A series of Charpy impact tests were conducted on Z3CN20.09M after different long-term thermal aging time. The test results indicated that the Charpy impact energy of Z3CN20.09M cast stainless steel decreased rapidly at an early stage and then almost saturated after thermal aging of 10,000 h. Furthermore, J-resistance curves were measured for CT specimens of longitudinal and circumferential pipe orientations. It showed that there was no obvious difference in the fracture characteristics of Z3CN20.09M in different sampling directions. In addition, the observed stretch zone width (SZW) revealed that the value of initiation fracture toughness J SZW was significantly lower than that of fracture toughness J IC, indicating a low actual crack initiation energy due to long-term thermal aging.

Factors influencing the thermally-induced strength degradation of B/Al composites

NASA Technical Reports Server (NTRS)

Dicarlo, J. A.

1982-01-01

Literature data related to the thermally-induced strength degradation of B/Al composites were examined in the light of fracture theories based on reaction-controlled fiber weakening. Under the assumption of a parabolic time-dependent growth for the interfacial reaction product, a Griffith-type fracture model was found to yield simple equations whose predictions were in good agreement with data for boron fiber average strength and for B/Al axial fracture strain. The only variables in these equations were the time and temperature of the thermal exposure and an empirical factor related to fiber surface smoothness prior to composite consolidation. Such variables as fiber diameter and aluminum alloy composition were found to have little influence. The basic and practical implications of the fracture model equations are discussed.

THERMO-HYDRO-MECHANICAL MODELING OF WORKING FLUID INJECTION AND THERMAL ENERGY EXTRACTION IN EGS FRACTURES AND ROCK MATRIX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robert Podgorney; Chuan Lu; Hai Huang

2012-01-01

Development of enhanced geothermal systems (EGS) will require creation of a reservoir of sufficient volume to enable commercial-scale heat transfer from the reservoir rocks to the working fluid. A key assumption associated with reservoir creation/stimulation is that sufficient rock volumes can be hydraulically fractured via both tensile and shear failure, and more importantly by reactivation of naturally existing fractures (by shearing), to create the reservoir. The advancement of EGS greatly depends on our understanding of the dynamics of the intimately coupled rock-fracture-fluid-heat system and our ability to reliably predict how reservoirs behave under stimulation and production. Reliable performance predictions ofmore » EGS reservoirs require accurate and robust modeling for strongly coupled thermal-hydrological-mechanical (THM) processes. Conventionally, these types of problems have been solved using operator-splitting methods, usually by coupling a subsurface flow and heat transport simulators with a solid mechanics simulator via input files. An alternative approach is to solve the system of nonlinear partial differential equations that govern multiphase fluid flow, heat transport, and rock mechanics simultaneously, using a fully coupled, fully implicit solution procedure, in which all solution variables (pressure, enthalpy, and rock displacement fields) are solved simultaneously. This paper describes numerical simulations used to investigate the poro- and thermal- elastic effects of working fluid injection and thermal energy extraction on the properties of the fractures and rock matrix of a hypothetical EGS reservoir, using a novel simulation software FALCON (Podgorney et al., 2011), a finite element based simulator solving fully coupled multiphase fluid flow, heat transport, rock deformation, and fracturing using a global implicit approach. Investigations are also conducted on how these poro- and thermal-elastic effects are related to fracture permeability evolution.« less

Elevated temperature crack growth

NASA Technical Reports Server (NTRS)

Malik, S. N.; Vanstone, R. H.; Kim, K. S.; Laflen, J. H.

1987-01-01

The objective of the Elevated Temperature Crack Growth Program is to evaluate proposed nonlinear fracture mechanics methods for application to hot section components of aircraft gas turbine engines. Progress during the past year included linear-elastic fracture mechanics data reduction on nonlinear crack growth rate data on Alloy 718. The bulk of the analytical work centered on thermal gradient problems and proposed fracture mechanics parameters. Good correlation of thermal gradient experimental displacement data and finite element prediction was obtained.

Fracture resistance of metal-free composite crowns-effects of fiber reinforcement, thermal cycling, and cementation technique.

PubMed

Lehmann, Franziska; Eickemeyer, Grit; Rammelsberg, Peter

2004-09-01

The improved mechanical properties of contemporary composites have resulted in their extensive use for the restoration of posterior teeth. However, the influence of fiber reinforcement, cementation technique, and physical stress on the fracture resistance of metal-free crowns is unknown. This in vitro study evaluated the effect of fiber reinforcement, physical stress, and cementation methods on the fracture resistance of posterior metal-free Sinfony crowns. Ninety-six extracted human third molars received a standardized tooth preparation: 0.5-mm chamfer preparation and occlusal reduction of 1.3 to 1.5 mm. Sinfony (nonreinforced crowns, n=48) and Sinfony-Vectris (reinforced crowns, n=48) crowns restoring original tooth contour were prepared. Twenty-four specimens of each crown type were cemented, using either glass ionomer cement (GIC) or resin cement. Thirty-two crowns (one third) were stored in humidity for 48 hours. Another third was exposed to 10,000 thermal cycles (TC) between 5 degrees C and 55 degrees C. The remaining third was treated with thermal cycling and mechanical loading (TCML), consisting of 1.2 million axial loads of 50 N. The artificial crowns were then vertically loaded with a steel sphere until failure occurred. Significant differences in fracture resistance (N) between experimental groups were assessed by nonparametric Mann-Whitney U-test (alpha=.05). Fifty percent of the Sinfony and Sinfony-Vectris crowns cemented with glass ionomer cement loosened after thermal cycling. Thermal cycling resulted in a significant reduction in the mean fracture resistance for Sinfony crowns cemented with GIC, from 2037 N to 1282 N (P=.004). Additional fatigue produced no further effects. Fiber reinforcement significantly increased fracture resistance, from 1555 N to 2326 N (P=.001). The minimal fracture resistance was above 600 N for all combinations of material, cement and loading. Fracture resistance of metal-free Sinfony crowns was significantly increased by fiber reinforcement. Adhesive cementation may be recommended to avoid cementation failure.

Could the Geminid meteoroid stream be the result of long-term thermal fracture?

NASA Astrophysics Data System (ADS)

Ryabova, G.

2015-01-01

The previous models by Ryabova have shown that the Geminid meteoroid stream has a cometary origin, so asteroid (3200) Phaethon (the Geminids' parent body) is probably a dead comet. Recently (in 2009 and 2012) some weak activity was observed (Jewitt and Li, 2010, 2013), but it was not a cometary activity. Recurrent brightening of Phaethon at perihelion could be the result of thermal fracture and decomposition. In this study we model the long term dust release from Phaethon based on this mechanism. It is unlikely that the Geminid meteoroid stream (or its low-active wide component) was generated by long-time thermal fracture.

Development of an analytical solution for thermal single-well injection-withdrawal tests in horizontally fractured reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, Yoojin

In this study, we have developed an analytical solution for thermal single-well injection-withdrawal tests in horizontally fractured reservoirs where fluid flow through the fracture is radial. The dimensionless forms of the governing equations and the initial and boundary conditions in the radial flow system can be written in a form identical to those in the linear flow system developed by Jung and Pruess [Jung, Y., and K. Pruess (2012), A Closed-Form Analytical Solution for Thermal Single-Well Injection-Withdrawal Tests, Water Resour. Res., 48, W03504, doi:10.1029/2011WR010979], and therefore the analytical solutions developed in Jung and Pruess (2012) can be applied to computemore » the time dependence of temperature recovery at the injection/withdrawal well in a horizontally oriented fracture with radial flow.« less

Factors influencing the thermally-induced strength degradation of B/Al composites

NASA Technical Reports Server (NTRS)

Dicarlo, J. A.

1983-01-01

Literature data related to the thermally-induced strength degradation of B/Al composites were examined in the light of fracture theories based on reaction-controlled fiber weakening. Under the assumption of a parabolic time-dependent growth for the interfacial reaction product, a Griffith-type fracture model was found to yield simple equations whose predictions were in good agreement with data for boron fiber average strength and for B/Al axial fracture strain. The only variables in these equations were the time and temperature of the thermal exposure and an empirical factor related to fiber surface smoothness prior to composite consolidation. Such variables as fiber diameter and aluminum alloy composition were found to have little influence. The basic and practical implications of the fracture model equations are discussed. Previously announced in STAR as N82-24297

Factors affecting the thermal shock behavior of yttria stabilized hafnia based graphite and tungsten composites.

NASA Technical Reports Server (NTRS)

Lineback, L. D.; Manning, C. R.

1971-01-01

Hafnia-based composites containing either graphite or tungsten were investigated as rocket nozzle throat inserts in solid propellant rocket engines. The thermal shock resistance of these materials is considered in terms of macroscopic thermal conductivity, thermal expansion, modulus of elasticity, and compressive fracture stress. The effect of degree of hafnia stabilization, density, and graphite or tungsten content upon these parameters is discussed. The variation of the ratio of elastic modulus to compressive fracture stress with density and its effect upon thermal shock resistance of these materials are discussed in detail.

Thermal convection in three-dimensional fractured porous media

NASA Astrophysics Data System (ADS)

Mezon, C.; Mourzenko, V. V.; Thovert, J.-F.; Antoine, R.; Fontaine, F.; Finizola, A.; Adler, P. M.

2018-01-01

Thermal convection is numerically computed in three-dimensional (3D) fluid saturated isotropically fractured porous media. Fractures are randomly inserted as two-dimensional (2D) convex polygons. Flow is governed by Darcy's 2D and 3D laws in the fractures and in the porous medium, respectively; exchanges take place between these two structures. Results for unfractured porous media are in agreement with known theoretical predictions. The influence of parameters such as the fracture aperture (or fracture transmissivity) and the fracture density on the heat released by the whole system is studied for Rayleigh numbers up to 150 in cubic boxes with closed-top conditions. Then, fractured media are compared to homogeneous porous media with the same macroscopic properties. Three major results could be derived from this study. The behavior of the system, in terms of heat release, is determined as a function of fracture density and fracture transmissivity. First, the increase in the output flux with fracture density is linear over the range of fracture density tested. Second, the increase in output flux as a function of fracture transmissivity shows the importance of percolation. Third, results show that the effective approach is not always valid, and that the mismatch between the full calculations and the effective medium approach depends on the fracture density in a crucial way.

Thermal behavior of crumb-rubber modified asphalt concrete mixtures

NASA Astrophysics Data System (ADS)

Epps, Amy Louise

Thermal cracking is one of the primary forms of distress in asphalt concrete pavements, resulting from either a single drop in temperature to an extreme low or from multiple temperature cycles above the fracture temperature of the asphalt-aggregate mixture. The first mode described is low temperature cracking; the second is thermal fatigue. The addition of crumb-rubber, manufactured from scrap tires, to the binder in asphalt concrete pavements has been suggested to minimize both types of thermal cracking. Four experiments were designed and completed to evaluate the thermal behavior of crumb-rubber modified (CRM) asphalt-aggregate mixtures. Modified and unmodified mixture response to thermal stresses was measured in four laboratory tests. The Thermal Stress Restrained Specimen Test (TSRST) and the Indirect Tensile Test (IDT) were used to compare mixture resistance to low temperature cracking. Modified mixtures showed improved performance, and cooling rate did not affect mixture resistance according to the statistical analysis. Therefore results from tests with faster rates can predict performance under slower field rates. In comparison, predicted fracture temperatures and stresses (IDT) were generally higher than measured values (TSRST). In addition, predicted fracture temperatures from binder test results demonstrated that binder testing alone is not sufficient to evaluate CRM mixtures. Thermal fatigue was explored in the third experiment using conventional load-induced fatigue tests with conditions selected to simulate daily temperature fluctuations. Test results indicated that thermal fatigue may contribute to transverse cracking in asphalt pavements. Both unmodified and modified mixtures had a finite capacity to withstand daily temperature fluctuations coupled with cold temperatures. Modified mixtures again exhibited improved performance. The fourth experiment examined fracture properties of modified and unmodified mixtures using a common fracture toughness test. Results showed no effect from modification, but the small experiment size may have masked this effect. Reliability concepts were introduced to include risk and uncertainty in a comparison of mixture response measured in the laboratory and estimated environmental conditions. This comparison provided evidence that CRM mixtures exhibit improved resistance to both types of thermal cracking at high levels of reliability. In conclusion, a mix design and analysis framework for evaluating thermal behavior was recommended.

Electronics reliability fracture mechanics. Volume 2: Fracture mechanics

NASA Astrophysics Data System (ADS)

Kallis, J.; Duncan, L.; Buechler, D.; Backes, P.; Sandkulla, D.

1992-05-01

This is the second of two volumes. The other volume (WL-TR-92-3015) is 'Causes of Failures of Shop Replaceable Units and Hybrid Microcircuits.' The objective of the Electronics Reliability Fracture Mechanics (ERFM) program was to develop and demonstrate a life prediction technique for electronic assemblies, when subjected to environmental stresses of vibration and thermal cycling, based upon the mechanical properties of the materials and packaging configurations which make up an electronic system. The application of fracture mechanics to microscale phenomena in electronic assemblies was a pioneering research effort. The small scale made the experiments very difficult; for example, the 1-mil-diameter bond wires in microelectronic devices are 1/3 the diameter of a human hair. A number of issues had to be resolved to determine whether a fracture mechanics modelling approach is correct for the selected failures; specifically, the following two issues had to be resolved: What fraction of the lifetime is spent in crack initiation? Are macro fracture mechanics techniques, used in large structures such as bridges, applicable to the tiny structures in electronic equipment? The following structural failure mechanisms were selected for modelling: bondwire fracture from mechanical cycling; bondwire fracture from thermal (power) cycling; plated through hole (PTH) fracture from thermal cycling. The bondwire fracture test specimens were A1-1 percent Si wires, representative of wires used in the parts in the modules selected for detailed investigation in this program (see Vol. 1 of this report); 1-mil-diameter wires were tested in this program. The PTH test specimens were sections of 14-layer printed wiring boards of the type used.

Thermal Drawdown-Induced Flow Channeling in Fractured Geothermal Reservoirs

DOE PAGES

Fu, Pengcheng; Hao, Yue; Walsh, Stuart D. C.; ...

2015-06-30

In this paper, we investigate the flow-channeling phenomenon caused by thermal drawdown in fractured geothermal reservoirs. A discrete fracture network-based, fully coupled thermal–hydrological–mechanical simulator is used to study the interactions between fluid flow, temperature change, and the associated rock deformation. The responses of a number of randomly generated 2D fracture networks that represent a variety of reservoir characteristics are simulated with various injection-production well distances. We find that flow channeling, namely flow concentration in cooled zones, is the inevitable fate of all the scenarios evaluated. We also identify a secondary geomechanical mechanism caused by the anisotropy in thermal stress thatmore » counteracts the primary mechanism of flow channeling. This new mechanism tends, to some extent, to result in a more diffuse flow distribution, although it is generally not strong enough to completely reverse flow channeling. We find that fracture intensity substantially affects the overall hydraulic impedance of the reservoir but increasing fracture intensity generally does not improve heat production performance. Finally, increasing the injection-production well separation appears to be an effective means to prolong the production life of a reservoir.« less

Thermophysics of fractures on comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Höfner, S.; Vincent, J.-B.; Blum, J.; Davidsson, B. J. R.; Sierks, H.; El-Maarry, M. R.; Deller, J.; Hofmann, M.; Hu, X.; Pajola, M.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; Keller, H. U.; A'Hearn, M. F.; Auger, A.-T.; Barucci, M. A.; Bertaux, J.-L.; Bertini, I.; Bodewits, D.; Cremonese, G.; Da Deppo, V.; Debei, S.; De Cecco, M.; Fornasier, S.; Fulle, M.; Gicquel, A.; Groussin, O.; Gutiérrez, P. J.; Gutiérrez-Marqués, P.; Güttler, C.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Knollenberg, J.; Kovacs, G.; Kramm, J.-R.; Kührt, E.; Küppers, M.; La Forgia, F.; Lazzarin, M.; Lopez-Moreno, J. J.; Marzari, F.; Michalik, H.; Moissl-Fraund, R.; Moreno, F.; Mottola, S.; Naletto, G.; Oklay, N.; Preusker, F.; Scholten, F.; Shi, X.; Thomas, N.; Toth, I.; Tubiana, C.; Zitzmann, S.

2017-12-01

Context. The camera OSIRIS on board Rosetta obtained high-resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko (67P). Great parts of the nucleus surface are composed of fractured terrain. Aims: Fracture formation, evolution, and their potential relationship to physical processes that drive activity are not yet fully understood. Observed temperatures and gas production rates can be explained or interpreted with the presence of fractures by applying appropriate modelling methods. Methods: We followed a transient thermophysical model approach that includes radiative, conductive, and water-ice sublimation fluxes by considering a variety of heliocentric distances, illumination conditions, and thermophysical properties for a set of characteristic fracture geometries on the nucleus of 67P. We computed diurnal temperatures, heat fluxes, and outgassing behaviour in order to derive and distinguish the influence of the mentioned parameters on fractured terrain. Results: Our analysis confirms that fractures, as already indicated by former studies about concavities, deviate from flat-terrain topographies with equivalent properties, mostly through the effect of self-heating. Compared to flat terrain, illuminated cometary fractures are generally warmer, with smaller diurnal temperature fluctuations. Maximum sublimation rates reach higher peaks, and dust mantle quenching effects on sublimation rates are weaker. Consequently, the rough structure of the fractured terrain leads to significantly higher inferred surface thermal inertia values than for flat areas with identical physical properties, which might explain the range of measured thermal inertia on 67P. Conclusions: At 3.5 AU heliocentric distance, sublimation heat sinks in fractures converge to maximum values >50 W / m2 and trigger dust activity that can be related mainly to H2O. Fractures are likely to grow through the erosive interplay of alternating sublimation and thermal fatigue.

Insights to Engineered Geothermal System Performance Using Gringarten-Witherspoon-Ohnishi Analytical Solutions and Fracture Network Models

NASA Astrophysics Data System (ADS)

Doe, T.; McLaren, R.; Finilla, A.

2017-12-01

An enduring legacy of Paul Witherspoon and his students and colleagues has been both the development of geothermal energy and the bases of modern fractured-rock hydrogeology. One of the seminal contributions to the geothermal field was Gringarten, Witherspoon, and Ohnishi's analytical models for enhanced geothermal systems. Although discrete fracture network (DFN) modeling developed somewhat independently in the late 1970s, Paul Witherspoon's foresight in promoting underground in situ testing at the Stripa Mine in Sweden was a major driver in Lawrence Berkeley Laboratory's contributions to its development.This presentation looks extensions of Gringarten's analytical model into discrete fracture network modeling as a basis for providing further insights into the challenges and opportunities of engineered geothermal systems. The analytical solution itself has many insightful applications beyond those presented in the original paper. The definition of dimensionless time by itself shows that thermal breakthrough has a second power dependence on surface area and on flow rate. The fracture intensity also plays a strong role, as it both increases the surface area and decrease his flow rate per fracture. The improvement of EGS performance with fracture intensity reaches a limit where thermal depletion of the rock lags only slightly behind the thermal breakthrough of cold water in the fracture network.Simple network models, which couple a DFN generator (FracMan) with a hydrothermally coupled flow solver (HydroGeoSphere) expand on Gringarten's concepts to show that realistic heterogeneity of spacing and transmissivity significantly degrades EGS performance. EGS production in networks of stimulated fractures initially follows Gringarten's type curves, with a later deviation is the smaller rock blocks thermally deplete and the entire stimulated volume acts as a single sink. Three-dimensional models of EGS performance show the critical importance of the relative magnitudes of fluid pressure and stress gradients, preferential growth and aperture enhancement may change with depth creating preferential pathways through rock this cooler than the injection depth.

Influence of the Conditioning Method for Pre-Sintered Zirconia on the Shear Bond Strength of Bilayered Porcelain/Zirconia

PubMed Central

Spintzyk, Sebastian; Yamaguchi, Kikue; Sawada, Tomofumi; Schille, Christine; Schweizer, Ernst; Ozeki, Masahiko; Geis-Gerstorfer, Jürgen

2016-01-01

This study evaluated the bond strength of veneering porcelain with an experimental conditioner-coated zirconia. Pre-sintered Y-TZP specimens (n = 44) were divided in two groups based on conditioning type. After sintering, all sample surfaces were sandblasted and layered with veneering porcelain. Additionally, half of the specimens in each group underwent thermal cycling (10,000 cycles, 5–55 °C), and all shear bond strengths were measured. After testing, the failure mode of each fractured specimen was determined. Differences were tested by parametric and Fisher’s exact tests (α = 0.05). The differences in bond strength were not statistically significant. Adhesive fractures were dominantly observed for the non-thermal cycled specimens. After thermal cycling, the conditioner-coated group showed cohesive and mixed fractures (p = 0.0021), whereas the uncoated group showed more adhesive fractures (p = 0.0021). Conditioning of the pre-sintered Y-TZP did not change the shear bond strength of the veneering porcelain, but did improve the failure mode after thermal cycling. PMID:28773885

Effect of thermal fatigue on the structure and properties of Ni3Al-based alloy single crystals

NASA Astrophysics Data System (ADS)

Povarova, K. B.; Drozdov, A. A.; Bazyleva, O. A.; Bulakhtina, M. A.; Alad'ev, N. A.; Antonova, A. V.; Arginbaeva, E. G.; Morozov, A. E.

2014-05-01

The effect of thermal fatigue during tests of <001> and <111> single crystals according to the schedules 100 ai 850°C, 100 ai 1050°C, 100 ai 1100°C at a peak-to-peak stress Δσtc = 700-1000 MPa (sum of the maximum tensile and compressive stresses in a thermal cycle) on the structure, the fracture, and the fatigue life of an Ni3Al-based VKNA-1V alloy is studied. It is found that, at 103 thermal cycles, the <111> single crystals have the maximum thermal fatigue resistance at the maximum cycle temperature of 850 and 1050°C, and the properties of the <001> and <111> samples are almost the same at the maximum thermal cycle temperature of 1100°C. After thermal cycling at the maximum temperature of 850°C, the γ layers in the two-phase γ' + γ region in dendrites remain a single-phase structure, as in the as-cast material, and the layer thickness is 100-150 nm. When the maximum thermal cycle temperature increases to 1050 or 1100°C, the discontinuous γ-phase layers in the γ'(Ni3Al) matrix change their morphology and become shorter and wider (their thickness is 300-700 nm). The nickel-based supersaturated solid solution in these layers decomposes with the formation of secondary γ'(Ni3Al)-phase (γ'sec) precipitates in the form of cuboids 50 and 100 nm in size at the maximum cycle temperature of 1050 and 1100°C, respectively. The alternating stresses that appear during thermal cycling cause plastic deformation. As in nickel superalloys, this deformation at the first stage proceeds via the slip of screw dislocations along octahedral {111} planes. Networks of 60° dislocation segments form at γ'/γ interfaces in this case. Fracture begins at the lines of intersection of the slip planes of the {111} octahedron with the sample surface. During fractional, a crack passes from one octahedral plane to another and forms terraces and steps (crystallographic fracture); as a result, the fracture surface bends and becomes curved. In all cases, the fracture surfaces have a mixed brittle-ductile character with a combination of crystallographic and ductile (dimple) fracture elements.

Thermal annealing recovery of fracture toughness in HT9 steel after irradation to high doses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Byun, Thak Sang; Baek, Jong-Hyuk; Anderoglu, Osman

2013-08-03

The HT9 ferritic/martensitic steel with a nominal chemistry of Fe(bal.)–12%Cr–1%MoVW has been used as a primary core material for fast fission reactors such as FFTF because of its high resistance to radiationinduced swelling and embrittlement. Both static and dynamic fracture test results have shown that the HT9 steel can become brittle when it is exposed to high dose irradiation at a relatively low temperature 430 °C). This article aims at a comprehensive discussion on the thermal annealing recovery of fracture toughness in the HT9 steel after irradiation up to 3–148 dpa at 378–504 °C. A specimen reuse technique has beenmore » established and applied to this study: the fracture specimens were tested Charpy specimens or broken halves of Charpy bars (13 3 4 mm). The post-anneal fracture test results indicated that much of the radiation-induced damage can be recovered by a simple thermal annealing schedule: the fracture toughness was incompletely recovered by 550 °C annealing, while nearly complete or complete recovery occurred after 650 °C annealing. This indicates that thermal annealing is a feasible damage mitigation technique for the reactor components made of HT9 steel. The partial recovery is probably due to the non-removable microstructural damages such as void or gas bubble formation, elemental segregation and precipitation.« less

Rockfall triggering by cyclic thermal stressing of exfoliation fractures

USGS Publications Warehouse

Collins, Brian D.; Stock, Greg M.

2016-01-01

Exfoliation of rock deteriorates cliffs through the formation and subsequent opening of fractures, which in turn can lead to potentially hazardous rockfalls. Although a number of mechanisms are known to trigger rockfalls, many rockfalls occur during periods when likely triggers such as precipitation, seismic activity and freezing conditions are absent. It has been suggested that these enigmatic rockfalls may occur due to solar heating of rock surfaces, which can cause outward expansion. Here we use data from 3.5 years of field monitoring of an exfoliating granite cliff in Yosemite National Park in California, USA, to assess the magnitude and temporal pattern of thermally induced rock deformation. From a thermodynamic analysis, we find that daily, seasonal and annual temperature variations are sufficient to drive cyclic and cumulative opening of fractures. Application of fracture theory suggests that these changes can lead to further fracture propagation and the consequent detachment of rock. Our data indicate that the warmest times of the day and year are particularly conducive to triggering rockfalls, and that cyclic thermal forcing may enhance the efficacy of other, more typical rockfall triggers.

Scale dependency of fracture energy and estimates thereof via dynamic rupture solutions with strong thermal weakening

NASA Astrophysics Data System (ADS)

Viesca, R. C.; Garagash, D.

2013-12-01

Seismological estimates of fracture energy show a scaling with the total slip of an earthquake [e.g., Abercrombie and Rice, GJI 2005]. Potential sources for this scale dependency are coseismic fault strength reductions that continue with increasing slip or an increasing amount of off-fault inelastic deformation with dynamic rupture propagation [e.g., Andrews, JGR 2005; Rice, JGR 2006]. Here, we investigate the former mechanism by solving for the slip dependence of fracture energy at the crack tip of a dynamically propagating rupture in which weakening takes place by strong reductions of friction via flash heating of asperity contacts and thermal pressurization of pore fluid leading to reductions in effective normal stress. Laboratory measurements of small characteristic slip evolution distances for friction (~10 μm at low slip rates of μm-mm/s, possibly up to 1 mm for slip rates near 0.1 m/s) [e.g., Marone and Kilgore, Nature 1993; Kohli et al., JGR 2011] imply that flash weakening of friction occurs at small slips before any significant thermal pressurization and may thus have a negligible contribution to the total fracture energy [Brantut and Rice, GRL 2011; Garagash, AGU 2011]. The subsequent manner of weakening under thermal pressurization (the dominant contributor to fracture energy) spans a range of behavior from the deformation of a finite-thickness shear zone in which diffusion is negligible (i.e., undrained-adiabatic) to that in which large-scale diffusion obscures the existence of a thin shear zone and thermal pressurization effectively occurs by the heating of slip on a plane. Separating the contribution of flash heating, the dynamic rupture solutions reduce to a problem with a single parameter, which is the ratio of the undrained-adiabatic slip-weakening distance (δc) to the characteristic slip-on-a-plane slip-weakening distance (L*). However, for any value of the parameter, there are two end-member scalings of the fracture energy: for small slip, the undrained-adiabatic behavior expectedly results in fracture energy scaling as G ~ δ^2, and for large slip (where TP approaches slip on a plane) we find that G ~ δ^(2/3). This last result is a slight correction to estimates made assuming a constant, kinematically imposed slip rate and slip-on-a-plane TP resulting in G ~ δ^(1/2) [Rice, JGR 2006]. We compile fracture energy estimates of both continental and subduction zone earthquakes. In doing so, we incorporate independent estimates of fault prestress to distinguish fracture energy G from the parameter G' defined by Abercrombie and Rice [2005], which represents the energetic quantity that is most directly inferred following seismological estimates of radiated energy, seismic moment and source radius. We find that the dynamic rupture solutions (which account for the variable manner of thermal pressurization and result in a self-consistent slip rate history) allow for a close match of the estimated fracture energy over several orders of total event slip, further supporting the proposed explanation that fracture energy scaling may largely be attributed to a fault strength that weakens gradually with slip, and additionally, the potential prevalence of thermal pressurization.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stevens, D.L.; Simonen, F.A.; Strosnider, J. Jr.

The VISA (Vessel Integrity Simulation Analysis) code was developed as part of the NRC staff evaluation of pressurized thermal shock. VISA uses Monte Carlo simulation to evaluate the failure probability of a pressurized water reactor (PWR) pressure vessel subjected to a pressure and thermal transient specified by the user. Linear elastic fracture mechanics are used to model crack initiation and propagation. parameters for initial crack size, copper content, initial RT/sub NDT/, fluence, crack-initiation fracture toughness, and arrest fracture toughness are treated as random variables. This report documents the version of VISA used in the NRC staff report (Policy Issue frommore » J.W. Dircks to NRC Commissioners, Enclosure A: NRC Staff Evaluation of Pressurized Thermal Shock, November 1982, SECY-82-465) and includes a user's guide for the code.« less

Modeling thermal stress propagation during hydraulic stimulation of geothermal wells

NASA Astrophysics Data System (ADS)

Jansen, Gunnar; Miller, Stephen A.

2017-04-01

A large fraction of the world's water and energy resources are located in naturally fractured reservoirs within the earth's crust. Depending on the lithology and tectonic history of a formation, fracture networks can range from dense and homogeneous highly fractured networks to single large scale fractures dominating the flow behavior. Understanding the dynamics of such reservoirs in terms of flow and transport is crucial to successful application of engineered geothermal systems (also known as enhanced geothermal systems or EGS) for geothermal energy production in the future. Fractured reservoirs are considered to consist of two distinct separate media, namely the fracture and matrix space respectively. Fractures are generally thin, highly conductive containing only small amounts of fluid, whereas the matrix rock provides high fluid storage but typically has much smaller permeability. Simulation of flow and transport through fractured porous media is challenging due to the high permeability contrast between the fractures and the surrounding rock matrix. However, accurate and efficient simulation of flow through a fracture network is crucial in order to understand, optimize and engineer reservoirs. It has been a research topic for several decades and is still under active research. Accurate fluid flow simulations through field-scale fractured reservoirs are still limited by the power of current computer processing units (CPU). We present an efficient implementation of the embedded discrete fracture model, which is a promising new technique in modeling the behavior of enhanced geothermal systems. An efficient coupling strategy is determined for numerical performance of the model. We provide new insight into the coupled modeling of fluid flow, heat transport of engineered geothermal reservoirs with focus on the thermal stress changes during the stimulation process. We further investigate the interplay of thermal and poro-elastic stress changes in the reservoir. Combined with a analytical formulation for the injection temperatures in the open hole section of a geothermal well, the stress changes induced during the injection period of reservoir development can be studied.

Analysis of delamination related fracture processes in composites

NASA Technical Reports Server (NTRS)

Armanios, Erian A.

1988-01-01

Delamination related fracture processes in composite materials are discussed. Thermal and moisture influences on the free-edge delamination of laminated composites, fracture analysis of local delaminations in laminated composites, and strain energy release rates in belts are among the topics covered.

Hydraulic fracturing in granite under geothermal conditions

USGS Publications Warehouse

Solberg, P.; Lockner, D.; Byerlee, J.D.

1980-01-01

The experimental hydraulic fracturing of granite under geothermal conditions produces tensile fracture at rapid fluid injection rates and shear fracture at slow injection rates and elevated differential stress levels. A sudden burst of acoustic emission activity accompanies tensile fracture formation whereas the acoustic emission rate increases exponentially prior to shear fracture. Temperature does not significantly affect the failure mechanism, and the experimental results have not demonstrated the occurrence of thermal fracturing. A critical result of these experiments is that fluid injection at intermediate rates and elevated differential stress levels increases permeability by more than an order of magnitude without producing macroscopic fractures, and low-level acoustic emission activity occurs simultaneously near the borehole and propagates outward into the specimen with time. Permeability measurements conducted at atmospheric pressure both before and after these experiments show that increased permeability is produced by permanent structural changes in the rock. Although results of this study have not demonstrated the occurrence of thermal fracturing, they suggest that fluid injection at certain rates in situ may markedly increase local permeability. This could prove critical to increasing the efficiency of heat exchange for geothermal energy extraction from hot dry rock. ?? 1980.

Fine characterization rock thermal damage by acoustic emission technique

NASA Astrophysics Data System (ADS)

Kong, Biao; Li, Zenghua; Wang, Enyuan

2018-02-01

This paper examines the differences in the thermal mechanical properties and acoustic emission (AE) characteristics during the deformation and fracture of rock under the action of continuous heating and after high-temperature treatment. Using AE 3D positioning technology, the development and evolution of the internal thermal cracks and the time domain of AE signals in rock were analyzed. High-temperature treatment causes thermal damage to rock. Under the action of continuous heating, the phase characteristics of AE time series correspond to the five stages of rock thermal deformation and fracture, respectively: the micro-defect development stage, the threshold interval of rock micro-cracks, the crack initiation stage, the crack propagation stage, and the crack multistage propagation evolution. When the initial crack propagates, the crack initiation of the rock causes the AE signal to produce a sudden mutation change. Mechanical fraction characteristics during rock uniaxial compression after temperature treatment indicated that the decrease rate of the rock compressive strength, wave velocity, and elastic modulus are relatively large during uniaxial compression tests after high-temperature treatment. During the deformation and fracture of rock under loading, there is faster growth of AE counts and AE events, indicating an increase in the speed of rock deformation and fracture under loading. AE counts show obvious changes during the latter loading stages, whereas AE events show obvious changes during the loading process. The results obtained are valuable for rock thermal stability detection and evaluation in actual underground engineering.

Hydromechanical and Thermomechanical Behaviour of Elastic Fractures during Thermal Stimulation of Naturally Fractured Reservoirs

NASA Astrophysics Data System (ADS)

Jalali, Mohammadreza; Valley, Benoît

2015-04-01

During the last two decades, incentives were put in place in order to feed our societies in energy with reduced CO2 emissions. Various policies have been considered to fulfill this strategy such as replacing coal by natural gas in power plants, producing electricity using CO2 free resources, and CO2 sequestration as a remediation for large point-source emitters (e.g. oil sands facilities, coal-fired power plants, and cement kilns). Naturally fractured reservoirs (NFRs) are among those geological structures which play a crucial role in the mentioned energy revolution. The behavior of fractured reservoirs during production processes is completely different than conventional reservoirs because of the dominant effects of fractures on fluid flux, with attendant issues of fracture fabric complexity and lithological heterogeneity. The level of complexity increases when thermal effects are taking place - as during the thermal stimulation of these stress-sensitive reservoirs in order to enhance the gas production in tight shales and/or increase the local conductivity of the fractures during the development of enhanced geothermal systems - where temperature is introduced as another degree of freedom in addition to pressure and displacement (or effective stress). Study of these stress-pressure-temperature effects requires a thermo-hydro-mechanical (THM) coupling approach, which considers the simultaneous variation of effective stress, pore pressure, and temperature and their interactions. In this study, thermal, hydraulic and mechanical behavior of partially open and elastic fractures in a homogeneous, isotropic and low permeable porous rock is studied. In order to compare the hydromechanical (HM) and thermomechanical (TM) characteristics of these fractures, three different injection scenarios, i.e. constant isothermal fluid injection rate, constant cooling without any fluid injection and constant cold fluid injection, are considered. Both thermomechanical and hydromechanical behaviors become dominant at different time scales, i.e. HM effects is dominant at early time after injection initiation, whereas the TM effect becomes more dominant at later time as the temperature propagation is slower than pressure propagation in the rock due to different value of hydraulic and thermal diffusivities. Due to the relative similarity of thermoelasticity and poroelasticity on the mechanical behavior of fractures, an analogy between these two mechanisms is introduced which can be used to estimate the effect of one of the mechanisms based on the other one on the mechanical behavior of the considered medium in the cases where only one of the solution exists. There may be merit in developing this work to generate more accurate and higher order functions to represent fractures within a general analogy of THM coupled problems as the computational time of this approach is at least one order less than the conventional THM iterative approaches.

Synchrotron quantification of fracturing during maturation of shales

NASA Astrophysics Data System (ADS)

Figueroa Pilz, Fernando; Fauchille, Anne-Laure; Dowey, Patrick; Courtois, Loic; Bay, Brian; Ma, Lin; Taylor, Kevin; Mecklenburgh, Julian; Lee, Peter

2017-04-01

To understand both the hydrocarbon migration within and from shale rocks, and during hydraulic fracturing, is needed to evaluate and predict its environmental footprint. As a consequence, the time characterization of fracture networks in shale is particularly important. Time resolved synchrotron X-ray tomography was used to quantify the initiation and propagation of fractures during the simulated maturation of an organic-rich Kimmeridge Clay shale from the µm to mm scales. Scanning electron microscopy (SEM) observations were performed before and after maturation in order to compare the microstructure evolution and better understand the fracture location. Fracture and strain development during heating was quantified in 3D by Digital Volume Correlation (DVC) (Bay et al., 1999). The combination of DVC, X-Ray tomography and SEM obtained direct 4D strain measurements of the anisotropic mechanical behaviour of Kimmeridge shale with the temperature during an accelerated thermal maturation (Figueroa Pilz et al.). Such a combination has rarely been investigated in 4D at these scales in the past. In the study conditions, the results demonstrated the anisotropy in thermal expansion and the aperture fracture pathways through organic matter and clay matrix.

Thermal-stress fracture and fractography in UO/sub 2/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kennedy, C.R.; Bandyopadhyay, G.

1976-01-01

Pressed and sintered UO/sub 2/ pellets were thermally shocked by quenching into a water bath at room temperature. The cracking behavior and strength degradation, as measured by the diametral compression technique, in these quench tests are discussed. Fractography of the thermally shocked specimens by scanning-electron microscopy indicated predominantly intergranular fracture in UO/sub 2/ in severe thermal-shock tests. The implication of this observation is that intergranular cracking may occur during the initial heat up in a reactor. Because fission gas bubbles tend to migrate toward the grain boundary, preferential microcracking along the boundary may strongly affect subsequent fission gas release behavior.

Effect of Thermal Aging and Test Temperatures on Fracture Toughness of SS 316(N) Welds

NASA Astrophysics Data System (ADS)

Dutt, B. Shashank; Babu, M. Nani; Shanthi, G.; Moitra, A.; Sasikala, G.

2018-03-01

The effect of thermal aging and test temperatures on fracture toughness (J 0.2) of SS 316(N) weld material has been studied based on J-R curve evaluations. The aging of the welds was carried out at temperatures 370, 475 and 550 °C and for durations varying from 1000 to 20,000 h. The fracture toughness (J-R curve) tests were carried out at 380 and 550 °C for specimens after all aging conditions, including as-weld condition. The initiation fracture toughness (J 0.2) of the SS 316(N) weld material has shown degradation after 20,000-h aging durations and is reflected in all the test temperatures and aging temperatures. The fracture toughness after different aging conditions and test temperatures, including as-weld condition, was higher than the minimum specified value for this class of welds.

Fracture analysis near the mid-ocean plate boundary, Reykjavik-Hvalfjördur area, Iceland

NASA Astrophysics Data System (ADS)

Jefferis, Robert G.; Voight, Barry

1981-07-01

The geometry and thermal history of fractures have been determined at 59 stations from Reykjavik to Hvalfjördur in southwestern Iceland. The data provide information on crustal stress regimes in the vicinity of mid-ocean ridges. Two major, generalized fracture orientations are present (1) a northeast system, trend 010°-030°, except on Akranes where the orientation is 040°-060° (2) a broad east—west system containing one or more sets with strike between 070°-130°. Thermal history of the host rock and fractures was determined from secondary minerals in vugs and fractures. The thermal history indicates that the northeast fracture set opened while the area was within the relatively hot axial zone of active volcanism and rifting. Some of the east—west trending fractures also opened at this time but many formed later, after the area had begun to cool and drift from the active zone. The northeast fracture set is essentially parallel to the trend of dikes and normal faults in southwestern Iceland. They have been interpreted as extension fractures (resulting in about 0.4% maximum extension) forming generally from the same stress field associated with normal faulting and dike injection in the active zone. Fracturing in an east-west direction (estimated 0.1% maximum extension), mainly near the edge and outside the active zone, indicates a reorientation of this stress field. The dominant mechanism related to the origin of the east—west fractures may be thermoelastic stresses arising from axial and basal accretion and cooling of lithospheric plates. Both fracture systems are inferred to have formed, in the Griffiths idealization, under nearly biaxial effective compressive loading on the order of 200 bar. The discrepancy between this value and the kilobar-order strengths of short-time laboratory tests reflects such factors as high temperature stress corrosion and fatigue. Fracture propagation is assumed to have been stable, but governed primarily by lateral load-diminishing mechanisms rather than by progressive loading. These relaxation mechanisms may have been episodic (northeast-system fissure swarm activity) or steady-state (thermoelastic contraction) in time.

Evidence for tectonic, lithologic, and thermal controls on fracture system geometries in an andesitic high-temperature geothermal field

NASA Astrophysics Data System (ADS)

Massiot, Cécile; Nicol, Andrew; McNamara, David D.; Townend, John

2017-08-01

Analysis of fracture orientation, spacing, and thickness from acoustic borehole televiewer (BHTV) logs and cores in the andesite-hosted Rotokawa geothermal reservoir (New Zealand) highlights potential controls on the geometry of the fracture system. Cluster analysis of fracture orientations indicates four fracture sets. Probability distributions of fracture spacing and thickness measured on BHTV logs are estimated for each fracture set, using maximum likelihood estimations applied to truncated size distributions to account for sampling bias. Fracture spacing is dominantly lognormal, though two subordinate fracture sets have a power law spacing. This difference in spacing distributions may reflect the influence of the andesitic sequence stratification (lognormal) and tectonic faults (power law). Fracture thicknesses of 9-30 mm observed in BHTV logs, and 1-3 mm in cores, are interpreted to follow a power law. Fractures in thin sections (˜5 μm thick) do not fit this power law distribution, which, together with their orientation, reflect a change of controls on fracture thickness from uniform (such as thermal) controls at thin section scale to anisotropic (tectonic) at core and BHTV scales of observation. However, the ˜5% volumetric percentage of fractures within the rock at all three scales suggests a self-similar behavior in 3-D. Power law thickness distributions potentially associated with power law fluid flow rates, and increased connectivity where fracture sets intersect, may cause the large permeability variations that occur at hundred meter scales in the reservoir. The described fracture geometries can be incorporated into fracture and flow models to explore the roles of fracture connectivity, stress, and mineral precipitation/dissolution on permeability in such andesite-hosted geothermal systems.

Numerical simulation of multiple-physical fields coupling for thermal anomalies before earthquakes: A case study of the 2008 Wenchuan Ms8.0 earthquake in southwest China

NASA Astrophysics Data System (ADS)

Deng, Z.

2017-12-01

It has become a highly focused issue that thermal anomalies appear before major earthquakes. There are various hypotheses about the mechanism of thermal anomalies. Because of lacking of enough evidences, the mechanism is still require to be further researched. Gestation and occurrence of a major earthquake is related with the interaction of multi-physical fields. The underground fluid surging out the surface is very likely to be the reason for the thermal anomaly. This study tries to answer some question, such as how the geothermal energy transfer to the surface, and how the multiple-physical fields interacted. The 2008 Wenchuan Ms8.0 earthquake, is one of the largest evens in the last decade in China mainland. Remote sensing studies indicate that distinguishable thermal anomalies occurred several days before the earthquake. The heat anomaly value is more than 3 times the average in normal time and distributes along the Longmen Shan fault zone. Based on geological and geophysical data, 2D dynamic model of coupled stress, seepage and thermal fields (HTM model) is constructed. Then using the COMSOL multi-physics filed software, this work tries to reveal the generation process and distribution patterns of thermal anomalies prior to thrust-type major earthquakes. The simulation get the results: (1)Before the micro rupture, with the increase of compression, the heat current flows to the fault in the footwall on the whole, while in the hanging wall of the fault, particularly near the ground surface, the heat flow upward. In the fault zone, heat flow upward along the fracture surface, heat flux in the fracture zone is slightly larger than the wall rock;, but the value is all very small. (2)After the occurrence of the micro fracture, the heat flow rapidly collects to the faults. In the fault zones, the heat flow accelerates up along the fracture surfaces, the heat flux increases suddenly, and the vertical heat flux reaches to the maximum. The heat flux in the 3 fracture zones is obviously larger than that in the non fracture zone. The high heat flux anomaly can continue several days to one month. The simulation results is consistent with the reality earthquake cases.

Experimental investigation of temperature rise in bone drilling with cooling: A comparison between modes of without cooling, internal gas cooling, and external liquid cooling.

PubMed

Shakouri, Ehsan; Haghighi Hassanalideh, Hossein; Gholampour, Seifollah

2018-01-01

Bone fracture occurs due to accident, aging, and disease. For the treatment of bone fractures, it is essential that the bones are kept fixed in the right place. In complex fractures, internal fixation or external methods are used to fix the fracture position. In order to immobilize the fracture position and connect the holder equipment to it, bone drilling is required. During the drilling of the bone, the required forces to chip formation could cause an increase in the temperature. If the resulting temperature increases to 47 °C, it causes thermal necrosis of the bone. Thermal necrosis decreases bone strength in the hole and, subsequently, due to incomplete immobilization of bone, fracture repair is not performed correctly. In this study, attempts have been made to compare local temperature increases in different processes of bone drilling. This comparison has been done between drilling without cooling, drilling with gas cooling, and liquid cooling on bovine femur. Drilling tests with gas coolant using direct injection of CO 2 and N 2 gases were carried out by internal coolant drill bit. The results showed that with the use of gas coolant, the elevation of temperature has limited to 6 °C and the thermal necrosis is prevented. Maximum temperature rise reached in drilling without cooling was 56 °C, using gas and liquid coolant, a maximum temperature elevation of 43 °C and 42 °C have been obtained, respectively. This resulted in decreased possibility of thermal necrosis of bone in drilling with gas and liquid cooling. However, the results showed that the values obtained with the drilling method with direct gas cooling are independent of the rotational speed of drill.

Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-standing Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

2003-01-01

Strength, fracture toughness and fatigue behavior of free-standing thick thermal barrier coatings of plasma-sprayed ZrO2-8wt % Y2O3 were determined at ambient and elevated temperatures in an attempt to establish a database for design. Strength, in conjunction with deformation (stress-strain behavior), was evaluated in tension (uniaxial and trans-thickness), compression, and uniaxial and biaxial flexure; fracture toughness was determined in various load conditions including mode I, mode II, and mixed modes I and II; fatigue or slow crack growth behavior was estimated in cyclic tension and dynamic flexure loading. Effect of sintering was quantified through approaches using strength, fracture toughness, and modulus (constitutive relations) measurements. Standardization issues on test methodology also was presented with a special regard to material's unique constitutive relations.

A Review of Large-Scale Fracture Experiments Relevant to Pressure Vessel Integrity Under Pressurized Thermal Shock Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pugh, C.E.

2001-01-29

Numerous large-scale fracture experiments have been performed over the past thirty years to advance fracture mechanics methodologies applicable to thick-wall pressure vessels. This report first identifies major factors important to nuclear reactor pressure vessel (RPV) integrity under pressurized thermal shock (PTS) conditions. It then covers 20 key experiments that have contributed to identifying fracture behavior of RPVs and to validating applicable assessment methodologies. The experiments are categorized according to four types of specimens: (1) cylindrical specimens, (2) pressurized vessels, (3) large plate specimens, and (4) thick beam specimens. These experiments were performed in laboratories in six different countries. This reportmore » serves as a summary of those experiments, and provides a guide to references for detailed information.« less

Documentation of probabilistic fracture mechanics codes used for reactor pressure vessels subjected to pressurized thermal shock loading: Parts 1 and 2. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balkey, K.; Witt, F.J.; Bishop, B.A.

1995-06-01

Significant attention has been focused on the issue of reactor vessel pressurized thermal shock (PTS) for many years. Pressurized thermal shock transient events are characterized by a rapid cooldown at potentially high pressure levels that could lead to a reactor vessel integrity concern for some pressurized water reactors. As a result of regulatory and industry efforts in the early 1980`s, a probabilistic risk assessment methodology has been established to address this concern. Probabilistic fracture mechanics analyses are performed as part of this methodology to determine conditional probability of significant flaw extension for given pressurized thermal shock events. While recent industrymore » efforts are underway to benchmark probabilistic fracture mechanics computer codes that are currently used by the nuclear industry, Part I of this report describes the comparison of two independent computer codes used at the time of the development of the original U.S. Nuclear Regulatory Commission (NRC) pressurized thermal shock rule. The work that was originally performed in 1982 and 1983 to compare the U.S. NRC - VISA and Westinghouse (W) - PFM computer codes has been documented and is provided in Part I of this report. Part II of this report describes the results of more recent industry efforts to benchmark PFM computer codes used by the nuclear industry. This study was conducted as part of the USNRC-EPRI Coordinated Research Program for reviewing the technical basis for pressurized thermal shock (PTS) analyses of the reactor pressure vessel. The work focused on the probabilistic fracture mechanics (PFM) analysis codes and methods used to perform the PTS calculations. An in-depth review of the methodologies was performed to verify the accuracy and adequacy of the various different codes. The review was structured around a series of benchmark sample problems to provide a specific context for discussion and examination of the fracture mechanics methodology.« less

Fracture in Phenolic Impregnated Carbon Ablator

NASA Technical Reports Server (NTRS)

Agrawal, Parul; Chavez-Garcia, Jose F.

2011-01-01

The thermal protection materials used for spacecraft heat shields are subjected to various thermal-mechanical loads during an atmospheric entry which can threaten the structural integrity of the system. This paper discusses the development of a novel technique to understand the failure mechanisms inside thermal protection materials. The focus of research is Phenolic Impregnated Carbon Ablator (PICA). It has successfully flown on the Stardust spacecraft and is the TPS material chosen for the Mars Science Laboratory (MSL) and Dragon spacecraft. Although PICA has good thermal properties, structurally, it is a weak material. In order to thoroughly understand failure in PICA, fracture tests were performed on FiberForm* (precursor of PICA), virgin and charred PICA materials. Several samples of these materials were tested to investigate failure mechanisms at a microstructural scale. Stress-strain data were obtained simultaneously to estimate the fracture toughness. It was found that cracks initiated and grew in the FiberForm when a critical stress limit was reached such that the carbon fibers separated from the binder. However, both for virgin and charred PICA, crack initiation and growth occurred in the matrix (phenolic) phase. Both virgin and charred PICA showed greater strength values compared to FiberForm coupons, confirming that the presence of the porous matrix helps in absorbing the fracture energy.

Energy extraction from fractured geothermal reservoirs in low-permeability crystalline rock

NASA Astrophysics Data System (ADS)

Murphy, H. D.; Tester, J. W.; Grigsby, C. O.; Potter, R. M.

1981-08-01

The thermal performance and flow characteristics of two hot dry rock geothermal energy reservoirs created by the hydraulic fracturing of granitic rock are discussed. The reservoirs were produced by fracturing an injection well at a depth of 2.75 km and again 180 m deeper (rock temperature 185 C) on the west bank of the Valles Caldera, a dormant volcanic complex in northern New Mexico. Heat was extracted in a closed-loop operation by the injection of water into one well and the extraction of heated water from a separate well. Results of temperature measurements and thermal modeling for the first reservoir over an initial 75-day test period indicate a thermal exchange area of 8000 sq m, and coupled with flow rate surveys suggest an effective fracture radius of about 60 m with an average thermal power extracted of 4 MW. Evaluation of the second reservoir during a 32-day flow test indicates an effective heat transfer area of at least 45,000 sq m, and a mean reservoir volume nine times greater than that of the first reservoir. Further measurements have shown low flow impedances and downhole water losses for both reservoirs, with produced water of good quality and little insignificant induced seismic activity.

Electroperturbation of human stratum corneum fine structure by high voltage pulses: a freeze-fracture electron microscopy and differential thermal analysis study.

PubMed

Jadoul, A; Tanojo, H; Préat, V; Bouwstra, J A; Spies, F; Boddé, H E

1998-08-01

Application of high voltage pulses (HVP) to the skin has been shown to promote the transdermal drug delivery by a mechanism involving skin electroporation. The aim of this study was to detect potential changes in lipid phase and ultrastructure induced in human stratum corneum by various HVP protocols, using differential thermal analysis and freeze-fracture electron microscopy. Due to the time involved between the moment the electric field is switched off and the analysis, only "secondary" phenomena rather than primary events could be observed. A decrease in enthalpies for the phase transitions observed at 70 degrees C and 85 degrees C was detected by differential thermal analysis after HVP treatment. No changes in transition temperature could be seen. The freeze-fracture electron microscopy study revealed a dramatic perturbation of the lamellar ordering of the intercellular lipid after application of HVP. Most of the planes displayed rough surfaces. The lipid lamellae exhibited rounded off steps or a vanished stepwise order. There was no evidence for perturbation of the corneocytes content. In conclusion, the freeze-fracture electron microscopy and differential thermal analysis studies suggest that HVP application induces a general perturbation of the stratum corneum lipid ultrastructure.

Delamination onset in polymeric composite laminates under thermal and mechanical loads

NASA Technical Reports Server (NTRS)

Martin, Roderick H.

1991-01-01

A fracture mechanics damage methodology to predict edge delamination is described. The methodology accounts for residual thermal stresses, cyclic thermal stresses, and cyclic mechanical stresses. The modeling is based on the classical lamination theory and a sublaminate theory. The prediction methodology determines the strain energy release rate, G, at the edge of a laminate and compares it with the fatigue and fracture toughness of the composite. To verify the methodology, isothermal static tests at 23, 125, and 175 C and tension-tension fatigue tests at 23 and 175 C were conducted on laminates. The material system used was a carbon/bismaleimide, IM7/5260. Two quasi-isotropic layups were used. Also, 24 ply unidirectional double cantilever beam specimens were tested to determine the fatigue and fracture toughness of the composite at different temperatures. Raising the temperature had the effect of increasing the value of G at the edge for these layups and also to lower the fatigue and fracture toughness of the composite. The static stress to edge delamination was not affected by temperature but the number of cycles to edge delamination decreased.

Effect of Thermal Aging on the Mechanical Properties of Sn3.0Ag0.5Cu/Cu Solder Joints Under High Strain Rate Conditions

NASA Astrophysics Data System (ADS)

Nguyen, Van Luong; Kim, Ho-Kyung

2015-07-01

Shear tests with velocities between 0.5 m/s and 2.5 m/s were conducted to investigate the deformation characteristics of 0.76 mm lead-free Sn-3Ag-0.5Cu solder ball joints after thermal aging at 373 K up to 1000 h. A scanning electron microscope equipped with energy dispersive spectroscopy was then used to examine the fracture surfaces and microstructures of the solder joints. The results showed that the main failure mode of the solder joints was the brittle interfacial fracture mode with cleavage failure in the intermetallic compound (IMC). The maximum shear strength and the fracture toughness ( K C) of the solder joint decreased substantially after aging for the initial aging time, after which they decreased gradually with further aging or an increase in the strain rate. The evolution of the IMC layer when it was thicker and had coarser nodules due to thermal aging was the primary cause of the reduction in the shear strength and fracture toughness in this study.

75 FR 13 - Alternate Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock Events

Federal Register 2010, 2011, 2012, 2013, 2014

2010-01-04

...The Nuclear Regulatory Commission (NRC) is amending its regulations to provide alternate fracture toughness requirements for protection against pressurized thermal shock (PTS) events for pressurized water reactor (PWR) pressure vessels. This final rule provides alternate PTS requirements based on updated analysis methods. This action is desirable because the existing requirements are based on unnecessarily conservative probabilistic fracture mechanics analyses. This action reduces regulatory burden for those PWR licensees who expect to exceed the existing requirements before the expiration of their licenses, while maintaining adequate safety, and may choose to comply with the final rule as an alternative to complying with the existing requirements.

The mechanics and physics of fracturing: application to thermal aspects of crack propagation and to fracking.

PubMed

Cherepanov, Genady P

2015-03-28

By way of introduction, the general invariant integral (GI) based on the energy conservation law is presented, with mention of cosmic, gravitational, mass, elastic, thermal and electromagnetic energy of matter application to demonstrate the approach, including Coulomb's Law generalized for moving electric charges, Newton's Law generalized for coupled gravitational/cosmic field, the new Archimedes' Law accounting for gravitational and surface energy, and others. Then using this approach the temperature track behind a moving crack is found, and the coupling of elastic and thermal energies is set up in fracturing. For porous materials saturated with a fluid or gas, the notion of binary continuum is used to introduce the corresponding GIs. As applied to the horizontal drilling and fracturing of boreholes, the field of pressure and flow rate as well as the fluid output from both a horizontal borehole and a fracture are derived in the fluid extraction regime. The theory of fracking in shale gas reservoirs is suggested for three basic regimes of the drill mud permeation, with calculating the shape and volume of the local region of the multiply fractured rock in terms of the pressures of rock, drill mud and shale gas. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Contact thermal shock test of ceramics

NASA Technical Reports Server (NTRS)

Rogers, W. P.; Emery, A. F.

1992-01-01

A novel quantitative thermal shock test of ceramics is described. The technique employs contact between a metal-cooling rod and hot disk-shaped specimen. In contrast with traditional techniques, the well-defined thermal boundary condition allows for accurate analyses of heat transfer, stress, and fracture. Uniform equibiaxial tensile stresses are induced in the center of the test specimen. Transient specimen temperature and acoustic emission are monitored continuously during the thermal stress cycle. The technique is demonstrated with soda-lime glass specimens. Experimental results are compared with theoretical predictions based on a finite-element method thermal stress analysis combined with a statistical model of fracture. Material strength parameters are determined using concentric ring flexure tests. Good agreement is found between experimental results and theoretical predictions of failure probability as a function of time and initial specimen temperature.

Spurious heat conduction behavior of finite-size graphene nanoribbon under extreme uniaxial strain caused by the AIREBO potential

NASA Astrophysics Data System (ADS)

Yang, Xueming; Wu, Sihan; Xu, Jiangxin; Cao, Bingyang; To, Albert C.

2018-02-01

Although the AIREBO potential can well describe the mechanical and thermal transport of the carbon nanostructures under normal conditions, previous studies have shown that it may overestimate the simulated mechanical properties of carbon nanostructures in extreme strains near fracture. It is still unknown whether such overestimation would also appear in the thermal transport of nanostructrues. In this paper, the mechanical and thermal transport of graphene nanoribbon under extreme deformation conditions are studied by MD simulations using both the original and modified AIREBO potential. Results show that the cutoff function of the original AIREBO potential produces an overestimation on thermal conductivity in extreme strains near fracture stage. Spurious heat conduction behavior appears, e.g., the thermal conductivity of GNRs does not monotonically decrease with increasing strain, and even shows a ;V; shaped reversed and nonphysical trend. Phonon spectrum analysis show that it also results in an artificial blue shift of G peak and phonon stiffening of the optical phonon modes. The correlation between spurious heat conduction behavior and overestimation of mechanical properties near the fracture stage caused by the original AIREBO potential are explored and revealed.

Influence of Heat Treatment on Fracture Toughness and Wear Resistance of Nicral-Zro2 Multilayered Thermal Barrier Coating

NASA Astrophysics Data System (ADS)

Ye, Zibo; Wang, Guanghong

2018-04-01

The chemical composition and fracture toughness of thermal barrier coatings (TBCs) before and after heat treatment were characterized, and the cracks around the interface between the coating and the substrate could be successfully eliminated and meanwhile the porosity of the coatings tended to reduce. The XRD analysis revealed the coatings were composed of non-transformable tetragonal t' phase of ZrO2 and γ -(Ni, Cr) with minor Ni3Al (γ') precipitates. Additionally, the relationship between the heat treatment and wear resistance was systematically studied. The results indicated that both the hardness and fracture toughness increased after quenching process. The oxidation wear became more prominent after heat treatment, which probably resulted from the better bonding strength of coatings. Dense and homogeneous microstructure introduced by vacuum oil-quenching improved stabilization of the weight gain during thermal cycle test.

Effects of isothermal and cyclic exposures on interface structure and mechanical properties of FPalpha-Al2O3/aluminum composites. [polycrystaline alumina fibers

NASA Technical Reports Server (NTRS)

Kim, W. M.; Koczak, M. J.; Lawley, A.

1979-01-01

The microstructural and interface stability of FPalpha-Al203/Al-Li composites are investigated as a function of isothermal exposure at 500 C or thermal cycling between 140 and 500 C with hold time at Tmax. Interfacial morphology, growth kinetics, crystal structure, and composition of interfacial reaction products are characterized. Strength is monitored in the transverse orientation, and fracture mechanics is analyzed in terms of interface reaction products. The interfacial reaction product in FP/Al is Li2O.5Al2O3. Significant fiber-matrix reaction occurs during fabrication. The number of thermal cycles rather than total time at Tmax is the determining factor in strength degradation, thermal cycling giving rise to voids at the fiber-matrix interface. Extensive interface failures occur at composite fracture stresses below about 128 MPa; above this stress level failure is attributed to ductile matrix fracture.

Influence of the preparation design and artificial aging on the fracture resistance of monolithic zirconia crowns.

PubMed

Mitov, Gergo; Anastassova-Yoshida, Yana; Nothdurft, Frank Phillip; von See, Constantin; Pospiech, Peter

2016-02-01

The aim of this study was to evaluate the fracture resistance and fracture behavior of monolithic zirconia crowns in accordance with the preparation design and aging simulation method. An upper first molar was prepared sequentially with three different preparation designs: shoulderless preparation, 0.4 mm chamfer and 0.8 mm chamfer preparation. For each preparation design, 30 monolithic zirconia crowns were fabricated. After cementation on Cr-Co alloy dies, the following artificial aging procedures were performed: (1) thermal cycling and mechanical loading (TCML): 5000 cycles of thermal cycling 5℃-55℃ and chewing simulation (1,200,000 cycles, 50 N); (2) Low Temperature Degradation simulation (LTD): autoclave treatment at 137℃, 2 bar for 3 hours and chewing simulation; and (3) no pre-treatment (control group). After artificial aging, the crowns were loaded until fracture. The mean values of fracture resistance varied between 3414 N (LTD; 0.8 mm chamfer preparation) and 5712 N (control group; shoulderless preparation). Two-way ANOVA analysis showed a significantly higher fracture loads for the shoulderless preparation, whereas no difference was found between the chamfer preparations. In contrast to TCML, after LTD simulation the fracture strength of monolithic zirconia crowns decreased significantly. The monolithic crowns tested in this study showed generally high fracture load values. Preparation design and LTD simulation had a significant influence on the fracture strength of monolithic zirconia crowns.

Physical and numerical studies of a fracture system model

NASA Astrophysics Data System (ADS)

Piggott, Andrew R.; Elsworth, Derek

1989-03-01

Physical and numerical studies of transient flow in a model of discretely fractured rock are presented. The physical model is a thermal analogue to fractured media flow consisting of idealized disc-shaped fractures. The numerical model is used to predict the behavior of the physical model. The use of different insulating materials to encase the physical model allows the effects of differing leakage magnitudes to be examined. A procedure for determining appropriate leakage parameters is documented. These parameters are used in forward analysis to predict the thermal response of the physical model. Knowledge of the leakage parameters and of the temporal variation of boundary conditions are shown to be essential to an accurate prediction. Favorable agreement is illustrated between numerical and physical results. The physical model provides a data source for the benchmarking of alternative numerical algorithms.

Influent of Borax Decahydrate Composition as Additional Flux into Stoneware Bodies

NASA Astrophysics Data System (ADS)

Bakil, Siti Natrah Abd; Hussin, Rosniza; Bakar Aramjat, Abu

2017-08-01

Stoneware is vitrified, has less porosity and requires high sintering temperature. The influent of borax decahydrate composition at sintering temperature 1050°C and 1150°C on the thermal analysis, fracture surface, linear shrinkage, water absorption and modular of rapture (MOR) were investigated. Rectangular sample were produced by uniaxially pressing at 40MPa. The thermal behavior was determined by thermogravimetric and different thermal analysis (TGA-DTA). The Scanning electron microscopy (SEM) was used for fracture surface analysis. The water absorption (%) of the sample were determined using Archimedes’ method. The experimental result showed that content of borax decahydrate have influent the properties of stoneware bodies.

Thermal analysis of fractures at Cerberus Fossae, Mars: Detection of air convection in the porous debris apron

NASA Astrophysics Data System (ADS)

Antoine, R.; Lopez, T.; Baratoux, D.; Rabinowicz, M.; Kurita, K.

2011-08-01

This study investigates the cause of high nighttime temperatures within Cerberus Fossae, a system of fractures affecting the Central Elysium Planitia. The inner parts (walls and floor) of the fractures are up to 40 K warmer than the surrounding plains. However, several temperature profiles exhibit a local temperature minima occurring in the central part of the fractures. We examined first the influence of cooling efficiency at night in the case of a strong reduction of the sky proportion induced by the fracture's geometry. However, the lack of correlation between temperature and sky proportion, calculated from extracted Mars Orbiter Laser Altimeter (MOLA) profiles argues against this hypothesis. Albedo variations were considered but appear to be limited within the fractures, and are generally not correlated with the temperatures. Variations of the thermal properties of bedrocks exposures, debris aprons and sand dunes inferred from high-resolution images do not either correlate with temperature variations within the fractures. As none of these factors taken alone, or combined, can satisfactorily explain the temperature variations within and near the fracture, we suggest that geothermal heat transported by air convection within the porous debris aprons may contribute to explain high temperatures at night and the local minima on the fracture floor. The conditions for the occurrence of the suggested phenomenon and the consequences on the surface temperature are numerically explored. A conservative geothermal gradient of 20 mW/m 2 was used in the simulations, this value being consistent with either inferred lithosphere elastic thicknesses below the shield volcanoes of the Tharsis dome or values predicted from numerical simulations of the thermal evolution of Mars. The model results indicate that temperature differences of 10-20 K between the central and upper parts of the fracture are explained in the case of high Darcy velocities which require high permeability values (5 × 10 -6 m 2). The presence of coarse material composing the debris aprons may explain why this key criteria was met in the context of Cerberus Fossae.

A Study of Permeability Changes Due to Cold Fluid Circulation in Fractured Geothermal Reservoirs.

PubMed

Gholizadeh Doonechaly, Nima; Abdel Azim, Reda R; Rahman, Sheik S

2016-05-01

Reservoir behavior due to injection and circulation of cold fluid is studied with a shear displacement model based on the distributed dislocation technique, in a poro-thermoelastic environment. The approach is applied to a selected volume of Soultz geothermal reservoir at a depth range of 3600 to 3700 m. Permeability enhancement and geothermal potential of Soultz geothermal reservoir are assessed over a stimulation period of 3 months and a fluid circulation period of 14 years. This study-by shedding light onto another source of uncertainty-points toward a special role for the fracture surface asperities in predicting the shear dilation of fractures. It was also observed that thermal stress has a significant impact on changing the reservoir stress field. The effect of thermal stresses on reservoir behavior is more evident over longer circulation term as the rock matrix temperature is significantly lowered. Change in the fracture permeability due to the thermal stresses can also lead to the short circuiting between the injection and production wells which in turn decreases the produced fluid temperature significantly. The effect of thermal stress persists during the whole circulation period as it has significant impact on the continuous increase in the flow rate due to improved permeability over the circulation period. In the current study, taking into account the thermal stress resulted in a decrease of about 7 °C in predicted produced fluid temperature after 14 years of cold fluid circulation; a difference which notably influences the potential prediction of an enhanced geothermal system. © 2015, National Ground Water Association.

Technical Letter Report on the Cracking of Irradiated Cast Stainless Steels with Low Ferrite Content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Y.; Alexandreanu, B.; Natesan, K.

2014-11-01

Crack growth rate and fracture toughness J-R curve tests were performed on CF-3 and CF-8 cast austenite stainless steels (CASS) with 13-14% of ferrite. The tests were conducted at ~320°C in either high-purity water with low dissolved oxygen or in simulated PWR water. The cyclic crack growth rates of CF-8 were higher than that of CF-3, and the differences between the aged and unaged specimens were small. No elevated SCC susceptibility was observed among these samples, and the SCC CGRs of these materials were comparable to those of CASS alloys with >23% ferrite. The fracture toughness values of unirradiated CF-3more » were similar between unaged and aged specimens, and neutron irradiation decreased the fracture toughness significantly. The fracture toughness of CF-8 was reduced after thermal aging, and declined further after irradiation. It appears that while lowering ferrite content may help reduce the tendency of thermal aging embrittlement, it is not very effective to mitigate irradiation-induced embrittlement. Under a combined condition of thermal aging and irradiation, neutron irradiation plays a dominant role in causing embrittlement in CASS alloys.« less

Modeling Coupled Thermal-Hydrological-Chemical Processes in the Unsaturated Fractured Rock of Yucca Mountain, Nevada: Heterogeneity and Seepage

DOE Office of Scientific and Technical Information (OSTI.GOV)

S. Mukhopadhyay; E.L. Donnenthal; N. Spycher

An understanding of processes affecting seepage into emplacement tunnels is needed for correctly predicting the performance of underground radioactive waste repositories. It has been previously estimated that the capillary and vaporization barriers in the unsaturated fractured rock of Yucca Mountain are enough to prevent seepage under present day infiltration conditions. It has also been thought that a substantially elevated infiltration flux will be required to cause seepage after the thermal period is over. While coupled thermal-hydrological-chemical (THC) changes in Yucca Mountain host rock due to repository heating has been previously investigated, those THC models did not incorporate elements of themore » seepage model. In this paper, we combine the THC processes in unsaturated fractured rock with the processes affecting seepage. We observe that the THC processes alter the hydrological properties of the fractured rock through mineral precipitation and dissolution. We show that such alteration in the hydrological properties of the rock often leads to local flow channeling. We conclude that such local flow channeling may result in seepage under certain conditions, even with nonelevated infiltration fluxes.« less

Geothermal reservoir characterization through active thermal testing

NASA Astrophysics Data System (ADS)

Jung, Martin; Klepikova, Maria; Jalali, Mohammadreza; Fisch, Hansruedi; Loew, Simon; Amann, Florian

2016-04-01

Development and deployment of Enhanced Geothermal Systems (EGS) as renewable energy resources are part of the Swiss Energy Strategy 2050. To pioneer further EGS projects in Switzerland, a decameter-scale in-situ hydraulic stimulation and circulation (ISC) experiment has been launched at the Grimsel Test Site (GTS). The experiments are hosted in a low fracture density volume of the Grimsel granodiorite, similar to those expected at the potential enhanced geothermal system sites in the deep basement rocks of Northern Switzerland. One of the key goals of this multi-disciplinary experiment is to provide a pre- and post-stimulation characterization of the hydraulic and thermal properties of the stimulated fracture network with high resolution and to determine natural structures controlling the fluid flow and heat transport. Active thermal tests including thermal dilution tests and heat tracer tests allow for investigation of groundwater fluid flow and heat transport. Moreover, the spatial and temporal integrity of distributed temperature sensing (DTS) monitoring upgrades the potential and applicability of thermal tests in boreholes (e.g. Read et al., 2013). Here, we present active thermal test results and discuss the advantages and limitations of this method compared to classical approaches (hydraulic packer tests, solute tracer tests, flowing fluid electrical conductivity logging). The experimental tests were conducted in two boreholes intersected by a few low to moderately transmissive fault zones (fracture transmissivity of about 1E-9 m2/s - 1E-7 m2/s). Our preliminary results show that even in low-permeable environments active thermal testing may provide valuable insights into groundwater and heat transport pathways. Read T., O. Bour, V. Bense, T. Le Borgne, P. Goderniaux, M.V. Klepikova, R. Hochreutener, N. Lavenant, and V. Boschero (2013), Characterizing groundwater flow and heat transport in fractured rock using Fiber-Optic Distributed Temperature Sensing, Geophys. Res. Lett., 40, 2055-2059, doi:10.1002/grl.5039

Heat and Groundwater Flow in the San Gabriel Mountains, California

NASA Astrophysics Data System (ADS)

Newman, A. A.; Becker, M.; Laton, W. R., Jr.

2017-12-01

Groundwater flow paths in mountainous terrain often vary widely in both time and space. Such systems remain difficult to characterize due to fracture-dominated flow paths, high topographic relief, and sparse hydrologic data. We develop a hydrogeologic conceptual model of the Western San Gabriel Mountains in Southern California based on geophysical, thermal, and hydraulic head data. Boreholes are located along the San Gabriel Fault Zone (SGFZ) and cover a wide range of elevations to capture the heterogeneity of the hydrogeologic system. Long term (2016-2017) monitoring of temperature and hydraulic head was carried out in four shallow (300-600m depth) boreholes within the study area using fiber-optic distributed temperature sensing (DTS). Borehole temperature profiles were used to assess the regional groundwater flow system and local flows in fractures intersecting the borehole. DTS temperature profiles were compared with available borehole geophysical logs and head measurements collected with grouted vibrating wire pressure transducers (VWPT). Spatial and temporal variations in borehole temperature profiles suggest that advective heat transfer due to fluid flow affected the subsurface thermal regime. Thermal evidence of groundwater recharge and/or discharge and flow through discrete fractures was found in all four boreholes. Analysis of temporal changes to the flow system in response to seasonal and drilling-induced hydraulic forcing was useful in reducing ambiguities in noisy datasets and estimating interborehole relationships. Acoustic televiewer logs indicate fractures were primarily concentrated in densely fractured intervals, and only a minor decrease of fracture density was observed with depth. Anomalously high hydraulic gradients across the SGFZ suggest that the feature is a potential barrier to lateral flow. However, transient thermal anomalies consistent with groundwater flow within the SGFZ indicate this feature may be a potential conduit to vertical flow. This study builds upon the limited hydrogeologic understanding of the region and demonstrates the value of DTS in characterization efforts.

Influence of the preparation design and artificial aging on the fracture resistance of monolithic zirconia crowns

PubMed Central

Anastassova-Yoshida, Yana; Nothdurft, Frank Phillip; von See, Constantin; Pospiech, Peter

2016-01-01

PURPOSE The aim of this study was to evaluate the fracture resistance and fracture behavior of monolithic zirconia crowns in accordance with the preparation design and aging simulation method. MATERIALS AND METHODS An upper first molar was prepared sequentially with three different preparation designs: shoulderless preparation, 0.4 mm chamfer and 0.8 mm chamfer preparation. For each preparation design, 30 monolithic zirconia crowns were fabricated. After cementation on Cr-Co alloy dies, the following artificial aging procedures were performed: (1) thermal cycling and mechanical loading (TCML): 5000 cycles of thermal cycling 5℃–55℃ and chewing simulation (1,200,000 cycles, 50 N); (2) Low Temperature Degradation simulation (LTD): autoclave treatment at 137℃, 2 bar for 3 hours and chewing simulation; and (3) no pre-treatment (control group). After artificial aging, the crowns were loaded until fracture. RESULTS The mean values of fracture resistance varied between 3414 N (LTD; 0.8 mm chamfer preparation) and 5712 N (control group; shoulderless preparation). Two-way ANOVA analysis showed a significantly higher fracture loads for the shoulderless preparation, whereas no difference was found between the chamfer preparations. In contrast to TCML, after LTD simulation the fracture strength of monolithic zirconia crowns decreased significantly. CONCLUSION The monolithic crowns tested in this study showed generally high fracture load values. Preparation design and LTD simulation had a significant influence on the fracture strength of monolithic zirconia crowns. PMID:26949485

Methodology for Estimating Thermal and Neutron Embrittlement of Cast Austenitic Stainless Steels During Service in Light Water Reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chopra, O. K.; Rao, A. S.

2016-04-28

Cast austenitic stainless steel (CASS) materials, which have a duplex structure consisting of austenite and ferrite phases, are susceptible to thermal embrittlement during reactor service. In addition, the prolonged exposure of these materials, which are used in reactor core internals, to neutron irradiation changes their microstructure and microchemistry, and these changes degrade their fracture properties even further. This paper presents a revision of the procedure and correlations presented in NUREG/CR-4513, Rev. 1 (Aug. 1994) for predicting the change in fracture toughness and tensile properties of CASS components due to thermal aging during service in light water reactors (LWRs) at 280–330more » °C (535–625 °F). The methodology is applicable to CF-3, CF-3M, CF-8, and CF-8M materials with a ferrite content of up to 40%. The fracture toughness, tensile strength, and Charpy-impact energy of aged CASS materials are estimated from known material information. Embrittlement is characterized in terms of room-temperature (RT) Charpy-impact energy. The extent or degree of thermal embrittlement at “saturation” (i.e., the minimum impact energy that can be achieved for a material after long-term aging) is determined from the chemical composition of the material. Charpy-impact energy as a function of the time and temperature of reactor service is estimated from the kinetics of thermal embrittlement, which are also determined from the chemical composition. The fracture toughness J-R curve for the aged material is then obtained by correlating RT Charpy-impact energy with fracture toughness parameters. A common “predicted lower-bound” J-R curve for CASS materials of unknown chemical composition is also defined for a given grade of material, range of ferrite content, and temperature. In addition, guidance is provided for evaluating the combined effects of thermal and neutron embrittlement of CASS materials used in the reactor core internal components. The correlations for estimating the change in tensile strength, including the Ramberg/Osgood parameters for strain hardening, are also described.« less

Analysis of cracks induced by elevated temperature in rock using micro-focus X-ray CT

NASA Astrophysics Data System (ADS)

Cheon, D. S.; Park, E. S.

2016-12-01

Thermal energy storage facilities and deep borehole nuclear waste disposal in the underground are repeatedly applied by heat. The thermal stress induced by heat can generate micro-cracks and extend the existing micro-cracks of rocks. For long-term stabilities of the above facilities, the features of thermal induced cracks should be investigated. In this paper, we investigated occurred the features of thermal cracks using micro-focus X-ray CT before and after thermal experiments. Two different kinds of rock core specimens (limestone, granite) were heated within the furnace with the elevated temperatures of 250 °C, 400 °C and 550 °C. In thermal experiments, we heated rocks with the speed of 1.5 ºC /min to avoid thermal shock. Total 16 cases were subjected to X-ray imaging and post-processing to observe thermally induced fractures. Micro-cracks induced by thermal loading may not be extractable by a thresholding method such that the manual tracking within the ROI (Region of Interest) was implemented by using the VG Studio Software. Identified fractures were grouped by each object whose orientation was fitted by 3D plane. And then, its normal vector was computed and visualized. Nominal fractures (less than 10 voxel size) were excluded. Each fracture was projected on the 3D sphere and its volume was represented by color map. Thermal induced cracks in the limestone observed on CT images were very small. On the other hand, they could be more clearly observed in the granite. In case of limestone, the number of cracks is only 4 after heating up 550 °C and most of them occurred within the mineral. In case of granite, 157 cracks are detected both at the boundaries of minerals and within the mineral. In both rocks, the development of thermal cracks within a certain mineral was superior to them that occurred along the interface between minerals. After heating up to 550 °C the occurred cracks significantly increased. Crack volume was also similar pattern to the number of cracks. However the average volume of cracks in limestone is larger than granite. The normal vector of the cracks is similar to the bedding plane of limestone and texture of granite. These cracks affected the physical(density, elastic wave velocity) and mechanical properties(uniaxial compression strength , elastic modulus.

Thermal effects on shearing resistance of fractures in Tak granite

NASA Astrophysics Data System (ADS)

Khamrat, S.; Thongprapha, T.; Fuenkajorn, K.

2018-06-01

Triaxial shear tests have been performed on tension-induced fractures and smooth saw-cut surfaces in Tak granite under temperatures up to 773 K. The objective is to gain an understanding of the movement of shallow faults that cause seismic activities in the Tak batholith in the north of Thailand. The results indicate that the peak and residual shear strengths and fracture dilations notably decrease as the temperatures increase. The thermal effect is enhanced under higher confining pressures. The areas of the sheared-off asperities increase with temperature and confining pressure. A power equation can describe the increase of shear strengths with normal stress where the normal stress exponent is a linear function of the temperature. The strain energy principle is applied to incorporate the principal stresses and strains into a strength criterion. A linear relation between the distortional strain energy (Wd) and the mean strain energy (Wm) of the fractures is obtained. The Wd-Wm slope depends on the fracture roughness and strength of the asperities, which can be defined as a function of shear and mean strains and dilation of the fractures. This may allow predicting the peak strength of the shallow faults in the Tak batholith.

Computer Simulation of Fracture in Aerogels

NASA Technical Reports Server (NTRS)

Good, Brian S.

2006-01-01

Aerogels are of interest to the aerospace community primarily for their thermal properties, notably their low thermal conductivities. While the gels are typically fragile, recent advances in the application of conformal polymer layers to these gels has made them potentially useful as lightweight structural materials as well. In this work, we investigate the strength and fracture behavior of silica aerogels using a molecular statics-based computer simulation technique. The gels' structure is simulated via a Diffusion Limited Cluster Aggregation (DLCA) algorithm, which produces fractal structures representing experimentally observed aggregates of so-called secondary particles, themselves composed of amorphous silica primary particles an order of magnitude smaller. We have performed multi-length-scale simulations of fracture in silica aerogels, in which the interaction b e e n two secondary particles is assumed to be described by a Morse pair potential parameterized such that the potential range is much smaller than the secondary particle size. These Morse parameters are obtained by atomistic simulation of models of the experimentally-observed amorphous silica "bridges," with the fracture behavior of these bridges modeled via molecular statics using a Morse/Coulomb potential for silica. We consider the energetics of the fracture, and compare qualitative features of low-and high-density gel fracture.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brochard, J.; Charras, T.; Ghoudi, M.

Modifications to a computer code for ductile fracture assessment of piping systems with postulated circumferential through-wall cracks under static or dynamic loading are very briefly described. The modifications extend the capabilities of the CASTEM2000 code to the determination of fracture parameters under creep conditions. The main advantage of the approach is that thermal loads can be evaluated as secondary stresses. The code is applicable to piping systems for which crack propagation predictions differ significantly depending on whether thermal stresses are considered as primary or secondary stresses.

Could the Geminid meteoroid stream be the result of long-term thermal fracture?

NASA Astrophysics Data System (ADS)

Ryabova, G. O.

2015-10-01

The previous models by Ryabova have shown that the Geminid meteoroid stream has cometary origin, so asteroid (3200) Phaethon (the Geminid's parent body) is probably a dead comet. Recently (in 2009 and 2012) some week activity was observed (see Jewitt & Li, 2010, AJ, 140), but it was not the cometary activity. Recurrent brightening of Phaethon in perihelion could be the result of thermal fracture and decomposition. In this study we model the longterm dust release from Phaethon based on this mechanism.

Hygrothermomechanical fracture stress criteria for fiber composites with sense-parity

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Ginty, C. A.

1983-01-01

Hygrothermomechanical fracture stress criteria are developed and evaluated for unidirectional composites (plies) with sense-parity. These criteria explicity quantify the individual contributions of applied, hygral and thermal stresses as well as couplings among these stresses. The criteria are for maximum stress, maximum strain, internal friction, work-to-fracture and combined-stress fracture. Predicted results obtained indicate that first ply failure will occur at stress levels lower than those predicted using criteria currently available in the literature. Also, the contribution of the various stress couplings (predictable only by fracture criteria with sense-parity) is significant to first ply failure and attendant fracture modes.

Discrete Element Model for Simulations of Early-Life Thermal Fracturing Behaviors in Ceramic Nuclear Fuel Pellets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hai Huang; Ben Spencer; Jason Hales

2014-10-01

A discrete element Model (DEM) representation of coupled solid mechanics/fracturing and heat conduction processes has been developed and applied to explicitly simulate the random initiations and subsequent propagations of interacting thermal cracks in a ceramic nuclear fuel pellet during initial rise to power and during power cycles. The DEM model clearly predicts realistic early-life crack patterns including both radial cracks and circumferential cracks. Simulation results clearly demonstrate the formation of radial cracks during the initial power rise, and formation of circumferential cracks as the power is ramped down. In these simulations, additional early-life power cycles do not lead to themore » formation of new thermal cracks. They do, however clearly indicate changes in the apertures of thermal cracks during later power cycles due to thermal expansion and shrinkage. The number of radial cracks increases with increasing power, which is consistent with the experimental observations.« less

Effect of thermal cycling on composites reinforced with two differently sized silica-glass fibers.

PubMed

Meriç, Gökçe; Ruyter, I Eystein

2007-09-01

To evaluate the effects of thermal cycling on the flexural properties of composites reinforced with two differently sized fibers. Acid-washed, woven, fused silica-glass fibers, were heat-treated at 500 degrees C, silanized and sized with one of two sizing resins (linear poly(butyl methacrylate)) (PBMA), cross-linked poly(methyl methacrylate) (PMMA). Subsequently the fibers were incorporated into a polymer matrix. Two test groups with fibers and one control group without fibers were prepared. The flexural properties of the composite reinforced with linear PBMA-sized fibers were evaluated by 3-point bend testing before thermal cycling. The specimens from all three groups were thermally cycled in water (12,000 cycles, 5/55 degrees C, dwell time 30 s), and afterwards tested by 3-point bending. SEM micrographs were taken of the fibers and of the fractured fiber reinforced composites (FRC). The reduction of ultimate flexural strength after thermal cycling was less than 20% of that prior to thermal cycling for composites reinforced with linear PBMA-sized silica-glass fibers. The flexural strength of the composite reinforced with cross-linked PMMA-sized fibers was reduced to less than half of the initial value. This study demonstrated that thermal cycling differently influences the flexural properties of composites reinforced with different sized silica-glass fibers. The interfacial linear PBMA-sizing polymer acts as a stress-bearing component for the high interfacial stresses during thermal cycling due to the flexible structure of the linear PBMA above Tg. The cross-linked PMMA-sizing, however, acts as a rigid component and therefore causes adhesive fracture between the fibers and matrix after the fatigue process of thermal cycling and flexural fracture.

Self-Organizing Fluid Convection Patterns in an en Echelon Fault Array

NASA Astrophysics Data System (ADS)

Patterson, James W.; Driesner, Thomas; Matthai, Stephan K.

2018-05-01

We present three-dimensional numerical simulations of natural convection in buried, vertical en echelon faults in impermeable host rock. Despite the fractures being hydraulically disconnected, convection within each fracture alters the temperature field in the surrounding host rock, altering convection in neighboring fractures. This leads to self-organization of coherent patterns of upward/downward flow and heating/cooling of the host rock spanning the entire fault array. This "synchronization" effect occurs when fracture spacing is less than the width of convection cells within the fractures, which is controlled by fracture transmissivity (permeability times thickness) and heterogeneity. Narrow fracture spacing and synchronization enhance convective fluid flow within fractures and cause convection to initiate earlier, even lowering the critical transmissivity necessary for convection initiation. Heat flow through the en echelon region, however, is enhanced only in low-transmissivity fractures, while heat flow in high-permeability fractures is reduced due to thermal interference between fractures.

Thermal single-well injection-withdrawal tracer tests for determining fracture-matrix heat transfer area

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pruess, K.; Doughty, C.

2010-01-15

Single-well injection-withdrawal (SWIW) tracer tests involve injection of traced fluid and subsequent tracer recovery from the same well, usually with some quiescent time between the injection and withdrawal periods. SWIW are insensitive to variations in advective processes that arise from formation heterogeneities, because upon withdrawal, fluid parcels tend to retrace the paths taken during injection. However, SWIW are sensitive to diffusive processes, such as diffusive exchange of conservative or reactive solutes between fractures and rock matrix. This paper focuses on SWIW tests in which temperature itself is used as a tracer. Numerical simulations demonstrate the sensitivity of temperature returns tomore » fracture-matrix interaction. We consider thermal SWIW response to the two primary reservoir improvements targeted with stimulation, (1) making additional fractures accessible to injected fluids, and (2) increasing the aperture and permeability of pre-existing fractures. It is found that temperature returns in SWIW tests are insensitive to (2), while providing a strong signal of more rapid temperature recovery during the withdrawal phase for (1).« less

Temperature-dependent change in the nature of glass fracture under electron bombardment

NASA Astrophysics Data System (ADS)

Kravchenko, A. A.

1991-04-01

We report the experimental discovery of a temperature-dependent change in the nature of glass fracture under low-energy (<10 keV) electron bombardment. This is shown to depend on the transition from the thermal-shock to the thermalfluctuation mechanism of fracture at the limiting temperature T1 = (Tg - 150) °C. The high-temperature cleavage fracture of K8 and TF1 glasses was studied and the threshold value of the critical power initiating cleavage fracture was determined (for the glasses studied Θthr = 50 70 W·sec·cm-2).

Cap rock efficiency of geothermal systems in fold-and-thrust belts: Evidence from paleo-thermal and structural analyses in Rosario de La Frontera geothermal area (NW Argentina)

NASA Astrophysics Data System (ADS)

Maffucci, R.; Corrado, S.; Aldega, L.; Bigi, S.; Chiodi, A.; Di Paolo, L.; Giordano, G.; Invernizzi, C.

2016-12-01

Cap rock characterization of geothermal systems is often neglected despite fracturing may reduce its efficiency and favours fluid migration. We investigated the siliciclastic cap rock of Rosario de La Frontera geothermal system (NW Argentina) in order to assess its quality as a function of fracture patterns and related thermal alteration. Paleothermal investigations (XRD on fine-grained fraction of sediments, organic matter optical analysis and fluid inclusions on veins) and 1D thermal modelling allowed us to distinguish the thermal fingerprint associated to sedimentary burial from that related to fluid migration. The geothermal system is hosted in a Neogene N-S anticline dissected by high angle NNW- and ENE-striking faults. Its cap rock can be grouped into two quality categories: rocks acting as good insulators, deformed by NNW-SSE and E-W shear fractures, NNE-SSW gypsum- and N-S-striking calcite-filled veins that developed during the initial stage of anticline growth. Maximum paleo-temperatures (< 60 °C) were experienced during deposition to folding phases. rocks acting as bad insulators, deformed by NNW-SSE fault planes and NNW- and WNW-striking sets of fractures associated to late transpressive kinematics. Maximum paleo-temperatures higher than about 115 °C are linked to fluid migration from the reservoir to surface (with a reservoir top at maximum depths of 2.5 km) along fault damage zones. This multi-method approach turned out to be particularly useful to trace the main pathways of hot fluids and can be applied in blind geothermal systems where either subsurface data are scarce or surface thermal anomalies are lacking.

Assessment of structural, thermal, and mechanical properties of portlandite through molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hajilar, Shahin, E-mail: shajilar@iastate.edu; Shafei, Behrouz, E-mail: shafei@iastate.edu

The structural, thermal, and mechanical properties of portlandite, the primary solid phase of ordinary hydrated cement paste, are investigated using the molecular dynamics method. To understand the effects of temperature on the structural properties of portlandite, the coefficients of thermal expansion of portlandite are determined in the current study and validated with what reported from the experimental tests. The atomic structure of portlandite equilibrated at various temperatures is then subjected to uniaxial tensile strains in the three orthogonal directions and the stress-strain curves are developed. Based on the obtained results, the effect of the direction of straining on the mechanicalmore » properties of portlandite is investigated in detail. Structural damage analysis is performed to reveal the failure mechanisms in different directions. The energies of the fractured surfaces are calculated in different directions and compared to those of the ideal surfaces available in the literature. The key mechanical properties, including tensile strength, Young's modulus, and fracture strain, are extracted from the stress-strain curves. The sensitivity of the obtained mechanical properties to temperature and strain rate is then explored in a systematic way. This leads to valuable information on how the structural and mechanical properties of portlandite are affected under various exposure conditions and loading rates. - Graphical abstract: Fracture mechanism of portlandite under uniaxial strain in the z-direction. - Highlights: • The structural, thermal, and mechanical properties of portlandite are investigated. • The coefficients of thermal expansion are determined. • The stress-strain relationships are studied in three orthogonal directions. • The effects of temperature and strain rate on mechanical properties are examined. • The plastic energy required for fracture in the crystalline structure is reported.« less

Transient Non Lin Deformation in Fractured Rock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sartori, Enrico

1998-10-14

MATLOC is a nonlinear, transient, two-dimensional (planer and axisymmetric), thermal stress, finite-element code designed to determine the deformation within a fractured rock mass. The mass is modeled as a nonlinear anistropic elastic material which can exhibit stress-dependent bi-linear locking behavior.

Model I, Mode II, and Mixed-Mode Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

NASA Astrophysics Data System (ADS)

Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

The mixed-mode fracture behavior of plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings was determined in air at 25 and 1316°C in asymmetric four-point flexure with single edge v-notched beam (SEVNB) test specimens. The mode I fracture toughness was found to be K Ic=1.15±0.07 and 0.98±0.13 MPa sqrt m , respectively, at 25 and 1316°C. The respective mode II fracture toughness values were K IIc=0.73±0.10 and 0.65±0.04 MPa sqrt m . Hence, there was an insignificant difference in either K Ic or K IIc between 25 and 1316°C for the coating material, whereas there was a noticeable distinction between K Ic and K IIc, resulting in K IIc/K Ic=0.65 at both temperatures. The empirical mixed-mode fracture criterion best described the coatings' mixed-mode fracture behavior among the four mixed-mode fracture theories considered. The angle of crack propagation was in reasonable agreement with the minimum strain energy density criterion. The effect of the directionality of the coating material in on K Ic was observed to be insignificant, while its sintering effect at 1316°C on K Ic was significant.

75 FR 10410 - Alternate Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock Events...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-08

... Toughness Requirements for Protection Against Pressurized Thermal Shock Events; Correcting Amendment AGENCY... Commission (NRC) is revising its regulations to add a table that was inadvertently omitted in a correction... toughness requirements for protection against pressurized thermal shock (PTS) events for pressurized water...

Diamond-silicon carbide composite and method

DOEpatents

Zhao, Yusheng [Los Alamos, NM

2011-06-14

Uniformly dense, diamond-silicon carbide composites having high hardness, high fracture toughness, and high thermal stability are prepared by consolidating a powder mixture of diamond and amorphous silicon. A composite made at 5 GPa/1673K had a measured fracture toughness of 12 MPam.sup.1/2. By contrast, liquid infiltration of silicon into diamond powder at 5 GPa/1673K produces a composite with higher hardness but lower fracture toughness.

Cold heavy oil production and production by radio-frequency electromagnetic radiation: Comparative numerical study

NASA Astrophysics Data System (ADS)

Davletbaev, Alfred; Kireev, Victor; Kovaleva, Liana; Zainullin, Aleksey; Minnigalimov, Rais

2016-12-01

Comparative analysis for "cold" heavy oil production from fractured well in low-permeability formation, as well as heavy oil production by radio-frequency electromagnetic heating has been carried out. The results of mathematical modeling for both these technologies taking into account different fracture's lengths show that the thermal method is most effective for more "short" fractures up to some their optimal size 5-10 m.

Enhancement of Fracture Toughness of Epoxy Nanocomposites by Combining Nanotubes and Nanosheets as Fillers

PubMed Central

Domun, Nadiim; Paton, Keith R.; Sainsbury, Toby; Zhang, Tao; Mohamud, Hibaaq

2017-01-01

In this work the fracture toughness of epoxy resin has been improved through the addition of low loading of single part and hybrid nanofiller materials. Functionalised multi-walled carbon nanotubes (f-MWCNTs) was used as single filler, increased the critical strain energy release rate, GIC, by 57% compared to the neat epoxy, at only 0.1 wt% filler content. Importantly, no degradation in the tensile or thermal properties of the nanocomposite was observed compared to the neat epoxy. When two-dimensional boron nitride nanosheets (BNNS) were added along with the one-dimensional f-MWCNTs, the fracture toughness increased further to 71.6% higher than that of the neat epoxy. Interestingly, when functionalised graphene nanoplatelets (f-GNPs) and boron nitride nanotubes (BNNTs) were used as hybrid filler, the fracture toughness of neat epoxy is improved by 91.9%. In neither of these hybrid filler systems the tensile properties were degraded, but the thermal properties of the nanocomposites containing boron nitride materials deteriorated slightly. PMID:29048345

Mechanical and thermal control of cleating and shearing in coal: examples from the Alabama coalbed methane field, USA

USGS Publications Warehouse

Pashin, Jack; Carroll, R.E.; Hatch, Joseph R.; Goldhaber, Martin B.

1999-01-01

Natural fractures provide most of the interconnected macroporosity in coal. Therefore, understanding the characteristics of these fractures and the associated mechanisms of formation is essential for effective coalbed methane exploration and field management. Natural fractures in coal can be divided into two general types: cleat and shear structures. Cleat has been studied for more than a century, yet the mechanisms of cleat formation remain poorly understood (see reviews by Close, 1993; Laubach et al.,1998). An important aspect of cleating is that systematic fracturing of coal is takes place in concert with devolatization and concomitant shrinkage of the coal matrix during thermal maturation (Ammosov and Eremin, 1960). Coal, furthermore, is a mechanically weak rock type that is subject to bedding-plane shear between more competent beds like shale, sandstone, and limestone. Yet, the significance of shear structures in coal has only begun to attract scientific interest (Hathaway and Gayer, 1996; Pashin, 1998).

Enhancement of Fracture Toughness of Epoxy Nanocomposites by Combining Nanotubes and Nanosheets as Fillers.

PubMed

Domun, Nadiim; Paton, Keith R; Hadavinia, Homayoun; Sainsbury, Toby; Zhang, Tao; Mohamud, Hibaaq

2017-10-19

In this work the fracture toughness of epoxy resin has been improved through the addition of low loading of single part and hybrid nanofiller materials. Functionalised multi-walled carbon nanotubes (f-MWCNTs) was used as single filler, increased the critical strain energy release rate, G IC , by 57% compared to the neat epoxy, at only 0.1 wt% filler content. Importantly, no degradation in the tensile or thermal properties of the nanocomposite was observed compared to the neat epoxy. When two-dimensional boron nitride nanosheets (BNNS) were added along with the one-dimensional f-MWCNTs, the fracture toughness increased further to 71.6% higher than that of the neat epoxy. Interestingly, when functionalised graphene nanoplatelets (f-GNPs) and boron nitride nanotubes (BNNTs) were used as hybrid filler, the fracture toughness of neat epoxy is improved by 91.9%. In neither of these hybrid filler systems the tensile properties were degraded, but the thermal properties of the nanocomposites containing boron nitride materials deteriorated slightly.

Modeling of heat flow and effective thermal conductivity of fractured media: Analytical and numerical methods

NASA Astrophysics Data System (ADS)

Nguyen, S. T.; Vu, M.-H.; Vu, M. N.; Tang, A. M.

2017-05-01

The present work aims to modeling the thermal conductivity of fractured materials using homogenization-based analytical and pattern-based numerical methods. These materials are considered as a network of cracks distributed inside a solid matrix. Heat flow through such media is perturbed by the crack system. The problem of heat flow across a single crack is firstly investigated. The classical Eshelby's solution, extended to the thermal conduction problem of an ellipsoidal inclusion embedding in an infinite homogeneous matrix, gives an analytical solution of temperature discontinuity across a non-conducting penny-shaped crack. This solution is then validated by the numerical simulation based on the finite elements method. The numerical simulation allows analyzing the effect of crack conductivity. The problem of a single crack is then extended to a medium containing multiple cracks. Analytical estimations for effective thermal conductivity, that take into account the interaction between cracks and their spatial distribution, are developed for the case of non-conducting cracks. Pattern-based numerical method is then employed for both cases non-conducting and conducting cracks. In the case of non-conducting cracks, numerical and analytical methods, both account for the spatial distribution of the cracks, fit perfectly. In the case of conducting cracks, the numerical analyzing of crack conductivity effect shows that highly conducting cracks weakly affect heat flow and the effective thermal conductivity of fractured media.

Fluid inclusions in calcite filled opening fractures of the Serra Alta Formation reveal paleotemperatures and composition of diagenetic fluids percolating Permian shales of the Paraná Basin

NASA Astrophysics Data System (ADS)

Teixeira, C. A. S.; Sawakuchi, A. O.; Bello, R. M. S.; Nomura, S. F.; Bertassoli, D. J.; Chamani, M. A. C.

2018-07-01

The thermal and diagenetic evolution of shale units has received renewed focus because of their emergence as unconventional hydrocarbon reservoirs. The Serra Alta Formation (SAF) is a Permian shale unit of the Paraná Basin, which is the largest South American cratonic basin. The SAF stands out as a pathway for aqueous fluids and hydrocarbon migration from the Irati organic-rich shales to the Pirambóia fluvial-eolian sandstone reservoirs. Vertical NNW and NNE opening fractures would be the main pathways for the migration of buried pore waters and aqueous fluids, besides the input of meteoric water. These fractures would be associated to the reactivation of basement discontinuities such as the Jacutinga (NE) and Guapiara (NW) faults. Thus, vertical NNE and NNW associated fractures would represent the main pathways for fluid migration in the studied area. The vertical calcite filled opening fractures from SAF record moderately low salinity (0-4.5 wt % of NaCl eq.) aqueous fluids, suggesting the input of meteoric water in the buried fracture system. Eutectic melting temperatures at -52±5 °C indicate an H2O + NaCl + CaCl2 system with CaCl2 or MgCl2 in solution. Homogenization temperatures recorded in fluid inclusion assemblages (FIAs) of calcite filled opening fractures indicate that the SAF in the studied area reached temperatures above 200 °C, suitable for generation of gaseous hydrocarbons. The recorded paleotemperatures point to a thermal peak associated with Serra Geral volcanic event during the Early Cretaceous, with the thermal effect of volcanic rock cap possibly overcoming the effect of intrusive igneous bodies. The detection of methane in SAF shale pores indicates conditions for hydrocarbon generation. However, additionally studies are necessary to confirm the thermogenic and/or biogenic origin of the methane within the SAF.

Experimental investigation of heat transport through single synthetic fractures

NASA Astrophysics Data System (ADS)

Pastore, Nicola; Cherubini, Claudia; Giasi, Concetta I.; Redondo, Jose M.

2017-04-01

In fractured geothermal reservoirs, heat transport is highly influenced by the presence of the fractures, so appropriate knowledge of heat behaviour in fractured porous media is essential for accurate prediction of the energy extraction in geothermal reservoirs. The present study focuses on the study of heat transport within single synthetic fractures. In particular manner several tests have been carried out in order to explore the role of fracture roughness, aperture variability and the fracture-matrix ratio on the heat transport dynamics. The Synfrac program together with a 3d printer have been used to build several fracture planes having different geometrical characteristics that have been moulded to generate concrete porous fractured blocks. The tests regard the observation of the thermal breakthrough curves obtained through a continuous flow injection in correspondence of eight thermocouples located uniformly on the fractured blocks. The physical model developed permits to reproduce and understand adequately some features of heat transport dynamics in fractured media. The results give emphasis on the errors of the assumptions commonly used in heat transport modelling.

Biomechanical Effect of Ferrule on Incisors Restored with a Fiberglass Post and Lithium-Disilicate Ceramic Crown after Thermal Cycling and Fatigue Loading.

PubMed

Valdivia, Andréa Dolores Correia Miranda; Rodrigues, Monise de Paula; Bicalho, Aline Aredes; Van Meerbeek, Bart; Sloten, Jos Vander; Pessoa, Roberto Sales E; Soares, Carlos José

2018-04-19

To evaluate the biomechanics of endodontically treated incisors restored with a fiberglass post and a CAD/CAM lithium-disilicate ceramic crown with/without a ferrule after thermal and mechanical aging. Twenty bovine incisors were divided into two groups (n = 10): 1. Fe, with a ferrule of 2 mm, and 2. NFe, without a ferrule. After endodontic treatment, the teeth were restored using a fiberglass post (Exacto 3, Angelus) and composite core (Tetric Ceram, Ivoclar Vivadent). They then received a CAD/CAM lithium-disilicate ceramic crown (IPS e.max CAD) luted using a self-adhesive composite (RelyX Unicem 2, 3M Oral Care). All specimens were subjected to 20,000 thermocycles and 2,400,000 simulated chewing cycles. Ceramic crown and root dentin strains (μS) were measured using strain gauges (n = 10) during 100-N loading before and after the thermal and mechanical aging, and upon fracture loading. The specimens were subsequently loaded to fracture (N). The stress distribution was analyzed using 3D individualized finite-element models created by micro-CT of experimental samples (n = 3). Strain data were analyzed using two-way ANOVA and Tukey's HSD test. Fracture resistance was analyzed using Student's t-test and fracture mode was analyzed using the chi-squared test (α = 0.05). After aging, NFe exhibited significantly higher root dentin deformation (buccal: 1248.0 ± 282.8; lingual: 516.2 ± 195.0; p < 0.001) than Fe (buccal, 554.0 ± 233.8; lingual: 311.8 ± 159.0; p < 0.001). The deformation measured on ceramic crowns was not influenced by ferrule presence or aging process. Significantly higher fracture resistance (N) was observed for the Fe (1099.6 ± 214.8) than the NFe group (675.3 ± 113.8) (p < 0.001). The NFe group revealed a lower fracture resistance:root strain ratio than did the Fe group. The stress levels on root dentin and fiberglass were lower for the Fe group. The NFe group showed increased root dentin strain after the aging process. The Fe group revealed higher fracture resistance, lower stress concentration on root dentin and fewer catastrophic fractures.

Imaging hydraulic fractures using temperature transients in the Belridge Diatomite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shahin, G.T.; Johnston, R.M.

1995-12-31

Results of a temperature transient analysis of Shell`s Phase 1 and Phase 2 Diatomite Steamdrive Pilots are used to image hydraulic injection fracture lengths, angles, and heat injectivities into the low-permeability formation. The Phase 1 Pilot is a limited-interval injection test. In Phase 2, steam is injected into two 350 ft upper and lower zones through separate hydraulic fractures. Temperature response of both pilots is monitored with sixteen logging observation wells. A perturbation analysis of the non-linear pressure diffusion and heat transport equations indicates that at a permeability of about 0.1 md or less, heat transport in the Diatomite tendsmore » to be dominated by thermal diffusivity, and pressure diffusion is dominated by the ratio of thermal expansion to fluid compressibility. Under these conditions, the temperature observed at a logging observation well is governed by a dimensionless quantity that depends on the perpendicular distance between the observation well and the hydraulic fracture, divided by the square root of time. Using this dependence, a novel method is developed for imaging hydraulic fracture geometry and relative heat injectivity from the temperature history of the pilot.« less

The equivalent thermal properties of a single fracture

NASA Astrophysics Data System (ADS)

Sangaré, D.; Thovert, J.-F.; Adler, P. M.

2008-10-01

The normal resistance and the tangential conductivity of a single fracture with Gaussian or self-affine surfaces are systematically studied as functions of the nature of the materials in contact and of the geometrical parameters. Analytical formulas are provided in the lubrication limit for fractures with sinusoidal apertures; these formulas are used to substantiate empirical formulas for resistance and conductivity. Other approximations based on the combination of series and parallel formulas are tested.

On thermal stress failure of the SNAP-19A RTG heat shield

NASA Technical Reports Server (NTRS)

Pitts, W. C.; Anderson, L. A.

1974-01-01

Results of a study on thermal stress problems in an amorphous graphite heat shield that is part of the launch-abort protect system for the SNAP-19A radio-isotope thermoelectric generators (RTG) that will be used on the Viking Mars Lander are presended. The first result is from a thermal stress analysis of a full-scale RTG heat source that failed to survive a suborbital entry flight test, possibly due to thermal stress failure. It was calculated that the maximum stress in the heat shield was only 50 percent of the ultimate strength of the material. To provide information on the stress failure criterion used for this calculation, some heat shield specimens were fractured under abort entry conditions in a plasma arc facility. It was found that in regions free of stress concentrations the POCO graphite heat shield material did fracture when the local stress reached the ultimate uniaxial stress of the material.

Misfit and fracture load of implant-supported monolithic crowns in zirconia-reinforced lithium silicate.

PubMed

Gomes, Rafael Soares; Souza, Caroline Mathias Carvalho de; Bergamo, Edmara Tatiely Pedroso; Bordin, Dimorvan; Del Bel Cury, Altair Antoninha

2017-01-01

In this study, marginal and internal misfit and fracture load with and without thermal-mechanical aging (TMA) of monolithic ZLS and lithium disilicate (LDS) crowns were evaluated. Crowns were milled using a computer-aided design/computer-aided manufacturing system. Marginal gaps (MGs), absolute marginal discrepancy (AMD), axial gaps, and occlusal gaps were measured by X-ray microtomography (n=8). For fracture load testing, crowns were cemented in a universal abutment, and divided into four groups: ZLS without TMA, ZLS with TMA, LDS without TMA, and LDS with TMA (n=10). TMA groups were subjected to 10,000 thermal cycles (5-55°C) and 1,000,000 mechanical cycles (200 N, 3.8 Hz). All groups were subjected to compressive strength testing in a universal testing machine at a crosshead speed of 1 mm/min until failure. Student's t-test was used to examine misfit, two-way analysis of variance was used to analyze fracture load, and Pearson's correlation coefficients for misfit and fracture load were calculated (α=0.05). The materials were analyzed according to Weibull distribution, with 95% confidence intervals. Average MG (p<0.001) and AMD (p=0.003) values were greater in ZLS than in LDS crowns. TMA did not affect the fracture load of either material. However, fracture loads of ZLS crowns were lower than those of LDS crowns (p<0.001). Fracture load was moderately correlated with MG (r=-0.553) and AMD (r=-0.497). ZLS with TMA was least reliable, according to Weibull probability. Within the limitations of this study, ZLS crowns had lower fracture load values and greater marginal misfit than did LDS crowns, although these values were within acceptable limits.

The Radiator-Enhanced Geothermal System

NASA Astrophysics Data System (ADS)

Hilpert, M.; Marsh, B. D.; Geiser, P.

2015-12-01

Standard Enhanced Geothermal Systems (EGS) have repeatedly been hobbled by the inability of rock to conductively transfer heat at rates sufficient to re-supply heat extracted convectively via artificially made fracture systems. At the root of this imbalance is the basic magnitude of thermal diffusivity for most rocks, which severely hampers heat flow once the cooled halos about fractures reach ~0.1 m or greater. This inefficiency is exacerbated by the standard EGS design of mainly horizontally constructed fracture systems with inflow and outflow access at the margins of the fracture network. We introduced an alternative system whereby the heat exchanger mimics a conventional radiator in an internal combustion engine, which we call a Radiator-EGS (i.e., RAD-EGS). The heat exchanger is built vertically with cool water entering the base and hot water extracted at the top. The RAD-EGS itself consists of a family of vertical vanes produced through sequential horizontal drilling and permeability stimulation through propellant fracking. The manufactured fracture zones share the orientation of the natural transmissive fracture system. As below about 700 m, S1 is vertical and the average strike of transmissive fractures parallels SHmax, creating vertical fractures that include S1 and SHmax requires drilling stacked laterals parallel to SHmax. The RAD-EGS is also based on the observation that the longevity of natural hydrothermal systems depends on thermal recharge through heat convection but not heat conduction. In this paper, we present numerical simulations that examine the effects of the depths of the injector and extraction wells, vane size, coolant flow rate, the natural crustal geothermal gradient, and natural regional background flow on geothermal energy extraction.

Lateral extrusion of a thermally weakened pluton overburden (Campiglia Marittima, Tuscany)

NASA Astrophysics Data System (ADS)

Vezzoni, Simone; Rocchi, Sergio; Dini, Andrea

2017-10-01

The ascent and emplacement of magmas in the upper crust modify the local pre-existing thermal and rheological settings. Such changes have important effects in producing anomalous structures, mass extrusion, rock fracturing, and in some conditions, hydrothermal mineralizations. In the Campiglia Marittima area, detailed field mapping led to the reconstruction of a local deformation history that overlaps, chronologically and spatially, with regional extension. This local deformation was triggered at the Miocene-Pliocene boundary by the intrusion of a monzogranitic pluton beneath a carbonate sedimentary sequence. The emplacement of the pluton produced a perturbation in the rheological behaviour of the carbonate host rocks, producing transient ductile conditions in the very shallow crust. The carbonate rocks were thermally weakened and flowed laterally, accumulating downslope of the pluton roof, mainly toward the east. As the thermal anomaly was decaying, the brittle-ductile boundary moved progressively back towards the pluton, and large tension gash-shaped volumes of fractured marble were generated. These fractured volumes were exploited by rising hydrothermal fluids generating sigmoidal skarn bodies and ore shoots. This work presents the Campiglia Marittima case study as a prime example of structural interference between regional extensional structures and local, lateral mass extrusion in a transient ductile rheological regime triggered by pluton emplacement.

Lateral extrusion of a thermally weakened pluton overburden (Campiglia Marittima, Tuscany)

NASA Astrophysics Data System (ADS)

Vezzoni, Simone; Rocchi, Sergio; Dini, Andrea

2018-06-01

The ascent and emplacement of magmas in the upper crust modify the local pre-existing thermal and rheological settings. Such changes have important effects in producing anomalous structures, mass extrusion, rock fracturing, and in some conditions, hydrothermal mineralizations. In the Campiglia Marittima area, detailed field mapping led to the reconstruction of a local deformation history that overlaps, chronologically and spatially, with regional extension. This local deformation was triggered at the Miocene-Pliocene boundary by the intrusion of a monzogranitic pluton beneath a carbonate sedimentary sequence. The emplacement of the pluton produced a perturbation in the rheological behaviour of the carbonate host rocks, producing transient ductile conditions in the very shallow crust. The carbonate rocks were thermally weakened and flowed laterally, accumulating downslope of the pluton roof, mainly toward the east. As the thermal anomaly was decaying, the brittle-ductile boundary moved progressively back towards the pluton, and large tension gash-shaped volumes of fractured marble were generated. These fractured volumes were exploited by rising hydrothermal fluids generating sigmoidal skarn bodies and ore shoots. This work presents the Campiglia Marittima case study as a prime example of structural interference between regional extensional structures and local, lateral mass extrusion in a transient ductile rheological regime triggered by pluton emplacement.

Offshore wellbore stability analysis based on fully coupled poro-thermo-elastic theory

NASA Astrophysics Data System (ADS)

Cao, Wenke; Deng, Jingen; Yu, Baohua; Liu, Wei; Tan, Qiang

2017-03-01

Drilling-induced tensile fractures are usually caused when the weight of mud is too high, and the effective tangential stress becomes tensile. It is thus hard to explain why tensile fractures are distributed along the lower part of a hole in an offshore exploration well when the mud weight is low. According to analysis, the reason could be the thermal effect, which cannot be ignored because of the drilling fluid and the cooling action of sea water during circulation. A heat transfer model is set up to obtain the temperature distribution of the wellbore and its formation by the finite difference method. Then, fully coupled poro-thermo-elastic theory is used to study the pore pressure and effective stress around the wellbore. By comparing it with both poroelastic and elastic models, it is indicated that the poroelastic effect is dominant at the beginning of circulation and inhibits tensile fractures from forming; then, the thermal effect becomes more important and decreases the effective tangential stress with the passing of time, so the drilling fluid and the cooling effect of sea water can cause tensile fractures to happen. Meanwhile, tensile fractures are shallow and not likely to lead to mud leakage with lower mud weight, which agrees with the actual drilling process. On the other hand, the fluid cooling effect could increase the strength of the rock and reduce the likelihood of shear failure, which would be beneficial for wellbore stability. So, the thermal effect cannot be neglected in offshore wellbore stability analysis, and mud weight and borehole exposure time should be controlled in the case of mud loss.

Mode I, Mode II, and Mixed-Mode Fracture of Plasma-sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

2003-01-01

The mixed-mode fracture behavior of plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings was determined in air at 25 and 1316 C in asymmetric four-point flexure with single edge v-notched beam (SEVNB) test specimens. The mode I fracture toughness was found to be K(sub Ic) = 1.15 plus or minus 0.07 and 0.98 plus or minus 0.13 MPa the square root of m, respectively, at 25 and 1316 C. The respective mode II fracture toughness values were K(sub IIc) = 0.73 plus or minus 0.10 and 0.65 plus or minus 0.04 MPa the square root of m. Hence, there was an insignificant difference in either K(sub Ic or K(sub IIc) between 25 and 1316 C for the coating material, whereas there was a noticeable distinction between K(sub Ic) and K(sub IIc), resulting in K(sub IIc) per K(sub Ic) = 0.65 at both temperatures. The empirical mixed-mode fracture criterion best described the coatings' mixed-mode fracture behavior among the four mixed-mode fracture theories considered. The angle of crack propagation was in reasonable agreement with the minimum strain energy density criterion. The effect of the directionality of the coating material in on K(sub Ic) was observed to be insignificant, while its sintering effect at 1316 C on K(sub Ic) was significant.

Three-Dimensional Modeling of Fracture Clusters in Geothermal Reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghassemi, Ahmad

The objective of this is to develop a 3-D numerical model for simulating mode I, II, and III (tensile, shear, and out-of-plane) propagation of multiple fractures and fracture clusters to accurately predict geothermal reservoir stimulation using the virtual multi-dimensional internal bond (VMIB). Effective development of enhanced geothermal systems can significantly benefit from improved modeling of hydraulic fracturing. In geothermal reservoirs, where the temperature can reach or exceed 350oC, thermal and poro-mechanical processes play an important role in fracture initiation and propagation. In this project hydraulic fracturing of hot subsurface rock mass will be numerically modeled by extending the virtual multiplemore » internal bond theory and implementing it in a finite element code, WARP3D, a three-dimensional finite element code for solid mechanics. The new constitutive model along with the poro-thermoelastic computational algorithms will allow modeling the initiation and propagation of clusters of fractures, and extension of pre-existing fractures. The work will enable the industry to realistically model stimulation of geothermal reservoirs. The project addresses the Geothermal Technologies Office objective of accurately predicting geothermal reservoir stimulation (GTO technology priority item). The project goal will be attained by: (i) development of the VMIB method for application to 3D analysis of fracture clusters; (ii) development of poro- and thermoelastic material sub-routines for use in 3D finite element code WARP3D; (iii) implementation of VMIB and the new material routines in WARP3D to enable simulation of clusters of fractures while accounting for the effects of the pore pressure, thermal stress and inelastic deformation; (iv) simulation of 3D fracture propagation and coalescence and formation of clusters, and comparison with laboratory compression tests; and (v) application of the model to interpretation of injection experiments (planned by our industrial partner) with reference to the impact of the variations in injection rate and temperature, rock properties, and in-situ stress.« less

Imbedded-Fracture Formulation of THMC Processes in Fractured Media

NASA Astrophysics Data System (ADS)

Yeh, G. T.; Tsai, C. H.; Sung, R.

2016-12-01

Fractured media consist of porous materials and fracture networks. There exist four approaches to mathematically formulating THMC (Thermal-Hydrology-Mechanics-Chemistry) processes models in the system: (1) Equivalent Porous Media, (2) Dual Porosity or Dual Continuum, (3) Heterogeneous Media, and (4) Discrete Fracture Network. The first approach cannot explicitly explore the interactions between porous materials and fracture networks. The second approach introduces too many extra parameters (namely, exchange coefficients) between two media. The third approach may make the problems too stiff because the order of material heterogeneity may be too much. The fourth approach ignore the interaction between porous materials and fracture networks. This talk presents an alternative approach in which fracture networks are modeled with a lower dimension than the surrounding porous materials. Theoretical derivation of mathematical formulations will be given. An example will be illustrated to show the feasibility of this approach.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robert Radtke

The manufacture of thermally stable diamond (TSP) cutters for drill bits used in petroleum drilling requires the brazing of two dissimilar materials--TSP diamond and tungsten carbide. The ENDURUS{trademark} thermally stable diamond cutter developed by Technology International, Inc. exhibits (1) high attachment (shear) strength, exceeding 345 MPa (50,000 psi), (2) TSP diamond impact strength increased by 36%, (3) prevents TSP fracture when drilling hard rock, and (4) maintains a sharp edge when drilling hard and abrasive rock. A novel microwave brazing (MWB) method for joining dissimilar materials has been developed. A conventional braze filler metal is combined with microwave heating whichmore » minimizes thermal residual stress between materials with dissimilar coefficients of thermal expansion. The process results in preferential heating of the lower thermal expansion diamond material, thus providing the ability to match the thermal expansion of the dissimilar material pair. Methods for brazing with both conventional and exothermic braze filler metals have been developed. Finite element modeling (FEM) assisted in the fabrication of TSP cutters controllable thermal residual stress and high shear attachment strength. Further, a unique cutter design for absorbing shock, the densification of otherwise porous TSP diamond for increased mechanical strength, and diamond ion implantation for increased diamond fracture resistance resulted in successful drill bit tests.« less

Pressure vessel fracture, fatigue, and life management: PVP-Volume 233

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhandari, S.; Milella, P.P.; Pennell, W.E.

1992-01-01

This volume contains papers relating to the structural integrity assessment of pressure vessels and piping, with special emphasis on the effects of aging. The papers are organized in the following five areas: (1) pressure vessel life management; (2) fracture characterization using local and dual-parameter approaches; (3) stratification and thermal fatigue; (4) creep, fatigue, and fracture; and (5) integrated approach to integrity assessment of pressure components. Separate abstracts were prepared for 39 papers in this conference.

Coupled transport, mixing and biogeochemical reactions in fractured media: experimental observations and modelling at the Ploemeur fractured rock observatory

NASA Astrophysics Data System (ADS)

Le Borgne, T.; Bochet, O.; Klepikova, M.; Kang, P. K.; Shakas, A.; Aquilina, L.; Dufresne, A.; Linde, N.; Dentz, M.; Bour, O.

2016-12-01

Transport processes in fractured media and associated reactions are governed by multiscale heterogeneity ranging from fracture wall roughness at small scale to broadly distributed fracture lengths at network scale. This strong disorder induces a variety of emerging phenomena, including flow channeling, anomalous transport and heat transfer, enhanced mixing and reactive hotspot development. These processes are generally difficult to isolate and monitor in the field because of the high degree of complexity and coupling between them. We report in situ experimental observations from the Ploemeur fractured rock observatory (http://hplus.ore.fr/en/ploemeur) that provide new insights on the dynamics of transport and reaction processes in fractured media. These include dipole and push pull tracer tests that allow understanding and modelling anomalous transport processes characterized by heavy-tailed residence time distributions (Kang et al. 2015), thermal push pull tests that show the existence of highly channeled flow with a strong control on fracture matrix exchanges (Klepikova et al. 2016) and time lapse hydrogeophysical monitoring of saline tracer tests that allow quantifying the distribution of transport length scales governing dispersion processes (Shakas et al. 2016). These transport processes are then shown to induce rapid oxygen delivery and mixing at depth leading to massive biofilm development (Bochet et al., in prep.). Hence, this presentation will attempt to link these observations made at different scales to quantify and model the coupling between flow channeling, non-Fickian transport, mixing and chemical reactions in fractured media. References: Bochet et al. Biofilm blooms driven by enhanced mixing in fractured rock, in prep. Klepikova et al. 2016, Heat as a tracer for understanding transport processes in fractured media: theory and field assessment from multi-scale thermal push-pull tracer tests, Water Resour. Res. 52Shakas et al. 2016, Hydrogeophysical characterization of transport processes in fractured rock by combining push-pull and single-hole ground penetrating radar experiments, Water Resour. Res. 52 Kang et al. 2015, Impact of velocity correlation and distribution on transport in fractured media : Field evidence and theoretical model, Water Resour. Res., 51

The effect of porosity and microcracking on the thermomechanical properties of cordierite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shyam, A.; Bruno, G.; Watkins, T. R.

2015-08-28

The effect of porosity and microcracking on the mechanical properties (strength, fracture toughness, Young’s modulus, and fracture energy) and thermal expansion of diesel particulate filter (DPF) grade cordierite materials has been investigated. A method to deconvolute the effect of porosity and microcracking on Young’s modulus is proposed. In addition, the microcrack density and the pore morphology factor are calculated by applying a micromechanical differential scheme. The values of the investigated mechanical properties are shown to decrease with an increase in porosity, but the thermal expansion values are insensitive to porosity. The variation in mechanical properties as a function of porositymore » leads to distinct porosity dependence of thermal shock resistance for crack initiation and crack propagation for DPF grade synthetic cordierite.« less

Modeling of Propagation of Interacting Cracks Under Hydraulic Pressure Gradient

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Hai; Mattson, Earl Douglas; Podgorney, Robert Karl

A robust and reliable numerical model for fracture initiation and propagation, which includes the interactions among propagating fractures and the coupling between deformation, fracturing and fluid flow in fracture apertures and in the permeable rock matrix, would be an important tool for developing a better understanding of fracturing behaviors of crystalline brittle rocks driven by thermal and (or) hydraulic pressure gradients. In this paper, we present a physics-based hydraulic fracturing simulator based on coupling a quasi-static discrete element model (DEM) for deformation and fracturing with conjugate lattice network flow model for fluid flow in both fractures and porous matrix. Fracturingmore » is represented explicitly by removing broken bonds from the network to represent microcracks. Initiation of new microfractures and growth and coalescence of the microcracks leads to the formation of macroscopic fractures when external and/or internal loads are applied. The coupled DEM-network flow model reproduces realistic growth pattern of hydraulic fractures. In particular, simulation results of perforated horizontal wellbore clearly demonstrate that elastic interactions among multiple propagating fractures, fluid viscosity, strong coupling between fluid pressure fluctuations within fractures and fracturing, and lower length scale heterogeneities, collectively lead to complicated fracturing patterns.« less

Development of a finite element based thermal cracking performance prediction model.

DOT National Transportation Integrated Search

2009-09-15

Low-temperature cracking of hot-mix asphalt (HMA) pavements continues to be a leading cause of : premature pavement deterioration in regions of cold climate and/or where significant thermal cycling : occurs. Recent advances in fracture testing and mo...

Observed source parameters for dynamic rupture with non-uniform initial stressand relatively high fracture energy

USGS Publications Warehouse

Beeler, Nicholas M.; Kilgore, Brian D.; McGarr, Arthur F.; Fletcher, Jon Peter B.; Evans, John R.; Steven R. Baker,

2012-01-01

We have conducted dynamic rupture propagation experiments to establish the relations between in-source stress drop, fracture energy and the resulting particle velocity during slip of an unconfined 2 m long laboratory fault at normal stresses between 4 and 8 MPa. To produce high fracture energy in the source we use a rough fault that has a large slip weakening distance. An artifact of the high fracture energy is that the nucleation zone is large such that precursory slip reduces fault strength over a large fraction of the total fault length prior to dynamic rupture, making the initial stress non-uniform. Shear stress, particle velocity, fault slip and acceleration were recorded coseismically at multiple locations along strike and at small fault-normal distances. Stress drop increases weakly with normal stress. Average slip rate depends linearly on the fault strength loss and on static stress drop, both with a nonzero intercept. A minimum fracture energy of 1.8 J/m2 and a linear slip weakening distance of 33 μm are inferred from the intercept. The large slip weakening distance also affects the average slip rate which is reduced by in-source energy dissipation from on-fault fracture energy.Because of the low normal stress and small per event slip (∼86 μm), no thermal weakening such as melting or pore fluid pressurization occurs in these experiments. Despite the relatively high fracture energy, and the very low heat production, energy partitioning during these laboratory earthquakes is very similar to typical earthquake source properties. The product of fracture energy and fault area is larger than the radiated energy. Seismic efficiency is low at ∼2%. The ratio of apparent stress to static stress drop is ∼27%, consistent with measured overshoot. The fracture efficiency is ∼33%. The static and dynamic stress drops when extrapolated to crustal stresses are 2–7.3 MPa and in the range of typical earthquake stress drops. As the relatively high fracture energy reduces the slip velocities in these experiments, the extrapolated average particle velocities for crustal stresses are 0.18–0.6 m/s. That these experiments are consistent with typical earthquake source properties suggests, albeit indirectly, that thermal weakening mechanisms such as thermal pressurization and melting which lead to near complete stress drops, dominate earthquake source properties only for exceptional events unless crustal stresses are low.

The thermo-mechanical behaviour of W-Cu metal matrix composites for fusion heat sink applications: The influence of the Cu content

NASA Astrophysics Data System (ADS)

Tejado, E.; Müller, A. v.; You, J.-H.; Pastor, J. Y.

2018-01-01

Copper and its alloys are used as heat sink materials for next generation fusion devices and will be joined to tungsten as an armour material. However, the joint of W and Cu experiences high thermal stresses when exposed to high heat loads so an interlayer material could effectively ensure the lifetime of the component by reducing the thermal mismatch. Many researchers have published results on the production of W-Cu composites aiming attention at its thermal conductivity; nevertheless, the mechanical performance of these composites remains poor. This paper reports the characterization of the thermo-mechanical behaviour of W-Cu composites produced via a liquid Cu melt infiltration of porous W preform. This technique was applied to produce composites with 15, 30 and 40 wt% Cu. The microstructure, thermal properties, and mechanical performance were investigated and measured from RT to 800 °C. The results demonstrated that high densification and superior mechanical properties can indeed be achieved via this manufacturing route. The mechanical properties (elastic modulus, fracture toughness, and strength) of the composites show a certain dependency on the Cu content; fracture mode shifts from the dominantly brittle fracture of W particles with constrained deformation of the Cu phase at low Cu content to the predominance of the ductile fracture of Cu when its ratio is higher. Though strong degradation is observed at 800 °C, the mechanical properties at operational temperatures, i.e. below 350 °C, remain rather high-even better than W/Cu materials reported previously. In addition, we demonstrated that the elastic modulus, and therefore the coefficient of thermal expansion, can be tailored via control of the W skeleton's porosity. As a result, the W-Cu composites presented here would successfully drive away heat produced in the fusion chamber avoiding the mismatch between materials while contributing to the structural support of the system.

Fracture Mechanical Analysis of Open Cell Ceramic Foams Under Thermal Shock Loading

NASA Astrophysics Data System (ADS)

Settgast, C.; Abendroth, M.; Kuna, M.

2016-11-01

Ceramic foams made by replica techniques containing sharp-edged cavities, which are potential crack initiators and therefore have to be analyzed using fracture mechanical methods. The ceramic foams made of novel carbon bonded alumina are used as filters in metal melt filtration applications, where the filters are exposed to a thermal shock. During the casting process the filters experience a complex thermo-mechanical loading, which is difficult to measure. Modern numerical methods allow the simulation of such complex processes. As a simplified foam structure an open Kelvin cell is used as a representative volume element. A three-dimensional finite element model containing realistic sharp-edged cavities and three-dimensional sub-models along these sharp edges are used to compute the transient temperature, stress and strain fields at the Kelvin foam. The sharp edges are evaluated using fracture mechanical methods like the J-integral technique. The results of this study describe the influence of the pore size, relative density of the ceramic foam, the heat transfer and selected material parameters on the fracture mechanical behaviour.

Effect of Nb on Delayed Fracture Resistance of Ultra-High Strength Martensitic Steels

NASA Astrophysics Data System (ADS)

Song, Rongjie; Fonstein, Nina; Pottore, Narayan; Jun, Hyun Jo; Bhattacharya, Debanshu; Jansto, Steve

Ultra-high strength steels are materials of considerable interest for automotive and structural applications and are increasingly being used in those areas. Higher strength, however, makes steels more prone to hydrogen embrittlement (HE). The effects of Nb and other alloying elements on the hydrogen-induced delayed fracture resistance of cold rolled martensitic steels with ultra-high strength 2000 MPa were studied using an acid immersion test, thermal desorption analysis (TDA) and measuring of permeation. The microstructure was characterized by high resolution field emission Scanning Electron Microscopy (SEM) with Electron Backscattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM). It was shown that the combined addition of Nb significantly improved the delayed fracture resistance of investigated steel. The addition of Nb to alloyed martensitic steels resulted in very apparent grain refinement of the prior austenite grain size. The Nb microalloyed steel contained a lower diffusible hydrogen content during thermal desorption analysis as compared to the base steel and had a higher trapped hydrogen amount after charging. The reason that Nb improved the delayed fracture resistance of steels can be attributed mostly to both hydrogen trapping and grain refinement.

In vitro comparison of fracture load of implant-supported, zirconia-based, porcelain- and composite-layered restorations after artificial aging.

PubMed

Komine, Futoshi; Taguchi, Kohei; Fushiki, Ryosuke; Kamio, Shingo; Iwasaki, Taro; Matsumura, Hideo

2014-01-01

This study evaluated fracture load of single-tooth, implant-supported, zirconia-based, porcelain- and indirect composite-layered restorations after artificial aging. Forty-four zirconia-based molar restorations were fabricated on implant abutments and divided into four groups, namely, zirconia-based all-ceramic restorations (ZAC group) and three types of zirconia-based composite-layered restorations (ZIC-P, ZIC-E, and ZIC groups). Before layering an indirect composite material, the zirconia copings in the ZIC-P and ZIC-E groups were primed with Clearfil Photo Bond and Estenia Opaque Primer, respectively. All restorations were cemented on the abutments with glass-ionomer cement and then subjected to thermal cycling and cyclic loading. All specimens survived thermal cycling and cyclic loading. The fracture load of the ZIC-P group (2.72 kN) was not significantly different from that of the ZAC group (3.05 kN). The fracture load of the zirconia-based composite-layered restoration primed with Clearfil Photo Bond (ZIC-P) was comparable to that of the zirconia-based all-ceramic restoration (ZAC) after artificial aging.

NASA-UVA Light Aerospace Alloy and Structures Technology Program (LA2ST)

NASA Technical Reports Server (NTRS)

Gangloff, Richard P.; Scully, John R.; Stoner, Glenn E.; Thornton, Earl A.; Wawner, Franklin E., Jr.; Wert, John A.

1993-01-01

The NASA-UVA Light Aerospace Alloy and Structures Technology (LA2ST) Program continues a high level of activity. Progress achieved between 1 Jan. and 30 Jun. 1993 is reported. The objective of the LA2ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light weight aerospace alloys, composites, and thermal gradient structures in collaboration with NASA-Langley researchers. The following projects are addressed: environmental fatigue of Al-Li-Cu alloys; mechanisms of localized corrosion and environmental fracture in Al-Cu-Li-Mg-Ag alloy X2095 and compositional variations; the effect of zinc additions on the precipitation and stress corrosion cracking behavior of alloy 8090; hydrogen interactions with Al-Li-Cu alloy 2090 and model alloys; metastable pitting of aluminum alloys; cryogenic fracture toughness of Al-Cu-Li + In alloys; the fracture toughness of Weldalite (TM); elevated temperature cracking of advanced I/M aluminum alloys; response of Ti-1100/SCS-6 composites to thermal exposure; superplastic forming of Weldalite (TM); research to incorporate environmental effects into fracture mechanics fatigue life prediction codes such as NASA FLAGRO; and thermoviscoplastic behavior.

Misfit and fracture load of implant-supported monolithic crowns in zirconia-reinforced lithium silicate

PubMed Central

GOMES, Rafael Soares; de SOUZA, Caroline Mathias Carvalho; BERGAMO, Edmara Tatiely Pedroso; BORDIN, Dimorvan; DEL BEL CURY, Altair Antoninha

2017-01-01

Abstract Zirconia-reinforced lithium silicate (ZLS) is a ceramic that promises to have better mechanical properties than other materials with the same indications as well as improved adaptation and fracture strength. Objective In this study, marginal and internal misfit and fracture load with and without thermal-mechanical aging (TMA) of monolithic ZLS and lithium disilicate (LDS) crowns were evaluated. Material and methods Crowns were milled using a computer-aided design/computer-aided manufacturing system. Marginal gaps (MGs), absolute marginal discrepancy (AMD), axial gaps, and occlusal gaps were measured by X-ray microtomography (n=8). For fracture load testing, crowns were cemented in a universal abutment, and divided into four groups: ZLS without TMA, ZLS with TMA, LDS without TMA, and LDS with TMA (n=10). TMA groups were subjected to 10,000 thermal cycles (5-55°C) and 1,000,000 mechanical cycles (200 N, 3.8 Hz). All groups were subjected to compressive strength testing in a universal testing machine at a crosshead speed of 1 mm/min until failure. Student’s t-test was used to examine misfit, two-way analysis of variance was used to analyze fracture load, and Pearson’s correlation coefficients for misfit and fracture load were calculated (α=0.05). The materials were analyzed according to Weibull distribution, with 95% confidence intervals. Results Average MG (p<0.001) and AMD (p=0.003) values were greater in ZLS than in LDS crowns. TMA did not affect the fracture load of either material. However, fracture loads of ZLS crowns were lower than those of LDS crowns (p<0.001). Fracture load was moderately correlated with MG (r=-0.553) and AMD (r=-0.497). ZLS with TMA was least reliable, according to Weibull probability. Conclusion Within the limitations of this study, ZLS crowns had lower fracture load values and greater marginal misfit than did LDS crowns, although these values were within acceptable limits. PMID:28678947

High Temperature Mechanical Properties of Free-Standing HVOF CoNiCrAlY Coatings by Lateral Compression of Circular Tube

NASA Astrophysics Data System (ADS)

Waki, Hiroyuki; Nakamura, Kyousuke; Yamaguchi, Itsuki; Kobayashi, Akira

MCrAlY, M means Co and/or Ni, sprayed coating is used to protect a super alloy substrate from corrosion or oxidation in a gas turbine blade. However, the mechanical properties are not well-known, because there are few proper measurement methods for a thin coating at high temperature. Authors have developed the new easy method to measure the mechanical properties using the lateral compression of a circular tube. The method is useful to apply to a thin coating because it does not need chucking and manufacturing a test piece is very easy. The method is also easily applicable to high temperature measurement. In this study, high temperature mechanical properties, Young's modulus, bending strength and fracture strain, of CoNiCrAlY coatings by HVOF were systematically measured. The results obtained were as follows: Young's modulus and bending strength suddenly decreased beyond 400˜450°C. The Young's modulus and bending strength thermally treated at higher than 1050°C was significantly higher than that of virgin CoNiCrAlY coating. It was found that higher thermal treatment in atmosphere was the most effective in increasing the Young's modulus and bending strength. It was also found that the improvement of Young's modulus was primarily caused by not the effect of TGO but the sintering and diffusion of unfused particles. On the contrary, the fracture strain increased beyond 400°C differently from the bending strength. The fracture strains of CoNiCrAlY thermally treated in vacuum were higher than those of CoNiCrAlY treated in atmosphere. It was found that higher thermal treatment in vacuum was the most effective in increasing the fracture strain.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanaka, T.; Shimizu, S.; Ogata, Y.

For the primary coolant piping of PWRs in Japan, cast duplex stainless steel which is excellent in terms of strength, corrosion resistance, and weldability has conventionally been used. The cast duplex stainless steel contains the ferrite phase in the austenite matrix and thermal aging after long term service is known to change its material characteristics. It is considered appropriate to apply the methodology of elastic plastic fracture mechanics for an evaluation of the integrity of the primary coolant piping after thermal aging. Therefore we evaluated the integrity of the primary coolant piping for an initial PWR plant in Japan bymore » means of elastic plastic fracture mechanics. The evaluation results show that the crack will not grow into an unstable fracture and the integrity of the piping will be secured, even when such through wall crack length is assumed to equal the fatigue crack growth length for a service period of up to 60 years.« less

Interlaminar fracture toughness of thermoplastic composites

NASA Technical Reports Server (NTRS)

Hinkley, J. A.; Johnston, N. J.; Obrien, T. K.

1988-01-01

Edge delamination tension and double cantilever beam tests were used to characterize the interlaminar fracture toughness of continuous graphite-fiber composites made from experimental thermoplastic polyimides and a model thermoplastic. Residual thermal stresses, known to be significant in materials processed at high temperatures, were included in the edge delamination calculations. In the model thermoplastic system (polycarbonate matrix), surface properties of the graphite fiber were shown to be significant. Critical strain energy release rates for two different fibers having similar nominal tensile properties differed by 30 to 60 percent. The reason for the difference is not clear. Interlaminar toughness values for the thermoplastic polyimide composites (LARC-TPI and polyimidesulfone) were 3 to 4 in-lb/sq in. Scanning electron micrographs of the EDT fracture surfaces suggest poor fiber/matrix bonding. Residual thermal stresses account for up to 32 percent of the strain energy release in composites made from these high-temperature resins.

Fracture Toughness Evaluation of Space Shuttle External Tank Thermal Protection System Polyurethane Foam Insulation Materials

NASA Technical Reports Server (NTRS)

McGill, Preston; Wells, Doug; Morgan, Kristin

2006-01-01

Experimental evaluation of the basic fracture properties of Thermal Protection System (TPS) polyurethane foam insulation materials was conducted to validate the methodology used in estimating critical defect sizes in TPS applications on the Space Shuttle External Fuel Tank. The polyurethane foam found on the External Tank (ET) is manufactured by mixing liquid constituents and allowing them to react and expand upwards - a process which creates component cells that are generally elongated in the foam rise direction and gives rise to mechanical anisotropy. Similarly, the application of successive foam layers to the ET produces cohesive foam interfaces (knitlines) which may lead to local variations in mechanical properties. This study reports the fracture toughness of BX-265, NCFI 24-124, and PDL-1034 closed-cell polyurethane foam as a function of ambient and cryogenic temperatures and knitline/cellular orientation at ambient pressure.

Experimental investigation of the hydraulic and heat-transfer properties of artificially fractured granite.

PubMed

Luo, Jin; Zhu, Yongqiang; Guo, Qinghai; Tan, Long; Zhuang, Yaqin; Liu, Mingliang; Zhang, Canhai; Xiang, Wei; Rohn, Joachim

2017-01-05

In this paper, the hydraulic and heat-transfer properties of two sets of artificially fractured granite samples are investigated. First, the morphological information is determined using 3D modelling technology. The area ratio is used to describe the roughness of the fracture surface. Second, the hydraulic properties of fractured granite are tested by exposing samples to different confining pressures and temperatures. The results show that the hydraulic properties of the fractures are affected mainly by the area ratio, with a larger area ratio producing a larger fracture aperture and higher hydraulic conductivity. Both the hydraulic apertureand the hydraulic conductivity decrease with an increase in the confining pressure. Furthermore, the fracture aperture decreases with increasing rock temperature, but the hydraulic conductivity increases owing to a reduction of the viscosity of the fluid flowing through. Finally, the heat-transfer efficiency of the samples under coupled hydro-thermal-mechanical conditions is analysed and discussed.

Experimental investigation of the hydraulic and heat-transfer properties of artificially fractured granite

PubMed Central

Luo, Jin; Zhu, Yongqiang; Guo, Qinghai; Tan, Long; Zhuang, Yaqin; Liu, Mingliang; Zhang, Canhai; Xiang, Wei; Rohn, Joachim

2017-01-01

In this paper, the hydraulic and heat-transfer properties of two sets of artificially fractured granite samples are investigated. First, the morphological information is determined using 3D modelling technology. The area ratio is used to describe the roughness of the fracture surface. Second, the hydraulic properties of fractured granite are tested by exposing samples to different confining pressures and temperatures. The results show that the hydraulic properties of the fractures are affected mainly by the area ratio, with a larger area ratio producing a larger fracture aperture and higher hydraulic conductivity. Both the hydraulic apertureand the hydraulic conductivity decrease with an increase in the confining pressure. Furthermore, the fracture aperture decreases with increasing rock temperature, but the hydraulic conductivity increases owing to a reduction of the viscosity of the fluid flowing through. Finally, the heat-transfer efficiency of the samples under coupled hydro-thermal-mechanical conditions is analysed and discussed. PMID:28054594

Formulations for Stronger Solid Oxide Fuel-Cell Electrolytes

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Goldsby, John C.; Choi, Sung R.

2004-01-01

Tests have shown that modification of chemical compositions can increase the strengths and fracture toughnesses of solid oxide fuel-cell (SOFC) electrolytes. Heretofore, these solid electrolytes have been made of yttria-stabilized zirconia, which is highly conductive for oxygen ions at high temperatures, as needed for operation of fuel cells. Unfortunately yttria-stabilized zirconia has a high coefficient of thermal expansion, low resistance to thermal shock, low fracture toughness, and low mechanical strength. The lack of strength and toughness are especially problematic for fabrication of thin SOFC electrolyte membranes needed for contemplated aeronautical, automotive, and stationary power-generation applications. The modifications of chemical composition that lead to increased strength and fracture toughness consist in addition of alumina to the basic yttria-stabilized zirconia formulations. Techniques for processing of yttria-stabilized zirconia/alumina composites containing as much as 30 mole percent of alumina have been developed. The composite panels fabricated by these techniques have been found to be dense and free of cracks. The only material phases detected in these composites has been cubic zirconia and a alumina: this finding signifies that no undesired chemical reactions between the constituents occurred during processing at elevated temperatures. The flexural strengths and fracture toughnesses of the various zirconia-alumina composites were measured in air at room temperature as well as at a temperature of 1,000 C (a typical SOFC operating temperature). The measurements showed that both flexural strength and fracture toughness increased with increasing alumina content at both temperatures. In addition, the modulus of elasticity and the thermal conductivity were found to increase and the density to decrease with increasing alumina content. The oxygen-ion conductivity at 1,000 C was found to be unchanged by the addition of alumina.

Multiphysics processes in partially saturated fractured rock: Experiments and models from Yucca Mountain

NASA Astrophysics Data System (ADS)

Rutqvist, Jonny; Tsang, Chin-Fu

2012-09-01

The site investigations at Yucca Mountain, Nevada, have provided us with an outstanding data set, one that has significantly advanced our knowledge of multiphysics processes in partially saturated fractured geological media. Such advancement was made possible, foremost, by substantial investments in multiyear field experiments that enabled the study of thermally driven multiphysics and testing of numerical models at a large spatial scale. The development of coupled-process models within the project have resulted in a number of new, advanced multiphysics numerical models that are today applied over a wide range of geoscientific research and geoengineering applications. Using such models, the potential impact of thermal-hydrological-mechanical (THM) multiphysics processes over the long-term (e.g., 10,000 years) could be predicted and bounded with some degree of confidence. The fact that the rock mass at Yucca Mountain is intensively fractured enabled continuum models to be used, although discontinuum models were also applied and are better suited for analyzing some issues, especially those related to predictions of rockfall within open excavations. The work showed that in situ tests (rather than small-scale laboratory experiments alone) are essential for determining appropriate input parameters for multiphysics models of fractured rocks, especially related to parameters defining how permeability might evolve under changing stress and temperature. A significant laboratory test program at Yucca Mountain also made important contributions to the field of rock mechanics, showing a unique relation between porosity and mechanical properties, a time dependency of strength that is significant for long-term excavation stability, a decreasing rock strength with sample size using very large core experiments, and a strong temperature dependency of the thermal expansion coefficient for temperatures up to 200°C. The analysis of in situ heater experiments showed that fracture closure/opening caused by changes in normal stress across fractures was the dominant mechanism for thermally induced changes in intrinsic fracture permeability during rock mass heating/cooling and that fracture shear dilation appears to be less significant. Significant effort was devoted to predicting the long-term stability of underground excavations under (mechanical) strength degradation and seismic loading, perhaps one of the most challenging tasks within the project. We note that such long-term strength degradation is actually an example of a chemically mediated process governed by underlying (microscopic) stress corrosion and chemical diffusion processes. In the Yucca Mountain Project, such chemically mediated mechanical changes were considered implicitly through model calibrations against laboratory and in situ heater experiments at temperatures anticipated to be experienced by the rock. A possible future research direction would be to simulate such processes mechanistically in a complete coupled THMC framework where C denotes chemical processes.

Geochemical changes and fracture development in Woodford Shale cores following hydrous pyrolysis under uniaxial confinement

USGS Publications Warehouse

Birdwell, Justin E.; Lewan, Michael D.; Miller, Michael; Baez, Luis; Beeney, Ken; Sonnenberg, Steve

2013-01-01

A uniaxial confinement clamp was used on Woodford Shale cores in hydrous pyrolysis experiments to study fracture development during thermal maturation. The clamp simulates overburden in that it prevents cores from expanding perpendicular to bedding fabric during the volume-increasing reactions associated with petroleum generation. Cores were cut from a slab of immature Woodford Shale and subjected to hydrous pyrolysis under confinement at 300, 330, and 365 °C for 72 hours to induce thermal maturities ranging from early bitumen to maximum expelled-oil generation. Two additional cores were used as experimental controls: (1) a confined core was saturated with water by heating it to 100 °C under hydrous pyrolysis conditions for 72 hours to use for characterization of the original rock, and (2) an unconfined core was heated at 365 °C for 72 hours to evaluate the effects of confinement on petroleum generation and expulsion. X-ray computed tomography (X-CT) imaging and other analyses identified five distinct beds within the cored interval. Using a tentative classification system, beds 1, 2, and 3 are described as dolomitic marlstone (DM) with total organic carbon (TOC) contents of 7.7, 5.8, and 7.7 wt. %, respectively; bed 4 is a cherty quartzose claystone (CQC) with TOC content of 5.5 wt. %; and bed 5 is a quartzose claystone with TOC content of 10.9 wt. %. Bed samples all had similar Rock-Eval hydrogen indices (600 ± 46 mg S2/g-TOC) and Tmax values (433 ± 2 °C), demonstrating organic matter uniformity and low thermal maturity. The X-CT scan of the core heated to 100 °C showed preexisting fractures that were nearly perpendicular to the bedding fabric primarily in the low-TOC DM bed 2 and CQC bed 4. Heating led to enhancement of preexisting fractures in the confined cores with the greatest enhancement occurring in CQC bed 4. The fractures increased in size and intensity with temperature. This is attributed to the internal pressure generated by volume-increasing reactions during the conversion of kerogen to bitumen and bitumen to oil and gas. The unconfined core heated to 365 °C showed no enhanced fracturing and its X-CT-scan resembled that of the 100 °C confined core. Comparison of the oil and gas yields from the confined and unconfined cores heated to 365 °C showed no significant differences, indicating that product expulsion is not inhibited by the procedure used in this study. These results also indicate that fracturing during thermal maturation is driven primarily by the enhancement of existing fractures.

Molecular dynamics studies of thermal dissipation during shock induced spalling

NASA Astrophysics Data System (ADS)

Xiang, Meizhen; Hu, Haibo; Chen, Jun; Liao, Yi

2013-09-01

Under shock loadings, the temperature of materials may vary dramatically during deformation and fracture processes. Thus, thermal effect is important for constructing dynamical failure models. Existing works on thermal dissipation effects are mostly from meso- to macro-scale levels based on phenomenological assumptions. The main purpose of the present work is to provide several atomistic scale perspectives about thermal dissipation during spall fracture by nonequilibrium molecular dynamics simulations on single-crystalline and nanocrystalline Pb. The simulations show that temperature arising starts from the vicinity of voids during spalling. The thermal dissipation rate in void nucleation stage is much higher than that in the later growth and coalescence stages. Both classical spallation and micro-spallation are taken into account. Classical spallation is corresponding to spallation phenomenon where materials keep in solid state during shock compression and release stages, while micro-spallation is corresponding to spallation phenomenon where melting occurs during shock compression and release stages. In classical spallation, whether residuary dislocations are produced in pre-spall stages has significant influences on thermal dissipation rate during void growth and coalescence. The thermal dissipation rates decrease as shock intensity increases. When the shock intensity exceeds the threshold of micro-spallation, the thermal dissipation rate in void nucleation stage drops precipitously. It is found that grain boundaries mainly influence the thermal dissipation rate in void nucleation stage in classical spallation. In micro-spallation, the grain boundary effects are insignificant.

A nonlinear high temperature fracture mechanics basis for strainrange partitioning

NASA Technical Reports Server (NTRS)

Kitamura, Takayuki; Halford, Gary R.

1989-01-01

A direct link was established between Strainrange Partitioning (SRP) and high temperature fracture mechanics by deriving the general SRP inelastic strain range versus cyclic life relationships from high temperature, nonlinear, fracture mechanics considerations. The derived SRP life relationships are in reasonable agreement based on the experience of the SRP behavior of many high temperature alloys. In addition, fracture mechanics has served as a basis for derivation of the Ductility-Normalized SRP life equations, as well as for examination of SRP relations that are applicable to thermal fatigue life prediction. Areas of additional links between nonlinear fracture mechanics and SRP were identified for future exploration. These include effects of multiaxiality as well as low strain, nominally elastic, long life creep fatigue interaction.

Control of the permeability of fractures in geothermal rocks

NASA Astrophysics Data System (ADS)

Faoro, Igor

This thesis comprises three journal articles that will be submitted for publication (Journal of Geophysical Research-Solid Earth). Their respective titles are: "Undrained through Drained Evolution of Permeability in Dual Permeability Media" by Igor Faoro, Derek Elsworth and Chris Marone, "Evolution of Stiffness and Permeability in Fractures Subject to Thermally-and Mechanically-Activated Dissolution" by Igor Faoro, Derek Elsworth Chris Marone; "Linking permeability and mechanical damage for basalt from Mt. Etna volcano (Italy)" by Igor Faoro, Sergio Vinciguerra, Chris Marone and Derek Elsworth. Undrained through Drained Evolution of Permeability in Dual Permeability Media: temporary permeability changes of fractured aquifers subject to earthquakes have been observed and recorded worldwide, but their comprehension still remains a complex issue. In this study we report on flow-through fracture experiments on cracked westerly cores that reproduce, at laboratory scale, those (steps like) permeability changes that have been recorded when earthquakes occur. In particular our experiments show that under specific test boundary conditions, rapid increments of pore pressure induce transient variations of flow rate of the fracture whose peak magnitudes decrease as the variations of the effective stresses increase. We identify that the observed hydraulic behavior of the fracture is due to two principal mechanisms of origin; respectively mechanical (shortening of core) and poro-elastic (radial diffusion of the pore fluid into the matrix of the sample) whose interaction cause respectively an instantaneous opening and then a progressive closure of the fracture. Evolution of Stiffness and Permeability in Fractures Subject to Thermally-and Mechanically-Activated Dissolution: we report the results of radial flow-through experiments conducted on heated samples of Westerly granite. These experiments are performed to examine the influence of thermally and mechanically activated dissolution on the mechanical (stiffness) and transport (stress-permeability) characteristics of fractures. The sample is thermally stressed to 80 °C and measurements of the constrained axial stress acting on the sample and of the flow rate of the fracture are recorded with time. Net efflux of dissolved mineral mass is also measured periodically to provide a record of rates of net mass removal. During the experiment the fracture permeability shows high sensitivity to the changing conditions of stress and temperature but no significant permanent variation of permeability have been recorded once the thermal cycle ends. Linking permeability and mechanical damage for basalt from Mt. Etna volcano (Italy): volcanic edifices, such as Mt. Etna volcano (Italy), are affected from repeated episodes of pressurization due to magma emplacement from deep reservoirs to shallow depths. This mechanism pressurizes the large aquifers within the edifice and increases the level of crack damage within the rocks of the edifice over extended periods of times. In order to improve our understanding of the complex coupling between circulating fluids and the development of crack damage we performed flow-through tests using cylindrical cores of Etna Basalt (Etna, Italy) cyclically loaded either by constant increments of the principal stress: sigma1 (deviatoric condition), or by increments of the effective confining pressure: sigma1 = sigma 2 = sigma3 (isostatic conditions). Under hydrostatic stresses, the permeability values of the intact sample decrease linearly with the increments of pressure and range between 5.2*10-17 m2 and 1.5*10-17m2. At deviatoric stresses (up to 60 MPa) the permeability from the initial value of 5*10-17 m2 slightly decays to the minimum value of 2*10 -17 m2 observed when the axial deviatoric stresses range between 40 MPa and 60 MPa. For higher deviatoric stresses, increases to 10-16 m2 are then observed up to the peak stress at 92 MPa. After failure the permeability persisted steady at the value of 8*10-16 m2 for the whole duration of the test, independently from the applied stress. We interpreted the decrease observed as due to the progressive closure of the voids space, as the axial load is incremented.

Three-dimensional modelling of thermal stress in floating zone silicon crystal growth

NASA Astrophysics Data System (ADS)

Plate, Matiss; Krauze, Armands; Virbulis, Jānis

2018-05-01

During the growth of large diameter silicon single crystals with the industrial floating zone method, undesirable level of thermal stress in the crystal is easily reached due to the inhomogeneous expansion as the crystal cools down. Shapes of the phase boundaries, temperature field and elastic material properties determine the thermal stress distribution in the solid mono crystalline silicon during cylindrical growth. Excessive stress can lead to fracture, generation of dislocations and altered distribution of intrinsic point defects. Although appearance of ridges on the crystal surface is the decisive factor of a dislocation-free growth, the influence of these ridges on the stress field is not completely clear. Here we present the results of thermal stress analysis for 4” and 5” diameter crystals using a quasi-stationary three dimensional mathematical model including the material anisotropy and the presence of experimentally observed ridges which cannot be addressed with axis-symmetric models. The ridge has a local but relatively strong influence on thermal stress therefore its relation to the origin of fracture is hypothesized. In addition, thermal stresses at the crystal rim are found to increase for a particular position of the crystal radiation reflector.

Thermal Testing and Quality Assurance of BGA LCC & QFN Electronic Packages

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuper, Cameron Mathias

The purpose of this project is to experimentally validate the thermal fatigue life of solder interconnects for a variety of surface mount electronic packages. Over the years, there has been a significant amount of research and analysis in the fracture of solder joints on printed circuit boards. Solder is important in the mechanical and electronic functionality of the component. It is important throughout the life of the product that the solder remains crack and fracture free. The specific type of solder used in this experiment is a 63Sn37Pb eutectic alloy. Each package was surrounded conformal coating or underfill material.

Evaluation on the characteristics of tin-silver-bismuth solder

NASA Astrophysics Data System (ADS)

Xia, Z.; Shi, Y.; Chen, Z.

2002-02-01

Tin-silver-bismuth solder is characterized by its lower melting point, good wetting behavior, and good mechanical property for which it is expected to be a new lead-free solder to replace tin-lead solder. In this article, Sn-3.33Ag-4.83Bi solder was investigated concerning its physical, spreading, and mechanical properties under specific conditions. Cooling curves and DSC results showed that it was close to eutectic composition (m.p. 210° 212 °C). Coefficiency of thermal expansion (CTE) of this solder, between that of PCBs and copper substrates, was beneficial to alleviate the thermal mismatch of the substrates. It was also a good electrical and thermal conductor. Using a rosin-based, mildly activated (RMA) flux, a spreading test indicated that SnAgBi solder paste had good solderability. Meanwhile, the solder had high tensile strength and fracture energy. Its fracture mechanism was a mixture of ductile and brittle fracture morphology. The metallographic and EDAX analyses indicated that it was composed of a tin-based solid solution and some intermetallic compound (IMC) that could strengthen the substrate. However, these large needle-like IMCs would cut the substrate and this resulted in the decreasing of the toughness of the solder.

Fracture in Phenolic Impregnated Carbon Ablator

NASA Technical Reports Server (NTRS)

Agrawal, Parul; Chavez-Garcia, Jose; Pham, John

2013-01-01

This paper describes the development of a novel technique to understand the failure mechanisms inside thermal protection materials. The focus of this research is on the class of materials known as phenolic impregnated carbon ablators. It has successfully flown on the Stardust spacecraft and is the thermal protection system material chosen for the Mars Science Laboratory and SpaceX Dragon spacecraft. Although it has good thermal properties, structurally, it is a weak material. To understand failure mechanisms in carbon ablators, fracture tests were performed on FiberForm(Registered TradeMark) (precursor), virgin, and charred ablator materials. Several samples of these materials were tested to investigate failure mechanisms at a microstructural scale. Stress-strain data were obtained simultaneously to estimate the tensile strength and toughness. It was observed that cracks initiated and grew in the FiberForm when a critical stress limit was reached such that the carbon fibers separated from the binder. However, both for virgin and charred carbon ablators, crack initiation and growth occurred in the matrix (phenolic) phase. Both virgin and charred carbon ablators showed greater strength values compared with FiberForm samples, confirming that the presence of the porous matrix helps in absorbing the fracture energy.

Fractography of glasses and ceramics II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frechette, V.D.; Varner, J.R.

1991-01-01

Topics addressed include finite element stress analysis and crack path prediction of imploding CRT; fractography and fracture mechanics of combustion growth diamond thin films; the fracture behavior of machineable hydroxyapatite; a fractal approach to crack branching (bifurcation) in glass; the fracture of glass-ionomer cements; the effect of quartz particle size on the strength and toughness of whitewares; and a proposed standard practice for fractographic analysis of monolithic advanced ceramics. Also treated are thermal exposure effects on ceramic matrix composites, fractography applied to rock core analysis, fractography of flexurally fractured glass rods, the fractographic determination of K(IC) and effects of microstructuralmore » effects in ceramics.« less

Enceladus' Geysers and Small-scale Thermal Hot Spots: Spatial Correlations and Implications

NASA Astrophysics Data System (ADS)

Porco, C.; Helfenstein, P.; Goguen, J.

2016-12-01

The geysering south polar terrain (SPT) of Enceladus has been a major focus of the Cassini mission ever since Cassini's first sighting of it in images taken in early 2005 (1). A high resolution imaging survey of the region conducted over the course of seven years resulted in the identification of 100 geysers erupting from the four main fractures crossing the SPT (2). The Cassini Visual and Infrared Mapping Spectrometer (VIMS) detected enhanced thermal emission arising from these fractures and taking the form of small-scale ( ≤ 10 meter) discrete spots (3,4). Four of these hot spot observations have already been spatially associated with four geysers on the Baghdad Sulcus fracture (2). The inferred spatial correlation and small size of each hot spot eliminated shear heating along the near-surface walls of the fractures as the source of the heat and erupting materials. Instead, it was concluded that condensation of vapor (and liquid), and the deposition of latent heat, on the near-surface vent walls, and the subsequent conduction of that heat to the surface, was the source of the observed thermal emission. This indicated that the hot spots are the secondary signature of a geyser eruption process deeply rooted in the moon's sub-surface liquid water reservoir (2). We extend the examination of these relationships to include seven additional VIMS observations of hot spots. At the present time, we have associated a total of 11 VIMS hot spot observations with 13 (maybe 14) geysers distributed over all four tiger stripe fractures. It's not uncommon for the locations of multiple (often two but sometimes three) surveyed geysers to overlap within estimated uncertainties. This can occur when they have different 3D orientations, making them identifiable in our 2014 survey as distinct features; However, the raw, thermally unmodeled VIMS maps, with their (relatively) coarse resolution, may register at that location only one corresponding hot spot. It is also possible that closely overlapping clusters of geysers in the survey represent a single geyser that changes its direction over the course of an Enceladus orbit as its vent widens and narrows with the diurnally varying normal stresses. Nonetheless, future thermal modeling of these VIMS hot spots should help constrain the conditions in the near-surface vents from which the geysers erupt.

Thermo-Mechanical and Thermal Behavior of High-Temperature Structural Materials.

DTIC Science & Technology

1980-12-31

glass insulating tape to prevent fracture due to unknown stresses at Lhe rod ends. Because of the very high density of cracks in the alumina, this...143. [31] 0. L. Bowie, J. Math. Phys. 35 (1956) 60. [32] F. Erdogan : in Fracture Mechanics of Ceramics, Vol. 1, ed. by R. C. f Bradt, D. P. H

A new thermo-mechanical coupled DEM model with non-spherical grains for thermally induced damage of rocks

NASA Astrophysics Data System (ADS)

Chen, Zhiqiang; Jin, Xu; Wang, Moran

2018-07-01

Thermally induced damage often occurs in rocks in geophysical systems. Discrete element method (DEM) is a useful tool to model this thermo-mechanical coupled process owing to its explicit representation of fracture initiation and propagation. However, the previous DEM models for this are mostly based on spherical discrete elements, which are not able to capture all consequences (e.g. high ratio of compressive to tensile strength) of real rocks (e.g. granite) composed of complex-geometry grains. In order to overcome this intrinsic limitation, we present a new model allowing to mimick thermally induced damage of brittle rock with non-spherical grains. After validations, the new model is used to study thermal gradient cracking with a special emphasis on the effects from rock heterogeneity. The obtained fracture initiation and propagation are consistent with experimental observations, which demonstrates the ability of current model to reproduce the thermally induced damage of rocks. Meanwhile, the results show that rock heterogeneity influences thermal gradient cracking significantly, and more micro cracks uniformly scattering around the borehole are induced in the heterogeneous sample, which is not good for applications such as nuclear waste disposal. The present model provides a promising approach at micro-scale to explore mechanisms of thermally induced damage of rocks in geological engineering.

Thermal drawdown-induced flow channeling in a single fracture in EGS

DOE PAGES

Guo, Bin; Fu, Pengcheng; Hao, Yue; ...

2016-01-28

Here, the evolution of flow pattern along a single fracture and its effects on heat production is a fundamental problem in the assessments of engineered geothermal systems (EGS). The channelized flow pattern associated with ubiquitous heterogeneity in fracture aperture distribution causes non-uniform temperature decrease in the rock body, which makes the flow increasingly concentrated into some preferential paths through the action of thermal stress. This mechanism may cause rapid heat production deterioration of EGS reservoirs. In this study, we investigated the effects of aperture heterogeneity on flow pattern evolution in a single fracture in a low-permeability crystalline formation. We developedmore » a numerical model on the platform of GEOS to simulate the coupled thermo-hydro-mechanical processes in a penny-shaped fracture accessed via an injection well and a production well. We find that aperture heterogeneity generally exacerbates flow channeling and reservoir performance generally decreases with longer correlation length of aperture field. The expected production life is highly variable (5 years to beyond 30 years) when the aperture correlation length is longer than 1/5 of the well distance, whereas a heterogeneous fracture behaves similar to a homogeneous one when the correlation length is much shorter than the well distance. Besides, the mean production life decreases with greater aperture standard deviation only when the correlation length is relatively long. Although flow channeling is inevitable, initial aperture fields and well locations that enable tortuous preferential paths tend to deliver long heat production lives.« less

3D J-Integral Capability in Grizzly

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spencer, Benjamin; Backman, Marie; Chakraborty, Pritam

2014-09-01

This report summarizes work done to develop a capability to evaluate fracture contour J-Integrals in 3D in the Grizzly code. In the current fiscal year, a previously-developed 2D implementation of a J-Integral evaluation capability has been extended to work in 3D, and to include terms due both to mechanically-induced strains and due to gradients in thermal strains. This capability has been verified against a benchmark solution on a model of a curved crack front in 3D. The thermal term in this integral has been verified against a benchmark problem with a thermal gradient. These developments are part of a largermore » effort to develop Grizzly as a tool that can be used to predict the evolution of aging processes in nuclear power plant systems, structures, and components, and assess their capacity after being subjected to those aging processes. The capabilities described here have been developed to enable evaluations of Mode- stress intensity factors on axis-aligned flaws in reactor pressure vessels. These can be compared with the fracture toughness of the material to determine whether a pre-existing flaw would begin to propagate during a pos- tulated pressurized thermal shock accident. This report includes a demonstration calculation to show how Grizzly is used to perform a deterministic assessment of such a flaw propagation in a degraded reactor pressure vessel under pressurized thermal shock conditions. The stress intensity is calculated from J, and the toughness is computed using the fracture master curve and the degraded ductile to brittle transition temperature.« less

High-resolution cross-borehole thermal tracer testing in granite: preliminary field results

NASA Astrophysics Data System (ADS)

Brixel, Bernard; Klepikova, Maria; Jalali, Mohammadreza; Amann, Florian; Loew, Simon

2017-04-01

Understanding how heat is transported, stored and exchanged across fractured media is becoming increasingly relevant in our society, as manifested from the growing popularity of modern technologies relying on the subsurface to either source or store heat. One good example is the utilization of heat from deep hydrothermal or petrothermal systems to generate electricity for base load power generation, a technology also known as deep geothermal energy (DGE). While very attractive in principle, the number of geothermal fields producing economical levels of electricity to this day is still very limited - largely due to the difficulty of either locating deep reservoirs that are both sufficiently hot and permeable or, in the absence of the latter, creating them. In this context, the Swiss Competence Center for Energy Research - Supply of Electricity (SCCER - SoE) is carrying out an in situ stimulation and circulation (ISC) experiment at the Grimsel Test Site (GTS), an underground rock lab located in the Aar massif, in the Swiss Alps. The circulation experiment planned for the post-stimulation phase represents one of the key components of this experimental research program, and the outcome of this test is expected to ultimately provide key insights in the factors controlling the performance of enhanced geothermal reservoirs. Therefore, to support the design of this experiment, short-term thermal tracer tests (TTT) were conducted with the objective to (i) assess the feasibility of conducting TTTs in a relatively intact granite (where fluid flow is controlled by a limited number of discrete fractures); (ii) determine optimal experimental setups; and to ultimately (iii) monitor thermal breakthroughs at high spatial and temporal resolution, providing insights on heat transport and complementing the characterization of hydrogeological conditions carried out through conventional means (e.g. hydraulic and/or solute tracer tests). Presented herein are the results of a 10-day thermal tracer test conducted by continuously injecting water at 40°C (ambient groundwater temperatures average around 12-13 °C) across a discrete fractured zone, isolated with packers. Monitoring was achieved using a combination of discrete temperature sensors (PT1000) and FO DTS (Silixa XT system) deployed along a network of both packed-off and open boreholes situated approx. 6-20 m apart from the injection zone. Thermal breakthrough was observed in multiple boreholes, as early as 6-7 hours following the injection of hot water. The rate of increase in temperatures was observed to significantly diminish over time, allowing water in the fracture carrying the majority of heat to reach a temperature of 17°C at the closest observation location. Furthermore, temperature declined along the fracture length. These data allowed us identifying the precise location of conductive fractures, thereby improving our understanding of the connectivity structure of our experimental rock volume. In addition, these results provide significant insights on heat transport and the efficiency of heat-exchange between fractures and the surrounding rock mass at Grimsel.

Thermal conductivity anisotropy of rocks

NASA Astrophysics Data System (ADS)

Lee, Youngmin; Keehm, Youngseuk; Shin, Sang Ho

2013-04-01

The interior heat of the lithosphere of the Earth is mainly transferred by conduction that depends on thermal conductivity of rocks. Many sedimentary and metamorphic rocks have thermal conductivity anisotropy, i.e. heat is preferentially transferred in the direction parallel to the bedding and foliation of these rocks. Deming (JGR, 1994) proposed an empirical relationship between K(perp) and anisotropy (K(par)/K(perp)) using 89 measurements on rock samples from literatures. In Deming's model, thermal conductivity is almost isotropic for K(perp) > 4 W/mK, but anisotropy is exponentially increasing with decreasing K(perp), with final anisotropy of ~2.5 at K(perp) < 1.0 W/mK. However, Davis et al. (JGR, 2007) argued that there is little evidence for Deming's suggestion that thermal conductivity anisotropy of all rocks increases systematically to about 2.5 for rocks with low thermal conductivity. Davis et al. insisted that Deming's increase in anisotropy for 1 < K(perp) < 4 W/mK with decreasing K(perp) could be due to the fractures filled with air or water, which causes thermal conductivity anisotropy. To test Deming's suggestion and Davis et al.'s argument on thermal conductivity anisotropy, we measured thermal conductivity parallel (K(par)) and perpendicular (K(perp)) to bedding or foliation and performed analytical & numerical modeling. Our measurements on 53 rock samples show the anisotropy range from 0.79 to 1.36 for 1.84 < K(prep) < 4.06 W/mK. Analytical models show that anisotropy can increase or stay the same at the range of 1 < K(perp) < 4 W/mK. Numerical modeling for gneiss shows that anisotropy ranges 1.21 to 1.36 for 2.5 < K(perp) < 4.8 W/mK. Another numerical modeling with interbedded coal layers in high thermal conductivity rocks (3.5 W/mK) shows anisotropy of 1.87 when K(perp) is 1.7 W/mK. Finally, numerical modeling with fractures indicates that the fractures does not seem to affect thermal conductivity anisotropy significantly. In conclusion, our preliminary results imply that thermal conductivity anisotropy can increase or stay at low value in the range of 1.0 < K(perp) < 4.0 W/mK. Both cases are shown to be possible through lab measurements and analytical & numerical modeling.

Fracture mechanics analyses of ceramic/veneer interface under mixed-mode loading.

PubMed

Wang, Gaoqi; Zhang, Song; Bian, Cuirong; Kong, Hui

2014-11-01

Few studies have focused on the interface fracture performance of zirconia/veneer bilayered structure, which plays an important role in dental all-ceramic restorations. The purpose of this study was to evaluate the fracture mechanics performance of zirconia/veneer interface in a wide range of mode-mixities (at phase angles ranging from 0° to 90°), and to examine the effect of mechanical properties of the materials and the interface on the fracture initiation and crack path of an interfacial crack. A modified sandwich test configuration with an oblique interfacial crack was proposed and calibrated to choose the appropriate geometry dimensions by means of finite element analysis. The specimens with different interface inclination angles were tested to failure under three-point bending configuration. Interface fracture parameters were obtained with finite element analyses. Based on the interfacial fracture mechanics, three fracture criteria for crack kinking were used to predict crack initiation and propagation. In addition, the effects of residual stresses due to coefficient of thermal expansion mismatch between zirconia and veneer on the crack behavior were evaluated. The crack initiation and propagation were well predicted by the three fracture criteria. For specimens at phase angle of 0, the cracks propagated in the interface; whereas for all the other specimens the cracks kinked into the veneer. Compressive residual stresses in the veneer can improve the toughness of the interface structure. The results suggest that, in zirconia/veneer bilayered structure the veneer is weaker than the interface, which can be used to explain the clinical phenomenon that veneer chipping rate is larger than interface delamination rate. Consequently, a veneer material with larger fracture toughness is needed to decrease the failure rate of all-ceramic restorations. And the coefficient of thermal expansion mismatch of the substrates can be larger to produce larger compressive stresses in the veneer. Copyright © 2014 Elsevier Ltd. All rights reserved.

Microfracture spacing distributions and the evolution of fracture patterns in sandstones

NASA Astrophysics Data System (ADS)

Hooker, J. N.; Laubach, S. E.; Marrett, R.

2018-03-01

Natural fracture patterns in sandstone were sampled using scanning electron microscope-based cathodoluminescence (SEM-CL) imaging. All fractures are opening-mode and are fully or partially sealed by quartz cement. Most sampled fractures are too small to be height-restricted by sedimentary layers. At very low strains (<∼0.001), fracture spatial distributions are indistinguishable from random, whereas at higher strains, fractures are generally statistically clustered. All 12 large (N > 100) datasets show spacings that are best fit by log-normal size distributions, compared to exponential, power law, or normal distributions. The clustering of fractures suggests that the locations of natural factures are not determined by a random process. To investigate natural fracture localization, we reconstructed the opening history of a cluster of fractures within the Huizachal Group in northeastern Mexico, using fluid inclusions from synkinematic cements and thermal-history constraints. The largest fracture, which is the only fracture in the cluster visible to the naked eye, among 101 present, opened relatively late in the sequence. This result suggests that the growth of sets of fractures is a self-organized process, in which small, initially isolated fractures grow and progressively interact, with preferential growth of a subset of fractures developing at the expense of growth of the rest. Size-dependent sealing of fractures within sets suggests that synkinematic cementation may contribute to fracture clustering.

Residual Tensile Property of Plain Woven Jute Fiber/Poly(Lactic Acid) Green Composites during Thermal Cycling

PubMed Central

Katogi, Hideaki; Takemura, Kenichi; Akiyama, Motoki

2016-01-01

This study investigated the residual tensile properties of plain woven jute fiber reinforced poly(lactic acid) (PLA) during thermal cycling. Temperature ranges of thermal cycling tests were 35–45 °C and 35–55 °C. The maximum number of cycles was 103 cycles. The quasi-static tensile tests of jute fiber, PLA, and composite were conducted after thermal cycling tests. Thermal mechanical analyses of jute fiber and PLA were conducted after thermal cycling tests. Results led to the following conclusions. For temperatures of 35–45 °C, tensile strength of composite at 103 cycles decreased 10% compared to that of composite at 0 cycles. For temperatures of 35–55 °C, tensile strength and Young’s modulus of composite at 103 cycles decreased 15% and 10%, respectively, compared to that of composite at 0 cycles. Tensile properties and the coefficient of linear expansion of PLA and jute fiber remained almost unchanged after thermal cycling tests. From observation of a fracture surface, the length of fiber pull out in the fracture surface of composite at 103 cycles was longer than that of composite at 0 cycles. Therefore, tensile properties of the composite during thermal cycling were decreased, probably because of the decrease of interfacial adhesion between the fiber and resin. PMID:28773694

Development of Fracture Mechanics Maps for Composite Materials. Volume 2.

DTIC Science & Technology

1985-12-01

AD-A169 663 DEP 1/3UR OIOST l uNCL~ss~~n HUCI S I B M 11 1*2 AF,:P,.-TR-?5,-4150 DEVELOPMENT OF FRACTURE MECHANICS MAPS FOR COMPOSITE MATERIALS Dr. H...coIo. Development of N/A N/A N/A N/A Fracture Mechanics Maps for Composite Materials 12. PERSONAL AUTHORISI Editor (Dr. H. W. Bergmann) 13. TYPE OF...GROUP SUB GR. Fiber Reinforced Composites , Dynamic Test, Thermal Cycling, 1I1 04 Quality Control, Static Test, Stress Concentrations 01 03 19

Laser notching ceramics for reliable fracture toughness testing

DOE PAGES

Barth, Holly D.; Elmer, John W.; Freeman, Dennis C.; ...

2015-09-19

A new method for notching ceramics was developed using a picosecond laser for fracture toughness testing of alumina samples. The test geometry incorporated a single-edge-V-notch that was notched using picosecond laser micromachining. This method has been used in the past for cutting ceramics, and is known to remove material with little to no thermal effect on the surrounding material matrix. This study showed that laser-assisted-machining for fracture toughness testing of ceramics was reliable, quick, and cost effective. In order to assess the laser notched single-edge-V-notch beam method, fracture toughness results were compared to results from other more traditional methods, specificallymore » surface-crack in flexure and the chevron notch bend tests. Lastly, the results showed that picosecond laser notching produced precise notches in post-failure measurements, and that the measured fracture toughness results showed improved consistency compared to traditional fracture toughness methods.« less

Investigation of Post-Flight Solid Rocket Booster Thermal Protection System

NASA Technical Reports Server (NTRS)

Nelson, Linda A.

2006-01-01

After every Shuttle mission, the Solid Rocket Boosters (SRBs) are recovered and observed for missing material. Most of the SRB is covered with a cork-based thermal protection material (MCC-l). After the most recent shuttle mission, STS-114, the forward section of the booster appeared to have been impacted during flight. The darkened fracture surfaces indicated that this might have occurred early in flight. The scope of the analysis included microscopic observations to assess the degree of heat effects and locate evidence of the impact source as well as chemical analysis of the fracture surfaces and recovered foreign material using Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy/Energy Dispersive Spectroscopy. The amount of heat effects and presence of soot products on the fracture surface indicated that the material was impacted prior to SRB re-entry into the atmosphere. Fragments of graphite fibers found on these fracture surfaces were traced to slag inside the Solid Rocket Motor (SRM) that forms during flight as the propellant is spent and is ejected throughout the descent of the SRB after separation. The direction of the impact mark matches with the likely trajectory of SRBs tumbling prior to re-entry.

Sensitivity analysis of coupled processes and parameters on the performance of enhanced geothermal systems.

PubMed

Pandey, S N; Vishal, Vikram

2017-12-06

3-D modeling of coupled thermo-hydro-mechanical (THM) processes in enhanced geothermal systems using the control volume finite element code was done. In a first, a comparative analysis on the effects of coupled processes, operational parameters and reservoir parameters on heat extraction was conducted. We found that significant temperature drop and fluid overpressure occurred inside the reservoirs/fracture that affected the transport behavior of the fracture. The spatio-temporal variations of fracture aperture greatly impacted the thermal drawdown and consequently the net energy output. The results showed that maximum aperture evolution occurred near the injection zone instead of the production zone. Opening of the fracture reduced the injection pressure required to circulate a fixed mass of water. The thermal breakthrough and heat extraction strongly depend on the injection mass flow rate, well distances, reservoir permeability and geothermal gradients. High permeability caused higher water loss, leading to reduced heat extraction. From the results of TH vs THM process simulations, we conclude that appropriate coupling is vital and can impact the estimates of net heat extraction. This study can help in identifying the critical operational parameters, and process optimization for enhanced energy extraction from a geothermal system.

77 FR 21594 - Duke Energy Carolinas, LLC; Environmental Assessment and Finding of No Significant Impact, Oconee...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-10

... of light-water nuclear power reactors provide adequate margins of safety during any condition of... toughness requirements for protection against pressurized thermal shock (PTS) events. The proposed action... for Protection Against Pressurized Thermal Shock Events,'' and 10 CFR part 50 Appendix G, ``Fracture...

Thermally stable diamond brazing

DOEpatents

Radtke, Robert P [Kingwood, TX

2009-02-10

A cutting element and a method for forming a cutting element is described and shown. The cutting element includes a substrate, a TSP diamond layer, a metal interlayer between the substrate and the diamond layer, and a braze joint securing the diamond layer to the substrate. The thickness of the metal interlayer is determined according to a formula. The formula takes into account the thickness and modulus of elasticity of the metal interlayer and the thickness of the TSP diamond. This prevents the use of a too thin or too thick metal interlayer. A metal interlayer that is too thin is not capable of absorbing enough energy to prevent the TSP diamond from fracturing. A metal interlayer that is too thick may allow the TSP diamond to fracture by reason of bending stress. A coating may be provided between the TSP diamond layer and the metal interlayer. This coating serves as a thermal barrier and to control residual thermal stress.

In-Situ X-ray Tomography Observation of Structure Evolution in 1,3,5-Triamino-2,4,6-Trinitrobenzene Based Polymer Bonded Explosive (TATB-PBX) under Thermo-Mechanical Loading.

PubMed

Yuan, Zeng-Nian; Chen, Hua; Li, Jing-Ming; Dai, Bin; Zhang, Wei-Bin

2018-05-04

In order to study the fracture behavior and structure evolution of 1,3,5-Triamino-2,4,6-Trinitrobenzene (TATB)-based polymer bonded explosive in thermal-mechanical loading, in-situ studies were performed on X-ray computed tomography system using quasi-static Brazilian test. The experiment temperature was set from −20 °C to 70 °C. Three-dimensional morphology of cracks at different temperatures was obtained through digital image process. The various fracture modes were compared by scanning electron microscopy. Fracture degree and complexity were defined to quantitatively characterize the different types of fractures. Fractal dimension was used to characterize the roughness of the crack surface. The displacement field of particles in polymer bonded explosive (PBX) was used to analyze the interior structure evolution during the process of thermal-mechanical loading. It was found that the brittleness of PBX reduced, the fracture got more tortuous, and the crack surface got smoother as the temperature rose. At lower temperatures, especially lower than glass transition temperature of binders, there were slipping and shear among particles, and particles tended to displace and disperse; while at higher temperatures, especially above the glass transition temperature of binders, there was reorganization of particles and particles tended to merge, disperse, and reduce sizes, rather than displacing.

Integration of fracturing dynamics and pressure transient analysis for hydraulic fracture evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arihara, N.; Abbaszadeh, M.; Wright, C.A.

This paper presents pre- and post-fracture pressure transient analysis, combined with net fracture pressure interpretation, for a well in a naturally fractured geothermal reservoir. Integrated analysis was performed to achieve a consistent interpretation of the created fracture geometry, propagation, conductivity, shrinkage, reservoir flow behavior, and formation permeability characteristics. The interpreted data includes two-rate pre-frac injection tests, step-rate injection tests, a series of pressure falloff tests, and the net fracturing pressure from a massive fracture treatment. Pressure transient analyses were performed utilizing advanced well test interpretation techniques and a thermal reservoir simulator with fracture propagation option. Hydraulic fracture propagation analysis wasmore » also performed Milt a generalized 3-D dynamic fracture growth model simulator. Three major conclusions resulted from the combined analysis: (1) that an increasing number of hydraulic fractures were being simultaneously propagated during the fracture treatment. (2) that the reservoir behaved as a composite reservoir Keith the outer region permeability being greater than the permeability of the region immediately surrounding the wellbore, and (3) that the created fractures extended into the outer region during the fracture treatment but retreated to the inner region several days after stimulation had ceased. These conclusions were apparent from independent pressure transient analysis and from independent hydraulic fracture propagation analysis. Integrated interpretation, however, increased the confidence in these conclusions and greatly aided the quantification of the created hydraulic fracture geometry and characterization of the reservoir permeability.« less

A Fracture Mechanics Approach to Thermal Shock Investigation in Alumina-Based Refractory

NASA Astrophysics Data System (ADS)

Volkov-Husović, T.; Heinemann, R. Jančić; Mitraković, D.

2008-02-01

The thermal shock behavior of large grain size, alumina-based refractories was investigated experimentally using a standard water quench test. A mathematical model was employed to simulate the thermal stability behavior. Behavior of the samples under repeated thermal shock was monitored using ultrasonic measurements of dynamic Young's modulus. Image analysis was used to observe the extent of surface degradation. Analysis of the obtained results for the behavior of large grain size samples under conditions of rapid temperature changes is given.

Progressive Failure Analysis of Advanced Composites

DTIC Science & Technology

2008-07-25

Fracture angle. αii Coefficients of thermal expansion . βii Coefficients of hygroscopic expansion . β Shear response factor. ηL Coefficient of... thermal expansion in the longitudinal and transverse direc- tions. To enable the calculation of the thermal stresses, the user should define in the...development of this second VUMAT subroutine was planned for the second year of this project). 4.2 Input into Abaqus explicit 4.2.1 Shell elements

A numerical study of EGS heat extraction process based on a thermal non-equilibrium model for heat transfer in subsurface porous heat reservoir

NASA Astrophysics Data System (ADS)

Chen, Jiliang; Jiang, Fangming

2016-02-01

With a previously developed numerical model, we perform a detailed study of the heat extraction process in enhanced or engineered geothermal system (EGS). This model takes the EGS subsurface heat reservoir as an equivalent porous medium while it considers local thermal non-equilibrium between the rock matrix and the fluid flowing in the fractured rock mass. The application of local thermal non-equilibrium model highlights the temperature-difference heat exchange process occurring in EGS reservoirs, enabling a better understanding of the involved heat extraction process. The simulation results unravel the mechanism of preferential flow or short-circuit flow forming in homogeneously fractured reservoirs of different permeability values. EGS performance, e.g. production temperature and lifetime, is found to be tightly related to the flow pattern in the reservoir. Thermal compensation from rocks surrounding the reservoir contributes little heat to the heat transmission fluid if the operation time of an EGS is shorter than 15 years. We find as well the local thermal equilibrium model generally overestimates EGS performance and for an EGS with better heat exchange conditions in the heat reservoir, the heat extraction process acts more like the local thermal equilibrium process.

Modeling coupled thermal-hydrological-chemical processes in theunsaturated fractured rock of Yucca Mountain, Nevada: Heterogeneity andseepage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukhopadhyay, Sumit; Sonnenthal, Eric L.; Spycher, Nicolas

An understanding of processes affecting seepage intoemplacement tunnels is needed for correctly predicting the performance ofunderground radioactive waste repositories. It has been previouslyestimated that the capillary and vaporization barriers in the unsaturatedfractured rock of Yucca Mountain are enough to prevent seepage underpresent day infiltration conditions. It has also been thought that asubstantially elevated infiltration flux will be required to causeseepage after the thermal period is over. While coupledthermal-hydrological-chemical (THC) changes in Yucca Mountain host rockdue to repository heating has been previously investigated, those THCmodels did not incorporate elements of the seepage model. In this paper,we combine the THC processes inmore » unsaturated fractured rock with theprocesses affecting seepage. We observe that the THC processes alter thehydrological properties of the fractured rock through mineralprecipitation and dissolution. We show that such alteration in thehydrological properties of the rock often leads to local flow channeling.We conclude that such local flow channeling may result in seepage undercertain conditions, even with nonelevated infiltrationfluxes.« less

Self-healing polymer cement composites for geothermal wellbore applications

NASA Astrophysics Data System (ADS)

Rod, K. A.; Fernandez, C.; Childers, I.; Koech, P.; Um, W.; Roosendaal, T.; Nguyen, M.; Huerta, N. J.; Chun, J.; Glezakou, V. A.

2017-12-01

Cement is vital for controlling leaks from wellbores employed in oil, gas, and geothermal operations by sealing the annulus between the wellbore casing and geologic formation. Wellbore cement failure due to physical and chemical stresses is common and can result in significant environmental consequences and ultimately significant financial costs due to remediation efforts. To date numerous alternative cement blends have been proposed for the oil and gas industry. Most of these possess poor mechanical properties, or are not designed to work in high temperature environments. This research investigates novel polymer-cement composites which could function at most geothermal temperatures. Thermal stability and mechanical strength of the polymer is attributed to the formation of a number of chemical interactions between the polymer and cement matrix including covalent bonds, hydrogen bonding, and van der Waals interactions. It has been demonstrated that the bonding between cement and casing is more predictable when polymer is added to cement and can even improve healing of adhesion break when subjected to stresses such as thermal shock. Fractures have also been healed, effectively reducing permeability with fractures up to 0.3-0.5mm apertures, which is two orders of magnitude larger than typical wellbore fractures. Additionally, tomography analysis was used to determine internal structure of the cement polymer composite and imaging reveals that polymers fill fractures in the cement and between the cement and casing. By plugging fractures that occur in wellbore cement, reducing permeability of fractures, both environmental safety and economics of subsurface operations will be improved for geothermal energy and oil and gas production.

Geology of the platanares geothermal area, Departamento de Copan, Honduras

USGS Publications Warehouse

Heiken, G.; Ramos, N.; Duffield, W.; Musgrave, J.; Wohletz, K.; Priest, S.; Aldrich, J.; Flores, W.; Ritchie, A.; Goff, F.; Eppler, D.; Escobar, C.

1991-01-01

Platanares is located 16 km west of Santa Rosa de Copan, Honduras, along the Quebrada del Agua Caliente. The thermal manifestations are along faults in tuffs, tuffaceous sedimentary rocks, and lavas of the Padre Miguel Group. These tuffs are silicified near the faults, are fractured, and may provide the fracture permeability necessary for the hydrothermal system. Tuffs are overlain by a wedge of terrace gravels up to 60 m thick. Quaternary conglomerates of the Quebrada del Agua Caliente are cemented by silica sinter. The Platanares area contains numerous faults, all of which appear to be extensional. There are four groups of faults (N80/sup 0/E to N70/sup 0/W, N30/sup 0/ to 60/sup 0/W, N40/sup 0/ to 65/sup 0/E, and N00/sup 0/ to 05/sup 0/W). All hot springs at this site are located along faults that trend mostly northwest and north. Twenty-eight spring groups were described over an area of 0.2 km/sup 2/; half were boiling. Based on surface temperatures and flow rates, between 0.7 and 1.0 MW thermal energy is estimated for the area. The increased temperature of the stream flowing through the thermal area indicates that several megawatts of thermal energy are being added to the stream. We recommend that a dipole-dipole resistivity line be run along the Quebrada del Agua Caliente to identify zones of fracture permeability associated with buried faults and hot water reservoirs within those fault zones. A thermal gradient corehole should be drilled at Platanares to test temperatures, lithologies, and permeability of the hydrothermal system.

Effects of Thermal Cycling on Thermal Expansion and Mechanical Properties of Sic Fiber-reinforced Reaction-bonded Si3n4 Composites

NASA Technical Reports Server (NTRS)

Bhatt, R. T.; Palczer, A. R.

1994-01-01

Thermal expansion curves for SiC fiber-reinforced reaction-bonded Si3N4 matrix composites (SiC/RBSN) and unreinforced RBSN were measured from 25 to 1400 C in nitrogen and in oxygen. The effects of fiber/matrix bonding and cycling on the thermal expansion curves and room-temperature tensile properties of unidirectional composites were determined. The measured thermal expansion curves were compared with those predicted from composite theory. Predicted thermal expansion curves parallel to the fiber direction for both bonding cases were similar to that of the weakly bonded composites, but those normal to the fiber direction for both bonding cases resulted in no net dimensional changes at room temperature, and no loss in tensile properties from the as-fabricated condition. In contrast, thermal cycling in oxygen for both composites caused volume expansion primarily due to internal oxidation of RBSN. Cyclic oxidation affected the mechanical properties of the weakly bonded SiC/RBSN composites the most, resulting in loss of strain capability beyond matrix fracture and catastrophic, brittle fracture. Increased bonding between the SiC fiber and RBSN matrix due to oxidation of the carbon-rich fiber surface coating and an altered residual stress pattern in the composite due to internal oxidation of the matrix are the main reasons for the poor mechanical performance of these composites.

2017 Accomplishments – Tritium Aging Studies on Stainless Steel Weldments and Heat-Affected Zones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgan, Michael J.; Hitchcock, Dale; Krentz, Tim

In this study, the combined effects tritium and decay helium in forged and welded Types 304L and 21-6-9 stainless steels were studied. To measure these effects, fracture mechanic specimens were thermally precharged with tritium and aged for approximately 17 years to build in decay helium from tritium decay prior to testing. The results are compared to earlier measurements on the same alloys and weldments (4-5, 8-9). In support of Enhanced Surveillance, “Tritium Effects on Materials”, the fracture toughness properties of long-aged tritium-charged stainless-steel base metals and weldments were measured and compared to earlier measurements. The fracture-toughness data were measured bymore » thermally precharging as-forged and as-welded specimens with tritium gas at 34.5 MPa and 350°C and aging for approximately 17 years to build-in decay helium prior to testing. These data result from the longest aged specimens ever tested in the history of the tritium effects programs at Savannah River and the fracture toughness values measured were the lowest ever recorded for tritium-exposed stainless steel. For Type 21-6-9 stainless steel, fracture toughness values were reduced to less than 2-4% of the as-forged values to 41 lbs / in specimens that contained more than 1300 appm helium from tritium decay. The fracture toughness properties of long-aged weldments were also measured. The fracture toughness reductions were not as severe because the specimens did not retain as much tritium from the charging and aging as did the base metals. For Type 304L weldments, the specimens in this study contained approximately 600 appm helium and their fracture toughness values averaged 750 lbs / in. The results for other steels and weldments are reported and additional tests will be conducted during FY18.« less

Thermo-hydraulic characterization of a fractured shallow reservoir in Bergen (Norway) to improve the efficiency of a BHE field

NASA Astrophysics Data System (ADS)

Mandrone, Giuseppe; Giordano, Nicolò; Bastesen, Eivind; Wheeler, Walter; Chicco, Jessica

2017-04-01

Sustainable thermal energy production from GSHP systems is greatly dependent on the thermo-hydraulic field, yet there are few realistic case studies which capture the dynamics of such systems. Here we present initial work on the static model for one such case example. A BHE field consisting of 12 ground heat exchangers in fractured crystalline rock has been supplying thermal energy for the past 20 years to meet the heating needs of a school located in Bergen, Norway. In recent years the heat pump COP has significantly decreased, which has been ascribed to a depletion of the extractable energy surrounding the BHEs, that is, by extracting more energy in the heating season than is naturally replaced in the summer. A numerical model of the underground is constructed to show the thermal depletion and determine a sustainable thermal use of the shallow reservoir (0-200 m). At this stage, the model represents the geology and structure of the underground, which consists of metamorphic rocks of the Nordåsvatnet Complex (Minor Bergen Arc, Ordovician): amphibolites, micaschists, augen gneisses and quartz-schists depict the first 200 m below ground level. Preliminary well tests in some of these BHEs showed how complex and heterogeneous is the hydrogeological field. Some wells are clearly connected, others show hydraulic head difference of more than 15 m even though they are close by. Future flow tracer tests and down-hole fracture characterization will be carried out for in-depth representation of the flow field. Here we present and discuss laboratory thermal measurements on samples collected in the area, especially a comparison of two thermal conductivity measurement techniques. Thermal conductivity measurements were carried out with the thermal conductivity scanner by Lippmann and Rauen GbR and with the KD2 Pro by Decagon Devices. The optical scanning technology and the transient line source method were therefore compared to get the most valuable results. Electrical resistivity and seismic wave measurements were also performed on some samples to investigate possible relationships between these physical properties.

Materials and Process Specifications and Standards

DTIC Science & Technology

1977-11-01

Integrity Requirements; Fracture Control 65 5.9.3 Some Special Problems in Electronic 66 Materials Specifications 5.9.3.1 Thermal Stresses 66...fatigue and fracture and by defining human engineering concepts. Conform to OSHA regulations such as toxicity, noise levels etc. Develop...Standardization Society of the Valves and Fittings Industry. 41 4.6.2.4 OTHER ORGANIZATIONS There are a number of standards-making organizations that cannot

Oxygen and carbon isotope ratios of hydrothermal minerals from Yellowstone drill cores

USGS Publications Warehouse

Sturchio, N.C.; Keith, T.E.C.; Muehlenbachs, K.

1990-01-01

Oxygen and carbon isotope ratios were measured for hydrothermal minerals (silica, clay and calcite) from fractures and vugs in altered rhyolite, located between 28 and 129 m below surface (in situ temperatures ranging from 81 to 199??C) in Yellowstone drill holes. The purpose of this study was to investigate the mechanism of formation of these minerals. The ??18O values of the thirty-two analyzed silica samples (quartz, chalcedony, ??-cristobalite, and ??-cristobalite) range from -7.5 to +2.8???. About one third of the silica 7samples have ??18O values that are consistent with isotopic equilibrium with present thermal waters; most of the other silica samples appear to have precipitated from water enriched in 18O (up to 4.7???) relative to present thermal water, assuming precipitation at present in situ temperatures. Available data on fluid-inclusion homogenization temperatures in hydrothermal quartz indicate that silica precipitation occurred mostly at temperatures above those measured during drilling and imply that 15O enrichments in water during silica precipitation were generally larger than those estimated from present conditions. Similarly, clay minerals (celadonite and smectite) have ??18O values higher (by 3.5 to 7.9???) than equilibrium values under present conditions. In contrast, all eight analyzed calcite samples are close to isotopic equilibrium with present thermal waters. The frequent incidence of apparent 18O enrichment in thermal water from which the hydrothermal minerals precipitated may indicate that a higher proportion of strongly 18O-enriched deep hydrothermal fluid once circulated through shallow portions of the Yellowstone system, or that a recurring transient 18O-enrichment effect occurs at shallow depths and is caused either by sudden decompressional boiling or by isotopic exchange at low water/rock ratios in new fractures. The mineralogy and apparent 18O enrichments of hydrothermal fracture-filling minerals are consistent with deposition during transient boiling or rock-water exchange (fracturing) events. ?? 1990.

Effects of load and thermal histories on mechanical behavior of materials; Proceedings of the Symposium, Denver, CO, Feb. 25, 26, 1987

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liaw, P.K.; Nicholas, T.

This volume includes topics on fatigue crack propagation; isothermal and thermal-mechanical fatigue; and microstructure, fracture, and damage. Papers are presented on transients in fatigue crack growth, elevated-temperature fatigue crack propagation, the role of crack closure in crack retardation in P/M and I/M aluminum alloys, the acoustic interrogation of fatigue overload effects, and the effects of frequency and environment on crack growth in Inconel 718. Special attention is given to isothermal fatigue failure mechanisms in low-tin lead-based solder, the stress and strain controlled low-cycle fatigue of Pb-Sn solder for electronic packaging applications, load sequence effects on the deformation of isolated microplasticmore » grains, and thermal fatigue of stainless steel. Other papers are on the influence of thermal aging on the creep crack growth behavior of a Cr-Mo steel, the effect of cyclic loading on the fracture toughness of a modified 4340 steel, and the effects of hot rolling condition and boron microalloying on phase transformation and microstructure in niobium-bearing interstitial free steel.« less

An investigation on microstructure and mechanical property of thermally aged stainless steel weld overlay cladding

NASA Astrophysics Data System (ADS)

Cao, X. Y.; Zhu, P.; Ding, X. F.; Lu, Y. H.; Shoji, T.

2017-04-01

Microstructural evolution and mechanical property change of E308L stainless steel weld overlay cladding aged at 400 °C for 400, 1000 and 5000 h were investigated by transmission electron microscope (TEM) and small punch test (SPT). The results indicated that thermal aging had no obvious effect on the volume fraction of ferrite, but can cause microstructural evolution by spinodal decomposotion and G-phase precipitation in the ferrite phase. Spinodal decomposition took place after aging up to 1000 h, while G-phase formed along dislocations, and growed up to 2-11 nm after aging for 5000 h. The total energy for inducing deformation and fracture by the small punch tests decreased with the increase of thermal aging time, and this decline was associated with spinodal decomposition and G-phase precipitation. Plastic deformation of the aged ferrite proceeded via formation of curvilinear slip bands. Nucleation of microcracks occurred at the δ/γ interface along the slip bands. The hardening of the ferrite and high stress concentration on δ/γ phase interface resulted in brittle fracture and phase boundary separation after thermal aging.

Applications of Geothermally-Produced Colloidal Silica in Reservoir Management - Smart Gels

DOE Data Explorer

Hunt, Jonathan

2013-01-31

In enhanced geothermal systems (EGS) the reservoir permeability is often enhanced or created using hydraulic fracturing. In hydraulic fracturing, high fluid pressures are applied to confined zones in the subsurface usually using packers to fracture the host rock. This enhances rock permeability and therefore conductive heat transfer to the circulating geothermal fluid (e.g. water or supercritical carbon dioxide). The ultimate goal is to increase or improve the thermal energy production from the subsurface by either optimal designs of injection and production wells or by altering the fracture permeability to create different zones of circulation that can be exploited in geothermal heat extraction. Moreover, hydraulic fracturing can lead to the creation of undesirable short-circuits or fast flow-paths between the injection and extraction wells leading to a short thermal residence time, low heat recovery, and thus a short-life of the EGS. A potential remedy to these problems is to deploy a cementing (blocking, diverting) agent to minimize short-cuts and/or create new circulation cells for heat extraction. A potential diverting agent is the colloidal silica by-product that can be co-produced from geothermal fluids. Silica gels are abundant in various surface and subsurface applications, yet they have not been evaluated for EGS applications. In this study we are investigating the benefits of silica gel deployment on thermal response of an EGS, either by blocking short-circuiting undesirable pathways as a result of diverting the geofluid to other fractures; or creating, within fractures, new circulation cells for harvesting heat through newly active surface area contact. A significant advantage of colloidal silica is that it can be co-produced from geothermal fluids using an inexpensive membrane-based separation technology that was developed previously using DOE-GTP funding. This co-produced silica has properties that potentially make it useful as a fluid diversion agent for subsurface applications. Colloidal silica solutions exist as low-viscosity fluids during their “induction period” but then undergo a rapid increase in viscosity (gelation) to form a solid gel. The length of the induction period can be manipulated by varying the properties of the solution, such as silica concentration and colloid size. We believe it is possible to produce colloidal silica gels suitable for use as diverting agents for blocking undesirable fast-paths which result in short-circuiting the EGS once hydraulic fracturing has been deployed. In addition, the gels could be used in conventional geothermal fields to increase overall energy recovery by modifying flow.

A Predictive Framework for Thermomechanical Fatigue Life of High Silicon Molybdenum Ductile Cast Iron Based on Considerations of Strain Energy Dissipation

NASA Astrophysics Data System (ADS)

Avery, Katherine R.

Isothermal low cycle fatigue (LCF) and anisothermal thermomechanical fatigue (TMF) tests were conducted on a high silicon molybdenum (HiSiMo) cast iron for temperatures up to 1073K. LCF and out-of-phase (OP) TMF lives were significantly reduced when the temperature was near 673K due to an embrittlement phenomenon which decreases the ductility of HiSiMo at this temperature. In this case, intergranular fracture was predominant, and magnesium was observed at the fracture surface. When the thermal cycle did not include 673K, the failure mode was predominantly transgranular, and magnesium was not present on the fracture surface. The in-phase (IP) TMF lives were unaffected when the thermal cycle included 673K, and the predominant failure mode was found to be transgranular fracture, regardless of the temperature. No magnesium was present on the IP TMF fracture surfaces. Thus, the embrittlement phenomenon was found to contribute to fatigue damage only when the temperature was near 673K and a tensile stress was present. To account for the temperature- and stress-dependence of the embrittlement phenomenon on the TMF life of HiSiMo cast iron, an original model based on the cyclic inelastic energy dissipation is proposed which accounts for temperature-dependent differences in the rate of fatigue damage accumulation in tension and compression. The proposed model has few empirical parameters. Despite the simplicity of the model, the predicted fatigue life shows good agreement with more than 130 uniaxial low cycle and thermomechanical fatigue tests, cyclic creep tests, and tests conducted at slow strain rates and with hold times. The proposed model was implemented in a multiaxial formulation and applied to the fatigue life prediction of an exhaust manifold subjected to severe thermal cycles. The simulation results show good agreement with the failure locations and number of cycles to failure observed in a component-level experiment.

Nonlinear Constitutive Relations for High Temperature Applications

NASA Technical Reports Server (NTRS)

1983-01-01

The topics of discussion addressed were material behavior, design analysis, deformation kinetics, metallurgical characterization, mechanical subelement models, stress analysis, fracture mechanics, viscoplasticity, and thermal loading.

Assessment of crack growth in a space shuttle main engine first-stage, high-pressure fuel turbopump blade

NASA Technical Reports Server (NTRS)

Abdul-Aziz, Ali

1993-01-01

A two-dimensional finite element fracture mechanics analysis of a space shuttle main engine (SSME) turbine blade firtree was performed using the MARC finite element code. The analysis was conducted under combined effects of thermal and mechanical loads at steady-state conditions. Data from a typical engine stand cycle of the SSME were used to run a heat transfer analysis and, subsequently, a thermal structural fracture mechanics analysis. Temperature and stress contours for the firtree under these operating conditions were generated. High stresses were found at the firtree lobes where crack initiation was triggered. A life assessment of the firtree was done by assuming an initial and a final crack size.

Experimental and numerical simulation of dissolution and precipitation: implications for fracture sealing at Yucca Mountain, Nevada

NASA Astrophysics Data System (ADS)

Dobson, Patrick F.; Kneafsey, Timothy J.; Sonnenthal, Eric L.; Spycher, Nicolas; Apps, John A.

2003-05-01

Plugging of flow paths caused by mineral precipitation in fractures above the potential repository at Yucca Mountain, Nevada could reduce the probability of water seeping into the repository. As part of an ongoing effort to evaluate thermal-hydrological-chemical (THC) effects on flow in fractured media, we performed a laboratory experiment and numerical simulations to investigate mineral dissolution and precipitation under anticipated temperature and pressure conditions in the repository. To replicate mineral dissolution by vapor condensate in fractured tuff, water was flowed through crushed Yucca Mountain tuff at 94 °C. The resulting steady-state fluid composition had a total dissolved solids content of about 140 mg/l; silica was the dominant dissolved constituent. A portion of the steady-state mineralized water was flowed into a vertically oriented planar fracture in a block of welded Topopah Spring Tuff that was maintained at 80 °C at the top and 130 °C at the bottom. The fracture began to seal with amorphous silica within 5 days. A 1-D plug-flow numerical model was used to simulate mineral dissolution, and a similar model was developed to simulate the flow of mineralized water through a planar fracture, where boiling conditions led to mineral precipitation. Predicted concentrations of the major dissolved constituents for the tuff dissolution were within a factor of 2 of the measured average steady-state compositions. The mineral precipitation simulations predicted the precipitation of amorphous silica at the base of the boiling front, leading to a greater than 50-fold decrease in fracture permeability in 5 days, consistent with the laboratory experiment. These results help validate the use of a numerical model to simulate THC processes at Yucca Mountain. The experiment and simulations indicated that boiling and concomitant precipitation of amorphous silica could cause significant reductions in fracture porosity and permeability on a local scale. However, differences in fluid flow rates and thermal gradients between the experimental setup and anticipated conditions at Yucca Mountain need to be factored into scaling the results of the dissolution/precipitation experiments and associated simulations to THC models for the potential Yucca Mountain repository.

Fracture characterization in a deep geothermal reservoir

NASA Astrophysics Data System (ADS)

Rühaak, Wolfram; Hehn, Vera; Hassanzadegan, Alireza; Tischner, Torsten

2017-04-01

At the geothermal research drilling Horstberg in North West Germany studies for the characterization of a vertical fracture are performed. The fracture was created by a massive hydraulic stimulation in 2003 in approx. 3700 m depth within rocks of the middle Buntsandstein. The fracture surface is in the order of 100,000 m2, depending on the flow rate at which water is injected. Besides hydraulic characterization, multiple tracer tests are planned. At the depth of interest the reservoir temperature is around 150 °C, pressure is around 600 bar (60 MPa) and due to salinity the water density is around 1200 kg/m3. Knowledge of tracer stability and behavior at these reservoir conditions is limited. Additionally, the planned tracer tests will be performed within one single borehole. In a closed cycle water is injected into the inner pipe of the well (tubing), which is separated by a permanent packer from the outer pipe (annulus). The water is produced back from the annulus approximately 150 m above the injection point. Thus, the circulation of thermal water between two sandstone layers via an artificial fracture can be achieved. Tests will be carried out with different flow rates and accordingly with different pressures, resulting in different fracture areas. Due to this test setup tracer signals will be stacked and will remain for a longer time in the fracture - which is the reason why different tracers are required. For an optimal characterization both conservative and reactive tracers will be used and different injection methods (continuous, instantaneous and pulsed) will be applied. For a proper setup of the tracer test numerical modelling studies are performed in advance. The relevant thermal, hydraulic and chemical processes (mainly adsorption and degredation) are coupled, resulting in a THC model; additionally the dependence of fracture aperture and area on fluid pressure has to be considered. Instead of applying a mechanically coupled model (THMC) a simplified approach is applied which takes the pressure dependence of the fracture permeability into account by using constitutive relations. Results of this modeling study will be presented together with details of the planned field study.

Novel highly dispersible, thermally stable core/shell proppants for geothermal applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Childers, Ian M.; Endres, Mackenzie; Burns, Carolyne

The use of proppants during reservoir stimulation in tight oil and gas plays requires the introduction of highly viscous fluids to transport the proppants (µm–mm) with the fracturing fluid. The highly viscous fluids required result in increased pump loads and energy costs. Furthermore, although proppant deployment with fracturing fluids is a standard practice for unconventional oil and gas stimulation operations, there are only a few examples in the US of the applying proppant technology to geothermal energy production. This is due to proppant dissolution, proppant flowback and loss of permeability associated with the extreme temperatures found in enhanced geothermal systemsmore » (EGS). This work demonstrates proof-of-concept of a novel, CO2-responsive, lightweight sintered-bauxite/polymer core/shell proppant. The polymer shell has two main roles; 1) increase the stability of the proppant dispersion in water without the addition of rheology modifiers, and 2) once at the fracture network react with CO2 to promote particle aggregation and prop fractures open. In this work, both of these roles are demonstrated together with the thermal and chemical stability of the materials showing the potential of these CO2-responsive proppants as an alternative proppant technology for geothermal and unconventional oil/gas applications.« less

Determining the spatial altitude of the hydraulic fractures.

NASA Astrophysics Data System (ADS)

Khamiev, Marsel; Kosarev, Victor; Goncharova, Galina

2016-04-01

Mathematical modeling and numerical simulation are the most widely used approaches for the solving geological problems. They imply software tools which are based on Monte Carlo method. The results of this project presents shows the possibility of using PNL tool to determine fracturing location. The modeled media is a homogeneous rock (limestone) cut by a vertical borehole (d=216 mm) with metal casing 9 mm thick. The cement sheath is 35 mm thick. The borehole is filled with fresh water. The rock mass is cut by crack, filled with a mixture of doped (gadolinium oxide Gd2O3) proppant (75%) and water (25%). A pulse neutron logging (PNL) tool is used for quality control in hydraulic fracturing operations. It includes a fast neutron source (so-called "neutron generator") and a set of thermal (or epithermal) neutron-sensing devices, forming the so-called near (ND) and far (FD) detectors. To evaluate neutron properties various segments (sectors) of the rock mass, the detector must register only neutrons that come from this very formation. It's possible if detecting block includes some (6 for example) thermal neutron detectors arranged circumferentially inside the tool. As a result we get few independent well logs, each accords with define rock sector. Afterwards synthetic logs processing we can determine spatial position of the hydraulic fracture.

Fracture behavior of reinforced aluminum alloy matrix composites using thermal imaging tools

NASA Astrophysics Data System (ADS)

Avdelidis, N. P.; Exarchos, D.; Vazquez, P.; Ibarra-Castanedo, C.; Sfarra, S.; Maldague, X. P. V.; Matikas, T. E.

2016-05-01

In this work the influence of the microstructure at the vicinity of the interface on the fracture behavior of particulate-reinforced aluminum alloy matrix composites (Al/SiCp composites) is studied by using thermographic tools. In particular, infrared thermography was used to monitor the plane crack propagation behavior of the materials. The deformation of solid materials is almost always accompanied by heat release. When the material becomes deformed or is damaged and fractured, a part of the energy necessary to initiate and propagate the damage is transformed in an irreversible way into heat. The thermal camera detects the heat wave, generated by the thermo-mechanical coupling and the intrinsic dissipated energy during mechanical loading of the sample. By using an adapted detector, thermography records the two dimensional "temperature" field as it results from the infrared radiation emitted by the object. The principal advantage of infrared thermography is its noncontact, non-destructive character. This methodology is being applied to characterise the fracture behavior of the particulate composites. Infrared thermography is being used to monitor the plane crack propagation behavior of such materials. Furthermore, an innovative approach to use microscopic measurements using IR microscopic lenses was attempted, in order to enable smaller features (in the micro scale) to be imaged with accuracy and assurance.

Nondestructive evaluation of plasma-sprayed thermal barrier coatings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrews, D.J.; Taylor, J.A.T.

Acoustic emission has been used as a nondestructive evaluation technique to examine the thermal shock response of thermal barrier coatings. In this study, samples of partially stabilized zirconia powder were sprayed and acoustic emission (AE) data were taken in a series of thermal shock tests in an effort to correlate AE with a given failure mechanism. Microstructural evidence was examined using parallel beam x-ray diffraction and optical microscopy. The AE data are discussed in terms of cumulative amplitude distributions and the use of this technique to characterize fracture events.

Experimental and statistical study on fracture boundary of non-irradiated Zircaloy-4 cladding tube under LOCA conditions

NASA Astrophysics Data System (ADS)

Narukawa, Takafumi; Yamaguchi, Akira; Jang, Sunghyon; Amaya, Masaki

2018-02-01

For estimating fracture probability of fuel cladding tube under loss-of-coolant accident conditions of light-water-reactors, laboratory-scale integral thermal shock tests were conducted on non-irradiated Zircaloy-4 cladding tube specimens. Then, the obtained binary data with respect to fracture or non-fracture of the cladding tube specimen were analyzed statistically. A method to obtain the fracture probability curve as a function of equivalent cladding reacted (ECR) was proposed using Bayesian inference for generalized linear models: probit, logit, and log-probit models. Then, model selection was performed in terms of physical characteristics and information criteria, a widely applicable information criterion and a widely applicable Bayesian information criterion. As a result, it was clarified that the log-probit model was the best among the three models to estimate the fracture probability in terms of the degree of prediction accuracy for both next data to be obtained and the true model. Using the log-probit model, it was shown that 20% ECR corresponded to a 5% probability level with a 95% confidence of fracture of the cladding tube specimens.

Strength and Fracture Toughness of Solid Oxide Fuel Cell Electrolyte Material Improved

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Choi, Sung R.

2002-01-01

Solid oxide fuel cells (SOFC) are being developed for various applications in the automobile, power-generation, and aeronautics industries. Recently, the NASA Glenn Research Center has been exploring the possibility of using SOFC's for aeropropulsion under its Zero Carbon Dioxide Emission Technology (ZCET) Program. 10-mol% yttriastabilized zirconia (10YSZ) is a very good anionic conductor at high temperatures and is, therefore, used as an oxygen solid electrolyte in SOFC. However, it has a high thermal expansion coefficient, low thermal shock resistance, low fracture toughness, and poor mechanical strength. For aeronautic applications, the thin ceramic electrolyte membrane of the SOFC needs to be strong and tough. Therefore, we have been investigating the possibility of enhancing the strength and fracture toughness of the 10YSZ electrolyte without degrading its electrical conductivity to an appreciable extent. We recently demonstrated that the addition of alumina to zirconia electrolyte increases its strength as well as its fracture toughness. Zirconia-alumina composites containing 0 to 30 mol% of alumina were fabricated by hot pressing. The hot pressing procedure was developed and various hot pressing parameters were optimized, resulting in dense, crackfree panels of composite materials. Cubic zirconia and a-alumina were the only phases detected, indicating that there was no chemical reaction between the constituents during hot pressing at elevated temperatures. Flexure strength sf and fracture toughness K(sub IC) of the various zirconia-alumina composites were measured at room temperature as well as at 1000 C in air. Both properties showed systematic improvement with increased alumina addition at room temperature and at 1000 C. Use of these modified electrolytes with improved strength and fracture toughness should prolong the life and enhance the performance of SOFC in aeronautics and other applications.

Fracture Characterization in the Astor Pass Geothermal Field, Nevada

NASA Astrophysics Data System (ADS)

Walsh, D. C.; Reeves, D. M.; Pohll, G.; Lyles, B. F.; Cooper, C. A.

2011-12-01

The Astor Pass geothermal field, near Pyramid Lake, NV, is under study as a site of potential geothermal energy production. Three wells have been completed in the graben of this typical Basin and Range geologic setting. Lithologies include a layer of unconsolidated sediment (basin fill) underlain by various tertiary volcanic units and granodiorite and metavolcanic basement rock. Characterization of fractures within the relatively impermeable rock matrix is being conducted for the three wells. Statistical analysis of fracture orientation, densities, and spacing obtained from borehole imaging logs is used to determine stress orientation and to generate a statistically equivalent Discrete Fracture Network (DFN) model. Fractures at depth are compared to fracture data collected in nearby outcrops of the same lithologic stratigraphy. Fracture geometry and density is correlated to mechanically discrete layers within the stratigraphy to test whether variations in fracturing can be attributed to variations in Young's modulus. Correlation of fracture geometry and densities with spinner flowmeter logs and distributed temperature sensor records are made in an effort to identify potential flowing fracture zones intersecting the borehole. Mean fracture aperture is obtained from open fracture counts and reservoir-scale transmissivity values (computed from a 30 day pump test) in the absence of readily available aperture data. The goal of this thorough fracture characterization is to create a physically relevant model which may be coupled with a multipurpose fluid flow and thermal simulator for investigation of geothermal reservoir behavior, particularly at the borehole scale.

Modeling and stress analysis of large format InSb focal plane arrays detector under thermal shock

NASA Astrophysics Data System (ADS)

Zhang, Li-Wen; Meng, Qing-Duan; Zhang, Xiao-Ling; Yu, Qian; Lv, Yan-Qiu; Si, Jun-Jie

2013-09-01

Higher fracture probability, appearing in large format InSb infrared focal plane arrays detector under thermal shock loadings, limits its applicability and suitability for large format equipment, and has been an urgent problem to be solved. In order to understand the fracture mechanism and improve the reliability, three dimensional modeling and stress analysis of large format InSb detector is necessary. However, there are few reports on three dimensional modeling and simulation of large format InSb detector, due to huge meshing numbers and time-consuming operation to solve. To solve the problems, basing on the thermal mismatch displacement formula, an equivalent modeling method is proposed in this paper. With the proposed equivalent modeling method, employing the ANSYS software, three dimensional large format InSb detector is modeled, and the maximum Von Mises stress appearing in InSb chip dependent on array format is researched. According to the maximum Von Mises stress location shift and stress increasing tendency, the adaptability range of the proposed equivalent method is also derived, that is, for 16 × 16, 32 × 32 and 64 × 64 format, its adaptability ranges are not larger than 64 × 64, 256 × 256 and 1024 × 1024 format, respectively. Taking 1024 × 1024 InSb detector as an example, the Von Mises stress distribution appearing in InSb chip, Si readout integrated circuits and indium bump arrays are described, and the causes are discussed in detail. All these will provide a feasible research plan to identify the fracture origins of InSb chip and reduce fracture probability for large format InSb detector.

Constant-load delayed fracture test of atmospherically corroded high strength steels

NASA Astrophysics Data System (ADS)

Akiyama, Eiji; Matsukado, Katsuhiro; Li, Songjie; Tsuzaki, Kaneaki

2011-07-01

Constant load tests of circumferentially notched round bar specimens of high strength steels after cyclic corrosion test and outdoor exposure have been performed to demonstrate that delayed fracture occurs when the hydrogen content from the environment, H E, exceeds the critical hydrogen content for delayed fracture, H C. During the constant load tests the humidity around the specimen was increased in stepwise manner to increase hydrogen entry. After fracture the specimen was kept at the humidity long enough to homogenize hydrogen in the specimen and to obtain more quantitative hydrogen content by thermal desorption analysis. H E of the fractured specimens was higher than H C, and H E of the specimens not fractured was lower than H C. This result confirms that the balance between H C and H E determines the occurrence of delayed fracture and that hydrogen-content-based evaluation of susceptibility to delayed fracture is reasonable. To certify the increase of H E with increase in humidity, electrochemical hydrogen permeation test was carried out. The hydrogen permeation current density was increased especially at 98%RH. Enhancement of hydrogen entry with increase in CCT number was also shown by the test.

Thermal behavior modeling of a cabinet direct solar dryer as influenced by sensible heat storage in a fractured porous medium

NASA Astrophysics Data System (ADS)

Sandali, Messaoud; Boubekri, Abdelghani; Mennouche, Djamel

2018-05-01

Numerical simulation method has been employed to improve the thermal performance of cabinet direct solar dryer. The present study focused on the numerical simulation of a direct solar dryer with integration of a flat layer of fractured porous medium above the absorber plate in the aim to store thermal energy by sensible heat. Several calculations were conducted, using the finite volume method with a two-dimensional unsteady model implemented in the Fluent CFD software. The porous medium has been integrated with different thickness to show the influence of the medium thickness on the thermal performance of solar dryer. Different kinds of materials have been tested and studied. The effect of porosity of porous medium has been studied. The obtained results showed that the temperature of drying air is increased by 4°C with integration of porous medium. The increasing in the thickness of the porous medium by 1cm leads to increase the temperature of drying air by 2°C. The increasing of the medium porosity by 10% leads to decrease the temperature of drying air by 1°C. The best material is the one that has a highest specific heat and thermal conductivity.

Thermomechanical Modeling of Sintered Silver - A Fracture Mechanics-based Approach: Extended Abstract: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paret, Paul P; DeVoto, Douglas J; Narumanchi, Sreekant V

Sintered silver has proven to be a promising candidate for use as a die-attach and substrate-attach material in automotive power electronics components. It holds promise of greater reliability than lead-based and lead-free solders, especially at higher temperatures (less than 200 degrees Celcius). Accurate predictive lifetime models of sintered silver need to be developed and its failure mechanisms thoroughly characterized before it can be deployed as a die-attach or substrate-attach material in wide-bandgap device-based packages. We present a finite element method (FEM) modeling methodology that can offer greater accuracy in predicting the failure of sintered silver under accelerated thermal cycling. Amore » fracture mechanics-based approach is adopted in the FEM model, and J-integral/thermal cycle values are computed. In this paper, we outline the procedures for obtaining the J-integral/thermal cycle values in a computational model and report on the possible advantage of using these values as modeling parameters in a predictive lifetime model.« less

Dynamic fracture development in response to extreme summer temperatures: 27/7/2014, Långören Island, Finland

NASA Astrophysics Data System (ADS)

Leith, Kerry; Perras, Matthew; Siren, Topias; Rantanen, Tuomas; Heinonen, Suvi; Loew, Simon

2017-04-01

Long periods of exceptionally high temperatures in Finland and California during the summer of 2014 were associated with the formation of large 'exfoliation' or 'sheeting' fractures in bedrock surfaces. Videos taken at both locations show sharp fractures forming along the edge of thin (<1 m) bedrock sheets several meters across, before the rock surface appears to jump and buckle in the hot summer sun. Long striations visible on the surface of the rock at Långören Island are the result of boulders being dragged over the landscape during the last glacial period (>15,000 years ago), hinting at the rarity of the recent events on the otherwise undamaged surface. In order to uncover the mechanisms driving this remarkable event, we installed a unique low-cost monitoring system to track the behavior of the new Långören Island fracture through the summer of 2016. This included a local meteorological station, Arduino-based rock temperature profiles, acoustic emission measurements, and a 3G-enabled all-in-one PC for live data communication. Coupled with GPR data, field mapping, and a local DEM derived from a 'Go-Pro on a stick' structure from motion capture, we generate a unique insight into the conditions at the time of the 2014 event, and potential active micro-fracturing during a hot period in 2016. Our models suggest rock surface temperatures approached 40°C during 2014, almost ten degrees above the peak air temperature. The mid- to late-afternoon timing of fracturing was associated with peak thermal stress in the upper 1 m of bedrock, consistent with 2016 observations, where measured surface temperatures of around 35°C generate a thermal front that coincides with a series of acoustic emission events on a sensor installed in a borehole near the crest of the fracture.

Initial Probabilistic Evaluation of Reactor Pressure Vessel Fracture with Grizzly and Raven

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spencer, Benjamin; Hoffman, William; Sen, Sonat

2015-10-01

The Grizzly code is being developed with the goal of creating a general tool that can be applied to study a variety of degradation mechanisms in nuclear power plant components. The first application of Grizzly has been to study fracture in embrittled reactor pressure vessels (RPVs). Grizzly can be used to model the thermal/mechanical response of an RPV under transient conditions that would be observed in a pressurized thermal shock (PTS) scenario. The global response of the vessel provides boundary conditions for local models of the material in the vicinity of a flaw. Fracture domain integrals are computed to obtainmore » stress intensity factors, which can in turn be used to assess whether a fracture would initiate at a pre-existing flaw. These capabilities have been demonstrated previously. A typical RPV is likely to contain a large population of pre-existing flaws introduced during the manufacturing process. This flaw population is characterized stastistically through probability density functions of the flaw distributions. The use of probabilistic techniques is necessary to assess the likelihood of crack initiation during a transient event. This report documents initial work to perform probabilistic analysis of RPV fracture during a PTS event using a combination of the RAVEN risk analysis code and Grizzly. This work is limited in scope, considering only a single flaw with deterministic geometry, but with uncertainty introduced in the parameters that influence fracture toughness. These results are benchmarked against equivalent models run in the FAVOR code. When fully developed, the RAVEN/Grizzly methodology for modeling probabilistic fracture in RPVs will provide a general capability that can be used to consider a wider variety of vessel and flaw conditions that are difficult to consider with current tools. In addition, this will provide access to advanced probabilistic techniques provided by RAVEN, including adaptive sampling and parallelism, which can dramatically decrease run times.« less

Permanent effect of a cryogenic spill on fracture properties of structural steels

NASA Astrophysics Data System (ADS)

Keseler, H.; Westermann, I.; Kandukuri, S. Y.; Nøkleby, J. O.; Holmedal, B.

2015-12-01

Fracture analysis of a standard construction steel platform deck, which had been exposed to a liquid nitrogen spill, showed that the brittle fracture started at a flaw in the weld as a consequence of low-temperature embrittlement and thermal stresses experienced by the material. In the present study, the permanent effect of a cryogenic spill on the fracture properties of carbon steels has been investigated. Charpy V-notch impact testing was carried out at 0 °C using specimens, from the platform deck material. The average impact energy appeared to be below requirements only for transverse specimens. No pre-existing damage was found when examining the fracture surfaces and cross sections in the scanning electron microscope. Specimens of the platform deck material and a DOMEX S355 MCD carbon steel were tensile tested immersed in liquid nitrogen. Both steels showed a considerable increase in yield- and fracture strength and a large increase in the Lüders strain compared to the room temperature behavior. A cryogenic spill was simulated by applying a constant tensile force to the specimens for 10 min, at -196 C. Subsequent tensile tests at room temperature showed no significant influence on the stress-strain curve of the specimens. A small amount of microcracks were found after holding a DOMEX S355 MCD specimen at a constant force below the yield point. In a platform deck material tensile tested to fracture in liquid nitrogen, cracks associated with elongated MnS inclusions were found through the whole test region. These cracks probably formed as a result of the inclusions having a higher thermal contraction rate than the steel, causing decohesion at the inclusion-matrix interface on cooling. Simultaneous deformation may have caused formation of cracks. Both the microcracks and sulphide related damage may give permanently reduced impact energy after a cryogenic exposure.

Effect of Measured Welding Residual Stresses on Crack Growth

NASA Technical Reports Server (NTRS)

Hampton, Roy W.; Nelson, Drew; Doty, Laura W. (Technical Monitor)

1998-01-01

Welding residual stresses in thin plate A516-70 steel and 2219-T87 aluminum butt weldments were measured by the strain-gage hole drilling and X-ray diffraction methods. The residual stress data were used to construct 3D strain fields which were modeled as thermally induced strains. These 3D strain fields were then analyzed with the WARP31) FEM fracture analysis code in order to predict their effect on fatigue and on fracture. For analyses of fatigue crack advance and subsequent verification testing, fatigue crack growth increments were simulated by successive saw-cuts and incremental loading to generate, as a function of crack length, effects on crack growth of the interaction between residual stresses and load induced stresses. The specimen experimental response was characterized and compared to the WARM linear elastic and elastic-plastic fracture mechanics analysis predictions. To perform the fracture analysis, the plate material's crack tearing resistance was determined by tests of thin plate M(T) specimens. Fracture analyses of these specimen were performed using WARP31D to determine the critical Crack Tip Opening Angle [CTOA] of each material. These critical CTOA values were used to predict crack tearing and fracture in the weldments. To verify the fracture predictions, weldment M(T) specimen were tested in monotonic loading to fracture while characterizing the fracture process.

Intergranular fracture in irradiated Inconel X-750 containing very high concentrations of helium and hydrogen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Judge, Colin D.; Gauquelin, Nicolas; Walters, Lori

2015-02-01

In recent years, it has been determined that Inconel X-750 CANDU spacers have lost strength and material ductility following irradiation in reactor. The irradiated fracture behaviour of ex-service material was also found to be entirely intergranular. The heavily thermalized flux spectrum in a CANDU reactor results in transmutation of 58Ni to 59Ni. The 59Ni itself has unusually high thermal neutron reaction cross-sections of the type: (n, γ), (n, p), and (n,α). The latter two reactions, in particular, contribute to a significant enhancement of the atomic displacements in addition to creating high concentrations of hydrogen and helium within the material. Metallographicmore » examinations by transmission electron microscopy (TEM) have confirmed the presence of helium bubbles in the matrix and aligned along grain boundaries and matrix-precipitate interfaces. He bubble size and density are found to be highly dependent on the irradiation temperature and material microstructure; the bubbles are larger within grain boundary precipitates. TEM specimens extracted from fracture surfaces and crack tips give direct evidence linking crack propagation with grain boundary He bubbles.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simonen, F.A.; Johnson, K.I.; Liebetrau, A.M.

The VISA-II (Vessel Integrity Simulation Analysis code was originally developed as part of the NRC staff evaluation of pressurized thermal shock. VISA-II uses Monte Carlo simulation to evaluate the failure probability of a pressurized water reactor (PWR) pressure vessel subjected to a pressure and thermal transient specified by the user. Linear elastic fracture mechanics methods are used to model crack initiation and propagation. Parameters for initial crack size and location, copper content, initial reference temperature of the nil-ductility transition, fluence, crack-initiation fracture toughness, and arrest fracture toughness are treated as random variables. This report documents an upgraded version of themore » original VISA code as described in NUREG/CR-3384. Improvements include a treatment of cladding effects, a more general simulation of flaw size, shape and location, a simulation of inservice inspection, an updated simulation of the reference temperature of the nil-ductility transition, and treatment of vessels with multiple welds and initial flaws. The code has been extensively tested and verified and is written in FORTRAN for ease of installation on different computers. 38 refs., 25 figs.« less

Shock and thermal metamorphism of basalt by nuclear explosion, Nevada test site

USGS Publications Warehouse

James, O.B.

1969-01-01

Olivine trachybasalt metamorphosed by nuclear explosion is classified into categories of progressive metamorphism: (i) Weak. Plagioclase is microfractured, and augite cotainis fine twin lamellae. (ii) Moderate. Plagioclase is converted to glass, and mafic minerals show intragranular deformation (undulatory extinction, twin lamellae, and, possibly, deformation lamellae), but rock texture is preserved. (iii) Moderately strong. Plagioclase glass shows small-scale flow, mafic minerals are fractured and show intragranular deformation, and rocks contain tension fractures. (iv) Strong. Plagioclase glass is vesicular, augite is minutely fractured, and olivine is coarsely fragmented, shows mosaic extinction, distinctive lamellar structures, and is locally recrystallized. (v) Intense. Rocks are converted to inhomogeneous basaltic glass.

Mechanical properties of high-temperature superconducting wires. Ph.D. Thesis - Illinois Inst. of Tech.

NASA Technical Reports Server (NTRS)

Goretta, K. C.; Cluff, J. A.; Joo, J.; Lanagan, M. T.; Singh, J. P.; Vasanthamohan, N.; Xin, Y.; Wong, K. W.

1995-01-01

Bending strength, fracture toughness, and elastic modulus data were acquired for YBa2Cu3O(x), Bi2Sr2CaCu2O(x) (Bi,Pb)2Sr2Ca2Cu3O(x), and Tl2Ba2Ca2Cu3O(x) bars. These data and thermal expansion coefficients strongly suggest that the maximum possible tensile strain without fracture of bulk tapes or wires is approximately equals 0.2%. In Ag-clad conductors, residual stresses will be of limited benefit, but fractures produced by larger strains can be accommodated by shunting current through the Ag.

Thermal analysis and experimental study of end-pumped Nd: YLF laser at 1053 nm

NASA Astrophysics Data System (ADS)

El-Agmy, R. M.; Al-Hosiny, N.

2017-12-01

We have numerically analyzed the thermal effects in Nd: YLF laser rod. The calculations of temperature and stress distributions in the Nd: YLF laser rod was performed with finite element (FE) simulations. The calculations showed that the laser rod could be pumped up to a power of 40 W without fracture caused by thermal stress. The calculated thermal lens power of thermally induced lens in Nd: YLF ( σ-polarization) laser rod was analyzed and validated experimentally with two independent techniques. A Shack-Hartmann wavefront sensor and a Mach-Zehnder interferometer were used for direct measurements of focal thermal lens at different pump powers. The obtained measurements were coinciding with the FE simulations.

Environmental Barrier Coating (EBC) Durability Modeling; An Overview and Preliminary Analysis

NASA Technical Reports Server (NTRS)

Abdul-Aziz, A.; Bhatt, R. T.; Grady, J. E.; Zhu, D.

2012-01-01

A study outlining a fracture mechanics based model that is being developed to investigate crack growth and spallation of environmental barrier coating (EBC) under thermal cycling conditions is presented. A description of the current plan and a model to estimate thermal residual stresses in the coating and preliminary fracture mechanics concepts for studying crack growth in the coating are also discussed. A road map for modeling life and durability of the EBC and the results of FEA model(s) developed for predicting thermal residual stresses and the cracking behavior of the coating are generated and described. Further initial assessment and preliminary results showed that developing a comprehensive EBC life prediction model incorporating EBC cracking, degradation and spalling mechanism under stress and temperature gradients typically seen in turbine components is difficult. This is basically due to mismatch in thermal expansion difference between sub-layers of EBC as well as between EBC and substrate, diffusion of moisture and oxygen though the coating, and densification of the coating during operating conditions as well as due to foreign object damage, the EBC can also crack and spall from the substrate causing oxidation and recession and reducing the design life of the EBC coated substrate.

The effect of Al intermediate layer on thermal resistance of EB-PVD yttria-stabilized zirconia coatings on titanium substrate

NASA Astrophysics Data System (ADS)

Panin, Alexey; Panin, Victor; Kazachenok, Marina; Shugurov, Artur; Sinyakova, Elena; Martynov, Sergey; Rusyaev, Andrey; Kasterov, Artur

2017-12-01

The yttria-stabilized zirconia coatings sprayed on titanium substrates by the electron beam physical vapor deposition were subjected to thermal annealing in air at 1000°C for 1, 30 and 60 min. The delamination and fracture of the coatings are studied by the scanning electron microscopy and X-ray diffraction. It is shown that a magnetron sputtered Al interlayer between the coating and the substrate considerably improves the thermal resistance of ceramic coatings.

Long-term thermal effects on injectivity evolution during CO 2 storage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vilarrasa, Victor; Rinaldi, Antonio P.; Rutqvist, Jonny

Carbon dioxide (CO 2 ) is likely to reach the bottom of injection wells at a colder temperature than that of the storage formation, causing cooling of the rock. This cooling, together with overpressure, tends to open up fractures, which may enhance injectivity. Here, we investigate cooling effects on injectivity enhancement by modeling the In Salah CO 2 storage site and a theoretical, long-term injection case. We use stress-dependent permeability functions that predict an increase in permeability as the effective stress acting normal to fractures decreases. Normal effective stress can decrease either due to overpressure or cooling. We calibrate ourmore » In Salah model, which includes a fracture zone perpendicular to the well, obtaining a good fitting with the injection pressure measured at KB-502 and the rapid CO 2 breakthrough that occurred at the observation well KB-5 located 2 km away from the injection well. CO 2 preferentially advances through the fracture zone, which becomes two orders of magnitude more permeable than the rest of the reservoir. Nevertheless, the effect of cooling on the long-term injectivity enhancement is limited in pressure dominated storage sites, like at In Salah, because most of the permeability enhancement is due to overpressure. But, thermal effects enhance injectivity in cooling dominated storage sites, which may decrease the injection pressure by 20%, saving a significant amount of compression energy all over the duration of storage projects. Overall, our simulation results show that cooling has the potential to enhance injectivity in fractured reservoirs.« less

Long-term thermal effects on injectivity evolution during CO 2 storage

DOE PAGES

Vilarrasa, Victor; Rinaldi, Antonio P.; Rutqvist, Jonny

2017-08-22

Carbon dioxide (CO 2 ) is likely to reach the bottom of injection wells at a colder temperature than that of the storage formation, causing cooling of the rock. This cooling, together with overpressure, tends to open up fractures, which may enhance injectivity. Here, we investigate cooling effects on injectivity enhancement by modeling the In Salah CO 2 storage site and a theoretical, long-term injection case. We use stress-dependent permeability functions that predict an increase in permeability as the effective stress acting normal to fractures decreases. Normal effective stress can decrease either due to overpressure or cooling. We calibrate ourmore » In Salah model, which includes a fracture zone perpendicular to the well, obtaining a good fitting with the injection pressure measured at KB-502 and the rapid CO 2 breakthrough that occurred at the observation well KB-5 located 2 km away from the injection well. CO 2 preferentially advances through the fracture zone, which becomes two orders of magnitude more permeable than the rest of the reservoir. Nevertheless, the effect of cooling on the long-term injectivity enhancement is limited in pressure dominated storage sites, like at In Salah, because most of the permeability enhancement is due to overpressure. But, thermal effects enhance injectivity in cooling dominated storage sites, which may decrease the injection pressure by 20%, saving a significant amount of compression energy all over the duration of storage projects. Overall, our simulation results show that cooling has the potential to enhance injectivity in fractured reservoirs.« less

Fracture Behaviour of Plasma Sprayed Thermal Barrier Coatings

NASA Astrophysics Data System (ADS)

Malzbender, Jürgen; Wakui, Takashi; Wessel, Egbert; Steinbrech, Rolf W.

Thermal barrier coatings (TBCs) of plasma sprayed yttria stabilised zirconia (YSZ) are increasingly utilised for heat exposed components of advanced gas turbines1,2. An important reason for the application of zirconia coatings is the low thermal conductivity of this ceramic material which is further diminished in a TBC by the high concentration of spraying induced microstructural defects, e.g. crack-shaped defects between and within the spraying splats. Thus with TBCs on gas cooled turbine components stiff temperature gradients can be realised as an important prerequisite for an increased thermal efficiency of the energy conversion process.

Effect of additive particles on mechanical, thermal, and cell functioning properties of poly(methyl methacrylate) cement

PubMed Central

Khandaker, Morshed; Vaughan, Melville B; Morris, Tracy L; White, Jeremiah J; Meng, Zhaotong

2014-01-01

The most common bone cement material used clinically today for orthopedic surgery is poly(methyl methacrylate) (PMMA). Conventional PMMA bone cement has several mechanical, thermal, and biological disadvantages. To overcome these problems, researchers have investigated combinations of PMMA bone cement and several bioactive particles (micrometers to nanometers in size), such as magnesium oxide, hydroxyapatite, chitosan, barium sulfate, and silica. A study comparing the effect of these individual additives on the mechanical, thermal, and cell functional properties of PMMA would be important to enable selection of suitable additives and design improved PMMA cement for orthopedic applications. Therefore, the goal of this study was to determine the effect of inclusion of magnesium oxide, hydroxyapatite, chitosan, barium sulfate, and silica additives in PMMA on the mechanical, thermal, and cell functional performance of PMMA. American Society for Testing and Materials standard three-point bend flexural and fracture tests were conducted to determine the flexural strength, flexural modulus, and fracture toughness of the different PMMA samples. A custom-made temperature measurement system was used to determine maximum curing temperature and the time needed for each PMMA sample to reach its maximum curing temperature. Osteoblast adhesion and proliferation experiments were performed to determine cell viability using the different PMMA cements. We found that flexural strength and fracture toughness were significantly greater for PMMA specimens that incorporated silica than for the other specimens. All additives prolonged the time taken to reach maximum curing temperature and significantly improved cell adhesion of the PMMA samples. The results of this study could be useful for improving the union of implant-PMMA or bone-PMMA interfaces by incorporating nanoparticles into PMMA cement for orthopedic and orthodontic applications. PMID:24920906

Effect of additive particles on mechanical, thermal, and cell functioning properties of poly(methyl methacrylate) cement.

PubMed

Khandaker, Morshed; Vaughan, Melville B; Morris, Tracy L; White, Jeremiah J; Meng, Zhaotong

2014-01-01

The most common bone cement material used clinically today for orthopedic surgery is poly(methyl methacrylate) (PMMA). Conventional PMMA bone cement has several mechanical, thermal, and biological disadvantages. To overcome these problems, researchers have investigated combinations of PMMA bone cement and several bioactive particles (micrometers to nanometers in size), such as magnesium oxide, hydroxyapatite, chitosan, barium sulfate, and silica. A study comparing the effect of these individual additives on the mechanical, thermal, and cell functional properties of PMMA would be important to enable selection of suitable additives and design improved PMMA cement for orthopedic applications. Therefore, the goal of this study was to determine the effect of inclusion of magnesium oxide, hydroxyapatite, chitosan, barium sulfate, and silica additives in PMMA on the mechanical, thermal, and cell functional performance of PMMA. American Society for Testing and Materials standard three-point bend flexural and fracture tests were conducted to determine the flexural strength, flexural modulus, and fracture toughness of the different PMMA samples. A custom-made temperature measurement system was used to determine maximum curing temperature and the time needed for each PMMA sample to reach its maximum curing temperature. Osteoblast adhesion and proliferation experiments were performed to determine cell viability using the different PMMA cements. We found that flexural strength and fracture toughness were significantly greater for PMMA specimens that incorporated silica than for the other specimens. All additives prolonged the time taken to reach maximum curing temperature and significantly improved cell adhesion of the PMMA samples. The results of this study could be useful for improving the union of implant-PMMA or bone-PMMA interfaces by incorporating nanoparticles into PMMA cement for orthopedic and orthodontic applications.

Turbine Engine Hot Section Technology, 1984

NASA Technical Reports Server (NTRS)

1984-01-01

Presentations were made concerning the hot section environment and behavior of combustion liners, turbine blades, and waves. The presentations were divided into six sessions: instrumentation, combustion, turbine heat transfer, structural analysis, fatigue and fracture, and surface properties. The principal objective of each session was to disseminate research results to date, along with future plans. Topics discussed included modeling of thermal and fluid flow phenomena, structural analysis, fatigue and fracture, surface protective coatings, constitutive behavior, stress-strain response, and life prediction methods.

Thermal Exposure and Environment Effects on Tension, Fracture and Fatigue of 5XXX Alloys Tested in Different Orientations

DTIC Science & Technology

2017-12-27

were determined and the effects of changes in loading rate and solution on this susceptibility were determined. Technical Approach The technical... approach followed in this completed work has been to conduct quasi- static fracture and fatigue experiments on 5XXX commercial aluminum alloys of interest...Metallic Materials Studied by Correlative Tomography", in 38th Riso International Symposium on Materials Science - IOP Conf. Series: Materials Science

Effects of asphalt rejuvenator on thermal and mechanical properties on oxidized hot mixed asphalt pavements

NASA Astrophysics Data System (ADS)

Farace, Nicholas A.; Buttlar, William G.; Reis, Henrique

2016-04-01

The utilization of asphalt rejuvenator, and its effectiveness for restoring thermal and mechanical properties was investigated via Disk-shaped Compact Tension (DC(T)) and acoustic emission (AE) testing for determining mechanical properties and embrittlement temperatures of the mixtures. During the DC(T) testing the fracture energies and peak loads were used to measure the resistance of the rejuvenated asphalt to low temperature cracking. The AE testing monitored the acoustic emission activity while the specimens were cooled from room temperature to -40 °C to estimate the temperature at which thermal cracking began (i.e. the embrittlement temperature). First, a baseline response was obtained by obtaining the mechanical and thermal response of virgin HMA samples and HMA samples that had been exposed to oxidative aging for 36 hours at 135°C. The results showed the virgin samples had much higher peak loads and fracture energies than the 36 hours aged samples. Acoustic Emission showed similar results with the virgin samples having embrittlement temperatures 10 °C cooler than the 36 hours aged specimens. Then, overaged for 36 hours specimens were treated different amounts of rejuvenator (10%, 15%, and 20% by weight of binder content) and left to dwell for increased amount of time periods varying from one to eight weeks. It was observed that the AE results showed an improvement of embrittlement temperature with increasing with the dwell times. The 8 weeks specimens had cooler embrittlement temperatures than the virgin specimens. Finally, the low temperature effects on fracture energy and peak load of the rejuvenated asphalt was investigated. Rejuvenator was applied (10% by weight of binder) to specimens aged 36 hours at 135 °C, and the dwell time was varied from 1 to 4 weeks. The results showed that the peak loads were restored to levels of the virgin specimens, and the fracture energies improved to levels beyond that of the virgin specimens. The results also showed a general trend of improvement for the AE testing of the embrittlement temperature.

Rheological and Performance Research on a Regenerable Polyvinyl Alcohol Fracturing Fluid

PubMed Central

Shang, Xiaosen; Ding, Yunhong; Wang, Yonghui; Yang, Lifeng

2015-01-01

A regenerable polyvinyl alcohol/organic boron fracturing fluid system with 1.6 wt% polyvinyl alcohol (PVOH) and 1.2 wt% organic boron (OBT) was studied, and its main regeneration mechanism is the reversible cross-linking reaction between B(OH)4 - and hydroxyl groups of PVOH as the change of pH. Results of rheology evaluations show that both the apparent viscosity and the thermal stability of the fracturing fluid decreased with the regeneration number of times increasing. In addition, the apparent viscosity of the fluid which was without regeneration was more sensitive to the shear action compared with that of the fluid with regeneration once or twice. When the fracturing fluid was without regeneration, the elasticity was dominating due to the three-dimensional network structure of the formed gel; the viscosity gradually occupied the advantage when the fracturing fluid was regenerated once or twice. The settling velocity of proppant was accelerated by both the regeneration process and the increasing temperature, but it was decelerated when the proppant ratio increased. Results of core damage tests indicate that less permeability damage was caused by the PVOH/OBT fracturing fluid compared with that caused by the guar gum fracturing fluid after gel breaking. PMID:26641857

Rheological and Performance Research on a Regenerable Polyvinyl Alcohol Fracturing Fluid.

PubMed

Shang, Xiaosen; Ding, Yunhong; Wang, Yonghui; Yang, Lifeng

2015-01-01

A regenerable polyvinyl alcohol/organic boron fracturing fluid system with 1.6 wt% polyvinyl alcohol (PVOH) and 1.2 wt% organic boron (OBT) was studied, and its main regeneration mechanism is the reversible cross-linking reaction between B(OH)4- and hydroxyl groups of PVOH as the change of pH. Results of rheology evaluations show that both the apparent viscosity and the thermal stability of the fracturing fluid decreased with the regeneration number of times increasing. In addition, the apparent viscosity of the fluid which was without regeneration was more sensitive to the shear action compared with that of the fluid with regeneration once or twice. When the fracturing fluid was without regeneration, the elasticity was dominating due to the three-dimensional network structure of the formed gel; the viscosity gradually occupied the advantage when the fracturing fluid was regenerated once or twice. The settling velocity of proppant was accelerated by both the regeneration process and the increasing temperature, but it was decelerated when the proppant ratio increased. Results of core damage tests indicate that less permeability damage was caused by the PVOH/OBT fracturing fluid compared with that caused by the guar gum fracturing fluid after gel breaking.

Tensile and fracture properties of type 316 stainless steel after creep

NASA Astrophysics Data System (ADS)

Gan, D.

1982-12-01

The effects of creep on the mechanical properties of type 316 stainless steel were studied. Tensile and Charpy specimens were machined from the oversize specimens crept at 750 °C and 103 MPa. The ambient fracture energy was found to deteriorate rapidly after creep. The ambient yield stress was increased moderately, but the tensile ductility was severely reduced. The effects of intergranular carbides alone on mechanical properties were studied with specimens thermal aged without load. These carbides were shown to cause a moderate reduction in fracture energy and tensile ductility but had little effect on yield stress. Extensive grain boundary separations were observed on the fracture surfaces. SEM studies showed that these grain boundaries were covered with micro voids initiated by the dense intergranular carbides. Frequently, large dimples on grain boundary joined up and initiated shear fracture into the grain. In the crept specimens additional microstructural changes in the form of intragranular carbides and subgrain boundaries were observed. Both are responsible for the increase in yield stress and the further reduction in tensile ductility and fracture energy. The intragranular carbides also modified the size and density of the dimples on the fracture surfaces.

OpenACC directive-based GPU acceleration of an implicit reconstructed discontinuous Galerkin method for compressible flows on 3D unstructured grids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lou, Jialin; Xia, Yidong; Luo, Lixiang

2016-09-01

In this study, we use a combination of modeling techniques to describe the relationship between fracture radius that might be accomplished in a hypothetical enhanced geothermal system (EGS) and drilling distance required to create and access those fractures. We use a combination of commonly applied analytical solutions for heat transport in parallel fractures and 3D finite-element method models of more realistic heat extraction geometries. For a conceptual model involving multiple parallel fractures developed perpendicular to an inclined or horizontal borehole, calculations demonstrate that EGS will likely require very large fractures, of greater than 300 m radius, to keep interfracture drillingmore » distances to ~10 km or less. As drilling distances are generally inversely proportional to the square of fracture radius, drilling costs quickly escalate as the fracture radius decreases. It is important to know, however, whether fracture spacing will be dictated by thermal or mechanical considerations, as the relationship between drilling distance and number of fractures is quite different in each case. Information about the likelihood of hydraulically creating very large fractures comes primarily from petroleum recovery industry data describing hydraulic fractures in shale. Those data suggest that fractures with radii on the order of several hundred meters may, indeed, be possible. The results of this study demonstrate that relatively simple calculations can be used to estimate primary design constraints on a system, particularly regarding the relationship between generated fracture radius and the total length of drilling needed in the fracture creation zone. Comparison of the numerical simulations of more realistic geometries than addressed in the analytical solutions suggest that simple proportionalities can readily be derived to relate a particular flow field.« less

Thermal fracturing on comets. Applications to 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Attree, N.; Groussin, O.; Jorda, L.; Rodionov, S.; Auger, A.-T.; Thomas, N.; Brouet, Y.; Poch, O.; Kührt, E.; Knapmeyer, M.; Preusker, F.; Scholten, F.; Knollenberg, J.; Hviid, S.; Hartogh, P.

2018-03-01

We simulate the stresses induced by temperature changes in a putative hard layer near the surface of comet 67P/Churyumov-Gerasimenko with a thermo-viscoelastic model. Such a layer could be formed by the recondensation or sintering of water ice (and dust grains), as suggested by laboratory experiments and computer simulations, and would explain the high compressive strength encountered by experiments on board the Philae lander. Changes in temperature from seasonal insolation variation penetrate into the comet's surface to depths controlled by the thermal inertia, causing the material to expand and contract. Modelling this with a Maxwellian viscoelastic response on a spherical nucleus, we show that a hard, icy layer with similar properties to Martian permafrost will experience high stresses: up to tens of MPa, which exceed its material strength (a few MPa), down to depths of centimetres to a metre. The stress distribution with latitude is confirmed qualitatively when taking into account the comet's complex shape but neglecting thermal inertia. Stress is found to be comparable to the material strength everywhere for sufficient thermal inertia (≳50 J m-2 K-1 s-1/2) and ice content (≳45% at the equator). In this case, stresses penetrate to a typical depth of 0.25 m, consistent with the detection of metre-scale thermal contraction crack polygons all over the comet. Thermal fracturing may be an important erosion process on cometary surfaces which breaks down material and weakens cliffs.

Mechanical Properties of Layered La2Zr2O7 Thermal Barrier Coatings

NASA Astrophysics Data System (ADS)

Guo, Xingye; Li, Li; Park, Hyeon-Myeong; Knapp, James; Jung, Yeon-Gil; Zhang, Jing

2018-04-01

Lanthanum zirconate (La2Zr2O7) has been proposed as a promising thermal barrier coating (TBC) material due to its low thermal conductivity and high stability at high temperatures. In this work, both single and double-ceramic-layer (DCL) TBC systems of La2Zr2O7 and 8 wt.% yttria-stabilized zirconia (8YSZ) were prepared using air plasma spray (APS) technique. The thermomechanical properties and microstructure were investigated. Thermal gradient mechanical fatigue (TGMF) tests were applied to investigate the thermal cycling performance. The results showed that DCL La2Zr2O7 + 8YSZ TBC samples lasted fewer cycles compared with single-layered 8YSZ TBC samples in TGMF tests. This is because DCL La2Zr2O7 TBC samples had higher residual stress during the thermal cycling process, and their fracture toughness was lower than that of 8YSZ. Bond strength test results showed that 8YSZ TBC samples had higher bond strength compared with La2Zr2O7. The erosion rate of La2Zr2O7 TBC samples was higher than that of 8YSZ samples, due to the lower critical erodent velocity and fracture toughness of La2Zr2O7. DCL porous 8YSZ + La2Zr2O7 had a lower erosion rate than other SCL and DCL La2Zr2O7 coatings, suggesting that porous 8YSZ serves as a stress-relief buffer layer.

Thermal fatigue and thermal shock in bedrock: An attempt to unravel the geomorphic processes and products

NASA Astrophysics Data System (ADS)

Hall, Kevin; Thorn, Colin E.

2014-02-01

Widespread acceptance in science at-large notwithstanding, the ability of thermal stresses to produce thermal fatigue (TF) and/or thermal shock (TS) in bedrock and coarse debris in the field is often doubted. Commonly called insolation weathering in geomorphology, the results of questionable laboratory experiments have led many geomorphologists to consider terrestrial temperatures to be inadequate to generate thermally induced stresses leading to rock failure; the exceptions are the action of fire or lightning. We comprehensively survey the general scientific literature on TF and TS while rigorously scrutinizing that relating to geomorphology. Findings indicate theoretical and experimental information is adequate to establish the feasibility of TF and TS in rock stemming from rock temperatures monitored in the field. While TS may exhibit fracture patterns that are uniquely diagnostic, those of TF lack any such attributes. It would appear unlikely that TF can prepare or weaken rock to increase the likelihood of TS. The question of whether widespread polygonal versus rectilinear cracking is diagnostic of TS is presently an open one as possible explanations invoke process(es) and/or host material(s) and, consequently, to assign palaeoenvironmental significance to such fracture patterns is premature at this time. Further geomorphological laboratory research into TF and TS is merited as sufficient theoretical underpinning already exists. However, laboratory experimentation needs to be much more rigorously defined and executed and is faced with significant hurdles if it is to be effectively linked to field observations.

Characterization of thermal tracer tests and heat exchanges in fractured media

NASA Astrophysics Data System (ADS)

de La Bernardie, Jérôme; Bour, Olivier; Guihéneuf, Nicolas; Chatton, Eliot; Labasque, Thierry; Longuevergne, Laurent; Le Lay, Hugo; Koch, Florian; Gerard, Marie-Françoise; Lavenant, Nicolas; Le Borgne, Tanguy

2016-04-01

Geothermal energy is a renewable energy source particularly attractive due to associated low greenhouse gas emission rates. Crystalline rocks are in general considered of poor interest for geothermal applications at shallow depths (< 100m), because of the low permeability of the medium. In some cases, fractures may enhance permeability, but thermal energy storage at these shallow depths is still remaining very challenging because of the low storativity of the medium. Within this framework, the purpose of this study is to test the possibility of efficient thermal energy storage in shallow fractured rocks with a single well semi open loop heat exchanger (standing column well). For doing so, several heat tracer tests have been achieved along a borehole between two connected fractures. The heat tracer tests have been achieved at the experimental site of Ploemeur (H+ observatory network). The tracer tests consist in monitoring the temperature in the upper fracture while injecting hot water in the deeper one thanks to a field boiler. For such an experimental setup, the main difficulty to interpret the data comes from the requirement for separating the temperature advective signal of the tracer test (temperature recovery) from the heat increase due to injection of hot water through the borehole which induces heat losses all along the injection tube in the water column. For doing so, in addition to a double straddle packer used for isolating the injection chamber, the particularity of the experimental set up is the use of fiber optic distributed temperature sensing (FO-DTS); an innovative technology which allows spatial and temporal monitoring of the temperature all along the well. Thanks to this tool, we were able to estimate heat increases coming from diffusion along the injection tube which is found much lower than localized temperature increases resulting from tracer test recovery. With local temperatures probes, separating both effects would not have been feasible. We also show through signal processing how diffusive and advective effects may be differentiated. This allowed us to estimate temperature recovery for different heat tracer durations and setups. In particular we show that temperature recovery is highly dependent on hydraulic configuration such as perfect dipole or fully convergent heat tracer tests.

Application of uniaxial confining-core clamp with hydrous pyrolysis in petrophysical and geochemical studies of source rocks at various thermal maturities

USGS Publications Warehouse

Lewan, Michael D.; Birdwell, Justin E.; Baez, Luis; Beeney, Ken; Sonnenberg, Steve

2013-01-01

Understanding changes in petrophysical and geochemical parameters during source rock thermal maturation is a critical component in evaluating source-rock petroleum accumulations. Natural core data are preferred, but obtaining cores that represent the same facies of a source rock at different thermal maturities is seldom possible. An alternative approach is to induce thermal maturity changes by laboratory pyrolysis on aliquots of a source-rock sample of a given facies of interest. Hydrous pyrolysis is an effective way to induce thermal maturity on source-rock cores and provide expelled oils that are similar in composition to natural crude oils. However, net-volume increases during bitumen and oil generation result in expanded cores due to opening of bedding-plane partings. Although meaningful geochemical measurements on expanded, recovered cores are possible, the utility of the core for measuring petrophysical properties relevant to natural subsurface cores is not suitable. This problem created during hydrous pyrolysis is alleviated by using a stainless steel uniaxial confinement clamp on rock cores cut perpendicular to bedding fabric. The clamp prevents expansion just as overburden does during natural petroleum formation in the subsurface. As a result, intact cores can be recovered at various thermal maturities for the measurement of petrophysical properties as well as for geochemical analyses. This approach has been applied to 1.7-inch diameter cores taken perpendicular to the bedding fabric of a 2.3- to 2.4-inch thick slab of Mahogany oil shale from the Eocene Green River Formation. Cores were subjected to hydrous pyrolysis at 360 °C for 72 h, which represents near maximum oil generation. One core was heated unconfined and the other was heated in the uniaxial confinement clamp. The unconfined core developed open tensile fractures parallel to the bedding fabric that result in a 38 % vertical expansion of the core. These open fractures did not occur in the confined core, but short, discontinuous vertical fractures on the core periphery occurred as a result of lateral expansion.

The Role of Hydrogen-Enhanced Strain-Induced Lattice Defects on Hydrogen Embrittlement Susceptibility of X80 Pipeline Steel

NASA Astrophysics Data System (ADS)

Hattori, M.; Suzuki, H.; Seko, Y.; Takai, K.

2017-08-01

Studies to date have not completely determined the factors influencing hydrogen embrittlement of ferrite/bainite X80 pipeline steel. Hydrogen embrittlement susceptibility was evaluated based on fracture strain in tensile testing. We conducted a thermal desorption analysis to measure the amount of tracer hydrogen corresponding to that of lattice defects. Hydrogen embrittlement susceptibility and the amount of tracer hydrogen significantly increased with decreasing crosshead speed. Additionally, a significant increase in the formation of hydrogen-enhanced strain-induced lattice defects was observed immediately before the final fracture. In contrast to hydrogen-free specimens, the fracture surface of the hydrogen-charged specimens exhibited shallower dimples without nuclei, such as secondary phase particles. These findings indicate that the presence of hydrogen enhanced the formation of lattice defects, particularly just prior to the occurrence of final fracture. This in turn enhanced the formation of shallower dimples, thereby potentially causing premature fracture of X80 pipeline steel at lower crosshead speeds.

Thermal Shock Behavior of Single Crystal Oxide Refractive Concentrators for High Temperatures Solar Thermal Propulsion

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Choi, Sung R.; Jacobson, Nathan S.; Miller, Robert A.

1999-01-01

Single crystal oxides such as yttria-stabilized zirconia (Y2O3-ZrO2), yttrium-aluminum-garnet (Y3Al5O12, or YAG), magnesium oxide (MgO) and sapphire (Al2O3) have been considered as refractive secondary concentrator materials for high temperature solar propulsion applications. However, thermal mechanical reliability of the oxide components in severe thermal environments during space mission sun/shade transitions is of great concern. In this paper, critical mechanical properties of these oxide crystals are determined by the indentation technique. Thermal shock resistance of the oxides is evaluated using a high power CO, laser under high temperature-high thermal gradients. Thermal stress fracture behavior and failure mechanisms of these oxide materials are investigated under various temperature and heating conditions.

Modeling of heat extraction from variably fractured porous media in Enhanced Geothermal Systems

DOE PAGES

Hadgu, Teklu; Kalinina, Elena Arkadievna; Lowry, Thomas Stephen

2016-01-30

Modeling of heat extraction in Enhanced Geothermal Systems is presented. The study builds on recent studies on the use of directional wells to improve heat transfer between doublet injection and production wells. The current study focuses on the influence of fracture orientation on production temperature in deep low permeability geothermal systems, and the effects of directional drilling and separation distance between boreholes on heat extraction. The modeling results indicate that fracture orientation with respect to the well-pair plane has significant influence on reservoir thermal drawdown. As a result, the vertical well doublet is impacted significantly more than the horizontal wellmore » doublet« less

Thermal Stress Analysis for Ceramics Stalk in the Low Pressure Die Casting Machine

NASA Astrophysics Data System (ADS)

Noda, Nao-Aki; Hendra, Nao-Aki; Takase, Yasushi; Li, Wenbin

Low pressure die casting (LPDC) is defined as a net shape casting technology in which the molten metal is injected at high speeds and pressure into a metallic die. The LPDC process is playing an increasingly important role in the foundry industry as a low-cost and high-efficiency precision forming technique. The LPDC process is that the permanent die and filling systems are placed over the furnace containing the molten alloy. The filling of the cavity is obtained by forcing the molten metal by means of a pressurized gas in order to rise into a ceramic tube, which connects the die to the furnace. The ceramics tube called stalk has high temperature resistance and high corrosion resistance. However, attention should be paid to the thermal stress when the stalk is dipped into the molten aluminum. It is important to develop the design of the stalk to reduce the risk of fracture because of low fracture toughness of ceramics. In this paper, therefore, the finite element method is applied to calculate the thermal stresses when the stalk is dipped into the crucible by varying the dipping speeds and dipping directions. It is found that the thermal stress can be reduced by dipping slowly if the stalk is dipped into the crucible vertically, while the thermal stress can be reduced by dipping fast if it is dipped horizontally.

Toughening Mechanisms in Silica-Filled Epoxy Nanocomposites

NASA Astrophysics Data System (ADS)

Patel, Binay S.

Epoxies are widely used as underfill resins throughout the microelectronics industry to mechanically couple and protect various components of flip-chip assemblies. Generally rigid materials largely surround underfill resins. Improving the mechanical and thermal properties of epoxy resins to better match those of their rigid counterparts can help extend the service lifetime of flip-chip assemblies. Recently, researchers have demonstrated that silica nanoparticles are effective toughening agents for lightly-crosslinked epoxies. Improvements in the fracture toughness of silica-filled epoxy nanocomposites have primarily been attributed to two toughening mechanisms: particle debonding with subsequent void growth and matrix shear banding. Various attempts have been made to model the contribution of these toughening mechanisms to the overall fracture energy observed in silica-filled epoxy nanocomposites. However, disparities still exist between experimental and modeled fracture energy results. In this dissertation, the thermal, rheological and mechanical behavior of eight different types of silica-filled epoxy nanocomposites was investigated. Each nanocomposite consisted of up to 10 vol% of silica nanoparticles with particle sizes ranging from 20 nm to 200 nm, with a variety of surface treatments and particle structures. Fractographical analysis was conducted with new experimental approaches in order to accurately identify morphological evidence for each proposed toughening mechanism. Overall, three major insights into the fracture behavior of real world silica-filled epoxy nanocomposites were established. First, microcracking was observed as an essential toughening mechanism in silica-filled epoxy nanocomposites. Microcracking was observed on the surface and subsurface of fractured samples in each type of silica-filled epoxy nanocomposite. The additional toughening contribution of microcracking to overall fracture energy yielded excellent agreement between experimental and modeled fracture energy results. Furthermore, the contribution of microcracking was most prevalent at lower filler contents which suggests that the presence of microcracking may account for the previously unexplained improvements in fracture behavior attained in silica-filled epoxy nanocomposites at low filler contents. Secondly, surface modification through the application of three different propriety surface treatments ("A", "B" and "C") was found to greatly influence the processibility and fracture behavior of silica-filled epoxy nanocomposites. B-treated silica nanoparticles were found to readily form micron-scale agglomerates, settled during nanocomposite curing and showed no improvement in fracture toughness with increasing filler content. In contrast, the nanocomposites consisting of A-treated and C-treated silica nanoparticles yielded morphologies primarily containing well-dispersed nanoparticles. Therefore, fracture toughness improved with increasing filler content. Finally, particle porosity was found to have no significant effect on fracture behavior for the range of silica-filled epoxy nanocomposites investigated. Lower density porous silica nanoparticles were just as effective toughening agents as higher density non-porous silica nanoparticles. Consequently, the potential exists for the use of toughened-epoxies in lightweight structural applications.

Tensile properties of SiC/aluminum filamentary composites - Thermal degradation effects

NASA Technical Reports Server (NTRS)

Skinner, A.; Koczak, M. J.; Lawley, A.

1982-01-01

Aluminium metal matrix composites with a low cost fiber, e.g. SiC, provide for an attractive combination of high elastic modulus and longitudinal strengths coupled with a low density. SiC (volume fraction 0.55)-aluminum (6061) systems have been studied in order to optimize fiber composite strength and processing parameters. A comparison of two SiC/aluminum composites produced by AVCO and DWA is provided. Fiber properties are shown to alter composite tensile properties and fracture morphology. The room temperature tensile strengths appear to be insensitive to thermal exposures at 500 C up to 150 h. The elastic modulus of the composites also appears to be stable up to 400 C, however variations in the loss modulus are apparent. The fracture morphology reflects the quality of the interfacial bond, fiber strengths and fiber processing.

Mechanisms of boron fiber strengthening by thermal treatment

NASA Technical Reports Server (NTRS)

Dicarlo, J. A.

1979-01-01

The fracture strain for boron on tungsten fibers can be improved by heat treatment under vacuum or argon environments. The mechanical basis for this improvement is thermally-induced axial contraction of the entire fiber, whereby strength-controlling core flaws are compressed and fiber fracture strain increased by the value of the contraction strain. By highly sensitive measurements of fiber density and volume, the physical mechanisms responsible for contraction under both environments was identified as boron atom diffusion out of the fiber sheath. The fiber contracts because the average volume of the resulting microvoid was determined to be only 0.26 + or - 0.09 the average atomic volume of the removed atom. The basic and practical implications of these results are discussed with particular emphasis on the theory, use, and limitations of heat-induced contraction as a simple cost-effective secondary processing method.

New developments in measurements technology relevant to the studies of deep geological repositories in bedded salt

NASA Astrophysics Data System (ADS)

Mao, N. H.; Ramirez, A. L.

1980-10-01

Developments in measurement technology are presented which are relevant to the studies of deep geological repositories for nuclear waste disposal during all phases of development, i.e., site selection, site characterization, construction, operation, and decommission. Emphasis was placed on geophysics and geotechnics with special attention to those techniques applicable to bedded salt. The techniques are grouped into sections as follows: tectonic environment, state of stress, subsurface structures, fractures, stress changes, deformation, thermal properties, fluid transport properties, and other approaches. Several areas that merit further research and developments are identified. These areas are: in situ thermal measurement techniques, fracture detection and characterization, in situ stress measurements, and creep behavior. The available instrumentations should generally be improved to have better resolution and accuracy, enhanced instrument survivability, and reliability for extended time periods in a hostile environment.

Borehole Stability in High-Temperature Formations

NASA Astrophysics Data System (ADS)

Yan, Chuanliang; Deng, Jingen; Yu, Baohua; Li, Wenliang; Chen, Zijian; Hu, Lianbo; Li, Yang

2014-11-01

In oil and gas drilling or geothermal well drilling, the temperature difference between the drilling fluid and formation will lead to an apparent temperature change around the borehole, which will influence the stress state around the borehole and tend to cause borehole instability in high geothermal gradient formations. The thermal effect is usually not considered as a factor in most of the conventional borehole stability models. In this research, in order to solve the borehole instability in high-temperature formations, a calculation model of the temperature field around the borehole during drilling is established. The effects of drilling fluid circulation, drilling fluid density, and mud displacement on the temperature field are analyzed. Besides these effects, the effect of temperature change on the stress around the borehole is analyzed based on thermoelasticity theory. In addition, the relationships between temperature and strength of four types of rocks are respectively established based on experimental results, and thermal expansion coefficients are also tested. On this basis, a borehole stability model is established considering thermal effects and the effect of temperature change on borehole stability is also analyzed. The results show that the fracture pressure and collapse pressure will both increase as the temperature of borehole rises, and vice versa. The fracture pressure is more sensitive to temperature. Temperature has different effects on collapse pressures due to different lithological characters; however, the variation of fracture pressure is unrelated to lithology. The research results can provide a reference for the design of drilling fluid density in high-temperature wells.

3D convection in a fractured porous medium : influence of fracture network parameters and comparison to homogeneous approach.

NASA Astrophysics Data System (ADS)

Mezon, Cécile; Mourzenko, Valeri; François Thovert, Jean; Antoine, Raphael; Fontaine, Fabrice; Finizola, Anthony; Adler, Pierre Michel

2016-04-01

In the crust, fractures/faults can provide preferential pathways for fluid flow or act as barriers preventing the flow across these structures. In hydrothermal systems (usually found in fractured rock masses), these discontinuities may play a critical role at various scales, controlling fluid flows and heat transfer. The thermal convection is numerically computed in 3D fluid satured isotropically fractured porous media. Fractures are inserted as 2D convex polygons, which are randomly located. The fluid is assumed to satisfy 2D and 3D Darcy's law in the fractures and in the porous medium, respectively; exchanges take place between these two structures. First, checks were performed on an unfractured porous medium and the convection cells do start for the theoretical value of Ra, namely 4pi². 2D convection was verified up to Ra=800. Second, all fractured simulations were made for Rayleigh numbers (Ra) < 150, cubic boxes and closed-top conditions. The influence of parameters such as fracture aperture (or fracture transmissivity) and fracture density on the heat released by the whole system is studied. Then, the effective permeability of each fractured system is calculated. This last calculation enables the comparison between all fractured models and models of homogeneous medium with the same macroscopic properties. First, the heat increase released by the system as a function of fracture transmissivity and fracture density is determined. Second, results show that the effective approach is valid for low Ra (< 70), and that the mismatch between the full calculations and the effective medium approach for Ra higher than 70 depends on the fracture density in a crucial way. Third, the study also reveals that equivalent properties could be deduced from these computations in order to estimate the heat released by a fractured system from an homogeneous approach.

Computational methods for fracture analysis of heavy-section steel technology (HSST) pressure vessel experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bass, B.R.; Bryan, R.H.; Bryson, J.W.

This paper summarizes the capabilities and applications of the general-purpose and special-purpose computer programs that have been developed for use in fracture mechanics analyses of HSST pressure vessel experiments. Emphasis is placed on the OCA/USA code, which is designed for analysis of pressurized-thermal-shock (PTS) conditions, and on the ORMGEN/ADINA/ORVIRT system which is used for more general analysis. Fundamental features of these programs are discussed, along with applications to pressure vessel experiments.

Fracturing And Liquid CONvection

DOE Office of Scientific and Technical Information (OSTI.GOV)

2012-02-29

FALCON has been developed to enable simulation of the tightly coupled fluid-rock behavior in hydrothermal and engineered geothermal system (EGS) reservoirs, targeting the dynamics of fracture stimulation, fluid flow, rock deformation, and heat transport in a single integrated code, with the ultimate goal of providing a tool that can be used to test the viability of EGS in the United States and worldwide. Reliable reservoir performance predictions of EGS systems require accurate and robust modeling for the coupled thermal­hydrological­mechanical processes.

Fracture surface analysis in composite and titanium bonding: Part 1: Titanium bonding

NASA Technical Reports Server (NTRS)

Sanderson, K. A.; Wightman, J. P.

1985-01-01

Fractured lap shear Ti 6-4 adherends bonded with polyphenyquinoxaline (PPQ) and polysulfone were analyzed. The effects of adherend pretreatment, stress level, thermal aging, anodizing voltage, and modified adhesive of Ti 6-4 adherend bonded with PPQ on lap shear strength were studied. The effect of adherend pretreatment on lap shear strength was investigated for PS samples. Results of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) used to study the surface topography and surface composition are also discussed.

YELLOWSTONE MAGMATIC-HYDROTHERMAL SYSTEM, U. S. A.

USGS Publications Warehouse

Fournier, R.O.; Pitt, A.M.; ,

1985-01-01

At Yellowstone National Park, the deep permeability and fluid circulation are probably controlled and maintained by repeated brittle fracture of rocks in response to local and regional stress. Focal depths of earthquakes beneath the Yellowstone caldera suggest that the transition from brittle fracture to quasi-plastic flow takes place at about 3 to 4 km. The maximum temperature likely to be attained by the hydrothermal system is 350 to 450 degree C, the convective thermal output is about 5. 5 multiplied by 10**9 watts, and the minimum average thermal flux is about 1800 mW/m**2 throughout 2,500 km**2. The average thermal gradient between the heat source and the convecting hydrothermal system must be at least 700 to 1000 degree C/km. Crystallization and partial cooling of about 0. 082 km**3 of basalt or 0. 10 km**3 of rhyolite annually could furnish the heat discharged in the hot-spring system. The Yellowstone magmatic-hydrothermal system as a whole appears to be cooling down, in spite of a relatively large rate of inflation of the Yellowstone caldera.

Geology of the Azacualpa geothermal site, Departamento de Comayagua Honduras, Central America: Field report. Geologia del area geotermica de Azacualpa Departamento de Comayagua, Honduras, America Central: Informe de camps (in English and Spanish)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eppler, D.; Baldridge, S.; Perry, F.

1987-03-01

Thermal waters at the Azacualpa geothermal site are surfacing along fractures in the Atima Formation associated with the main north-south-trending Zacapa fault and the subordinate north-south-trending splays of the main fault. Permeability appears to be related to these fractures rather than to formation permeability in either the limestones of the Atima Formation or the Valle de Angeles Group red beds. Attitudes of lower Valle de Angeles Group red beds do not vary appreciably with distance away from the Zacapa fault, suggesting that the system is not behaving like a listric normal fault at depth. The ''Jaitique structure,'' as conjectured bymore » R. Fakundiny (1985), does not appear to have any manifestation at the surface in terms of structures that can be seen or measured in the bedrock. Its existence is considered unlikely at the present time. Calorimetry calculations indicate that the thermal anomaly at the Azacualpa site is producing approx.4.4 thermal megawatts.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmad Ghassemi

Geothermal energy is recovered by circulating water through heat exchange areas within a hot rock mass. Geothermal reservoir rock masses generally consist of igneous and metamorphic rocks that have low matrix permeability. Therefore, cracks and fractures play a significant role in extraction of geothermal energy by providing the major pathways for fluid flow and heat exchange. Therefore, knowledge of the conditions leading to formation of fractures and fracture networks is of paramount importance. Furthermore, in the absence of natural fractures or adequate connectivity, artificial fractures are created in the reservoir using hydraulic fracturing. Multiple fractures are preferred because of themore » large size necessary when using only a single fracture. Although the basic idea is rather simple, hydraulic fracturing is a complex process involving interactions of high pressure fluid injections with a stressed hot rock mass, mechanical interaction of induced fractures with existing natural fractures, and the spatial and temporal variations of in-situ stress. As a result, it is necessary to develop tools that can be used to study these interactions as an integral part of a comprehensive approach to geothermal reservoir development, particularly enhanced geothermal systems. In response to this need we have developed advanced poro-thermo-chemo-mechanical fracture models for rock fracture research in support of EGS design. The fracture propagation models are based on a regular displacement discontinuity formulation. The fracture propagation studies include modeling interaction of induced fractures. In addition to the fracture propagation studies, two-dimensional solution algorithms have been developed and used to estimate the impact of pro-thermo-chemical processes on fracture permeability and reservoir pressure. Fracture permeability variation is studied using a coupled thermo-chemical model with quartz reaction kinetics. The model is applied to study quartz precipitation/dissolution, as well as the variation in fracture aperture and pressure. Also, a three-dimensional model of injection/extraction has been developed to consider the impact poro- and thermoelastic stresses on fracture slip and injection pressure. These investigations shed light on the processes involved in the observed phenomenon of injection pressure variation (e.g., in Coso), and allow the assessment of the potential of thermal and chemical stimulation strategies.« less

Fracture performance of computer-aided manufactured zirconia and alloy crowns.

PubMed

Rosentritt, Martin; Behr, Michael; Thaller, Christian; Rudolph, Heike; Feilzer, Albert

2009-09-01

To compare the fracture resistance and fracture performance of CAD/CAM zirconia and alloy crowns. One electrophoretic deposition alumina ceramic (Wolceram, Wolceram) and 4 zirconia-based systems (ce.novation, ce.novation; Cercon, DeguDent; Digizon, Amann Girrbach; and Lava, 3M ESPE) were investigated. A porcelain-fused-to-metal method (Academy, Bego Medical) was used in either conventional casting technique or laser sintering. Sixteen crowns of each material were fabricated and veneered with glass-ceramic as recommended by the manufacturers. Crown and root dimensions were measured, and 8 crowns of each system were adhesively bonded or conventionally cemented. After the crowns were artificially aged in a simulated oral environment (1,200,000 mechanical loads with 50 N; 3,000 thermal cycles with distilled water between 5 degrees C and 55 degrees C; 2 minutes per cycle), fracture resistance and fracture patterns were determined and defect sizes investigated. The fracture force varied between 1,111 N and 2,038 N for conventional cementation and between 1,181 N and 2,295 N for adhesive bonding. No significant differences were found between adhesive and conventional cementations. Fracture patterns presented mostly as a chipping of the veneering, in single cases as a fracture of the core, and in 1 case as a fracture of the tooth. Crown material and cementation do not have any significant influence on the fracture force and fracture performance of all-ceramic and metal-based crowns. Therefore, it may be concluded that adhesive bonding is not necessary for the application of high-strength ceramics.

The Shear Strength and Fracture Behavior of Sn-Ag- xSb Solder Joints with Au/Ni-P/Cu UBM

NASA Astrophysics Data System (ADS)

Lee, Hwa-Teng; Hu, Shuen-Yuan; Hong, Ting-Fu; Chen, Yin-Fa

2008-06-01

This study investigates the effects of Sb addition on the shear strength and fracture behavior of Sn-Ag-based solders with Au/Ni-P/Cu underbump metallization (UBM) substrates. Sn-3Ag- xSb ternary alloy solder joints were prepared by adding 0 wt.% to 10 wt.% Sb to a Sn-3.5Ag alloy and joining them with Au/Ni-P/Cu UBM substrates. The solder joints were isothermally stored at 150°C for up to 625 h to study their microstructure and interfacial reaction with the UBM. Single-lap shear tests were conducted to evaluate the mechanical properties, thermal resistance, and failure behavior. The results show that UBM effectively suppressed intermetallic compound (IMC) formation and growth during isothermal storage. The Sb addition helped to refine the Ag3Sn compounds, further improving the shear strength and thermal resistance of the solders. The fracture behavior evolved from solder mode toward the mixed mode and finally to the IMC mode with increasing added Sb and isothermal storage time. However, SnSb compounds were found in the solder with 10 wt.% Sb; they may cause mechanical degradation of the solder after long-term isothermal storage.

Fracture mode, microstructure and temperature-dependent elastic moduli for thermoelectric composites of PbTe-PbS with SiC nanoparticle additions

NASA Astrophysics Data System (ADS)

Ni, Jennifer E.; Case, Eldon D.; Schmidt, Robert D.; Wu, Chun-I.; Hogan, Timothy P.; Trejo, Rosa M.; Lara-Curzio, Edgar; Kanatzidis, Mercouri G.

2013-12-01

Twenty-six (Pb0.95Sn0.05Te)0.92(PbS)0.08-0.055% PbI2-SiC nanoparticle (SiCnp) composite thermoelectric specimens were either hot pressed or pulsed electric current sintered (PECS). Bloating (a thermally induced increase in porosity, P, for as-densified specimens) was observed during annealing at temperatures >603 K for hot-pressed specimens and PECS-processed specimens from wet milled powders, but in contrast seven out of seven specimens densified by PECS from dry milled powders showed no observable bloating following annealing at temperatures up to 936 K. In this study, bloating in the specimens was accessed via thermal annealing induced changes in (i) porosity measured by scanning electron microscopy on fractured specimen surfaces, (ii) specimen volume and (iii) elastic moduli. The moduli were measured by resonant ultrasound spectroscopy. SiCnp additions (1-3.5 vol.%) changed the fracture mode from intergranular to transgranular, inhibited grain growth, and limited bloating in the wet milled PECS specimens. Inhibition of bloating likely occurs due to cleaning of contamination from powder particle surfaces via PECS processing which has been reported previously in the literature.

Geothermic analysis of high temperature hydrothermal activities area in Western plateau of Sichuan province, China

NASA Astrophysics Data System (ADS)

Zhang, J.

2016-12-01

There is a high temperature hydrothermal activity area in the western plateau of Sichuan. More than 200 hot springs points have been found in the region, including 11 hot spring water temperature above local boiling point. Most of these distribute along Jinshajjiang fracture, Dege-Xiangcheng fracture, Ganzi-Litang fracture as well as Xianshuihe fracture, and form three high-temperature hydrothermal activity strips in the NW-SE direction. Using gravity, magnetic, seismic and helium isotope data, this paper analyzed the crust-mantle heat flow structure, crustal heat source distribution and water heating system. The results show that the geothermal activity mainly controlled by the "hot" crust. The ratio of crustal heat flow and surface heat flow is higher than 60%. In the high temperature hydrothermal activities area, there is lower S wave velocity zone with Vs<3.2 km/s in 15 30 km depth in middle and lower crust. Basing on the S wave velocity inversion temperature of crust-mantle, it has been found that there is a high temperature layer with 850 1000 ° in 20 40 km depth. It is the main heat source of high temperature hydrothermal activity area of western Sichuan. Our argument is that atmospheric precipitation, surface water infiltrated along the fault fracture into the crustal deep, heating by crustal hot source, and circulation to surface become high temperature hot water. Geothermal water mainly reserve in the Triassic strata of the containing water good carbonate rocks, and in the intrusive granite which is along the fault zone. The thermal energy of Surface heat thermal activities mainly comes from the high-temperature hot source which is located in the middle and lower crust. Being in the deep crustal fracture, the groundwater infiltrated to the deep crust and absorbed heat, then, quickly got back to the surface and formed high hot springs.

Deformation and the timing of gas generation and migration in the eastern Brooks Range foothills, Arctic National Wildlife Refuge, Alaska

USGS Publications Warehouse

Parris, T.M.; Burruss, R.C.; O'Sullivan, P. B.

2003-01-01

Along the southeast border of the 1002 Assessment Area in the Arctic National Wildlife Refuge, Alaska, an explicit link between gas generation and deformation in the Brooks Range fold and thrust belt is provided through petrographic, fluid inclusion, and stable isotope analyses of fracture cements integrated with zircon fission-track data. Predominantly quartz-cemented fractures, collected from thrusted Triassic and Jurassic rocks, contain crack-seal textures, healed microcracks, and curved crystals and fluid inclusion populations, which suggest that cement growth occurred before, during, and after deformation. Fluid inclusion homogenization temperatures (175-250??C) and temperature trends in fracture samples suggest that cements grew at 7-10 km depth during the transition from burial to uplift and during early uplift. CH4-rich (dry gas) inclusions in the Shublik Formation and Kingak Shale are consistent with inclusion entrapment at high thermal maturity for these source rocks. Pressure modeling of these CH4-rich inclusions suggests that pore fluids were overpressured during fracture cementation. Zircon fission-track data in the area record postdeposition denudation associated with early Brooks Range deformation at 64 ?? 3 Ma. With a closure temperature of 225-240??C, the zircon fission-track data overlap homogenization temperatures of coeval aqueous inclusions and inclusions containing dry gas in Kingak and Shublik fracture cements. This critical time-temperature relationship suggests that fracture cementation occurred during early Brooks Range deformation. Dry gas inclusions suggest that Shublik and Kingak source rocks had exceeded peak oil and gas generation temperatures at the time structural traps formed during early Brooks Range deformation. The timing of hydrocarbon generation with respect to deformation therefore represents an important exploration risk for gas exploration in this part of the Brooks Range fold and thrust belt. The persistence of gas high at thermal maturity levels suggests, however, that significant volumes of gas may have been generated.

Modeling of coupled heat transfer and reactive transport processesin porous media: Application to seepage studies at Yucca Mountain, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukhopadhyay, Sumit; Sonnenthal, Eric L.; Spycher, Nicolas

When hot radioactive waste is placed in subsurface tunnels, a series of complex changes occurs in the surrounding medium. The water in the pore space of the medium undergoes vaporization and boiling. Subsequently, vapor migrates out of the matrix pore space, moving away from the tunnel through the permeable fracture network. This migration is propelled by buoyancy, by the increased vapor pressure caused by heating and boiling, and through local convection. In cooler regions, the vapor condenses on fracture walls, where it drains through the fracture network. Slow imbibition of water thereafter leads to gradual rewetting of the rock matrix.more » These thermal and hydrological processes also bring about chemical changes in the medium. Amorphous silica precipitates from boiling and evaporation, and calcite from heating and CO2 volatilization. The precipitation of amorphous silica, and to a much lesser extent calcite, results in long-term permeability reduction. Evaporative concentration also results in the precipitation of gypsum (or anhydrite), halite, fluorite and other salts. These evaporative minerals eventually redissolve after the boiling period is over, however, their precipitation results in a significant temporary decrease in permeability. Reduction of permeability is also associated with changes in fracture capillary characteristics. In short, the coupled thermal-hydrological-chemical (THC) processes dynamically alter the hydrological properties of the rock. A model based on the TOUGHREACT reactive transport software is presented here to investigate the impact of THC processes on flow near an emplacement tunnel at Yucca Mountain, Nevada. We show how transient changes in hydrological properties caused by THC processes often lead to local flow channeling and saturation increases above the tunnel. For models that include only permeability changes to fractures, such local flow channeling may lead to seepage relative to models where THC effects are ignored. However, coupled THC seepage models that include both permeability and capillary changes to fractures may not show this additional seepage.« less

Modeling of coupled heat transfer and reactive transport processesin porous media: Application to seepage studies at Yucca Mountain, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukhopadhyay, S.; Sonnenthal, E.L.; Spycher, N.

When hot radioactive waste is placed in subsurface tunnels, a series of complex changes occurs in the surrounding medium. The water in the pore space of the medium undergoes vaporization and boiling. Subsequently, vapor migrates out of the matrix pore space, moving away from the tunnel through the permeable fracture network. This migration is propelled by buoyancy, by the increased vapor pressure caused by heating and boiling, and through local convection. In cooler regions, the vapor condenses on fracture walls, where it drains through the fracture network. Slow imbibition of water thereafter leads to gradual rewetting of the rock matrix.more » These thermal and hydrological processes also bring about chemical changes in the medium. Amorphous silica precipitates from boiling and evaporation, and calcite from heating and CO{sub 2} volatilization. The precipitation of amorphous silica, and to a much lesser extent calcite, results in long-term permeability reduction. Evaporative concentration also results in the precipitation of gypsum (or anhydrite), halite, fluorite and other salts. These evaporative minerals eventually redissolve after the boiling period is over, however, their precipitation results in a significant temporary decrease in permeability. Reduction of permeability is also associated with changes in fracture capillary characteristics. In short, the coupled thermal-hydrological-chemical (THC) processes dynamically alter the hydrological properties of the rock. A model based on the TOUGHREACT reactive transport software is presented here to investigate the impact of THC processes on flow near an emplacement tunnel at Yucca Mountain, Nevada. We show how transient changes in hydrological properties caused by THC processes often lead to local flow channeling and saturation increases above the tunnel. For models that include only permeability changes to fractures, such local flow channeling may lead to seepage relative to models where THC effects are ignored. However, coupled THC seepage models that include both permeability and capillary changes to fractures may not show this additional seepage.« less

The effect of manufacturing conditions on discontinuity population and fatigue fracture behavior in carbon/epoxy composites

NASA Astrophysics Data System (ADS)

Hakim, Issa; Laquai, Rene; Walter, David; Mueller, Bernd; Graja, Paul; Meyendorf, Norbert; Donaldson, Steven

2017-02-01

Carbon fiber composites have been increasingly used in aerospace, military, sports, automotive and other fields due to their excellent properties, including high specific strength, high specific modulus, corrosion resistance, fatigue resistance, and low thermal expansion coefficient. Interlaminar fracture is a serious failure mode leading to a loss in composite stiffness and strength. Discontinuities formed during manufacturing process degrade the fatigue life and interlaminar fracture resistance of the composite. In his study, three approaches were implemented and their results were correlated to quantify discontinuities effecting static and fatigue interlaminar fracture behavior of carbon fiber composites. Samples were fabricated by hand layup vacuum bagging manufacturing process under three different vacuum levels, indicated High (-686 mmHg), Moderate (-330 mmHg) and Poor (0 mmHg). Discontinuity content was quantified through-thickness by destructive and nondestructive techniques. Eight different NDE methods were conducted including imaging NDE methods: X-Ray laminography, ultrasonic, high frequency eddy current, pulse thermography, pulse phase thermography and lock-in-thermography, and averaging NDE techniques: X-Ray refraction and thermal conductivity measurements. Samples were subsequently destructively serial sectioned through-thickness into several layers. Both static and fatigue interlaminar fracture behavior under Mode I were conducted. The results of several imaging NDE methods revealed the trend in percentages of discontinuity. However, the results of averaging NDE methods showed a clear correlation since they gave specific values of discontinuity through-thickness. Serial sectioning exposed the composite's internal structure and provided a very clear idea about the type, shape, size, distribution and location of most discontinuities included. The results of mechanical testing showed that discontinuities lead to a decrease in Mode I static interlaminar fracture toughness and a decrease in Mode I cyclic strain energy release rates fatigue life. Finally, all approaches were correlated: the resulted NDE percentages and parameters were correlated with the features revealed by the destructive test of serial sectioning and static and fatigue values in order to quantify discontinuities such as delamination and voids.

Hafnia-rich mixed oxide ceramics of the system HfO2-ZrO2-TiO2 for heaters and heat exchangers in electrothermal thrusters: The effects of titania on selected electrical and mechanical properties of Hafnia-rich mixed oxides in the system Hafnia-Zirconia-Titania, volume 1

NASA Technical Reports Server (NTRS)

Staszak, Paul Russell; Wirtz, G. P.; Berg, M.; Brown, S. D.

1988-01-01

A study of the effects of titania on selected properties of hafnia-rich mixed oxides in the system hafnia-zirconia-titania (HZT) was made in the region 5 to 20 mol percent titania. The studied properties included electrical conductivity, thermal expansion, and fracture strength and toughness. The effects of titania on the properties were studied for the reduced state as well as the oxidized state of the sintered mixed oxides. X-ray analysis showed that the materials were not always single phase. The oxidized compositions went from being monoclinic solid solutions at low titania additions to having three phases (two monoclinic and a titanate phase) at high additions of titania. The reduced compositions showed an increasing cubic phase presence mixed with the monoclinic phase as titania was added. The electrical conductivity increased with temperature at approximately 0.1 mhos/cm at 1700 C for all compositions. The thermal expansion coefficient decreased with increasing titania as did the monoclinic to tetragonal transformation temperature. The fracture strength of the oxidized bars tended to decrease with the addition of titania owing to the presence of the second phase titania. The fracture strength of the reduced bars exhibited a minimum corresponding to a two-phase region of monoclinic and cubic phases. When the second phases were suppressed, the titania tended to increase the fracture strength slightly in both the oxidized and reduced states. The fracture toughness followed similar trends.

Fracture analysis of radial scientific instrument module registration fittings of the space telescope

NASA Technical Reports Server (NTRS)

Springfield, C. W., Jr.

1985-01-01

The space telescope contains various scientific instrument (SI) modules which are mounted to the Focal Plane Structure (FPS) in a statically determinate manner. This is accomplished by using three registration fittings per SI module, one resisting three translations, another resisting two and the third resisting only one. Due to thermal insulating requirements these fittings are complex devices composed of numerous pieces. The structural integrity of these fittings is of great importance to the safety of the orbiter transporting the telescope, so in addition to the stress analyses performed during the design of these components, fracture susceptibility also needs to be considered. The pieces of the registration fittings for the Radial SI Module containing the Wide Field Planetary Camera are examined to determine which would endanger the orbiter if they fractured and what is the likelihood of their fracture. The latter is stated in terms of maximum allowable initial flaw sizes in these pieces.

Tempered glass and thermal shock of ceramic materials

NASA Technical Reports Server (NTRS)

Bunnell, L. Roy

1992-01-01

A laboratory experiment is described that shows students the different strengths and fracture toughnesses between tempered and untempered glass. This paper also describes how glass is tempered and the materials science aspects of the process.

Mechanical Properties of Plasma-Sprayed ZrO2-8 wt% Y2O3 Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Zhu, Dongming; Miller, Robert A.

2004-01-01

Mechanical behavior of free standing, plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings, including strength, fracture toughness, fatigue, constitutive relation, elastic modulus, and directionality, has been determined under various loading-specimen configurations. This report presents and describes a summary of mechanical properties of the plasma-sprayed coating material to provide them as a design database.

Effect of Sintering on Mechanical and Physical Properties of Plasma-Sprayed Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

2004-01-01

The effect of sintering on mechanical and physical properties of free-standing plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings (TBCs) was determined by annealing them at 1316 C in air. Mechanical and physical properties of the TBCs, including strength, modes I and II fracture toughness, elastic modulus, Poisson s response, density, microhardness, fractography, and phase stability, were determined at ambient temperature as a function of annealing time ranging from 0 to 500 h. All mechanical and physical properties, except for the amount of monoclinic phase, increased significantly in 5 to 100 h and then reached a plateau above 100 h. Annealing resulted in healing of microcracks and pores and in grain growth, accompanying densification of the TBC s body due to the sintering effect. However, an inevitable adverse effect also occurred such that the desired lower thermal conductivity and good expansivity, which makes the TBCs unique in thermal barrier applications, were degraded upon annealing. A model was proposed to assess and quantify all the property variables in response to annealing in a normalized scheme. Directionality of as-sprayed TBCs appeared to have an insignificant effect on their properties, as determined via fracture toughness, microhardness, and elastic modulus measurements.

FAVOR: A new fracture mechanics code for reactor pressure vessels subjected to pressurized thermal shock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dickson, T.L.

1993-01-01

This report discusses probabilistic fracture mechanics (PFM) analysis which is a major element of the comprehensive probabilistic methodology endorsed by the NRC for evaluation of the integrity of Pressurized Water Reactor (PWR) pressure vessels subjected to pressurized-thermal-shock (PTS) transients. It is anticipated that there will be an increasing need for an improved and validated PTS PFM code which is accepted by the NRC and utilities, as more plants approach the PTS screening criteria and are required to perform plant-specific analyses. The NRC funded Heavy Section Steel Technology (HSST) Program at Oak Ridge National Laboratories is currently developing the FAVOR (Fracturemore » Analysis of Vessels: Oak Ridge) PTS PFM code, which is intended to meet this need. The FAVOR code incorporates the most important features of both OCA-P and VISA-II and contains some new capabilities such as PFM global modeling methodology, the capability to approximate the effects of thermal streaming on circumferential flaws located inside a plume region created by fluid and thermal stratification, a library of stress intensity factor influence coefficients, generated by the NQA-1 certified ABAQUS computer code, for an adequate range of two and three dimensional inside surface flaws, the flexibility to generate a variety of output reports, and user friendliness.« less

FAVOR: A new fracture mechanics code for reactor pressure vessels subjected to pressurized thermal shock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dickson, T.L.

1993-04-01

This report discusses probabilistic fracture mechanics (PFM) analysis which is a major element of the comprehensive probabilistic methodology endorsed by the NRC for evaluation of the integrity of Pressurized Water Reactor (PWR) pressure vessels subjected to pressurized-thermal-shock (PTS) transients. It is anticipated that there will be an increasing need for an improved and validated PTS PFM code which is accepted by the NRC and utilities, as more plants approach the PTS screening criteria and are required to perform plant-specific analyses. The NRC funded Heavy Section Steel Technology (HSST) Program at Oak Ridge National Laboratories is currently developing the FAVOR (Fracturemore » Analysis of Vessels: Oak Ridge) PTS PFM code, which is intended to meet this need. The FAVOR code incorporates the most important features of both OCA-P and VISA-II and contains some new capabilities such as PFM global modeling methodology, the capability to approximate the effects of thermal streaming on circumferential flaws located inside a plume region created by fluid and thermal stratification, a library of stress intensity factor influence coefficients, generated by the NQA-1 certified ABAQUS computer code, for an adequate range of two and three dimensional inside surface flaws, the flexibility to generate a variety of output reports, and user friendliness.« less

Infrared monitoring of hydrothermal echanges occurring in a fracture

NASA Astrophysics Data System (ADS)

Neuville, Amélie; Flekkøy, Eirik; Galland, Olivier; Gundersen, Olav; Jørgen Måløy, Knut

2014-05-01

We aim to characterize the heat exchange that occurs when water flows through a fracture at a different temperature from that of the surrounding rock. This happens during many man-made or natural processes. For instance, injection of water in the context of geothermal power plants or sudden mechanical movements (e.g. rockfalls, landslides, earthquakes) that transport water. It is presently challenging to estimate the heat transfer and temperature inside a fractured medium where water is flowing, despite various numerical models which have been proposed [Neuville et al, 2010, 2013; Kolditz et Clauser, 1998; Heuer, 1991]. The difficulties arise from the complexity of the fracture network, the fracture topography, as well as complex hydraulic flow (e.g. recirculation) and heat exchanges. As a consequence, various hypotheses were made in the models. More experimental data are required in order to calibrate these models, validate or refute the hypotheses. Our work aims to provide temperature data at the fracture scale, in an experiment where the pressure gradient an fracture topography are controlled, with slow hydraulic flow. This required to develop a setup from scratch. An infrared camera and thermistors are used to monitor the temperature in space and time. Water is injected through a partly natural rough fracture with impermeable walls. The bottom part of the fracture is a larvikite stone with a rough surface (presumably this surface was obtained from mode I fracturing), and the top part is a layer which is transparent in the infrared range. As a consequence the infrared camera is expected to measure the temperature at the interface between this transparent layer and the water. The topography of the surface of the rock was reconstituted using a photogrammetry software [MicMac, IGN], and compared to measurements made with a mechanical profiler. Using this geometry we carefully localize the temperature observations (infrared camera and thermistors) and correlate the temperature variations with the topography. Preliminary comparisons with simulations from a coupled lattice Boltzmann method that solves both the complete Navier-Stokes and advection-diffusion equations in three-dimensions are also presented. N. Heuer, T. Küpper and D. Windelberg, Mathematical model of a Hot Dry Rock system, Geophys. J. Int. 105, 659-664 (1991). O. Kolditz and C. Clauser, Numerical simulation of flow and heat transefer in fractured cristalline rocks: application to the hot dry rock site in Rosemanowes (U.K.), Geothermics, 27, 1, p 1-23, (1998). MicMac, IGN: sofware developed by the French Institut Géographique National (IGN) A. Neuville, R. Toussaint, and J. Schmittbuhl, Hydro-thermal flows in a self-affine rough fracture, Phys. Rev. E, 82, 036,317, (2010). A. Neuville, E.G. Flekkøy, R. Toussaint, Influence of asperities on fluid and thermal flow in a fracture: a coupled Lattice Boltzmann study. Journal of Geophysical Research, 118, 7, 3394-3407, (2013).

Prediction of thermal cycling induced matrix cracking

NASA Technical Reports Server (NTRS)

Mcmanus, Hugh L.

1992-01-01

Thermal fatigue has been observed to cause matrix cracking in laminated composite materials. A method is presented to predict transverse matrix cracks in composite laminates subjected to cyclic thermal load. Shear lag stress approximations and a simple energy-based fracture criteria are used to predict crack densities as a function of temperature. Prediction of crack densities as a function of thermal cycling is accomplished by assuming that fatigue degrades the material's inherent resistance to cracking. The method is implemented as a computer program. A simple experiment provides data on progressive cracking of a laminate with decreasing temperature. Existing data on thermal fatigue is also used. Correlations of the analytical predictions to the data are very good. A parametric study using the analytical method is presented which provides insight into material behavior under cyclical thermal loads.

Characterization of Low-Melting-Point Sn-Bi-In Lead-Free Solders

NASA Astrophysics Data System (ADS)

Li, Qin; Ma, Ninshu; Lei, YongPing; Lin, Jian; Fu, HanGuang; Gu, Jian

2016-11-01

Development of lead-free solders with low melting temperature is important for substitution of Pb-based solders to reduce direct risks to human health and the environment. In the present work, Sn-Bi-In solders were studied for different ratios of Bi and Sn to obtain solders with low melting temperature. The microstructure, thermal properties, wettability, mechanical properties, and reliability of joints with Cu have been investigated. The results show that the microstructures of the Sn-Bi-In solders were composed of β-Sn, Bi, and InBi phases. The intermetallic compound (IMC) layer was mainly composed of Cu6Sn5, and its thickness increased slightly as the Bi content was increased. The melting temperature of the solders was around 100°C to 104°C. However, when the Sn content exceeded 50 wt.%, the melting range became larger and the wettability became worse. The tensile strength of the solder alloys and solder joints declined with increasing Bi content. Two fracture modes (IMC layer fracture and solder/IMC mixed fracture) were found in solder joints. The fracture mechanism of solder joints was brittle fracture. In addition, cleavage steps on the fracture surface and coarse grains in the fracture structure were comparatively apparent for higher Bi content, resulting in decreased elongation for both solder alloys and solder joints.

Extended Hall-Petch Relationships for Yield, Cleavage and Intergranular Fracture Strengths of bcc Steel and Its Deformation and Fracture Behaviors

NASA Astrophysics Data System (ADS)

Heo, N. H.; Heo, Y.-U.; Kwon, S. K.; Kim, N. J.; Kim, S.-J.; Lee, H.-C.

2018-03-01

Extended Hall-Petch relationships for yield ( σy ), cleavage ( σ_{cl} ) and intergranular fracture ( σ_{ig} ) strengths of pure iron have been established through the direct calculation of the proportional constant (k) and the estimation of the friction stress (σ0 ) . The magnitude orders of k and σ0 are generally ky < k_{cl} < k_{ig} and σ_{y0} < σ_{cl0} < σ_{ig0} , respectively. Based on the Hall-Petch relationships, micro-yielding in a bcc steel occurs at the instance that the pile-up dislocations within a specific grain showing the Schmid factor of 0.5 propagate into the neighboring grain. The initial brittle crack is formed at the instance that the flow strength exceeds the brittle fracture strength. Once the brittle crack is formed, it grows catastrophically. Due to the smallest and ky and σ_{y0} , the cleavage and the intergranular fracture occur always after micro-yielding. The {100} cleavage fracture of the steel is due to the lowest theoretical {100} cleavage strength. Due to the thermal components included in cleavage and intergranular fracture strengths, they show also the temperature and strain rate dependence observed in yield strength. The increase in susceptibility to brittle fracture with decreasing temperature and increasing strain rate is due to the increase in dislocation density which causes the high work hardening rate.

Simulation of Laser Induced Thermal Damage in Nd:YVO4 Crystals

NASA Astrophysics Data System (ADS)

Nagi, Richie

Neodymium-doped yttrium orthovanadate (Nd:YVO4) is a commonly used gain medium in Diode Pumped Solid State (DPSS) lasers, but high heat loading of Nd:YVO4 at high pump powers (≥ 5 W) leads to thermal distortions and crystal fracture, which limits the utility of Nd:YVO 4 for high power applications. In this thesis, a Nd:YVO4 crystal suffered thermal damage during experiments for investigating the optical gain characteristics of the crystal. This thesis examines the thermal damage mechanisms in detail. Principally, laser induced melting, as well as laser induced thermal stress fracture were studied, all in the absence of stimulated emission in the crystal. The optical system for coupling the pump laser light into the crystal was first simulated in Zemax, an optical design software, and the simulations were then compared to the experimental coupling efficiency results, which were found to be in agreement. The simulations for the laser coupling system were then used in conjunction with LASCAD, a finite element analysis software, to obtain the temperatures inside the crystal, as a function of optical power coupled into the crystal. The temperature simulations were then compared to the experimental results, which were in excellent agreement, and the temperature simulations were then generalized to other crystal geometries and Nd doping levels. Zemax and LASCAD were also used to simulate the thermal stress in the crystal as a function of the coupled optical power, and the simulations were compared to experiments, both of which were found to be in agreement. The thermal stress simulations were then generalized to different crystal geometries and Nd doping levels as well.

Regelation and ice segregation

NASA Technical Reports Server (NTRS)

Miller, Robert D.

1988-01-01

Macroscopic processes can have an important effect on the state of regolith water. The two primary mechanisms responsible for the formation of segregated ice on Earth, thermally induced regelation and hydraulic fracturing, are reviewed while their potential importance on Mars is examined. While regelation is the dominant terrestrial process, it requires a warmer and wetter environment than currently exists on Mars. In this respect, the conditions required for hydraulic fracturing are less demanding. In assessing its potential importance on Mars, it is noted that hydraulic fracturing can produce a localized zone of high pressure water that could readily disrupt an overburden of frozen ground. Such a process, it is concluded, may have triggered the release of groundwater that led to the formation of the major outflow channels.

Electronics reliability fracture mechanics. Volume 1: Causes of failures of shop replaceable units and hybrid microcircuits

NASA Astrophysics Data System (ADS)

Kallis, J.; Buechler, D.; Erickson, J.; Westerhuyzen, D. V.; Strokes, R.

1992-05-01

This is the first of two volumes. The other volume (WL-TR-91-3119) is 'Fracture Mechanics'. The objective of the Electronics Reliability Fracture Mechanics (ERFM) program was to develop and demonstrate a life prediction technique for electronic assemblies, when subjected to environmental stress of vibration and thermal cycling, based upon the mechanical properties of the materials and packaging configurations which make up an electronic system. A detailed investigation was performed of the following two shop replaceable units (SRUs): Timing and Control Module (P/N 3562102) and Linear Regulator Module (P/N 3569800). The SRUs are in the Programmable Signal Processor (3137042) Line Replaceable Unit (LRU) of the Hughes AN/APG-63 Radar for the F-15 Aircraft.

A multicomponent tracer field experiment to measure the flow volume, surface area, and rectilinear spacing of fractures away from the wellbore

NASA Astrophysics Data System (ADS)

Cathles, L. M.; Sanford, W. E.; Hawkins, A.; Li, Y. V.

2017-12-01

The nature of flow in fractured porous media is important to almost all subsurface processes including oil and gas recovery, contaminant transport and remediation, CO2 sequestration, and geothermal heat extraction. One would like to know, under flowing conditions, the flow volume, surface area, effective aperture, and rectilinear spacing of fractures in a representative volume of rock away from the well bore, but no methods currently allow acquisition of this data. It could, however, be collected by deploying inert tracers with a wide range of aqueous diffusion constants (e.g., rapidly diffusing heat to non-diffusing nanoparticle) in the following fashion: The flow volume is defined by the heated volume measured by resistivity surveys. The fracture volume within this flow volume is indicate by the nanoparticle transit time. The average fracture spacing is indicated by the evolving thermal profile in the monitor and the production wells (measured by fiber optic cable), and by the retention of absorbing tracers. The average fracture aperture is determined by permeability measurements and the average fracture separation. We have proposed a field test to redundantly measure these fracture parameters in the fractured Dakota Sandstone where it approaches the surface in Ft Collins, Colorado. Five 30 m deep wells (an injection, production, and 3 monitor wells) cased to 20 m are proposed. The experiments will involve at least 9 different tracers. The planned field test and its potential significance will be described.

Nanomechanical characterization of alumina coatings grown on FeCrAl alloy by thermal oxidation.

PubMed

Frutos, E; González-Carrasco, J L; Polcar, T

2016-04-01

This work studies the feasibility of using repetitive-nano-impact tests with a cube-corner tip and low loads for obtaining quantitative fracture toughness values in thin and brittle coatings. For this purpose, it will be assumed that the impacts are able to produce a cracking, similar to the pattern developed for the classical fracture toughness tests in bulk materials, and therefore, from the crack developed in the repetitive impacts it will be possible to evaluate the suitability of the classical indentation models (Anstins and Laugier) for measuring fracture toughness. However, the length of this crack has to be lower than 10% of the total coating thickness to avoid substrate contributions. For this reason, and in order to ensure a small plastic region localized at the origin of the crack tip, low load values (or small distance between the indenter tip and the surface) have to be used. In order to demonstrate the validity of this technique, repetitive-nano-impact will be done in a fine and dense oxide layer (α-Al2O3), which has been developed on the top of oxide dispersion strengthened (ODS) FeCrAl alloys (PM 2000) by thermal oxidation at elevated temperatures. Moreover, it will be shown how it is possible to know with each new impact the crack geometry evolution from Palmqvist crack to half-penny crack, being able to study the proper evolution of the different values of fracture toughness in terms of both indentation models and as a function of the strain rate, ε̇, decreasing. Thereby, fracture toughness values for α-Al2O3 layer decrease from ~4.40MPam , for high ϵ̇ value (10(3)s(-1)), to ~3.21MPam, for quasi-static ϵ̇ value (10(-3)s(-1)). On the other hand, ϵ̇ a new process to obtain fracture toughness values will be analysed, when the classical indentation models are not met. These values are typically found in the literature for bulk α-Al2O3, demonstrating the use of repetitive-nano-impact tests which not only provide qualitative information about fracture resistance of the materials but it also can be used to obtain quantitative information as fracture toughness values in the case of brittle materials. Copyright © 2016 Elsevier Ltd. All rights reserved.

Fractal patterns of fracture in sandwich composite materials under biaxial tension

NASA Astrophysics Data System (ADS)

Fang, Jing; Yao, Xuefeng; Qi, Jia

1996-04-01

The paper presents a successful experiment to generate a fractal pattern of branching cracks in a brittle material sandwiched in ductile plates. A glass sheet bonded between two polycarbonate plates was heated at different levels of temperatures and the stress field due to the difference of thermal coefficients of the materials was solved by combining the results from isochromatic fringes and thermal stress analysis. At a critical degree of temperature, a crack was initiated at a point and soon produced crack branches to release the stored energy. A tree—like fractal patterns of the branch cracks was then developed with the growth of the branches that subsequently produced more branches on their ways of propagation. The fractal dimension of the fracture pattern was evaluated and the mechanism of the fragmentation was analyzed with the help of the residual stress field of isochromatic and isoclinic patterns.

Could the Geminid meteoroid stream be the result of long-term thermal fracture?

NASA Astrophysics Data System (ADS)

Ryabova, G. O.

2018-06-01

The previous models by Ryabova showed that the Geminid meteoroid stream has cometary origin, so the asteroid (3200) Phaethon (the Geminid's parent body) is probably a dead comet. In 2009, 2012, and 2016, some weak activity was observed, but it was not cometary activity (see Jewitt & Li). Recurrent brightening of Phaethon at perihelion could be the result of thermal fracture and decomposition. In this study, we model the long-term (5 000 years) dust release from Phaethon in perihelion with velocities specific for this mechanism. The results of these dust ejections cannot be observed from the Earth now, or even in this century. Only around the year 2260, when the Phaethon descending node should intersect the Earth's orbit, this special component of the Geminid meteoroid stream will also approach the Earth. The perihelion activity should cease in 400 years, when the Phaethon perihelion will move away from the Sun.

Ceramic heat exchanger

DOEpatents

LaHaye, Paul G.; Rahman, Faress H.; Lebeau, Thomas P. E.; Severin, Barbara K.

1998-01-01

A tube containment system. The tube containment system does not significantly reduce heat transfer through the tube wall. The contained tube is internally pressurized, and is formed from a ceramic material having high strength, high thermal conductivity, and good thermal shock resistance. The tube containment system includes at least one ceramic fiber braid material disposed about the internally pressurized tube. The material is disposed about the tube in a predetermined axial spacing arrangement. The ceramic fiber braid is present in an amount sufficient to contain the tube if the tube becomes fractured. The tube containment system can also include a plurality of ceramic ring-shaped structures, in contact with the outer surface of the tube, and positioned between the tube and the ceramic fiber braid material, and/or at least one transducer positioned within tube for reducing the internal volume and, therefore, the energy of any shrapnel resulting from a tube fracture.

Ceramic heat exchanger

DOEpatents

LaHaye, P.G.; Rahman, F.H.; Lebeau, T.P.; Severin, B.K.

1998-06-16

A tube containment system is disclosed. The tube containment system does not significantly reduce heat transfer through the tube wall. The contained tube is internally pressurized, and is formed from a ceramic material having high strength, high thermal conductivity, and good thermal shock resistance. The tube containment system includes at least one ceramic fiber braid material disposed about the internally pressurized tube. The material is disposed about the tube in a predetermined axial spacing arrangement. The ceramic fiber braid is present in an amount sufficient to contain the tube if the tube becomes fractured. The tube containment system can also include a plurality of ceramic ring-shaped structures, in contact with the outer surface of the tube, and positioned between the tube and the ceramic fiber braid material, and/or at least one transducer positioned within tube for reducing the internal volume and, therefore, the energy of any shrapnel resulting from a tube fracture. 6 figs.

Mechanisms of boron fiber strengthening by thermal treatment

NASA Technical Reports Server (NTRS)

Dicarlo, J. A.

1979-01-01

The fracture strain for boron on tungsten fibers was studied for improvement by heat treatment under vacuum or argon environments. The mechanical basis for this improvement is thermally-induced axial contraction of the entire fiber, whereby strength-controlling core flaws are compressed and fiber fracture strain increased by the value of the contraction strain. By highly sensitive measurements of fiber density and volume, the physical mechanism responsible for contraction under both environments was identified as boron atom diffusion out of the fiber sheath. The fiber contracts because the average volume of the resulting microvoid was determined to be only 0.26 plus or minus 0.09 the average atomic volume of the removed atom. The basic and practical implications of these results are discussed with particular emphasis on the theory, use, and limitations of heat-induced contraction as a simple cost-effective secondary processing method.

Parametrization in models of subcritical glass fracture: Activation offset and concerted activation

NASA Astrophysics Data System (ADS)

Rodrigues, Bruno Poletto; Hühn, Carolin; Erlebach, Andreas; Mey, Dorothea; Sierka, Marek; Wondraczek, Lothar

2017-08-01

There are two established but fundamentally different empirical approaches to parametrize the rate of subcritical fracture in brittle materials. While both are relying on a thermally activated reaction of bond rupture, the difference lies in the way as to how the externally applied stresses affect the local energy landscape. In the consideration of inorganic glasses, the strain energy is typically taken as an off-set on the activation barrier. As an alternative interpretation, the system’s volumetric strain-energy is added to its thermal energy. Such an interpretation is consistent with the democratic fiber bundle model. Here, we test this approach of concerted activation against macroscopic data of bond cleavage activation energy, and also against ab initio quantum chemical simulation of the energy barrier for cracking in silica. The fact that both models are able to reproduce experimental observation to a remarkable degree highlights the importance of a holistic consideration towards non-empirical understanding.

Heavy-section steel technology and irradiation programs-retrospective and prospective views

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nanstad, Randy K; Bass, Bennett Richard; Rosseel, Thomas M

In 1965, the Atomic Energy Commission (AEC), at the advice of the Advisory Committee on Reactor Safeguards (ACRS), initiated the process that resulted in the establishment of the Heavy Section Steel Technology (HSST) Program at Oak Ridge National Laboratory (ORNL). Dr. Spencer H. Bush of Battelle Northwest Laboratory, the man being honored by this symposium, representing the ACRS, was one of the Staff Advisors for the program and helped to guide its technical direction. In 1989, the Heavy-Section Steel Irradiation (HSSI) Program, formerly the HSST task on irradiation effects, was formed as a separate program, and this year the HSST/HSSImore » Programs, sponsored by the U.S. Nuclear Regulatory Commission (USNRC), celebrate 40 years of continuous research oriented toward the safety of light-water nuclear reactor pressure vessels. This paper presents a summary of results from those programs with a view to future activities. The HSST Program was established in 1967 and initially included extensive investigations of heavy-section low-alloy steel plates, forgings, and welds, including metallurgical studies, mechanical properties, fracture toughness (quasi-static and dynamic), fatigue crack-growth, and crack arrest toughness. Also included were irradiation effects studies, thermal shock analyses, testing of thick-section tensile and fracture specimens, and non-destructive testing. In the subsequent decades, the HSST Program conducted extensive large-scale experiments with intermediate-size vessels (with varying size flaws) pressurized to failure, similar experiments under conditions of thermal shock and even pressurized thermal shock (PTS), wide-plate crack arrest tests, and biaxial tests with cruciform-shaped specimens. Extensive analytical and numerical studies accompanied these experiments, including the development of computer codes such as the recent Fracture Analysis of Vessels Oak Ridge (FAVOR) code currently being used for PTS evaluations. In the absence of radiation damage to the RPV, fracture of the vessel is improbable. However, exposure to high energy neutrons can result in embrittlement of radiation-sensitive RPV materials. The HSSI Program has conducted a series of experiments to assess the effects of neutron irradiation on RPV material behavior, especially fracture toughness. These studies have included RPV plates and welds, varying chemical compositions, and fracture toughness specimens up to 4 in. thickness. The results of these investigations, in conjunction with results from commercial reactor surveillance programs, are used to develop a methodology for the prediction of radiation effects on RPV materials. Results from the HSST and HSSI Program are used by the USNRC in the evaluation of RPV integrity and regulation of overall nuclear plant safety.« less

Potential Experimental Topics for EGS Collab Experiment 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnston, Henry; Mattson, Earl; Blankenship, Douglas

To facilitate the success of FORGE, the DOE GTO has initiated a new research effort, the EGS Collab project, which will utilize readily accessible underground facilities that can refine our understanding of rock mass response to stimulation and provide a test bed at intermediate (~10 m) scale for the validation of thermal-hydrological-mechanical-chemical modeling approaches as well as novel monitoring tools. The first two EGS Experiments 1 and 2 are planned be performed under different stress/fracture conditions, and will evaluate different stimulation processes: Experiment 1 will focus on hydrofracturing of a competent rock mass, while Experiment 2 will concentrate on hydroshearingmore » of a rock mass that contains natural fractures. Experiment 3 is scheduled to begin in 2019 will build off the lessons learned in Experiments 1 and 2 and will investigate alternate stimulation and operation methods to improve heat extraction in an EGS reservoir. This paper evaluates potential experiments that could potentially be conducted in Experiment 3. The two technical parameters defining energy extracted from EGS reservoirs with the highest economic uncertainty and risk are the production well flow rates and the reservoir thermal drawdown rate. A review of historical and currently on-going EGS studies has identified that over 1/2 of the projects have identified heat extraction challenges during their operation associated with these two parameters as well as some additional secondary issues. At present, no EGS reservoir has continuously produced flow rates on the order of 80 kg/s. Short circuiting (i.e. early thermal breakthrough) has been identified in numerous cases. In addition, working fluid loss (i.e. the difference between the injected fluid mass and the extracted fluid mass as compared to the injected mass) has been as high as 90%. Finally, the engineering aspects of operating a true EGS multi-fracture reservoir such as repairing/modifying fractures and controlling working fluid fluxes within multiple fractures for the effective EGS fracture management has not been sufficiently studied. To examine issues such as these, EGS Collab Experiment 3 may be conducted in the testbeds prepared for Experiments 1 and 2 by improving the previously performed stimulations, or conducted at a new site performing new stimulations with alternate method. Potential experiments may include using different stimulation and working fluids, evaluating different stimulation methods, using proppants to enhance permeability, and other high-risk high-reward methods that can be evaluated at the 10-m scale environment.« less

The effect of processing temperature and time on the structure and fracture characteristics of self-reinforced composite poly(methyl methacrylate).

PubMed

Wright, D D; Gilbert, J L; Lautenschlager, E P

1999-08-01

A novel material, self-reinforced composite poly(methyl methacrylate) (SRC-PMMA) has been previously developed in this laboratory. It consists of high-strength PMMA fibers embedded in a matrix of PMMA derived from the fibers. As a composite material, uniaxial SRC-PMMA has been shown to have greatly improved flexural, tensile, fracture toughness and fatigue properties when compared to unreinforced PMMA. Previous work examined one empirically defined processing condition. This work systematically examines the effect of processing time and temperature on the thermal properties, fracture toughness and fracture morphology of SRC-PMMA produced by a hot compaction method. Differential scanning calorimetry (DSC) shows that composites containing high amounts of retained molecular orientation exhibit both endothermic and exothermic peaks which depend on processing times and temperatures. An exothermic release of energy just above Tg is related to the release of retained molecular orientation in the composites. This release of energy decreases linearly with increasing processing temperature or time for the range investigated. Fracture toughness results show a maximum fracture toughness of 3.18 MPa m1/2 for samples processed for 65 min at 128 degrees C. Optimal structure and fracture toughness are obtained in composites which have maximum interfiber bonding and minimal loss of molecular orientation. Composite fracture mechanisms are highly dependent on processing. Low processing times and temperatures result in more interfiber/matrix fracture, while higher processing times and temperatures result in higher ductility and more transfiber fracture. Excessive processing times result in brittle failure. Copyright 1999 Kluwer Academic Publishers

Stress Intensity Solutions of Thermally Induced Cracks in Combustor Liner Hot Spots Using Finite Element Analysis (FEA)

DTIC Science & Technology

2005-12-01

EPFM elastic-plastic fracture mechanics FCG fatigue crack growth FEA finite element analysis FKN ANSYS FEA command for contact pair stiffness FTOLN...current TMF research is too general for thermal gradient applications . Moreover, the nature of a cyclically heated, localized region of higher...when separating this problem into the general engineering issues that are germane to the application , one can find much published research that is

Analysis of the flow property of aluminum alloy AA6016 based on the fracture morphology using the hydroforming technology

NASA Astrophysics Data System (ADS)

Lang, Lihui; Zhang, Quanda; Sun, Zhiying; Wang, Yao

2017-09-01

In this paper, the hydraulic bulging experiments were respectively carried out using AA6016-T4 aluminum alloy and AA6016-O aluminum alloy, and the deformation properties and fracture mechanism of aluminum alloy under the conditions of thermal and hydraulic were analyzed. Firstly, the aluminum alloy AA6016 was dealt with two kinds of heat treatment systems such as solid solution heat treatment adding natural ageing and full annealing, then the aluminum alloy such as AA6016-T4 and AA6016-O were obtained. In the same working environment, the two kinds of materials were used in the process of hydraulic bulging experiments, according to the observation and measurement of the deformation sizes of grid circles and material thicknesses near the fracture region, the flow properties and development trend of fracture defect of the materials were analyzed comprehensively from the perspective of qualitative analysis and quantitative analysis; Secondly, the two kinds of materials were sampled in different regions of the fracture area and the microstructure morphology of the fracture was observed by the scanning electron microscope (SEM). The influence laws of the heat treatment systems on the fracture defect of the aluminum alloy under the condition of the liquid pressure were studied preliminarily by observing the distribution characteristics of the fracture microstructure morphology of dimple. At the same time, the experimental research on the ordinary stamping forming process of AA6016-O was carried out and the influence law of different forming process on the fracture defect of the aluminum alloy material was studied by observing the distribution of the fracture microstructure morphology; Finally, the development process of the fracture defect of aluminum alloy sheet was described theoretically from the view of the stress state.

Fracture strength of lithium disilicate crowns compared to polymer-infiltrated ceramic-network and zirconia reinforced lithium silicate crowns.

PubMed

Sieper, Kim; Wille, Sebastian; Kern, Matthias

2017-10-01

The aim of this study was to evaluate the fracture strength of crowns made from current CAD/CAM materials. In addition the influence of crown thickness and chewing simulation on the fracture strength was evaluated. Crowns were fabricated from lithium disilicate, zirconia reinforced lithium silicate (ZLS-ceramic) and a polymer-infiltrated ceramic-network (PICN) with an occlusal thickness of 1.0mm or 1.5mm, respectively (n=16). Crowns were cemented on composite dies. Subgroups of eight specimens were loaded with 5kg in a chewing simulator for 1,200,000 cycles with thermal cycling. Finally, all specimens were loaded until fracture in a universal testing machine. Three-way ANOVA was used to detect statistical interaction. Differences regarding the materials were tested with two-way ANOVA, following one-way ANOVA and a post-hoc Tukey's-Test. All crowns survived the chewing simulation. The material had a significant influence on the fracture resistance (p≤0.05). Lithium disilicate achieved the highest values of fracture strength in almost all groups followed by ZLS-ceramic. PICN achieved the lowest values of fracture strength. Chewing simulation increased the fracture strength of thick lithium disilicate crown significantly. Greater occlusal thickness of all crown materials resulted in higher crown fracture strength before chewing simulation. After chewing simulation occlusal thickness of lithium disilicate and PICN crowns had no significant influence on the fracture strength. All crowns revealed fracture strength above the clinically expected loading forces. Therefore the durability of the tested CAD/CAM materials seems promising also in an occlusal thickness of 1.0mm. Copyright © 2017 Elsevier Ltd. All rights reserved.

Quantitative Analysis of Thermal Anomalies in the DFDP-2B Borehole, New Zealand

NASA Astrophysics Data System (ADS)

Janků-Čápová, Lucie; Sutherland, Rupert; Townend, John

2017-04-01

The DFDP-2B borehole, which was drilled in the Whataroa Valley, South Island, New Zealand in late 2014, provides a unique opportunity to study the conditions in the hanging wall of a plate boundary fault, the Alpine Fault, which is late in its seismic cycle. High geothermal gradient of > 125°C/km encountered in the borehole drew attention to the thermal structure of the valley, as well as of the Alpine Fault's hanging wall as a whole. A detailed analysis of temperature logs measured during drilling of the DFDP-2B borehole, reveals two distinct portions of the signal containing information on different processes. The long-wavelength portion of the temperature signal, i.e. the overall trend (hundreds of metres), reflects the response of the rock environment to the disturbance caused by drilling and permits an estimation of the thermal diffusivity of the rock based on the rate of temperature recovery. The short-wavelength (tens of metres to tens of centimetres) signal represents the local anomalies caused by lithological variations or, more importantly, by fluid flow into or out of the borehole along fractures. By analysing these distinct features, we can identify anomalous zones that manifest in other wireline data (resistivity, BHTV) and are likely attributable to permeable fractures. Here we present a novel method of quantitative analysis of the short-wavelength temperature anomalies. This method provides a precise and objective way to determine the position, width and amplitude of temperature anomalies and facilitates the interpretation of temperature logs, which is of a particular importance in estimation of flow in a fractured aquifer.

Carbide Derived Carbon Super Capacitor Application

NASA Astrophysics Data System (ADS)

Appelgate, James; Bauer, Dave; Quirin, James; Lofland, S. E.; Hettinger, J. D.; Heon, M.; Gogotsi, Y.

2010-02-01

Supercapacitors can be applied into many different fields from nano-robots to high density energy storage. Growing TiC films from a know recipe and removing the transition metal element, Titanium, by chlorination leaves a carbon film that can then be applied as an electrode in a super capacitor. The problem is when the Titanium is removed from the film the stress induced by this process causes the films to fracture into isolated islands. The islands allow electrons to travel across them every easily, but there is no transfer of electrons from island to island. We present results of an investigation of a technique control the location of the fractures and use them to our benefit. Ideally, we want to create them to fracture in parallel lines. To force these fractures into straight lines we will purchase substrates with thermal SiO2 created on the surface of Si. Using an etching process we will removed a channel of SiO2 the same as the thickness of the TiC film we plan on growing. These channels will allow the fractures to form in a correlated way creating a straight line. )

Environmental controls on micro fracture processes in shelf ice

NASA Astrophysics Data System (ADS)

Sammonds, Peter

2013-04-01

The recent retreat and collapse of the ice shelves on the Antarctic Peninsula has been associated with regional atmospheric warming, oceanic warming, increased summer melt and shelf flexure. Although the cause of collapse is a matter of active discussion, the process is that of fracture of a creep-brittle material, close to its melting point. The environmental controls on how fracturing initiates, at a micro-scale, strongly determine the macroscopic disintegration of ice shelves. In particular the shelf temperature profile controls the plasticity of the ice shelf; the densification of shelf ice due to melting and re-freezing affects the crack tip stress intensity; the accretion of marine ice at the bottom of the shelf imposes a thermal/mechanical discontinuity; saline environments control crack tip stress corrosion; cyclic loading promotes sub-critical crack propagation. These strong environmental controls on shelf ice fracture means that assessing shelf stability is a non-deterministic problem. How these factors may be parameterized in ice shelf models, through the use of fracture mechanisms maps, is discussed. The findings are discussed in relation to the stability of Larsen C.

A Periglacial Analog for Landforms in Gale Crater, Mars

NASA Technical Reports Server (NTRS)

Oehler, Dorothy Z.

2013-01-01

Several features in a high thermal inertia (TI) unit at Gale crater can be interpreted within a periglacial framework. These features include polygonally fractured terrain (cf. ice-wedge polygons), circumferential patterns of polygonal fractures (cf. relict pingos with ice-wedge polygons on their surfaces), irregularly-shaped and clustered depressions (cf. remnants of collapsed pingos and ephemeral lakes), and a general hummocky topography (cf. thermokarst). This interpretation would imply a major history of water and ice in Gale crater, involving permafrost, freeze-thaw cycles, and perhaps ponded surface water.

Periodic surface instabilities in stressed polymer solids

NASA Astrophysics Data System (ADS)

Tsukruk, Vladimir V.; Reneker, Darrell H.

1995-03-01

The surface morphology of isothermally grown polymer single crystals of polypropylene is observed by atomic force microscopy. The distinguishing features of the polymer single crystals studied are periodic undulations and transverse fractures (cracks) across the single crystal laths. Up to 20 wrinkles are observed near the edges of the cracks. The periodicity of these surface perturbations is 400+/-100 nm and the amplitude is 6+/-3 nm. The formation of the periodic modulations and transverse fractures is attributed to surface stress relief caused by the uniaxial thermal contraction of polymer solids.

Structural and optical behavior due to thermal effects in end-pumped Yb:YAG disk lasers.

PubMed

Sazegari, Vahid; Milani, Mohammad Reza Jafari; Jafari, Ahmad Khayat

2010-12-20

We employ a Monte Carlo ray-tracing code along with the ANSYS package to predict the optical and structural behavior in end-pumped CW Yb:YAG disk lasers. The presence of inhomogeneous temperature, stress, and strain distributions is responsible for many deleterious effects for laser action through disk fracture, strain-induced birefringence, and thermal lensing. The thermal lensing, in turn, results in the optical phase distortion in solid-state lasers. Furthermore, the dependence of optical phase distortion on variables such as the heat transfer coefficient, the cooling fluid temperature, and crystal thickness is discussed.

Finite Element Modeling of Non-linear Coupled Interacting Fault System

NASA Astrophysics Data System (ADS)

Xing, H. L.; Zhang, J.; Wyborn, D.

2009-04-01

PANDAS - Parallel Adaptive static/dynamic Nonlinear Deformation Analysis System - a novel supercomputer simulation tool is developed for simulating the highly non-linear coupled geomechanical-fluid flow-thermal systems involving heterogeneously fractured geomaterials. PANDAS includes the following key components: Pandas/Pre, ESyS_Crustal, Pandas/Thermo, Pandas/Fluid and Pandas/Post as detailed in the following: • Pandas/Pre is developed to visualise the microseismicity events recorded during the hydraulic stimulation process to further evaluate the fracture location and evolution and geological setting of a certain reservoir, and then generate the mesh by it and/or other commercial graphics software (such as Patran) for the further finite element analysis of various cases; The Delaunay algorithm is applied as a suitable method for mesh generation using such a point set; • ESyS_Crustal is a finite element code developed for the interacting fault system simulation, which employs the adaptive static/dynamic algorithm to simulate the dynamics and evolution of interacting fault systems and processes that are relevant on short to mediate time scales in which several dynamic phenomena related with stick-slip instability along the faults need to be taken into account, i.e. (a). slow quasi-static stress accumulation, (b) rapid dynamic rupture, (c) wave propagation and (d) corresponding stress redistribution due to the energy release along the multiple fault boundaries; those are needed to better describe ruputure/microseimicity/earthquake related phenomena with applications in earthquake forecasting, hazard quantification, exploration, and environmental problems. It has been verified with various available experimental results[1-3]; • Pandas/Thermo is a finite element method based module for the thermal analysis of the fractured porous media; the temperature distribution is calculated from the heat transfer induced by the thermal boundary conditions without/with the coupled fluid effects and the geomechanical energy conversion for the pure/coupled thermal analysis. • Pandas/Fluid is a finite element method based module for simulating the fluid flow in the fractured porous media; the fluid flow velocity and pressure are calculated from energy equilibrium equations without/together with the coupling effects of the thermal and solid rock deformation for an independent/coupled fluid flow analysis; • Pandas/Post is to visualise the simulation results through the integration of VTK and/or Patran. All the above modules can be used independently/together to simulate individual/coupled phenomena (such as interacting fault system dynamics, heat flow and fluid flow) without/with coupling effects. PANDAS has been applied to the following issues: • visualisation of the microseismic events to monitor and determine where/how the underground rupture proceeds during a hydraulic stimulation, to generate the mesh using the recorded data for determining the domain of the ruptured zone and to evaluate the material parameters (i.e. the permeability) for the further numerical analysis; • interacting fault system simulation to determine the relevant complicated dynamic rupture process. • geomechanical-fluid flow coupling analysis to investigate the interactions between fluid flow and deformation in the fractured porous media under different loading conditions. • thermo-fluid flow coupling analysis of a fractured geothermal reservoir system. PANDAS will be further developed for a multiscale simulation of multiphase dynamic behaviour for a certain fractured geothermal reservoir. More details and additional application examples will be given during the presentation. References [1] Xing, H. L., Makinouchi, A. and Mora, P. (2007). Finite element modeling of interacting fault system, Physics of the Earth and Planetary Interiors, 163, 106-121.doi:10.1016/j.pepi.2007.05.006 [2] Xing, H. L., Mora, P., Makinouchi, A. (2006). An unified friction description and its application to simulation of frictional instability using finite element method. Philosophy Magazine, 86, 3453-3475 [3] Xing, H. L., Mora, P.(2006). Construction of an intraplate fault system model of South Australia, and simulation tool for the iSERVO institute seed project.. Pure and Applied Geophysics. 163, 2297-2316. DOI 10.1007/s00024-006-0127-x

Fracture patterns at lava-ice contacts on Kokostick Butte, OR, and Mazama Ridge, Mount Rainier, WA: Implications for flow emplacement and cooling histories

NASA Astrophysics Data System (ADS)

Lodge, Robert W. D.; Lescinsky, David T.

2009-09-01

Cooling lava commonly develop polygonal joints that form equant hexagonal columns. Such fractures are formed by thermal contraction resulting in an isotropic tensional stress regime. However, certain linear cooling fracture patterns observed at some lava-ice contacts do not appear to fit the model for formation of cooling fractures and columns because of their preferred orientations. These fracture types include sheet-like (ladder-like rectangular fracture pattern), intermediate (pseudo-aligned individual column-bounding fractures), and pseudopillow (straight to arcuate fractures with perpendicular secondary fractures caused by water infiltration) fractures that form the edges of multiple columns along a single linear fracture. Despite the relatively common occurrence of these types of fractures at lava-ice contacts, their significance and mode of formation have not been fully explored. This study investigates the stress regimes responsible for producing these unique fractures and their significance for interpreting cooling histories at lava-ice contacts. Data was collected at Kokostick Butte dacite flow at South Sister, OR, and Mazama Ridge andesite flow at Mount Rainier, WA. Both of these lava flows have been interpreted as being emplaced into contact with ice and linear fracture types have been observed on their ice-contacted margins. Two different mechanisms are proposed for the formation of linear fracture networks. One possible mechanism for the formation of linear fracture patterns is marginal bulging. Melting of confining ice walls will create voids into which flowing lava can deform resulting in margin-parallel tension causing margin-perpendicular fractures. If viewed from the ice-wall, these fractures would be steeply dipping, linear fractures. Another possible mechanism for the formation of linear fracture types is gravitational settling. Pure shear during compression and settling can result in a tensional environment with similar consequences as marginal inflation. In addition to this, horizontally propagating cooling fractures will be directly influenced by viscous strain caused by the settling of the flow. This would cause preferential opening of fractures horizontally, resulting in vertically oriented fractures. It is important to note that the proposed model for the formation of linear fractures is dependent on contact with and confinement by glacial ice. The influence of flow or movement on cooling fracture patterns has not been extensively discussed in previous modeling of cooling fractures. Rapid cooling of lava by the interaction with water and ice will increase the ability to the capture and preserve perturbations in the stress regime.

Mechanical and thermal properties of conventional and microcellular injection molded poly (lactic acid)/poly (ε-caprolactone) blends.

PubMed

Zhao, Haibin; Zhao, Guoqun

2016-01-01

In view of their complementary properties, blending polylactide (PLA) with poly (ε-caprolactone) (PCL) becomes a good choice to improve PLA's properties without compromising its biodegradability. A series of blends of biodegradable PLA and PCL with different mass fraction were prepared by melt mixing. Standard tensile bars were produced by both conventional and microcellular injection molding to study their mechanical and thermal properties. With the increase in PCL content, the blend showed decreased tensile strength and modulus; however, elongation was dramatically increased. With the addition of PCL, the failure mode changed from brittle fracture of the neat PLA to ductile fracture of the blend as demonstrated by tensile test. Various theoretical models based on dispersion and interface adhesion were used to predict the Young's modulus and the results shows the experimental data are consistent with the predictions of the foam model and Kerner-Uemura-Takayangi model. The thermal behavior of the blends was investigated by DSC and TGA. The melting temperature and the degree of crystallinity of PCL in the PLA/PCL did not significantly change with the PCL content increasing in the whole range of blends composition. Copyright © 2015 Elsevier Ltd. All rights reserved.

Development of a Rolling Process Design Tool for Use in Improving Hot Roll Slab Recovery (Quarterly Report: Q3-FY03)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Couch, R; Wang, P

2003-07-31

In this quarter, an FEM simulation has been performed to compare the shape of the deformed slab after the 8th reduction pass with the experimental metrology data provided by Alcoa Technical Center (ATC). Also, a bug in the thermal contact algorithm used in parallel processing have been identified and corrected for consistent thermal solutions between the rollers and the slab. The overall shape of the slab at the end of the 8th pass is shown in Figure 1. Comparison of the sectional views at the center plane along the length of the slab for both experiment and simulation, shows thatmore » the curvature at the slab mouth at the centerline is slightly higher than the experimental result as shown in Figure 2. We are currently focusing on tuning the parameter values used in the simulation and a more complete parametric study for validation is underway. Also, unexpected fracture occurred along the surface of the slab in the 9th pass as shown in Figure 3. We believe that the reason is due to previously noted inadequacies in the fracture model at low strain rates and high stress triaxiality. We are expecting to receive a modified fracture model based on additional experiment shortly from Alcoa.« less

Processing, thermal and mechanical behaviour of PEI/MWCNT/carbon fiber nanostructured laminate

NASA Astrophysics Data System (ADS)

Santos, L. F. P.; Ribeiro, B.; Hein, L. R. O.; Botelho, E. C.; Costa, M. L.

2017-11-01

In this work, nanostructured composites of polyetherimide (PEI) with addition of functionalized multiwall carbon nanotube (MWCNT) were processed via solution mixing. After processing, these nanocomposites were evaluated by thermogravimetry (TGA), dynamic-mechanical analysis (DMA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Subsequently, the nanocomposite was processed with carbon fibers by using hot compression molding. In order to evaluate interlaminar fracture strength, the processed laminates were mechanically evaluated by interlaminar shear strength (ILSS) and compression shear test (CST). Also, the Weibull distribution was employed to help in the statistical treatment of the data obtained from the mechanical tests. With regards to the fracture of the specimens, optical microscopy was used for the evaluation of the material. The addition of 1 wt% of MWCNT in the polymer matrix increased both thermal stability and viscoelastic behavior of the material. These improvements positively impacted the mechanical properties, generating a 16% and 58% increase in the short-beam strength and apparent interlaminar shear, respectively. In addition, it can be verified from morphological analysis of the fracture a change in the failure mode of the laminate by the incorporation of MWCNT. This behavior can be proven from CST test where there was no presence of the shear force by compression.

Fracture Analysis of Vessels. Oak Ridge FAVOR, v06.1, Computer Code: Theory and Implementation of Algorithms, Methods, and Correlations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, P. T.; Dickson, T. L.; Yin, S.

The current regulations to insure that nuclear reactor pressure vessels (RPVs) maintain their structural integrity when subjected to transients such as pressurized thermal shock (PTS) events were derived from computational models developed in the early-to-mid 1980s. Since that time, advancements and refinements in relevant technologies that impact RPV integrity assessment have led to an effort by the NRC to re-evaluate its PTS regulations. Updated computational methodologies have been developed through interactions between experts in the relevant disciplines of thermal hydraulics, probabilistic risk assessment, materials embrittlement, fracture mechanics, and inspection (flaw characterization). Contributors to the development of these methodologies include themore » NRC staff, their contractors, and representatives from the nuclear industry. These updated methodologies have been integrated into the Fracture Analysis of Vessels -- Oak Ridge (FAVOR, v06.1) computer code developed for the NRC by the Heavy Section Steel Technology (HSST) program at Oak Ridge National Laboratory (ORNL). The FAVOR, v04.1, code represents the baseline NRC-selected applications tool for re-assessing the current PTS regulations. This report is intended to document the technical bases for the assumptions, algorithms, methods, and correlations employed in the development of the FAVOR, v06.1, code.« less

Experimental study of the fracture toughness of a ceramic/ceramic-matrix composite sandwich structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Z.; Taya, M.; Dunn, M.L.

A hybrid experimental-numerical approach has been used to measure the fracture resistance of a sandwich structure consisting of a 304 stainless steel/partially stabilized zirconia ceramic-matrix composite crack-arresting layer embedded in a partially stabilized zirconia ceramic specimen. The mode 1 fracture toughness increases significantly when the crack propagates from the ceramic into the ceramic-matrix composite region. The increased toughening due to the stainless steel particles is explained reasonably well by a toughening model based on processing-induced thermal residual stresses. In addition, several experimental modifications were made to the chevron-notch wedge-loaded double cantilever beam specimen to overcome numerous problems encountered in generatingmore » a precrack in the small, brittle specimens used in this study.« less

[Interface bond and compatibility between Mark II machining ceramic and vita VM9 veneering porcelain].

PubMed

Liu, Tian-Shuang; Li, Zhen-Chun; Chen, Xiao-Dong

2009-04-01

To investigate the interface bond and thermal compatibility between Mark II machining ceramic and Vita VM9 veneering porcelain. A bar shaped specimen (30 mm x 15 mm x 1 mm in size) of Mark II block was prepared, with 0.5 mm-deep notch (vertical to the long axis of specimen) at the middle of the bottom surface. The upper surface was veneered with 0.3 mm VM9 dentin base porcelain. Then the specimen was fractured from the notching site and the fracture surface was examined under scanning electron microscope (SEM) and electron microprobe analyzer (EMPA) with electron beam of 1 microm in diameter. Another ten specimens (30 mm x 15 mm x 1.5 mm in size) were fabricated and the temperature of thermal shock resistance were tested. SEM observation showed tight bond between these two materials and EMPA results showed penetration of Al element from Mark II block into veneering porcelain and Ca element from veneering porcelain into Mark II block occurred after sintering baking. The average temperature of thermal shock resistance for specimens in this study was (194.0+/-10.3) degrees C. Cracks were mainly distributed in veneering porcelain. Chemical bond exists between the Mark II machining ceramic and Vita VM9 veneering porcelain, and there is good thermal compatibility between them.

Residual stress prediction in a powder bed fusion manufactured Ti6Al4V hip stem

NASA Astrophysics Data System (ADS)

Barrett, Richard A.; Etienne, Titouan; Duddy, Cormac; Harrison, Noel M.

2017-10-01

Powder bed fusion (PBF) is a category of additive manufacturing (AM) that is particularly suitable for the production of 3D metallic components. In PBF, only material in the current build layer is at the required melt temperature, with the previously melted and solidified layers reducing in temperature, thus generating a significant thermal gradient within the metallic component, particularly for laser based PBF components. The internal thermal stresses are subsequently relieved in a post-processing heat-treatment step. Failure to adequately remove these stresses can result in cracking and component failure. A prototype hip stem was manufactured from Ti6Al4V via laser PBF but was found to have fractured during over-seas shipping. This study examines the evolution of thermal stresses during the laser PBF manufacturing and heat treatment processes of the hip stem in a 2D finite element analysis (FEA) and compares it to an electron beam PBF process. A custom written script for the automatic conversion of a gross geometry finite element model into a thin layer- by-layer finite element model was developed. The build process, heat treatment (for laser PBF) and the subsequent cooling were simulated at the component level. The results demonstrate the effectiveness of the heat treatment in reducing PBF induced thermal stresses, and the concentration of stresses in the region that fractured.

Microstructure and yield strength effects on hydrogen and tritium induced cracking in HERF (high-energy-rate-forged) stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgan, M J; Tosten, M H

1989-01-01

Rising-load J-integral measurements and falling-load threshold stress intensity measurements were used to characterize hydrogen and tritium induced cracking in high-energy-rate-forged (HERF) 21-6-9 stainless steel. Samples having yield strengths in the range 517--930 MPa were thermally charged with either hydrogen or tritium and tested at room temperature in either air or high-pressure hydrogen gas. In general, the hydrogen isotopes reduced the fracture toughness by affecting the fracture process. Static recrystallization in the HERF microstructures affected the material's fracture toughness and its relative susceptibility to hydrogen and tritium induced fracture. In hydrogen-exposed samples, the reduction in fracture toughness was primarily dependent onmore » the susceptibility of the microstructure to intergranular fracture and only secondarily affected by strength in the range of 660 to 930 MPa. Transmission-electron microscopy observations revealed that the microstructures least susceptible to hydrogen-induced intergranular cracking contained patches of fully recrystallized grains. These grains are surrounded by highly deformed regions containing a high number density of dislocations. The microstructure can best be characterized as duplex'', with soft recrystallized grains embedded in a hard, deformed matrix. The microstructures most susceptible to hydrogen-induced intergranular fracture showed no well-developed recrystallized grains. The patches of recrystallized grains seemed to act as crack barriers to hydrogen-induced intergranular fracture. In tritium-exposed-and-aged samples, the amount of static recrystallization also affected the fracture toughness properties but to a lesser degree. 7 refs., 25 figs.« less

76 FR 42715 - Arthritis Advisory Committee; Notice of Meeting

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-19

.... These drugs are being developed for the treatment of a variety of chronic painful conditions including osteoarthritis, chronic lower back pain, diabetic peripheral neuropathy, post-herpetic neuralgia, chronic pancreatitis, endometriosis, interstitial cystitis, vertebral fracture, thermal injury, and cancer pain. The...

77 FR 1697 - Arthritis Advisory Committee; Notice of Meeting

Federal Register 2010, 2011, 2012, 2013, 2014

2012-01-11

.... These drugs are being developed for the treatment of a variety of chronic painful conditions including osteoarthritis, chronic lower back pain, diabetic peripheral neuropathy, post-herpetic neuralgia, chronic pancreatitis, endometriosis, interstitial cystitis, vertebral fracture, thermal injury, and cancer pain. The...

10 CFR 50.61a - Alternate fracture toughness requirements for protection against pressurized thermal shock events.

Code of Federal Regulations, 2014 CFR

2014-01-01

...-lb energy level produced by irradiation. The ΔT30 value is utilized under the provisions of paragraph... this section, with RTMAX-X values accounting for the effects of annealing and subsequent irradiation...

10 CFR 50.61a - Alternate fracture toughness requirements for protection against pressurized thermal shock events.

Code of Federal Regulations, 2013 CFR

2013-01-01

...-lb energy level produced by irradiation. The ΔT30 value is utilized under the provisions of paragraph... this section, with RTMAX-X values accounting for the effects of annealing and subsequent irradiation...

10 CFR 50.61a - Alternate fracture toughness requirements for protection against pressurized thermal shock events.

Code of Federal Regulations, 2012 CFR

2012-01-01

...-lb energy level produced by irradiation. The ΔT30 value is utilized under the provisions of paragraph... this section, with RTMAX-X values accounting for the effects of annealing and subsequent irradiation...

10 CFR 50.61a - Alternate fracture toughness requirements for protection against pressurized thermal shock events.

Code of Federal Regulations, 2011 CFR

2011-01-01

...-lb energy level produced by irradiation. The ΔT30 value is utilized under the provisions of paragraph... this section, with RTMAX-X values accounting for the effects of annealing and subsequent irradiation...

THERMAL TECHNOLOGY TESTED FOR CONTAMINANT RECOVERY

EPA Science Inventory

A research project on steam enhanced remediation (SER) for the recovery of dense nonaqueous phase liquid (DNAPL) from fractured limestone has been undertaken at the former Loring Air Force Base Quarry site in Limestone, ME. Participants in the project include the Maine Departmen...

Bovine xenograft application for treatment of a metatarsal nonunion fracture in an alpaca (Vicugna pacos).

PubMed

Longo, F; Finotti, L; Bellini, L; Zavan, B; Busetto, R; Isola, M

2016-05-01

A 15-year-old female huacaya alpaca (Vicugna pacos) was referred because of a non-weight-bearing lameness (4/4) in the left pelvic limb caused by a grade three open metatarsal fracture. The referring veterinarian treated the fracture with conservative management using bandages, but it progressively evolved to a non-union. Clinical examination revealed external wounds on the medial and lateral surfaces of the metatarsus. Radiographs confirmed an open, nonarticular, displaced, diaphyseal fracture of the left metatarsus. Cancellous bone was sourced from bovine proximal and distal femur epiphyses, followed by a thermal shock procedure to achieve decellularisation, to produce a xenograft. Open reduction and internal fixation of the fracture using locking plates was performed. Alignment of the fracture fragments was corrected and the xenograft was placed at the debrided fracture site to stimulate and harness osteogenesis in situ. Clinical and radiographic follow-up was performed up to 40 weeks postoperatively. Clinical evaluations revealed that the alpaca gradually increased weight bearing following bandage removal 10 days after surgery. Serial radiographs showed correct alignment of the left metatarsus, progressive bone modelling and, complete bone union at 12 weeks. Ten months postoperatively the alpaca showed no signs of lameness and resumed normal activity. For management of a metatarsal non-union, a combination of bovine xenograft application and angular stable internal fixation progressed toward an excellent long-term recovery.

Hot and Steamy Fractures in the Philippines: The Geological Characterization and Permeability Evaluation of Fractures in the Southern Negros Geothermal Field, Philippines

NASA Astrophysics Data System (ADS)

Pastoriza, L. R.; Holdsworth, R.; McCaffrey, K. J. W.; Dempsey, E. D.; Walker, R. J.; Gluyas, J.; Reyes, J. K.

2016-12-01

Fluid flow pathway characterization is critical to geothermal exploration and exploitation. It requires a good understanding of the structural evolution, fault distribution and fluid flow properties. A dominantly fieldwork-based approach has been used to evaluate the potential fracture permeability characteristics of a typical high-temperature geothermal reservoir in the Southern Negros Geothermal Field, Philippines. This is a liquid-dominated geothermal resource hosted in the andesitic to dacitic Quaternary Cuernos de Negros Volcano in Negros Island. Fieldwork reveals two main fracture groups based on fault rock characteristics, alteration type, relative age of deformation, and associated thermal manifestation, with the younger fractures mainly related to the development of the modern geothermal system. Palaeostress analyses of cross-cutting fault and fracture arrays reveal a progressive counterclockwise rotation of stress axes from the (?)Pliocene up to the present-day, which is consistent with the regional tectonic models. A combined slip and dilation tendency analysis of the mapped faults indicates that NW-SE structures should be particularly promising drilling targets. Frequency versus length and aperture plots of fractures across six to eight orders of magnitude show power-law relationships with a change in scaling exponent in the region of 100 to 500m length-scales. Finally, evaluation of the topology of the fracture branches shows the dominance of Y-nodes that are mostly doubly connected suggesting good connectivity and permeability within the fracture networks. The results obtained in this study illustrate the value of methods that can be globally applied during exploration to better characterize fracture systems in geothermal reservoirs using multiscale datasets.

Hot and steamy fractures in the Philippines: the characterisation and permeability evaluation of fractures of the Southern Negros Geothermal Field, Negros Oriental, Philippines

NASA Astrophysics Data System (ADS)

Pastoriza, Loraine; Holdsworth, Robert; McCaffrey, Kenneth; Dempsey, Eddie; Walker, Richard; Gluyas, Jon; Reyes, Jonathan

2017-04-01

Fluid flow pathway characterisation is critical to geothermal exploration and exploitation. It requires a good understanding of the structural evolution, fault distribution and fluid flow properties. A dominantly fieldwork-based approach has been used to evaluate the potential fracture permeability characteristics of a typical high-temperature geothermal reservoir in the Southern Negros Geothermal Field, Philippines. This is a liquid-dominated geothermal resource hosted in the andesitic to dacitic Quaternary Cuernos de Negros Volcano in Negros Island. Fieldwork reveals two main fracture groups based on fault rock characteristics, alteration type, relative age of deformation, and associated thermal manifestation, with the younger fractures mainly related to the development of the modern geothermal system. Palaeostress analyses of cross-cutting fault and fracture arrays reveal a progressive counterclockwise rotation of stress axes from the (?)Pliocene up to the present-day, which is consistent with the regional tectonic models. A combined slip and dilation tendency analysis of the mapped faults indicates that NW-SE structures should be particularly promising drilling targets. Frequency versus length and aperture plots of fractures across six to eight orders of magnitude show power-law relationships with a change in scaling exponent in the region of 100 to 500m length-scales. Finally, evaluation of the topology of the fracture branches shows the dominance of Y-nodes that are mostly doubly connected suggesting good connectivity and permeability within the fracture networks. The results obtained in this study illustrate the value of methods that can be globally applied during exploration to better characterize fracture systems in geothermal reservoirs using multiscale datasets.

Thermal and thermomechanical calculations of deep-rock nuclear waste disposal with the enhanced SANGRE code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heuze, F.E.

1983-03-01

An attempt to model the complex thermal and mechanical phenomena occurring in the disposal of high-level nuclear wastes in rock at high power loading is described. Such processes include melting of the rock, convection of the molten material, and very high stressing of the rock mass, leading to new fracturing. Because of the phase changes and the wide temperature ranges considered, realistic models must provide for coupling of the thermal and mechanical calculations, for large deformations, and for steady-state temperature-depenent creep of the rock mass. Explicit representation of convection would be desirable, as would the ability to show fracture developmentmore » and migration of fluids in cracks. Enhancements to SNAGRE consisted of: array modifications to accommodate complex variations of thermal and mechanical properties with temperature; introduction of the ability of calculate thermally induced stresses; improved management of the minimum time step and minimum temperature step to increase code efficiency; introduction of a variable heat-generation algorithm to accommodate heat decay of the nuclear materials; streamlining of the code by general editing and extensive deletion of coding used in mesh generation; and updating of the program users' manual. The enhanced LLNL version of the code was renamed LSANGRE. Phase changes were handled by introducing sharp variations in the specific heat of the rock in a narrow range about the melting point. The accuracy of this procedure was tested successfully on a melting slab problem. LSANGRE replicated the results of both the analytical solution and calculations with the finite difference TRUMP code. Following enhancement and verification, a purely thermal calculation was carried to 105 years. It went beyond the extent of maximum melt and into the beginning of the cooling phase.« less

Seismic and aseismic deformations and impact on reservoir permeability: The case of EGS stimulation at The Geysers, California, USA

NASA Astrophysics Data System (ADS)

Jeanne, Pierre; Rutqvist, Jonny; Rinaldi, Antonio Pio; Dobson, Patrick F.; Walters, Mark; Hartline, Craig; Garcia, Julio

2015-11-01

In this paper, we use the Seismicity-Based Reservoir Characterization approach to study the spatiotemporal dynamics of an injection-induced microseismic cloud, monitored during the stimulation of an enhanced geothermal system, and associated with the Northwest Geysers Enhanced Geothermal System (EGS) Demonstration project (California). We identified the development of a seismically quiet domain around the injection well surrounded by a seismically active domain. Then we compare these observations with the results of 3-D Thermo-Hydro-Mechanical simulations of the EGS, which accounts for changes in permeability as a function of the effective normal stress and the plastic strain. The results of our modeling show that (1) the aseismic domain is caused by both the presence of the injected cold water and by thermal processes. These thermal processes cause a cooling-stress reduction, which prevent shear reactivation and favors fracture opening by reducing effective normal stress and locally increasing the permeability. This process is accompanied by aseismic plastic shear strain. (2) In the seismic domain, microseismicity is caused by the reactivation of the preexisting fractures, resulting from an increase in injection-induced pore pressure. Our modeling indicates that in this domain, permeability evolves according to the effective normal stress acting on the shear zones, whereas shearing of preexisting fractures may have a low impact on permeability. We attribute this lack of permeability gain to the fact that the initial permeabilities of these preexisting fractures are already high (up to 2 orders of magnitude higher than the host rock) and may already be fully dilated by past tectonic straining.

Insights into contaminant transport from unconventional oil and gas developments from analog system analysis of methane-bearing thermal springs in the northern Canadian Rocky Mountains

NASA Astrophysics Data System (ADS)

Ferguson, Grant; Grasby, Stephen E.

2018-03-01

Natural gas is currently being produced from shales of the Montney and Liard basins in western Canada. Production requires hydraulic fracturing due to the low permeability of the shales in the basins. Stratigraphically equivalent shales are present in the northern Canadian Rocky Mountains. Thermal springs with notable hydrocarbon concentrations occur where large-scale faults intersect the same shale units that are the focus of gas development, indicating that under certain circumstances, connection of deep fractured shales to the land surface is possible. To constrain these conditions, simulations were conducted for the spring with the highest hydrocarbon flux (Toad River Spring), results of which indicate that in order to supply sufficient water to a fault to support measurable advection, the effective permeability of the shales in these structurally deformed areas must be one to four orders of magnitude higher than in areas of active gas production to the east. The spatial scale of enhanced permeability is much greater than that which is achieved by hydraulic fracturing and the mechanism of maintaining high pressures at depth is more persistent in time. Examination of groundwater velocities suggests that upward migration of solutes from hydraulic fracturing may take decades to centuries. Results also indicate that any temperature anomaly will be associated with transport along a fault at such velocities. No such temperature anomaly has been documented in regions with unconventional oil and gas development to date. Such an anomaly would be diagnostic of a deep solute source.

Fracture behavior of metal-ceramic fixed dental prostheses with frameworks from cast or a newly developed sintered cobalt-chromium alloy.

PubMed

Krug, Klaus-Peter; Knauber, Andreas W; Nothdurft, Frank P

2015-03-01

The aim of this study was to investigate the fracture behavior of metal-ceramic bridges with frameworks from cobalt-chromium-molybdenum (CoCrMo), which are manufactured using conventional casting or a new computer-aided design/computer-aided manufacturing (CAD/CAM) milling and sintering technique. A total of 32 metal-ceramic fixed dental prostheses (FDPs), which are based on a nonprecious metal framework, was produced using a conventional casting process (n = 16) or a new CAD/CAM milling and sintering process (n = 16). Eight unveneered frameworks were manufactured using each of the techniques. After thermal and mechanical aging of half of the restorations, all samples were subjected to a static loading test in a universal testing machine, in which acoustic emission monitoring was performed. Three different critical forces were revealed: the fracture force (F max), the force at the first reduction in force (F decr1), and the force at the critical acoustic event (F acoust1). With the exception of the veneered restorations with cast or sintered metal frameworks without artificial aging, which presented a statistically significant but slightly different F max, no statistically significant differences between cast and CAD/CAM sintered and milled FDPs were detected. Thermal and mechanical loading did not significantly affect the resulting forces. Cast and CAD/CAM milled and sintered metal-ceramic bridges were determined to be comparable with respect to the fracture behavior. FDPs based on CAD/CAM milled and sintered frameworks may be an applicable and less technique-sensitive alternative to frameworks that are based on conventionally cast frameworks.

Residual stress and damage-induced critical fracture on CO2 laser treated fused silica

NASA Astrophysics Data System (ADS)

Matthews, M. J.; Stolken, J. S.; Vignes, R. M.; Norton, M. A.; Yang, S.; Cooke, J. D.; Guss, G. M.; Adams, J. J.

2009-10-01

Localized damage repair and polishing of silica-based optics using mid- and far-IR CO2 lasers has been shown to be an effective method for increasing optical damage threshold in the UV. However, it is known that CO2 laser heating of silicate surfaces can lead to a level of residual stress capable of causing critical fracture either during or after laser treatment. Sufficient control of the surface temperature as a function of time and position is therefore required to limit this residual stress to an acceptable level to avoid critical fracture. In this work we present the results of 351 nm, 3ns Gaussian damage growth experiments within regions of varying residual stress caused by prior CO2 laser exposures. Thermally stressed regions were non-destructively characterized using polarimetry and confocal Raman microscopy to measure the stress induced birefringence and fictive temperature respectively. For 1~40s square pulse CO2 laser exposures created over 0.5-1.25kW/cm2 with a 1-3mm 1/e2 diameter beam (Tmax~1500-3000K), the critical damage site size leading to fracture increases weakly with peak temperature, but shows a stronger dependence on cooling rate, as predicted by finite element hydrodynamics simulations. Confocal micro-Raman was used to probe structural changes to the glass over different thermal histories and indicated a maximum fictive temperature of 1900K for Tmax>=2000K. The effect of cooling rate on fictive temperature caused by CO2 laser heating are consistent with finite element calculations based on a Tool-Narayanaswamy relaxation model.

Increased wound complication with intramedullary screw fixation of clavicle fractures: Is it thermal necrosis?

PubMed

Domos, Peter; Tytherleigh-Strong, Graham; Van Rensburg, Lee

2017-01-01

Adult mid-shaft clavicle fractures are common injuries. For displaced fractures, open reduction with plate or intramedullary (IM) fixation is the widely used techniques. All methods have their own potential drawbacks, especially related to local soft tissue complications. There is little information about outcome and management of local wound complications after clavicle fracture fixations. Ninety-seven patients underwent open reduction and internal fixation, 17 were treated with IM screw fixation and 80 with plate fixation. Wound complication occurred in eight patients (8.2%) and rates differed significantly between IM and plate fixations (29.4% vs. 3.8%). Patients were assessed on average 58.3 months with visual analogue pain scores (VASs), Oxford Shoulder Score (OSS), and QuickDash (QD) score. Five patients had wound breakdown and three patients had wound erythema. In seven patients with stable fixation, it was possible to "dress and suppress" with average 3 weeks of oral antibiotics. One patient had unstable fixation and required longer antibiotic treatment with early screw removal. One patient developed a chronic discharging wound, requiring debridement and later plate removal. At final follow-up, all wounds remained healed, bony union was achieved in all. The average scores were: VAS 1, OSS 46, and QD 4.5. Good function with dry healed wound and united clavicle can be achieved. Further studies are required to investigate the difference in soft tissue complication rates, which may be due to the IM technique of retrograde drilling with a guide wire and due to aseptic thermal bone necrosis, rather than true infection.

Air-cooled volcanoes ? New insights on convective airflow process within Miyakejima and Piton de la Fournaise volcanoes

NASA Astrophysics Data System (ADS)

Antoine, R.; Geshi, N.; Kurita, K.; Aoki, Y.; Ichihara, M.; Staudacher, T.; Bachelery, P.

2012-04-01

Subsurface airflow in the unsaturated zone of the soil has been extensively investigated in a variety of disciplines such as mining, nuclear waste or agriculture science. In volcanology, the recent discovery of subsurface airflow close to the terminal cone of Piton de La Fournaise volcano (La Réunion Island, France) provides for the first time insights into the convective behavior of air within the unsaturated layer [1]. The characteristics of the aerothermal system, its occurrence in other volcanoes, its ability to transport heat during quiescent periods and the perturbation of this system before eruptions are the key questions we want to address following this discovery. In this study, we present observations of subsurface convective airflow within opened fractures located at the summit of Miyakejima and Piton de la Fournaise volcanoes from anemometric and temperature data. Two anemometers and thermocouples were placed at the surface and at the center of the fracture at two-meter depth during a diurnal cycle. Six thermocouples also measured the temperature at 1 meter-depth, on a profile set perpendicularly to the fracture. Finally, a thermal camera was used to make punctual measurements of the surface temperature of the fracture. At Miyakejima, two surveys were realized in winter 2010 and summer 2011. During the winter, mild air exit was detected from the fracture with a central vertical velocity of 20 to 50 cm/s. The temperature of the site was constant during the diurnal cycle (~ 22°C), leading to a maximum temperature contrast of 15°C between the fracture and the atmosphere just before sunrise. During summer, a different hydrodynamic behavior was observed: Air inflow was detected during the whole diurnal cycle with a mean velocity of 20 cm/s. The temperature of the fracture followed the temperature of the atmosphere at 2 meters-depth. In the case of Piton de la Fournaise volcano, the same convective behavior was observed at two different fractures during winter 2008 and summer 2010. Moreover, the velocities and temperature contrast between the fracture and the atmosphere were close to the ones recorded at Miyakejima. Finally, the temperature profiles realized across the fractures and confirmed by the infrared thermography data allowed us to define the convective patterns. This study represents the first detection and characterization of air convection at a seasonal scale within fractures on volcanoes. It constitutes a preliminary step to further investigations dedicated to the understanding of the perturbation of such systems before eruptions. [1] Antoine R., Baratoux D., Rabinowicz M., Fontaine F.J., Bachèlery P., Staudacher T., Saracco G., Finizola A., Thermal infrared images analysis of a quiescent cone on Piton de La Fournaise volcano: Evidence for convective air flow within an unconsolidated soil, Journal of Volcanology and Geothermal Research, Volume 183, Issues 3-4, 2009, Pages 228-244.

Development of a natural degradable polymer for orthopaedic use.

PubMed

Knowles, J C

1993-01-01

Currently, there are a large variety of degradable polymers available for use in surgery, which are generally based on blends and copolymers of poly(L-lactide) (PLLA) and poly(L-glycolide) (PGA). The major demand for these materials is for suturing of wounds, but the materials are also being developed for use in orthopaedic surgery for fracture reduction. The development of these materials is on two fronts, the first involving conventional fracture fixation design of plates. The second is to produce simple devices such as rods and to use the degradable materials for treatment of specific fracture types such as fractures of the olecranon. These materials have the advantage of possessing initially enhanced mechanical properties, although their relatively quick degradation profile diminishes these properties. As an alternative we are developing polyhydroxybutyrate (PHB) and its copolymers with polyhydroxyvalerate (PHV). This range of polymers mab be easily thermally processed, are very cheap and easily available. The polymer also has the significant advantage of being piezoelectric. This is discussed.

Numerical simulations of heat transfer through fractured rock for an enhanced geothermal system development in Seokmodo, Korea

NASA Astrophysics Data System (ADS)

Shin, Jiyoun; Kim, Kyung-Ho; Hyun, Yunjung; Lee, Kang-Keun

2010-05-01

Estimating the expected capacity and efficiency of energy is a crucial issue in the construction of geothermal plant. It is the lasting temperature of extracted geothermal water that determines the effectiveness of enhanced geothermal systems (EGS), so the heat transfer processes in geothermal reservoirs under site-specific geologic conditions should be understood first. The construction of the first geothermal plant in Korea is under planning in Seokmodo, where a few flowing artesian wells showing relatively high water temperature of around 70°C were discovered lately. The site of interest is a part of the island region, consisting of the reclaimed land surrounded by the sea and small mountains. Geothermal gradient measures approximately 45°C/km and the geothermal water is as saline as seawater. Geologic structure in this region is characterized by the fractured granite. In this study, thermo-hydrological (TH) numerical simulations for the temperature evolution in a fractured geothermal reservoir under the supposed injection-extraction operating conditions were carried out using TOUGH2. Multiple porosity model which is useful to calculate the transient interporosity flow in TH coupled heat transfer problem was used in simulations. Several fracture planes which had been investigated in the field were assigned to have highly permeable properties in order to avoid the averaging approximation and describe the dominant flow through the fractures. This heterogeneous model showed the rise of relatively hot geothermal water in the densely fractured region. The temperature of the extracted geothermal water also increased slowly for 50 years due to the rising flow through the fractures. The most sensitive factor which affects the underground thermal distribution and temperature of geothermal water was permeability of the medium. Change in permeabilities of rock and fracture within the range of 1 order might cause such an extreme change in the temperature of geothermal water that the measurement of the permeability should be performed through a very careful process in order to guarantee a reliable simulation. As the fracture spacing became narrower, overall thermal distribution appeared to be similar to that from EPM model. This suggests that EPM model, which is easy to design and takes less time, can be replaced for the densely fractured medium. Change in fracture aperture within the range of that of actual rocks did not cause a remarkable difference in temperature distribution, which means that measuring accuracy of the actual aperture value in rocks is relatively less important. This demonstrates that the distribution and the structure of fracture system make a great contribution to the whole simulation for fluid and heat flow mechanisms in geologic medium, and thus require an intensive geologic investigation for the fractures including strike and dip information, permeability and connecting relation. In addition, the simulation results show that the heterogeneous model can include the description for the significant fracture flow and it can be a practical tool for a site-specific simulation for EGS sites. This preliminary simulation was useful to estimate the scale of the geothermal reservoir and the energy potential in Seokmodo and it can be further expanded to a long-term simulation to predict the evolution of the geothermal reservoir under the potential EGS operations. Acknowledgement: This study was financially supported by KIGAM, KETEP and BK21.

MANTECH Project Book

DTIC Science & Technology

1991-01-01

degrade due to thermal cyclingmultiple repairs, and/or corrosion. Depending on the service history and alloy, reduced properties result from carbide U...subsystem 91 titanitun alloys 85 cleanliness gas turbine engines 85 titani •-n aluminide 81 tolerance control 92 tool breaqkage 95 tool fracture 95 tools

Fault-controlled permeability and fluid flow in low-porosity crystalline rocks: an example from naturally fractured geothermal systems in the Southern Andes

NASA Astrophysics Data System (ADS)

Arancibia, G.; Roquer, T.; Sepúlveda, J.; Veloso, E. A.; Morata, D.; Rowland, J. V.

2017-12-01

Fault zones can control the location, emplacement, and evolution of economic mineral deposits and geothermal systems by acting as barriers and/or conduits to crustal fluid flow (e.g. magma, gas, oil, hydro-geothermal and groundwater). The nature of the fault control permeability is critical in the case of fluid flow into low porosity/permeability crystalline rocks, since structural permeability provides the main hydraulic conductivity to generate a natural fractured system. However, several processes accompanying the failure of rocks (i.e. episodic permeability given by cycling ruptures, mineral precipitation from fluids in veins, dissolution of minerals in the vicinity of a fracture) promote a complex time-dependent and enhancing/reducing fault-controlled permeability. We propose the Southern Volcanic Zone (Southern Andes, Chile) as a case study to evaluate the role of the structural permeability in low porosity crystalline rocks belonging to the Miocene North Patagonian Batholith. Recently published studies propose a relatively well-constrained first-order role of two active fault systems, the arc-parallel (NS to NNE trending) Liquiñe Ofqui Fault System and the arc-oblique (NW trending) Andean Transverse Fault Zones, in fluid flow at crustal scales. We now propose to examine the Liquiñe ( 39°S) and Maihue ( 40°S) areas as sites of interaction between these fault systems, in order to evaluate a naturally fractured geothermal system. Preliminary results indicate upwelling of thermal water directly from fractured granite or from fluvial deposits overlying granitoids. Measured temperatures of thermal springs suggest a low- to medium-enthalpy system, which could potentially be harnessed for use in geothermal energy applications (e.g. heating, wood dryer and green house), which are much needed in Southern Chile. Future work will aim to examine the nature of structural permeability from the regional to the microscopic scale connecting the paleo- and current- fluid flow through the fractured media. Results will contribute to a better understanding of geothermal systems in the Andean tectonic setting and of naturally fractured reservoirs in low-porosity crystalline rocks around the world. Acknowledgments: This work is funded by CEGA-FONDAP/CONICYT #15090013 and VRI-PUENTE #P1703/2017.

Mechanical Properties and Thermal Shock Resistance Analysis of BNNT/Si3N4 Composites

NASA Astrophysics Data System (ADS)

Wang, Shouren; Wang, Gaoqi; Wen, Daosheng; Yang, Xuefeng; Yang, Liying; Guo, Peiquan

2018-04-01

BNNT/Si3N4 ceramic composites with different weight amount of BNNT fabricated by hot isostatic pressing were introduced. The mechanical properties and thermal shock resistance of the composites were investigated. The results showed that BNNT-added ceramic composites have a finer and more uniform microstructure than that of BNNT-free Si3N4 ceramic because of the retarding effect of BNNT on Si3N4 grain growth. The addition of 1.5 wt.% BNNT results in simultaneous increase in flexural strength, fracture toughness, and thermal shock resistance. The analysis of the results indicates that BNNT brings many thermal transport channels in the microstructure, increasing the efficiency of thermal transport, therefore results in increase of thermal shock resistance. In addition, BNNT improves the residual flexural strength of composites by crack deflection, bridging, branching and pinning, which increase the crack propagation resistance.

Scale Model Simulation of Enhanced Geothermal Reservoir Creation

NASA Astrophysics Data System (ADS)

Gutierrez, M.; Frash, L.; Hampton, J.

2012-12-01

Geothermal energy technology has successfully provided a means of generating stable base load electricity for many years. However, implementation has been spatially limited to limited availability of high quality traditional hydro-thermal resources possessing the combination of a shallow high heat flow anomaly and an aquifer with sufficient permeability and continuous fluid recharge. Enhanced Geothermal Systems (EGS) has been proposed as a potential solution to enable additional energy production from the non-conventional hydro-thermal resources. Hydraulic fracturing is considered the primary means of creating functional EGS reservoirs at sites where the permeability of the rock is too limited to allow cost effective heat recovery. EGS reservoir creation requires improved fracturing methodology, rheologically controllable fracturing fluids, and temperature hardened proppants. Although large fracture volumes (several cubic km) have been created in the field, circulating fluid through these full volumes and maintaining fracture volumes have proven difficult. Stimulation technology and methodology as used in the oil and gas industry for sedimentary formations are well developed; however, they have not sufficiently been demonstrated for EGS reservoir creation. Insufficient data and measurements under geothermal conditions make it difficult to directly translate experience from the oil and gas industries to EGS applications. To demonstrate the feasibility of EGS reservoir creation and subsequent geothermal energy production, and to improve the understanding of hydraulic and propping in EGS reservoirs, a heated true-triaxial load cell with a high pressure fluid injection system was developed to simulate an EGS system from stimulation to production. This apparatus is capable of loading a 30x30x30 cubic cm rock sample with independent principal stresses up to 13 MPa while simultaneously providing heating up to 180 degree C. Multiple orientated boreholes of 5 to 10 mm diameter may be drilled into the sample while at reservoir conditions. This allows for simulation of borehole damage as well as injector-producer schemes. Dual 70 MPa syringe pumps set to flow rates between 10 nL/min and 60 mL/min injecting into a partially cased borehole allow for fully contained fracturing treatments. A six sensor acoustic emission (AE) array is used for geometric fracture location estimation during intercept borehole drilling operations. Hydraulic sensors and a thermocouple array allow for additional monitoring and data collection as relevant to computer model validation as well as field test comparisons. The results from preliminary tests inside and outside of the cell demonstrate the functionality of the equipment while also providing some novel data on the propagation and flow characteristics of hydraulic fractures themselves.

Thermal shock and erosion resistant tantalum carbide ceramic material

NASA Technical Reports Server (NTRS)

Honeycutt, L., III; Manning, C. R. (Inventor)

1978-01-01

Ceramic tantalum carbide artifacts with high thermal shock and mechanical erosion resistance are provided by incorporating tungsten-rhenium and carbon particles in a tantalum carbide matrix. The mix is sintered by hot pressing to form the ceramic article which has a high fracture strength relative to its elastic modulus and thus has an improved thermal shock and mechanical erosion resistance. The tantalum carbide is preferable less than minus 100 mesh, the carbon particles are preferable less than minus 100 mesh, and the tungsten-rhenium particles are preferable elongate, having a length to thickness ratio of at least 2/1. Tungsten-rhenium wire pieces are suitable as well as graphite particles.

Mechanical Properties and Fracture Behaviors of the As-Extruded Mg-5Al-3Ca Alloys Containing Yttrium at Elevated Temperature.

PubMed

Son, Hyeon-Taek; Kim, Yong-Ho; Kim, Taek-Soo; Lee, Seong-Hee

2016-02-01

Effects of yttrium (Y) addition on mechanical properties and fracture behaviors of the as-extruded Mg-Al-Ca based alloys at elevated temperature were investigated by a tensile test. After hot extrusion, the average grain size was refined by Y addition and eutectic phases were broken down into fine particles. Y addition to Mg-5Al-3Ca based alloy resulted in the improvement of strength and ductility at elevated temperature due to fine grain and suppression of grain growth by formation of thermally stable Al2Y intermetallic compound.

Finite-element modelling of thermal micracking in fresh and consolidated marbles

NASA Astrophysics Data System (ADS)

Weiss, T.; Fuller, E.; Siegesmund, S.

2003-04-01

The initial stage of marble weathering is supposed to be controlled by thermal microcracking. Due to the anisotropy of the thermal expansion coefficients of calcite, the main rock forming mineral in marble, stresses are caused which lead to thermally-induced microcracking, especially along the grain boundaries. The so-called "granular disintegration" is a frequent weathering phenomenon observed for marbles. The controlling parameters are the grain size, grain shape and grain orientation. We use a finite-element approach to constrain magnitude and directional dependence of thermal degradation. Therefore, different assumptions are validated including the fracture toughness of the grain boundaries, the effects of the grain-to-grain orientation and bulk lattice preferred orientation (here referred to as texture). The resulting thermal microcracking and bulk rock thermal expansion anisotropy are validated. It is evident that thermal degradation depends on the texture. Strongly textured marbles exhibit a clear directional dependence of thermal degradation and a smaller bulk thermal degradation than randomly oriented ones. The effect of different stone consolidants in the pore space of degraded marble is simulated and its influence on mechanical properties such as tensile strength are evaluated.

Development and Fatigue Testing of Ceramic Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dong-Ming; Choi, Sung R.; Miller, Robert A.

2004-01-01

Ceramic thermal barrier coatings will play an increasingly important role in future gas turbine engines because of their ability to effectively protect the engine components and further raise engine temperatures. Durability of the coating systems remains a critical issue with the ever-increasing temperature requirements. Thermal conductivity increase and coating degradation due to sintering and phase changes are known to be detrimental to coating performance. There is a need to characterize the coating thermal fatigue behavior and temperature limit, in order to potentially take full advantage of the current coating capability. In this study, thermal conductivity and cyclic fatigue behaviors of plasma-sprayed ZrO2-8wt%Y2O3 thermal barrier coatings were evaluated under high temperature, large thermal gradient and thermal cycling conditions. The coating degradation and failure processes were assessed by real-time monitoring of the coating thermal conductivity under the test conditions. The ceramic coating crack initiation and propagation driving forces and failure modes under the cyclic thermal loads will be discussed in light of the high temperature mechanical fatigue and fracture testing results.

Geochemistry, Comparative Analysis, and Physical and Chemical Characteristics of the Thermal Waters East of Hot Springs National Park, Arkansas, 2006-09

USGS Publications Warehouse

Kresse, Timothy M.; Hays, Phillip D.

2009-01-01

A study was conducted by the U.S Geological Survey in cooperation with the Arkansas State Highway and Transportation Department to characterize the source and hydrogeologic conditions responsible for thermal water in a domestic well 5.5 miles east of Hot Springs National Park, Hot Springs, Arkansas, and to determine the degree of hydraulic connectivity between the thermal water in the well and the hot springs in Hot Springs National Park. The water temperature in the well, which was completed in the Stanley Shale, measured 33.9 degrees Celsius, March 1, 2006, and dropped to 21.7 degrees Celsius after 2 hours of pumping - still more than 4 degrees above typical local groundwater temperature. A second domestic well located 3 miles from the hot springs in Hot Springs National Park was discovered to have a thermal water component during a reconnaissance of the area. This second well was completed in the Bigfork Chert and field measurement of well water revealed a maximum temperature of 26.6 degrees Celsius. Mean temperature for shallow groundwater in the area is approximately 17 degrees Celsius. The occurrence of thermal water in these wells raised questions and concerns with regard to the timing for the appearance of the thermal water, which appeared to coincide with construction (including blasting activities) of the Highway 270 bypass-Highway 70 interchange. These concerns were heightened by the planned extension of the Highway 270 bypass to the north - a corridor that takes the highway across a section of the eroded anticlinal complex responsible for recharge to the hot springs of Hot Springs National Park. Concerns regarding the possible effects of blasting associated with highway construction near the first thermal well necessitated a technical review on the effects of blasting on shallow groundwater systems. Results from available studies suggested that propagation of new fractures near blasting sites is of limited extent. Vibrations from blasting can result in rock collapse for uncased wells completed in highly fractured rock. However, the propagation of newly formed large fractures that potentially could damage well structures or result in pirating of water from production wells appears to be of limited possibility based on review of relevant studies. Characteristics of hydraulic conductivity, storage, and fracture porosity were interpreted from flow rates observed in individual wells completed in the Bigfork Chert and Stanley Shale; from hydrographs produced from continuous measurements of water levels in wells completed in the Arkansas Novaculite, the Bigfork Chert, and Stanley Shale; and from a potentiometric-surface map constructed using water levels in wells throughout the study area. Data gathered from these three separate exercises showed that fracture porosity is much greater in the Bigfork Chert relative to that in the Stanley Shale, shallow groundwater flows from elevated recharge areas with exposures of Bigfork Chert along and into streams within the valleys formed on exposures of the Stanley Shale, and there was no evidence of interbasin transfer of groundwater within the shallow flow system. Fifteen shallow wells and two cold-water springs were sampled from the various exposed formations in the study area to characterize the water quality and geochemistry for the shallow groundwater system and for comparison to the geochemistry of the hot springs in Hot Springs National Park. For the quartz formations (novaculite, chert, and sandstone formations), total dissolved solids concentrations were very low with a median concentration of 23 milligrams per liter, whereas the median concentration for groundwater from the shale formations was 184 milligrams per liter. Ten hot springs in Hot Springs National Park were sampled for the study. Several chemical constituents for the hot springs, including pH, total dissolved solids, major cations and anions, and trace metals, show similarity with the shale formations

Modelling explicit fracture of nuclear fuel pellets using peridynamics

NASA Astrophysics Data System (ADS)

Mella, R.; Wenman, M. R.

2015-12-01

Three dimensional models of explicit cracking of nuclear fuel pellets for a variety of power ratings have been explored with peridynamics, a non-local, mesh free, fracture mechanics method. These models were implemented in the explicitly integrated molecular dynamics code LAMMPS, which was modified to include thermal strains in solid bodies. The models of fuel fracture, during initial power transients, are shown to correlate with the mean number of cracks observed on the inner and outer edges of the pellet, by experimental post irradiation examination of fuel, for power ratings of 10 and 15 W g-1 UO2. The models of the pellet show the ability to predict expected features such as the mid-height pellet crack, the correct number of radial cracks and initiation and coalescence of radial cracks. This work presents a modelling alternative to empirical fracture data found in many fuel performance codes and requires just one parameter of fracture strain. Weibull distributions of crack numbers were fitted to both numerical and experimental data using maximum likelihood estimation so that statistical comparison could be made. The findings show P-values of less than 0.5% suggesting an excellent agreement between model and experimental distributions.

Adequacy of Current State Setbacks for Directional High-Volume Hydraulic Fracturing in the Marcellus, Barnett, and Niobrara Shale Plays.

PubMed

Haley, Marsha; McCawley, Michael; Epstein, Anne C; Arrington, Bob; Bjerke, Elizabeth Ferrell

2016-09-01

There is an increasing awareness of the multiple potential pathways leading to human health risks from hydraulic fracturing. Setback distances are a legislative method to mitigate potential risks. We attempted to determine whether legal setback distances between well-pad sites and the public are adequate in three shale plays. We reviewed geography, current statutes and regulations, evacuations, thermal modeling, air pollution studies, and vapor cloud modeling within the Marcellus, Barnett, and Niobrara Shale Plays. The evidence suggests that presently utilized setbacks may leave the public vulnerable to explosions, radiant heat, toxic gas clouds, and air pollution from hydraulic fracturing activities. Our results suggest that setbacks may not be sufficient to reduce potential threats to human health in areas where hydraulic fracturing occurs. It is more likely that a combination of reasonable setbacks with controls for other sources of pollution associated with the process will be required. Haley M, McCawley M, Epstein AC, Arrington B, Bjerke EF. 2016. Adequacy of current state setbacks for directional high-volume hydraulic fracturing in the Marcellus, Barnett, and Niobrara Shale Plays. Environ Health Perspect 124:1323-1333; http://dx.doi.org/10.1289/ehp.1510547.

Thermo-mechanical properties of high aspect ratio silica nanofiber filled epoxy composites

NASA Astrophysics Data System (ADS)

Ren, Liyun

The optimization of thermo-mechanical properties of polymer composites at low filler loadings is of great interest in both engineering and scientific fields. There have been several studies on high aspect ratio fillers as novel reinforcement phase for polymeric materials. However, facile synthesis method of high aspect ratio nanofillers is limited. In this study, a scalable synthesis method of high aspect ratio silica nanofibers is going to be presented. I will also demonstrate that the inclusion of high aspect ratio silica nanofibers in epoxy results in a significant improvement of epoxy thermo-mechanical properties at low filler loadings. With silica nanofiber concentration of 2.8% by volume, the Young's modulus, ultimate tensile strength and fracture toughness of epoxy increased ~23, ~28 and ~50%, respectively, compared to unfilled epoxy. At silica nanofiber volume concentration of 8.77%, the thermal expansion coefficient decreased by ˜40% and the thermal conductivity was improved by ˜95% at room temperature. In the current study, the influence of nano-sized silica filler aspect ratio on mechanical and thermal behavior of epoxy nanocomposites were studied by comparing silica nanofibers to spherical silica nanoparticles (with aspect ratio of one) at various filler loadings. The significant reinforcement of composite stiffness is attributed to the variation of the local stress state in epoxy due to the high aspect ratio of the silica nanofiber and the introduction of a tremendous amount of interfacial area between the nanofillers and the epoxy matrix. The fracture mechanisms of silica nanofiber filled epoxy were also investigated. The existence of high aspect ratio silica nanofiber promotes fracture energy dissipation by crack deflection, crack pinning as well as debonding with fiber pull-out leading to enhanced fracture toughness. High aspect ratio fillers also provide significant reduction of photon scattering due to formation of a continuous fiber network within the composite. The resulting silica nanofiber filled epoxy would be widely applicable as underfill and encapsulant in advanced electronic packaging industry because of its electrically insulating, low cost and ease of processability.

Mechanical characterization of hydroxyapatite, thermoelectric materials and doped ceria

NASA Astrophysics Data System (ADS)

Fan, Xiaofeng

For a variety of applications of brittle ceramic materials, porosity plays a critical role structurally and/or functionally, such as in engineered bone scaffolds, thermoelectric materials and in solid oxide fuel cells. The presence of porosity will affect the mechanical properties, which are essential to the design and application of porous brittle materials. In this study, the mechanical property versus microstructure relations for bioceramics, thermoelectric (TE) materials and solid oxide fuel cells were investigated. For the bioceramic material hydroxyapatite (HA), the Young's modulus was measured using resonant ultrasound spectroscopy (RUS) as a function of (i) porosity and (ii) microcracking damage state. The fracture strength was measured as a function of porosity using biaxial flexure testing, and the distribution of the fracture strength was studied by Weibull analysis. For the natural mineral tetrahedrite based solid solution thermoelectric material (Cu10Zn2As4S13 - Cu 12Sb4S13), the elastic moduli, hardness and fracture toughness were studied as a function of (i) composition and (ii) ball milling time. For ZiNiSn, a thermoelectric half-Heusler compound, the elastic modulus---porosity and hardness---porosity relations were examined. For the solid oxide fuel cell material, gadolina doped ceria (GDC), the elastic moduli including Young's modulus, shear modulus, bulk modulus and Poisson's ratio were measured by RUS as a function of porosity. The hardness was evaluated by Vickers indentation technique as a function of porosity. The results of the mechanical property versus microstructure relations obtained in this study are of great importance for the design and fabrication of reliable components with service life and a safety factor. The Weibull modulus, which is a measure of the scatter in fracture strength, is the gauge of the mechanical reliability. The elastic moduli and Poisson's ratio are needed in analytical or numerical models of the thermal and mechanical stresses arising from in-service thermal gradients, thermal transients and/or mechanical loading. Hardness is related to a material's wear resistance and machinability, which are two essential considerations in fabrication and application.

Geothermal Reservoir Well Stimulation Program: technology transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1980-05-01

Each of the following types of well stimulation techniques are summarized and explained: hydraulic fracturing; thermal; mechanical, jetting, and drainhole drilling; explosive and implosive; and injection methods. Current stimulation techniques, stimulation techniques for geothermal wells, areas of needed investigation, and engineering calculations for various techniques. (MHR)

Mechanical properties of neat polymer matrix materials and their unidirectional carbon fiber-reinforced composites

NASA Technical Reports Server (NTRS)

Zimmerman, Richard S.; Adams, Donald F.

1988-01-01

The mechanical properties of two neat resin systems for use in carbon fiber epoxy composites were characterized. This included tensile and shear stiffness and strengths, coefficients of thermal and moisture expansion, and fracture toughness. Tests were conducted on specimens in the dry and moisture-saturated states, at temperatures of 23, 82 and 121 C. The neat resins tested were American Cyanamid 1806 and Union Carbide ERX-4901B(MPDA). Results were compared to previously tested neat resins. Four unidirectional carbon fiber reinforced composites were mechanically characterized. Axial and transverse tension and in-plane shear strengths and stiffness were measured, as well as transverse coefficients of thermal and moisture expansion. Tests were conducted on dry specimens only at 23 and 100 C. The materials tested were AS4/3502, AS6/5245-C, T300/BP907, and C6000/1806 unidirectional composites. Scanning electron microscopic examination of fracture surfaces was performed to permit the correlation of observed failure modes with the environmental test conditions.

Time/Temperature Dependent Tensile Strength of SiC and Al2O3-Based Fibers

NASA Technical Reports Server (NTRS)

Yun, Hee Mann; DiCarlo, James A.

1997-01-01

In order to understand and model the thermomechanical behavior of fiber-reinforced composites, stress-rupture, fast-fracture, and warm-up rupture studies were conducted on various advanced SiC and Al2O3-based fibers in the,temperature range from 20 to 1400 C in air as well as in inert environments. The measured stress-rupture, fast fracture, and warm-up rupture strengths were correlated into a single master time/temperature-dependent strength plot for each fiber type using thermal activation and slow crack growth theories. It is shown that these plots are useful for comparing and selecting fibers for CMC and MMC reinforcement and that, in comparison to stress rupture tests, the fast-fracture and warm-up tests can be used for rapid generation of these plots.

An integrated methodology for sub-surface fracture characterization using microseismic data: A case study at the NW Geysers

NASA Astrophysics Data System (ADS)

Aminzadeh, Fred; Tafti, Tayeb A.; Maity, Debotyam

2013-04-01

Geothermal and unconventional hydrocarbon reservoirs are often characterized by low permeability and porosity. So, they are difficult to produce and require stimulation techniques, such as thermal shear deactivation and hydraulic fracturing. Fractures provide porosity for fluid storage and permeability for fluid movement and play an important role in production from this kind of reservoirs. Hence, characterization of fractures has become a vitally important consideration in every aspect of exploration, development and production so as to provide additional energy resources for the world. During the injection or production of fluid, induced seismicity (micro-seismic events) can be caused by reactivated shears created fractures or the natural fractures in shear zones and faults. Monitoring these events can help visualize fracture growth during injection stimulation. Although the locations of microseismic events can be a useful characterization tool and have been used by many authors, we go beyond these locations to characterize fractures more reliably. Tomographic inversion, fuzzy clustering, and shear wave splitting are three methods that can be applied to microseismic data to obtain reliable characteristics about fractured areas. In this article, we show how each method can help us in the characterization process. In addition, we demonstrate how they can be integrated with each other or with other data for a more holistic approach. The knowledge gained might be used to optimize drilling targets or stimulation jobs to reduce costs and maximize production. Some of the concepts discussed in this paper are general in nature, and may be more applicable to unconventional hydrocarbon reservoirs than the metamorphic and igneous reservoir rocks at The Geysers geothermal field.

Post-depositional fracturing and subsidence of pumice flow deposits: Lascar Volcano, Chile.

PubMed

Whelley, Patrick L; Jay, J; Calder, E S; Pritchard, M E; Cassidy, N J; Alcaraz, S; Pavez, A

Unconsolidated pyroclastic flow deposits of the 1993 eruption of Lascar Volcano, Chile, have, with time, become increasingly dissected by a network of deeply penetrating fractures. The fracture network comprises orthogonal sets of decimeter-wide linear voids that form a pseudo-polygonal grid visible on the deposit surface. In this work, we combine shallow surface geophysical imaging tools with remote sensing observations and direct field measurements of the deposit to investigate these fractures and their underlying causal mechanisms. Based on ground penetrating radar images, the fractures are observed to have propagated to depths of up to 10 m. In addition, orbiting radar interferometry shows that deposit subsidence of up to 1 cm/year -1 occurred between 1993 and 1996 with continued subsidence occurring at a slower rate thereafter. In situ measurements show that 1 m below the surface, the 1993 deposits remain 5°C to 15°C hotter, 18 years after emplacement, than adjacent deposits. Based on the observed subsidence as well as estimated cooling rates, the fractures are inferred to be the combined result of deaeration, thermal contraction, and sedimentary compaction in the months to years following deposition. Significant environmental factors, including regional earthquakes in 1995 and 2007, accelerated settling at punctuated moments in time. The spatially variable fracture pattern relates to surface slope and lithofacies variations as well as substrate lithology. Similar fractures have been reported in other ignimbrites but are generally exposed only in cross section and are often attributed to formation by external forces. Here we suggest that such interpretations should be invoked with caution, and deformation including post-emplacement subsidence and fracturing of loosely packed ash-rich deposits in the months to years post-emplacement is a process inherent in the settling of pyroclastic material.

2017 GTO Project review Laboratory Evaluation of EGS Shear Stimulation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauer, Stephen J.

The objectives and purpose of this research has been to produce laboratory-based experimental and numerical analyses to provide a physics-based understanding of shear stimulation phenomena (hydroshearing) and its evolution during stimulation. Water was flowed along fractures in hot and stressed fractured rock, to promote slip. The controlled laboratory experiments provide a high resolution/high quality data resource for evaluation of analysis methods developed by DOE to assess EGS “behavior” during this stimulation process. Segments of the experimental program will provide data sets for model input parameters, i.e., material properties, and other segments of the experimental program will represent small scale physicalmore » models of an EGS system, which may be modeled. The coupled lab/analysis project has been a study of the response of a fracture in hot, water-saturated fractured rock to shear stress experiencing fluid flow. Under this condition, the fracture experiences a combination of potential pore pressure changes and fracture surface cooling, resulting in slip along the fracture. The laboratory work provides a means to assess the role of “hydroshearing” on permeability enhancement in reservoir stimulation. Using the laboratory experiments and results to define boundary and input/output conditions of pore pressure, thermal stress, fracture shear deformation and fluid flow, and models were developed and simulations completed by the University of Oklahoma team. The analysis methods are ones used on field scale problems. The sophisticated numerical models developed contain parameters present in the field. The analysis results provide insight into the role of fracture slip on permeability enhancement-“hydroshear” is to be obtained. The work will provide valuable input data to evaluate stimulation models, thus helping design effective EGS.« less

In-vitro performance and fracture strength of thin monolithic zirconia crowns

PubMed Central

Weigl, Paul; Wu, Yanyun; Felber, Roland; Lauer, Hans-Christoph

2018-01-01

PURPOSE All-ceramic restorations required extensive tooth preparation. The purpose of this in vitro study was to investigate a minimally invasive preparation and thickness of monolithic zirconia crowns, which would provide sufficient mechanical endurance and strength. MATERIALS AND METHODS Crowns with thickness of 0.2 mm (group 0.2, n=32) or of 0.5 mm (group 0.5, n=32) were milled from zirconia and fixed with resin-based adhesives (groups 0.2A, 0.5A) or zinc phosphate cements (groups 0.2C, 0.5C). Half of the samples in each subgroup (n=8) underwent thermal cycling and mechanical loading (TCML)(TC: 5℃ and 55℃, 2×3,000 cycles, 2 min/cycle; ML: 50 N, 1.2×106 cycles), while the other samples were stored in water (37℃/24 h). Survival rates were compared (Kaplan-Maier). The specimens surviving TCML were loaded to fracture and the maximal fracture force was determined (ANOVA; Bonferroni; α=.05). The fracture mode was analyzed. RESULTS In both 0.5 groups, all crowns survived TCML, and the comparison of fracture strength among crowns with and without TCML showed no significant difference (P=.628). Four crowns in group 0.2A and all of the crowns in group 0.2C failed during TCML. The fracture strength after 24 hours of the cemented 0.2 mm-thick crowns was significantly lower than that of adhesive bonded crowns. All cemented crowns provided fracture in the crown, while about 80% of the adhesively bonded crowns fractured through crown and die. CONCLUSION 0.5 mm thick monolithic crowns possessed sufficient strength to endure physiologic performance, regardless of the type of cementation. Fracture strength of the 0.2 mm cemented crowns was too low for clinical application. PMID:29713427

Refined Three-Dimensional Modelling of Thermally-Driven Flow in the Bormio System (Central Italian Alps)

NASA Astrophysics Data System (ADS)

Volpi, Giorgio; Riva, Federico; Frattini, Paolo; Battista Crosta, Giovanni; Magri, Fabien

2016-04-01

Thermal springs are widespread in the European Alps, where more than 80 geothermal sites are known and exploited. The quantitative assessment of those thermal flow systems is a challenging issue and requires accurate conceptual model and a thorough understanding of thermo-hydraulic properties of the aquifers. Accordingly in the last years, several qualitative studies were carried out to understand the heat and fluid transport processes driving deep fluids from the reservoir to the springs. Our work focused on thermal circulation and fluid outflows of the area around Bormio (Central Italian Alps), where nine geothermal springs discharge from dolomite bodies located close to a regional alpine thrust, called the Zebrù Line. At this site, water is heated in deep circulation systems and vigorously upwells at temperature of about 40°C. The aim of this paper is to explore the mechanisms of heat and fluid transport in the Bormio area by carrying out refined steady and transient three-dimensional finite element simulations of thermally-driven flow and to quantitatively assess the source area of the thermal waters. The full regional model (ca. 700 km2) is discretized with a highly refined triangular finite element planar grid obtained with Midas GTS NX software. The structural 3D features of the regional Zebrù thrust are built by interpolating series of geological cross sections using Fracman. A script was developed to convert and implement the thrust grid into FEFLOW mesh that comprises ca. 4 million elements. The numerical results support the observed discharge rates and temperature field within the simulated domain. Flow and temperature patterns suggest that thermal groundwater flows through a deep system crossing both sedimentary and metamorphic lithotypes, and a fracture network associated to the thrust system. Besides providing a numerical framework to simulate complex fractured systems, this example gives insights into the influence of deep alpine structures on groundwater circulation that underlies the development of many hydrothermal systems.

Hydrogeologic characterization of a fractured granitic rock aquifer, Raymond, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cohen, Andrew J.B.

1993-10-01

The hydrogeologic properties of a shallow, fractured granitic rock aquifer in the foothills of the Sierra Nevada, California were investigated via the analysis of borehole geophysical logs and pumping tests. The drawdowns produced during these tests are not indicative of any simple conceptual aquifer model, and borehole logs show that the granite is intensely fractured. These observations are suggestive of a complex fracture-flow geometry which is extremely difficult to decipher. However, through the measurement of orientations of individual subsurface fractures from acoustic televiewer logs, and correlation between particular fractures and electrical resistivity and thermal-pulse flowmeter logs, it was found thatmore » the aquifer is, in general, comprised of two subhorizontal and nearly parallel zones of unloading fractures. Downhole flowmeter measurements taken in several wells provide further evidence for the inferred dual-layer structure of the aquifer, as well as yield quantitative measures of the contribution of flow from each zone. Analysis of drawdowns in pumped wells reveals that there are zones of relatively high transmissivity immediately around them. It was found that these properties, as well as a nearby zone of lower transmissivity, can account for their observed drawdowns. A numerical model was constructed to test whether these major heterogeneities could also account for the drawdowns in observation wells. This stepwise analysis of both the geophysical and hydrological data resulted in the formulation of a conceptual model of the aquifer which is consistent with observations, and which can account for its behavior when subjected to pumping.« less

Effect of ferrule on the fracture resistance of mandibular premolars with prefabricated posts and cores

PubMed Central

2017-01-01

PURPOSE This study evaluated fracture resistance with regard to ferrule lengths and post reinforcement on endodontically treated mandibular premolars incorporating a prefabricated post and resin core. MATERIALS AND METHODS One hundred extracted mandibular premolars were randomly divided into 5 groups (n=20): intact teeth (NR); endodontically treated teeth (ETT) without post (NP); ETT restored with a prefabricated post with ferrule lengths of either 0 mm (F0), 1 mm (F1), or 2 mm (F2). Prepared teeth were restored with metal crowns. A thermal cycling test was performed for 1,000 cycles. Loading was applied at an angle of 135 degrees to the axis of the tooth using a universal testing machine with a crosshead speed of 2.54 mm/min. Fracture loads were analyzed by one-way ANOVA and Tukey HSD test using a statistical program (α=.05). RESULTS There were statistical differences in fracture loads among groups (P<.001). The fracture load of F2 (237.7 ± 83.4) was significantly higher than those of NP (155.6 ± 74.3 N), F0 (98.8 ± 43.3 N), and F1 (152.8 ± 78.5 N) (P=.011, P<.001, and P=.008, respectively). CONCLUSION Fracture resistance of ETT depends on the length of the ferrule, as shown by the significantly increased fracture resistance in the 2 mm ferrule group (F2) compared to the groups with shorter ferrule lengths (F0, F1) and without post (NP). PMID:29142639

Stress-induced, time-dependent fracture closure at hydrothermal conditions

USGS Publications Warehouse

Beeler, N.M.; Hickman, S.H.

2004-01-01

Time-dependent closure of fractures in quartz was measured in situ at 22-530??C temperature and 0.1-150 MPa water pressure. Unlike previous crack healing and rock permeability studies, in this study, fracture aperture is monitored directly and continuously using a windowed pressure vessel, a long-working-distance microscope, and reflected-light interferometry. Thus the fracture volume and geometry can be measured as a function of time, temperature, and water pressure. Relatively uniform closure occurs rapidly at temperatures and pressures where quartz becomes significantly soluble in water. During closure the aperture is reduced by as much as 80% in a few hours. We infer that this closure results from the dissolution of small particles or asperities that prop the fracture open. The driving force for closure via dissolution of the prop is the sum of three chemical potential terms: (1) the dissolution potential, proportional to the logarithm of the degree of undersaturation of the solution; (2) the coarsening potential, proportional to the radius of curvature of the prop; and (3) the pressure solution potential, proportional to the effective normal stress at the contact between propping particles and the fracture wall. Our observations suggest that closure is controlled by a pressure solution-like process. The aperture of dilatant fractures and microcracks in the Earth that are similar to those in our experiments, such as ones generated from thermal stressing or brittle failure during earthquake rupture and slip, will decrease rapidly with time, especially if the macroscopic stress is nonhydrostatic.

Stress-induced, time-dependent fracture closure at hydrothermal conditions

NASA Astrophysics Data System (ADS)

Beeler, N. M.; Hickman, S. H.

2004-02-01

Time-dependent closure of fractures in quartz was measured in situ at 22-530°C temperature and 0.1-150 MPa water pressure. Unlike previous crack healing and rock permeability studies, in this study, fracture aperture is monitored directly and continuously using a windowed pressure vessel, a long-working-distance microscope, and reflected-light interferometry. Thus the fracture volume and geometry can be measured as a function of time, temperature, and water pressure. Relatively uniform closure occurs rapidly at temperatures and pressures where quartz becomes significantly soluble in water. During closure the aperture is reduced by as much as 80% in a few hours. We infer that this closure results from the dissolution of small particles or asperities that prop the fracture open. The driving force for closure via dissolution of the prop is the sum of three chemical potential terms: (1) the dissolution potential, proportional to the logarithm of the degree of undersaturation of the solution; (2) the coarsening potential, proportional to the radius of curvature of the prop; and (3) the pressure solution potential, proportional to the effective normal stress at the contact between propping particles and the fracture wall. Our observations suggest that closure is controlled by a pressure solution-like process. The aperture of dilatant fractures and microcracks in the Earth that are similar to those in our experiments, such as ones generated from thermal stressing or brittle failure during earthquake rupture and slip, will decrease rapidly with time, especially if the macroscopic stress is nonhydrostatic.

Ultra high temperature ceramics for hypersonic vehicle applications.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tandon, Rajan; Dumm, Hans Peter; Corral, Erica L.

2006-01-01

HfB{sub 2} and ZrB{sub 2} are of interest for thermal protection materials because of favorable thermal stability, mechanical properties, and oxidation resistance. We have made dense diboride ceramics with 2 to 20 % SiC by hot pressing at 2000 C and 5000 psi. High-resolution transmission electron microscopy (TEM) shows very thin grain boundary phases that suggest liquid phase sintering. Fracture toughness measurements give RT values of 4 to 6 MPam{sup 1/2}. Four-pt flexure strengths measured in air up to 1450 C were as high as 450-500 MPa. Thermal diffusivities were measured to 2000 C for ZrB{sub 2} and HfB{sub 2}more » ceramics with SiC contents from 2 to 20%. Thermal conductivities were calculated from thermal diffusivities and measured heat capacities. Thermal diffusivities were modeled using different two-phase composite models. These materials exhibit excellent high temperature properties and are attractive for further development for thermal protection systems.« less

Temperature dependence of thermal pressure for NaCl

NASA Astrophysics Data System (ADS)

Singh, Chandra K.; Pande, Brijesh K.; Pandey, Anjani K.

2018-05-01

Engineering applications of the materials can be explored upto the desired limit of accuracy with the better knowledge of its mechanical and thermal properties such as ductility, brittleness and Thermal Pressure. For the resistance to fracture (K) and plastic deformation (G) the ratio K/G is treated as an indication of ductile or brittle character of solids. In the present work we have tested the condition of ductility and brittleness with the calculated values of K/G for the NaCl. It is concluded that the nature of NaCl can be predicted upto high temperature simply with the knowledge of its elastic stiffness constant only. Thermoelastic properties of materials at high temperature is directly related to thermal pressure and volume expansion of the materials. An expression for the temperature dependence of thermal pressure is formulated using basic thermodynamic identities. It is observed that thermal pressure ΔPth calculated for NaCl by using Kushwah formulation is in good agreement with the experimental values also the thermal pressure increases with the increase in temperature.

Damage Accumulation and Failure of Plasma-Sprayed Thermal Barrier Coatings under Thermal Gradient Cyclic Conditions

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Choi, Sung R.; Ghosn, Louis J.; Miller, rober A.

2005-01-01

Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future engine higher fuel efficiency and lower emission goals. A fundamental understanding of the sintering and thermal cycling induced delamination of thermal barrier coating systems under engine-like heat flux conditions will potentially help to improve the coating temperature capability. In this study, a test approach is established to emphasize the real-time monitoring and assessment of the coating thermal conductivity, which can initially increase under the steady-state high temperature thermal gradient test due to coating sintering, and later decrease under the thermal gradient cyclic test due to coating cracking and delamination. Thermal conductivity prediction models have been established for a ZrO2-(7- 8wt%)Y2O3 model coating system in terms of heat flux, time, and testing temperatures. The coating delamination accumulation is then assessed based on the observed thermal conductivity response under the combined steady-state and cyclic thermal gradient tests. The coating thermal gradient cycling associated delaminations and failure mechanisms under simulated engine heat-flux conditions will be discussed in conjunction with the coating sintering and fracture testing results.

Fracture in Phenolic Impregnated Carbon Ablator

NASA Technical Reports Server (NTRS)

Agrawal, Parul; Chavez-Garcia, Jose F.

2011-01-01

The thermal protection materials used for spacecraft heat shields are subjected to various thermal-mechanical loads during an atmospheric reentry which can threaten the structural integrity of the system. This paper discusses the development of a novel technique to understand the failure mechanisms inside the thermal protection material, Phenolic Impregnated Carbon Ablator (PICA). PICA has successfully flown on the Stardust spacecraft and was the TPS material chosen for the Mars Science Laboratory (MSL), that will fly in 2011. Although PICA has good thermal properties, structurally, it is a weak material. To thoroughly understand failure in PICA, experiments were performed using FiberForm(Registered TradeMark) (precursor of PICA), virgin and furnace-charred PICA. Several small samples were tested inside an electron microscope to investigate the failure mechanisms. Micrographs were obtained before and after the failure in order to study crack initiation and growth. Videos were obtained to capture failure mechanisms in real time. Stress-strain data was obtained simultaneously for all the samples with the help of a data acquisition system, integrated to the mechanical stages. It was found that cracks initiated and grew in the FiberForm when a critical stress limit was reached such that the carbon fibers separated from the binder. However, both for virgin and charred PICA, crack initiation and growth occurred in the matrix (phenolic) phase. Both virgin and charred PICA showed greater strength values compared to FiberForm coupons, confirming that the presence of the porous matrix helps in absorbing the fracture energy.

[Interface bond and compatibility between GI-II glass/alumina composite and Vitadur alpha veneering porcelain].

PubMed

Meng, Yukun; Chao, Yonglie; Liao, Yunmao

2002-01-01

Multiple layer techniques were commonly employed in fabricating all-ceramic restorations. Bond and compatibility between layers were vitally important for the clinical success of the restorations. The purposes of this study were to investigate the bond of the interface between the GI-II glass/alumina composite and Vitadur alpha veneering porcelain, and to study the thermal compatibility between them. Prepared a bar shaped specimen of GI-II glass/alumina composite 25 mm x 5 mm x 1 mm in size, with bottom surface pre-notched. The upper surface was veneered with Vitadur alpha veneering porcelain (0.2 mm opaque dentin and 0.6 mm dentin porcelain), then fractured and the fracture surface were examined under scanning electron microscope (SEM) and electron microprobe analyzer (EMPA) with electron beam of 10 micrometer in diameter; ten all-ceramic single crowns for an upper right central incisor were fabricated and the temperatures of thermal shock resistance were tested. SEM observation showed tight bond between the composite and the porcelain; The results of EMPA showed that penetration of Na, Al elements from glass/alumina into veneering porcelain and Si, K, Ca elements from veneering porcelain into glass/alumina occurred after sintering baking; The temperature of thermal shock resistance for anterior crowns in this study was 158 +/- 10.3 degrees C, cracks were mainly distributed in veneering porcelain with thicker layer. Chemical bond exists between the GI-II glass/alumina composite and Vitadur alpha veneering porcelain, and there is good thermal compatibility between them.

Structural and heat-flow implications of infrared anomalies at Mt. Hood, Oregon

USGS Publications Warehouse

Friedman, Jules D.; Frank, David

1977-01-01

Surface thermal features occur in an area of 9700 m2 at Mt. Hood, on the basis of an aerial line-scan survey made April 26, 1973. The distribution of the thermal areas below the summit of Mt. Hood, shown on planimetrically corrected maps at 1:12,000, suggests structural control by a fracture system and brecciated zone peripheral to a hornblende-dacite plug dome (Crater Rock), and by a concentric fracture system that may have been associated with development of the present crater. The extent and inferred temperature of the thermal areas permits a preliminary estimate of a heat discharge of 10 megawatts, by analogy with similar fumarole and thermal fields of Mt. Baker, Washington. This figure includes a heat loss of 4 megawatts (MW) via conduction, diffusion, evaporation, and radiation to the atmosphere, and a somewhat less certain loss of 6MW via fumarolic mass transfer of vapor and advective heat loss from runoff and ice melt. The first part of the estimate is based on two-point models for differential radiant exitance and differential flux via conduction, diffusion, evaporation, and radiation from heat balance of the ground surface. Alternate methods for estimating volcanogenic geothermal flux that assume a quasi-steady state heat flow also yield estimates in the 5-11 MW range. Heat loss equivalent to cooling of the dacite plug dome is judged to be insufficient to account for the heat flux at the fumarole fields.

Diagenetic alteration of impact spherules in the Neoarchean Monteville layer, South Africa

USGS Publications Warehouse

Kohl, I.; Simonson, B.M.; Berke, M.

2006-01-01

Intercontinental correlation of distal Archean impact ejecta layers can be used to help create a global time-stratigraphic framework for early Earth events. For example, an impact spherule layer in the Neoarchean Monteville Formation (Griqualand West Basin, South Africa) may be correlated with layers in one or more formations in Western Australia. To help assess the degree to which diagenetic alteration would hinder such correlations, we performed a petrographic study of spherules in the Monteville layer. Most of the spherules in the Monteville layer have botryoidal rims composed of radial-fibrous K-feldspar, but compaction and replacement have greatly altered their appearance and mineralogy. Moreover, the Monteville spherule layer consists of three main subunits, and spherule compaction varies between subunits as well as across the Griqualand West region. Compaction is about three times greater in a medial spherulerich subunit as compared to a basal subunit rich in large intraclasts, resulting in better preservation of the shapes of melt particles in the latter. However, spherule rims have omparable numbers of fractures in both subunits, indicating the melt particles were fractured prior to compaction. Some spherules contain mica ribbons with a septarian geometry. Fracturing via rapid thermal quenching could help explain all of these features. f hot spherules possessing crystalline rims were thermally shocked when they hit the ocean, fractures would have the observed geometries and provide pathways for fluid infiltration and local replacement of glass by mica. Although heavily distorted, impact spherules in the Monteville layer are very similar to those in the Hesta occurrence of the Neoarchean Jeerinah spherule layer of the Hamersley Basin, even showing similar diagenetic histories. In this instance, diagenetic alteration may actually help rather than hinder intercontinental correlation of impact spherule layers. ??2006 Geological Society of America.

Seismic and aseismic deformations and impact on reservoir permeability: The case of EGS stimulation at The Geysers, California, USA

DOE PAGES

Jeanne, Pierre; Rutqvist, Jonny; Rinaldi, Antonio Pio; ...

2015-10-27

In this paper, we use the Seismicity-Based Reservoir Characterization approach to study the spatiotemporal dynamics of an injection-induced microseismic cloud, monitored during the stimulation of an enhanced geothermal system, and associated with the Northwest Geysers Enhanced Geothermal System (EGS) Demonstration project (California). We identified the development of a seismically quiet domain around the injection well surrounded by a seismically active domain. Then we compare these observations with the results of 3-D Thermo-Hydro-Mechanical simulations of the EGS, which accounts for changes in permeability as a function of the effective normal stress and the plastic strain. The results of our modeling showmore » that the aseismic domain is caused by both the presence of the injected cold water and by thermal processes. These thermal processes cause a cooling-stress reduction, which prevent shear reactivation and favors fracture opening by reducing effective normal stress and locally increasing the permeability. This process is accompanied by aseismic plastic shear strain. In the seismic domain, microseismicity is caused by the reactivation of the preexisting fractures, resulting from an increase in injection-induced pore pressure. Our modeling indicates that in this domain, permeability evolves according to the effective normal stress acting on the shear zones, whereas shearing of preexisting fractures may have a low impact on permeability. We attribute this lack of permeability gain to the fact that the initial permeabilities of these preexisting fractures are already high (up to 2 orders of magnitude higher than the host rock) and may already be fully dilated by past tectonic straining.« less

Seismic and aseismic deformations and impact on reservoir permeability: The case of EGS stimulation at The Geysers, California, USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeanne, Pierre; Rutqvist, Jonny; Rinaldi, Antonio Pio

In this paper, we use the Seismicity-Based Reservoir Characterization approach to study the spatiotemporal dynamics of an injection-induced microseismic cloud, monitored during the stimulation of an enhanced geothermal system, and associated with the Northwest Geysers Enhanced Geothermal System (EGS) Demonstration project (California). We identified the development of a seismically quiet domain around the injection well surrounded by a seismically active domain. Then we compare these observations with the results of 3-D Thermo-Hydro-Mechanical simulations of the EGS, which accounts for changes in permeability as a function of the effective normal stress and the plastic strain. The results of our modeling showmore » that the aseismic domain is caused by both the presence of the injected cold water and by thermal processes. These thermal processes cause a cooling-stress reduction, which prevent shear reactivation and favors fracture opening by reducing effective normal stress and locally increasing the permeability. This process is accompanied by aseismic plastic shear strain. In the seismic domain, microseismicity is caused by the reactivation of the preexisting fractures, resulting from an increase in injection-induced pore pressure. Our modeling indicates that in this domain, permeability evolves according to the effective normal stress acting on the shear zones, whereas shearing of preexisting fractures may have a low impact on permeability. We attribute this lack of permeability gain to the fact that the initial permeabilities of these preexisting fractures are already high (up to 2 orders of magnitude higher than the host rock) and may already be fully dilated by past tectonic straining.« less

FEMCAM Analysis of SULTAN Test Results for ITER Nb3SN Cable-conduit Conductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuhu Zhai, Pierluigi Bruzzone, Ciro Calzolaio

2013-03-19

Performance degradation due to filament fracture of Nb3 Sn cable-in-conduit conductors (CICCs) is a critical issue in large-scale magnet designs such as ITER which is currently being constructed in the South of France. The critical current observed in most SULTAN TF CICC samples is significantly lower than expected and the voltage-current characteristic is seen to have a much broader transition from a single strand to the CICC. Moreover, most conductors exhibit the irreversible degradation due to filament fracture and strain relaxation under electromagnetic cyclic loading. With recent success in monitoring thermal strain distribution and its evolution under the electromagnetic cyclicmore » loading from in situ measurement of critical temperature, we apply FEMCAM which includes strand filament breakage and local current sharing effects to SULTAN tested CICCs to study Nb3 Sn strain sensitivity and irreversible performance degradation. FEMCAM combines the thermal bending effect during cool down and the EM bending effect due to locally accumulating Lorentz force during magnet operation. It also includes strand filament fracture and related local current sharing for the calculation of cable n value. In this paper, we model continuous performance degradation under EM cyclic loading based on strain relaxation and the transition broadening upon cyclic loading to the extreme cases seen in SULTAN test data to better quantify conductor performance degradation.« less

Effect of Particle and Carbide Grain Sizes on a HVOAF WC-Co-Cr Coating for the Future Application on Internal Surfaces: Microstructure and Wear

NASA Astrophysics Data System (ADS)

Pulsford, J.; Kamnis, S.; Murray, J.; Bai, M.; Hussain, T.

2018-01-01

The use of nanoscale WC grain or finer feedstock particles is a possible method of improving the performance of WC-Co-Cr coatings. Finer powders are being pursued for the development of coating internal surfaces, as less thermal energy is required to melt the finer powder compared to coarse powders, permitting spraying at smaller standoff distances. Three WC-10Co-4Cr coatings, with two different powder particle sizes and two different carbide grain sizes, were sprayed using a high velocity oxy-air fuel (HVOAF) thermal spray system developed by Castolin Eutectic-Monitor Coatings Ltd., UK. Powder and coating microstructures were characterized using XRD and SEM. Fracture toughness and dry sliding wear performance at three loads were investigated using a ball-on-disk tribometer with a WC-Co counterbody. It was found that the finer powder produced the coating with the highest microhardness, but its fracture toughness was reduced due to increased decarburization compared to the other powders. The sprayed nanostructured powder had the lowest microhardness and fracture toughness of all materials tested. Unlubricated sliding wear testing at the lowest load showed the nanostructured coating performed best; however, at the highest load this coating showed the highest specific wear rates with the other two powders performing to a similar, better standard.

Thermomechanics of candidate coatings for advanced gas reactor fuels

NASA Astrophysics Data System (ADS)

Nosek, A.; Conzen, J.; Doescher, H.; Martin, C.; Blanchard, J.

2007-09-01

Candidate fuel/coating combinations for an advanced, coated-fuel particle for a gas-cooled fast reactor (GFR) have been evaluated. These all-ceramic fuel forms consist of a fuel kernel made of UC or UN, surrounded with two shells (a buffer and a coating) made of TiC, SiC, ZrC, TiN, or ZrN. These carbides and nitrides are analyzed with finite element models to determine the stresses produced in the micro fuel particles from differential thermal expansion, fission gas release, swelling, and creep during particle fabrication and reactor operation. This study will help determine the feasibility of different fuel and coating combinations and identify the critical loads. The analysis shows that differential thermal expansion of the fuel and coating dictate the amount of stress for changing temperatures (such as during fabrication), and that the coating creep is able to mitigate an otherwise overwhelming amount of stress from fuel swelling. Because fracture is a likely mode of failure, a fracture mechanics study is also included to identify the relative likelihood of catastrophic fracture of the coating and resulting gas release. Overall, the analysis predicts that UN/ZrC is the best thermomechanical fuel/coating combination for mitigating the stress within the new fuel particle, but UN/TiN and UN/ZrN could also be strong candidates if their unknown creep rates are sufficiently large.

Thermally anomalous features in the subsurface of Enceladus's south polar terrain

NASA Astrophysics Data System (ADS)

Le Gall, A.; Leyrat, C.; Janssen, M. A.; Choblet, G.; Tobie, G.; Bourgeois, O.; Lucas, A.; Sotin, C.; Howett, C.; Kirk, R.; Lorenz, R. D.; West, R. D.; Stolzenbach, A.; Massé, M.; Hayes, A. H.; Bonnefoy, L.; Veyssière, G.; Paganelli, F.

2017-03-01

Saturn's moon Enceladus is an active world. In 2005, the Cassini spacecraft witnessed for the first time water-rich jets venting from four anomalously warm fractures (called sulci) near its south pole1,2. Since then, several observations have provided evidence that the source of the material ejected from Enceladus is a large underground ocean, the depth of which is still debated3-6. Here, we report on the first and only opportunity that Cassini's RADAR instrument7,8 had to observe Enceladus's south polar terrain closely, targeting an area a few tens of kilometres north of the active sulci. Detailed analysis of the microwave radiometry observations highlights the ongoing activity of the moon. The instrument recorded the microwave thermal emission, revealing a warm subsurface region with prominent thermal anomalies that had not been identified before. These anomalies coincide with large fractures, similar or structurally related to the sulci. The observations imply the presence of a broadly distributed heat production and transport system below the south polar terrain with 'plate-like' features and suggest that a liquid reservoir could exist at a depth of only a few kilometres under the ice shell at the south pole. The detection of a possible dormant sulcus further suggests episodic geological activity.

An Investigation of High-Cycle Fatigue Models for Metallic Structures Exhibiting Snap-Through Response

NASA Technical Reports Server (NTRS)

Przekop, Adam; Rizzi, Stephen A.; Sweitzer, Karl A.

2007-01-01

A study is undertaken to develop a methodology for determining the suitability of various high-cycle fatigue models for metallic structures subjected to combined thermal-acoustic loadings. Two features of this problem differentiate it from the fatigue of structures subject to acoustic loading alone. Potentially large mean stresses associated with the thermally pre- and post-buckled states require models capable of handling those conditions. Snap-through motion between multiple post-buckled equilibrium positions introduces very high alternating stress. The thermal-acoustic time history response of a clamped aluminum beam structure with geometric and material nonlinearities is determined via numerical simulation. A cumulative damage model is employed using a rainflow cycle counting scheme and fatigue estimates are made for 2024-T3 aluminum using various non-zero mean fatigue models, including Walker, Morrow, Morrow with true fracture strength, and MMPDS. A baseline zero-mean model is additionally considered. It is shown that for this material, the Walker model produces the most conservative fatigue estimates when the stress response has a tensile mean introduced by geometric nonlinearity, but remains in the linear elastic range. However, when the loading level is sufficiently high to produce plasticity, the response becomes more fully reversed and the baseline, Morrow, and Morrow with true fracture strength models produce the most conservative fatigue estimates.

Fracture mechanics analysis for various fiber/matrix interface loadings

NASA Technical Reports Server (NTRS)

Naik, R. A.; Crews, J. H., Jr.

1991-01-01

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Fracture mechanics analysis for various fiber/matrix interface loadings

NASA Technical Reports Server (NTRS)

Naik, Rajiv A.; Crews, John H., Jr.

1992-01-01

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, theory avoiding fractional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Fracture mechanics analysis for various fiber/matrix interface loadings

NASA Technical Reports Server (NTRS)

Naik, R. A.; Crews, J. H., Jr.

1991-01-01

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. An F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Effect of coupling agent on durian skin fibre nanocomposite reinforced polypropylene

NASA Astrophysics Data System (ADS)

Siti Nur E'zzati, M. A.; Anuar, H.; Siti Munirah Salimah, A. R.

2018-01-01

This paper reports on the development of a composite-based natural fiber to reduce the reliance on petroleum-based product in order to amplify environmental awareness. The production of Durian Skin Nanofiber (DSNF) was conducted using biological fermentation method via rhizopus oryzae in order to obtain the nano dimension of the particle size. Polypropylene (PP) and DSNF were produced using Haake internal mixer via melt blending technique. The significant effect of maleic anhydride grafted polypropylene (MAPP) on the properties of PP/DSNF nanocomposite was investigated to study its mechanical properties which are tensile strength and thermal stability using thermogravimetric (TGA) and differential scanning analysis (DSC). The tensile property of PP nanocomposites increased from 33 MPa to 38 MPa with the presence of MAPP. The addition of MAPP also increased the thermal stability of PP/DSNF nanocomposite where the char residue increased by 52%. Besides that, the thermal degradation of PP/DSNF and PP/DSNF-MAPP were higher than PP where they exerted higher amount of weight loss at an elevated temperature. The percentage of crystallinity, %Xc, of PP nanocomposites improved with the addition of MAPP by 35% based on the differential scanning calorimetry (DSC) result. The SEM analysis showed that the PP/DSNF-MAPP exerts ductile fracture while PP/DSNF exerts brittle fracture.

Influence of fibre and filler reinforcement of plastic brackets: an in vitro study.

PubMed

Faltermeier, Andreas; Rosentritt, Martin; Faltermeier, Rupert; Müssig, Dieter

2007-06-01

In spite of their popularity in fulfilling aesthetic requirements, plastic brackets still present some disadvantages because of their low elastic modulus, decreased fracture toughness, and reduced wear resistance. Fibre-reinforced composites are well established in dentistry and consist of a polymer matrix in which reinforcing fibres are embedded. Stress is transferred from the polymer matrix to the fibres which present a high tensile strength. Hence, the mechanical properties of polymers could be improved. The purpose of this study was to compare fracture strength, fracture toughness and flexural strength of an experimental fibre-reinforced bracket material, an SiO(2) filler-reinforced bracket and an unfilled plastic bracket material (control group). Experimental brackets and specialized bars were manufactured. Tests were performed after thermal cycling (5 degrees C/55 degrees C) the samples in an artificial oral environment of a device to simulate mastication. Statistical evaluation was undertaken. The median, 25th and 75th percentiles were calculated and a Mann-Whitney U-test was performed. In this study two findings were obvious. (1) Filler reinforcement of plastic brackets improved fracture strength and fracture toughness in comparison with the unfilled bracket material. (2) Glass fibre reinforcement of orthodontic bracket materials resulted in the greatest enhancement of the mechanical properties in comparison with the other test groups. Therefore, the application of glass fibres in plastic brackets is a successful method to enhance fracture strength.

Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chopra, O. K.; Shack, W. J.

2008-01-21

In light water reactors, austenitic stainless steels (SSs) are used extensively as structural alloys in reactor core internal components because of their high strength, ductility, and fracture toughness. However, exposure to high levels of neutron irradiation for extended periods degrades the fracture properties of these steels by changing the material microstructure (e.g., radiation hardening) and microchemistry (e.g., radiation-induced segregation). Experimental data are presented on the fracture toughness and crack growth rates (CGRs) of wrought and cast austenitic SSs, including weld heat-affected-zone materials, that were irradiated to fluence levels as high as {approx} 2x 10{sup 21} n/cm{sup 2} (E > 1more » MeV) ({approx} 3 dpa) in a light water reactor at 288-300 C. The results are compared with the data available in the literature. The effects of material composition, irradiation dose, and water chemistry on CGRs under cyclic and stress corrosion cracking conditions were determined. A superposition model was used to represent the cyclic CGRs of austenitic SSs. The effects of neutron irradiation on the fracture toughness of these steels, as well as the effects of material and irradiation conditions and test temperature, have been evaluated. A fracture toughness trend curve that bounds the existing data has been defined. The synergistic effects of thermal and radiation embrittlement of cast austenitic SS internal components have also been evaluated.« less

Contact zone permeability at intrusion boundaries: New results from hydraulic testing and geophysical logging in the Newark Rift Basin, New York, USA

USGS Publications Warehouse

Matter, J.M.; Goldberg, D.S.; Morin, R.H.; Stute, M.

2006-01-01

Hydraulic tests and geophysical logging performed in the Palisades sill and the underlying sedimentary rocks in the NE part of the Newark Rift Basin, New York, USA, confirm that the particular transmissive zones are localized within the dolerite-sedimentary rock contact zone and within a narrow interval below this contact zone that is characterized by the occurrence of small layers of chilled dolerite. Transmissivity values determined from fluid injection, aquifer testing, and flowmeter measurements generally fall in the range of 8.1E-08 to 9.95E-06 m2/s and correspond to various scales of investigation. The analysis of acoustic and optical BHTV images reveals two primary fracture sets within the dolerite and the sedimentary rocks - subhorizontal fractures, intersected by subvertical ones. Despite being highly fractured either with subhorizontal, subvertical or both fracture populations, the dolerite above and the sedimentary rocks below the contact zone and the zone with the layers of chilled dolerite are significantly less conductive. The distribution of the particular conductive intervals is not a function of the two dominant fracture populations or their density but rather of the intrusion path of the sill. The intrusion caused thermal fracturing and cracking of both formations, resulting in higher permeability along the contact zone. ?? Springer-Verlag 2005.

Probabilistic Simulation of Progressive Fracture in Bolted-Joint Composite Laminates

NASA Technical Reports Server (NTRS)

Minnetyan, L.; Singhal, S. N.; Chamis, C. C.

1996-01-01

This report describes computational methods to probabilistically simulate fracture in bolted composite structures. An innovative approach that is independent of stress intensity factors and fracture toughness was used to simulate progressive fracture. The effect of design variable uncertainties on structural damage was also quantified. A fast probability integrator assessed the scatter in the composite structure response before and after damage. Then the sensitivity of the response to design variables was computed. General-purpose methods, which are applicable to bolted joints in all types of structures and in all fracture processes-from damage initiation to unstable propagation and global structure collapse-were used. These methods were demonstrated for a bolted joint of a polymer matrix composite panel under edge loads. The effects of the fabrication process were included in the simulation of damage in the bolted panel. Results showed that the most effective way to reduce end displacement at fracture is to control both the load and the ply thickness. The cumulative probability for longitudinal stress in all plies was most sensitive to the load; in the 0 deg. plies it was very sensitive to ply thickness. The cumulative probability for transverse stress was most sensitive to the matrix coefficient of thermal expansion. In addition, fiber volume ratio and fiber transverse modulus both contributed significantly to the cumulative probability for the transverse stresses in all the plies.

Parameters affecting mechanical and thermal responses in bone drilling: A review.

PubMed

Lee, JuEun; Chavez, Craig L; Park, Joorok

2018-04-11

Surgical bone drilling is performed variously to correct bone fractures, install prosthetics, or for therapeutic treatment. The primary concern in bone drilling is to extract donor bone sections and create receiving holes without damaging the bone tissue either mechanically or thermally. We review current results from experimental and theoretical studies to investigate the parameters related to such effects. This leads to a comprehensive understanding of the mechanical and thermal aspects of bone drilling to reduce their unwanted complications. This review examines the important bone-drilling parameters of bone structure, drill-bit geometry, operating conditions, and material evacuation, and considers the current techniques used in bone drilling. We then analyze the associated mechanical and thermal effects and their contributions to bone-drilling performance. In this review, we identify a favorable range for each parameter to reduce unwanted complications due to mechanical or thermal effects. Copyright © 2018 Elsevier Ltd. All rights reserved.

A numerical simulation of machining glass by dual CO 2-laser beams

NASA Astrophysics Data System (ADS)

Jiao, Junke; Wang, Xinbing

2008-03-01

In the flat panel display (FPD) industry, lasers may be used to cut glass plates. In order to reduce the possibility of fracture in the process of cutting glass by lasers, the thermal stress has to be less than the critical rupture strength. In this paper, a dual-laser-beam method is proposed, where an off-focus CO 2-laser beam was used to preheat the glass sample to reduce the thermal gradients and a focused CO 2-laser beam was used to machine the glass. The distribution of the thermal stress and the temperature was simulated by using finite element analysis software, Ansys. The thermal stress was studied both when the glass sample was machined by a single CO 2-laser beam and by dual CO 2-laser beams. It was concluded that the thermal stress can be reduced by means of the dual-laser-beam method.

Thermal stresses in the laser disc from a tetragonal c-cut crystal

NASA Astrophysics Data System (ADS)

Yumashev, K. V.; Loiko, P. A.

2014-12-01

Analytical expressions for thermal stresses and strains, as well as displacements, are obtained for the laser disc from a tetragonal crystal cut along the [0 0 1] axis under plane stress approximation, for the first time, to our knowledge. This study illustrates that, in polar coordinates, the normal stresses, σr and σθ, are angular independent, while the shear one τrθ is zero. The thermal strains, εr and εθ, and displacements, u and υ, depend on both radial and tangential coordinates; this dependence has the shape of a four-leaf rose. For considered crystal cutting with isotropic in-plane thermal expansion, the displacements are not pure radial (υ≠0). The values of stresses, strains and displacements are calculated for the disc from a c-cut yttrium vanadate laser crystal, Nd:YVO4. The thermal fracture issues are analyzed for this crystal.

Elevated Temperature Properties of Titanium Carbide Base Ceramals Containing Nickel or Iron

NASA Technical Reports Server (NTRS)

Cooper, A L; Colteryahn, L E

1951-01-01

Elevated-temperature properties of titanium carbide base ceramals containing nickel or iron were determined in oxidation, modulus of rupture, tensile strength, and thermal-shock resistance. These materials followed the general growth law and exhibited two stages in oxidation. The following tensile strengths were found at 2000 degrees F: 13.3 weight percent nickel, 16, 150 pounds per square inch; 11.8 weight percent iron, 12,500 pounds per square inch; unalloyed titanium carbide, 16,450 pounds per square inch. Nickel or iron additions to titanium carbide improved the thermal-shock resistance, nickel more. The path of fracture in tensile and thermal-shock specimens was found to progress approximately 50 percent intergranularly and 50 percent transgranularly.

Effect of thermal profile on cyclic flaw growth in aluminum

NASA Technical Reports Server (NTRS)

Engstrom, W. L.

1975-01-01

Surface flawed and single edge notch tension specimens of 2219-T851 and -T87 aluminum were tested to determine static fracture characteristics and base line (constant amplitude, constant temperature) cyclic flaw growth behavior. Subsequent testing was then conducted in which flawed specimens were subjected to a thermal profile in which the applied stress was varied simultaneously with the temperature. The profile used represents a simplified space shuttle orbiter load/temperature flight cycle. Test temperatures included the range from 144K (-200 F) up to 450K (350 F). The measured flaw growth rates obtained from the thermal profile tests were then compared with rates predicted by assuming linear cumulative damage of base line rates.

The friction and wear of TPS fibers

NASA Technical Reports Server (NTRS)

Bascom, W. D.; Wong, S.

1987-01-01

The sliding friction behavior of single filaments of SiO2, SiC, and an aluminoborosilicate has been determined. These fibers are used in thermal protection systems (TPS) and are subject to damage during weaving and aero-maneuvering. All fibers exhibited stick-slip friction indicating the successive formation and rupture of strong junctions between the contacting filaments. The static frictional resistance of the sized SiC filament was 4X greater than for the same filament after heat cleaning. This result suggests that the sizing is an organic polymer with a high shear yield strength. Heat cleaning exposes the SiC surface and/or leaves an inorganic residue so that the adhesional contact between filaments has a low fracture energy and frictional sliding occurs by brittle fracture. The frictional resistances of the sized and heat cleaned SiO2 and glass filaments were all comparable to that of the heat cleaned SiC. It would appear that the sizings as well as the heat cleaned surfaces of the silica and glass have low fracture energies so that the sliding resistance is determined by brittle fracture.

Nonlinear dynamics of ice-wedge networks and resulting sensitivity to severe cooling events.

PubMed

Plug, L J; Werner, B T

2002-06-27

Patterns of subsurface wedges of ice that form along cooling-induced tension fractures, expressed at the ground surface by ridges or troughs spaced 10 30 m apart, are ubiquitous in polar lowlands. Fossilized ice wedges, which are widespread at lower latitudes, have been used to infer the duration and mean temperature of cold periods within Proterozoic and Quaternary climates, and recent climate trends have been inferred from fracture frequency in active ice wedges. Here we present simulations from a numerical model for the evolution of ice-wedge networks over a range of climate scenarios, based on the interactions between thermal tensile stress, fracture and ice wedges. We find that short-lived periods of severe cooling permanently alter the spacing between ice wedges as well as their fracture frequency. This affects the rate at which the widths of ice wedges increase as well as the network's response to subsequent climate change. We conclude that wedge spacing and width in ice-wedge networks mainly reflect infrequent episodes of rapidly falling ground temperatures rather than mean conditions.

Diagenesis and fracture development in the Bakken Formation, Williston Basin; implications for reservoir quality in the middle member

USGS Publications Warehouse

Pitman, Janet K.; Price, Leigh C.; LeFever, Julie A.

2001-01-01

The middle member of the Bakken Formation is an attractive petroleum exploration target in the deeper part of the Williston Basin because it is favorably positioned with respect to source and seal units. Progressive rates of burial and minor uplift and erosion of this member led to a stable thermal regime and, consequently, minor variations in diagenesis across much of the basin. The simple diagenetic history recorded in sandstones and siltstones in the middle member can, in part, be attributed to the closed, low-permeability nature of the Bakken petroleum system during most of its burial history. Most diagenesis ceased in the middle member when oil entered the sandstones and siltstones in the Late Cretaceous. Most oil in the Bakken Formation resides in open, horizontal fractures in the middle member. Core analysis reveals that sandstones and siltstones associated with thick mature shales typically have a greater density of fractures than sandstones and siltstones associated with thin mature shales. Fractures were caused by superlithostatic pressures that formed in response to increased fluid volumes in the source rocks during hydrocarbon generation

Regression-based reduced-order models to predict transient thermal output for enhanced geothermal systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mudunuru, Maruti Kumar; Karra, Satish; Harp, Dylan Robert

Reduced-order modeling is a promising approach, as many phenomena can be described by a few parameters/mechanisms. An advantage and attractive aspect of a reduced-order model is that it is computational inexpensive to evaluate when compared to running a high-fidelity numerical simulation. A reduced-order model takes couple of seconds to run on a laptop while a high-fidelity simulation may take couple of hours to run on a high-performance computing cluster. The goal of this paper is to assess the utility of regression-based reduced-order models (ROMs) developed from high-fidelity numerical simulations for predicting transient thermal power output for an enhanced geothermal reservoirmore » while explicitly accounting for uncertainties in the subsurface system and site-specific details. Numerical simulations are performed based on equally spaced values in the specified range of model parameters. Key sensitive parameters are then identified from these simulations, which are fracture zone permeability, well/skin factor, bottom hole pressure, and injection flow rate. We found the fracture zone permeability to be the most sensitive parameter. The fracture zone permeability along with time, are used to build regression-based ROMs for the thermal power output. The ROMs are trained and validated using detailed physics-based numerical simulations. Finally, predictions from the ROMs are then compared with field data. We propose three different ROMs with different levels of model parsimony, each describing key and essential features of the power production curves. The coefficients in the proposed regression-based ROMs are developed by minimizing a non-linear least-squares misfit function using the Levenberg–Marquardt algorithm. The misfit function is based on the difference between numerical simulation data and reduced-order model. ROM-1 is constructed based on polynomials up to fourth order. ROM-1 is able to accurately reproduce the power output of numerical simulations for low values of permeabilities and certain features of the field-scale data. ROM-2 is a model with more analytical functions consisting of polynomials up to order eight, exponential functions and smooth approximations of Heaviside functions, and accurately describes the field-data. At higher permeabilities, ROM-2 reproduces numerical results better than ROM-1, however, there is a considerable deviation from numerical results at low fracture zone permeabilities. ROM-3 consists of polynomials up to order ten, and is developed by taking the best aspects of ROM-1 and ROM-2. ROM-1 is relatively parsimonious than ROM-2 and ROM-3, while ROM-2 overfits the data. ROM-3 on the other hand, provides a middle ground for model parsimony. Based on R 2-values for training, validation, and prediction data sets we found that ROM-3 is better model than ROM-2 and ROM-1. For predicting thermal drawdown in EGS applications, where high fracture zone permeabilities (typically greater than 10 –15 m 2) are desired, ROM-2 and ROM-3 outperform ROM-1. As per computational time, all the ROMs are 10 4 times faster when compared to running a high-fidelity numerical simulation. In conclusion, this makes the proposed regression-based ROMs attractive for real-time EGS applications because they are fast and provide reasonably good predictions for thermal power output.« less

Regression-based reduced-order models to predict transient thermal output for enhanced geothermal systems

DOE PAGES

Mudunuru, Maruti Kumar; Karra, Satish; Harp, Dylan Robert; ...

2017-07-10

Reduced-order modeling is a promising approach, as many phenomena can be described by a few parameters/mechanisms. An advantage and attractive aspect of a reduced-order model is that it is computational inexpensive to evaluate when compared to running a high-fidelity numerical simulation. A reduced-order model takes couple of seconds to run on a laptop while a high-fidelity simulation may take couple of hours to run on a high-performance computing cluster. The goal of this paper is to assess the utility of regression-based reduced-order models (ROMs) developed from high-fidelity numerical simulations for predicting transient thermal power output for an enhanced geothermal reservoirmore » while explicitly accounting for uncertainties in the subsurface system and site-specific details. Numerical simulations are performed based on equally spaced values in the specified range of model parameters. Key sensitive parameters are then identified from these simulations, which are fracture zone permeability, well/skin factor, bottom hole pressure, and injection flow rate. We found the fracture zone permeability to be the most sensitive parameter. The fracture zone permeability along with time, are used to build regression-based ROMs for the thermal power output. The ROMs are trained and validated using detailed physics-based numerical simulations. Finally, predictions from the ROMs are then compared with field data. We propose three different ROMs with different levels of model parsimony, each describing key and essential features of the power production curves. The coefficients in the proposed regression-based ROMs are developed by minimizing a non-linear least-squares misfit function using the Levenberg–Marquardt algorithm. The misfit function is based on the difference between numerical simulation data and reduced-order model. ROM-1 is constructed based on polynomials up to fourth order. ROM-1 is able to accurately reproduce the power output of numerical simulations for low values of permeabilities and certain features of the field-scale data. ROM-2 is a model with more analytical functions consisting of polynomials up to order eight, exponential functions and smooth approximations of Heaviside functions, and accurately describes the field-data. At higher permeabilities, ROM-2 reproduces numerical results better than ROM-1, however, there is a considerable deviation from numerical results at low fracture zone permeabilities. ROM-3 consists of polynomials up to order ten, and is developed by taking the best aspects of ROM-1 and ROM-2. ROM-1 is relatively parsimonious than ROM-2 and ROM-3, while ROM-2 overfits the data. ROM-3 on the other hand, provides a middle ground for model parsimony. Based on R 2-values for training, validation, and prediction data sets we found that ROM-3 is better model than ROM-2 and ROM-1. For predicting thermal drawdown in EGS applications, where high fracture zone permeabilities (typically greater than 10 –15 m 2) are desired, ROM-2 and ROM-3 outperform ROM-1. As per computational time, all the ROMs are 10 4 times faster when compared to running a high-fidelity numerical simulation. In conclusion, this makes the proposed regression-based ROMs attractive for real-time EGS applications because they are fast and provide reasonably good predictions for thermal power output.« less

Used Fuel Disposal in Crystalline Rocks. FY15 Progress Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yifeng

2015-08-20

The objective of the Crystalline Disposal R&D Work Package is to advance our understanding of long-term disposal of used fuel in crystalline rocks and to develop necessary experimental and computational capabilities to evaluate various disposal concepts in such media. Chapter headings are as follows: Fuel matrix degradation model and its integration with performance assessments, Investigation of thermal effects on the chemical behavior of clays, Investigation of uranium diffusion and retardation in bentonite, Long-term diffusion of U(VI) in bentonite: dependence on density, Sorption and desorption of plutonium by bentonite, Dissolution of plutonium intrinsic colloids in the presence of clay and asmore » a function of temperature, Laboratory investigation of colloid-facilitated transport of cesium by bentonite colloids in a crystalline rock system, Development and demonstration of discrete fracture network model, Fracture continuum model and its comparison with discrete fracture network model.« less

Toughness Enhancement of Commercial Poly (Hydroxybutyrate-co-Valerate) (PHBV) by Blending with a Thermoplastic Polyurethane (TPU)

NASA Astrophysics Data System (ADS)

González-Ausejo, Jennifer; Sánchez-Safont, Estefania; Cabedo, Luis; Gamez-Perez, Jose

2016-11-01

Poly(hydroxyl butyrate-co-valerate) (PHBV) is a biopolymer synthesized by microorganisms that is fully biodegradable with improved thermal and tensile properties with respect to some commodity plastics. However, it presents an intrinsic brittleness that limits its potential application in replacing plastics in packaging applications. Films made of blends of PHBV with different contents of thermoplastic polyurethane (TPU) were prepared by single screw extruder and their fracture toughness behavior was assessed by means of the essential work of fracture (EWF) Method. As the crack propagation was not always stable, a partition method has been used to compare all formulations and to relate results with the morphology of the blends. Indeed, fully characterization of the different PHBV/TPU blends showed that PHBV was incompatible with TPU. The blends showed an improvement of the toughness fracture, finding a maximum with intermediate TPU contents.

ICESat-2 laser Nd:YVO4 amplifier

NASA Astrophysics Data System (ADS)

Sawruk, Nicholas W.; Burns, Patrick M.; Edwards, Ryan E.; Litvinovitch, Viatcheslav; Martin, Nigel; Witt, Greg; Fakhoury, Elias; Iskander, John; Pronko, Mark S.; Troupaki, Elisavet; Bay, Michael M.; He, Charles C.; Wang, Liqin L.; Cavanaugh, John F.; Farrokh, Babak; Salem, Jonathan A.; Baker, Eric

2018-02-01

We report on the cause and corrective actions of three amplifier crystal fractures in the space-qualified laser systems used in NASA Goddard Space Flight Center's (GSFC) Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2). The ICESat-2 lasers each contain three end-pumped Nd:YVOO4 amplifier stages. The crystals are clamped between two gold plated copper heat spreaders with an indium foil thermal interface material, and the crystal fractures occurred after multiple years of storage and over a year of operational run-time. The primary contributors are high compressive loading of the NdYVO4 crystals at the beginning of life, a time dependent crystal stress caused by an intermetallic reaction of the gold plating and indium, and slow crack growth resulting in a reduction in crystal strength over time. An updated crystal mounting scheme was designed, analyzed, fabricated and tested. Thee fracture slab failure analysis, finite-element modeling and corrective actions are presented.

Cold Cracking During Direct-Chill Casting

NASA Astrophysics Data System (ADS)

Eskin, D. G.; Lalpoor, M.; Katgerman, L.

Cold cracking phenomenon is the least studied, yet very important defect occurring during direct chill casting. The spontaneous nature of this defect makes its systematic study almost impossible, and the computer simulation of the thermomechanical behavior of the ingot during its cooling after the end of solidification requires constitutive parameters of high-strength aluminum alloys in the as-cast condition, which are not readily available. In this paper we describe constitutive behavior of high strength 7xxx series aluminum alloys in the as-cast condition based on experimentally measured tensile properties at different strain rates and temperatures, plane strain fracture toughness at different temperatures, and thermal contraction. In addition, fracture and structure of the specimens and real cold-cracked billets are examined. As a result a fracture-mechanics-based criterion of cold cracking is suggested based on the critical crack length, and is validated upon pilot-scale billet casting.

Techniques for increasing boron fiber fracture strain

NASA Technical Reports Server (NTRS)

Dicarlo, J. A.

1977-01-01

Improvement in the strain-to-failure of CVD boron fibers is shown possible by contracting the tungsten boride core region and its inherent flaws. The results of three methods are presented in which etching and thermal processing techniques were employed to achieve core flaw contraction by internal stresses available in the boron sheath. After commercially and treatment induced surface flaws were removed from 203 micrometers (8 mil) fibers, the core flaw was observed to be essentially the only source of fiber fracture. Thus, fiber strain-to-failure was found to improve by an amount equal to the treatment induced contraction on the core flaw. Commercial feasibility considerations suggest as the most cost effective technique that method in which as-produced fibers are given a rapid heat treatment above 700 C. Preliminary results concerning the contraction kinetics and fracture behavior observed are presented and discussed both for high vacuum and argon gas heat treatment environments.

Combined bending and thermal fatigue of high-temperature metal-matrix composites - Computational simulation

NASA Technical Reports Server (NTRS)

Gotsis, Pascal K.; Chamis, Christos C.

1992-01-01

The nonlinear behavior of a high-temperature metal-matrix composite (HT-MMC) was simulated by using the metal matrix composite analyzer (METCAN) computer code. The simulation started with the fabrication process, proceeded to thermomechanical cyclic loading, and ended with the application of a monotonic load. Classical laminate theory and composite micromechanics and macromechanics are used in METCAN, along with a multifactor interaction model for the constituents behavior. The simulation of the stress-strain behavior from the macromechanical and the micromechanical points of view, as well as the initiation and final failure of the constituents and the plies in the composite, were examined in detail. It was shown that, when the fibers and the matrix were perfectly bonded, the fracture started in the matrix and then propagated with increasing load to the fibers. After the fibers fractured, the composite lost its capacity to carry additional load and fractured.

Effects of ATR-2 Irradiation to High Fluence on Nine RPV Surveillance Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nanstad, Randy K.; Odette, George R.; Almirall, Nathan

2017-05-01

The reactor pressure vessel (RPV) in a light-water reactor (LWR) represents the first line of defense against a release of radiation in case of an accident. Thus, regulations that govern the operation of commercial nuclear power plants require conservative margins of fracture toughness, both during normal operation and under accident scenarios. In the unirradiated condition, the RPV has sufficient fracture toughness such that failure is implausible under any postulated condition, including pressurized thermal shock (PTS) in pressurized water reactors (PWR). In the irradiated condition, however, the fracture toughness of the RPV may be severely degraded, with the degree of toughnessmore » loss dependent on the radiation sensitivity of the materials. The available embrittlement predictive models and our present understanding of radiation damage are not fully quantitative, and do not treat all potentially significant variables and issues, particularly considering extension of operation to 80y.« less

Combined thermal and bending fatigue of high-temperature metal-matrix composites: Computational simulation

NASA Technical Reports Server (NTRS)

Gotsis, Pascal K.

1991-01-01

The nonlinear behavior of a high-temperature metal-matrix composite (HT-MMC) was simulated by using the metal matrix composite analyzer (METCAN) computer code. The simulation started with the fabrication process, proceeded to thermomechanical cyclic loading, and ended with the application of a monotonic load. Classical laminate theory and composite micromechanics and macromechanics are used in METCAN, along with a multifactor interaction model for the constituents behavior. The simulation of the stress-strain behavior from the macromechanical and the micromechanical points of view, as well as the initiation and final failure of the constituents and the plies in the composite, were examined in detail. It was shown that, when the fibers and the matrix were perfectly bonded, the fracture started in the matrix and then propagated with increasing load to the fibers. After the fibers fractured, the composite lost its capacity to carry additional load and fractured.

Development and Testing of Ceramic Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Choi, Sung R.; Miller, Robert A.

2004-01-01

Ceramic thermal barrier coatings will play an increasingly important role in future gas turbine engines because of their ability to effectively protect the engine components and further raise engine temperatures. Durability of the coating systems remains a critical issue with the ever-increasing temperature requirements. Thermal conductivity increase and coating degradation due to sintering and phase changes are known to be detrimental to coating performance. There is a need to characterize the coating behavior and temperature limits, in order to potentially take full advantage of the current coating capability, and also accurately assess the benefit gained from advanced coating development. In this study, thermal conductivity behavior and cyclic durability of plasma-sprayed ZrO2-8wt%Y2O3 thermal barrier coatings were evaluated under laser heat-flux simulated high temperature, large thermal gradient and thermal cycling conditions. The coating degradation and failure processes were assessed by real-time monitoring of the coating thermal conductivity under the test conditions. The ceramic coating crack propagation driving forces and resulting failure modes will be discussed in light of high temperature mechanical fatigue and fracture testing results.

Development of high temperature materials for solid propellant rocket nozzle applications. [tantalum carbides-tungsten fiber composites

NASA Technical Reports Server (NTRS)

Manning, C. R., Jr.; Honeycutt, L., III

1974-01-01

Evaluation of tantalum carbide-tungsten fiber composites has been completed as far as weight percent carbon additions and weight percent additions of tungsten fiber. Extensive studies were undertaken concerning Young's Modulus and fracture strength of this material. Also, in-depth analysis of the embrittling effects of the extra carbon additions on the tungsten fibers has been completed. The complete fabrication procedure for the tantalum carbide-tungsten fiber composites with extra carbon additions is given. Microprobe and metallographic studies showed the effect of extra carbon on the tungsten fibers, and evaluation of the thermal shock parameter fracture strength/Young's Modulus is included.

Turbine Engine Hot Section Technology 1986

NASA Technical Reports Server (NTRS)

1986-01-01

The Turbine Engine Hot Section Technology (HOST) Project of the NASA Lewis Research Center sponsored a workshop to discuss current research pertinent to turbine engine durability problems. Presentations were made concerning the hot section environment and the behavior of combustion liners, turbine blades, and turbine vanes. The presentations were divided into six sessions: Instrumentation, Combustion, Turbine Heat Transfer, Structural Analysis, Fatigue and Fracture, and Surface Protection. Topics discussed included modeling of thermal and fluid-flow phenomena, structural analysis, fatigue and fracture, surface protective coatings, constitutive behavior of materials, stress-strain response, and life-prediction methods. Researchers from industry, academia, and government presented results of their work sponsored by the HOST project.

Dispersion toughened ceramic composites and method for making same

DOEpatents

Stinton, David P.; Lackey, Walter J.; Lauf, Robert J.

1986-01-01

Ceramic composites exhibiting increased fracture toughness are produced by the simultaneous codeposition of silicon carbide and titanium disilicide by chemical vapor deposition. A mixture of hydrogen, methyltrichlorosilane and titanium tetrachloride is introduced into a furnace containing a substrate such as graphite or silicon carbide. The thermal decomposition of the methyltrichlorosilane provides a silicon carbide matrix phase and the decomposition of the titanium tetrachloride provides a uniformly dispersed second phase of the intermetallic titanium disilicide within the matrix phase. The fracture toughness of the ceramic composite is in the range of about 6.5 to 7.0 MPa.sqroot.m which represents a significant increase over that of silicon carbide.

Dispersion toughened ceramic composites and method for making same

DOEpatents

Stinton, D.P.; Lackey, W.J.; Lauf, R.J.

1984-09-28

Ceramic composites exhibiting increased fracture toughness are produced by the simultaneous codeposition of silicon carbide and titanium disilicide by chemical vapor deposition. A mixture of hydrogen, methyltrichlorosilane and titanium tetrachloride is introduced into a furnace containing a substrate such as graphite or silicon carbide. The thermal decomposition of the methyltrichlorosilane provides a silicon carbide matrix phase and the decomposition of the titanium tetrachloride provides a uniformly dispersed second phase of the intermetallic titanium disilicide within the matrix phase. The fracture toughness of the ceramic composite is in the range of about 6.5 to 7.0 MPa..sqrt..m which represents a significant increase over that of silicon carbide.

A Thermally Re-mendable Cross-Linked Polymeric Material

NASA Astrophysics Data System (ADS)

Chen, Xiangxu; Dam, Matheus A.; Ono, Kanji; Mal, Ajit; Shen, Hongbin; Nutt, Steven R.; Sheran, Kevin; Wudl, Fred

2002-03-01

We have developed a transparent organic polymeric material that can repeatedly mend or ``re-mend'' itself under mild conditions. The material is a tough solid at room temperature and below with mechanical properties equaling those of commercial epoxy resins. At temperatures above 120°C, approximately 30% (as determined by solid-state nuclear magnetic resonance spectroscopy) of ``intermonomer'' linkages disconnect but then reconnect upon cooling, This process is fully reversible and can be used to restore a fractured part of the polymer multiple times, and it does not require additional ingredients such as a catalyst, additional monomer, or special surface treatment of the fractured interface.

The surface crack problem for a functionally graded coating bonded to a homogeneous layer

NASA Astrophysics Data System (ADS)

Kasmalkar, Maheendra B.

In the continuing search for materials which can withstand the grueling requirements of modern day applications, Functionally Graded Materials (FGMs) seem to be a promising alternative to conventional materials. These nonhomogeneous materials offer better interfacial properties by improving bond strength and reducing thermal mismatch. Before putting these materials into application, an important step in the design of FGMs is the stress analysis and fracture characterization. The fracture performance of FGM coatings on homogeneous substrates is the focus of this study. In this study, various internal and surface crack configurations in the coating and the substrate are subjected to mechanical and thermal loads. The analysis is linear elastic. The thermo-mechanical properties of the FGM coating are assumed to vary exponentially with the spatial coordinate. The equilibrium equations are solved using integral transforms. The resulting singular integral equations are solved using numerical integration. The results of interest for this mode I formulation are the stress intensity factors and the crack opening displacements. The effects of the nonhomogeneity parameter and various dimensionless length parameters are studied. One of the most important outcomes of this study is the theoretical proof that "kink" in material property at the interface does not introduce any singularity. In the numerical results it is observed that generally the stress intensity factors tend to increase with material nonhomogeneity. Also, it is observed that the substrate thickness tends to suppress cracking in the coating. In pure thermal loading, the surface cracks may either be arrested or there might be crack closure. The stress intensity factors from different loadings can be added up to obtain the resultant stress intensity factor for multiple loading. Results in this study have wide-ranging applications. They can be applied to thermal barrier coatings on turbine components, combustion chambers, parts of the airframe for the "Space Plane", soil mechanics, bone fractures and many more applications where the material is macroscopically nonhomogeneous. Thus this study solves a basic problem common to a variety of applications in diverse fields.

Opportunity In Situ Geologic Context of Aqueous Alteration Along Offsets in the Rim of Endeavour Crater

NASA Technical Reports Server (NTRS)

Crumpler, L. S.; Arvidson, R. E.; Farrand, W. H.; Golombek, M. P.; Grant, J. A.; Ming, D. W.; Mittlefehldt, D. W.; Parker, T. J.

2015-01-01

Mars Exploration Rover Opportunity traversed 7.9 km and 27 degrees of arc along the rim of the 22 km-diameter Noachian "Endeavour" impact crater since its arrival 1200 sols ago. Areas of aqueous and low-grade thermal alteration, and changes in structure, attitude, and macroscopic texture of outcrops are notable across several discontinuities between segments of the crater rim. The discontinuities and other post-impact joints and fractures coincide with sites of apparent deep fluid circulation processes responsible for thermal and chemical alteration of local outcrops.

Evaluation of fracture toughness and mechanical properties of ternary thiol-ene-methacrylate systems as resin matrix for dental restorative composites.

PubMed

Beigi, Saeed; Yeganeh, Hamid; Atai, Mohammad

2013-07-01

Study and evaluation of fracture toughness, flexural and dynamic mechanical properties, and crosslink density of ternary thiol-ene-methacrylate systems and comparison with corresponding conventional methacrylate system were considered in the present study. Urethane tetra allyl ether monomer (UTAE) was synthesized as ene monomer. Different formulations were prepared based on combination of UTAE, BisGMA/TEGDMA and a tetrathiol monomer (PETMP). The photocuring reaction was conducted under visible light using BD/CQ combination as photoinitiator system. Mechanical properties were evaluated via measuring flexural strength, flexural modulus and fracture toughness. Scanning electron microscopy (SEM) was utilized to study the morphology of the fractured specimen's cross section. Viscoelastic properties of the samples were also determined by dynamic mechanical thermal analysis (DMTA). The same study was performed on a conventional methacrylate system. The data were analyzed and compared by ANOVA and Tukey HSD tests (significance level=0.05). The results showed improvement in fracture toughness of the specimens containing thiol-ene moieties. DMTA revealed a lower glass transition temperature and more homogenous structure for thiol-ene containing specimens in comparison to the system containing merely methacrylate monomer. The flexural modulus and flexural strength of the specimens with higher thiol-ene content were lower than the neat methacrylate system. The SEM micrographs of the fractured surface of specimens with higher methacrylate content were smooth and mirror-like (shiny) which represent brittle fracture. The thiol-ene-methacrylate system can be used as resin matrix of dental composites with enhanced fracture toughness in comparison to the methacrylate analogous. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

On the interfacial fracture resistance of resin-bonded zirconia and glass-infiltrated graded zirconia

PubMed Central

Chai, Herzl; Kaizer, Marina; Chughtai, Asima; Tong, Hui; Tanaka, Carina; Zhang, Yu

2015-01-01

Objective A major limiting factor for the widespread use of zirconia in prosthetic dentistry is its poor resin-cement bonding capabilities. We show that this deficiency can be overcome by infiltrating the zirconia cementation surface with glass. Current methods for assessing the fracture resistance of resin-ceramic bonds are marred by uneven stress distribution at the interface, which may result in erroneous interfacial fracture resistance values. We have applied a wedge-loaded double-cantilever-beam testing approach to accurately measure the interfacial fracture resistance of adhesively bonded zirconia-based restorative materials. Methods The interfacial fracture energy GC was determined for adhesively bonded zirconia, graded zirconia and feldspathic ceramic bars. The bonding surfaces were subjected to sandblasting or acid etching treatments. Baseline GC was measured for bonded specimens subjected to 7 days hydration at 37 °C. Long-term GC was determined for specimens exposed to 20,000 thermal cycles between 5 and 55 °C followed by 2-month aging at 37 °C in water. The test data were interpreted with the aid of a 2D finite element fracture analysis. Results The baseline and long-term GC for graded zirconia was 2–3 and 8 times that for zirconia, respectively. More significantly, both the baseline and long-term GC of graded zirconia were similar to those for feldspathic ceramic. Significance The interfacial fracture energy of feldspathic ceramic and graded zirconia was controlled by the fracture energy of the resin cement while that of zirconia by the interface. GC for the graded zirconia was as large as for feldspathic ceramic, making it an attractive material for use in dentistry. PMID:26365987

Ultrahigh Thermal Conductive yet Superflexible Graphene Films.

PubMed

Peng, Li; Xu, Zhen; Liu, Zheng; Guo, Yan; Li, Peng; Gao, Chao

2017-07-01

Electrical devices generate heat at work. The heat should be transferred away immediately by a thermal manager to keep proper functions, especially for high-frequency apparatuses. Besides high thermal conductivity (K), the thermal manager material requires good foldability for the next generation flexible electronics. Unfortunately, metals have satisfactory ductility but inferior K (≤429 W m -1 K -1 ), and highly thermal-conductive nonmetallic materials are generally brittle. Therefore, fabricating a foldable macroscopic material with a prominent K is still under challenge. This study solves the problem by folding atomic thin graphene into microfolds. The debris-free giant graphene sheets endow graphene film (GF) with a high K of 1940 ± 113 W m -1 K -1 . Simultaneously, the microfolds render GF superflexible with a high fracture elongation up to 16%, enabling it more than 6000 cycles of ultimate folding. The large-area multifunctional GFs can be easily integrated into high-power flexible devices for highly efficient thermal management. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stress Intensity of Delamination in a Sintered-Silver Interconnection: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeVoto, D. J.; Paret, P. P.; Wereszczak, A. A.

2014-08-01

In automotive power electronics packages, conventional thermal interface materials such as greases, gels, and phase-change materials pose bottlenecks to heat removal and are also associated with reliability concerns. The industry trend is toward high thermal performance bonded interfaces for large-area attachments. However, because of coefficient of thermal expansion mismatches between materials/layers and resultant thermomechanical stresses, adhesive and cohesive fractures could occur, posing a reliability problem. These defects manifest themselves in increased thermal resistance. This research aims to investigate and improve the thermal performance and reliability of sintered-silver for power electronics packaging applications. This has been experimentally accomplished by the synthesismore » of large-area bonded interfaces between metalized substrates and copper base plates that have subsequently been subjected to thermal cycles. A finite element model of crack initiation and propagation in these bonded interfaces will allow for the interpretation of degradation rates by a crack-velocity (V)-stress intensity factor (K) analysis. A description of the experiment and the modeling approach are discussed.« less

A Methodology for Calculating EGS Electricity Generation Potential Based on the Gringarten Model for Heat Extraction From Fractured Rock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Augustine, Chad

Existing methodologies for estimating the electricity generation potential of Enhanced Geothermal Systems (EGS) assume thermal recovery factors of 5% or less, resulting in relatively low volumetric electricity generation potentials for EGS reservoirs. This study proposes and develops a methodology for calculating EGS electricity generation potential based on the Gringarten conceptual model and analytical solution for heat extraction from fractured rock. The electricity generation potential of a cubic kilometer of rock as a function of temperature is calculated assuming limits on the allowed produced water temperature decline and reservoir lifetime based on surface power plant constraints. The resulting estimates of EGSmore » electricity generation potential can be one to nearly two-orders of magnitude larger than those from existing methodologies. The flow per unit fracture surface area from the Gringarten solution is found to be a key term in describing the conceptual reservoir behavior. The methodology can be applied to aid in the design of EGS reservoirs by giving minimum reservoir volume, fracture spacing, number of fractures, and flow requirements for a target reservoir power output. Limitations of the idealized model compared to actual reservoir performance and the implications on reservoir design are discussed.« less

Fracturing, fluid-rock interaction and mineralisation during the seismic cycle along the Alpine Fault

NASA Astrophysics Data System (ADS)

Williams, Jack N.; Toy, Virginia G.; Smith, Steven A. F.; Boulton, Carolyn

2017-10-01

The Alpine Fault has a <50 m wide geochemically distinct hanging-wall alteration zone. Using a combination of petrological and cathodoluminescence (CL) microscopy, Energy Dispersive Spectroscopy and X-ray diffraction, we document the habitat and mineralising phases of macro- and micro-fractures within the alteration zone using samples derived from outcrop and the Deep Fault Drilling Project. Veins predominantly contain calcite, chlorite, K-feldspar or muscovite. Gouge-filled fractures are also observed and reflect filling from mechanical wear and chlorite mineralisation. CL imaging suggests that each calcite vein was opened and sealed in one episode, possibly corresponding to a single seismic cycle. The thermal stability of mineralising phases and their mutually cross-cutting relationships indicates a cyclic history of fracture opening and mineralisation that extends throughout the seismogenic zone. Cataclasites contain intragranular veins that are hosted within quartzofeldspathic clasts, as well as veins that cross-cut clasts and the surrounding matrix. Intragranular calcite veins formed prior to or during cataclasis. Cross-cutting veins are interpreted to have formed by fracturing of relatively indurated cataclasites after near-surface slip localisation within the Alpine Fault's principal slip zone gouges (PSZs). These observations clearly demonstrate that shear strain is most localised in the shallowest part of the seismogenic zone.

Effect of far-field stresses and residual stresses incorporation in predicting fracture toughness of carbon nanotube reinforced yttria stabilized zirconia

NASA Astrophysics Data System (ADS)

Mahato, Neelima; Nisar, Ambreen; Mohapatra, Pratyasha; Rawat, Siddharth; Ariharan, S.; Balani, Kantesh

2017-10-01

Yttria-stabilized zirconia (YSZ) is a potential thermal insulating ceramic for high temperature applications (>1000 °C). YSZ reinforced with multi-walled carbon nanotubes (MWNTs) was processed via spark plasma sintering to produce dense, crack-free homogeneous sample and avoid any degradation of MWNTs when sintered using conventional routes. Despite porosity, the addition of MWNT has a profound effect in improving the damage tolerance of YSZ by allowing the retention of tetragonal phase. However, at some instances, the crack lengths in the MWNT reinforced YSZ matrices have been found to be longer than the standalone counterparts. Therefore, it becomes inappropriate to apply Anstis equation to calculate fracture toughness values. In this regard, a combined analytical cum numerical method is used to estimate the theoretical fracture toughness and quantitatively analyze the mechanics of matrix cracking in the reinforced composite matrices incorporating the effects of various factors (such as far-field stresses, volume fraction of MWNTs, change in the modulus and Poisson's ratio values along with the increase in porosity, and bridging and phase transformation mechanism) affecting the fracture toughness of YSZ-MWNT composites. The results suggest that the incorporation of far-field stresses cannot be ignored in estimating the theoretical fracture toughness of YSZ-MWNT composites.

Influences of Cutting Speed and Material Mechanical Properties on Chip Deformation and Fracture during High-Speed Cutting of Inconel 718.

PubMed

Wang, Bing; Liu, Zhanqiang; Hou, Xin; Zhao, Jinfu

2018-03-21

The paper aims to investigate the influences of material constitutive and fracture parameters in addition to cutting speed on chip formation during high-speed cutting of Inconel 718. Finite element analyses for chip formation are conducted with Johnson-Cook constitutive and fracture models. Meanwhile, experiments of high-speed orthogonal cutting are performed to verify the simulation results with cutting speeds ranging from 50 m/min to 7000 m/min. The research indicates that the chip morphology transforms from serrated to fragmented at the cutting speed of 7000 m/min due to embrittlement of the workpiece material under ultra-high cutting speeds. The parameter of shear localization sensitivity is put forward to describe the influences of material mechanical properties on serrated chip formation. The results demonstrate that the effects of initial yield stress and thermal softening coefficient on chip shear localization are much more remarkable than the other constitutive parameters. For the material fracture parameters, the effects of initial fracture strain and exponential factor of stress state on chip shear localization are more much prominent. This paper provides guidance for controlling chip formation through the adjustment of material mechanical properties and the selection of appropriate cutting parameters.

Influences of Cutting Speed and Material Mechanical Properties on Chip Deformation and Fracture during High-Speed Cutting of Inconel 718

PubMed Central

Hou, Xin; Zhao, Jinfu

2018-01-01

The paper aims to investigate the influences of material constitutive and fracture parameters in addition to cutting speed on chip formation during high-speed cutting of Inconel 718. Finite element analyses for chip formation are conducted with Johnson–Cook constitutive and fracture models. Meanwhile, experiments of high-speed orthogonal cutting are performed to verify the simulation results with cutting speeds ranging from 50 m/min to 7000 m/min. The research indicates that the chip morphology transforms from serrated to fragmented at the cutting speed of 7000 m/min due to embrittlement of the workpiece material under ultra-high cutting speeds. The parameter of shear localization sensitivity is put forward to describe the influences of material mechanical properties on serrated chip formation. The results demonstrate that the effects of initial yield stress and thermal softening coefficient on chip shear localization are much more remarkable than the other constitutive parameters. For the material fracture parameters, the effects of initial fracture strain and exponential factor of stress state on chip shear localization are more much prominent. This paper provides guidance for controlling chip formation through the adjustment of material mechanical properties and the selection of appropriate cutting parameters. PMID:29561770

Hydrogen-Assisted Crack Propagation in Austenitic Stainless Steel Fusion Welds

NASA Astrophysics Data System (ADS)

Somerday, B. P.; Dadfarnia, M.; Balch, D. K.; Nibur, K. A.; Cadden, C. H.; Sofronis, P.

2009-10-01

The objective of this study was to characterize hydrogen-assisted crack propagation in gas-tungsten arc (GTA) welds of the nitrogen-strengthened, austenitic stainless steel 21Cr-6Ni-9Mn (21-6-9), using fracture mechanics methods. The fracture initiation toughness and crack growth resistance curves were measured using fracture mechanics specimens that were thermally precharged with 230 wppm (1.3 at. pct) hydrogen. The fracture initiation toughness and slope of the crack growth resistance curve for the hydrogen-precharged weld were reduced by as much as 60 and 90 pct, respectively, relative to the noncharged weld. A physical model for hydrogen-assisted crack propagation in the welds was formulated from microscopy evidence and finite-element modeling. Hydrogen-assisted crack propagation proceeded by a sequence of microcrack formation at the weld ferrite, intense shear deformation in the ligaments separating microcracks, and then fracture of the ligaments. One salient role of hydrogen in the crack propagation process was promoting microcrack formation at austenite/ferrite interfaces and within the ferrite. In addition, hydrogen may have facilitated intense shear deformation in the ligaments separating microcracks. The intense shear deformation could be related to the development of a nonuniform distribution of hydrogen trapped at dislocations between microcracks, which in turn created a gradient in the local flow stress.

Adequacy of Current State Setbacks for Directional High-Volume Hydraulic Fracturing in the Marcellus, Barnett, and Niobrara Shale Plays

PubMed Central

Haley, Marsha; McCawley, Michael; Epstein, Anne C.; Arrington, Bob; Bjerke, Elizabeth Ferrell

2016-01-01

Background: There is an increasing awareness of the multiple potential pathways leading to human health risks from hydraulic fracturing. Setback distances are a legislative method to mitigate potential risks. Objectives: We attempted to determine whether legal setback distances between well-pad sites and the public are adequate in three shale plays. Methods: We reviewed geography, current statutes and regulations, evacuations, thermal modeling, air pollution studies, and vapor cloud modeling within the Marcellus, Barnett, and Niobrara Shale Plays. Discussion: The evidence suggests that presently utilized setbacks may leave the public vulnerable to explosions, radiant heat, toxic gas clouds, and air pollution from hydraulic fracturing activities. Conclusions: Our results suggest that setbacks may not be sufficient to reduce potential threats to human health in areas where hydraulic fracturing occurs. It is more likely that a combination of reasonable setbacks with controls for other sources of pollution associated with the process will be required. Citation: Haley M, McCawley M, Epstein AC, Arrington B, Bjerke EF. 2016. Adequacy of current state setbacks for directional high-volume hydraulic fracturing in the Marcellus, Barnett, and Niobrara Shale Plays. Environ Health Perspect 124:1323–1333; http://dx.doi.org/10.1289/ehp.1510547 PMID:26895553

DUSEL and the future of deep terrestrial microbiology (Invited)

NASA Astrophysics Data System (ADS)

Onstott, T. C.; Peters, C. A.; Murdoch, L. C.; Elsworth, D.; Sonnenthal, E. L.; Kieft, T.; Boutt, D. F.; Germanovich, L.; Glaser, S. D.; Wang, H. F.; Roggenthen, B.; Lesko, K.; Cushman, P.; Stetler, L. D.; Bang, S.; Anderson, C.

2009-12-01

DUSEL will take advantage of the existing subsurface architecture of the deepest mine in the U.S. to provide a platform for launching new exploration into the deep terrestrial biosphere. Multi-year experiments are currently being designed to delineate the relationships between microbial diversity and activity and hydraulic connectivity, temperature, pressure, strain rate and multiphase fluids. Unlike the physics experiments, which will be located close to the center of the mine, most of these experiments will be located at the periphery in existing tunnels at 100 to 2400 m depth in order to access fluid fill fractures with boreholes. Hydrological models suggest that DUSEL could sample ~100 km3 volume for microbial biogeographic and transport studies. The high-capacity underground water filtration plant used to generate ultrapure water for neutrino detectors will readily supply water for microbiology coring projects reducing microbial contamination. This will be essential for the drilling platform located at 2400 m depth that will drill down to 7+ km and 120oC in search of the upper temperature limit for life. Another advantage of underground coring is that the drilling fluid pressure will be much less than that of the fracture water, which means that when the coring bit intersects a water-filled fracture, the fracture water will flow into the core barrel reducing the contamination of fracture surfaces in the cores. The ultra-low radiation background counting facility to be located at 1475 m depth will potentially enable 106 times improvement in the detection limit for subsurface microbial respiration rates using radioactive tracers. The Coupled Thermal-Hydrological-Mechanical-Chemical-Biological, block-heating experiment will examine how the microbial communities within fractures respond to the increased thermal and fluid flux. The Fracture Processes Facility is not only designed to determine what controls rock strength, but could also determine to what extent subsurface chemoautotrophic activity is regulated by tectonic episodicity. The DUSEL CO2 Facility will investigate how microbial activity is impacted by CO2 injection and whether microbial activity has a significant impact upon long-term sequestration of CO2. These three experiments represent a subset of the integrated suite of experiments planned for the first 5 years, but many more microbial experiments can be accommodated within DUSEL. With its unique experimental assets, km-scale spatial access and multi-decade observational lifetime, DUSEL will usher in the next generation of exploration into the deep terrestrial biosphere and not only reveal the answers to many of its well-hidden secrets, but perhaps to the origin of life itself.

Distinct Element Modeling of the Large Block Test

NASA Astrophysics Data System (ADS)

Carlson, S. R.; Blair, S. C.; Wagoner, J. L.

2001-12-01

The Yucca Mountain Site Characterization Project is investigating Yucca Mountain, Nevada as a potential nuclear waste repository site. As part of this effort, the Large Block, a 3m x 3m x 4.5m rectangular prism of Topopah Spring tuff, was excavated at Fran Ridge near Yucca Mountain. The Large Block was heated to a peak temperature of 145\\deg C along a horizontal plane 2.75m below the top of the block over a period of about one-year. Displacements were measured in three orthogonal directions with an array of six Multiple Point Borehole Extensometers (MPBX) and were numerically simulated in three dimensions with 3DEC, a distinct element code. The distinct element method was chosen to incorporate discrete fractures in the simulations. The model domain was extended 23m below the ground surface and, in the subsurface, 23m outward from each vertical face so that fixed displacement boundary conditions could be applied well away from the heated portion of the block. A single continuum model and three distinct element models, incorporating six to twenty eight mapped fractures, were tested. Two thermal expansion coefficients were tested for the six-fracture model: a higher value taken from laboratory measurements and a lower value from an earlier field test. The MPBX data show that the largest displacements occurred in the upper portion of the block despite the higher temperatures near the center. The continuum model was found to under-predict the MPBX displacements except in the east west direction near the base of the block. The high thermal expansion model over-predicted the MPBX displacements except in the north south direction near the top of the block. The highly fractured model under-predicted most of the MPBX displacements and poorly simulated the cool-down portion of the test. Although no model provided the single best fit to all of the MPBX data, the six and seven fracture models consistently provided good fits and in most cases showed much improvement over the other three models. Both provided particularly good fits to the east west displacements in the upper portion of the block throughout the entire test. This exercise demonstrates that distinct element models can surpass continuum models in their ability to simulate fractured rock mass deformation, but care needs to be taken in the selection of fractures incorporated in the models. *This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

Comparison of Thermo-Elastic and Poro-Elastic Effects during Shear Stimulation of Desert Peak EGS Well 27-15 Using a Coupled Thermal-Hydrological-Mechanical Simulator

NASA Astrophysics Data System (ADS)

Kelkar, S.; Dempsey, D.; Hickman, S. H.; Davatzes, N. C.; Moos, D.; Zemach, E.

2013-12-01

High-temperature rock formations at moderate depths with low permeability are candidates for Enhanced Geothermal Systems (EGS) projects. Hydraulic stimulation can be employed in such systems to create flow paths with low hydraulic impedance while maintaining significant heat transfer area to avoid premature cooling of the formation and the creation of short-circuit flow paths. Here we present results from a coupled thermal-hydrological-mechanical numerical model of a successful EGS stimulation in well 27-15 at the Desert Peak Geothermal Field, Nevada. This stimulation was carried out over two different depth intervals and multiple injection pressures, beginning in September 2010. The subject of this study is the initial shear stimulation phase, which was carried out at depths of 0.9 to 1.1 km over a period of about 100 days. The reservoir temperature at these depths is ~182 to 195° C. This treatment consisted of injection of 20 to 30° C water at wellhead pressures (WHP) of 1.5, 2.2, 3.1 and 3.7 MPa followed by periods of shut-in. To avoid hydraulic fracturing, these pressure steps were intentionally selected to stay below the minimum principal stress measured in the well. The injectivity did not change at WHP steps of 1.5 and 2.2 MPa, but improved significantly during injection at 3.1 MPa, from about 0.1 to 1.5 kg s-1 MPa-1. This improvement was attributed to self-propping shear failure of pre-existing natural fractures. The model incorporates physical processes thought to be important during this low-pressure shear stimulation phase. The relatively long periods of injection of water that was significantly cooler than the ambient formation temperature required incorporating in the model both thermo-mechanical and poroelastic effects, which were coupled to fluid flow via Mohr-Coulomb failure and shear-induced increases in fracture permeability. This model resulted in a good match to the wellhead injection data recorded during the stimulation. This numerical model was also used to separate the thermo-mechanical and poroelastic effects, compare their spatial and temporal evolution and carry out sensitivity analyses. To varying degrees, model results depended on variations in permeability anisotropy, elastic and thermal rock properties, Mohr-Coulomb parameters of static and dynamic friction and cohesion, shear-dilatation parameters, injection pressure and length of the injection zone. The thermoelastic and poroelastic effects are realized over different time scales, and their magnitudes are governed by different material properties; in general, model results show greater sensitivity to variations in the coefficient of thermal expansion than in the Biot poroelastic factor. Both thermal and poroelastic contributions to stressing of fractures significantly impact the onset as well as the magnitude of shear-induced permeability gains realized during this low-pressure stimulation.

Fluid-driven fracture and melt transport through lithosphere on earth and terrestrial planets

NASA Astrophysics Data System (ADS)

Fialko, Yuri Alex

Fluid-driven fracture is a fundamental geophysical phenomenon operating in planetary interiors on many scales. A few examples of geological processes involving fluid transport via self-induced fractures include melt segregation in the mantle, magma ascent through the lithosphere, crustal accretion at mid-ocean ridges and volcanic "hot spots", migration of metamorphic and sedimentary fluids in the crust, etc. Overall, fluid-driven (in particular, magma-driven) fracture plays a major role in chemical differentiation of the upper mantle. Because our ability to make direct observations of the dynamics and styles of fluid-driven fracture is quite limited, our understanding of this phenomenon relies on theoretical models that use fundamental physical principles and available field data to constrain the behavior of fluid-driven cracks at depth. This thesis proposes new and more accurate ways of theoretical and experimental description of magma transport in self-induced fractures, or dikes. Dike propagation is a complex process that involves elastic and inelastic deformation of the host rocks, rock fracture, viscous flow of magma, heat transfer, and phase transitions (e.g., rock crystallization and fusion, volatile exolution etc.). We consider relationships between different physical processes associated with magma transport in dikes by solving appropriate boundary value problems of continuum mechanics and heat and mass transfer. The first chapter of this thesis revises existing interpretations of available experimental data bearing on the role of fracture resistance in the overall energy balance during dike propagation. It is shown for the first time that the experimental data indicate that the rock tensile fracture energy, which is not a material property at elevated confining pressures, may substantially increase under in-situ stress conditions. The second chapter concentrates on the interaction between magma flow, heat transfer and phase changes associated with dike emplacement, and discusses some important implications of our results for the generation of the Earth's crust at mid-ocean ridges. In particular, we find that the thermal arrest lengths of typical mid-ocean ridge dikes are of the order of the wavelength of crustal thickness variations and transform fault spacing along slow spreading ridges. This suggests that thermal controls on the crustal melt delivery system could be an important factor in modulating these variations. The third chapter deals with fluid-mechanical aspects of lateral dike propagation in volcanic rift zones. We demonstrate the existence of a feedback between viscous pressure losses during magma transport at depth and the along-strike surface topography of a rift zone. Our estimated values of the along-strike slopes resulting from such a feedback are in general agreement with observations in Hawaiian rift zones. The fourth chapter explores mechanisms of emplacement of giant dike swarms that might have played a role in splitting continents and producing mass extinctions. We reconcile field observations of chilled margins, low crustal contamination, and large dike thicknesses with the theoretically inferred turbulent mode of magma flow in such dikes.

Evidences of volcanic unrest on high-temperature fumaroles by satellite thermal monitoring: The case of Santa Ana volcano, El Salvador

NASA Astrophysics Data System (ADS)

Laiolo, M.; Coppola, D.; Barahona, F.; Benítez, J. E.; Cigolini, C.; Escobar, D.; Funes, R.; Gutierrez, E.; Henriquez, B.; Hernandez, A.; Montalvo, F.; Olmos, R.; Ripepe, M.; Finizola, A.

2017-06-01

On October 1st, 2005, Santa Ana volcano (El Salvador) underwent a VEI 3 phreatomagmatic eruption after approximately one century of rest. Casualties and damages to some of the local infrastructures and surrounding plantations were followed by the evacuation of the nearby communities. The analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) infrared data reveals that the main explosion was preceded by a one-year-long thermal unrest, associated to the development of a fumaroles field, located at the western rim of the summit crater lake. By combining space-based thermal flux and ground-based measurements (seismicity, sulfur emissions and lake temperatures), we suggest that the activity observed at Santa Ana between 2004 and 2005 was driven by the gradual intrusion of an undegassed magma body at a very shallow depth. Magma injection induced thermal anomalies associated with sustained degassing from the fumaroles field and promoted the interaction between the magmatic-hydrothermal system and the overlying water table. This process culminated into the VEI 3 phreatomagmatic eruption of October 2005 that strongly modified the shallow structure of the crater area. The subsequent three-years-long activity resulted from self-sealing of the fracture system and by the opening of a new fracture network directly connecting the deeper hydrothermal system with the crater lake. Our results show that satellite-based thermal data allow us to detect the expansion of the high-temperature fumarolic field. This may precede an explosive eruption and/or a lava dome extrusion. In particular, we show that thermal records can be analyzed with other geochemical (i.e. SO2 emissions) and geophysical (seismicity) data to track a shallow magmatic intrusion interacting with the surrounding hydrothermal system. This provides a remarkable support for volcano monitoring and eruption forecasting, particularly in remote areas where permanent ground data acquisition is hazardous, expensive and difficult.

SO2 flux and the thermal power of volcanic eruptions

NASA Astrophysics Data System (ADS)

Henley, Richard W.; Hughes, Graham O.

2016-09-01

A description of the dynamics, chemistry and energetics governing a volcanic system can be greatly simplified if the expansion of magmatic gas can be assumed to be adiabatic as it rises towards the surface. The conditions under which this assumption is valid are clarified by analysis of the transfer of thermal energy into the low conductivity wallrocks traversed by fractures and vents from a gas phase expanding over a range of mass flux rates. Adiabatic behavior is predicted to be approached typically within a month after perturbations in the release of source gas have stabilized, this timescale being dependent upon only the characteristic length scale on which the host rock is fractured and the thermal diffusivity of the rock. This analysis then enables the thermal energy transport due to gas release from volcanoes to be evaluated using observations of SO2 flux with reference values for the H2O:SO2 ratio of volcanic gas mixtures discharging through high temperature fumaroles in arc and mantle-related volcanic systems. Thermal power estimates for gas discharge are 101.8 to 104.1 MWH during quiescent, continuous degassing of arc volcanoes and 103.7 to 107.3 MWH for their eruptive stages, the higher value being the Plinean Pinatubo eruption in 1991. Fewer data are available for quiescent stage mantle-related volcanoes (Kilauea 102.1 MWH) but for eruptive events power estimates range from 102.8 MWH to 105.5 MWH. These estimates of thermal power and mass of gas discharges are commensurate with power estimates based on the total mass of gas ejected during eruptions. The sustained discharge of volcanic gas during quiescent and short-lived eruptive stages can be related to the hydrodynamic structure of volcanic systems with large scale gaseous mass transfer from deep in the crust coupled with episodes of high level intrusive activity and gas release.

Graphite/Cyanate Ester Face Sheets for Adaptive Optics

NASA Technical Reports Server (NTRS)

Bennett, Harold; Shaffer, Joseph; Romeo, Robert

2008-01-01

It has been proposed that thin face sheets of wide-aperture deformable mirrors in adaptive-optics systems be made from a composite material consisting of cyanate ester filled with graphite. This composite material appears to offer an attractive alternative to low-thermal-expansion glasses that are used in some conventional optics and have been considered for adaptive-optics face sheets. Adaptive-optics face sheets are required to have maximum linear dimensions of the order of meters or even tens of meters for some astronomical applications. If the face sheets were to be made from low-thermal-expansion glasses, then they would also be required to have thicknesses of the order of a millimeter so as to obtain the optimum compromise between the stiffness needed for support and the flexibility needed to enable deformation to controlled shapes by use of actuators. It is difficult to make large glass sheets having thicknesses less than 3 mm, and 3-mm-thick glass sheets are too stiff to be deformable to the shapes typically required for correction of wavefronts of light that has traversed the terrestrial atmosphere. Moreover, the primary commercially produced candidate low-thermal-expansion glass is easily fractured when in the form of thin face sheets. Graphite-filled cyanate ester has relevant properties similar to those of the low-expansion glasses. These properties include a coefficient of thermal expansion (CTE) of the order of a hundredth of the CTEs of other typical mirror materials. The Young s modulus (which quantifies stiffness in tension and compression) of graphite-filled cyanate ester is also similar to the Young's moduli of low-thermal-expansion glasses. However, the fracture toughness of graphite-filled cyanate ester is much greater than that of the primary candidate low-thermal-expansion glass. Therefore, graphite-filled cyanate ester could be made into nearly unbreakable face sheets, having maximum linear dimensions greater than a meter and thicknesses of the order of a millimeter, that would satisfy the requirements for use in adaptive optics.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jewitt, David, E-mail: jewitt@ucla.edu

Asteroids near the Sun can attain equilibrium temperatures sufficient to induce surface modification from thermal fracture, desiccation, and decomposition of hydrated silicates. We present optical observations of nine asteroids with perihelia <0.25 AU (sub-solar temperatures {>=}800 K) taken to search for evidence of thermal modification. We find that the broadband colors of these objects are diverse but statistically indistinguishable from those of planet-crossing asteroids having perihelia near 1 AU. Furthermore, images of these bodies taken away from perihelion show no evidence for on-going mass-loss (model-dependent limits {approx}<1 kg s{sup -1}) that might result from thermal disintegration of the surface. Wemore » conclude that, while thermal modification may be an important process in the decay of near-Sun asteroids and in the production of debris, our new data provide no evidence for it.« less

Effect of prior-austenite grain refinement on microstructure, mechanical properties and thermal embrittlement of 9Cr-1Mo-0.1C steel

NASA Astrophysics Data System (ADS)

Karthikeyan, T.; Dash, Manmath Kumar; Ravikirana; Mythili, R.; Panneer Selvi, S.; Moitra, A.; Saroja, S.

2017-10-01

The effect of 'conventional normalizing and tempering' (CNT) and 'double austenitization based normalizing and tempering' (DNT) heat treatments on the microstructure, tensile, creep and impact toughness properties of 9Cr-1Mo steel has been studied. The tempered martensite microstructure obtained through DNT treatment exhibited smaller sizes of prior-austenite grains/martensite packets (28 μm/11 μm) compared to the CNT treatment (44 μm/14 μm). The tempered martensite morphology was largely retained after long-term thermal aging at 550 °C/5000 h, while the M23C6 and M2(C,N) type of precipitates were found to act as nucleation sites for precipitation of brittle Fe2Mo Laves phase. The grain refinement by DNT was found to be beneficial for minimizing the ductile-to-brittle transition characteristics (25 °C lower ductile-to-brittle transition temperature and 70 J higher upper shelf energy) over the CNT. Thermal embrittlement occurred in both heated treated steels, but the transition temperature of aged DNT steel remained below room temperature. Fractured Charpy specimens revealed ductile failure by void coalescence for high temperature tests, and a quasi-cleavage fracture at low temperatures with few isolated occurrence of intergranular crack in thermal embrittled steel. The DNT treated steel resulted in similar or better tensile and creep properties, when compared to the CNT treatment. The homogeneous fine grained tempered martensite microstructure obtained by DNT treatment resulted in improved embrittlement resistance and mechanical properties over the conventional treatment.

Molybdenum sealing glass-ceramic composition

DOEpatents

Eagan, Robert J.

1976-01-01

The invention relates to a glass-ceramic composition having low hydrogen and helium permeability properties, along with high fracture strength, a thermal coefficient of expansion similar to that of molybdenum, and adaptable for hermetically sealing to molybdenum at temperatures of between about 900.degree. and about 950.degree.C. to form a hermatically sealed insulator body.

Periodontal Emergencies in General Practice.

PubMed

Wadia, Reena; Ide, Mark

2017-05-01

Diagnosing and managing periodontal emergencies is a common part of general dental practice. This article summarises the presentation, aetiology and management of the key periodontal emergencies, including gingival abscess, periodontal abscess, peri-coronitis/peri-coronal abscess, perio-endo lesion/ abscess, necrotising gingivitis and periodontitis, acute herpetic gingivostomatitis, acute physical/chemical/thermal injury and subgingival root fracture.

Processing and Characterization of Cellulose Nanocrystals/Polylactic Acid Nanocomposite Films

Treesearch

Erin Sullivan; Robert Moon; Kyriaki Kalaitzidou

2015-01-01

The focus of this study is to examine the effect of cellulose nanocrystals (CNC) on the properties of polylactic acid (PLA) films. The films are fabricated via melt compounding and melt fiber spinning followed by compression molding. Film fracture morphology, thermal properties, crystallization behavior, thermo-mechanical behavior, and mechanical behavior were...

Simulating Microfracture In Metal-Matrix Composites

NASA Technical Reports Server (NTRS)

Mital, Subodh K.; Chamis, Christos C.; Gotsis, Pascal K.

1994-01-01

Computational procedures developed for simulating microfracture in metal-matrix/fiber composite materials under mechanical and/or thermal loads at ambient and high temperatures. Procedures evaluate microfracture behavior of composites, establish hierarchies and sequences of fracture modes, and examine influences of compliant layers and partial debonding on properties of composites and on initiation of microfractures in them.

NASA NDE Program

NASA Technical Reports Server (NTRS)

Generazio, Ed; Burke, Eric

2015-01-01

The current activities in the National Aeronautics and Space Administration Nondestructive Evaluation (NDE) Program are presented. The topics covered include organizational communications, orbital weld inspection, electric field imaging, fracture critical probability of detection validation, monitoring of thermal protection systems, physical and document standards, image quality indicators, integrity of composite pressure vessels, and NDE for additively manufactured components.

The Mixed Processing Models Development Of Thermal Fracture And Laser Ablation On Glass Substrate

NASA Astrophysics Data System (ADS)

Huang, Kuo-Cheng; Wu, Wen-Hong; Tseng, Shih-Feng; Hwang, Chi-Hung

2011-01-01

As the industries of cell phone and LCD TV were vigorously flourishing and the manufacturing requirements for LCD glass substrate were getting higher, the thermal fracture cutting technology (TFCT) has progressively become the main technology for LCD glass substrate cutting. Due to using laser as the heat source, the TFCT has many advantages, such as uniform heating, small heat effect zone, and high cutting speed, smooth cutting surface and low residual stress, etc. Moreover, a general laser ablation processing or traditional diamond wheel cutting does not have the last two advantages. The article presents a mixed processing of glass substrate, which consists of TFCT and laser ablation mechanisms, and how to enhance the cutting speed with little ablation laser energy. In this study, a 10W Nd:YAG laser and a 40W CO2 laser are used as the heat source of TFCT and laser ablation processing, respectively. The result indicates that the speed of the mixed processing is more than twice the speed of TFCT. Furthermore, after the mixed processing, the residual stresses in the glass substrates are also smaller.

Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 °C

NASA Astrophysics Data System (ADS)

Tung, Hsiao-Ming; Mo, Kun; Stubbins, James F.

2014-04-01

The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials' life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 °C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman-Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures.

Dispersed metal-toughened ceramics and ceramic brazing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moorhead, A.J.; Tiegs, T.N.; Lauf, R.J.

1983-01-01

An alumina (Al/sub 2/O/sub 3/) based material that contains approximately 1 vol % finely dispersed platinum or chromium was developed for use in high temperature thermal-shock resistant electrical insulators. The work at ORNL is divided into two areas: (1) development of DMT ceramics; and (2) development of brazing filler metals suitable for making ceramic-to-ceramic and ceramic-to-metal brazements. The DMT ceramics and brazements are intended for service at elevated temperatures and at high stress levels in the dirty environments of advanced heat engines. The development and characterization of DMT ceramics includes processing (powder preparation, densification and heat treatment) and detailed measurementmore » of mechanical and physical properties (strength, fracture toughness, and thermal conductivity). The brazing work includes: (1) the formulation and melting of small quantities of experimental brazing filler metals; (2) evaluation of the wetting and bonding behavior of these filler metals on Al/sub 2/O/sub 3/, partially stabilized zirconia and ..cap alpha..-SiC in a sessile drop apparatus; and (3) determine the short-term strength and fracture toughness of brazements.« less

Origin(s) of the local structures at the Philae landing site and possible implications on the formation and evolution of the 67P nucleus

NASA Astrophysics Data System (ADS)

Poulet, F.; Lucchetti, A.; Bibring, J. P.

2016-12-01

The in situ images of the 67P/Churyumov-Gerasimenko nucleus acquired by the CIVA cameras on-board PHILAE revealed a rough, irregular and inhomogeneous terrains dominated by fractures and agglomerates of consolidated materials. While the composition of these materials is unknown, they provide unique structures to constrain the conditions prevailing at the surface of a comet and also possibly to the nucleus formation. A quantitative analysis of some microscopic structures (namely fractures and grains that look like pebbles) will be presented using a manual extraction from the CIVA data set with the software ArcGIS. Fractures/cracks are rather ubiquitous at various spatial scales with network and size (from sub-cm to 10 cm) well correlated to the texture of the landscape. The pebble size distribution are reasonably well fitted by power-laws having different cumulative indexes. The nature of the landscape of the landing site will be then discussed in relation to both endogenic and exogenic processes that could have sculpted it. The block seen in CIVA#1 is interpreted to be a close-up of fractured boulders/cliff belonging to the boulder field identified from the orbit near Abydos, this boulder field being itself the result of gravitational regressive erosion due to sublimation (Lucchetti et al. 2016). The observed fractures are best explained by thermal insolation leading to thermal fatigue and/or to loss of volatile materials (e.g., desiccation). This surficial fragmentation (up to >10 cm length) could generate macroscopic erosion that is also visible at larger scale from the orbit. While the pebbles are difficult to be formed by any current physical processes, there is at least an intriguing possibility that they are remnants of primordial accretion processes, as there are several lines of evidence that the nucleus could be primordial (Davidsson et al., 2016), and not a collisional rubble piles of a large body (Morbidelli and Rickman A&A, 2015). We thus speculate that the Abydos landscape could be in favour of pebble accretion model instead of runaway coagulation model with a formation location in the outer region of the Solar System.

Preparation of poly (arylene ether nitrile)/NzdFeB composite film with excellent thermal properties and tensile strength

NASA Astrophysics Data System (ADS)

Pan, Hai; Xu, Mingzhen; Liu, Xiaobo

2017-12-01

PEN/NdFeB composite films were prepared by the solution casting method. The thermal properties, fracture morphology and tensile strength of the composite films were tested by DSC, TGA, SEM and electromechanical universal testing machine, respectively. The results reveal that the composite film has good thermal properties and tensile strength. Glass-transition temperature and decomposition temperatures at weight loss of 5% ot the composite films retain at 166±1 C and 462±4 C, respectively. The composite film with 5 wt.% NdFeB has the best tensile strength value for 100.5 MPa. In addition, it was found that the NdFeB filler was well dispersed in PEN matrix by SEM analysis.

Structural design considerations for micromachined solid-oxide fuel cells

NASA Astrophysics Data System (ADS)

Srikar, V. T.; Turner, Kevin T.; Andrew Ie, Tze Yung; Spearing, S. Mark

Micromachined solid-oxide fuel cells (μSOFCs) are among a class of devices being investigated for portable power generation. Optimization of the performance and reliability of such devices requires robust, scale-dependent, design methodologies. In this first analysis, we consider the structural design of planar, electrolyte-supported, μSOFCs from the viewpoints of electrochemical performance, mechanical stability and reliability, and thermal behavior. The effect of electrolyte thickness on fuel cell performance is evaluated using a simple analytical model. Design diagrams that account explicitly for thermal and intrinsic residual stresses are presented to identify geometries that are resistant to fracture and buckling. Analysis of energy loss due to in-plane heat conduction highlights the importance of efficient thermal isolation in microscale fuel cell design.

Effect of Isothermal Aging and Thermal Cycling on Interfacial IMC Growth and Fracture Behavior of SnAgCu/Cu Joints

NASA Astrophysics Data System (ADS)

Li, Xiaoyan; Li, Fenghui; Guo, Fu; Shi, Yaowu

2011-01-01

The growth behavior of interfacial intermetallic compounds (IMCs) of SnAgCu/Cu soldered joints was investigated during the reflow process, isothermal aging, and thermal cycling with a focus on the influence of these parameters on growth kinetics. The SnAgCu/Cu soldered joints were isothermally aged at 125°C, 150°C, and 175°C while the thermal cycling was performed within the temperature ranges from -25°C to 125°C and -40°C to 125°C. It was observed that a Cu6Sn5 layer formed, followed by rapid coarsening at the solder/Cu interface during reflowing. The grain size of the interfacial Cu6Sn5 was found to increase with aging time, and the morphology evolved from scallop-like to needle-like to rod-like and finally to particles. The rod-like Ag3Sn phase was formed on the solder side in front of the previously formed Cu6Sn5 layer. However, when subject to an increase of the aging time, the Cu3Sn phase was formed at the interface of the Cu6Sn5 layer and Cu substrate. The IMC growth rate increased with aging temperature for isothermally aged joints. During thermal cycling, the thickness of the IMC layer was found to increase with the number of thermal cycles, although the growth rate was slower than that for isothermal aging. The dwell time at the high-temperature end of the thermal cycles was found to significantly influence the growth rate of the IMCs. The growth of the IMCs, for both isothermal aging and thermal cycling, was found to be Arrhenius with aging temperature, and the corresponding diffusion factor and activation energy were obtained by data fitting. The tensile strength of the soldered joints decreased with increasing aging time. Consequently, the fracture site of the soldered joints migrated from the solder matrix to the interfacial Cu6Sn5 layer. Finally, the shear strength of the joints was found to decrease with both an increase in the number of thermal cycles and a decrease in the dwell temperature at the low end of the thermal cycle.

High-temperature superconductor bulk magnets that can trap magnetic fields of over 17 tesla at 29 K.

PubMed

Tomita, Masaru; Murakami, Masato

2003-01-30

Large-grain high-temperature superconductors of the form RE-Ba-Cu-O (where RE is a rare-earth element) can trap magnetic fields of several tesla at low temperatures, and so can be used for permanent magnet applications. The magnitude of the trapped field is proportional to the critical current density and the volume of the superconductor. Various potential engineering applications for such magnets have emerged, and some have already been commercialized. However, the range of applications is limited by poor mechanical stability and low thermal conductivity of the bulk superconductors; RE-Ba-Cu-O magnets have been found to fracture during high-field activation, owing to magnetic pressure. Here we present a post-fabrication treatment that improves the mechanical properties as well as thermal conductivity of a bulk Y-Ba-Cu-O magnet, thereby increasing its field-trapping capacity. First, resin impregnation and wrapping the materials in carbon fibre improves the mechanical properties. Second, a small hole drilled into the centre of the magnet allows impregnation of Bi-Pb-Sn-Cd alloy into the superconductor and inclusion of an aluminium wire support, which results in a significant enhancement of thermal stability and internal mechanical strength. As a result, 17.24 T could be trapped, without fracturing, in a bulk Y-Ba-Cu-O sample of 2.65 cm diameter at 29 K.

Natural radioactivity in geothermal waters, Alhambra Hot Springs and nearby areas, Jefferson County, Montana

USGS Publications Warehouse

Leonard, Robert B.; Janzer, Victor J.

1978-01-01

Radioactive hot springs issue from a fault zone in crystalline rock of the Boulder batholith at Alhambra, Jefferson County, in southwestern Montana. The discharge contains high concentrations of radon, and the gross alpha activity and the concentration of adium-226 exceed maximum levels recommended by the Environmental Protection Agency for drinking water. Part of the discharge is diverted for space heating, bathing, and domestic use. The radioactive thermal waters at measured temperatures of about 60°C are of the sodium bicarbonate type and saturated with respect to calcium carbonate. Radium-226 in the rock and on fractured surfaces or coprecipitated with calcium carbonate probably is the principal source of radon that is dissolved in the thermal water and discharged with other gases from some wells and springs. Local surface water and shallow ground water are of the calcium bicarbonate type and exhibit low background activity. The temperature, percent sodium, and radioactivity of mixed waters adjacent to the fault zone increase with depth. Samples from most of the major hot springs in southwestern Montana have been analyzed for gross alpha and beta activity. The high level of radioactivity at Alhambra appears to be related to leaching of radioactive material from siliceous veins by ascending thermal waters and is not a normal characteristic of hot springs issuing from fractured crystalline rock in Montana.

In-service Inspection Ultrasonic Testing of Reactor Pressure Vessel Welds for Assessing Flaw Density and Size Distribution per 10 CFR 50.61a, Alternate Fracture Toughness Requirements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sullivan, Edmund J.; Anderson, Michael T.; Norris, Wallace

2012-09-17

Pressurized thermal shock (PTS) events are system transients in a pressurized water reactor (PWR) in which there is a rapid operating temperature cool-down that results in cold vessel temperatures with or without repressurization of the vessel. The rapid cooling of the inside surface of the reactor pressure vessel (RPV) causes thermal stresses that can combine with stresses caused by high pressure. The aggregate effect of these stresses is an increase in the potential for fracture if a pre-existing flaw is present in a material susceptible to brittle failure. The ferritic, low alloy steel of the reactor vessel beltline adjacent tomore » the core, where neutron radiation gradually embrittles the material over the lifetime of the plant, can be susceptible to brittle fracture. The PTS rule, described in the Code of Federal Regulations, Title 10, Section 50.61 (§50.61), “Fracture Toughness Requirements for Protection against Pressurized Thermal Shock Events,” adopted on July 23, 1985, establishes screening criteria to ensure that the potential for a reactor vessel to fail due to a PTS event is deemed to be acceptably low. The U.S. Nuclear Regulatory Commission (NRC) completed a research program that concluded that the risk of through-wall cracking due to a PTS event is much lower than previously estimated. The NRC subsequently developed a rule, §50.61a, published on January 4, 2010, entitled “Alternate Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock Events” (75 FR 13). Use of the new rule by licensees is optional. The §50.61a rule differs from §50.61 in that it requires licensees who choose to follow this alternate method to analyze the results from periodic volumetric examinations required by the ASME Code, Section XI, Rules for Inservice Inspection (ISI) of Nuclear Power Plants. These analyses are intended to determine if the actual flaw density and size distribution in the licensee’s reactor vessel beltline welds are bounded by the flaw density and size distribution values used in the PTS technical basis. Under a contract with the NRC, Pacific Northwest National Laboratory (PNNL) has been working on a program to assess the ability of current inservice inspection (ISI)-ultrasonic testing (UT) techniques, as qualified through ASME Code, Appendix VIII, Supplements 4 and 6, to detect small fabrication or inservice-induced flaws located in RPV welds and adjacent base materials. As part of this effort, the investigators have pursued an evaluation, based on the available information, of the capability of UT to provide flaw density/distribution inputs for making RPV weld assessments in accordance with §50.61a. This paper presents the results of an evaluation of data from the 1993 Browns Ferry Nuclear Plant, Unit 3, Spirit of Appendix VIII reactor vessel examination, a comparison of the flaw density/distribution from this data with the distribution in §50.61a, possible reasons for differences, and plans and recommendations for further work in this area.« less

EFFECT OF SODIUM HYDROXIDE AND SUPERCRITICAL FLUID TREATMENTS ON UNRETTED KENAF FIBERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simmons, Kevin L.; Fifield, Leonard S.; Laddha, Sachin

2010-05-17

Kenaf fibers have been gaining great interest for use in the fabrication of both thermoset and thermoplastic composites. However, the inherent fiber surface properties limit their application. In response to the uneconomical, energy inefficient and environmentally unfavorable issues of the standard fiber retting process, we applied chemical modifications of kenaf fibers as alternative retting treatments and investigated the overall performance of the modified fibers. Alkaline solution and super critical alcohol were used as fiber treatments and their effects on the fiber properties were compared. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the thermal properties ofmore » fibers. The change of in chemical composition of the fibers with treatment is discussed in the context of the thermal decomposition behavior. The cellulose crystal structure and total crystallinity of the kenaf fibers were characterized by X-ray diffraction (XRD). Field emission scanning electron microscopy (SEM) was employed to examine the morphological changes of fiber surface and fiber cross-section after both alkaline and super critical alcohol treatments. The mechanical behavior of fibers before and after treatment was explored by tenacity testing and the fracture mechanism was evidenced by observing the fracture surfaces. The effect of chemical treatment duration on the fiber performance was also discussed. It was found that the alkaline treated kenaf fibers showed higher thermal stability than untreated fibers, while TGA results indicated that supercritical alcohol was more efficient in removing the non-cellulosic portions. XRD data confirmed the removal of amorphous structural components such as pectin, hemicellulose and lignin as well as amorphous cellulose for the treated kenaf fibers. SEM images showed that both treatments were effective in removing impurities and coating materials on the fiber surface. The rough fracture morphology observed by SEM indicates that ultimate fibril pull-out occurred.« less

Dependencies of pore pressure on elastic wave velocities and Vp/Vs ratio for thermally cracked gabbro

NASA Astrophysics Data System (ADS)

Nishimura, K.; Uehara, S. I.; Mizoguchi, K.

2015-12-01

Marine seismic refraction have found that there are high Vp/Vs ratio regions in oceanic crusts at subducting oceanic plates (e.g, Cascadia subduction zone (2.0-2.8) (Audet et al., 2009)). Previous studies based on laboratory measurements indicated that Vp/Vs ratio is high when porosity and/or pore pressure is high (Christensen, 1984; Peacock et al., 2011). Although several studies have investigated the relationships between fracture distributions and Vp, Vs (e.g., Wang et al., 2012; Blake et al., 2013), the relationships for rocks (e.g., gabbro and basalt) composing oceanic crust are still unclear. This study reports the results of laboratory measurements of Vp, Vs (transmission method) at controlled confining and pore pressure and estimation of Vp/Vs ratio for thermally cracked gabbro which mimic highly fractured rocks in the high Vp/Vs ratio zone, in order to declare the dependence of fracture distributions on Vp/Vs. For the measurements, we prepared three type specimens; a non-heated intact specimen, specimens heated up to 500 °C and 700 °C for 24 hours. Porosities of intact, 500 °C and 700 °C specimens measured under the atmospheric pressure are 0.5, 3.4 and 3.5%, respectively. Measurements were conducted at a constant confining pressure of 50 MPa, with decreasing pore pressure from 49 to 0.1 MPa and then increasing to 49 MPa. While Vp/Vs for the intact specimen is almost constant at elevated pore pressure, the Vp/Vs values for the thermally cracked ones were 2.0~2.2 when pore pressure was larger than 30 MPa. In future, we will reveal the relationship between the measured elastic wave velocities and the characteristics of the microfracture distribution. This work was supported by JSPS Grant-in-Aid for Scientific Research (Grant Number 26400492).

The Damage Law of HTPB Propellant under Thermomechanical Loading

NASA Astrophysics Data System (ADS)

Liu, Cheng-wu; Yang, Jian-hong; Wang, Xian-meng; Ma, Yong-kang

2016-01-01

By way of measuring the acoustic emission (AE) signals of Hydroxyl-terminated polybutadiene (HTPB) propellant in condition of uniform speed, and combined with the scanning electron microscopy (SEM) fracture surface observation, the damage law of HTPB composite solid propellant under thermomechanical loading was studied. The results show that the effects of thermomechanical loading on HTPB propellant are related to the time and can be divided into three different stages. In the first stage, thermal air aging dominates; in the second stage, interface damage is dominant; and in the third stage, thermal air aging is once again dominant.

Development of composite ceramic materials with improved thermal conductivity and plasticity based on garnet-type oxides

NASA Astrophysics Data System (ADS)

Golovkina, L. S.; Orlova, A. I.; Boldin, M. S.; Sakharov, N. V.; Chuvil'deev, V. N.; Nokhrin, A. V.; Konings, R.; Staicu, D.

2017-06-01

Powders based on the complex garnet-type oxide Y2.5Nd0.5Al5O12 - x wt. % Ni (x = 0, 10, 20) were prepared using wet chemistry methods. Ceramics based on these compounds were obtained by Spark Plasma Sintering (SPS) with a relative densities: 99%. 4% (TD = 4.77 g/cm3 (0%)), 97.6% (TD = 4.88 g/cm3 (10%)), 94.4% (TD = 5.06 g/cm3 (20%)). The influence of nickel concentration on the mechanical (fracture toughness, microhardness) and thermophysical (thermal conductivity) properties of the composites was studied.

Atomistic modeling of BN nanofillers for mechanical and thermal properties: a review.

PubMed

Kumar, Rajesh; Parashar, Avinash

2016-01-07

Due to their exceptional mechanical properties, thermal conductivity and a wide band gap (5-6 eV), boron nitride nanotubes and nanosheets have promising applications in the field of engineering and biomedical science. Accurate modeling of failure or fracture in a nanomaterial inherently involves coupling of atomic domains of cracks and voids as well as a deformation mechanism originating from grain boundaries. This review highlights the recent progress made in the atomistic modeling of boron nitride nanofillers. Continuous improvements in computational power have made it possible to study the structural properties of these nanofillers at the atomistic scale.

Apparently spontaneous fracture of a granitic exfoliation dome: observations and monitoring

NASA Astrophysics Data System (ADS)

Collins, B. D.; Stock, G. M.; Eppes, M. C.; Lewis, S. W.; Corbett, S.; Smith, J. B.

2016-12-01

Exfoliation sheet formation has attracted scientific attention for more than two centuries. Although a number of theories have been proposed, firm understanding of the cause of exfoliation has proved elusive, partly because observations of their formation are scarce. The 2014-2016 spontaneous exfoliation of Twain Harte Dome, located in the western foothills of California's Sierra Nevada Mesozoic granitic batholith, provides an unprecedented opportunity to study this phenomenon. Understanding such events can offer direct insight into similar exfoliating environments where spontaneous rock fracturing generates related geohazards such as rock falls. Twain Harte Dome fractured energetically on at least 5 occasions in August and September 2014, with slabs of rock thrust into the air 40 cm in a few seconds time and surficial fracture of rock occurring over a total area of 2,800 m2. Several of these events were witnessed first-hand and recorded by video. Additional (but non-energetic) cracking occurred during August 2015, followed by another energetic fracturing event in June 2016 over a much smaller (16 m2) area that again sent granite slabs airborne. No previous spontaneous exfoliation had been recorded here over the past 90 years and no obvious trigger (e.g., earthquake) occurred prior to the recent events. Using high-resolution topographic and fracture mapping, acoustic emission monitoring, and environmental monitoring, we show that these fracture events are correlated with hot summer periods - an indication that thermal stresses likely have an important role in causing exfoliation. Surface crackmeter, and subsurface borehole extensometer and rock bolt force measurements strengthen this relationship, with stresses and deformations spiking during hot summer afternoons. Our instrumentation data captured one of the exfoliation events and show that cumulative stress and deformation increases may have acted as precursor signals to the apparently spontaneous rock exfoliation.

Assessment of the Influence of Fractures on the Dynamics of Coal Seam Fires by Numerical Experiments

NASA Astrophysics Data System (ADS)

Wuttke, Manfred W.; Zeng, Qiang

2016-04-01

Uncontrolled burning coal seam fires still constitute major problems for the coal industry by destroying the resource, a serious hazard for the local people by severe environmental pollution, and a tremendous threat to the global environment by the emission of greenhouse gases and aerosols. In particular when the seams are lying shallow the alteration of the immediate surrounding of the coal seam fire feeds back on the dynamics of the fire. Thermal stress induced fracturing produces direct connections of the fire zone with the atmosphere. This influences the supply with oxygen, the venting of the exhaust gases, and the dissipation of heat. The first two processes are expected to enhance the fire propagation whereas the latter effect should slow it down. With our dedicated coal seam fire code ACME ("Amendable Coal-fire Modeling Exercise") we study these coupled effects of fractures in simulations of typical coal seam fire scenarios based on data from Xinjiang, China. Fractures are predefined as 1D/2D objects in a 2D/3D model geometry and are opened depending on the passage of the heat wave produced by the coal seam fire.

Characterization of AISI 4140 borided steels

NASA Astrophysics Data System (ADS)

Campos-Silva, I.; Ortiz-Domínguez, M.; López-Perrusquia, N.; Meneses-Amador, A.; Escobar-Galindo, R.; Martínez-Trinidad, J.

2010-02-01

The present study characterizes the surface of AISI 4140 steels exposed to the paste-boriding process. The formation of Fe 2B hard coatings was obtained in the temperature range 1123-1273 K with different exposure times, using a 4 mm thick layer of boron carbide paste over the material surface. First, the growth kinetics of boride layers at the surface of AISI 4140 steels was evaluated. Second, the presence and distribution of alloying elements on the Fe 2B phase was measured using the Glow Discharge Optical Emission Spectrometry (GDOES) technique. Further, thermal residual stresses produced on the borided phase were evaluated by X-ray diffraction (XRD) analysis. The fracture toughness of the iron boride layer of the AISI 4140 borided steels was estimated using a Vickers microindentation induced-fracture testing at a constant distance of 25 μm from the surface. The force criterion of fracture toughness was determined from the extent of brittle cracks, both parallel and perpendicular to the surface, originating at the tips of an indenter impression. The fracture toughness values obtained by the Palmqvist crack model are expressed in the form KC( π/2) > KC > KC(0) for the different applied loads and experimental parameters of the boriding process.

Ground Penetrating Radar Investigation of Sinter Deposits at Old Faithful Geyser and Immediately Adjacent Hydrothermal Features, Yellowstone National Park, Wyoming, USA

NASA Astrophysics Data System (ADS)

Foley, D.; Lynne, B. Y.; Jaworowski, C.; Heasler, H.; Smith, G.; Smith, I.

2015-12-01

Ground Penetrating Radar (GPR) was used to evaluate the characteristics of the shallow subsurface siliceous sinter deposits around Old Faithful Geyser. Zones of fractures, areas of subsurface alteration and pre-eruption hydrologic changes at Old Faithful Geyser and surrounding hydrothermal mounds were observed. Despite being viewed directly by about 3,000,000 people a year, shallow subsurface geologic and hydrologic conditions on and near Old Faithful Geyser are poorly characterized. GPR transects of 5754 ft (1754m) show strong horizontal to sub-horizontal reflections, which are interpreted as 2.5 to 4.5 meters of sinter. Some discontinuities in reflections are interpreted as fractures in the sinter, some of which line up with known hydrothermal features and some of which have little to no surface expression. Zones with moderate and weak amplitude reflections are interpreted as sinter that has been hydrothermally altered. Temporal changes from stronger to weaker reflections are correlated with the eruption cycle of Old Faithful Geyser, and are interpreted as post-eruption draining of shallow fractures, followed by pre-eruption fracture filling with liquid or vapor thermal fluids.

Residual thermal and moisture influences on the strain energy release rate analysis of edge delamination

NASA Technical Reports Server (NTRS)

Obrien, T. K.; Raju, I. S.; Garber, D. P.

1985-01-01

A laminated plate theory analysis is developed to calculate the strain energy release rate associated with edge delamination growth in a composite laminate. The analysis includes the contribution of residual thermal and moisture stresses to the strain energy released. The strain energy release rate, G, increased when residual thermal effects were combined with applied mechanical strains, but then decreased when increasing moisture content was included. A quasi-three-dimensional finite element analysis indicated identical trends and demonstrated these same trends for the individual strain energy release rate components, G sub I and G sub II, associated with interlaminar tension and shear. An experimental study indicated that for T300/5208 graphite-epoxy composites, the inclusion of residual thermal and moisture stresses did not significantly alter the calculation of interlaminar fracture toughness from strain energy release rate analysis of edge delamination data taken at room temperature, ambient conditions.

Investigation of mechanical and thermal properties of microwave-sintered lunar simulant materials using 2.45 GHz radiation

NASA Technical Reports Server (NTRS)

Meek, T. T.

1990-01-01

The mechanical and thermal properties of lunar simulant material were investigated. An alternative method of examining thermal shock in microwave-sintered lunar samples was researched. A computer code was developed that models how the fracture toughness of a thermally shocked lunar simulant sample is related to the sample hardness as measured by a micro-hardness indentor apparatus. This technique enables much data to be gathered from a few samples. Several samples were sintered at different temperatures and for different times at the temperatures. The melting and recrystallization characteristics of a well-studied binary system were also investigated to see if the thermodynamic barrier for the nucleation of a crystalline phase may be affected by the presence of a microwave field. The system chosen was the albite (sodium alumino silicate) anorthite system (calcium alumino silicate). The results of these investigations are presented.

A review of carbide fuel corrosion for nuclear thermal propulsion applications

NASA Astrophysics Data System (ADS)

Pelaccio, Dennis G.; El-Genk, Mohamed S.; Butt, Darryl P.

1993-10-01

At the operation conditions of interest in nuclear thermal propulsion reactors, carbide materials have been known to exhibit a number of life limiting phenomena. These include the formation of liquid, loss by vaporization, creep and corresponding gas flow restrictions, and local corrosion and fuel structure degradation due to excessive mechanical and/or thermal loading. In addition, the radiation environment in the reactor core can produce a substantial change in its local physical properties, which can produce high thermal stresses and corresponding stress fractures (cracking). Time-temperature history and cyclic operation of the nuclear reactor can also accelerate some of these processes. The University of New Mexico's Institute for Space Nuclear Power Studies, under NASA sponsorship has recently initiated a study to model the complicated hydrogen corrosion process. In support of this effort, an extensive review of the open literature was performed, and a technical expert workshop was conducted. This paper summarizes the results of this review.

A Review of Carbide Fuel Corrosion for Nuclear Thermal Propulsion Applications

NASA Astrophysics Data System (ADS)

Pelaccio, Dennis G.; El-Genk, Mohamed S.; Butt, Darryl P.

1994-07-01

At the operation conditions of interest in nuclear thermal propulsion reactors, carbide materials have been known to exhibit a number of life limiting phenomena. These include the formation of liquid, loss by vaporization, creep and corresponding gas flow restrictions, and local corrosion and fuel structure degradation due to excessive mechanical and/or thermal loading. In addition, the radiation environment in the reactor core can produce a substantial change in its local physical properties, which can produce high thermal stresses and corresponding stress fractures (cracking). Time-temperature history and cyclic operation of the nuclear reactor can also accelerate some of these processes. The University of New Mexico's Institute for Space Nuclear Power Studies, under NASA sponsorship has recently initiated a study to model the complicated hydrogen corrosion process. In support of this effort, an extensive review of the open literature was performed, and a technical expert workshop was conducted. This paper summarizes the results of this review.

Geophysical logging and thermal imaging near the Hemphill Road TCE National Priorities List Superfund site near Gastonia, North Carolina

USGS Publications Warehouse

Antolino, Dominick J.; Chapman, Melinda J.

2017-03-27

Borehole geophysical logs and thermal imaging data were collected by the U.S. Geological Survey near the Hemphill Road TCE (trichloroethylene) National Priorities List Superfund site near Gastonia, North Carolina, during August 2014 through February 2015. In an effort to assist the U.S. Environmental Protection Agency in the development of a conceptual groundwater model for the assessment of current contaminant distribution and future migration of contaminants, surface geological mapping and borehole geophysical log and thermal imaging data collection, which included the delineation of more than 600 subsurface features (primarily fracture orientations), was completed in five open borehole wells and two private supply bedrock wells. In addition, areas of possible groundwater discharge within a nearby creek downgradient of the study site were determined based on temperature differences between the stream and bank seepage using thermal imagery.

Roles of strain and domain boundaries on the phase transition stability of VO2 thin films

NASA Astrophysics Data System (ADS)

Jian, Jie; Chen, Aiping; Chen, Youxing; Zhang, Xinghang; Wang, Haiyan

2017-10-01

The fundamental phase transition mechanism and the stability of the semiconductor-to-metal phase transition properties during multiple thermal cycles have been investigated on epitaxial vanadium dioxide (VO2) thin films via both ex situ heating and in situ heating by transmission electron microscopy (TEM). VO2 thin films were deposited on c-cut sapphire substrates by pulsed laser deposition. Ex situ studies show the broadening of transition sharpness (ΔT) and the width of thermal hysteresis (ΔH) after 60 cycles. In situ TEM heating studies reveal that during thermal cycles, large strain was accumulated around the domain boundaries, which was correlated with the phase transition induced lattice constant change and the thermal expansion. It suggests that the degradation of domain boundary structures in the VO2 films not only caused the transition property reduction (e.g., the decrease in ΔT and ΔH) but also played an important role in preventing the film from fracture during thermal cycles.

2016 Accomplishments. Tritium aging studies on stainless steel. Forging process effects on the fracture toughness properties of tritium-precharged stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgan, Michael J.

Forged austenitic stainless steels are used as the materials of construction for pressure vessels designed to contain tritium at high pressure. These steels are highly resistant to tritium-assisted fracture but their resistance can depend on the details of the forging microstructure. During FY16, the effects of forging strain rate and deformation temperature on the fracture toughness properties of tritium-exposed-and-aged Type 304L stainless steel were studied. Forgings were produced from a single heat of steel using four types of production forging equipment – hydraulic press, mechanical press, screw press, and high-energy-rate forging (HERF). Each machine imparted a different nominal strain ratemore » during the deformation. The objective of the study was to characterize the J-Integral fracture toughness properties as a function of the industrial strain rate and temperature. The second objective was to measure the effects of tritium and decay helium on toughness. Tritium and decay helium effects were measured by thermally precharging the as-forged specimens with tritium gas at 34.5 MPa and 350°C and aging for up to five years at -80°C to build-in decay helium prior to testing. The results of this study show that the fracture toughness properties of the as-forged steels vary with forging strain rate and forging temperature. The effect is largely due to yield strength as the higher-strength forgings had the lower toughness values. For non-charged specimens, fracture toughness properties were improved by forging at 871°C versus 816°C and Screw-Press forgings tended to have lower fracture toughness values than the other forgings. Tritium exposures reduced the fracture toughness values remarkably to fracture toughness values averaging 10-20% of as-forged values. However, forging strain rate and temperature had little or no effect on the fracture toughness after tritium precharging and aging. The result was confirmed by fractography which indicated that fracture modes in the tritium-exposed specimens were similar for all forgings. Another FY16 objective was to prepare fracture toughness specimens from Types 304L and 21-6-9 stainless steel weldments and heat-affected zones (HAZ) for tritium charging.« less

Compositional and microstructural design of highly bioactive P2O5-Na2O-CaO-SiO2 glass-ceramics.

PubMed

Peitl, Oscar; Zanotto, Edgar D; Serbena, Francisco C; Hench, Larry L

2012-01-01

Bioactive glasses having chemical compositions between 1Na(2)O-2CaO-3SiO(2) (1N2C3S) and 1.5Na(2)O-1.5CaO-3SiO(2) (1N1C2S) containing 0, 4 and 6 wt.% P(2)O(5) were crystallized through two stage thermal treatments. By carefully controlling these treatments we separately studied the effects on the mechanical properties of two important microstructural features not studied before, crystallized volume fraction and crystal size. Fracture strength, elastic modulus and indentation fracture toughness were measured as a function of crystallized volume fraction for a constant crystal size. Glass-ceramics with a crystalline volume fraction between 34% and 60% exhibited a three-fold improvement in fracture strength and an increase of 40% in indentation fracture toughness compared with the parent glass. For the optimal crystalline concentration (34% and 60%) these mechanical properties were then measured for different grain sizes, from 5 to 21 μm. The glass-ceramic with the highest fracture strength and indentation fracture toughness was that with 34% crystallized volume fracture and 13 μm crystals. Compared with the parent glass, the average fracture strength of this glass-ceramic was increased from 80 to 210 MPa, and the fracture toughness from 0.60 to 0.95 MPa.m(1/2). The increase in indentation fracture toughness was analyzed using different theoretical models, which demonstrated that it is due to crack deflection. Fortunately, the elastic modulus E increased only slightly; from 60 to 70 GPa (the elastic modulus of biomaterials should be as close as possible to that of cortical bone). In summary, the flexural strength of our best material (215 MPa) is significantly greater than that of cortical bone and comparable with that of apatite-wollastonite (A/W) bioglass ceramics, with the advantage that it shows a much lower elastic modulus. These results thus provide a relevant guide for the design of bioactive glass-ceramics with improved microstructure. Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Fracturing of doleritic intrusions and associated contact zones: Implications for fluid flow in volcanic basins

NASA Astrophysics Data System (ADS)

Senger, Kim; Buckley, Simon J.; Chevallier, Luc; Fagereng, Åke; Galland, Olivier; Kurz, Tobias H.; Ogata, Kei; Planke, Sverre; Tveranger, Jan

2015-02-01

Igneous intrusions act as both carriers and barriers to subsurface fluid flow and are therefore expected to significantly influence the distribution and migration of groundwater and hydrocarbons in volcanic basins. Given the low matrix permeability of igneous rocks, the effective permeability in- and around intrusions is intimately linked to the characteristics of their associated fracture networks. Natural fracturing is caused by numerous processes including magma cooling, thermal contraction, magma emplacement and mechanical disturbance of the host rock. Fracturing may be locally enhanced along intrusion-host rock interfaces, at dyke-sill junctions, or at the base of curving sills, thereby potentially enhancing permeability associated with these features. In order to improve our understanding of fractures associated with intrusive bodies emplaced in sedimentary host rocks, we have investigated a series of outcrops from the Karoo Basin of the Eastern Cape province of South Africa, where the siliciclastic Burgersdorp Formation has been intruded by various intrusions (thin dykes, mid-sized sheet intrusions and thick sills) belonging to the Karoo dolerite. We present a quantified analysis of fracturing in- and around these igneous intrusions based on five outcrops at three individual study sites, utilizing a combination of field data, high-resolution lidar virtual outcrop models and image processing. Our results show a significant difference between the three sites in terms of fracture orientation. The observed differences can be attributed to contrasting intrusion geometries, outcrop geometry (for lidar data) and tectonic setting. Two main fracture sets were identified in the dolerite at two of the sites, oriented parallel and perpendicular to the contact respectively. Fracture spacing was consistent between the three sites, and exhibits a higher degree of variation in the dolerites compared to the host rock. At one of the study sites, fracture frequency in the surrounding host rock increases slightly toward the intrusion at approximately 3 m from the contact. We conclude by presenting a conceptual fluid flow model, showing permeability enhancement and a high potential for fluid flow-channeling along the intrusion-host rock interfaces.

Geothermal Resource Evaluation at Naval Air Station Fallon, Nevada

DTIC Science & Technology

1987-08-01

20 4. Mainside Topographic Map Showing Warm Wells and Thermal Gradient H oles... Oligocene and early Miocene periods. These troughs were sites of intense hyohtic to andesitic volcanism and coeval faulting. The orientation and age...volcanic sequence, (2) intervolcanic sediments in the volcanic sequence. (3) a fractured reservoir within uwderlying Mio- Oligocene acid tuffs and

Turbine Engine Hot Section Technology (HOST)

NASA Technical Reports Server (NTRS)

1982-01-01

Research and plans concerning aircraft gas turbine engine hot section durability problems were discussed. Under the topics of structural analysis, fatigue and fracture, surface protective coatings, combustion, turbine heat transfer, and instrumentation specific points addressed were the thermal and fluid environment around liners, blades, and vanes, material coatings, constitutive behavior, stress-strain response, and life prediction methods for the three components.

10 CFR 50.61 - Fracture toughness requirements for protection against pressurized thermal shock events.

Code of Federal Regulations, 2012 CFR

2012-01-01

... (b)(6) of this section, with RTPTS accounting for the effects of annealing and subsequent irradiation...) ΔRTNDT is the mean value of the transition temperature shift, or change in RTNDT, due to irradiation, and... may not exceed twice those values. (D) The irradiation temperature of the Charpy specimens in the...

10 CFR 50.61 - Fracture toughness requirements for protection against pressurized thermal shock events.

Code of Federal Regulations, 2014 CFR

2014-01-01

... (b)(6) of this section, with RTPTS accounting for the effects of annealing and subsequent irradiation...) ΔRTNDT is the mean value of the transition temperature shift, or change in RTNDT, due to irradiation, and... may not exceed twice those values. (D) The irradiation temperature of the Charpy specimens in the...

10 CFR 50.61 - Fracture toughness requirements for protection against pressurized thermal shock events.

Code of Federal Regulations, 2013 CFR

2013-01-01

... (b)(6) of this section, with RTPTS accounting for the effects of annealing and subsequent irradiation...) ΔRTNDT is the mean value of the transition temperature shift, or change in RTNDT, due to irradiation, and... may not exceed twice those values. (D) The irradiation temperature of the Charpy specimens in the...

10 CFR 50.61 - Fracture toughness requirements for protection against pressurized thermal shock events.

Code of Federal Regulations, 2010 CFR

2010-01-01

... accounting for the effects of annealing and subsequent irradiation. (c) Calculation of RT PTS. RTPTS must be... shift, or change in RTNDT, due to irradiation, and must be calculated using Equation 3. Equation 3... irradiation temperature of the Charpy specimens in the capsule must equal the vessel wall temperature at the...

10 CFR 50.61 - Fracture toughness requirements for protection against pressurized thermal shock events.

Code of Federal Regulations, 2011 CFR

2011-01-01

... (b)(6) of this section, with RTPTS accounting for the effects of annealing and subsequent irradiation...) ΔRTNDT is the mean value of the transition temperature shift, or change in RTNDT, due to irradiation, and... may not exceed twice those values. (D) The irradiation temperature of the Charpy specimens in the...

Investigation on thermal oxidative aging of nitrile rubber (NBR) O-rings under compression stress

NASA Astrophysics Data System (ADS)

Liu, X. R.; Zhang, W. F.; Lou, W. T.; Huang, Y. X.; Dai, W.

2017-11-01

The degradation behaviors of nitrile rubber O-rings exposure to air under compression were investigated at three elevated temperatures. The physical and mechanical properties of the aging samples before and after exposure at selected time were studied by measuring weight loss, tensile strength and elongation at break. The Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and fracture morphology were used to reveal the microstructural changes of the aging samples. The results indicate that the weight decreased with exposure time and temperature. Based on the results of the crosslinking density, the crosslinking predominates during the most of aging process. The significant changes in tensile strength and elongation at break also indicate the severe degradation in air. The fracture morphology results show that the fracture surface after 64 days of exposure to air turns rough and present defects. The ATR-FTIR results demonstrate that the hydroxyl groups were formed for the samples aged in air.

Development of a Rolling Process Design Tool for Use in Improving Hot Roll Slab Recovery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Couch, R; Wang, P

2003-05-06

In this quarter, our primary effort has been focused on model verification, emphasizing on consistency in result for parallel and serial simulation runs, Progress has been made in refining the parallel thermal algorithms and in diminishing discretization effects in the contact region between the rollers and slab. We have received the metrology data of the ingot profile at the end of the fifth pass from Alcoa. Detailed comparisons between the data and the initial simulation result are being performed. Forthcoming from Alcoa are modifications to the fracture model based on additional experiments at lower strain rates. The original fracture model,more » was implemented in the finite element code, but damage in the rolling simulation was not correct due to the modeling errors at lower strain rates and high stress triaxiality. Validation simulations for the fracture model will continue when the experimentally-based adjustments to the parameter values become available.« less

Numerical methods for coupled fracture problems

NASA Astrophysics Data System (ADS)

Viesca, Robert C.; Garagash, Dmitry I.

2018-04-01

We consider numerical solutions in which the linear elastic response to an opening- or sliding-mode fracture couples with one or more processes. Classic examples of such problems include traction-free cracks leading to stress singularities or cracks with cohesive-zone strength requirements leading to non-singular stress distributions. These classical problems have characteristic square-root asymptotic behavior for stress, relative displacement, or their derivatives. Prior work has shown that such asymptotics lead to a natural quadrature of the singular integrals at roots of Chebyhsev polynomials of the first, second, third, or fourth kind. We show that such quadratures lead to convenient techniques for interpolation, differentiation, and integration, with the potential for spectral accuracy. We further show that these techniques, with slight amendment, may continue to be used for non-classical problems which lack the classical asymptotic behavior. We consider solutions to example problems of both the classical and non-classical variety (e.g., fluid-driven opening-mode fracture and fault shear rupture driven by thermal weakening), with comparisons to analytical solutions or asymptotes, where available.

Properties and rapid sintering of a nanostructured tetragonal zirconia composites

NASA Astrophysics Data System (ADS)

Shon, In-Jin; Yoon, Jin-Kook; Hong, Kyung-Tae

2017-09-01

4YSZ is generally used as oxygen sensors, fuel cells, thermal barrier and hip and knee joint replacements as a result of these excellent properties with its high biocompatibility, low density, good resistance against corrosion, high ionic conductivity, hard phase and melting point. However, 4YTZ with coarse grain has low resistance to wear and abrasion because of low hardness and low fracture toughness at room temperature. The fracture toughness and hardness of a 4YTZ can be improved by forming nanostructured composites and addition of a second hard phase. In this study, nanostuctured 4YTZ-graphene composites with nearly full density were achieved using high-frequency induction heated sintering for one min at a pressure of 80 MPa. The rapid consolidation and addition of graphene to 4YTZ retained the nano-scale structure of the ceramic by inhibiting grain growth. The grain size of 4YTZ was reduced remarkably by the addition of graphene and the addition of graphene to 4YTZ greatly improved the fracture toughness without decrease of hardness.

Comments on ''precipitation in partially stabilized zirconia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Claussen, N.

Bansal and Heuer (Am. Ceram. Soc., 58: 235-38(1975)) have concluded that the useful mechanical properties of PSZ, i.e. good fracture toughness and thermal shock resistance, can be attributed to a fine dispersion of monoclinic precipitates in the cubic grains. These coherent precipitates are thought to impede crack propagation, according to a model proposed by Lange, (Philos. Mag., 22: 983-92(1970)) which is based on the concept that a crack front possesses a line energy; i.e. the fracture energy of a composite dispersion increases when the crack front, pinned by the dispersions, bows out between the pinning positions. It is felt thatmore » this model cannot be applied to PSZ nor can the precipitates contribute significantly to the relatively high fracture energy of PSZ compared with other energy-dissipation processes. Data and information are presented showing that it is unjustified to consider this material as an example of evidence that the small precipitates in the grains contribute to the good properties of PSZ. (JRD)« less

Coupled THM processes in EDZ of crystalline rocks using an elasto-plastic cellular automaton

NASA Astrophysics Data System (ADS)

Pan, Peng-Zhi; Feng, Xia-Ting; Huang, Xiao-Hua; Cui, Qiang; Zhou, Hui

2009-05-01

This paper aims at a numerical study of coupled thermal, hydrological and mechanical processes in the excavation disturbed zones (EDZ) around nuclear waste emplacement drifts in fractured crystalline rocks. The study was conducted for two model domains close to an emplacement tunnel; (1) a near-field domain and (2) a smaller wall-block domain. Goodman element and weak element were used to represent the fractures in the rock mass and the rock matrix was represented as elasto-visco-plastic material. Mohr-Coulomb criterion and a non-associated plastic flow rule were adopted to consider the viscoplastic deformation in the EDZ. A relation between volumetric strain and permeability was established. Using a self-developed EPCA2D code, the elastic, elasto-plastic and creep analyses to study the evolution of stress and deformations, as well as failure and permeability evolution in the EDZ were conducted. Results indicate a strong impact of fractures, plastic deformation and time effects on the behavior of EDZ especially the evolution of permeability around the drift.

Porous media of the Red River Formation, Williston Basin, North Dakota: a possible Sedimentary Enhanced Geothermal System

NASA Astrophysics Data System (ADS)

Hartig, Caitlin M.

2018-01-01

Fracture-stimulated enhanced geothermal systems (EGS) can be developed in both crystalline rocks and sedimentary basins. The Red River Formation (Ordovician) is a viable site for development of a sedimentary EGS (SEGS) because the formation temperatures exceed 140 °C and the permeability is 0.1-38 mD; fracture stimulation can be utilized to improve permeability. The spatial variations of the properties of the Red River Formation were analyzed across the study area in order to understand the distribution of subsurface formation temperatures. Maps of the properties of the Red River Formation-including depth to the top of the formation, depth to the bottom of the formation, porosity, geothermal gradient, heat flow, and temperature-were produced by the Kriging interpolation method in ArcGIS. In the future, these results may be utilized to create a reservoir simulation model of an SEGS in the Red River Formation; the purpose of this model would be to ascertain the thermal response of the reservoir to fracture stimulation.

Permeability in fractured rocks from deep geothermal boreholes in the Upper Rhine Graben

NASA Astrophysics Data System (ADS)

Vidal, Jeanne; Whitechurch, Hubert; Genter, Albert; Schmittbuhl, Jean; Baujard, Clément

2015-04-01

Permeability in fractured rocks from deep geothermal boreholes in the Upper Rhine Graben Vidal J.1, Whitechurch H.1, Genter A.2, Schmittbuhl J.1, Baujard C.2 1 EOST, Université de Strasbourg 2 ES-Géothermie, Strasbourg The thermal regime of the Upper Rhine Graben (URG) is characterized by a series of geothermal anomalies on its French part near Soultz-sous-Forêts, Rittershoffen and in the surrounding area of Strasbourg. Sedimentary formations of these areas host oil field widely exploited in the past which exhibit exceptionally high temperature gradients. Thus, geothermal anomalies are superimposed to the oil fields which are interpreted as natural brine advection occurring inside a nearly vertical multi-scale fracture system cross-cutting both deep-seated Triassic sediments and Paleozoic crystalline basement. The sediments-basement interface is therefore very challenging for geothermal industry because most of the geothermal resource is trapped there within natural fractures. Several deep geothermal projects exploit local geothermal energy to use the heat or produce electricity and thus target permeable fractured rocks at this interface. In 1980, a geothermal exploration well was drilled close to Strasbourg down to the Permian sediments at 3220 m depth. Bottom hole temperature was estimated to 148°C but the natural flow rate was too low for an economic profitability (<7 L/s). Petrophysics and reservoir investigations based on core analysis revealed a low matrix porosity with fracture zones spatially isolated and sealed in the sandstone formations. Any stimulation operation was planned and the project was abandoned. The Soultz-sous-Forêts project, initiated in 1986, explored during more than 30 years the experimental geothermal site by drilling five boreholes, three of which extend to 5 km depth. They identified a temperature of 200° C at 5 km depth in the granitic basement but with a variable flow rate. Hydraulic and chemical stimulation operations were applied in order to increase the initial low permeability by reactivating and dissolving sealed fractures in basement. The productivity was considerably improved and allows geothermal exploitation at 165° C and 20 L/s. Recent studies revealed the occurrences of permeable fractures in the limestones of Muschelkalk and the sandstones of Buntsandstein also. For the ongoing project at Rittershoffen, two deep boreholes, drilled down to 2.7 km depth target a reservoir in the sandstones of Buntsandstein and in the granitic basement interface. The thermal, hydraulic and chemical stimulations of the first well lead the project to an economic profitability with a temperature of 170° C and an industrial flow rate of 70 L/s. The deep sedimentary cover and the top of the granitic basement are the main target of the geothermal project in the URG. Permeability of fractured rocks after drilling operations or stimulation operations demonstrates the viability of French industrial deep geothermal projects in the URG was also confirmed by several geothermal projects in Germany that target the similar sediments-basement interface (Landau and Insheim) or the deep Triassic sediments (Bruchsal and Brühl). In France, future geothermal projects are planned in particular in Strasbourg suburb to exploit the permeability of deep-seated fractured sediment-basement interface.

In vitro study of root fracture treated by CO2 laser and DP-bioactive glass paste.

PubMed

Wang, Yin-Lin; Lee, Bor-Shiunn; Tseng, Ching-Li; Lin, Feng-Huei; Lin, Chun-Pin

2008-01-01

An ideal material has yet to be discovered that can successfully treat vertical root fracture. Therefore, the purpose of this study was to use a continuous-wave CO2 laser of medium-energy density to fuse DP-bioactive glass paste (DPGP) to vertical root fracture. The DP-bioglass powder was based on a Na2O-CaO-SiO2-P2O5 system and it was mixed with phosphoric acid (65% concentration) with a powder/liquid ratio of 2 g/4 mL to form DPGP. The interaction of DPGP and dentin was analyzed by means of X-ray diffractometer (XRD) and differential thermal analysis/thermogravimetric analysis (DTA/TGA). Root fracture line was filled with DPGP followed by CO2 laser irradiation and the result was examined by scanning electron microscopy (SEM). The main crystal phase of DPGP was monocalcium phosphate monohydrate (Ca(H2PO4)2.H2O) and the phase transformed to dicalcium phosphate dihydrate (CaHPO4.2H2O) after mixing DPGP with dentin powder (DPG-D). Additionally, gamma-Ca2P2O7 and beta-Ca2P2O7 were identified when DPG-D was lased by CO2 laser. The reaction temperature was between 500 degrees C and 1100 degrees C. SEM results demonstrated that the fracture line was effectively sealed by DPGP. The chemical reaction of DPGP and dentin indicated that DPGP combined with CO2 laser is a potential regimen for the treatment of vertical root fracture.

Quantifying Cyclic Thermal Stresses Due to Solar Exposure in Rock Fragments in Gale Crater, Mars

NASA Astrophysics Data System (ADS)

Hallet, B.; Mackenzie-Helnwein, P.; Sletten, R. S.

2017-12-01

Curiosity and earlier rovers on Mars have revealed in detail rocky landscapes with decaying outcrops, rubble, stone-littered regolith, and bedrock exposures that reflect the weathering processes operating on rock exposed to Mars' cold and hyperarid environment. Evidence from diverse sources points to the importance of thermal stresses driven by cyclic solar exposure in contributing to the mechanical weathering of exposed rock and generation of regolith in various settings on Earth [1,2,3], and even more so on extraterrestrial bodies where large, rapid cyclic temperature variations are frequent (e.g. Mars [4], as well as comets [5], asteroids [6] and other airless bodies [7]). To study these thermal stresses, we use a 3d finite element (FE) model constrained by ground-based surface temperature measurements from Curiosity's Environmental Monitoring Station (REMS). The numerical model couples radiation and conduction with elastic response to determine the temperature and stress fields in individual rocks on the surface of Mars based on rock size and thermo-mechanical properties. We provide specific quantitative results for boulder-size basalt rocks resting on the ground using a realistic thermal forcing that closely matches the REMS temperature observations, and related thermal inertia data. Moreover, we introduce analytical studies showing that these numerical results can readily be generalized. They are quite universal, informing us about thermal stresses due to cyclic solar exposure in general, for rock fragments of different sizes, lithologies, and fracture- thermal- and mechanical-properties. Using Earth-analogue studies to gain insight, we also consider how the shapes, fractures, and surface details of rock fragments imaged by Curiosity likely reflect the importance of rock breakdown due to thermal stresses relative to wind-driven rock erosion and other surface processes on Mars. References:[1] McFadden L et al. (2005) Geol. Soc.Am. Bull. 117(1-2): 161-173 [2] Collins and Stock (2016) Nature Geoscience 9: 395-400 [3] Eppes M C et al. (2016) Geol. Soc.Am. Bull. 128(9-10), 1315-1338. [4] Eppes M C et al. (2015) Nature Communications 6:6712 [5] El-Maarry M R et al. (2015) Geophys. Res. Lett. 42:5170-5178 [6] Delbo M et al. (2014) Nature 508(7495): 233-236 [7] Molaro J L et al. (2017) Icarus 294, 247-261

Chemical and isotopic composition of the Monfortinho thermal water (Portugal): contribution to the aquifer conceptual model and resource evaluation

NASA Astrophysics Data System (ADS)

do Rosário Carvalho, Maria; Martins Carvalho, José

2015-04-01

Groundwaters from quartzite aquifers are usually cold waters with very low mineralization as consequence of circulation in fractured aquifers and rocks with very low solubility. In the Monfortinho, Beira Baixa region in Portugal, a thermal water occurs associated to a Ordovician quartzite syncline, the Penha Garcia syncline (Sequeira et al., 1999). The thermal water is used for balneology and supplies a thermal Spa trough boreholes discharging about 36 l/s. The syncline of Penha Garcia has NW-SE axis and is fractured by a NE-SW fault, where the valley of Ponsul river is developed. The natural discharge of the thermal aquifer occur at the SE edge of the syncline. The Monfortinho thermal water has temperature around 30 °C, pH of 5.45, very low mineralization, with electric conductivity about 35 uS/cm; the main dissolved specie is the SiO2 that reaches 24 mg/L, corresponding to 53% of the total dissolved solids. The chemical facies is of Na-HCO3 type. The d18O and d2H diagram indicates that Monfortinho water is derived from the local meteoric waters. The δ18O and δ2H content also pointed out a recharge area of the thermal aquifer above 400 m of elevation, with a isotopic gradient value of -0.15‰ d18O/100m. This elevation corresponds to the top of the eastern block of the syncline, suggesting that Ponsul fault is a negative barrier to groundwater flow and the thermal aquifer is developed only in eastern block of the syncline. The groundwater flows at about 600-700 m depth along the syncline base toward SE. The average rainfall in the region is 790 mm/year and the estimated recharge is about 17% (Carvalho, 2001) of the precipitation, corresponding to 134 mm/year and 4x105 m3/ano of hydrothermal resource. References: Carvalho, JM (2001). A Hidrogeologia das águas minerais naturais de Monfortinho. Geonovas, Rev. Assoc. Portg. Geólogos, Lisboa, v15, pp. 61-70 (in portuguese). Sequeira, AF, Cunha, PP, Ribeiro, ML (1999). Notícia Explicativa da Folha 25-B Salvaterra do Extremo. Departamento de Geologia, Instituto Geológico e Mineiro, 47 pp. (in portuguese).

Fracture behavior of nano-scale rubber-modified epoxies

NASA Astrophysics Data System (ADS)

Bacigalupo, Lauren N.

The primary focus of the first portion of this study is to compare physical and mechanical properties of a model epoxy that has been toughened with one of three different types of rubber-based modifier: a traditional telechelic oligomer (phase separates into micro-size particles), a core-shell latex particle (preformed nano-scale particles) and a triblock copolymer (self-assembles into nano-scale particles). The effect of modifier content on the physical properties of the matrix was determined using several thermal analysis methods, which provided insight into any inherent alterations of the epoxy matrix. Although the primary objective is to study the role of particle size on the fracture toughness, stiffness and strength were also determined since these properties are often reduced in rubber-toughened epoxies. It was found that since the CSR- and SBM-modified epoxies are composed of less rubber, thermal and mechanical properties of the epoxy were better maintained. In order to better understand the fracture behavior and mechanisms of the three types of rubber particles utilized in this study, extensive microscopy analysis was conducted. Scanning transmission electron microscopy (STEM) was used to quantify the volume fraction of particles, transmission optical microscopy (TOM) was used to determine plastic damage zone size, and scanning electron microscopy (SEM) was used to assess void growth in the plastic zone after fracture. By quantifying these characteristics, it was then possible to model the plastic damage zone size as well as the fracture toughness to elucidate the behavior of the rubber-modified epoxies. It was found that localized shear yielding and matrix void growth are the active toughening mechanisms in all rubber-modified epoxies in this study, however, matrix void growth was more prevalent. The second portion of this study investigated the use of three acrylate-based triblocks and four acrylate-based diblocks to modify a model epoxy system. By varying block lengths and the polarity of the epoxy-miscible blocks, a variety of morphologies were generated (such as spherical micelles, layer particles and worm-like micelles). It was found that in some cases, the epoxy-miscible block did not yield domains substantial enough to facilitate increases in toughness. Overall, the thermal and mechanical properties of the acrylate-based triblock- and diblock-modified epoxies were found to be similar to CTBN-modified epoxy, which was used as a control. However, there were properties that were improved with the acrylate-based diblock-modified epoxies when compared to the acrylate-based triblock modified epoxies. Specifically, the viscosity penalty of the diblock-modified epoxies was shown to be a marked improvement over the triblock-modified epoxies, especially given that the fracture toughness values are similar. This reduction in the viscosity penalty becomes an important criterion when considering processing procedures and applications. Additionally, comparing the morphology of the resulting modified-epoxies utilizing atomic force microscopy (AFM) and scanning electron microscopy (SEM) led to a better understanding of the relationship between the particle morphology obtained and the physical properties of the acrylate-based rubber-modified epoxy systems in this research.

The EGS Collab Project: Stimulation Investigations for Geothermal Modeling Analysis and Validation

NASA Astrophysics Data System (ADS)

Blankenship, D.; Kneafsey, T. J.

2017-12-01

The US DOE's EGS Collab project team is establishing a suite of intermediate-scale ( 10-20 m) field test beds for coupled stimulation and interwell flow tests. The multiple national laboratory and university team is designing the tests to compare measured data to models to improve measurement and modeling toolsets available for use in field sites and investigations such as DOE's Frontier Observatory for Research in Geothermal Energy (FORGE) Project. Our tests will be well-controlled, in situexperiments focused on rock fracture behavior, seismicity, and permeability enhancement. Pre- and post-test modeling will allow for model prediction and validation. High-quality, high-resolution geophysical and other fracture characterization data will be collected, analyzed, and compared with models and field observations to further elucidate the basic relationships between stress, induced seismicity, and permeability enhancement. Coring through the stimulated zone after tests will provide fracture characteristics that can be compared to monitoring data and model predictions. We will also observe and quantify other key governing parameters that impact permeability, and attempt to understand how these parameters might change throughout the development and operation of an Enhanced Geothermal System (EGS) project with the goal of enabling commercial viability of EGS. The Collab team will perform three major experiments over the three-year project duration. Experiment 1, intended to investigate hydraulic fracturing, will be performed in the Sanford Underground Research Facility (SURF) at 4,850 feet depth and will build on kISMET Project findings. Experiment 2 will be designed to investigate hydroshearing. Experiment 3 will investigate changes in fracturing strategies and will be further specified as the project proceeds. The tests will provide quantitative insights into the nature of stimulation (e.g., hydraulic fracturing, hydroshearing, mixed-mode fracturing, thermal fracturing) in crystalline rock under reservoir-like stress conditions and generate high-quality, high-resolution, diverse data sets to be simulated allowing model validation. Monitoring techniques will also be evaluated under controlled conditions identifying technologies appropriate for deeper full-scale EGS sites.

Using Fiber Optic Distributed Acoustic Sensing to Measure Hydromechanics in a Crystalline Rock Aquifer

NASA Astrophysics Data System (ADS)

Ciervo, C.; Becker, M.; Cole, M. C.; Coleman, T.; Mondanos, M.

2016-12-01

Measuring hydromechanical behavior in fractured rock is important for hydraulic fracturing and stimulation in petroleum reservoirs, predicting thermal effects in geothermal fields, and monitoring geologic carbon sequestration injection. We present a new method for measuring geomechanical response to fluid pressure in fractures that employs fiber optic Distributed Acoustic Sensing (DAS). DAS was designed to measure acoustic and seismic signals, often in petroleum wells. DAS seismic monitoring has been proposed as a particularly useful tool for performing seismic testing for carbon sequestration and geothermal projects because fiber optic cable is able to withstand high temperatures and pressures. DAS measures seismic vibration in the Hz to kHz frequency range by measuring strain rate in the fiber optic cable. We adapted this technology to measure rock strain in response to periodic hydraulic pulses in the mHz frequency range. A field experiment was conducted in a low-permeability fractured crystalline bedrock to test the ability of DAS to measure hydromechanical response to periodic pumping and injection. The fiber optic cable was coupled to the borehole wall using a flexible liner designed with an air coupled transducer to measure fluid pressure. Both strain and pressure were measured across a known fracture zone hydraulically connected to the pumping/injection well 30 m away. Periodic strain with amplitudes as small as 50 nm were measured in response to head amplitudes of 2 mm. Clean strain signals were detected at all tested periods of hydraulic oscillation ranging from 2 to 18 minutes. A non-linear relationship was found between opening and closing of the fracture (as measured by cable strain) and fluid pressure in the fracture. The response was also sensitive to the fiber optic cable design. This field test suggests potential for measuring hydraulic connectivity and hydromechanical behavior in fractured formations through cementing fiber optic cable in wellbores outside of well casings.

Thermal Fatigue Behavior of Air-Plasma Sprayed Thermal Barrier Coating with Bond Coat Species in Cyclic Thermal Exposure

PubMed Central

Lu, Zhe; Myoung, Sang-Won; Jung, Yeon-Gil; Balakrishnan, Govindasamy; Lee, Jeongseung; Paik, Ungyu

2013-01-01

The effects of the bond coat species on the delamination or fracture behavior in thermal barrier coatings (TBCs) was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination after flame thermal fatigue (FTF) for 1429 cycles. The TBC with the bond coat prepared by the air-plasma spray (APS) method showed a good condition at the interface between the top and bond coats after cyclic furnace thermal fatigue (CFTF) for 1429 cycles, whereas the TBCs with the bond coats prepared by the high-velocity oxygen fuel (HVOF) and low-pressure plasma spray (LPPS) methods showed a partial cracking (and/or delamination) and a delamination after 780 cycles, respectively. The TBCs with the bond coats prepared by the APS, HVOF and LPPS methods were fully delaminated (>50%) after 159, 36, and 46 cycles, respectively, during the thermal-shock tests. The TGO thickness in the TBCs was strongly dependent on the both exposure time and temperature difference tested. The hardness values were found to be increased only after the CFTF, and the TBC with the bond coat prepared by the APS showed the highest adhesive strength before and after the FTF. PMID:28811441

Evaluation of a novel multiple phase veneering ceramic.

PubMed

Sinthuprasirt, Pannapa; van Noort, Richard; Moorehead, Robert; Pollington, Sarah

2015-04-01

To produce a new veneering ceramic based on the production of a multiple phase glass-ceramic with improved performance in terms of strength and toughness. A composition of 60% leucite, 20% diopside and 20% feldspathic glass was prepared, blended and a heat treatment schedule of 930°C for 5 min was derived from differential thermal analysis (DTA) of the glasses. X-ray diffraction (XRD) and SEM analysis determined the crystalline phases and microstructure. Chemical solubility, biaxial flexural strength (BFS), fracture toughness, hardness, total transmittance and coefficient of thermal expansion (CTE) were all measured in comparison to a commercial veneering ceramic (VITA VM9). Thermal shock resistance of the leucite-diopside and VITA VM9 veneered onto a commercial high strength zirconia (Vita In-Ceram YZ) was also assessed. Statistical analysis was undertaken using Independent Samples t-test. Weibull analysis was employed to examine the reliability of the strength data. The mean chemical solubility was 6 μg/cm(2) for both ceramics (P=1.00). The mean BFS was 109 ± 8 MPa for leucite-diopside ceramic and 79 ± 11 MPa for VITA VM9 ceramic (P=0.01). Similarly, the leucite-diopside ceramic demonstrated a significantly higher fracture toughness and hardness. The average total transmittance was 46.3% for leucite-diopside ceramic and 39.8% for VITA VM9 (P=0.01). The leucite-diopside outperformed the VITA VM9 in terms of thermal shock resistance. Significance This novel veneering ceramic exhibits significant improvements in terms of mechanical properties, yet retains a high translucency and is the most appropriate choice as a veneering ceramic for a zirconia base core material. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Tracing Injection Fluids in Engineered Geothermal Systems

NASA Astrophysics Data System (ADS)

Rose, P. E.; Leecaster, K.; Mella, M.; Ayling, B.; Bartl, M. H.

2011-12-01

The reinjection of produced fluids is crucial to the effective management of geothermal reservoirs, since it provides a mechanism for maintaining reservoir pressures while allowing for the disposal of a toxic byproduct. Tracers are essential to the proper location of injection wells since they are the only known tool for reliably characterizing the flow patterns of recirculated fluids. If injection wells are placed too close to production wells, then reinjected fluids do not have sufficient residence time to extract heat from the reservoir and premature thermal breakthrough results. If injection wells are placed too far away, then the reservoir risks unacceptable pressure loss. Several thermally stable compounds from a family of very detectable fluorescent organic compounds (the naphthalene sulfonates) were characterized and found to be effective for use as geothermal tracers. Through batch-autoclave reactions, their Arrhenius pseudo-first-order decay-rate constants were determined. An analytical method was developed that allows for the laboratory determination of concentrations in the low parts-per-trillion range. Field experiments in numerous geothermal reservoirs throughout the world have confirmed the laboratory findings. Whereas conservative tracers such as the naphthalene sulfonates are effective tools for indicating interwell flow patterns and for measuring reservoir pore volumes, 'reactive' tracers can be used to constrain fracture surface area, which is the effective area for heat extraction. This is especially important for engineered geothermal system (EGS) wells, since reactive tracers can be used to measure fracture surface area immediately after drilling and while the well stimulation equipment is still on site. The reactive properties of these tracers that can be exploited to constrain fracture surface area are reversible sorption, contrasting diffusivity, and thermal decay. Laboratory batch- and flow-reactor experiments in combination with numerical simulation studies have served to identify candidate compounds for use as reactive tracers. An emerging class of materials that show promise for use as geothermal and EGS tracers are colloidal nanocrystals (quantum dots). These are semiconductor particles that fluoresce as a function of particle size. Preliminary laboratory experimentation has demonstrated that these thermally stable, water-soluble particles can serve as conservative tracers for geothermal applications. Likewise, they show promise as potential reactive tracers, since their surfaces can be modified to be reversibly sorptive and their diameters are sufficiently large to allow for contrasts in diffusivity with solute tracers.

Radiation and annealing response of WWER 440 beltline welding seams

NASA Astrophysics Data System (ADS)

Viehrig, Hans-Werner; Houska, Mario; Altstadt, Eberhard

2015-01-01

The focus of this paper is on the irradiation response and the effect of thermal annealing in weld materials extracted from decommissioned WWER 440 reactor pressure vessels of the nuclear power plant Greifswald. The characterisation is based on the measurement of the hardness, the yield stress, the Master Curve reference temperature, T0, and the Charpy-V transition temperature through the thickness of multi-layer beltline welding seams in the irradiated and the thermally annealed condition. Additionally, the weld bead structure was characterised by light microscopic studies. We observed a large variation in the through thickness T0 values in the irradiated as well as in thermally annealed condition. The T0 values measured with the T-S-oriented Charpy size SE(B) specimens cut from different thickness locations of the multilayer welding seams strongly depend on the intrinsic weld bead structure along the crack tip. The Master Curve, T0, and Charpy-V, TT47J, based ductile-to-brittle transition temperature progressions through the thickness of the multi-layer welding seam do not correspond to the forecast according to the Russian code. In general, the fracture toughness values at cleavage failure, KJc, measured on SE(B) specimens from the irradiated and large-scale thermally annealed beltline welding seams follow the Master Curve description, but more than the expected number lie outside the curves for 2% and 98% fracture probability. In this case the test standard ASTM E1921 indicates the investigated multi-layer weld metal as not uniform. The multi modal Master Curve based approach describes the temperature dependence of the specimen size adjusted KJc-1T values well. Thermal annealing at 475 °C for 152 h results in the expected decrease of the hardness and tensile strength and the shift of Master Curve and Charpy-V based ductile-to-brittle transition temperatures to lower values.

Effects of lithium insertion on thermal conductivity of silicon nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Wen; Institute of High Performance Computing, A*STAR, Singapore, Singapore 138632; Zhang, Gang, E-mail: zhangg@ihpc.a-star.edu.sg

2015-04-27

Recently, silicon nanowires (SiNWs) have been applied as high-performance Li battery anodes, since they can overcome the pulverization and mechanical fracture during lithiation. Although thermal stability is one of the most important parameters that determine safety of Li batteries, thermal conductivity of SiNWs with Li insertion remains unclear. In this letter, using molecular dynamics simulations, we study room temperature thermal conductivity of SiNWs with Li insertion. It is found that compared with the pristine SiNW, there is as much as 60% reduction in thermal conductivity with 10% concentration of inserted Li atoms, while under the same impurity concentration the reductionmore » in thermal conductivity of the mass-disordered SiNW is only 30%. With lattice dynamics calculations and normal mode decomposition, it is revealed that the phonon lifetimes in SiNWs decrease greatly due to strong scattering of phonons by vibrational modes of Li atoms, especially for those high frequency phonons. The observed strong phonon scattering phenomenon in Li-inserted SiNWs is similar to the phonon rattling effect. Our study serves as an exploration of thermal properties of SiNWs as Li battery anodes or weakly coupled with impurity atoms.« less

Effects of lithium insertion on thermal conductivity of silicon nanowires

NASA Astrophysics Data System (ADS)

Xu, Wen; Zhang, Gang; Li, Baowen

2015-04-01

Recently, silicon nanowires (SiNWs) have been applied as high-performance Li battery anodes, since they can overcome the pulverization and mechanical fracture during lithiation. Although thermal stability is one of the most important parameters that determine safety of Li batteries, thermal conductivity of SiNWs with Li insertion remains unclear. In this letter, using molecular dynamics simulations, we study room temperature thermal conductivity of SiNWs with Li insertion. It is found that compared with the pristine SiNW, there is as much as 60% reduction in thermal conductivity with 10% concentration of inserted Li atoms, while under the same impurity concentration the reduction in thermal conductivity of the mass-disordered SiNW is only 30%. With lattice dynamics calculations and normal mode decomposition, it is revealed that the phonon lifetimes in SiNWs decrease greatly due to strong scattering of phonons by vibrational modes of Li atoms, especially for those high frequency phonons. The observed strong phonon scattering phenomenon in Li-inserted SiNWs is similar to the phonon rattling effect. Our study serves as an exploration of thermal properties of SiNWs as Li battery anodes or weakly coupled with impurity atoms.

In Vitro Evaluation of the Effect of Chemical and Thermal Stress of the Mechanical Properties of Periodontal Curettes under Simulated Conditions of Sharpening Wear.

PubMed

De Pedro, Daniel; Puglisi, Rosario; Levi, Paul; Pascual, Andrés; Nart, José

To determine whether chemical and thermal stress as well as sharpening are aspects that must be considered to determine when a curette has become too weak to be used safely without the threat of breakage. A total sample of 35 curette blades was divided into 2 principal groups, control (groups 1 to 3) and experimental (groups 4 to 6). The control group was divided into 3 colour-coded groups of 19 similar curette blades and was only subjected to progressive sharpening wear (not sterilised). The test group included 16 Gracey curette blades that were subjected to various degrees of progressive wear and different numbers of sterilisation cycles in 3 subgroups (subgroup 4 had 5 sterilisation cycles; subgroup 5 had 30 cycles and experimental subgroup 6 had 55 cycles). Using a universal testing machine, all blades were tested for strength until they fractured. No evidence was found that the simple presence or absence of sterilisation cycles produced a statistically significant difference between the two studied groups (sterilised and not sterilised). However, when comparing the six subgroups that underwent different numbers of sterilisation cycles, the analysis showed that the more sterilisation cycles a curette underwent, the more likely the curette was to fracture (p = 0.047). Sterilisation by itself does not produce a significant change in the fracture strength, whereas the number of sterilisation cycles clearly weakens the instrument. Sterilisation is a factor to control when evaluating the life of a periodontal curette for the patients' and professionals' safety.

Effect of Groove Design and Post-Weld Heat Treatment on Microstructure and Mechanical Properties of P91 Steel Weld

NASA Astrophysics Data System (ADS)

Pandey, C.; Mahapatra, M. M.

2016-07-01

The martensitic creep-resistant steel designated as ASTM A335 for plate and as P91 for pipe is primarily used for high-temperature and high-pressure applications in steam power plants due to its excellent high-temperature properties such as high creep strength, high thermal conductivity, low thermal expansion, and so on. However, in the case of welded joints of such steels, the presence of an inter-critical heat-affected zone (IC-HAZ) can cause the joint to have lower creep strength than the base metal. In the present study, the effect of post-welding heat treatment (PWHT) and weld groove designs on the overall microstructure and mechanical properties of P91 steel pipe welds produced by the gas tungsten arc welding process was studied. Various regions of welded joints were characterized in detail for hardness and metallographic and tensile properties. Sub-size tensile samples were also tested to evaluate the mechanical properties of the weld metal and heat-affected zone (HAZ) with respect to PWHT. After PWHT, a homogenous microstructure was observed in the HAZ and tensile test fracture samples revealed shifting of the fracture location from the IC-HAZ to the fine-grained heat-affected zone. Before PWHT, the conventional V-grooved welded joints exhibited higher tensile strength compared to the narrow-grooved joints. However, after PWHT, both narrow- and V-grooved joints exhibited similar strength. Fractography of the samples indicates the presence of carbide precipitates such as Cr23C6, VC, and NbC on the fracture surface.

Nanomorphology of Itokawa regolith particles: Application to space-weathering processes affecting the Itokawa asteroid

NASA Astrophysics Data System (ADS)

Matsumoto, Toru; Tsuchiyama, Akira; Uesugi, Kentaro; Nakano, Tsukasa; Uesugi, Masayuki; Matsuno, Junya; Nagano, Takashi; Shimada, Akira; Takeuchi, Akihisa; Suzuki, Yoshio; Nakamura, Tomoki; Nakamura, Michihiko; Gucsik, Arnold; Nagaki, Keita; Sakaiya, Tatsuhiro; Kondo, Tadashi

2016-08-01

The morphological properties of 26 regolith particles from asteroid Itokawa were observed using scanning electron microscopes in combination with an investigation of their three-dimensional shapes obtained through X-ray microtomography. Surface observations of a cross section of the LL5 chondrite, and of crystals of olivine and pyroxene, were also performed for comparison. Some Itokawa particles have surfaces corresponding to walls of microdruses in the LL chondrite, where concentric polygonal steps develop and euhedral or subhedral grains exist. These formed through vapor growth owing to thermal annealing, which might have been caused by thermal metamorphism or shock-induced heating in Itokawa's parent body. Most of the Itokawa particles have more or less fractured surfaces, indicating that they were formed by disaggregation, probably caused by impacts. Itokawa particles with angular and rounded edges observed in computed tomography images are associated with surfaces exhibiting clear and faint structures, respectively. These surfaces can be interpreted by invoking different degrees of abrasion after regolith formation. A possible mechanism for the abrasion process is grain migration caused by impact-driven seismic waves. Space-weathered rims with blisters are distributed heterogeneously across the Itokawa regolith particles. This heterogeneous distribution can be explained by particle motion and fracturing, combined with solar-wind irradiation of the particle surfaces. The regolith activity-including grain motion, fracturing, and abrasion-might effectively act as refreshing process of Itokawa particles against space-weathered rim formation. The space-weathering processes affecting Itokawa would have developed simultaneously with space-weathered rim formation and regolith particle refreshment.

Hydrogen Embrittlement Susceptibility and Safety Control of Reheated CGHAZ in X80 Welded Pipeline

NASA Astrophysics Data System (ADS)

Deng, Qiushi; Zhao, Weimin; Jiang, Wei; Zhang, Timing; Li, Tingting; Zhao, Yujiao

2018-03-01

Coarse-grained heat-affected zone (CGHAZ) exhibits the highest hydrogen embrittlement (HE) susceptibility, which changes under the influence of thermal cycle. In this study, slow strain rate tension (SSRT) tests were conducted to investigate the HE susceptibility of reheated CGHAZs and the critical hydrogen pressure for fracture failure. Results show that intercritically reheated CGHAZ (ICCGHAZ) possesses the lowest HE resistance. Analyses of HE index and fracture indicate that the critical hydrogen pressure is 3.5 MPa. Microstructure analysis reveals that HE susceptibility is associated with multiple factors, such as phase composition, grain coarsening, HAB density, and MA constituent. Blocky necklace-like MA constituent along prior austenite boundaries plays a predominant role in intensifying the HE susceptibility of ICCGHAZ.

Composite structural materials

NASA Technical Reports Server (NTRS)

Loewy, Robert G.; Wiberley, Stephen E.

1987-01-01

The development and application of composite materials to aerospace vehicle structures which began in the mid 1960's has now progressed to the point where what can be considered entire airframes are being designed and built using composites. Issues related to the fabrication of non-resin matrix composites and the micro, mezzo and macromechanics of thermoplastic and metal matrix composites are emphasized. Several research efforts are presented. They are entitled: (1) The effects of chemical vapor deposition and thermal treatments on the properties of pitch-based carbon fiber; (2) Inelastic deformation of metal matrix laminates; (3) Analysis of fatigue damage in fibrous MMC laminates; (4) Delamination fracture toughness in thermoplastic matrix composites; (5) Numerical investigation of the microhardness of composite fracture; and (6) General beam theory for composite structures.

Preparation and properties of TiC-Ni cermets using Ni-plated TiC

NASA Astrophysics Data System (ADS)

Shin, Soon-Gi

2002-04-01

TiC powders were coated with Ni by a chemical plating technique and the pressed compacts sintered at 1623K. The density of the sintered bodies was 98-99%. Compared with mechanically-mixed powder, Ni-plated TiC powders gave a more uniform microstructure in which TiC particles were well dispersed in the Ni matrix. The cermets exhibited ductile fracture for TiC-70 vol.% Ni and brittle fracture for TiC-30 vol.% Ni. The flexural strength was improved by the homogeneous dispersion of TiC. The thermal expansion coefficient increased with a decrease in Ni content, following a nearly linear law of mixtures on the basis of volume fractions of pure TiC and Ni.

Modeling Thermal Pressurization Around Shallow Dikes Using Temperature-Dependent Hydraulic Properties: Implications for Deformation Around Intrusions

NASA Astrophysics Data System (ADS)

Townsend, Meredith R.

2018-01-01

Pressurization and flow of groundwater around igneous intrusions depend in part on the hydraulic diffusivity of the host rocks and processes that enhance diffusivity, such as fracturing, or decrease diffusivity, such as mineral precipitation during chemical alteration. Characterizing and quantifying the coupled effects of alteration, pore pressurization, and deformation have significant implications for deformation around intrusions, geothermal energy, contact metamorphism, and heat transfer at mid-ocean ridges. Fractures around dikes at Ship Rock, New Mexico, indicate that pore pressures in the host rocks exceeded hydrostatic conditions by at least 15 MPa following dike emplacement. Hydraulic measurements and petrographic analysis indicate that mineral precipitation clogged the pores of the host rock, reducing porosity from 0.25 to <0.10 and reducing permeability by 5 orders of magnitude. Field data from Ship Rock are used to motivate and constrain numerical models for thermal pore fluid pressurization adjacent to a meter-scale dike, using temperature-dependent hydraulic properties in the host rock as a proxy for porosity loss by mineral precipitation during chemical alteration. Reduction in permeability by chemical alteration has a negligible effect on pressurization. However, reduction in porosity by mineral precipitation increases fluid pressure by constricting pore volume and is identified as a potentially significant source of pressure. A scaling relationship is derived to determine when porosity loss becomes important; if permeability is low enough, pressurization by porosity loss outweighs pressurization by thermal expansion of fluids.

Fatigue crack propagation resistance of virgin and highly crosslinked, thermally treated ultra-high molecular weight polyethylene.

PubMed

Gencur, Sara J; Rimnac, Clare M; Kurtz, Steven M

2006-03-01

To prolong the life of total joint replacements, highly crosslinked ultra-high molecular weight polyethylenes (UHMWPEs) have been introduced to improve the wear resistance of the articulating surfaces. However, there are concerns regarding the loss of ductility and potential loss in fatigue crack propagation (FCP) resistance. The objective of this study was to evaluate the effects of gamma radiation-induced crosslinking with two different post-irradiation thermal treatments on the FCP resistance of UHMWPE. Two highly crosslinked and one virgin UHMWPE treatment groups (ram-extruded, orthopedic grade, GUR 1050) were examined. For the two highly crosslinked treatment groups, UHMWPE rods were exposed to 100 kGy and then underwent post-irradiation thermal processing either above the melt temperature or below the melt temperature (2 h-150 degrees C, 110 degrees C). Compact tension specimens were cyclically loaded to failure and the fatigue crack growth rate, da/dN, vs. cyclic stress intensity factor, DeltaK, behavior was determined and compared between groups. Scanning electron microscopy was used to examine fracture surface characteristics. Crosslinking was found to decrease the ability of UHMWPE to resist crack inception and propagation under cyclic loading. The findings also suggested that annealing as a post-irradiation treatment may be somewhat less detrimental to FCP resistance of UHMWPE than remelting. Scanning electron microscopy examination of the fracture surfaces demonstrated that the virgin treatment group failed in a more ductile manner than the two highly crosslinked treatment groups.

Finsler-Geometric Continuum Mechanics

DTIC Science & Technology

2016-05-01

gravitation and astrophysical applications. Physical Review D. 1977;16:1643–1663. 50. Ozakin A, Yavari A. A geometric theory of thermal stresses...to physical problems of tensile fracture, shear localization, and cavitation in solid bodies. The pseudo-Finsler approach is demonstrated to be more...Weyl-type transformation of the fundamental tensor, analytical and numerical solutions of representative example problems offer new physical insight

Microhardness, Friction and Wear of SiC and Si3N4 Materials as a Function of Load, Temperature and Environment.

DTIC Science & Technology

1980-10-01

rather than by microplasticity . At 500 C, on the other hand, Si showed substantial crack tip plasticity. Koss and Chan (47) have studied fracture along...materials prone to such chemomechanical effects, thermal desorption of adsorbed species will result in changes in hardness behaviour in addition to the

Influence of MWCNTs addition on mechanical and thermal behaviour of epoxy/kenaf multi-scale nanocomposite

NASA Astrophysics Data System (ADS)

Noor, N. A. M.; Razak, J. A.; Ismail, S.; Mohamad, N.; Yaakob, M. Y.; Theng, T. H.

2017-06-01

This research was conducted to develop kenaf reinforced epoxy/MWCNTs multi-scale composite using kenaf fibre and MWCNTs as the reinforcement in epoxy as the hosted matrix. The composites were produced by using a combination of hand lay-up and vacuum bagging process. The selection of optimum composition of epoxy-MWCNTs is based on the MWCNTs loading and the resulted mixture viscosity. Lower resin viscosity is required to allow good wetting and interaction between matrix and filler, which will yielded superior final performance of the fabricated composites. Therefore, different loading of MWCNTs (0.0 wt. %, 0.5 wt. %, 1.0 wt. %, 3.0 wt. %, 5.0 wt. %, 7.0 wt. %) were used to investigate the mechanical and thermal properties of the composites. As a result, the epoxy/kenaf/MWCNTs multi-scale composite at 1.0 wt. % of MWCNTs addition had yielded substantial improvement by 15.54 % in tensile strength and 90.54 % in fracture toughness. Besides, the fracture surface morphology of the selected samples were analysed via scanning electron microscopy (SEM) observation to further support the reinforcement characteristic of epoxy/kenaf/MWCNTs multi-scale composite.

Annular Air Leaks in a liquid hydrogen storage tank

NASA Astrophysics Data System (ADS)

Krenn, AG; Youngquist, RC; Starr, SO

2017-12-01

Large liquid hydrogen (LH2) storage tanks are vital infrastructure for NASA, the DOD, and industrial users. Over time, air may leak into the evacuated, perlite filled annular region of these tanks. Once inside, the extremely low temperatures will cause most of the air to freeze. If a significant mass of air is allowed to accumulate, severe damage can result from nominal draining operations. Collection of liquid air on the outer shell may chill it below its ductility range, resulting in fracture. Testing and analysis to quantify the thermal conductivity of perlite that has nitrogen frozen into its interstitial spaces and to determine the void fraction of frozen nitrogen within a perlite/frozen nitrogen mixture is presented. General equations to evaluate methods for removing frozen air, while avoiding fracture, are developed. A hypothetical leak is imposed on an existing tank geometry and a full analysis of that leak is detailed. This analysis includes a thermal model of the tank and a time-to-failure calculation. Approaches to safely remove the frozen air are analyzed, leading to the conclusion that the most feasible approach is to allow the frozen air to melt and to use a water stream to prevent the outer shell from chilling.

Consequences of the Thermal Transient on the Evolution of the Damaged Zone Around a Repository for Heat-Emitting High-Level Radioactive Waste in a Clay Formation: a Performance Assessment Perspective

NASA Astrophysics Data System (ADS)

Yu, Li; Weetjens, Eef; Sillen, Xavier; Vietor, Tim; Li, Xiangling; Delage, Pierre; Labiouse, Vincent; Charlier, Robert

2014-01-01

A proper evaluation of the perturbations of the host rock induced by the excavation and the emplacement of exothermic wastes is essential for the assessment of the long-term safety of high-level radioactive waste disposals in clay formations. The impact of the thermal transient on the evolution of the damaged zone (DZ) has been explored in the European Commission project TIMODAZ (thermal impact on the damaged zone around a radioactive waste disposal in clay host rocks, 2006-2010). This paper integrates the scientific results of the TIMODAZ project from a performance assessment (PA) point of view, showing how these results support and justify key PA assumptions and the values of PA model parameters. This paper also contextualises the significance of the thermal impact on the DZ from a safety case perspective, highlighting how the project outcomes result into an improved understanding of the thermo-hydro-mechanical behaviour of the clay host rocks. The results obtained in the TIMODAZ project strengthen the assessment basis of the safety evaluation of the current repository designs. There was no evidence throughout the TIMODAZ experimental observations of a temperature-induced additional opening of fractures nor of a significant permeability increase of the DZ. Instead, thermally induced plasticity, swelling and creep seem to be beneficial to the sealing of fractures and to the recovery of a very low permeability in the DZ, close to that of an undisturbed clay host rock. Results from the TIMODAZ project indicate that the favourable properties of the clay host rock, which guarantee the effectiveness of the safety functions of the repository system, are expected to be maintained after the heating-cooling cycle. Hence, the basic assumptions usually made in PA calculations so far are expected to remain valid, and the performance of the system should not be affected in a negative way by the thermal evolution of the DZ around a radioactive waste repository in clay host rock.

Effect of core ceramic grinding on fracture behaviour of bilayered zirconia veneering ceramic systems under two loading schemes.

PubMed

Jian, Yu-Tao; Tang, Tian-Yu; Swain, Michael V; Wang, Xiao-Dong; Zhao, Ke

2016-12-01

The aim of this in vitro study was to evaluate the effect of core ceramic grinding on the fracture behaviour of bilayered zirconia under two loading schemes. Interfacial surfaces of sandblasted zirconia disks (A) were ground with 80 (B), 120 (C) and 220 (D) grit diamond discs, respectively. Surface roughness and topographic analysis were performed using a confocal scanning laser microscope (CSLM) and a scanning electron microscopy (SEM). Relative monoclinic content was evaluated using X-ray diffraction analysis (XRD) then reevaluated after simulated veneer firing. Biaxial fracture strength (σ) and Weibull modulus (m) were calculated either with core in compression (subgroup Ac-Dc) or in tension (subgroup At-Dt). Facture surfaces were examined by SEM and energy dispersive X-ray spectroscopy (EDS). Maximum tensile stress at fracture was estimated by finite element analysis. Statistical data analysis was performed using Kruskal-Wallis and one-way ANOVA at a significance level of 0.05. As grit size of the diamond disc increased, zirconia surface roughness decreased (p<0.001). Thermal veneering treatment reversed the transformation of monoclinic phase observed after initial grinding. No difference in initial (p=0.519 for subgroups Ac-Dc) and final fracture strength (p=0.699 for subgroups Ac-Dc; p=0.328 for subgroups At-Dt) was found among the four groups for both loading schemes. While coarse grinding slightly increased final fracture strength reliability (m) for subgroups Ac-Dc. Two different modes of fracture were observed according to which material was on the bottom surface. Components of the liner porcelain remained on the zirconia surface after fracture for all groups. Technician grinding changed surface topography of zirconia ceramic material, but was not detrimental to the bilayered system strength after veneer application. Coarse grinding slightly improved the fracture strength reliability of the bilayered system tested with core in compression. It is recommended that veneering porcelain be applied directly after routine lab grinding of zirconia ceramic, and its application on rough zirconia cores may be preferred to enhance bond strength. Copyright © 2016. Published by Elsevier Ltd.

Research on graphite reinforced glass matrix composites

NASA Technical Reports Server (NTRS)

Prewo, K. M.; Thompson, E. R.

1981-01-01

A broad group of fibers and matrices were combined to create a wide range of composite properties. Primary material fabrication procedures were developed which readily permit the fabrication of flat plate and shaped composites. Composite mechanical properties were measured under a wide range of test conditions. Tensile, flexure mechanical fatigue, thermal fatigue, fracture toughness, and fatigue crack growth resistance were evaluated. Selected fiber-matrix combinations were shown to maintain their strength at up to 1300 K when tested in an inert atmosphere. Composite high temperature mechanical properties were shown to be limited primarily by the oxidation resistance of the graphite fibers. Composite thermal dimensional stability was measured and found to be excellent.

Metal matrix composites: Testing, analysis, and failure modes; Proceedings of the Symposium, Sparks, NV, Apr. 25, 26, 1988

NASA Technical Reports Server (NTRS)

Johnson, W. S. (Editor)

1989-01-01

The present conference discusses the tension and compression testing of MMCs, the measurement of advanced composites' thermal expansion, plasticity theory for fiber-reinforced composites, a deformation analysis of boron/aluminum specimens by moire interferometry, strength prediction methods for MMCs, and the analysis of notched MMCs under tensile loading. Also discussed are techniques for the mechanical and thermal testing of Ti3Al/SCS-6 MMCs, damage initiation and growth in fiber-reinforced MMCs, the shear testing of MMCs, the crack growth and fracture of continuous fiber-reinforced MMCs in view of analytical and experimental results, and MMC fiber-matrix interface failures.

Water and the thermal evolution of carbonaceous chondrite parent bodies

NASA Technical Reports Server (NTRS)

Grimm, Robert E.; Mcsween, Harry Y., Jr.

1989-01-01

Two hypotheses are proposed for the aqueous alteration of carbonaceous chondrites within their parent bodies, in which respectively the alteration occurs (1) throughout the parent body interior, or (2) in a postaccretional surface regolith; both models assume an initially homogeneous mixture of ice and rock that is heated through the decay of Al-26. Water is seen to exert a powerful influence on chondrite evolution through its role of thermal buffer, permitting substitution of a low temperature aqueous alteration for high temperature recrystallization. It is quantitatively demonstrated that liquid water may be introduced by either hydrothermal circulation, vapor diffusion from below, or venting due to fracture.

Microstructure and Mechanical Property of SiCf/SiC and Cf/SiC Composites

NASA Astrophysics Data System (ADS)

Lee, S. P.; Cho, K. S.; Lee, H. U.; Lee, J. K.; Bae, D. S.; Byun, J. H.

2011-10-01

The mechanical properties of SiC based composites reinforced with different types of fabrics have been investigated, in conjunction with the detailed analyses of their microstructures. The thermal shock properties of SiCf/SiC composites were also examined. All composites showed a dense morphology in the matrix region. Carbon coated PW-SiCf/SiC composites had a good fracture energy, even if their strength was lower than that of PW-Cf/SiC composites. SiCf/SiC composites represented a great reduction of flexural strength at the thermal shock temperature difference of 300 °C.

Thermal Shock Properties of a 2D-C/SiC Composite Prepared by Chemical Vapor Infiltration

NASA Astrophysics Data System (ADS)

Zhang, Chengyu; Wang, Xuanwei; Wang, Bo; Liu, Yongsheng; Han, Dong; Qiao, Shengru; Guo, Yong

2013-06-01

The thermal shock properties of a two-dimensional carbon fiber-reinforced silicon carbide composite with a multilayered self-healing coating (2D-C/SiC) were investigated in air. The composite was prepared by low-pressure chemical vapor infiltration. 2D-C/SiC specimens were thermally shocked for different cycles between 900 and 300 °C. The thermal shock resistance was characterized by residual tensile properties and mass variation. The change of the surface morphology and microstructural evolution of the composite were examined by a scanning electron microscope. In addition, the phase evolution on the surfaces was identified using an X-ray diffractometer. It is found that the composite retains its tensile strength within 20 thermal shock cycles. However, the modulus of 2D-C/SiC decreases gradually with increasing thermal shock cycles. Extensive pullout of fibers on the fractured surface and peeling off of the coating suggest that the damage caused by the thermal shock involves weakening of the bonding strength of coating/composite and fiber/matrix. In addition, the carbon fibers in the near-surface zone were oxidized through the matrix cracks, and the fiber/matrix interfaces delaminated when the composite was subjected to a larger number of thermal shock cycles.

Classification of Thermal Patterns at Karst Springs and Cave Streams

USGS Publications Warehouse

Luhmann, A.J.; Covington, M.D.; Peters, Albert J.; Alexander, S.C.; Anger, C.T.; Green, J.A.; Runkel, Anthony C.; Alexander, E.C.

2011-01-01

Thermal patterns of karst springs and cave streams provide potentially useful information concerning aquifer geometry and recharge. Temperature monitoring at 25 springs and cave streams in southeastern Minnesota has shown four distinct thermal patterns. These patterns can be divided into two types: those produced by flow paths with ineffective heat exchange, such as conduits, and those produced by flow paths with effective heat exchange, such as small fractures and pore space. Thermally ineffective patterns result when water flows through the aquifer before it can equilibrate to the rock temperature. Thermally ineffective patterns can be either event-scale, as produced by rainfall or snowmelt events, or seasonal scale, as produced by input from a perennial surface stream. Thermally effective patterns result when water equilibrates to rock temperature, and the patterns displayed depend on whether the aquifer temperature is changing over time. Shallow aquifers with seasonally varying temperatures display a phase-shifted seasonal signal, whereas deeper aquifers with constant temperatures display a stable temperature pattern. An individual aquifer may display more than one of these patterns. Since karst aquifers typically contain both thermally effective and ineffective routes, we argue that the thermal response is strongly influenced by recharge mode. ?? 2010 The Author(s). Journal compilation ?? 2010 National Ground Water Association.

Alaska Open-File Report 127 Assessment of Thermal Springs Sites in Southern Southeastern Alaska - Preliminary Results and Evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Motyka, Roman J.; Moorman, Mary A.; Reeder, John W.

1980-06-01

Information has been gathered on 13 reported thermal-spring sites, 12 in southern Southeastern Alaska and one in western British Columbia. Five of the reported sites could not be substantiated by DGGS. The eight known thermal spring sites are associated with grainitic terrain and, except for Baker Island Hot Springs, occur within or near intensively fractured Cretaceous-age pluons of the Coast Range Batholith. Thermal-spring surface temperatures range from 21 C (Twin Lakes) to 91.5 C (Bailey Bay). The greatest discharge occurs at Chief Shakes hot springs (450 1pm). Bell Island Hot Springs, which has about a 100-1 pm discharge and amore » 70 C temperature, has had the most development. Two previously unreported thermal-spring sites, Barnes Lake warm springs and Bradfield hot springs, have a low rate of discharge and respective surface temperatures of about 25 and 54 C. The known thermal springs probably originate from circulation of meteoric waters through deep-seated fracture and fault systems. The chemical constituents of the alkali-sulfate to alkali-chloride thermal waters are probably derived from interaction of the deeply circulating meteoric waters with the granitic wall rocks. Chemical geothermometry suggests subsurface temperatures of 55 to 151 C. If waters are being heated solely by conduction from wall rocks, circulation depths must be about 1.5 to 5 km, assuming geothermal gradients of 30 to 50 C/km. Variations in temperature, discharge, and chemistry were noted at several thermal springs for which previous records are available. A major decrease in silica and potassium concentrations at Chief Shakes hot springs is suggested by comparing recent analyses of water chemistry to Waring's (1917) original analysis. The rate of discharge at Bell Island Hot Springs may have increased by a factor of two since Waring's visit to the springs. Subsurface reservoirs associated with thermal springs in southern Southeastern Alaska are of low temperature and are probably limited in extent, compared to geothermal fields now being used elsewhere in the world. Only the Bell Island and Bailey Bay sites now offer any potential for generation of electricity; these sites could also be used for a variety of direct uses such as space heating, wood or lumber processing, and perhaps aquaculture. The other sites have less potential but could be used locally for space heating or agriculture enhancement.« less

Flexible parallel implicit modelling of coupled thermal-hydraulic-mechanical processes in fractured rocks

NASA Astrophysics Data System (ADS)

Cacace, Mauro; Jacquey, Antoine B.

2017-09-01

Theory and numerical implementation describing groundwater flow and the transport of heat and solute mass in fully saturated fractured rocks with elasto-plastic mechanical feedbacks are developed. In our formulation, fractures are considered as being of lower dimension than the hosting deformable porous rock and we consider their hydraulic and mechanical apertures as scaling parameters to ensure continuous exchange of fluid mass and energy within the fracture-solid matrix system. The coupled system of equations is implemented in a new simulator code that makes use of a Galerkin finite-element technique. The code builds on a flexible, object-oriented numerical framework (MOOSE, Multiphysics Object Oriented Simulation Environment) which provides an extensive scalable parallel and implicit coupling to solve for the multiphysics problem. The governing equations of groundwater flow, heat and mass transport, and rock deformation are solved in a weak sense (either by classical Newton-Raphson or by free Jacobian inexact Newton-Krylow schemes) on an underlying unstructured mesh. Nonlinear feedbacks among the active processes are enforced by considering evolving fluid and rock properties depending on the thermo-hydro-mechanical state of the system and the local structure, i.e. degree of connectivity, of the fracture system. A suite of applications is presented to illustrate the flexibility and capability of the new simulator to address problems of increasing complexity and occurring at different spatial (from centimetres to tens of kilometres) and temporal scales (from minutes to hundreds of years).

Relative Dating Via Fractures

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site]

This VIS image of the eastern part of the Tharsis region illustrates how fractures can be used in relative dating of a surface. The fractured materials on the right side of the image are embayed by younger volcanic flows originating to the west of the image. Note how the younger flows cover the ends of the fractures, and are not at all fractured themselves.

Image information: VIS instrument. Latitude 43.2, Longitude 269.4 East (90.6 West). 19 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

Numerical Simulations of the Natural Thermal Regime and Enhanced Geothermal Systems in the St. Lawrence Lowlands Basin, Quebec, Canad

NASA Astrophysics Data System (ADS)

Nowamooz, A.; Therrien, R.; Molson, J. W. H.; Gosselin, L.; Mathieu-Potvin, F.; Raymond, J.; Malo, M.; Comeau, F. A.; Bedard, K.

2017-12-01

An enhanced geothermal system (EGS) consists of injecting water into deep sedimentary or basement rocks, which have been hydraulically stimulated, and withdrawing this water for heat extraction. In this work, the geothermal potential of the St. Lawrence Lowlands Basin (SLLB), Quebec, Canada, is evaluated using numerical heat transport simulations. A 3D conceptual model was first developed based on a detailed geological model of the basin and using realistic ranges of hydrothermal properties of the geological formations. The basin thermal regime under natural conditions was simulated with the HydroGeoSphere model assuming non-isothermal single-phase flow, while the hydrothermal properties of the formations were predicted using the PEST parameter estimation package. The simulated basin temperatures were consistent with the measured bottom-hole temperatures (RMSE = 9%). The calibrated model revealed that the areas in the basin with EGS potential, where temperature exceeds 120 °C, are located at depths ranging from 3.5 to 5.5 km. In the second step of the work, the favorable areas are investigated in detail by conducting simulations in a discrete fracture network similar to the one proposed in the literature for the Rosemanowes geothermal site, UK. Simulations consider 4 main horizontal fractures having each an extent of 1000 m × 180 m, and 10 vertical fractures having each an extent of 1000 m × 45 m. The fracture spacing and aperture are uniform and equal to 15 m and 250 μm, respectively. Simulations showed that a commercial project in the SLLB, with conditions similar to those of the Rosemanowes site, would not feasible. However, sensitivity analyses have demonstrated that it would be possible to extract sufficient heat for a period of at least 20 years from a fractured reservoir in this basin under the following conditions: (1) a flow circulation rate below the desired target value (10 L/s instead of 50 L/s), which would require a flexible power plant; (2) an area of contact of at least 1 km2 between the geofluid and the rock matrix, which would require horizontal and multilateral drilling with hydraulic stimulation, and (3) an initial temperature of at least 150 °C in a conductive geological formation, which would require drilling to depths of 6500 m.

Columnar jointing - the mechanics of thermal contraction in cooling lavas

NASA Astrophysics Data System (ADS)

Lavallée, Y.; Iddon, F.; Hornby, A. J.; Kendrick, J. E.; von Aulock, F. W.; Wadsworth, F. B.

2014-12-01

Columnar joints are spectacular features of volcanic rocks, which form by cracking during cooling-induced contraction of lava. The process, and resultant geometry, manifests a complex interplay between heat dissipation, contraction and tensile strength, yet the formation temperature of such joints remains elusive. Here, we present results from a combination of field survey, thermo-analytical characterisation and mechanical investigation to constrain conditions favourable for columnar jointing. Columnar joints at Seljavellir, a basaltic lava flow at the base of Eyjafjallajökull volcano (Iceland) produce quadratic to heptagonal cross sectional patterns with column widths ranging from 20 to 70 cm in size. The fracture surfaces are characterised by striae with spacing (between 1 to 6 cm) that shares a positive linear relationship to the joint spacing. The striae exhibit both a rough and smooth portion, interpreted to express a change in deformation regime from a ductile response as stress builds up to a fully brittle, mode-I fracture propagation at high stress accumulation. To test the thermo-mechanics of columnar joints we developed an experimental setup to investigate the stress, strain-to-failure and temperature at which basalts undergo tensile failure during cooling from the solidus temperature of 980 °C. We find that fractures initiate at ~800 °C, revealed by a change in stress accumulation (i.e., Young modulus), and complete failure completes after some 0.4% strain at ~670 °C. We interpret the two-stage fracture dynamics as the cause for the change in fracture surface roughness observed in nature. We coupled this dataset with Brazil tensile tests at 30, 400, 600, 800 and 1000 °C. We note that the strain to failure decrease from 1% (>800 °C) to 0.4% (<800 °C). Complementary dilatometric measurements (at 3mN of normal stress and a rate of 2 C/min) constrain the expansion coefficient to be linear and equal to 10-5/°C below the solid temperature. Simple ratio between strain-to-failure and expansion coefficient suggests that 400 °C of cooling (from the solidus) is require to achieve tensile failure by thermal contraction, supporting the first suite of experiments. We conclude that columnar jointing is not a phenomenon that takes place in molten lava, but rather occurs well within the solid state of volcanic rocks.

Ductility and fracture in B2 FeAl alloys. Ph.D. Thesis Final Report

NASA Technical Reports Server (NTRS)

Crimp, Martin A.

1987-01-01

The mechanical behavior of B2FeAl alloys was studied. Stoichiometric Fe-50Al exhibits totally brittle behavior while iron-rich Fe-40Al yields and displays about 3% total strain. This change in behavior results from large decreases in the yield strength with iron-rich deviations from stoichiometry while the fracture stress remains essentially constant. Single crystal studies show that these yield strength decreases are directly related to decreases in the critical resolved shear stress for a group of zone axes /111/ set of (110) planes slip. This behavior is rationalized in terms of the decrease in antiphase boundary energy with decreasing aluminum content. The addition of boron results in improvements in the mechanical behavior of alloys on the iron-rich side of stoichiometry. These improvements are increased brittle fracture stresses of near-stoichiometric alloys, and enhanced ductility of up to 6% in Fe-40Al. These effects were attributed to increased grain boundary adhesion as reflected by changes in fracture mode from intergranular to transgranular failure. The increases in yield strength, which are observed in both polycrystals and single crystals, result from the quenching in of large numbers of thermal vacancies. Hall-Petch plots show that the cooling rate effects are a direct result of changes in the Hall-Petch intercept/lattice resistance flow.

Fracture toughness and Charpy impact properties of several RAFMS before and after irradiation in HFIR

NASA Astrophysics Data System (ADS)

Sokolov, M. A.; Tanigawa, H.; Odette, G. R.; Shiba, K.; Klueh, R. L.

2007-08-01

As part of the development of candidate reduced-activation ferritic steels for fusion applications, several steels, namely F82H, 9Cr-2WVTa steels and F82H weld metal, are being investigated in the joint DOE-JAEA collaboration program. Within this program, three capsules containing a variety of specimen designs were irradiated at two design temperatures in the ORNL High Flux Isotope Reactor (HFIR). Two capsules, RB-11J and RB-12J, were irradiated in the HFIR removable beryllium positions with europium oxide (Eu 2O 3) thermal neutron shields in place. Specimens were irradiated up to 5 dpa. Capsule JP25 was irradiated in the HFIR target position to 20 dpa. The design temperatures were 300 °C and 500 °C. Precracked third-sized V-notch Charpy (3.3 × 3.3 × 25.4 mm) and 0.18 T DC(T) specimens were tested to determine transition and ductile shelf fracture toughness before and after irradiation. The master curve methodology was applied to evaluate the fracture toughness transition temperature, T0. Irradiation induced shifts of T0 and reductions of JQ were compared with Charpy V-notch impact properties. Fracture toughness and Charpy shifts were also compared to hardening results.

Clues to the formation of Enceladus' south-polar terrain from simulations of funiscular plains formation

NASA Astrophysics Data System (ADS)

Bland, M. T.; McKinnon, W. B.

2013-12-01

Cassini imaging and thermal data have demonstrated that Enceladus' four south-polar linear-fractures are the source of both Enceladus' cryovolcanic plume and its extreme thermal emission. These long (130 km), parallel 'tiger stripes' are located within a young, quasi-circular, south-polar depression characterized by extensive tectonic deformation that includes sets of both small-scale fractures (possibly relic tiger stripes) [Patthoff and Kattenhorn 2011], and large-amplitude circumferential ridges. Between the tiger stripes themselves are broad regions of periodic, low amplitude (50-100 m), short-wavelength (1 km) ridges (dubbed 'funiscular' terrain) that generally run parallel to the larger tiger stripe fractures but occasionally intersect them at small angles [Spencer et al. 2009]. The formation of the south polar terrain (SPT) may be related to localized melting of Enceladus' ice layer [e.g., Collins and Goodman, 2007] but the detailed formation kinematics of the SPT and its specific tectonic structures is far from certain. Here we constrain the formation of the SPT by simulating the development of funiscular terrain specifically. This terrain dominates the central portion of the SPT, including regions immediately adjacent to the tiger stripes. The stripes are, in effect, large-scale fractures imbedded within the funiscular terrain; thus, any kinematic or dynamic prescription for SPT formation must account for funiscular morphology. The simplest formation mechanism consistent with the funiscular ridges is that of low-amplitude, short-wavelength folding of a thin surface layer. Barr and Pruess [2010] demonstrated the plausibility of this mechanism using an analytical model developed for folds forming on lava flow tops. We extend their analysis using finite element modeling of the contraction of a thin, brittle lithosphere overlying ductile ice. We find fold morphologies consistent with the funiscular terrain (50-100 m amplitude, 1.5 km wavelengths) for lithospheric thicknesses of 250-500 m assuming weak (~100 kPa) near surface ice and 10% shortening. Creation of short wavelengths and tight fold hinges requires kinematic fold growth that shortens the fold wavelength subsequent to establishment of a longer, initial dominant wavelength. Thicker lithospheres (1 km) also reproduce the deformation if strains exceed 10%, though fold amplitudes are lower and wavelengths longer in this case. The thin lithosphere required to produce funiscular morphologies require exceedingly high heat flow if intact (low porosity) ice is assumed (≥1 W m-2). Significant lithospheric porosity that depresses the ice thermal conductivity (e.g., by a factor of ~3 for 30% porosity [Shoshany et al. 2002]) is likely required, and could decrease the necessary heat flux to ~300 mW m-2. The thin lithosphere necessary for its formation might account for the funiscular terrain's limited spatial extent adjacent to the tiger stripes, the locus of SPT thermal activity. A compressive stress regime between the tensile tiger stripes suggests local accommodation of strain in a dominantly extensional setting that is likely modulated by tidally-induced shear.

Fracture Behaviors of Sn-Cu Intermetallic Compound Layer in Ball Grid Array Induced by Thermal Shock

NASA Astrophysics Data System (ADS)

Shen, Jun; Zhai, Dajun; Cao, Zhongming; Zhao, Mali; Pu, Yayun

2014-02-01

In this work, thermal shock reliability testing and finite-element analysis (FEA) of solder joints between ball grid array components and printed circuit boards with Cu pads were used to investigate the failure mechanism of solder interconnections. The morphologies, composition, and thickness of Sn-Cu intermetallic compounds (IMC) at the interface of Sn-3.0Ag-0.5Cu lead-free solder alloy and Cu substrates were investigated by scanning electron microscopy and transmission electron microscopy. Based on the experimental observations and FEA results, it can be recognized that the origin and propagation of cracks are caused primarily by the difference between the coefficient of thermal expansion of different parts of the packaged products, the growth behaviors and roughness of the IMC layer, and the grain size of the solder balls.

Experimental Investigation on Mechanical and Thermal Properties of Marble Dust Particulate-Filled Needle-Punched Nonwoven Jute Fiber/Epoxy Composite

NASA Astrophysics Data System (ADS)

Sharma, Ankush; Patnaik, Amar

2018-03-01

The present investigation evaluates the effects of waste marble dust, collected from the marble industries of Rajasthan, India, on the mechanical properties of needle-punched nonwoven jute fiber/epoxy composites. The composites with varying filler contents from 0 wt.% to 30 wt.% marble dust were prepared using vacuum-assisted resin-transfer molding. The influences of the filler material on the void content, tensile strength, flexural strength, interlaminar shear strength (ILSS), and thermal conductivity of the hybrid composites have been analyzed experimentally under the desired optimal conditions. The addition of marble dust up to 30 wt.% increases the flexural strength, ILSS, and thermal conductivity, but decreases the tensile strength. Subsequently, the fractured surfaces of the particulate-filled jute/epoxy composites were analyzed microstructurally by field-emission scanning electron microscopy.