Creep Behavior in Interlaminar Shear of a SiC/SiC Ceramic Composite with a Self-healing Matrix

NASA Astrophysics Data System (ADS)

Ruggles-Wrenn, M. B.; Pope, M. T.

2014-02-01

Creep behavior in interlaminar shear of a non-oxide ceramic composite with a multilayered matrix was investigated at 1,200 °C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon™ fibers woven in a five-harness-satin weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbide overlay applied. The interlaminar shear properties were measured. The creep behavior was examined for interlaminar shear stresses in the 16-22 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. In air and in steam, creep run-out defined as 100 h at creep stress was achieved at 16 MPa. Larger creep strains were accumulated in steam. However, creep strain rates and creep lifetimes were only moderately affected by the presence of steam. The retained properties of all specimens that achieved run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated.

Creep deformation and mechanisms in Haynes 230 at 800 °C and 900 °C

NASA Astrophysics Data System (ADS)

Pataky, Garrett J.; Sehitoglu, Huseyin; Maier, Hans J.

2013-11-01

Creep was studied in Haynes 230, a material candidate for the very high temperature reactor's intermediate heat exchanger, at 800 °C and 900 °C. This study focused on the differences between the behavior at the two elevated temperature, and using the microstructure, grain boundary serrations and triple junction strain concentrations were quantitatively identified. There was significant damage in the 900 °C samples and the creep was almost entirely tertiary. In contrast, the 800 °C sample exhibited secondary creep. Using an Arrhenius equation, the minimum creep rate exponents were found to be n ≈ 3 and n ≈ 5 for 900 °C and 800 °C, respectively. The creep mechanisms were identified as solute drag for n ≈ 3 and dislocation climb for n ≈ 5. Strain concentrations were identified at triple junctions and grain boundary serrations using high resolution digital image correlation overlaid on the microstructure. The grain boundary serrations restrict grain boundary sliding which may reduce the creep damage at triple junctions and extend the creep life of Haynes 230 at elevated temperatures.

Fatigue creep damage at the cement-bone interface: an experimental and a micro-mechanical finite element study

PubMed Central

Waanders, Daan; Janssen, Dennis; Miller, Mark A.; Mann, Kenneth A.; Verdonschot, Nico

2009-01-01

The goal of this study was to quantify the micromechanics of the cement-bone interface under tensile fatigue loading using finite element analysis (FEA) and to understand the underlying mechanisms that play a role in the fatigue behavior of this interface. Laboratory cement-bone specimens were subjected to a tensile fatigue load, while local displacements and crack growth on the specimen's surface were monitored. FEA models were created from these specimens based upon micro-computed tomography data. To accurately model interfacial gaps at the interface between the bone and cement, a custom-written erosion algorithm was applied to the bone model. A fatigue load was simulated in the FEA models while monitoring the local displacements and crack propagation. The results showed the FEA models were able to capture the general experimental creep damage behavior and creep stages of the interface. Consistent with the experiments, the majority of the deformation took place at the contact interface. Additionally, the FEA models predicted fatigue crack patterns similar to experimental findings. Experimental surface cracks correlated moderately with FEA surface cracks (r2=0.43), but did not correlate with the simulated crack volume fraction (r2=0.06). Although there was no relationship between experimental surface cracks and experimental creep damage displacement (r2=0.07), there was a strong relationship between the FEA crack volume fraction and the FEA creep damage displacement (r2=0.76). This study shows the additional value of FEA of the cement-bone interface relative to experimental studies and can therefore be used to optimize its mechanical properties. PMID:19682690

Effect of welding on creep damage evolution in P91B steel

NASA Astrophysics Data System (ADS)

Baral, J.; Swaminathan, J.; Chakrabarti, D.; Ghosh, R. N.

2017-07-01

Study of creep behavior of base metal (without weld) and welded specimens of P91B steel over a range of temperatures (600-650 °C) and stresses (50-180 MPa) showed similar values of minimum creep-rates for both specimens at higher stress regime (>100 MPa) whilst, significantly higher creep rates in the case of welded specimens at lower stress regime. Considering that welded specimen is comprised of two distinct structural regimes, i.e. weld affected zone and base metal, a method has been proposed for estimating the material parameters describing creep behavior of those regimes. Stress-strain distribution across welded specimen predicted from finite element analysis based on material parameters revealed preferential accumulation of stress and creep strain at the interface between weld zone and base metal. This is in-line with the experimental finding that creep rupture preferentially occurs at inter-critical heat affected zone in welded specimens owing to ferrite-martensite structure with coarse Cr23C6 particles.

Investigation of Macroscopic Brittle Creep Failure Caused by Microcrack Growth Under Step Loading and Unloading in Rocks

NASA Astrophysics Data System (ADS)

Li, Xiaozhao; Shao, Zhushan

2016-07-01

The growth of subcritical cracks plays an important role in the creep of brittle rock. The stress path has a great influence on creep properties. A micromechanics-based model is presented to study the effect of the stress path on creep properties. The microcrack model of Ashby and Sammis, Charles' Law, and a new micro-macro relation are employed in our model. This new micro-macro relation is proposed by using the correlation between the micromechanical and macroscopic definition of damage. A stress path function is also introduced by the relationship between stress and time. Theoretical expressions of the stress-strain relationship and creep behavior are derived. The effects of confining pressure on the stress-strain relationship are studied. Crack initiation stress and peak stress are achieved under different confining pressures. The applied constant stress that could cause creep behavior is predicted. Creep properties are studied under the step loading of axial stress or the unloading of confining pressure. Rationality of the micromechanics-based model is verified by the experimental results of Jinping marble. Furthermore, the effects of model parameters and the unloading rate of confining pressure on creep behavior are analyzed. The coupling effect of step axial stress and confining pressure on creep failure is also discussed. The results provide implications on the deformation behavior and time-delayed rockburst mechanism caused by microcrack growth on surrounding rocks during deep underground excavations.

DETERMINATION OF THE CREEP–FATIGUE INTERACTION DIAGRAM FOR ALLOY 617

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

Wright, J. K.; Carroll, L. J.; Sham, T. -L.

Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor. To evaluate the behavior of this material in the expected service conditions, creep-fatigue testing was performed. Testing has been performed primarily on a single heat of material at 850 and 950°C for total strain ranges of 0.3 to 1% and tensile hold times as long as 240 minutes. At 850°C, increases in the tensile hold duration degraded the creep fatigue resistance, at least to the investigated strain-controlled hold time of up to 60 minutes at the 0.3% strain range and 240 minutesmore » at the 1.0% strain range. At 950°C, the creep-fatigue cycles to failure becomes constant with increasing hold times, indicating saturation occurs at relatively short hold times. The creep and fatigue damage fractions have been calculated and plotted on a creep-fatigue interaction D-diagram. Results from earlier creep-fatigue tests at 800 and 1000°C on an additional heat of Alloy 617 are also plotted on the D-diagram. The methodology for calculating the damage fractions will be presented, and the effects of strain rate, strain range, temperature, hold time, and strain profile (i.e. holds in tension, compression or both) on the creep-fatigue damage will be explored.« less

Creep and intergranular cracking of Ni-Cr-Fe-C in 360[degree]C argon

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

Angeliu, T.M.; Was, G.S.

1994-06-01

The influence of carbon and chromium on the creep and intergranular (IG) cracking behavior of controlled-purity Ni-xCr-9Fe-yC alloys in 360 C argon was investigated using constant extension rate tension (CERT) and constant load tension (CLT) testing. The CERT test results at 360 C show that the degree of IG cracking increases with decreasing bulk chromium or carbon content. The CLT test results at 360 C and 430 C reveal that, as the amounts of chromium and carbon in solution decrease, the steady-state creep rate increases. The occurrence of severe IG cracking correlates with a high steady-state creep rate, suggesting thatmore » creep plays a role in the IG cracking behavior in argon at 360 C. The failure mode of IG cracking and the deformation mode of creep are coupled through the formation of grain boundary voids that interlink to form grain boundary cavities, resulting in eventual failure by IG cavitation and ductile overload of the remaining ligaments. Grain boundary sliding may be enhancing grain boundary cavitation by redistributing the stress from inclined to more perpendicular boundaries and concentrating stress at discontinuities for the boundaries oriented 45 deg with respect to the tensile axis. Additions of carbon or chromium, which reduce the creep rate over all stress levels, also reduce the amount of IG fracture in CERT experiments. A damage accumulation model was formulated and applied to CERT tests to determine whether creep damage during a CERT test controls failure. Results show that, while creep plays a significant role in CERT experiments, failure is likely controlled by ductile overload caused by reduction in area resulting from grain boundary void formation and interlinkage.« less

Progress Report on Long Hold Time Creep Fatigue of Alloy 617 at 850°C

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

Carroll, Laura Jill

Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor. To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include long hold times up to 240 minutes at maximum tensile strain were conducted at 850°C. In terms of the total number of cycles to failure, the fatigue resistance decreased when a hold time was added at peak tensile strain. Increases in the tensile hold duration degraded the creep-fatigue resistance, at least to the investigated strain controlled hold time of up to 60 minutes at themore » 0.3% strain range and 240 minutes at the 1.0% strain range. The creep-fatigue deformation mode is considered relative to the lack of saturation, or continually decreasing number of cycles to failure with increasing hold times. Additionally, preliminary values from the 850°C creep-fatigue data are calculated for the creep-fatigue damage diagram and have higher values of creep damage than those from tests at 950°C.« less

Procedures for characterizing an alloy and predicting cyclic life with the total strain version of Strainrange Partitioning

NASA Technical Reports Server (NTRS)

Saltsman, James F.; Halford, Gary R.

1989-01-01

Procedures are presented for characterizing an alloy and predicting cyclic life for isothermal and thermomechanical fatigue conditions by using the total strain version of strainrange partitioning (TS-SRP). Numerical examples are given. Two independent alloy characteristics are deemed important: failure behavior, as reflected by the inelastic strainrange versus cyclic life relations; and flow behavior, as indicated by the cyclic stress-strain-time response (i.e., the constitutive behavior). Failure behavior is characterized by conducting creep-fatigue tests in the strain regime, wherein the testing times are reasonably short and the inelastic strains are large enough to be determined accurately. At large strainranges, stress-hold, strain-limited tests are preferred because a high rate of creep damage per cycle is inherent in this type of test. At small strainranges, strain-hold cycles are more appropriate. Flow behavior is characterized by conducting tests wherein the specimen is usually cycled far short of failure and the wave shape is appropriate for the duty cycle of interest. In characterizing an alloy pure fatigue, or PP, failure tests are conducted first. Then depending on the needs of the analyst a series of creep-fatigue tests are conducted. As many of the three generic SRP cycles are featured as are required to characterize the influence of creep on fatigue life (i.e., CP, PC, and CC cycles, respectively, for tensile creep only, compressive creep only, and both tensile and compressive creep). Any mean stress effects on life also must be determined and accounted for when determining the SRP inelastic strainrange versus life relations for cycles featuring creep. This is particularly true for small strainranges. The life relations thus are established for a theoretical zero mean stress condition.

Deformation analysis of polymers composites: rheological model involving time-based fractional derivative

NASA Astrophysics Data System (ADS)

Zhou, H. W.; Yi, H. Y.; Mishnaevsky, L.; Wang, R.; Duan, Z. Q.; Chen, Q.

2017-05-01

A modeling approach to time-dependent property of Glass Fiber Reinforced Polymers (GFRP) composites is of special interest for quantitative description of long-term behavior. An electronic creep machine is employed to investigate the time-dependent deformation of four specimens of dog-bond-shaped GFRP composites at various stress level. A negative exponent function based on structural changes is introduced to describe the damage evolution of material properties in the process of creep test. Accordingly, a new creep constitutive equation, referred to fractional derivative Maxwell model, is suggested to characterize the time-dependent behavior of GFRP composites by replacing Newtonian dashpot with the Abel dashpot in the classical Maxwell model. The analytic solution for the fractional derivative Maxwell model is given and the relative parameters are determined. The results estimated by the fractional derivative Maxwell model proposed in the paper are in a good agreement with the experimental data. It is shown that the new creep constitutive model proposed in the paper needs few parameters to represent various time-dependent behaviors.

Damage Assessment of Creep Tested and Thermally Aged Udimet 520 Using Acousto-Ultrasonics

NASA Technical Reports Server (NTRS)

Gyekenyesi, Andrew L.; Kautz, Harold E.; Cao, Wei

2001-01-01

Due to elevated temperatures and excessive stresses, turbine components may experience creep behavior. As a result, it is desirable to monitor and assess the current condition of such components. This study employed the Acousto-Ultrasonics (AU) method in an effort to monitor the state of the material at various percentages of used up creep life in the nickel base alloy, Udimet 520. A stepped specimen (i.e., varying cross sectional area) was employed which allowed for a postmortem nondestructive evaluation (NDE) analysis of the various levels of used up life. The overall objectives here were two fold: First, a user friendly, graphical interface AU system was developed, and second the new AU system was applied as an NDE tool to assess distributed damage resulting from creep. The experimental results demonstrated that the AU method shows promise as an NDE tool capable of detecting material changes as a function of used up creep life. Furthermore, the changes in the AU parameters were mainly attributed to the case of combined load and elevated temperature (i.e., creep) and not simply because of a timed exposure at elevated temperature (i.e., heat treatment or thermal aging).

Influence of deformation behavior, oxydation, and temperature on the long time cyclic stress behavior of high temperature steels

NASA Technical Reports Server (NTRS)

Maile, K.

1982-01-01

The influence of different parameters on the creep-fatigue behavior of several steel alloys was investigated. The higher the temperature the lower the crack initiation value. Pauses during the cycle reduce the damage. Oxidation reduces and protective gas increases the lifetime. Prior loading and prior deformation reduce the lifetime. Short annealing slightly affects the cycle stress behavior. The test results do not satisfactorily agree with methods of extrapolation and damage accumulation.

Finite Element Creep Damage Analyses and Life Prediction of P91 Pipe Containing Local Wall Thinning Defect

NASA Astrophysics Data System (ADS)

Xue, Jilin; Zhou, Changyu

2016-03-01

Creep continuum damage finite element (FE) analyses were performed for P91 steel pipe containing local wall thinning (LWT) defect subjected to monotonic internal pressure, monotonic bending moment and combined internal pressure and bending moment by orthogonal experimental design method. The creep damage lives of pipe containing LWT defect under different load conditions were obtained. Then, the creep damage life formulas were regressed based on the creep damage life results from FE method. At the same time a skeletal point rupture stress was found and used for life prediction which was compared with creep damage lives obtained by continuum damage analyses. From the results, the failure lives of pipe containing LWT defect can be obtained accurately by using skeletal point rupture stress method. Finally, the influence of LWT defect geometry was analysed, which indicated that relative defect depth was the most significant factor for creep damage lives of pipe containing LWT defect.

Assessment of microalloying effects on the high temperature fatigue behavior of NiAl

NASA Technical Reports Server (NTRS)

Noebe, R. D.; Lerch, B. A.; Rao, K. B. S.

1995-01-01

Binary NiAl suffers from a lack of strength and poor creep properties at and above 1000 K. Poor creep resistance in turn affects low cycle fatigue (LCF) lives at low strain ranges due to the additional interactions of creep damage. One approach for improving these properties involved microalloying with either Zr or N. As an integral part of a much larger alloying program the low cycle fatigue behavior of Zr and N doped nickel aluminides produced by extrusion of prealloyed powders has been investigated. Strain controlled LCF tests were performed in air at 1000 K. The influence of these microalloying additions on the fatigue life and cyclic stress response of polycrystalline NiAl are discussed.

Creep rupture analysis of a beam resting on high temperature foundation

NASA Technical Reports Server (NTRS)

Gu, Randy J.; Cozzarelli, Francis A.

1988-01-01

A simplified uniaxial strain controlled creep damage law is deduced with the use of experimental observation from a more complex strain dependent law. This creep damage law correlates the creep damage, which is interpreted as the density variation in the material, directly with the accumulated creep strain. Based on the deduced uniaxial strain controlled creep damage law, a continuum mechanical creep rupture analysis is carried out for a beam resting on a high temperature elastic (Winkler) foundation. The analysis includes the determination of the nondimensional time for initial rupture, the propagation of the rupture front with the associated thinning of the beam, and the influence of creep damage on the deflection of the beam. Creep damage starts accumulating in the beam as soon as the load is applied, and a creep rupture front develops at and propagates from the point at which the creep damage first reaches its critical value. By introducing a series of fundamental assumptions within the framework of technical Euler-Bernoulli type beam theory, a governing set of integro-differential equations is derived in terms of the nondimensional bending moment and the deflection. These governing equations are subjected to a set of interface conditions at the propagating rupture front. A numerical technique is developed to solve the governing equations together with the interface equations, and the computed results are presented and discussed in detail.

Investigation of a Novel NDE Method for Monitoring Thermomechanical Damage and Microstructure Evolution in Ferritic-Martensitic Steels for Generation IV Nuclear Energy Systems

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

Nagy, Peter

2013-09-30

The main goal of the proposed project is the development of validated nondestructive evaluation (NDE) techniques for in situ monitoring of ferritic-martensitic steels like Grade 91 9Cr-1Mo, which are candidate materials for Generation IV nuclear energy structural components operating at temperatures up to ~650{degree}C and for steam-generator tubing for sodium-cooled fast reactors. Full assessment of thermomechanical damage requires a clear separation between thermally activated microstructural evolution and creep damage caused by simultaneous mechanical stress. Creep damage can be classified as "negligible" creep without significant plastic strain and "ordinary" creep of the primary, secondary, and tertiary kind that is accompanied bymore » significant plastic deformation and/or cavity nucleation and growth. Under negligible creep conditions of interest in this project, minimal or no plastic strain occurs, and the accumulation of creep damage does not significantly reduce the fatigue life of a structural component so that low-temperature design rules, such as the ASME Section III, Subsection NB, can be applied with confidence. The proposed research project will utilize a multifaceted approach in which the feasibility of electrical conductivity and thermo-electric monitoring methods is researched and coupled with detailed post-thermal/creep exposure characterization of microstructural changes and damage processes using state-of-the-art electron microscopy techniques, with the aim of establishing the most effective nondestructive materials evaluation technique for particular degradation modes in high-temperature alloys that are candidates for use in the Next Generation Nuclear Plant (NGNP) as well as providing the necessary mechanism-based underpinnings for relating the two. Only techniques suitable for practical application in situ will be considered. As the project evolves and results accumulate, we will also study the use of this technique for monitoring other GEN IV materials. Through the results obtained from this integrated materials behavior and NDE study, new insight will be gained into the best nondestructive creep and microstructure monitoring methods for the particular mechanisms identified in these materials. The proposed project includes collaboration with a national laboratory partner and the results will also serve as a foundation to guide the efforts of scientists in the DOE laboratory, university, and industrial communities concerned with the technological challenges of monitoring creep and microstructural evolution in materials planned to be used in Generation IV Nuclear Energy Systems.« less

Fault zone structure and kinematics from lidar, radar, and imagery: revealing new details along the creeping San Andreas Fault

NASA Astrophysics Data System (ADS)

DeLong, S.; Donnellan, A.; Pickering, A.

2017-12-01

Aseismic fault creep, coseismic fault displacement, distributed deformation, and the relative contribution of each have important bearing on infrastructure resilience, risk reduction, and the study of earthquake physics. Furthermore, the impact of interseismic fault creep in rupture propagation scenarios, and its impact and consequently on fault segmentation and maximum earthquake magnitudes, is poorly resolved in current rupture forecast models. The creeping section of the San Andreas Fault (SAF) in Central California is an outstanding area for establishing methodology for future scientific response to damaging earthquakes and for characterizing the fine details of crustal deformation. Here, we describe how data from airborne and terrestrial laser scanning, airborne interferometric radar (UAVSAR), and optical data from satellites and UAVs can be used to characterize rates and map patterns of deformation within fault zones of varying complexity and geomorphic expression. We are evaluating laser point cloud processing, photogrammetric structure from motion, radar interferometry, sub-pixel correlation, and other techniques to characterize the relative ability of each to measure crustal deformation in two and three dimensions through time. We are collecting new and synthesizing existing data from the zone of highest interseismic creep rates along the SAF where a transition from a single main fault trace to a 1-km wide extensional stepover occurs. In the stepover region, creep measurements from alignment arrays 100 meters long across the main fault trace reveal lower rates than those in adjacent, geomorphically simpler parts of the fault. This indicates that deformation is distributed across the en echelon subsidiary faults, by creep and/or stick-slip behavior. Our objectives are to better understand how deformation is partitioned across a fault damage zone, how it is accommodated in the shallow subsurface, and to better characterize the relative amounts of fault creep and potential stick-slip fault behavior across the plate boundary at these sites in order to evaluate the potential for rupture propagation in large earthquakes.

Creep and cracking of concrete hinges: insight from centric and eccentric compression experiments.

PubMed

Schlappal, Thomas; Schweigler, Michael; Gmainer, Susanne; Peyerl, Martin; Pichler, Bernhard

2017-01-01

Existing design guidelines for concrete hinges consider bending-induced tensile cracking, but the structural behavior is oversimplified to be time-independent. This is the motivation to study creep and bending-induced tensile cracking of initially monolithic concrete hinges systematically. Material tests on plain concrete specimens and structural tests on marginally reinforced concrete hinges are performed. The experiments characterize material and structural creep under centric compression as well as bending-induced tensile cracking and the interaction between creep and cracking of concrete hinges. As for the latter two aims, three nominally identical concrete hinges are subjected to short-term and to longer-term eccentric compression tests. Obtained material and structural creep functions referring to centric compression are found to be very similar. The structural creep activity under eccentric compression is significantly larger because of the interaction between creep and cracking, i.e. bending-induced cracks progressively open and propagate under sustained eccentric loading. As for concrete hinges in frame-like integral bridge construction, it is concluded (i) that realistic simulation of variable loads requires consideration of the here-studied time-dependent behavior and (ii) that permanent compressive normal forces shall be limited by 45% of the ultimate load carrying capacity, in order to avoid damage of concrete hinges under sustained loading.

Draft ASME Boiler and Pressure Vessel Code Section III, Division 5, Section HB, Subsection B, Code Case for Alloy 617 and Background Documentation

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

Wright, Julie Knibloe

2015-08-01

Alloy 617 is the leading candidate material for an intermediate heat exchanger for the very high temperature reactor. To evaluate the behavior of this material in the expected service conditions, strain controlled cyclic tests that include long hold times up to 240 minutes at maximum tensile strain were conducted at 850°C. In terms of the total number of cycles to failure, the fatigue resistance decreased when a hold time was added at peak tensile strain. Increases in the tensile hold duration degraded the creep fatigue resistance, at least to the investigated strain controlled hold time of up to 60 minutesmore » at the 0.3% strain range and 240 minutes at the 1.0% strain range. The creep fatigue deformation mode is considered relative to the lack of saturation, or continually decreasing number of cycles to failure with increasing hold times. Additionally, preliminary values from the 850°C creep fatigue data are calculated for the creep fatigue damage diagram and have higher values of creep damage than those from tests at 950°C.« less

Evaluation of CVI SiC/SiC Composites for High Temperature Applications

NASA Technical Reports Server (NTRS)

Kiser, D.; Almansour, A.; Smith, C.; Gorican, D.; Phillips, R.; Bhatt, R.; McCue, T.

2017-01-01

Silicon carbide fiber reinforced silicon carbide (SiC/SiC) composites are candidate materials for various high temperature turbine engine applications because of their high specific strength and good creep resistance at temperatures of 1400 C (2552 F) and higher. Chemical vapor infiltration (CVI) SiC/SiC ceramic matrix composites (CMC) incorporating Sylramic-iBN SiC fiber were evaluated via fast fracture tensile tests (acoustic emission damage characterization to assess cracking behavior), tensile creep testing, and microscopy. The results of this testing and observed material behavior degradation mechanisms are reviewed.

Creep-Fatigue Damage Investigation and Modeling of Alloy 617 at High Temperatures

NASA Astrophysics Data System (ADS)

Tahir, Fraaz

The Very High Temperature Reactor (VHTR) is one of six conceptual designs proposed for Generation IV nuclear reactors. Alloy 617, a solid solution strengthened Ni-base superalloy, is currently the primary candidate material for the tubing of the Intermediate Heat Exchanger (IHX) in the VHTR design. Steady-state operation of the nuclear power plant at elevated temperatures leads to creep deformation, whereas loading transients including startup and shutdown generate fatigue. A detailed understanding of the creep-fatigue interaction in Alloy 617 is necessary before it can be considered as a material for nuclear construction in ASME Boiler and Pressure Vessel Code. Current design codes for components undergoing creep-fatigue interaction at elevated temperatures require creep-fatigue testing data covering the entire range from fatigue-dominant to creep-dominant loading. Classical strain-controlled tests, which produce stress relaxation during the hold period, show a saturation in cycle life with increasing hold periods due to the rapid stress-relaxation of Alloy 617 at high temperatures. Therefore, applying longer hold time in these tests cannot generate creep-dominated failure. In this study, uniaxial isothermal creep-fatigue tests with non-traditional loading waveforms were designed and performed at 850 and 950°C, with an objective of generating test data in the creep-dominant regime. The new loading waveforms are hybrid strain-controlled and force-controlled testing which avoid stress relaxation during the creep hold. The experimental data showed varying proportions of creep and fatigue damage, and provided evidence for the inadequacy of the widely-used time fraction rule for estimating creep damage under creep-fatigue conditions. Micro-scale damage features in failed test specimens, such as fatigue cracks and creep voids, were quantified using a Scanning Electron Microscope (SEM) to find a correlation between creep and fatigue damage. Quantitative statistical imaging analysis showed that the microstructural damage features (cracks and voids) are correlated with a new mechanical driving force parameter. The results from this image-based damage analysis were used to develop a phenomenological life-prediction methodology called the effective time fraction approach. Finally, the constitutive creep-fatigue response of the material at 950°C was modeled using a unified viscoplastic model coupled with a damage accumulation model. The simulation results were used to validate an energy-based constitutive life-prediction model, as a mechanistic model for potential component and structure level creep-fatigue analysis.

Effect of Mechanical and Thermal Loading Histories on Residual Properties of SiCf/SiC Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Almansour, Amjad; Kiser, Doug; Smith, Craig; Bhatt, Ram; Gorican, Dan; Phillips, Ron; McCue, Terry R.

2017-01-01

Silicon Carbide based Ceramic Matrix Composites (CMCs) are attractive materials for use in high-temperature structural applications in the aerospace and nuclear industries. Under high stresses and temperatures, creep degradation is the dominant damage mechanism in CMCs. Consequently, chemical vapor infiltration (CVI) SiCf/SiC ceramic matrix composites (CMC) incorporating SylramicTM-iBN SiC fibers coated with boron nitride (BN) interphase and CVI-SiC matrix were tested to examine creep behavior in air at a range of elevated temperatures of (2200 - 2700 F). Samples that survived creep tests were evaluated via RT fast fracture tensile tests to determine residual properties, with the use of acoustic emission (AE) to assess stress dependent damage initiation and progression. Microscopy of regions within the gage section of the tested specimens was performed. Observed material degradation mechanisms are discussed.

Slow crack growth versus creep cavity coalescence: Competing failure mechanisms during high-temperature deformation of advanced ceramics

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

Jenkins, M.G.; Kohles, S.S.; Stevens, T.L.

1996-12-31

Duality of failure mechanisms (slow crack growth from pre-existing defects versus cumulative creep damage) is examined in a silicon nitride advanced ceramic recently tested at elevated-temperatures. Static (constant stress over time), dynamic (monotonically-increasing stress over time), and cyclic (fluctuating stress over time) fatigue behaviors were evaluated in tension in ambient air at temperatures of 1150, 1260, and 1370{degrees}C for a hot-isostatically pressed monolithic {beta}-silicon nitride. At 1150{degrees}C, all three types of fatigue results showed the similar failure mechanism of slow crack growth (SCG). At 1260 and 1370{degrees}C the failure mechanism was more complex. Failure under static fatigue was dominated bymore » the accumulation of creep damage via diffusion-controlled cavities. In dynamic fatigue, failure occurred by SCG at high stress rates (>10{sup {minus}2}MPa/s) and by creep damage at low stress rates ({le}10{sup {minus}2} MPa/s). For cyclic fatigue, such rate effects influenced the stress rupture results in which times to failure were greater for dynamic and cyclic fatigue than for static fatigue. Elucidation of failure mechanisms is necessary for accurate prediction of long-term survivability and reliability of structural ceramics.« less

Creep Damage Analysis of a Lattice Truss Panel Structure

NASA Astrophysics Data System (ADS)

Jiang, Wenchun; Li, Shaohua; Luo, Yun; Xu, Shugen

2017-01-01

The creep failure for a lattice truss sandwich panel structure has been predicted by finite element method (FEM). The creep damage is calculated by three kinds of stresses: as-brazed residual stress, operating thermal stress and mechanical load. The creep damage at tensile and compressive loads have been calculated and compared. The creep rate calculated by FEM, Gibson-Ashby and Hodge-Dunand models have been compared. The results show that the creep failure is located at the fillet at both tensile and creep loads. The damage rate at the fillet at tensile load is 50 times as much as that at compressive load. The lattice truss panel structure has a better creep resistance to compressive load than tensile load, because the creep and stress triaxiality at the fillet has been decreased at compressive load. The maximum creep strain at the fillet and the equivalent creep strain of the panel structure increase with the increase of applied load. Compared with Gibson-Ashby model and Hodge-Dunand models, the modified Gibson-Ashby model has a good prediction result compared with FEM. However, a more accurate model considering the size effect of the structure still needs to be developed.

Some aspects of thermomechanical fatigue of AISI 304L stainless steel: Part I. creep- fatigue damage

NASA Astrophysics Data System (ADS)

Zauter, R.; Christ, H. J.; Mughrabi, H.

1994-02-01

Thermomechanical fatigue (TMF) tests on the austenitic stainless steel AISI 304L have been conducted under “true≓ plastic-strain control in vacuum. This report considers the damage oc-curring during TMF loading. It is shown how the temperature interval and the phasing (in-phase, out-of-phase) determine the mechanical response and the lifetime of the specimens. If creep-fatigue interaction takes place during in-phase cycling, the damage occurs inside the ma-terial, leading to intergranular cracks which reduce the lifetime considerably. Out-of-phase cy-cling inhibits creep-induced damage, and no lifetime reduction occurs, even if the material is exposed periodically to temperatures in the creep regime. A formula is proposed which allows prediction of the failure mode, depending on whether creep-fatigue damage occurs or not. At a given strain rate, the formula is able to estimate the temperature of transition between pure fatigue and creep-fatigue damage.

Low Cycle Fatigue and Creep-Fatigue Behavior of Alloy 617 at High Temperature

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

Cabet, Celine; Carroll, Laura; Wright, Richard

Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the Very High Temperature Nuclear Reactor (VHTR), expected to have an outlet temperature as high as 950 degrees C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanism/s and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 degreesmore » C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens, although evidence of grain boundary cavitation was not observed. Despite the absence of grain boundary cavitation to accelerate crack propagation, the addition of a hold time at peak tensile strain was detrimental to cycle life. This suggests that creepfatigue interaction may occur by a different mechanism or that the environment may be partially responsible for accelerating failure.« less

A continuous damage model based on stepwise-stress creep rupture tests

NASA Technical Reports Server (NTRS)

Robinson, D. N.

1985-01-01

A creep damage accumulation model is presented that makes use of the Kachanov damage rate concept with a provision accounting for damage that results from a variable stress history. This is accomplished through the introduction of an additional term in the Kachanov rate equation that is linear in the stress rate. Specification of the material functions and parameters in the model requires two types of constituting a data base: (1) standard constant-stress creep rupture tests, and (2) a sequence of two-step creep rupture tests.

Damage Assessment of Heat Resistant Steels through Electron BackScatter Diffraction Strain Analysis under Creep and Creep-Fatigue Conditions

NASA Astrophysics Data System (ADS)

Fujiyama, Kazunari; Kimachi, Hirohisa; Tsuboi, Toshiki; Hagiwara, Hiroyuki; Ogino, Shotaro; Mizutani, Yoshiki

EBSD(Electron BackScatter Diffraction) analyses were conducted for studying the quantitative microstructural metrics of creep and creep-fatigue damage for austenitic SUS304HTB boiler tube steel and ferritic Mod.9Cr piping steel. KAM(Kernel Average Misorientation) maps and GOS(Grain Orientation Spread) maps were obtained for these samples and the area averaged values KAMave and GOSave were obtained. While the increasing trends of these misorientation metrics were observed for SUS304HTB steel, the decreasing trends were observed for damaged Mod.9Cr steel with extensive recovery of subgrain structure. To establish more universal parameter representing the accumulation of damage to compensate these opposite trends, the EBSD strain parameters were introduced for converting the misorientation changes into the quantities representing accumulated permanent strains during creep and creep-fatigue damage process. As KAM values were dependent on the pixel size (inversely proportional to the observation magnification) and the permanent strain could be expressed as the shear strain which was the product of dislocation density, Burgers vector and dislocation movement distance, two KAM strain parameters MεKAMnet and MεδKAMave were introduced as the sum of product of the noise subtracted KAMnet and the absolute change from initial value δKAMave with dislocation movement distance divided by pixel size. MεδKAMave parameter showed better relationship both with creep strain in creep tests and accumulated creep strain range in creep-fatigue tests. This parameter can be used as the strain-based damage evaluation and detector of final failure.

Failure Mechanisms and Damage Model of Ductile Cast Iron Under Low-Cycle Fatigue Conditions

NASA Astrophysics Data System (ADS)

Wu, Xijia; Quan, Guangchun; MacNeil, Ryan; Zhang, Zhong; Sloss, Clayton

2014-10-01

Strain-controlled low-cycle fatigue (LCF) tests were conducted on ductile cast iron (DCI) at strain rates of 0.02, 0.002, and 0.0002/s in the temperature range from room temperature to 1073 K (800 °C). A constitutive-damage model was developed within the integrated creep-fatigue theory (ICFT) framework on the premise of strain decomposition into rate-independent plasticity and time-dependent creep. Four major damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement (IE), (iii) creep, and (iv) oxidation were considered in a nonlinear creep-fatigue interaction model which represents the overall damage accumulation process consisting of oxidation-assisted fatigue crack nucleation and propagation in coalescence with internally distributed damage ( e.g., IE and creep), leading to final fracture. The model was found to agree with the experimental observations of the complex DCI-LCF phenomena, for which the linear damage summation rule would fail.

Creep-Fatigue Relationsihps in Electroactive Polymer Systems and Predicted Effects in an Actuator Design

NASA Technical Reports Server (NTRS)

Vinogradov, Aleksandra M.; Ihlefeld, Curtis M.; Henslee, Issac

2009-01-01

The paper concerns the time-dependent behavior of electroactive polymers (EAP) and their use in advanced intelligent structures for space exploration. Innovative actuator design for low weight and low power valves required in small plants planned for use on the moon for chemical analysis is discussed. It is shown that in-depth understanding of cyclic loading effects observed through accelerated creep rates due to creep-fatigue interaction in polymers is critical in terms of proper functioning of EAP based actuator devices. In the paper, an overview of experimental results concerning the creep properties and cyclic creep response of a thin film piezoelectric polymer polyvinylidene fluoride (PVDF) is presented. The development of a constitutive creep-fatigue interaction model to predict the durability and service life of electroactive polymers is discussed. A novel method is proposed to predict damage accumulation and fatigue life of polymers under oyclic loading conditions in the presence of creep. The study provides a basis for ongoing research initiatives at the NASA Kennedy Space Center in the pursuit of new technologies using EAP as active elements for lunar exploration systems.

Creep-Fatigue Interaction and Cyclic Strain Analysis in P92 Steel Based on Test

NASA Astrophysics Data System (ADS)

Ji, Dongmei; Zhang, Lai-Chang; Ren, Jianxing; Wang, Dexian

2015-04-01

This work focused on the interaction of creep and fatigue and cyclic strain analysis in high-chromium ferritic P92 steel based on load-controlled creep-fatigue (CF) tests and conventional creep test at 873 K. Mechanical testing shows that the cyclic load inhibits the propagation of creep damage in the P92 steel and CF interaction becomes more severe with the decrease in the holding period duration and stress ratio. These results are also verified by the analysis of cyclic strain. The fatigue lifetime reduces with the increasing of the holding period duration and it does not reduce much with the increasing stress ratio especially under the conditions of long holding period duration. The cyclic strains (i.e., the strain range and creep strain) of CF tests consist of three stages, which is the same as those for the conventional creep behavior. The microscopic fracture surface observations illustrated that two different kinds of voids are observed at the fracture surfaces and Laves phase precipitates at the bottom of the voids.

The strainrange conversion principle for treating cumulative fatigue damage in the creep range

NASA Technical Reports Server (NTRS)

Manson, S. S.

1983-01-01

A formula is derived for combining effects of successive hysteresis loops in the creep range of materials when one loop has excess tensile creep, while the other contains excess compressive creep. The resultant effect resembles single loops involving balanced tensile and compressive creep. The attempt to use the Interaction Damage Rule as a tool in combining loops of non-equal size and complex strainrange content has led to important new concepts useful in future studies of creep-fatigue. It turns out that the Interaction Damage Rule is basically an expression of how a set of hysteresis loops involving only single generic strains can combine to produce the same micromechanistic damage as the loop containing the combined strainranges which it analyzes. Making use of the underlying concept of Strainrange Partitioning that only the strainrange content of a hysteresis loop governs fatigue life, not order of introducing strainranges, a rational derivation of the Interaction Damage Rule is provided, showing also how it can effectively be used to synthesize independent loops and determine both damaging and healing effects.

Assessment of Creep Deformation, Damage, and Rupture Life of 304HCu Austenitic Stainless Steel Under Multiaxial State of Stress

NASA Astrophysics Data System (ADS)

Sahoo, K. C.; Goyal, Sunil; Parameswaran, P.; Ravi, S.; Laha, K.

2018-03-01

The role of the multiaxial state of stress on creep deformation and rupture behavior of 304HCu austenitic stainless steel was assessed by performing creep rupture tests on both smooth and notched specimens of the steel. The multiaxial state of stress was introduced by incorporating circumferential U-notches of different root radii ranging from 0.25 to 5.00 mm on the smooth specimens of the steel. Creep tests were carried out at 973 K over the stress range of 140 to 220 MPa. In the presence of notch, the creep rupture strength of the steel was found to increase with the associated decrease in rupture ductility. Over the investigated stress range and notch sharpness, the strengthening was found to increase drastically with notch sharpness and tended toward saturation. The fractographic studies revealed the mixed mode of failure consisting of transgranular dimples and intergranular creep cavitation for shallow notches, whereas the failure was predominantly intergranular for relatively sharper notches. Detailed finite element analysis of stress distribution across the notch throat plane on creep exposure was carried out to assess the creep failure of the material in the presence of notch. The reduction in von-Mises stress across the notch throat plane, which was greater for sharper notches, increased the creep rupture strength of the material. The variation in fracture behavior of the material in the presence of notch was elucidated based on the von-Mises, maximum principal, and hydrostatic stresses. Electron backscatter diffraction analysis of creep strain distribution across the notch revealed localized creep straining at the notch root for sharper notches. A master curve for predicting creep rupture life under the multiaxial state of stress was generated considering the representative stress having contributions from both the von-Mises and principal stress components of the stress field in the notch throat plane. Rupture ductility was also predicted based on the multiaxial state of stress.

Thermomechanical Fatigue of Ductile Cast Iron and Its Life Prediction

NASA Astrophysics Data System (ADS)

Wu, Xijia; Quan, Guangchun; MacNeil, Ryan; Zhang, Zhong; Liu, Xiaoyang; Sloss, Clayton

2015-06-01

Thermomechanical fatigue (TMF) behaviors of ductile cast iron (DCI) were investigated under out-of-phase (OP), in-phase (IP), and constrained strain-control conditions with temperature hold in various temperature ranges: 573 K to 1073 K, 723 K to 1073 K, and 433 K to 873 K (300 °C to 800 °C, 450 °C to 800 °C, and 160 °C to 600 °C). The integrated creep-fatigue theory (ICFT) model was incorporated into the finite element method to simulate the hysteresis behavior and predict the TMF life of DCI under those test conditions. With the consideration of four deformation/damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement, (iii) creep, and (iv) oxidation, as revealed from the previous study on low cycle fatigue of the material, the model delineates the contributions of these physical mechanisms in the asymmetrical hysteresis behavior and the damage accumulation process leading to final TMF failure. This study shows that the ICFT model can simulate the stress-strain response and life of DCI under complex TMF loading profiles (OP and IP, and constrained with temperature hold).

Continuum Damage Mechanics Used to Predict the Creep Life of Monolithic Ceramics

NASA Technical Reports Server (NTRS)

Powers, Lynn M.; Jadaan, Osama M.

1998-01-01

Significant improvements in propulsion and power generation for the next century will require revolutionary advances in high-temperature materials and structural design. Advanced ceramics are candidate materials for these elevated temperature applications. High-temperature and long-duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. An analytical methodology in the form of the integrated design program-Ceramics Analysis and Reliability Evaluation of Structures/Creep (CARES/Creep) has been developed by the NASA Lewis Research Center to predict the life of ceramic structural components subjected to creep rupture conditions. This program utilizes commercially available finite element packages and takes into account the transient state of stress and creep strain distributions (stress relaxation as well as the asymmetric response to tension and compression). The creep life of a component is discretized into short time steps, during which the stress distribution is assumed constant. Then, the damage is calculated for each time step on the basis of a modified Monkman-Grant (MMG) creep rupture criterion. The cumulative damage is subsequently calculated as time elapses in a manner similar to Miner's rule for cyclic fatigue loading. Failure is assumed to occur when the normalized cumulative damage at any point in the component reaches unity. The corresponding time is the creep rupture life for that component.

A damage mechanics based general purpose interface/contact element

NASA Astrophysics Data System (ADS)

Yan, Chengyong

Most of the microelectronics packaging structures consist of layered substrates connected with bonding materials, such as solder or epoxy. Predicting the thermomechanical behavior of these multilayered structures is a challenging task in electronic packaging engineering. In a layered structure the most complex part is always the interfaces between the strates. Simulating the thermo-mechanical behavior of such interfaces, is the main theme of this dissertation. The most commonly used solder material, Pb-Sn alloy, has a very low melting temperature 180sp°C, so that the material demonstrates a highly viscous behavior. And, creep usually dominates the failure mechanism. Hence, the theory of viscoplasticity is adapted to describe the constitutive behavior. In a multilayered assembly each layer has a different coefficient of thermal expansion. Under thermal cycling, due to heat dissipated from circuits, interfaces and interconnects experience low cycle fatigue. Presently, the state-of-the art damage mechanics model used for fatigue life predictions is based on Kachanov (1986) continuum damage model. This model uses plastic strain as a damage criterion. Since plastic strain is a stress path dependent value, the criterion does not yield unique damage values for the same state of stress. In this dissertation a new damage evolution equation based on the second law of thermodynamic is proposed. The new criterion is based on the entropy of the system and it yields unique damage values for all stress paths to the final state of stress. In the electronics industry, there is a strong desire to develop fatigue free interconnections. The proposed interface/contact element can also simulate the behavior of the fatigue free Z-direction thin film interconnections as well as traditional layered interconnects. The proposed interface element can simulate behavior of a bonded interface or unbonded sliding interface, also called contact element. The proposed element was verified against laboratory test data presented in the literature. The results demonstrate that the proposed element and the damage law perform very well. The most important scientific contribution of this dissertation is the proposed damage criterion based on second law of thermodynamic and entropy of the system. The proposed general purpose interface/contact element is another contribution of this research. Compared to the previous adhoc interface elements proposed in the literature, the new one is, much more powerful and includes creep, plastic deformations, sliding, temperature, damage, cyclic behavior and fatigue life in a unified formulation.

Low cycle fatigue and creep-fatigue behavior of Ni-based alloy 230 at 850 C

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

Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A

Strain-controlled low cycle fatigue (LCF) and creep-fatigue testing of Ni-based alloy 230 were carried out at 850 C. The material creep-fatigue life decreased compared with its low cycle fatigue life at the same total strain range. Longer hold time at peak tensile strain further reduced the material creep-fatigue life. Based on the electron backscatter diffraction, a novel material deformation characterization method was applied, which revealed that in low cycle fatigue testing as the total strain range increased, the deformation was segregated to grain boundaries since the test temperature was higher than the material equicohesive temperature and grain boundaries became weakermore » regions compared with grains. Creep-fatigue tests enhanced the localized deformation, resulting in material interior intergranular cracking, and accelerated material damage. Precipitation in alloy 230 helped slip dispersion, favorable for fatigue property, but grain boundary cellular precipitates formed after material exposure to the elevated temperature had a deleterious effect on the material low cycle fatigue and creep-fatigue property.« less

Life prediction methodology for thermal-mechanical fatigue and elevated temperature creep design

NASA Astrophysics Data System (ADS)

Annigeri, Ravindra

Nickel-based superalloys are used for hot section components of gas turbine engines. Life prediction techniques are necessary to assess service damage in superalloy components resulting from thermal-mechanical fatigue (TMF) and elevated temperature creep. A new TMF life model based on continuum damage mechanics has been developed and applied to IN 738 LC substrate material with and without coating. The model also characterizes TMF failure in bulk NiCoCrAlY overlay and NiAl aluminide coatings. The inputs to the TMF life model are mechanical strain range, hold time, peak cycle temperatures and maximum stress measured from the stabilized or mid-life hysteresis loops. A viscoplastic model is used to predict the stress-strain hysteresis loops. A flow rule used in the viscoplastic model characterizes the inelastic strain rate as a function of the applied stress and a set of three internal stress variables known as back stress, drag stress and limit stress. Test results show that the viscoplastic model can reasonably predict time-dependent stress-strain response of the coated material and stress relaxation during hold times. In addition to the TMF life prediction methodology, a model has been developed to characterize the uniaxial and multiaxial creep behavior. An effective stress defined as the applied stress minus the back stress is used to characterize the creep recovery and primary creep behavior. The back stress has terms representing strain hardening, dynamic recovery and thermal recovery. Whenever the back stress is greater than the applied stress, the model predicts a negative creep rate observed during multiple stress and multiple temperature cyclic tests. The model also predicted the rupture time and the remaining life that are important for life assessment. The model has been applied to IN 738 LC, Mar-M247, bulk NiCoCrAlY overlay coating and 316 austenitic stainless steel. The proposed model predicts creep response with a reasonable accuracy for wide range of loading cases such as uniaxial tension, tension-torsion and tension-internal pressure loading.

Relationship between fatigue life in the creep-fatigue region and stress-strain response

NASA Technical Reports Server (NTRS)

Berkovits, A.; Nadiv, S.

1988-01-01

On the basis of mechanical tests and metallographic studies, strainrange partitioned lives were predicted by introducing stress-strain materials parameters into the Universal Slopes Equation. This was the result of correlating fatigue damage mechanisms and deformation mechanisms operating at elevated temperatures on the basis of observed mechanical and microstructural behavior. Correlation between high temperature fatigue and stress strain properties for nickel base superalloys and stainless steel substantiated the method. Parameters which must be evaluated for PP- and CC- life are the maximum stress achievable under entirely plastic and creep conditions respectively and corresponding inelastic strains, and the elastic modulus. For plasticity/creep interaction conditions (PC and CP) two more pairs of stress strain parameters must be ascertained.

NASALIFE - Component Fatigue and Creep Life Prediction Program

NASA Technical Reports Server (NTRS)

Gyekenyesi, John Z.; Murthy, Pappu L. N.; Mital, Subodh K.

2014-01-01

NASALIFE is a life prediction program for propulsion system components made of ceramic matrix composites (CMC) under cyclic thermo-mechanical loading and creep rupture conditions. Although the primary focus was for CMC components, the underlying methodologies are equally applicable to other material systems as well. The program references empirical data for low cycle fatigue (LCF), creep rupture, and static material properties as part of the life prediction process. Multiaxial stresses are accommodated by Von Mises based methods and a Walker model is used to address mean stress effects. Varying loads are reduced by the Rainflow counting method or a peak counting type method. Lastly, damage due to cyclic loading and creep is combined with Minor's Rule to determine damage due to cyclic loading, damage due to creep, and the total damage per mission and the number of potential missions the component can provide before failure.

Elevated temperature creep and fracture properties of the 62Cu-35Au-3Ni braze alloy

NASA Astrophysics Data System (ADS)

Stephens, J. J.; Greulich, F. A.

1995-06-01

The Cu-Au-Ni braze alloys are used for metal/ceramic brazes in electronic assemblies because of their good wetting characteristics and low vapor pressure. We have studied the tensile creep properties of annealed 62Cu-35Au-3Ni alloy over the temperature range 250 °C to 750 °C. Two power-law equations have been developed for the minimum creep rate as a function of true stress and temperature. At the highest temperatures studied (650 °C and 750 °C), the minimum creep rate is well described with a stress exponent of 3.0, which can be rationalized in the context of Class I solid solution strengthening. The inverted shape of the creep curves observed at these temperatures is also consistent with Class I alloy behavior. At lower temperatures, power-law creep is well described with a stress exponent of 7.5, and normal three-stage creep curves are observed. Intergranular creep damage, along with minimum values of strain to fracture, is most apparent at 450 °C and 550 °C. The lower stress exponent in the Class I alloy regime helps to increase the strain to fracture at higher temperatures (650 °C and 750 °C). The minimum creep rate behavior of the 62Cu-35Au-3Ni alloy is also compared with those of the 74.2Cu-25. 8Au alloy and pure Cu. This comparison indicates that the 62Cu-35Au-3Ni has considerably higher creep strength than pure Cu. This fact suggests that the 62Cu-35Au-3Ni braze alloy can be used in low mismatch metal-to-ceramic braze joints such as Mo to metallized alumina ceramic with few problems. However, careful joint design may be essential for the use of this alloy in high thermal mismatch metal-to-ceramic braze joints.

Autonomous Repair Mechanism of Creep Damage in Fe-Au and Fe-Au-B-N Alloys

NASA Astrophysics Data System (ADS)

Zhang, S.; Kwakernaak, C.; Tichelaar, F. D.; Sloof, W. G.; Kuzmina, M.; Herbig, M.; Raabe, D.; Brück, E.; van der Zwaag, S.; van Dijk, N. H.

2015-12-01

The autonomous repair mechanism of creep cavitation during high-temperature deformation has been investigated in Fe-Au and Fe-Au-B-N alloys. Combined electron-microscopy techniques and atom probe tomography reveal how the improved creep properties result from Au precipitation within the creep cavities, preferentially formed on grain boundaries oriented perpendicular to the applied stress. The selective precipitation of Au atoms at the free creep cavity surface results in pore filling, and thereby, autonomous repair of the creep damage. The large difference in atomic size between the Au and Fe strongly hampers the nucleation of precipitates in the matrix. As a result, the matrix acts as a reservoir for the supersaturated solute until damage occurs. Grain boundaries and dislocations are found to act as fast transport routes for solute gold from the matrix to the creep cavities. The mechanism responsible for the self-healing can be characterized by a simple model for cavity growth and cavity filling.

Progress Report on Alloy 617 Notched Specimen Testing

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

McMurtrey, Michael David; Wright, Richard Neil; Lillo, Thomas Martin

Creep behavior of Alloy 617 has been extensively characterized to support the development of a draft Code Case to qualify Alloy 617 in Section III division 5 of the ASME Boiler and Pressure Vessel Code. This will allow use of Alloy 617 in construction of nuclear reactor components at elevated temperatures and longer periods of time (up to 950°C and 100,000 hours). Prior to actual use, additional concerns not considered in the ASME code need to be addressed. Code Cases are based largely on uniaxial testing of smooth gage specimens. In service conditions, components will generally be under multi axialmore » loading. There is also the concern of the behavior at discontinuities, such as threaded components. To address the concerns of multi axial creep behavior and at geometric discontinuities, notched specimens have been designed to create conditions representative of the states that service components experience. Two general notch geometries have been used for these series of tests: U notch and V notch specimens. The notches produce a tri axial stress state, though not uniform across the specimen. Characterization of the creep behavior of the U notch specimens and the creep rupture behavior of the V notch specimens provides a good approximation of the behavior expected of actual components. Preliminary testing and analysis have been completed and are reported in this document. This includes results from V notch specimens tested at 900°C and 800°C. Failure occurred in the smooth gage section of the specimen rather than at the root of the notch, though some damage was present at the root of the notch, where initial stress was highest. This indicates notch strengthening behavior in this material at these temperatures.« less

Thermomechanical Fatigue Durability of T650-35/PMR-15 Sheet Molding Compound

NASA Technical Reports Server (NTRS)

Castelli, Michael G.; Sutter, James K.; Benson, Dianne

1998-01-01

Although polyimide based composites have been used for many years in a wide variety of elevated temperature applications, very little work has been done to examine the durability and damage behavior under more prototypical thermomechanical fatigue (TMF) loadings. Synergistic effects resulting from simultaneous temperature and load cycling can potentially lead to enhanced, if not unique, damage modes and contribute to a number of nonlinear deformation responses. The goal of this research was to examine the effects of a TMF loading spectrum, representative of a gas turbine engine compressor application, on a polyimide sheet molding compound (SMC). High performance SMCs present alternatives to prepreg forms with great potential for low cost component production through less labor intensive, more easily automated manufacturing. To examine the issues involved with TMF, a detailed experimental investigation was conducted to characterize the durability of a T650-35/PMR-15 SMC subjected to TMF mission cycle loadings. Fatigue damage progression was tracked through macroscopic deformation and elastic stiffness. Additional properties, such as the glass transition temperature (T(sub g) and dynamic mechanical properties were examined. The fiber distribution orientation was also characterized through a detailed quantitative image analysis. Damage tolerance was quantified on the basis of residual static tensile properties after a prescribed number of TMF missions. Detailed microstructural examinations were conducted using optical and scanning electron microscopy to characterize the local damage. The imposed baseline TMF missions had only a modest impact on inducing fatigue damage with no statistically significant degradation occurring in the measured macroscopic properties. Microstructural damage was, however, observed subsequent to 100 h of TMF cycling which consisted primarily of fiber debonding and transverse cracking local to predominantly transverse fiber bundles. The TMF loadings did introduce creep related effects (strain accumulation) which led to rupture in some of the more aggressive stress scenarios examined. In some cases this creep behavior occurred at temperatures in excess of 150 C below commonly cited values for T(sub g). Thermomechanical exploratory creep tests revealed that the SMC was subject to time dependent deformation at stress/temperature thresholds of 150 MPa/230 C and 170 MPa/180 C.

Property Evaluation and Damage Evolution of Environmental Barrier Coatings and Environmental Barrier Coated SiC/SiC Ceramic Matrix Composite Sub-Elements

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Halbig, Michael; Jaskowiak, Martha; Hurst, Janet; Bhatt, Ram; Fox, Dennis S.

2014-01-01

This paper describes recent development of environmental barrier coatings on SiC/SiC ceramic matrix composites. The creep and fatigue behavior at aggressive long-term high temperature conditions have been evaluated and highlighted. Thermal conductivity and high thermal gradient cyclic durability of environmental barrier coatings have been evaluated. The damage accumulation and complex stress-strain behavior environmental barrier coatings on SiCSiC ceramic matrix composite turbine airfoil subelements during the thermal cyclic and fatigue testing of have been also reported.

Creep and Environmental Durability of EBC/CMCs Under Imposed Thermal Gradient Conditions

NASA Technical Reports Server (NTRS)

Appleby, Matthew; Morscher, Gregory N.; Zhu, Dongming

2013-01-01

Interest in SiC fiber-reinforced SiC ceramic matrix composite (CMC) environmental barrier coating (EBC) systems for use in high temperature structural applications has prompted the need for characterization of material strength and creep performance under complex aerospace turbine engine environments. Stress-rupture tests have been performed on SiC/SiC composites systems, with varying fiber types and coating schemes to demonstrate material behavior under isothermal conditions. Further testing was conducted under exposure to thermal stress gradients to determine the effect on creep resistance and material durability. In order to understand the associated damage mechanisms, emphasis is placed on experimental techniques as well as implementation of non-destructive evaluation; including electrical resistivity monitoring. The influence of environmental and loading conditions on life-limiting material properties is shown.

Micro-Macro Analysis and Phenomenological Modelling of Salt Viscous Damage and Application to Salt Caverns

NASA Astrophysics Data System (ADS)

Zhu, Cheng; Pouya, Ahmad; Arson, Chloé

2015-11-01

This paper aims to gain fundamental understanding of the microscopic mechanisms that control the transition between secondary and tertiary creep around salt caverns in typical geological storage conditions. We use a self-consistent inclusion-matrix model to homogenize the viscoplastic deformation of halite polycrystals and predict the number of broken grains in a Representative Elementary Volume of salt. We use this micro-macro modeling framework to simulate creep tests under various axial stresses, which gives us the critical viscoplastic strain at which grain breakage (i.e., tertiary creep) is expected to occur. The comparison of simulation results for short-term and long-term creep indicates that the initiation of tertiary creep depends on the stress and the viscoplastic strain. We use the critical viscoplastic deformation as a yield criterion to control the transition between secondary and tertiary creep in a phenomenological viscoplastic model, which we implement into the Finite Element Method program POROFIS. We model a 850-m-deep salt cavern of irregular shape, in axis-symmetric conditions. Simulations of cavern depressurization indicate that a strain-dependent damage evolution law is more suitable than a stress-dependent damage evolution law, because it avoids high damage concentrations and allows capturing the formation of a damaged zone around the cavity. The modeling framework explained in this paper is expected to provide new insights to link grain breakage to phenomenological damage variables used in Continuum Damage Mechanics.

Creep crack growth by grain boundary cavitation under monotonic and cyclic loading

NASA Astrophysics Data System (ADS)

Wen, Jian-Feng; Srivastava, Ankit; Benzerga, Amine; Tu, Shan-Tung; Needleman, Alan

2017-11-01

Plane strain finite deformation finite element calculations of mode I crack growth under small scale creep conditions are carried out. Attention is confined to isothermal conditions and two time histories of the applied stress intensity factor: (i) a monononic increase to a plateau value subsequently held fixed; and (ii) a cyclic time variation. The crack growth calculations are based on a micromechanics constitutive relation that couples creep deformation and damage due to grain boundary cavitation. Grain boundary cavitation, with cavity growth due to both creep and diffusion, is taken as the sole failure mechanism contributing to crack growth. The influence on the crack growth rate of loading history parameters, such as the magnitude of the applied stress intensity factor, the ratio of the applied minimum to maximum stress intensity factors, the loading rate, the hold time and the cyclic loading frequency, are explored. The crack growth rate under cyclic loading conditions is found to be greater than under monotonic creep loading with the plateau applied stress intensity factor equal to its maximum value under cyclic loading conditions. Several features of the crack growth behavior observed in creep-fatigue tests naturally emerge, for example, a Paris law type relation is obtained for cyclic loading.

Irradiation creep and swelling of AISI 316 to exposures of 130 dpa at 385?400$deg;C

NASA Astrophysics Data System (ADS)

Garner, F. A.; Porter, D. L.

1988-07-01

The creep and swelling of AISI 316 stainless steel have been studied at 385 to 400°C in EBR-II to doses of 130 dpa. Most creep capsules were operated at constant stress and temperature but mid-life changes in these variables were also made. This paper concentrates on the behavior of the 20% cold-worked condition but five other conditions were also studied. Swelling at ⩽ 400° C was found to lose the sensitivity to stress exhibited at higher temperatures while the creep rate was found to retain linear dependencies on both stress and swelling rate. The creep coefficients extracted at 400°C agree with those found in other experiments conducted at higher temperatures. In the temperature range of ⩽ 400° C, swelling is in the recombinationdominated regime and the swelling rate falls strongly away from the ~1%/dpa rate observed at higher temperatures. These lower rates of creep and swelling, coupled with the attainment of high damage levels without failure, encourage the use of AISI 316 in the construction of water-cooled fusion first walls operating at temperatures below 400°C.

The physical and mechanical metallurgy of advanced O+BCC titanium alloys

NASA Astrophysics Data System (ADS)

Cowen, Christopher John

This thesis comprises a systematic study of the microstructural evolution, phase transformation behavior, elevated-temperature creep behavior, room-temperature and elevated-temperature tensile behavior, and room-temperature fatigue behavior of advanced titanium-aluminum-niobium (Ti-Al-Nb) alloys with and without boron additions. The specific alloys studied were: Ti-5A1-45Nb (at%), Ti-15Al-33Nb (at%), Ti-15Al-33Nb-0.5B (at%), Ti-15Al-33Nb-5B (at%), Ti-21Al-29Nb (at%), Ti-22Al-26Nb (at%), and Ti-22Al-26Nb-5B (at%). The only alloy composition that had been previously studied before this thesis work began was Ti-22Al-26Nb (at%). Publication in peer-reviewed material science journals of the work performed in this thesis has made data available in the scientific literature that was previously non-existent. The knowledge gap for Ti-Al-Nb phase equilibria over the compositional range of Ti-23Al-27Nb (at%) to Ti-12Al-38Nb (at%) that existed before this work began was successfully filled. The addition of 5 at% boron to the Ti-15Al-33Nb alloy produced 5-9 volume percent boride phase needles within the microstructure. The chemical composition of the boride phase measured by electron microprobe was determined to be approximately B 2TiNb. The lattice parameters of the boride phase were simulated through density functional theory calculations by collaborators at the Air Force Research Laboratory based on the measured composition. Using the simulated lattice parameters, electron backscatter diffraction kikuchi patterns and selected area electron diffraction patterns obtained from the boride phase were successfully indexed according to the space group and site occupancies of the B27 orthorhombic crystal structure. This suggests that half the Ti (c) Wyckoff positions are occupied by Ti atoms and the other half are occupied by Nb atoms in the boride phase lattice. Creep deformation behavior is the main focus of this thesis and in particular understanding the dominant creep deformation mechanisms as a function of stress, temperature, and strain rate. Microstructure-creep relationships for Ti-Al-Nb-xB alloys were developed with the understanding gained. A rule-of-mixtures empirical model based on constituent phase volume fractions and strain rates was developed to predict the minimum creep rates of two-phase O+BCC microstructures. The most innovative results of this thesis were produced through the development of an in-situ creep testing methodology. The creep deformation evolution was chronicled in-situ during high temperature creep experiments, while creep displacement versus time data was simultaneously obtained. The in-situ experiments revealed that prior-BCC grain boundaries were the locus of damage accumulation during creep deformation. A methodology that allows in-situ observation of surface creep deformation as a function of creep displacement has yet to be presented in the literature.

Thermal Fatigue and Fracture Behavior of Ceramic Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

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

2001-01-01

Thermal fatigue and fracture behavior of plasma-sprayed ceramic thermal barrier coatings has been investigated under high heat flux and thermal cyclic conditions. The coating crack propagation is studied under laser heat flux cyclic thermal loading, and is correlated with dynamic fatigue and strength test results. The coating stress response and inelasticity, fatigue and creep interactions, and interface damage mechanisms during dynamic thermal fatigue processes are emphasized.

Low cycle fatigue and creep fatigue interaction behavior of 9Cr-0.5Mo-1.8W-V-Nb heat-resistant steel at high temperature

NASA Astrophysics Data System (ADS)

Wang, Xiaowei; Zhang, Wei; Gong, Jianming; Wahab, Magd Abdel

2018-07-01

In this paper, Low Cycle Fatigue (LCF) and Creep-Fatigue Interaction (CFI) behavior of 9Cr-0.5Mo-1.8 W-V-Nb heat-resistant steel (ASME Grade P92 steel) at elevated temperature of 600 °C are investigated. Strain controlled LCF tests are conducted in fully reversed triangular waveform at different strain amplitudes ranging from 0.2% to 0.8%. CFI tests are conducted at 0.4% strain amplitude in trapezoid waveform with tensile hold time varying from 1 min to 60 min and compressive hold time varying from 1 min to 10 min. During LCF and CFI loadings, the evolution of cyclic stress, mean stress and stress relaxation behavior are investigated. It turns out that the softening behavior and lifetime degradation are dependent on strain amplitude, hold time and hold direction. In addition, the microstructure evolution and fracture behavior are characterized by optical, scanning and transmission electron microscope. The initial rapid softening behavior is attributed to the quick elimination of low angle boundaries, whereas no obvious microstructure alteration appears in the stable stage. Fracture behavior analysis reveals creep voids in long-term CFI tests facilitates the initiation and propagation of secondary cracks. The different responses of outer surface oxidation layer during cycling provides an explanation for severer damage of compressive hold and also accounts for the observed various fracture behavior of failed samples.

Complexities of high temperature metal fatigue: Some steps toward understanding

NASA Technical Reports Server (NTRS)

Manson, S. S.; Halford, G. R.

1983-01-01

After pointing out many of the complexities that attend high temperature metal fatigue beyond those already studied in the sub-creep range, a description of the micromechanisms of deformation and fracture is presented for several classes of materials that were studied over the past dozen years. Strainrange Partitioning (SRP) is used as a framework for interpreting the results. Several generic types of behavior were observed with regard both to deformation and fracture and each is discussed in the context of the micromechanisms involved. Treatment of cumulative fatigue damage and the possibility of ""healing'' of damage in successive loading loops, has led to a new interpretation of the Interaction Damage Rule of SRP. Using the concept of ""equivalent micromechanistic damage'' -- that the same damage on a microscopic scale is induced if the same hysteresis loops are generated, element for element -- it turns out the Interaction Damage Rule essentially compounds a number of variants of hysteresis loops, all of which have the same damage according to SRP concepts, into a set of loops each containing only one of the generic SRP strainranges. Thus the damage associcated with complex loops comprising several types of strainrange is analyzed by considering a combination of loops each containing only one type of strainrange. This concept is expanded to show how several independent loops can combine to ""heal'' creep damage in a complex loading history.

Circular Functions Based Comprehensive Analysis of Plastic Creep Deformations in the Fiber Reinforced Composites

NASA Astrophysics Data System (ADS)

Monfared, Vahid

2016-12-01

Analytically based model is presented for behavioral analysis of the plastic deformations in the reinforced materials using the circular (trigonometric) functions. The analytical method is proposed to predict creep behavior of the fibrous composites based on basic and constitutive equations under a tensile axial stress. New insight of the work is to predict some important behaviors of the creeping matrix. In the present model, the prediction of the behaviors is simpler than the available methods. Principal creep strain rate behaviors are very noteworthy for designing the fibrous composites in the creeping composites. Analysis of the mentioned parameter behavior in the reinforced materials is necessary to analyze failure, fracture, and fatigue studies in the creep of the short fiber composites. Shuttles, spaceships, turbine blades and discs, and nozzle guide vanes are commonly subjected to the creep effects. Also, predicting the creep behavior is significant to design the optoelectronic and photonic advanced composites with optical fibers. As a result, the uniform behavior with constant gradient is seen in the principal creep strain rate behavior, and also creep rupture may happen at the fiber end. Finally, good agreements are found through comparing the obtained analytical and FEM results.

FY17 Status Report on the Micromechanical Finite Element Modeling of Creep Fracture of Grade 91 Steel

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

Messner, M. C.; Truster, T. J.; Cochran, K. B.

Advanced reactors designed to operate at higher temperatures than current light water reactors require structural materials with high creep strength and creep-fatigue resistance to achieve long design lives. Grade 91 is a ferritic/martensitic steel designed for long creep life at elevated temperatures. It has been selected as a candidate material for sodium fast reactor intermediate heat exchangers and other advanced reactor structural components. This report focuses on the creep deformation and rupture life of Grade 91 steel. The time required to complete an experiment limits the availability of long-life creep data for Grade 91 and other structural materials. Design methodsmore » often extrapolate the available shorter-term experimental data to longer design lives. However, extrapolation methods tacitly assume the underlying material mechanisms causing creep for long-life/low-stress conditions are the same as the mechanisms controlling creep in the short-life/high-stress experiments. A change in mechanism for long-term creep could cause design methods based on extrapolation to be non-conservative. The goal for physically-based microstructural models is to accurately predict material response in experimentally-inaccessible regions of design space. An accurate physically-based model for creep represents all the material mechanisms that contribute to creep deformation and damage and predicts the relative influence of each mechanism, which changes with loading conditions. Ideally, the individual mechanism models adhere to the material physics and not an empirical calibration to experimental data and so the model remains predictive for a wider range of loading conditions. This report describes such a physically-based microstructural model for Grade 91 at 600° C. The model explicitly represents competing dislocation and diffusional mechanisms in both the grain bulk and grain boundaries. The model accurately recovers the available experimental creep curves at higher stresses and the limited experimental data at lower stresses, predominately primary creep rates. The current model considers only one temperature. However, because the model parameters are, for the most part, directly related to the physics of fundamental material processes, the temperature dependence of the properties are known. Therefore, temperature dependence can be included in the model with limited additional effort. The model predicts a mechanism shift for 600° C at approximately 100 MPa from a dislocation- dominated regime at higher stress to a diffusion-dominated regime at lower stress. This mechanism shift impacts the creep life, notch-sensitivity, and, likely, creep ductility of Grade 91. In particular, the model predicts existing extrapolation methods for creep life may be non-conservative when attempting to extrapolate data for higher stress creep tests to low stress, long-life conditions. Furthermore, the model predicts a transition from notchstrengthening behavior at high stress to notch-weakening behavior at lower stresses. Both behaviors may affect the conservatism of existing design methods.« less

Numerical Simulation of Creep Characteristic for Composite Rock Mass with Weak Interlayer

NASA Astrophysics Data System (ADS)

Li, Jian-guang; Zhang, Zuo-liang; Zhang, Yu-biao; Shi, Xiu-wen; Wei, Jian

2017-06-01

The composite rock mass with weak interlayer is widely exist in engineering, and it’s essential to research the creep behavior which could cause stability problems of rock engineering and production accidents. However, due to it is difficult to take samples, the losses and damages in delivery and machining process, we always cannot get enough natural layered composite rock mass samples, so the indirect test method has been widely used. In this paper, we used ANSYS software (a General Finite Element software produced by American ANSYS, Inc) to carry out the numerical simulation based on the uniaxial compression creep experiments of artificial composite rock mass with weak interlayer, after experimental data fitted. The results show that the laws obtained by numerical simulations and experiments are consistent. Thus confirmed that carry out numerical simulation for the creep characteristics of rock mass with ANSYS software is feasible, and this method can also be extended to other underground engineering of simulate the weak intercalations.

Finite strain transient creep of D16T alloy: identification and validation employing heterogeneous tests

NASA Astrophysics Data System (ADS)

Shutov, A. V.; Larichkin, A. Yu

2017-10-01

A cyclic creep damage model, previously proposed by the authors, is modified for a better description of the transient creep of D16T alloy observed in the finite strain range under rapidly changing stresses. The new model encompasses the concept of kinematic hardening, which allows us to account for the creep-induced anisotropy. The model kinematics is based on the nested multiplicative split of the deformation gradient, proposed by Lion. The damage evolution is accounted for by the classical Kachanov-Rabotnov approach. The material parameters are identified using experimental data on cyclic torsion of thick-walled samples with different holding times between load reversals. For the validation of the proposed material model, an additional experiment is analyzed. Although this additional test is not involved in the identification procedure, the proposed cyclic creep damage model describes it accurately.

Modeling the mechanical response of PBX 9501

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

Ragaswamy, Partha; Lewis, Matthew W; Liu, Cheng

2010-01-01

An engineering overview of the mechanical response of Plastic-Bonded eXplosives (PBXs), specifically PBX 9501, will be provided with emphasis on observed mechanisms associated with different types of mechanical testing. Mechanical tests in the form of uniaxial tension, compression, cyclic loading, creep (compression and tension), and Hopkinson bar show strain rate and temperature dependence. A range of mechanical behavior is observed which includes small strain recoverable response in the form of viscoelasticity; change in stiffness and softening beyond peak strength due to damage in the form microcracks, debonding, void formation and the growth of existing voids; inelastic response in the formmore » of irrecoverable strain as shown in cyclic tests, and viscoelastic creep combined with plastic response as demonstrated in creep and recovery tests. The main focus of this paper is to elucidate the challenges and issues involved in modeling the mechanical behavior of PBXs for simulating thermo-mechanical responses in engineering components. Examples of validation of a constitutive material model based on a few of the observed mechanisms will be demonstrated against three point bending, split Hopkinson pressure bar and Brazilian disk geometry.« less

Effect of misalignment on mechanical behavior of metals in creep. [computer programs

NASA Technical Reports Server (NTRS)

Wu, H. C.

1979-01-01

Application of the endochronic theory of viscoplasticity to creep, creep recovery, and stress relaxation at the small strain and short time range produced the following results: (1) The governing constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation were derived by imposing appropriate constraints on the general constitutive equation of the endochronic theory. (2) A set of material constants was found which correlate strain-hardening, creep, creep recovery, and stress relaxation. (3) The theory predicts with reasonable accuracy the creep and creep recovery behaviors at short time. (4) The initial strain history prior to the creep stage affects the subsequent creep significantly. (5) A critical stress was established for creep recovery. A computer program, written for the misalignment problem is reported.

Creep behavior and in-depth microstructural characterization of dissimilar joints

PubMed Central

Kauffmann, F; Klein, T; Klenk, A; Maile, K

2013-01-01

The 700 °C power plants currently under development will utilize Ni-base alloys such as alloy 617 for components to be operated at temperatures >650 °C. Due to economic reasons for components or parts of components which are subjected to temperatures <650 °C, 2% Cr or 9–12% Cr steels is used, depending on the required mechanical properties. This makes the dissimilar joining of Ni-base alloys and Cr steels a necessity in these plants. Experimental investigations show that these joints have to be identified as weak points with regard to damage development under creep and creep-fatigue loading. The present investigation focuses on welds between the alloy 617 and 2% Cr steel. Under creep load the fracture occurs near the fusion line between the 2% Cr steel base metal and alloy 617 weld metal. To explain the reasons for this fracture location, the microstructure of this fusion line was investigated using TEM and FIB techniques after welding and after creep loading. The TEM investigations have shown a small zone in the weld metal near the fusion line exhibiting chromium depletion and clearly reduced amounts of chromium carbides, leading to a weakening of this zone. PMID:27877551

A New Ductility Exhaustion Model for High Temperature Low Cycle Fatigue Life Prediction of Turbine Disk Alloys

NASA Astrophysics Data System (ADS)

Zhu, Shun-Peng; Huang, Hong-Zhong; Li, Haiqing; Sun, Rui; Zuo, Ming J.

2011-06-01

Based on ductility exhaustion theory and the generalized energy-based damage parameter, a new viscosity-based life prediction model is introduced to account for the mean strain/stress effects in the low cycle fatigue regime. The loading waveform parameters and cyclic hardening effects are also incorporated within this model. It is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature low cycle fatigue conditions. In the developed model, dynamic viscosity is used to describe the flow behavior. This model provides a better prediction of Superalloy GH4133's fatigue behavior when compared to Goswami's ductility model and the generalized damage parameter. Under non-zero mean strain conditions, moreover, the proposed model provides more accurate predictions of Superalloy GH4133's fatigue behavior than that with zero mean strains.

Crack initiation modeling of a directionally-solidified nickel-base superalloy

NASA Astrophysics Data System (ADS)

Gordon, Ali Page

Combustion gas turbine components designed for application in electric power generation equipment are subject to periodic replacement as a result of cracking, damage, and mechanical property degeneration that render them unsafe for continued operation. In view of the significant costs associated with inspecting, servicing, and replacing damaged components, there has been much interest in developing models that not only predict service life, but also estimate the evolved microstructural state of the material. This thesis explains manifestations of microstructural damage mechanisms that facilitate fatigue crack nucleation in a newly-developed directionally-solidified (DS) Ni-base superalloy components exposed to elevated temperatures and high stresses. In this study, models were developed and validated for damage and life prediction using DS GTD-111 as the subject material. This material, proprietary to General Electric Energy, has a chemical composition and grain structure designed to withstand creep damage occurring in the first and second stage blades of gas-powered turbines. The service conditions in these components, which generally exceed 600°C, facilitate the onset of one or more damage mechanisms related to fatigue, creep, or environment. The study was divided into an empirical phase, which consisted of experimentally simulating service conditions in fatigue specimens, and a modeling phase, which entailed numerically simulating the stress-strain response of the material. Experiments have been carried out to simulate a variety of thermal, mechanical, and environmental operating conditions endured by longitudinally (L) and transversely (T) oriented DS GTD-111. Both in-phase and out-of-phase thermo-mechanical fatigue tests were conducted. In some cases, tests in extreme environments/temperatures were needed to isolate one or at most two of the mechanisms causing damage. Microstructural examinations were carried out via SEM and optical microscopy. A continuum crystal plasticity model was used to simulate the material behavior in the L and T orientations. The constitutive model was implemented in ABAQUS and a parameter estimation scheme was developed to obtain the material constants. A physically-based model was developed for correlating crack initiation life based on the experimental life data and predictions are made using the crack initiation model. Assuming a unique relationship between the damage fraction and cycle fraction with respect to cycles to crack initiation for each damage mode, the total crack initiation life has been represented in terms of the individual damage components (fatigue, creep-fatigue, creep, and oxidation-fatigue) observed at the end state of crack initiation.

Microtexture Analysis and Modeling of Ambient Fatigue and Creep-Fatigue Damages in Ti-6Al-4V Alloy

NASA Astrophysics Data System (ADS)

Kumar, Jalaj; Singh, A. K.; Raman, S. Ganesh Sundara; Kumar, Vikas

2017-02-01

In the present investigation, microtexture analysis using electron back-scattered diffraction technique has been performed to study fatigue- and creep-fatigue damages and associated deformation structures in Ti-6Al-4V alloy. Special emphasis has been given to low-angle grain boundary configuration and its possible application as a damage indicator. Damage is mostly present in the form of voids as investigated through scanning electron microscopy. Stored deformation energies have been evaluated for the strain-controlled fatigue-, the stress-controlled fatigue-, and the creep-fatigue-tested samples. Stored deformation energies have also been analyzed vis-à-vis total damage energies to quantify the contribution of damages to various samples. A relation between the stored deformation energy and the applied strain amplitude has been proposed in this study.

A Continuum Damage Mechanics Model for the Static and Cyclic Fatigue of Cellular Composites

PubMed Central

Huber, Otto

2017-01-01

The fatigue behavior of a cellular composite with an epoxy matrix and glass foam granules is analyzed and modeled by means of continuum damage mechanics. The investigated cellular composite is a particular type of composite foam, and is very similar to syntactic foams. In contrast to conventional syntactic foams constituted by hollow spherical particles (balloons), cellular glass, mineral, or metal place holders are combined with the matrix material (metal or polymer) in the case of cellular composites. A microstructural investigation of the damage behavior is performed using scanning electron microscopy. For the modeling of the fatigue behavior, the damage is separated into pure static and pure cyclic damage and described in terms of the stiffness loss of the material using damage models for cyclic and creep damage. Both models incorporate nonlinear accumulation and interaction of damage. A cycle jumping procedure is developed, which allows for a fast and accurate calculation of the damage evolution for constant load frequencies. The damage model is applied to examine the mean stress effect for cyclic fatigue and to investigate the frequency effect and the influence of the signal form in the case of static and cyclic damage interaction. The calculated lifetimes are in very good agreement with experimental results. PMID:28809806

Experimental and modeling results of creep fatigue life of Inconel 617 and Haynes 230 at 850 C

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

Chen, Xiang; Sokolov, Mikhail A; Sham, Sam

Creep fatigue testing of Ni-based superalloy Inconel 617 and Haynes 230 were conducted in the air at 850 C. Tests were performed with fully reversed axial strain control at a total strain range of 0.5%, 1.0% or 1.5% and hold time at maximum tensile strain for 3, 10 or 30 min. In addition, two creep fatigue life prediction methods, i.e. linear damage summation and frequency-modified tensile hysteresis energy modeling, were evaluated and compared with experimental results. Under all creep fatigue tests, Haynes 230 performed better than Inconel 617. Compared to the low cycle fatigue life, the cycles to failure formore » both materials decreased under creep fatigue test conditions. Longer hold time at maximum tensile strain would cause a further reduction in both material creep fatigue life. The linear damage summation could predict the creep fatigue life of Inconel 617 for limited test conditions, but considerably underestimated the creep fatigue life of Haynes 230. In contrast, frequency-modified tensile hysteresis energy modeling showed promising creep fatigue life prediction results for both materials.« less

Experimental and modeling results of creep-fatigue life of Inconel 617 and Haynes 230 at 850 °C

NASA Astrophysics Data System (ADS)

Chen, Xiang; Sokolov, Mikhail A.; Sham, Sam; Erdman, Donald L., III; Busby, Jeremy T.; Mo, Kun; Stubbins, James F.

2013-01-01

Creep-fatigue testing of Ni-based superalloy Inconel 617 and Haynes 230 were conducted in the air at 850 °C. Tests were performed with fully reversed axial strain control at a total strain range of 0.5%, 1.0% or 1.5% and hold time at maximum tensile strain for 3, 10 or 30 min. In addition, two creep-fatigue life prediction methods, i.e. linear damage summation and frequency-modified tensile hysteresis energy modeling, were evaluated and compared with experimental results. Under all creep-fatigue tests, Haynes 230 performed better than Inconel 617. Compared to the low cycle fatigue life, the cycles to failure for both materials decreased under creep-fatigue test conditions. Longer hold time at maximum tensile strain would cause a further reduction in both material creep-fatigue life. The linear damage summation could predict the creep-fatigue life of Inconel 617 for limited test conditions, but considerably underestimated the creep-fatigue life of Haynes 230. In contrast, frequency-modified tensile hysteresis energy modeling showed promising creep-fatigue life prediction results for both materials.

Irradiation creep due to SIPA under cascade damage conditions

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

Woo, C.H.; Garner, F.A.; Holt, R.A.

1992-12-31

This paper derives the relationships between void swelling and irradiation creep due to Stress-Induced Preferred Absorption (SIPA) and SIPA-Induced Growth (SIG) under cascade damage conditions in an irradiated pressurized tube. It is found that at low swelling rates irradiation creep is a major contribution to the total diametral strain rate of the tube, whereas at high swelling rates the creep becomes a minor contribution. The anisotropy of the corresponding dislocation structure is also predicted to decline as the swelling rate increases. The theoretical predictions are found to agree very well with experimental results.

Observation of creep behavior of cellulose electro-active paper (EAPap) actuator

NASA Astrophysics Data System (ADS)

Kim, Joo-Hyung; Lee, Sang-Woo; Yun, Gyu-Young; Yang, Chulho; Kim, Heung Soo; Kim, Jaehwan

2009-03-01

Understanding of creep effects on actuating mechanisms is important to precisely figure out the behavior of material. Creep behaviors of cellulose based Electro-Active Paper (EAPap) were studied under different constant loading conditions. We found the structural modification of microfibrils in EAPap after creep test. Structural differences of as-prepared and after creep tested samples were compared by SEM measurements. From the measured creep behaviors by different loading conditions, two different regions of induced strain and current were clearly observed as the measurement time increased. It is consider that local defects may occur and becomes micro-dimple or micro-crack formations in lower load cases as localized deformation proceeds, while the shrinkage of diameter of elongated fibers was observed only at the high level of loading. Therefore, cellulose nanofibers may play a role to be against the creep load and prevent the localized structural deformations. The results provide useful creep behavior and mechanism to understand the mechanical behavior of thin visco-elastic EAPap actuator.

Creep Deformation, Rupture Analysis, Heat Treatment and Residual Stress Measurement of Monolithic and Welded Grade 91 Steel for Power Plant Components

NASA Astrophysics Data System (ADS)

Shrestha, Triratna

Modified 9Cr-1 Mo (Grade 91) steel is currently considered as a candidate material for reactor pressure vessels (RPVs) and reactor internals for the Very High Temperature Reactor (VHTR), and in fossil-fuel fired power plants at higher temperatures and stresses. The tensile creep behavior of Grade 91 steel was studied in the temperature range of 600°C to 750°C and stresses between 35 MPa and 350 MPa. Heat treatment of Grade 91 steel was studied by normalizing and tempering the steel at various temperatures and times. Moreover, Thermo-Ca1c(TM) calculation was used to predict the precipitate stability and their evolution, and construct carbon isopleths of Grade 91 steel. Residual stress distribution across gas tungsten arc welds (GTAW) in Grade 91 steel was measured by the time-of-flight neutron diffraction using the Spectrometer for Materials Research at Temperature and Stress (SMARTS) diffractometer at Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, NM, USA. Analysis of creep results yielded stress exponents of ˜9-11 in the higher stress regime and ˜1 in the lower stress regime. The creep behavior of Grade 91 steel was described by the modified Bird-Mukherjee-Dorn relation. The rate-controlling creep deformation mechanism in the high stress regime was identified as the edge dislocation climb with a stress exponent of n = 5. On the other hand, the deformation mechanism in the Newtonian viscous creep regime (n = 1) was identified as the Nabarro-Herring creep. Creep rupture data were analyzed in terms of Monkman-Grant relation and Larson-Miller parameter. Creep damage tolerance factor and stress exponent were used to identify the cause of creep damage. The fracture surface morphology of the ruptured specimens was studied by scanning electron microscopy to elucidate the failure mechanisms. Fracture mechanism map for Grade 91 steel was developed based on the available material parameters and experimental observations. The microstructural evolution of heat treated steel was correlated with the differential scanning calorimetric study. The combination of microstructural studies with optical microscopy, scanning and transmission electron microscopy, microhardness profiles, and calorimetric plots helped in the understanding of the evolution of microstructure and precipitates in Grade 91 steel. The residual stresses were determined at the mid-thickness of the plate, 4.35 mm and 2.35 mm below the surface of the as-welded and post-weld heat treated plate. The residual stresses of the as-welded plate were compared with the post-weld heat treated plate. The post-weld heat treatment significantly reduced the residual stress in the base metal, heat affected zone, and the weld zone. Vickers microhardness profiles of the as-welded, and post-weld heat treated specimens were also determined and correlated with the observed residual stress profile and microstructure.

Creep of trabecular bone from the human proximal tibia

PubMed Central

Novitskaya, Ekaterina; Zin, Carolyn; Chang, Neil; Cory, Esther; Chen, Peter; D'Lima, Darryl; Sah, Robert L.; McKittrick, Joanna

2014-01-01

Creep is the deformation that occurs under a prolonged, sustained load and can lead to permanent damage in bone. Creep in bone is a complex phenomenon and varies with type of loading and local mechanical properties. Human trabecular bone samples from proximal tibia were harvested from a 71-year old female cadaver with osteoporosis. The samples were initially subjected to one cycle load up to 1% strain to determine the creep load. Samples were then loaded in compression under a constant stress for two hours and immediately unloaded. All tests were conducted with the specimens soaked in phosphate buffered saline with proteinase inhibitors at 37°C. Steady state creep rate and final creep strain were estimated from mechanical testing and compared with published data. The steady state creep rate correlated well with values obtained from bovine tibial and human vertebral trabecular bone, and was higher for lower density samples. Tissue architecture was analyzed by micro-computed tomography (μCT) both before and after creep testing to assess creep deformation and damage accumulated. Quantitative morphometric analysis indicated that creep induced changes in trabecular separation and the structural model index. A main mode of deformation was bending of trabeculae. PMID:24857486

Results of studying creep and long-term strength of metals at the Institute of Mechanics at the Lomonosov Moscow State University (To Yu. N. Rabotnov's Anniversary)

NASA Astrophysics Data System (ADS)

Lokoshchenko, A. M.

2014-01-01

Basic results of experimental and theoretical research of creep processes and long-term strength of metals obtained by researchers of the Institute of Mechanics at the Lomonosov Moscow State University are presented. These results further develop and refine the kinetic theory of creep and long-duration strength proposed by Yu. N. Rabotnov. Some problems arising in formulating various types of kinetic equations and describing experimental data for materials that can be considered as statically homogeneous materials (in studying the process of deformation and rupture of such materials, there is no need to study the evolution of individual cracks) are considered. The main specific features of metal creep models at constant and variable stresses, in uniaxial and complex stress states, and with allowance for one or two damage parameters are described. Criterial and kinetic approaches used to determine long-term strength under conditions of a complex stress state are considered. Methods of modeling the metal behavior in an aggressive medium are described. A possibility of using these models for solving engineering problems is demonstrated.

Influence of Constituents on Creep Properties of SiC/SiC Composites

NASA Technical Reports Server (NTRS)

Bhatt, R.; DiCarlo, J.

2016-01-01

SiC-SiC composites are being considered as potential candidate materials for next generation turbine components such as combustor liners, nozzle vanes and blades because of their low density, high temperature capability, and tailorable mechanical properties. These composites are essentially fabricated by infiltrating matrix into a stacked array of fibers or fiber preform by one or a combination of manufacturing methods such as, Melt Infiltration (MI) of molten silicon metal, Chemical Vapor Infiltration (CVI), Polymer Infiltration and Pyrolysis (PIP). To understand the influence of constituents, the SiC-SiC composites fabricated by MI, CVI, and PIP methods were creep tested in air between 12000 and 14500 degrees Centigrade for up to 500 hours. The failed specimens were analyzed under a scanning electron microscope to assess damage mechanisms. Also, knowing the creep deformation parameters of the fiber and the matrix under the testing conditions, the creep behavior of the composites was modeled and compared with the measured data. The implications of the results on the long term durability of these composites will be discussed.

Relationship between fatigue life in the creep-fatigue region and stress-strain response

NASA Technical Reports Server (NTRS)

Berkovits, A.; Nadiv, S.

1988-01-01

On the basis of mechanical tests and metallographic studies, strainrange partitioned lives were predicted by introducing stress-strain materials parameters into the Universal Slopes Equation. This was the result of correlating fatigue damage mechanisms and deformation mechanisms operating at elevated temperatures on the basis of observed mechanical and microstructural behavior. Correlation between high temperature fatigue and stress strain properties for nickel base superalloys and stainless steel substantiated the method. Parameters which must be evaluated for PP- and CC- life are the maximum stress achievable under entirely plastic and creep conditions respectively and corresponding inelastic strains, and the two more pairs of stress strain parameters must be ascertained.

A Lattice-Misfit-Dependent Damage Model for Non-linear Damage Accumulations Under Monotonous Creep in Single Crystal Superalloys

NASA Astrophysics Data System (ADS)

le Graverend, J.-B.

2018-05-01

A lattice-misfit-dependent damage density function is developed to predict the non-linear accumulation of damage when a thermal jump from 1050 °C to 1200 °C is introduced somewhere in the creep life. Furthermore, a phenomenological model aimed at describing the evolution of the constrained lattice misfit during monotonous creep load is also formulated. The response of the lattice-misfit-dependent plasticity-coupled damage model is compared with the experimental results obtained at 140 and 160 MPa on the first generation Ni-based single crystal superalloy MC2. The comparison reveals that the damage model is well suited at 160 MPa and less at 140 MPa because the transfer of stress to the γ' phase occurs for stresses above 150 MPa which leads to larger variations and, therefore, larger effects of the constrained lattice misfit on the lifetime during thermo-mechanical loading.

Creep resistance. [of high temperature alloys

NASA Technical Reports Server (NTRS)

Tien, J. K.; Malu, M.; Purushothaman, S.

1976-01-01

High-temperature structural applications usually require creep resistance because some average stress is maintained for prolonged periods. Alloy and microstructural design guidelines for creep resistance are presented through established knowledge on creep behavior and its functional dependences on alloy microstructure. Important considerations related to creep resistance of alloys as well as those that are harmful to high-temperature properties are examined. Although most of the creep models do not predict observed creep behavior quantitatively, they are sophisticated enough to provide alloy or microstructural design guidelines. It is shown that creep-resistant microstructures are usually in conflict with microstructures that improve such other properties as stress rupture ductility. Greater understanding of the effects of environments on creep and stress rupture behavior of materials is necessary before one can optimally design alloys for applications in different environments.

Modelling and analysis of creep deformation and fracture in a 1 Cr 1/2 Mo ferritic steel

NASA Astrophysics Data System (ADS)

Dyson, B. F.; Osgerby, D.

A quantitative model, based upon a proposed new mechanism of creep deformation in particle-hardened alloys, has been validated by analysis of creep data from a 13CrMo 4 4 (1Cr 1/2 Mo) material tested under a range of stresses and temperatures. The methodology that has been used to extract the model parameters quantifies, as a first approximation, only the main degradation (damage) processes - in the case of the 1CR 1/2 Mo steel, these are considered to be the parallel operation of particle-coarsening and a progressively increasing stress due to a constant-load boundary condition. These 'global' model parameters can then be modified (only slightly) as required to obtain a detailed description and 'fit' to the rupture lifetime and strain/time trajectory of any individual test. The global model parameter approach may be thought of as predicting average behavior and the detailed fits as taking account of uncertainties (scatter) due to variability in the material. Using the global parameter dataset, predictions have also been made of behavior under biaxial stressing; constant straining rate; constant total strain (stress relaxation) and the likely success or otherwise of metallographic and mechanical remanent lifetime procedures.

Endochronic theory of transient creep and creep recovery

NASA Technical Reports Server (NTRS)

Wu, H. C.; Chen, L.

1979-01-01

Short time creep and creep recovery were investigated by means of the endochronic theory of viscoplasticity. It is shown that the constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation can all ber derived from the general constitutive equation by imposing appropriate constraints. In this unified approach, the effect of strain-hardening is naturally accounted for when describing creep and creep recovery. The theory predicts with reasonable accuracy the creep and creep recovery behaviors for Aluminum 1100-0 at 150 C. It was found that the strain-rate history at prestraining stage affects the subsequent creep. A critical stress was also established for creep recovery. The theory predicts a forward creep for creep recovery stress greater than the critical stress. For creep recovery stress less than the critical stress, the theory then predicts a normal strain recovery.

Integrated Design Software Predicts the Creep Life of Monolithic Ceramic Components

NASA Technical Reports Server (NTRS)

1996-01-01

Significant improvements in propulsion and power generation for the next century will require revolutionary advances in high-temperature materials and structural design. Advanced ceramics are candidate materials for these elevated-temperature applications. As design protocols emerge for these material systems, designers must be aware of several innate features, including the degrading ability of ceramics to carry sustained load. Usually, time-dependent failure in ceramics occurs because of two different, delayedfailure mechanisms: slow crack growth and creep rupture. Slow crack growth initiates at a preexisting flaw and continues until a critical crack length is reached, causing catastrophic failure. Creep rupture, on the other hand, occurs because of bulk damage in the material: void nucleation and coalescence that eventually leads to macrocracks which then propagate to failure. Successful application of advanced ceramics depends on proper characterization of material behavior and the use of an appropriate design methodology. The life of a ceramic component can be predicted with the NASA Lewis Research Center's Ceramics Analysis and Reliability Evaluation of Structures (CARES) integrated design programs. CARES/CREEP determines the expected life of a component under creep conditions, and CARES/LIFE predicts the component life due to fast fracture and subcritical crack growth. The previously developed CARES/LIFE program has been used in numerous industrial and Government applications.

Effect of Creep and Oxidation on Reduced Creep-Fatigue life of Ni-based Alloy 617 at 850 C

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

Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A

Low cycle fatigue (LCF) and creep fatigue testing of Ni-based alloy 617 was carried out at 850 C. Compared with its LCF life, the material s creep fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep fatiguemore » tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material s fatigue life.« less

Creep-rupture behavior of candidate Stirling engine iron supperalloys in high-pressure hydrogen. Volume 2: Hydrogen creep-rupture behavior

NASA Technical Reports Server (NTRS)

Bhattacharyya, S.; Peterman, W.; Hales, C.

1984-01-01

The creep rupture behavior of nine iron base and one cobalt base candidate Stirling engine alloys is evaluated. Rupture life, minimum creep rate, and time to 1% strain data are analyzed. The 3500 h rupture life stress and stress to obtain 1% strain in 3500 h are also estimated.

Sandia/Stanford Unified Creep Plasticity Damage Model for ANSYS

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

Pierce, David M.; Vianco, Paul T.; Fossum, Arlo F.

2006-09-03

A unified creep plasticity (UCP) model was developed, based upon the time-dependent and time-independent deformation properties of the 95.5Sn-3.9Ag-0.6Cu (wt.%) soldier that were measured at Sandia. Then, a damage parameter, D, was added to the equation to develop the unified creep plasticity damage (UCPD) model. The parameter, D, was parameterized, using data obtained at Sandia from isothermal fatigue experiments on a double-lap shear test. The softwae was validated against a BGA solder joint exposed to thermal cycling. The UCPD model was put into the ANSYS finite element as a subroutine. So, the softwae is the subroutine for ANSYS 8.1.

Indentation Creep Behavior of Nugget Zone of Friction Stir Welded 2014 Aluminum Alloy

NASA Astrophysics Data System (ADS)

Das, Jayashree; Robi, P. S.; Sankar, M. Ravi

2018-04-01

The present study is aimed at evaluating the creep behavior of the nugget zone of friction welded 2014 Aluminum alloy by indentation creep tests. Impression creep testing was carried out at different temperatures of 300°C, 350°C and 400 °C with stress 124.77MPa, 187.16MPa, 249.55 MPa using a 1.0 mm diameter WC indenter. Experiments were conducted till the curve enters the steady state creep region. Constitutive modeling of creep behavior was carried out considering the temperature, stress and steady state creep rate. Microstructural investigation of the crept specimen at 400°C temperature and 187.16 MPa load was carried out and found that the small precipitates accumulate along the grain boundaries at the favorable conditions of the creep temperature and stress, new precipitates evolve due to the ageing. The grains are broken and deformed due to the creep phenomena.

The implication of gouge mineralogy evolution on fault creep: an example from The North Anatolian Fault, Turkey

NASA Astrophysics Data System (ADS)

Kaduri, M.; Gratier, J. P.; Renard, F.; Cakir, Z.; Lasserre, C.

2015-12-01

Aseismic creep is found along several sections of major active faults at shallow depth, such as the North Anatolian Fault in Turkey, the San Andreas Fault in California (USA), the Longitudinal Valley Fault in Taiwan, the Haiyuan fault in China and the El Pilar Fault in Venezuela. Identifying the mechanisms controlling creep and their evolution with time and space represents a major challenge for predicting the mechanical evolution of active faults, the interplay between creep and earthquakes, and the link between short-term observations from geodesy and the geological setting. Hence, studying the evolution of initial rock into damaged rock, then into gouge, is one of the key question for understanding the origin of fault creep. In order to address this question we collected samples from a dozen well-preserved fault outcrops along creeping and locked sections of the North Anatolian Fault. We used various methods such as microscopic and geological observations, EPMA, XRD analysis, combined with image processing, to characterize their mineralogy and strain. We conclude that (1) there is a clear correlation between creep localization and gouge composition. The locked sections of the fault are mostly composed of massive limestone. The creeping sections comprises clay gouges with 40-80% low friction minerals such as smectite, saponite, kaolinite, that facilitates the creeping. (2) The fault gouge shows two main structures that evolve with displacement: anastomosing cleavage develop during the first stage of displacement; amplifying displacement leads to layering development oblique or sub-parallel to the fault. (3) We demonstrate that the fault gouge result from a progressive evolution of initial volcanic rocks including dissolution of soluble species that move at least partially toward the damage zones and alteration transformations by fluid flow that weaken the gouge and strengthen the damage zone.

Creep Life Prediction of Ceramic Components Using the Finite Element Based Integrated Design Program (CARES/Creep)

NASA Technical Reports Server (NTRS)

Jadaan, Osama M.; Powers, Lynn M.; Gyekenyesi, John P.

1997-01-01

The desirable properties of ceramics at high temperatures have generated interest in their use for structural applications such as in advanced turbine systems. Design lives for such systems can exceed 10,000 hours. Such long life requirements necessitate subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this work is to present a design methodology for predicting the lifetimes of structural components subjected to multiaxial creep loading. This methodology utilizes commercially available finite element packages and takes into account the time varying creep stress distributions (stress relaxation). In this methodology, the creep life of a component is divided into short time steps, during which, the stress and strain distributions are assumed constant. The damage, D, is calculated for each time step based on a modified Monkman-Grant creep rupture criterion. For components subjected to predominantly tensile loading, failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity.

Effects of Amplitude Variations on Deformation and Damage Evolution in SnAgCu Solder in Isothermal Cycling

NASA Astrophysics Data System (ADS)

Wentlent, Luke; Alghoul, Thaer M.; Greene, Christopher M.; Borgesen, Peter

2018-02-01

Although apparently simpler than in thermal cycling, the behavior of SnAgCu (SAC) solder joints in cyclic bending or vibration is not currently well understood. The rate of damage has been shown to scale with the inelastic work per cycle, and excursions to higher amplitudes lead to an apparent softening, some of which remains so that damage accumulation is faster in subsequent cycling at lower amplitudes. This frequently leads to a dramatic breakdown of current damage accumulation rules. An empirical damage accumulation rule has been proposed to account for this, but any applicability to the extrapolation of accelerated test results to life under realistic long-term service conditions remains to be validated. This will require a better understanding of the underlying mechanisms. The present work provides experimental evidence to support recent suggestions that the observed behavior is a result of cycling-induced dislocation structures providing for increased diffusion creep. It is argued that this means that the measured work is an indicator of the instantaneous dislocation density, rather than necessarily reflecting the actual work involved in the creation of the damage.

Comparison of the dynamic fatigue behavior of two monolithic SiC and an Al{sub 2}O{sub 3}/SiC composite

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

Breder, K.; Tennery, V.J.

1994-09-01

Two monolithic silicon carbides, NT230 siliconized SiC from Norton Saint Gobain and sintered {beta}-SiC from Coors, and a silicon carbide particulate reinforced alumina ceramic composite from Lanxide, which all are candidate materials for pressurized heat exchangers in coal-fired power plants have been evaluated. The fast fracture flexure strength was measured as a function of temperature. All candidate materials retained a sufficient strength level up to 1400C. The susceptibility to slow crack growth (SCG) was evaluated by the dynamic fatigue method at 1100C and 1400C. None of the materials exhibited SCG at 1100C. At 1400C the siliconized SiC ceramic showed limitedmore » SCG and the composite ceramic exhibited creep damage when stressed to 50% of fast fracture strength at the intermediate and slow stressing rates. This prevented the evaluation of the SCG properties of this material at 1400C. Fractography supported the mechanical observations and with the exception of the specimens which exhibited creep damage, only the siliconized SiC showed a small SCG damage zone at long times at 1400C.« less

Creep-Rupture Behavior of Ni-Based Alloy Tube Bends for A-USC Boilers

NASA Astrophysics Data System (ADS)

Shingledecker, John

Advanced ultrasupercritical (A-USC) boiler designs will require the use of nickel-based alloys for superheaters and reheaters and thus tube bending will be required. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section II PG-19 limits the amount of cold-strain for boiler tube bends for austenitic materials. In this summary and analysis of research conducted to date, a number of candidate nickel-based A-USC alloys were evaluated. These alloys include alloy 230, alloy 617, and Inconel 740/740H. Uniaxial creep and novel structural tests and corresponding post-test analysis, which included physical measurements, simplified analytical analysis, and detailed microscopy, showed that different damage mechanisms may operate based on test conditions, alloy, and cold-strain levels. Overall, creep strength and ductility were reduced in all the alloys, but the degree of degradation varied substantially. The results support the current cold-strain limits now incorporated in ASME for these alloys for long-term A-USC boiler service.

Fatigue and Creep-Fatigue Deformation of an Ultra-Fine Precipitate Strengthened Advanced Austenitic Alloy

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

M.C. Carroll; L.J. Carroll

An advanced austenitic alloy, HT-UPS (high-temperature ultrafine-precipitation-strengthened), has been identified as an ideal candidate material for the structural components of fast reactors and energy-conversion systems. HT-UPS alloys demonstrate improved creep resistance relative to 316 stainless steel (SS) through additions of Ti and Nb, which precipitate to form a widespread dispersion of stable nanoscale metallic carbide (MC) particles in the austenitic matrix. The low-cycle fatigue and creep-fatigue behavior of an HT-UPS alloy have been investigated at 650 °C and a 1.0% total strain, with an R-ratio of -1 and hold times at peak tensile strain as long as 150 min. Themore » cyclic deformation response of HT-UPS is directly compared to that of standard 316 SS. The measured values for total cycles to failure are similar, despite differences in peak stress profiles and in qualitative observations of the deformed microstructures. Crack propagation is primarily transgranular in fatigue and creep-fatigue of both alloys at the investigated conditions. Internal grain boundary damage in the form of fine cracks resulting from the tensile hold is present for hold times of 60 min and longer, and substantially more internal cracks are quantifiable in 316 SS than in HT-UPS. The dislocation substructures observed in the deformed material differ significantly; an equiaxed cellular structure is observed in 316 SS, whereas in HT-UPS the microstructure takes the form of widespread and relatively homogenous tangles of dislocations pinned by the nanoscale MC precipitates. The significant effect of the fine distribution of precipitates on observed fatigue and creep-fatigue response is described in three distinct behavioral regions as it evolves with continued cycling.« less

Creep Life of Ceramic Components Using a Finite-Element-Based Integrated Design Program (CARES/CREEP)

NASA Technical Reports Server (NTRS)

Powers, L. M.; Jadaan, O. M.; Gyekenyesi, J. P.

1998-01-01

The desirable properties of ceramics at high temperatures have generated interest in their use for structural application such as in advanced turbine engine systems. Design lives for such systems can exceed 10,000 hours. The long life requirement necessitates subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this paper is to present a design methodology for predicting the lifetimes of structural components subjected to creep rupture conditions. This methodology utilizes commercially available finite element packages and takes into account the time-varying creep strain distributions (stress relaxation). The creep life, of a component is discretized into short time steps, during which the stress and strain distributions are assumed constant. The damage is calculated for each time step based on a modified Monkman-Grant creep rupture criterion. Failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity. The corresponding time will be the creep rupture life for that component. Examples are chosen to demonstrate the Ceramics Analysis and Reliability Evaluation of Structures/CREEP (CARES/CREEP) integrated design program, which is written for the ANSYS finite element package. Depending on the component size and loading conditions, it was found that in real structures one of two competing failure modes (creep or slow crack growth) will dominate. Applications to benchmark problems and engine components are included.

Creep Life of Ceramic Components Using a Finite-Element-Based Integrated Design Program (CARES/CREEP)

NASA Technical Reports Server (NTRS)

Gyekenyesi, J. P.; Powers, L. M.; Jadaan, O. M.

1998-01-01

The desirable properties of ceramics at high temperatures have generated interest in their use for structural applications such as in advanced turbine systems. Design lives for such systems can exceed 10,000 hours. The long life requirement necessitates subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this paper is to present a design methodology for predicting the lifetimes of structural components subjected to creep rupture conditions. This methodology utilized commercially available finite element packages and takes into account the time-varying creep strain distributions (stress relaxation). The creep life of a component is discretized into short time steps, during which the stress and strain distributions are assumed constant. The damage is calculated for each time step based on a modified Monkman-Grant creep rupture criterion. Failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity. The corresponding time will be the creep rupture life for that component. Examples are chosen to demonstrate the CARES/CREEP (Ceramics Analysis and Reliability Evaluation of Structures/CREEP) integrated design programs, which is written for the ANSYS finite element package. Depending on the component size and loading conditions, it was found that in real structures one of two competing failure modes (creep or slow crack growth) will dominate. Applications to benechmark problems and engine components are included.

Characterization of Time-Dependent Behavior of Ramming Paste Used in an Aluminum Electrolysis Cell

NASA Astrophysics Data System (ADS)

Orangi, Sakineh; Picard, Donald; Alamdari, Houshang; Ziegler, Donald; Fafard, Mario

2015-12-01

A new methodology was proposed for the characterization of time-dependent behavior of materials in order to develop a constitutive model. The material used for the characterization was ramming paste, a porous material used in an aluminum electrolysis cell, which is baked in place under varying loads induced by the thermal expansion of other components of the cell. In order to develop a constitutive model representing the paste mechanical behavior, it was necessary to get some insight into its behavior using samples which had been baked at different temperatures ranging from 200 to 1000 °C. Creep stages, effect of testing temperature on the creep, creep-recovery, as well as nonlinear creep were observed for designing a constitutive law. Uniaxial creep-recovery tests were carried out at two temperatures on the baked paste: ambient and higher. Results showed that the shape of creep curves was similar to a typical creep; recovery happened and the creep was shown to be nonlinear. Those experimental observations and the identification of nonlinear parameters of developed constitutive model demonstrated that the baked paste experiences nonlinear viscoelastic-viscoplastic behavior at different temperatures.

Mechanisms of High-Temperature Fatigue Failure in Alloy 800H

NASA Technical Reports Server (NTRS)

BhanuSankaraRao, K.; Schuster, H.; Halford, G. R.

1996-01-01

The damage mechanisms influencing the axial strain-controlled Low-Cycle Fatigue (LCF) behavior of alloy 800H at 850 C have been evaluated under conditions of equal tension/compression ramp rates (Fast-Fast (F-F): 4 X 10(sup -3)/s and Slow-Slow (S-S): 4 X 10(sup -5)/s) and asymmetrical ramp rates (Fast-Slow (F-S): 4 x 10(sup -3)/s / 4 X 10(sup -5/s and Slow-Fast (S-F): 4 X 10(sup -5) / 4 X 10(sup -3)/s) in tension and compression. The fatigue life, cyclic stress response, and fracture modes were significantly influenced by the waveform shape. The fatigue lives displayed by different loading conditions were in the following order: F-F greater than S-S greater than F-S greater than S-F. The fracture mode was dictated by the ramp rate adopted in the tensile direction. The fast ramp rate in the tensile direction led to the occurrence of transgranular crack initiation and propagation, whereas the slow ramp rate caused intergranular initiation and propagation. The time-dependent processes and their synergistic interactions, which were at the basis of observed changes in cyclic stress response and fatigue life, were identified. Oxidation, creep damage, dynamic strain aging, massive carbide precipitation, time-dependent creep deformation, and deformation ratcheting were among the several factors influencing cyclic life. Irrespective of the loading condition, the largest effect on life was exerted by oxidation processes. Deformation ratcheting had its greatest influence on life under asymmetrical loading conditions. Creep damage accumulated the greatest amount during the slow tensile ramp under S-F conditions.

Creep Behavior of a Sn-Ag-Bi Pb-Free Solder

PubMed Central

Vianco, Paul; Rejent, Jerome; Grazier, Mark; Kilgo, Alice

2012-01-01

Compression creep tests were performed on the ternary 91.84Sn-3.33Ag-4.83Bi (wt.%, abbreviated Sn-Ag-Bi) Pb-free alloy. The test temperatures were: −25 °C, 25 °C, 75 °C, 125 °C, and 160 °C (± 0.5 °C). Four loads were used at the two lowest temperatures and five at the higher temperatures. The specimens were tested in the as-fabricated condition or after having been subjected to one of two air aging conditions: 24 hours at either 125 °C or 150 °C. The strain-time curves exhibited frequent occurrences of negative creep and small-scale fluctuations, particularly at the slower strain rates, that were indicative of dynamic recrystallization (DRX) activity. The source of tertiary creep behavior at faster strain rates was likely to also be DRX rather than a damage accumulation mechanism. Overall, the strain-time curves did not display a consistent trend that could be directly attributed to the aging condition. The sinh law equation satisfactorily represented the minimum strain rate as a function of stress and temperature so as to investigate the deformation rate kinetics: dε/dtmin = Asinhn (ασ) exp (−ΔH/RT). The values of α, n, and ΔH were in the following ranges (±95% confidence interval): α, 0.010–0.015 (±0.005 1/MPa); n, 2.2–3.1 (±0.5); and ΔH, 54–66 (±8 kJ/mol). The rate kinetics analysis indicated that short-circuit diffusion was a contributing mechanism to dislocation motion during creep. The rate kinetics analysis also determined that a minimum creep rate trend could not be developed between the as-fabricated versus aged conditions. This study showed that the elevated temperature aging treatments introduced multiple changes to the Sn-Ag-Bi microstructure that did not result in a simple loss (“softening”) of its mechanical strength.

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

Kohnert, Aaron A.; Dasgupta, Dwaipayan; Wirth, Brian

In order to improve the accident tolerance of light water reactor (LWR) fuel, alternative cladding materials have been proposed to replace zirconium (Zr)-based alloys. Of these materials, there is a particular focus on iron-chromium-aluminum (FeCrAl) alloys due to much slower oxidation kinetics in high-temperature steam than Zr-alloys. This should decrease the energy release due to oxidation and allow the cladding to remain integral longer in the presence of high temperature steam, making accident mitigation more likely. As a continuation of the development for these alloys, the material response must be demonstrated to provide suitable radiation stability, in order to ensuremore » that there will not be significant dimensional changes (e.g., swelling), as well as quantifying the radiation hardening and radiation creep behavior. In this report, we describe the use of cluster dynamics modeling to evaluate the defect physics and damage accumulation behavior of FeCrAl alloys subjected to neutron irradiation, with a particular focus on irradiation-induced swelling and defect fluxes to dislocations that are required to model irradiation creep behavior.« less

Tensile and compressive creep behavior of extruded Mg–10Gd–3Y–0.5Zr (wt.%) alloy

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

Wang, H.; The State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240; Wang, Q.D., E-mail: wangqudong@sjtu.edu.cn

2015-01-15

The tensile and compressive creep behavior of an extruded Mg–10Gd–3Y–0.5Zr (wt.%) alloy was investigated at temperatures ranging from 200 °C to 300 °C and under stresses ranging from 30 MPa to 120 MPa. There existed an asymmetry in the tensile and compressive creep properties. The minimum creep rate of the alloy was slightly greater in tension than in compression. The measured values of the transient strain and initial creep rate in compression were greater than those in tension. The creep stress exponent was approximately 2.5 at low temperatures (T < 250 °C) and 3.4 at higher temperatures both in tensionmore » and in compression. The compression creep activation energy at low temperatures and high temperatures was 83.4 and 184.3 kJ/mol respectively, while one activation energy (184 kJ/mol) represented the tensile–creep behavior over the temperature range examined. Dislocation creep was suggested to be the main mechanism in tensile creep and in the high-temperature regime in compressive creep, while grain boundary sliding was suggested to dominate in the low-temperature regime in compressive creep. Precipitate free zones were observed near grain boundaries perpendicular to the loading direction in tension and parallel to the loading direction in compression. Electron backscattered diffraction analysis revealed that the texture changed slightly during creep. Non-basal slip was suggested to contribute to the deformation after basal slip was introduced. In the tensile–creep ruptured specimens, intergranular cracks were mainly observed at general high-angle boundaries. - Highlights: • Creep behavior of an extruded Mg–RE alloy was characterized by EBSD. • T5 aging treatment enhanced the tension–compression creep asymmetry. • The grains grew slightly during tensile creep, but not for compressive creep. • Precipitate free zones (PFZs) were observed at specific grain boundaries. • Intergranular fracture was dominant and cracks mainly originated at GHABs.« less

Creep behavior of uranium carbide-based alloys

NASA Technical Reports Server (NTRS)

Seltzer, M. S.; Wright, T. R.; Moak, D. P.

1975-01-01

The present work gives the results of experiments on the influence of zirconium carbide and tungsten on the creep properties of uranium carbide. The creep behavior of high-density UC samples follows the classical time-dependence pattern of (1) an instantaneous deformation, (2) a primary creep region, and (3) a period of steady-state creep. Creep rates for unalloyed UC-1.01 and UC-1.05 are several orders of magnitude greater than those measured for carbide alloys containing a Zr-C and/or W dispersoid. The difference in creep strength between alloyed and unalloyed materials varies with temperature and applied stress.

Room temperature creep behavior of Ti–Nb–Ta–Zr–O alloy

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

Zhang, Wei-dong

The room temperature creep behavior and deformation mechanisms of a Ti–Nb–Ta–Zr–O alloy, which is also called “gum metal”, were investigated with the nanoindentation creep and conventional creep tests. The microstructure was observed with electron backscattered diffraction analysis (EBSD) and transmission electron microscopy (TEM). The results show that the creep stress exponent of the alloy is sensitive to cold deformation history of the alloy. The alloy which was cold swaged by 85% shows high creep resistance and the stress exponent is approximately equal to 1. Microstructural observation shows that creep process of the alloy without cold deformation is controlled by dislocationmore » mechanism. The stress-induced α' martensitic phase transformation also occurs. The EBSD results show that the grain orientation changes after the creep tests, and thus, the creep of the cold-worked alloy is dominated by the shear deformation of giant faults without direct assistance from dislocations. - Highlights: •Nanoindentation was used to investigate room temperature creep behavior of gum metal. •The creep stress exponent of gum metal is sensitive to the cold deformation history. •The creep stress exponent of cold worked gum metal is approximately equal to 1. •The creep of the cold-worked gum metal is governed by the shear deformation of giant faults.« less

The influence of matrix microstructure and particle reinforcement on the creep behavior of 2219 aluminum

NASA Astrophysics Data System (ADS)

Krajewski, P. E.; Allison, J. E.; Jones, J. W.

1993-12-01

The influence of matrix microstructure and reinforcement with 15 vol pct of TiC particles on the creep behavior of 2219 aluminum has been examined in the temperature range of 150 ‡C to 250 ‡C. At 150 ‡C, reinforcement led to an improvement in creep resistance, while at 250 ‡C, both materials exhibited essentially identical creep behavior. Precipitate spacing in the matrix exerted the predominant influence on minimum creep rate in both the unreinforced and the reinforced materials over the temperature range studied. This behavior and the high-stress dependence of minimum creep rate are explained using existing constant structure models where, in the present study, precipitate spacing is identified as the pertinent substructure dimension. A modest microstructure-independent strengthening from particle reinforcement was observed at 150 ‡C and was accurately modeled by existing continuum mechanical models. The absence of reinforcement creep strengthening at 250 ‡C can be attributed to diffusional relaxation processes at the higher temperature.

Indentation experiments and simulation of ovine bone using a viscoelastic-plastic damage model

PubMed Central

Zhao, Yang; Wu, Ziheng; Turner, Simon; MacLeay, Jennifer; Niebur, Glen L.; Ovaert, Timothy C.

2015-01-01

Indentation methods have been widely used to study bone at the micro- and nanoscales. It has been shown that bone exhibits viscoelastic behavior with permanent deformation during indentation. At the same time, damage due to microcracks is induced due to the stresses beneath the indenter tip. In this work, a simplified viscoelastic-plastic damage model was developed to more closely simulate indentation creep data, and the effect of the model parameters on the indentation curve was investigated. Experimentally, baseline and 2-year postovariectomized (OVX-2) ovine (sheep) bone samples were prepared and indented. The damage model was then applied via finite element analysis to simulate the bone indentation data. The mechanical properties of yielding, viscosity, and damage parameter were obtained from the simulations. The results suggest that damage develops more quickly for OVX-2 samples under the same indentation load conditions as the baseline data. PMID:26136623

Modeling the Role of Dislocation Substructure During Class M and Exponential Creep. Revised

NASA Technical Reports Server (NTRS)

Raj, S. V.; Iskovitz, Ilana Seiden; Freed, A. D.

1995-01-01

The different substructures that form in the power-law and exponential creep regimes for single phase crystalline materials under various conditions of stress, temperature and strain are reviewed. The microstructure is correlated both qualitatively and quantitatively with power-law and exponential creep as well as with steady state and non-steady state deformation behavior. These observations suggest that creep is influenced by a complex interaction between several elements of the microstructure, such as dislocations, cells and subgrains. The stability of the creep substructure is examined in both of these creep regimes during stress and temperature change experiments. These observations are rationalized on the basis of a phenomenological model, where normal primary creep is interpreted as a series of constant structure exponential creep rate-stress relationships. The implications of this viewpoint on the magnitude of the stress exponent and steady state behavior are discussed. A theory is developed to predict the macroscopic creep behavior of a single phase material using quantitative microstructural data. In this technique the thermally activated deformation mechanisms proposed by dislocation physics are interlinked with a previously developed multiphase, three-dimensional. dislocation substructure creep model. This procedure leads to several coupled differential equations interrelating macroscopic creep plasticity with microstructural evolution.

Interface between fatigue, creep and stress-corrosion cracking on Ti6246 titanium alloy

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

Sarrazin-Baudoux, C.; Chabanne, Y.; Petit, J.

1999-07-01

The influence of mean stress on the fatigue crack growth behavior of a Ti6246 alloy has been studied in the near-threshold area at room temperature and at 500 C. Tests were performed at various constant K{sub max} levels in ambient air, high vacuum and humidified Argon. Conditions for the occurrence of an abnormal behavior consisting in the disappearance of the threshold for sufficiently high K{sub max} level, are discussed with respect to environment and temperature. This effect is observed in air and in vacuum for K{sub max} higher than 52 MPa{radical}m, and is related to an intrinsic creep damage processmore » which appears more efficient at room temperature than at 500 C and more accentuated in air than in vacuum. In humidified Argon, the critical Kmax level is reduced at 22 MPa{radical}m at 500 C, such a detrimental effect being related to a Stress Corrosion Cracking process induced by water vapor.« less

Creep, Fatigue and Fracture Behavior of Environmental Barrier Coating and SiC-SiC Ceramic Matrix Composite Systems: The Role of Environment Effects

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Ghosn, Louis J.

2015-01-01

Advanced environmental barrier coating (EBC) systems for low emission SiCSiC CMC combustors and turbine airfoils have been developed to meet next generation engine emission and performance goals. This presentation will highlight the developments of NASAs current EBC system technologies for SiC-SiC ceramic matrix composite combustors and turbine airfoils, their performance evaluation and modeling progress towards improving the engine SiCSiC component temperature capability and long-term durability. Our emphasis has also been placed on the fundamental aspects of the EBC-CMC creep and fatigue behaviors, and their interactions with turbine engine oxidizing and moisture environments. The EBC-CMC environmental degradation and failure modes, under various simulated engine testing environments, in particular involving high heat flux, high pressure, high velocity combustion conditions, will be discussed aiming at quantifying the protective coating functions, performance and durability, and in conjunction with damage mechanics and fracture mechanics approaches.

Low-temperature creep of austenitic stainless steels

NASA Astrophysics Data System (ADS)

Reed, R. P.; Walsh, R. P.

2017-09-01

Plastic deformation under constant load (creep) in austenitic stainless steels has been measured at temperatures ranging from 4 K to room temperature. Low-temperature creep data taken from past and unreported austenitic stainless steel studies are analyzed and reviewed. Creep at cryogenic temperatures of common austenitic steels, such as AISI 304, 310 316, and nitrogen-strengthened steels, such as 304HN and 3116LN, are included. Analyses suggests that logarithmic creep (creep strain dependent on the log of test time) best describe austenitic stainless steel behavior in the secondary creep stage and that the slope of creep strain versus log time is dependent on the applied stress/yield strength ratio. The role of cold work, strain-induced martensitic transformations, and stacking fault energy on low-temperature creep behavior is discussed. The engineering significance of creep on cryogenic structures is discussed in terms of the total creep strain under constant load over their operational lifetime at allowable stress levels.

In situ monitored in-pile creep testing of zirconium alloys

NASA Astrophysics Data System (ADS)

Kozar, R. W.; Jaworski, A. W.; Webb, T. W.; Smith, R. W.

2014-01-01

The experiments described herein were designed to investigate the detailed irradiation creep behavior of zirconium based alloys in the HALDEN Reactor spectrum. The HALDEN Test Reactor has the unique capability to control both applied stress and temperature independently and externally for each specimen while the specimen is in-reactor and under fast neutron flux. The ability to monitor in situ the creep rates following a stress and temperature change made possible the characterization of creep behavior over a wide stress-strain-rate-temperature design space for two model experimental heats, Zircaloy-2 and Zircaloy-2 + 1 wt%Nb, with only 12 test specimens in a 100-day in-pile creep test program. Zircaloy-2 specimens with and without 1 wt% Nb additions were tested at irradiation temperatures of 561 K and 616 K and stresses ranging from 69 MPa to 455 MPa. Various steady state creep models were evaluated against the experimental results. The irradiation creep model proposed by Nichols that separates creep behavior into low, intermediate, and high stress regimes was the best model for predicting steady-state creep rates. Dislocation-based primary creep, rather than diffusion-based transient irradiation creep, was identified as the mechanism controlling deformation during the transitional period of evolving creep rate following a step change to different test conditions.

Bend stress relaxation and tensile primary creep of a polycrystalline alpha-SiC fiber

NASA Technical Reports Server (NTRS)

Hee Man, Yun; Goldsby, Jon C.; Morscher, Gregory N.

1995-01-01

Understanding the thermomechanical behavior (creep and stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high temperature applications. It is important to understand and model the total creep of fibers at low strain levels where creep is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance. The objective of this paper is to compare and analyze bend stress relaxation and tensile creep data for alpha-SiC fibers produced by the Carborundum Co. (Niagara Falls, NY). This fiber is of current technical interest and is similar in composition to bulk alpha-SiC which has been studied under compressive creep conditions. The temperature, time, and stress dependences will be discussed for the stress relaxation and creep results. In addition, some creep and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable creep components of these materials. The data will be presented in order to model the deformation behavior and compare relaxation and/or creep behavior for relatively low deformation strain conditions of practical concern. Where applicable, the tensile creep results will be compared to bend stress relaxation data.

Effects of misalignment on mechanical behavior of metals in creep

NASA Technical Reports Server (NTRS)

Wu, H. C.

1981-01-01

Creep tests were conducted by means of a closed loop servocontrolled materials test system. The strain history prior to creep is carefully monitored. Tests were performed for aluminum alloy 6061-O at 150 C and were monitored by a PDP 11/04 minicomputer at a preset constant plastic strain rate prehistory. The results show that the plastic strain rate prior to creep plays a significant role in creep behavior. The endochronic theory of viscoplasticity was applied to describe the observed creep curves. Intrinsic time and strain rate sensitivity function concepts are employed and modified according to the present observation.

Accelerated Near-Threshold Fatigue Crack Growth Behavior of an Aluminum Powder Metallurgy Alloy

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Newman, John A.

2002-01-01

Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low DK, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = Kmin/Kmax). The near threshold accelerated FCG rates are exacerbated by increased levels of Kmax (Kmax less than 0.4 KIC). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and Kmax influenced accelerated crack growth is time and temperature dependent.

The effect of aluminium on the creep behavior of titanium aluminide alloys

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

Nandy, T.K.; Mishra, R.S.; Gogia, A.K.

Small increases in the Al content of Ti{sub 3}Al-Nb alloys are known to improve creep resistance at the expense of the room temperature ductility. Though considerable work has been done on the creep behavior of titanium aluminide alloys, a systematic investigation involving the role of Al on the creep of aluminides is lacking. In the present study the authors have therefore carried out a complete investigation on stress and temperature effects on two alloys with differing Al contents, Ti-24Al-15Nb and Ti-26Al-15Nb (nominal composition in at%) in order to understand the effect of Al in terms of power law creep behavior.more » The following conclusions are made: (1) A strong Al effect on the creep resistance of O phase alloys in the Ti-Al-Nb systems has been confirmed, through a study of stress and temperature effects on the creep behavior of the Ti-24Al-15Nb and the Ti-26Al-15Nb compositions. (2) It has been shown, however, that the small differences in Al do not affect either the activation energies for creep ({approximately}370 kJ/mole) or the creep mechanism (climb controlled creep with a stress exponent of 4). The activation energies and stress exponents are similar to that observed in single phase O alloys. (3) It is suggested that Al influences creep strength through an intrinsic effect on the pre-exponential term AD{sub o} in the power law creep equation. It is possible that this effect is related to a higher ordering energy of the O phase with increasing Al content.« less

Creep Behavior of Poly(lactic acid) Based Biocomposites

PubMed Central

Morreale, Marco; Mistretta, Maria Chiara; Fiore, Vincenzo

2017-01-01

Polymer composites containing natural fibers are receiving growing attention as possible alternatives for composites containing synthetic fibers. The use of biodegradable matrices obtained from renewable sources in replacement for synthetic ones is also increasing. However, only limited information is available about the creep behavior of the obtained composites. In this work, the tensile creep behavior of PLA based composites, containing flax and jute twill weave woven fabrics, produced through compression molding, was investigated. Tensile creep tests were performed at different temperatures (i.e., 40 and 60 °C). The results showed that the creep behavior of the composites is strongly influenced by the temperature and the woven fabrics used. As preliminary characterization, quasi-static tensile tests and dynamic mechanical tests were carried out on the composites. Furthermore, fabrics (both flax and jute) were tested as received by means of quasi-static tests and creep tests to evaluate the influence of fabrics mechanical behavior on the mechanical response of the resulting composites. The morphological analysis of the fracture surface of the tensile samples showed the better fiber-matrix adhesion between PLA and jute fabric. PMID:28772755

Creep Behavior of Poly(lactic acid) Based Biocomposites.

PubMed

Morreale, Marco; Mistretta, Maria Chiara; Fiore, Vincenzo

2017-04-08

Polymer composites containing natural fibers are receiving growing attention as possible alternatives for composites containing synthetic fibers. The use of biodegradable matrices obtained from renewable sources in replacement for synthetic ones is also increasing. However, only limited information is available about the creep behavior of the obtained composites. In this work, the tensile creep behavior of PLA based composites, containing flax and jute twill weave woven fabrics, produced through compression molding, was investigated. Tensile creep tests were performed at different temperatures (i.e., 40 and 60 °C). The results showed that the creep behavior of the composites is strongly influenced by the temperature and the woven fabrics used. As preliminary characterization, quasi-static tensile tests and dynamic mechanical tests were carried out on the composites. Furthermore, fabrics (both flax and jute) were tested as received by means of quasi-static tests and creep tests to evaluate the influence of fabrics mechanical behavior on the mechanical response of the resulting composites. The morphological analysis of the fracture surface of the tensile samples showed the better fiber-matrix adhesion between PLA and jute fabric.

Computer program for predicting creep behavior of bodies of revolution

NASA Technical Reports Server (NTRS)

Adams, R.; Greenbaum, G.

1971-01-01

Computer program, CRAB, uses finite-element method to calculate creep behavior and predict steady-state stresses in an arbitrary body of revolution subjected to a time-dependent axisymmetric load. Creep strains follow a time hardening law and a Prandtl-Reuss stress-strain relationship.

Primary and secondary creep in aluminum alloys as a solid state transformation

NASA Astrophysics Data System (ADS)

Fernández, R.; Bruno, G.; González-Doncel, G.

2016-08-01

Despite the massive literature and the efforts devoted to understand the creep behavior of aluminum alloys, a full description of this phenomenon on the basis of microstructural parameters and experimental conditions is, at present, still missing. The analysis of creep is typically carried out in terms of the so-called steady or secondary creep regime. The present work offers an alternative view of the creep behavior based on the Orowan dislocation dynamics. Our approach considers primary and secondary creep together as solid state isothermal transformations, similar to recrystallization or precipitation phenomena. In this frame, it is shown that the Johnson-Mehl-Avrami-Kolmogorov equation, typically used to analyze these transformations, can also be employed to explain creep deformation. The description is fully compatible with present (empirical) models of steady state creep. We used creep curves of commercially pure Al and ingot AA6061 alloy at different temperatures and stresses to validate the proposed model.

Effects of Environment on Creep Behavior of Nextel 720/Alumina-Mullite Ceramic Composite at 1200 deg C

DTIC Science & Technology

2008-03-01

creep life . This degradation increased with increasing temperatures. At 1000°, all specimens achieved creep run-out, defined as...strain measurement 29 Table 4. Summary of N720/AM creep data. Sample Environment Thermal Strain (%) E (GPa) Creep Stress (MPa) Creep Life (h...Material Creep Stress(MPa) Creep Life (h) Creep Strain (%) Secondary Creep Rate (s-1) N720/A 80 >100 0.798 1.5E-08 N720/A 100 41 1.520

Time-Dependent Behavior of Diabase and a Nonlinear Creep Model

NASA Astrophysics Data System (ADS)

Yang, Wendong; Zhang, Qiangyong; Li, Shucai; Wang, Shugang

2014-07-01

Triaxial creep tests were performed on diabase specimens from the dam foundation of the Dagangshan hydropower station, and the typical characteristics of creep curves were analyzed. Based on the test results under different stress levels, a new nonlinear visco-elasto-plastic creep model with creep threshold and long-term strength was proposed by connecting an instantaneous elastic Hooke body, a visco-elasto-plastic Schiffman body, and a nonlinear visco-plastic body in series mode. By introducing the nonlinear visco-plastic component, this creep model can describe the typical creep behavior, which includes the primary creep stage, the secondary creep stage, and the tertiary creep stage. Three-dimensional creep equations under constant stress conditions were deduced. The yield approach index (YAI) was used as the criterion for the piecewise creep function to resolve the difficulty in determining the creep threshold value and the long-term strength. The expression of the visco-plastic component was derived in detail and the three-dimensional central difference form was given. An example was used to verify the credibility of the model. The creep parameters were identified, and the calculated curves were in good agreement with the experimental curves, indicating that the model is capable of replicating the physical processes.

Study on the Tensile Creep Behavior of Carbon Nanotubes-Reinforced Sn-58Bi Solder Joints

NASA Astrophysics Data System (ADS)

Yang, Li; Liu, Haixiang; Zhang, Yaocheng

2018-01-01

The microstructure and tensile creep behavior of plain Sn-58Bi solder and carbon nanotubes (CNTs)-reinforced composite solder joints were investigated. The stress exponent n under different stresses and the creep activation energy Q c under different temperatures of solder joints were obtained by an empirical equation. The results reveal that the microstructure of the composite solder joint is refined and the tensile creep resistance is improved by CNTs. The improvement of creep behavior is due to the microstructural change of the composite solder joints, since the CNTs could provide more obstacles for dislocation pile-up, which enhances the values of the stress exponent and the creep activation energy. The steady-state tensile creep rates of plain solder and composite solder joints are increased with increasing temperature and applied stress. The tensile creep constitutive equations of plain solder and composite solder joints are written as \\dot{ɛ }_{s1} = 14.94( {σ /G} )^{3.7} \\exp ( { - 81444/RT} ) and \\dot{ɛ }_{s2} = 2.5( {σ /G} )^{4.38} \\exp ( { - 101582/RT} ) , respectively. The tensile creep mechanism of the solder joints is the effects of lattice diffusion determined by dislocation climbing.

Creep and creep-recovery of a thermoplastic resin and composite

NASA Technical Reports Server (NTRS)

Hiel, Clem

1988-01-01

The database on advanced thermoplastic composites, which is currently available to industry, contains little data on the creep and viscoelastic behavior. This behavior is nevertheless considered important, particularly for extended-service reliability in structural applications. The creep deformation of a specific thermoplastic resin and composite is reviewed. The problem to relate the data obtained on the resin to the data obtained on the composite is discussed.

Creep behavior of Grade 91 steel under uniaxial and multiaxial state of stress

NASA Astrophysics Data System (ADS)

Ren, Facai; Tang, Xiaoying

2017-09-01

Creep rupture behavior of Grade 91 heat-resistant steel used for steam cooler under uniaxial and multiaxial state of stress was investigated. Creep tests were conducted at the temperature of 923K under the stress 125MPa. The notch root radii (r) of doubled circumferentially U-notched specimens were 0.6 and 6 mm. The creep rupture life of Grade 91 steel was found to increase with the increasing of notch acuity ratio. The creep rupture mechanism was investigated based on the SEM fractography analysis.

Creep and creep rupture of laminated graphite/epoxy composites. Ph.D. Thesis. Final Report, 1 Oct. 1979 - 30 Sep. 1980

NASA Technical Reports Server (NTRS)

Dillard, D. A.; Morris, D. H.; Brinson, H. F.

1981-01-01

An incremental numerical procedure based on lamination theory is developed to predict creep and creep rupture of general laminates. Existing unidirectional creep compliance and delayed failure data is used to develop analytical models for lamina response. The compliance model is based on a procedure proposed by Findley which incorporates the power law for creep into a nonlinear constitutive relationship. The matrix octahedral shear stress is assumed to control the stress interaction effect. A modified superposition principle is used to account for the varying stress level effect on the creep strain. The lamina failure model is based on a modification of the Tsai-Hill theory which includes the time dependent creep rupture strength. A linear cumulative damage law is used to monitor the remaining lifetime in each ply.

Effects of Multiple Rejuvenation Cycles on Mechanical Properties and Microstructure of IN-738 Superalloy

NASA Astrophysics Data System (ADS)

Monti, Cosimo; Giorgetti, Alessandro; Tognarelli, Leonardo; Mastromatteo, Francesco

2018-05-01

The scope of this work is to show the effects of multiple applications of a rejuvenation treatment studied for IN-738 on both the microstructure and the mechanical properties of the creep-damaged superalloy and to check the recovery obtained after one and two rejuvenation cycles through creep and tensile tests, whose results will be compared with the performance of the virgin material. This work will show that this rejuvenation treatment is able to recover the microstructure of creep-damaged specimens after one and two applications and that the mechanical properties of the rejuvenated alloy are very similar to the virgin material even after two rejuvenation cycles.

Creep Behavior of Posidonia Shale at Elevated Pressure and Temperature

NASA Astrophysics Data System (ADS)

Rybacki, E.; Herrmann, J.; Wirth, R.; Dresen, G.

2017-12-01

Unconventional reservoir rocks are usually stimulated by repeated hydraulic fracturing operations. However, the production rate often decays with time that may arise from creep-induced fracture closure by proppant embedment. To examine experimentally the creep behavior of shales, we deformed immature carbonate-rich Posidonia shale at constant stress conditions and elevated temperatures between 50° and 200°C and confining pressures of 50 to 200 MPa. Samples showed transient creep in the semibrittle regime with high deformation rates at high differential stress, high temperature, and low confinement. Strain was mainly accommodated by deformation of the weak organic matter and phyllosilicates and by pore space reduction. At relatively low stress the samples deformed in the primary creep regime with continuously decelerating strain rate. The relation between strain and time can be described by an empirical power law equation, where the fitted parameters vary with temperature, pressure and stress. Our results suggest that healing of hydraulic fractures at low stresses by creep-induced proppant embedment is unlikely within a creep period of several years. At high differential stress (85-90% of the triaxial strength), as may be expected in situ at contact areas due to stress concentrations, the shale showed secondary creep, followed by tertiary creep until failure. In this regime, stress corrosion may induce microcrack propagation and coalescence. Secondary creep rates were also described by a power law that predicts faster fracture closure rates than for primary creep and likely contributes to production rate decline. Comparison of our data with published primary creep data on other shales suggest that the long-term creep behavior of shales can be correlated to their brittleness estimated from composition. Low creep strain is supported by a high fraction of strong minerals that can build up a load-bearing framework.

Effect of cold work on the stress corrosion cracking behavior of Alloy 690 in supercritical water environment

NASA Astrophysics Data System (ADS)

Chen, Kai; Du, Donghai; Gao, Wenhua; Guo, Xianglong; Zhang, Lefu; Andresen, Peter L.

2018-01-01

The stress corrosion cracking (SCC) behavior of Alloy 690 with 0, 20% and 30% cold work (CW) was studied in supercritical water (SCW) environment with an emphasis on CW and creep on the CGRs (CGR). SCC and creep CGRs increased with %CW, which correlated hardness very well. Microscopic characterization of the crack tip and fracture surface showed obvious cavity-like features, which is clear evidence of creep attack. The creep CGRs in inert gas were comparable to the SCC CGRs in SCW, indicating that creep is a major factor in crack growth. Increasing level of CW was found to increase the creep susceptibility, and high activation energies for creep crack growth were observed between 500 °C and 550 °C.

Correlation Between Intercritical Heat-Affected Zone and Type IV Creep Damage Zone in Grade 91 Steel

NASA Astrophysics Data System (ADS)

Wang, Yiyu; Kannan, Rangasayee; Li, Leijun

2018-04-01

A soft zone in Cr-Mo steel weldments has been reported to accompany the infamous Type IV cracking, the highly localized creep damage in the heat-affected zone of creep-resistant steels. However, the microstructural features and formation mechanism of this soft zone are not well understood. In this study, using microhardness profiling and microstructural verification, the initial soft zone in the as-welded condition was identified to be located in the intercritical heat-affected zone of P91 steel weldments. It has a mixed structure, consisting of Cr-rich re-austenitized prior austenite grains and fine Cr-depleted, tempered martensite grains retained from the base metal. The presence of these further-tempered retained grains, originating from the base metal, is directly responsible for the hardness reduction of the identified soft zone in the as-welded condition. The identified soft zone exhibits a high location consistency at three thermal stages. Local chemistry analysis and thermodynamic calculation show that the lower chromium concentrations inside these retained grains thermodynamically decrease their potentials for austenitic transformation during welding. Heterogeneous grain growth is observed in the soft zone during postweld heat treatment. The mismatch of strengths between the weak Cr-depleted grains and strong Cr-rich grains enhances the creep damage. Local deformation of the weaker Cr-depleted grains accelerates the formation of creep cavities.

Modeling Creep-Fatigue-Environment Interactions in Steam Turbine Rotor Materials for Advanced Ultra-supercritical Coal Power Plants

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

Shen, Chen

2014-04-01

The goal of this project is to model creep-fatigue-environment interactions in steam turbine rotor materials for advanced ultra-supercritical (A-USC) coal power Alloy 282 plants, to develop and demonstrate computational algorithms for alloy property predictions, and to determine and model key mechanisms that contribute to the damages caused by creep-fatigue-environment interactions.

Study on creep behavior of Grade 91 heat-resistant steel using theta projection method

NASA Astrophysics Data System (ADS)

Ren, Facai; Tang, Xiaoying

2017-10-01

Creep behavior of Grade 91 heat-resistant steel used for steam cooler was characterized using the theta projection method. Creep tests were conducted at the temperature of 923K under the stress ranging from 100-150MPa. Based on the creep curve results, four theta parameters were established using a nonlinear least square fitting method. Four theta parameters showed a good linearity as a function of stress. The predicted curves coincided well with the experimental data and creep curves were also modeled to the low stress level of 60MPa.

Investigation of Three Analytical Hypothesis for Determining Material Creep Behavior under Varied Loads, with an Application to 2024-T3 Aluminum-Alloy Sheet in Tension at 400 F

NASA Technical Reports Server (NTRS)

Berkovits, Avraham

1961-01-01

Three existing hypotheses are formulated mathematically to estimate tensile creep strain under varied loads and constant temperature from creep data obtained under constant load and constant temperature. hypotheses investigated include the time-hardening, strain-hardening, and life-fraction rules. Predicted creep behavior is compared with data obtained from tensile creep tests of 2024-T3 aluminum-alloy sheet at 400 F under cyclic-load conditions. creep strain under varied loads is presented on the basis of an equivalent stress, derived from the life-fraction rule, which reduces the varied-load case to a constant-load problem. Creep strain in the region of interest for structural design and rupture times, determined from the hypotheses investigated, are in fair agreement with data in most cases, although calculated values of creep strain are generally greater than the experimental values because creep recovery is neglected in the calculations.

Creep and stress rupture of a mechanically alloyed oxide dispersion and precipitation strengthened nickel-base superalloy

NASA Technical Reports Server (NTRS)

Howson, T. E.; Tien, J. K.; Mervyn, D. A.

1980-01-01

The creep and stress rupture behavior of a mechanically alloyed oxide dispersion strengthened (ODS) and gamma-prime precipitation strengthened nickel-base alloy (alloy MA 6000E) was studied at intermediate and elevated temperatures. At 760 C, MA 6000E exhibits the high creep strength characteristic of nickel-base superalloys and at 1093 C the creep strength is superior to other ODS nickel-base alloys. The stress dependence of the creep rate is very sharp at both test temperatures and the apparent creep activation energy measured around 760 C is high, much larger in magnitude than the self-diffusion energy. Stress rupture in this large grain size material is transgranular and crystallographic cracking is observed. The rupture ductility is dependent on creep strain rate, but usually is low. These and accompanying microstructural results are discussed with respect to other ODS alloys and superalloys and the creep behavior is rationalized by invoking a recently-developed resisting stress model of creep in materials strengthened by second phase particles.

Temperature dependence of creep compliance of highly cross-linked epoxy: A molecular simulation study

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

Khabaz, Fardin, E-mail: rajesh.khare@ttu.edu; Khare, Ketan S., E-mail: rajesh.khare@ttu.edu; Khare, Rajesh, E-mail: rajesh.khare@ttu.edu

2014-05-15

We have used molecular dynamics (MD) simulations to study the effect of temperature on the creep compliance of neat cross-linked epoxy. Experimental studies of mechanical behavior of cross-linked epoxy in literature commonly report creep compliance values, whereas molecular simulations of these systems have primarily focused on the Young’s modulus. In this work, in order to obtain a more direct comparison between experiments and simulations, atomistically detailed models of the cross-linked epoxy are used to study their creep compliance as a function of temperature using MD simulations. The creep tests are performed by applying a constant tensile stress and monitoring themore » resulting strain in the system. Our results show that simulated values of creep compliance increase with an increase in both time and temperature. We believe that such calculations of the creep compliance, along with the use of time temperature superposition, hold great promise in connecting the molecular insight obtained from molecular simulation at small length- and time-scales with the experimental behavior of such materials. To the best of our knowledge, this work is the first reported effort that investigates the creep compliance behavior of cross-linked epoxy using MD simulations.« less

Autonomous Filling of Grain-Boundary Cavities during Creep Loading in Fe-Mo Alloys

NASA Astrophysics Data System (ADS)

Zhang, S.; Fang, H.; Gramsma, M. E.; Kwakernaak, C.; Sloof, W. G.; Tichelaar, F. D.; Kuzmina, M.; Herbig, M.; Raabe, D.; Brück, E.; van der Zwaag, S.; van Dijk, N. H.

2016-10-01

We have investigated the autonomous repair of creep damage by site-selective precipitation in a binary Fe-Mo alloy (6.2 wt pct Mo) during constant-stress creep tests at temperatures of 813 K, 823 K, and 838 K (540 °C, 550 °C, and 565 °C). Scanning electron microscopy studies on the morphology of the creep-failed samples reveal irregularly formed deposits that show a close spatial correlation with the creep cavities, indicating the filling of creep cavities at grain boundaries by precipitation of the Fe2Mo Laves phase. Complementary transmission electron microscopy and atom probe tomography have been used to characterize the precipitation mechanism and the segregation at grain boundaries in detail.

Relation of structure to mechanical properties of thin thoria dispersion strengthened nickel-chromium (TD-NiCr alloy sheet

NASA Technical Reports Server (NTRS)

Whittenberger, J. D.

1975-01-01

A study of the relation between structure and mechanical properties of thin TD-NiCr sheet indicated that the elevated temperature tensile, stress-rupture, and creep strength properties depend primarily on the grain aspect ratio and sheet thickness. In general, the strength properties increased with increasing grain aspect ratio and sheet thickness. Tensile testing revealed an absence of ductility at elevated temperatures. A threshold stress for creep appears to exist. Even small amounts of prior creep deformation at elevated temperatures can produce severe creep damage.

Effect of a solid solution on the steady-state creep behavior of an aluminum matrix composite

NASA Astrophysics Data System (ADS)

Pandey, A. B.; Mishra, R. S.; Mahajan, Y. R.

1996-02-01

The effect of an alloying element, 4 wt pct Mg, on the steady-state creep behavior of an Al-10 vol pct SiCp composite has been studied. The Al-4 wt pct Mg-10 vol pct SiCp composite has been tested under compression creep in the temperature range 573 to 673 K. The steady-state creep data of the composite show a transition in the creep behavior (regions I and II) depending on the applied stress at 623 and 673 K. The low stress range data (region I) exhibit a stress exponent of about 7 and an activation energy of 76.5 kJ mol-1. These values conform to the dislocation-climb-controlled creep model with pipe diffusion as a rate-controlling mechanism. The intermediate stress range data (region II) exhibit high and variable apparent stress exponents, 18 to 48, and activation energy, 266 kJ mol-1, at a constant stress, σ = 50 MPa, for creep of this composite. This behavior can be rationalized using a substructure-invariant model with a stress exponent of 8 and an activation energy close to the lattice self-diffusion of aluminum together with a threshold stress. The creep data of the Al-Mg-A12O3f composite reported by Dragone and Nix also conform to the substructure-invariant model. The threshold stress and the creep strength of the Al-Mg-SiCp, composite are compared with those of the Al-Mg-Al2O3f and 6061 Al-SiCp.w, composites and discussed in terms of the load-transfer mechanism. Magnesium has been found to be very effective in improving the creep resistance of the Al-SiCp composite.

Creep rupture behavior of unidirectional advanced composites

NASA Technical Reports Server (NTRS)

Yeow, Y. T.

1980-01-01

A 'material modeling' methodology for predicting the creep rupture behavior of unidirectional advanced composites is proposed. In this approach the parameters (obtained from short-term tests) required to make the predictions are the three principal creep compliance master curves and their corresponding quasi-static strengths tested at room temperature (22 C). Using these parameters in conjunction with a failure criterion, creep rupture envelopes can be generated for any combination of in-plane loading conditions and ambient temperature. The analysis was validated experimentally for one composite system, the T300/934 graphite-epoxy system. This was done by performing short-term creep tests (to generate the principal creep compliance master curves with the time-temperature superposition principle) and relatively long-term creep rupture tensile tests of off-axis specimens at 180 C. Good to reasonable agreement between experimental and analytical results is observed.

Effects of Frequency and Environment on Fatigue Behavior of an Oxide-Oxide Ceramic Matrix Composite at 1200 Deg. C

DTIC Science & Technology

2006-06-01

Mehrman investigated the effects of prior fatigue on creep behavior, and concluded that a history of prior fatigue loading increases creep life of...as reduced susceptibility to oxidation [4]. Nextel™ 720/Alumina composite (N720/A), combines the strength and creep resistance of a di- phase...studied the response to creep and cyclic loading, respectively, and showed that the presence of steam severely degrades performance at 1200ºC [35

Investigation of the effect of aggregates' morphology on concrete creep properties by numerical simulations

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

Lavergne, F.; Sab, K., E-mail: karam.sab@enpc.fr; Sanahuja, J.

2015-05-15

Prestress losses due to creep of concrete is a matter of interest for long-term operations of nuclear power plants containment buildings. Experimental studies by Granger (1995) have shown that concretes with similar formulations have different creep behaviors. The aim of this paper is to numerically investigate the effect of size distribution and shape of elastic inclusions on the long-term creep of concrete. Several microstructures with prescribed size distribution and spherical or polyhedral shape of inclusions are generated. By using the 3D numerical homogenization procedure for viscoelastic microstructures proposed by Šmilauer and Bažant (2010), it is shown that the size distributionmore » and shape of inclusions have no measurable influence on the overall creep behavior. Moreover, a mean-field estimate provides close predictions. An Interfacial Transition Zone was introduced according to the model of Nadeau (2003). It is shown that this feature of concrete's microstructure can explain differences between creep behaviors.« less

Linking the fractional derivative and the Lomnitz creep law to non-Newtonian time-varying viscosity

NASA Astrophysics Data System (ADS)

Pandey, Vikash; Holm, Sverre

2016-09-01

Many of the most interesting complex media are non-Newtonian and exhibit time-dependent behavior of thixotropy and rheopecty. They may also have temporal responses described by power laws. The material behavior is represented by the relaxation modulus and the creep compliance. On the one hand, it is shown that in the special case of a Maxwell model characterized by a linearly time-varying viscosity, the medium's relaxation modulus is a power law which is similar to that of a fractional derivative element often called a springpot. On the other hand, the creep compliance of the time-varying Maxwell model is identified as Lomnitz's logarithmic creep law, making this possibly its first direct derivation. In this way both fractional derivatives and Lomnitz's creep law are linked to time-varying viscosity. A mechanism which yields fractional viscoelasticity and logarithmic creep behavior has therefore been found. Further, as a result of this linking, the curve-fitting parameters involved in the fractional viscoelastic modeling, and the Lomnitz law gain physical interpretation.

Linking the fractional derivative and the Lomnitz creep law to non-Newtonian time-varying viscosity.

PubMed

Pandey, Vikash; Holm, Sverre

2016-09-01

Many of the most interesting complex media are non-Newtonian and exhibit time-dependent behavior of thixotropy and rheopecty. They may also have temporal responses described by power laws. The material behavior is represented by the relaxation modulus and the creep compliance. On the one hand, it is shown that in the special case of a Maxwell model characterized by a linearly time-varying viscosity, the medium's relaxation modulus is a power law which is similar to that of a fractional derivative element often called a springpot. On the other hand, the creep compliance of the time-varying Maxwell model is identified as Lomnitz's logarithmic creep law, making this possibly its first direct derivation. In this way both fractional derivatives and Lomnitz's creep law are linked to time-varying viscosity. A mechanism which yields fractional viscoelasticity and logarithmic creep behavior has therefore been found. Further, as a result of this linking, the curve-fitting parameters involved in the fractional viscoelastic modeling, and the Lomnitz law gain physical interpretation.

Creep Behavior in Interlaminar Shear of a CVI SiC/SiC Composite at Elevated Temperatures in Air and Steam

DTIC Science & Technology

2012-03-22

upper use temperature under high tensile stress (allows long life , dimensional control, low residual CMC stress) Matrix Creep , Fiber Creep Long... creep life due to steam was more significant at 28%. However, at 22 MPa, the presence of steam appeared to be beneficial and extended creep

Effects of NaCl, pH, and Potential on the Static Creep Behavior of AA1100

NASA Astrophysics Data System (ADS)

Wan, Quanhe; Quesnel, David J.

2013-03-01

The creep rates of AA1100 are measured during exposure to a variety of aggressive environments. NaCl solutions of various concentrations have no influence on the steady-state creep behavior, producing creep rates comparable to those measured in lab air at room temperature. However, after an initial incubation period of steady strain rate, a dramatic increase of strain rate is observed on exposure to HCl solutions and NaOH solutions, as well as during cathodic polarization of specimens in NaCl solutions. Creep strain produces a continuous deformation and elongation of the sample surface that is comparable to slow strain rates at crack tips thought to control the kinetics of crack growth during stress corrosion cracking (SCC). In this experiment, we separate the strain and surface deformation from the complex geometry of the crack tip to better understand the processes at work. Based on this concept, two possible explanations for the environmental influences on creep strain rates are discussed relating to the anodic dissolution of the free surface and hydrogen influences on deformation mechanisms. Consistencies of pH dependence between corrosion creep and SCC at low pH prove a creep-involved SCC mechanism, while the discrepancies between corrosion creep behavior and previous SCC results at high pH indicate a rate-limit step change in the crack propagation of the SCC process.

Experimental Research on Creep Characteristics of Nansha Soft Soil

PubMed Central

Luo, Qingzi; Chen, Xiaoping

2014-01-01

A series of tests were performed to investigate the creep characteristics of soil in interactive marine and terrestrial deposit of Pearl River Delta. The secondary consolidation test results show that the influence of consolidation pressure on coefficient of secondary consolidation is conditional, which is decided by the consolidation state. The ratio of coefficient of secondary consolidation and coefficient of compressibility C a/C c is almost a constant, and the value is 0.03. In the shear-box test, the direct sheer creep failure of soil is mainly controlled by shear stress rather than the accumulation of shear strain. The triaxial creep features are closely associated with the drainage conditions, and consolidation can weaken the effect of creep. When the soft soil has triaxial creep damage, the strain rate will increase sharply. PMID:24526925

Experimental research on creep characteristics of Nansha soft soil.

PubMed

Luo, Qingzi; Chen, Xiaoping

2014-01-01

A series of tests were performed to investigate the creep characteristics of soil in interactive marine and terrestrial deposit of Pearl River Delta. The secondary consolidation test results show that the influence of consolidation pressure on coefficient of secondary consolidation is conditional, which is decided by the consolidation state. The ratio of coefficient of secondary consolidation and coefficient of compressibility (Ca/Cc) is almost a constant, and the value is 0.03. In the shear-box test, the direct sheer creep failure of soil is mainly controlled by shear stress rather than the accumulation of shear strain. The triaxial creep features are closely associated with the drainage conditions, and consolidation can weaken the effect of creep. When the soft soil has triaxial creep damage, the strain rate will increase sharply.

Indentation Size Effect on the Creep Behavior of a SnAgCu Solder

NASA Astrophysics Data System (ADS)

Han, Y. D.; Jing, H. Y.; Nai, S. M. L.; Xu, L. Y.; Tan, C. M.; Wei, J.

In the present study, nanoindentation studies of the 95.8Sn-3.5Ag-0.7Cu lead-free solder were conducted over a range of maximum loads from 20 mN to 100 mN, under a constant ramp rate of 0.05 s-1. The indentation scale dependence of creep behavior was investigated. The results revealed that the creep rate, creep strain rate and indentation stress are all dependent on the indentation depth. As the maximum load increased, an increasing trend in the creep rate was observed, while a decreasing trend in creep strain rate and indentation stress were observed. On the contrary, for the case of stress exponent value, no trend was observed and the values were found to range from 6.16 to 7.38. Furthermore, the experimental results also showed that the creep mechanism of the lead-free solder is dominated by dislocation climb.

Part-to-itself model inversion in process compensated resonance testing

NASA Astrophysics Data System (ADS)

Mayes, Alexander; Jauriqui, Leanne; Biedermann, Eric; Heffernan, Julieanne; Livings, Richard; Aldrin, John C.; Goodlet, Brent; Mazdiyasni, Siamack

2018-04-01

Process Compensated Resonance Testing (PCRT) is a non-destructive evaluation (NDE) method involving the collection and analysis of a part's resonance spectrum to characterize its material or damage state. Prior work used the finite element method (FEM) to develop forward modeling and model inversion techniques. In many cases, the inversion problem can become confounded by multiple parameters having similar effects on a part's resonance frequencies. To reduce the influence of confounding parameters and isolate the change in a part (e.g., creep), a part-to-itself (PTI) approach can be taken. A PTI approach involves inverting only the change in resonance frequencies from the before and after states of a part. This approach reduces the possible inversion parameters to only those that change in response to in-service loads and damage mechanisms. To evaluate the effectiveness of using a PTI inversion approach, creep strain and material properties were estimated in virtual and real samples using FEM inversion. Virtual and real dog bone samples composed of nickel-based superalloy Mar-M-247 were examined. Virtual samples were modeled with typically observed variations in material properties and dimensions. Creep modeling was verified with the collected resonance spectra from an incrementally crept physical sample. All samples were inverted against a model space that allowed for change in the creep damage state and the material properties but was blind to initial part dimensions. Results quantified the capabilities of PTI inversion in evaluating creep strain and material properties, as well as its sensitivity to confounding initial dimensions.

Creep-rupture behavior of 6 candidate stirling engine iron-base superalloys in high pressure hydrogen. Volume 1: Air creep-rupture behavior

NASA Technical Reports Server (NTRS)

Bhattacharyya, S.

1982-01-01

Four wrought alloys (A-286, IN 800H, N-155, and 19-9DL) and two cast alloys (CRM-6D and XF-818) were tested to determine their creep-rupture behavior. The wrought alloys were used in the form of sheets of 0.89 mm (0.035 in.) average thickness. The cast alloy specimens were investment cast and machined to 6.35 mm (0.250 in.) gage diameter. All specimens were tested to rupture in air at different times up to 3000 h over the temperature range of 650 C to 925 C (1200 F to 1700 F). Rupture life, minimum creep rate, and time to 1% creep strain were statistically analyzed as a function of stress at different temperatures. Temperature-compensated analysis was also performed to obtain the activation energies for rupture life, time to 1% creep strain, and the minimum creep rate. Microstructural and fracture analyses were also performed. Based on statistical analyses, estimates were made for stress levels at different temperatures to obtain 3500 h rupture life and time to 1% creep strain. Test results are to be compared with similar data being obtained for these alloys under 15 MPa (2175 psi) hydrogen.

The primary creep behavior of single crystal, nickel base superalloys PWA 1480 and PWA 1484

NASA Astrophysics Data System (ADS)

Wilson, Brandon Charles

Primary creep occurring at intermediate temperatures (650°C to 850°C) and loads greater than 500 MPa has been shown to result in severe creep strain, often exceeding 5-10%, during the first few hours of creep testing. This investigation examines how the addition of rhenium and changes in aging heat treatment affect the primary creep behavior of PWA 1480 and PWA 1484. To aid in the understanding of rhenium's role in primary creep, 3wt% Re was added to PWA 1480 to create a second generation version of PWA 1480. The age heat treatments used for creep testing were either 704°C/24 hr. or 871°C/32hr. All three alloys exhibited the presence of secondary gamma' confirmed by scanning electron microscopy and local electrode atom probe techniques. These aging heat treatments resulted in the reduction of the primary creep strain produced in PWA 1484 from 24% to 16% at 704°C/862 MPa and produced a slight dependence of the tensile properties of PWA 1480 on aging heat treatment temperature. For all test temperatures, the high temperature age resulted in a significant decrease in primary creep behavior of PWA 1484 and a longer lifetime for all but the lowest test temperature. The primary creep behavior of PWA 1480 and PWA 1480+Re did not display any significant dependence on age heat treatment. The creep rupture life of PWA 1480 is greater than PWA 1484 at 704°C, but significantly shorter at 760°C and 815°C. PWA 1480+Re, however, displayed the longest lifetime of all three alloys at both 704°C and 815°C (PWA 1480+Re was not tested at 760°C). Qualitative TEM analysis revealed that PWA 1484 deformed by large dislocation "ribbons" spanning large regions of material. PWA 1480, however, deformed primarily due to matrix dislocations and the creation of interfacial dislocation networks between the gamma and gamma' phases. PWA 1480+ contained stacking faults as well, though they acted on multiple slip systems generating work hardening and forcing the onset of secondary creep. X-ray diffraction and JMatPro calculations were also used to gain insight into the cause of the differences in behaviors.

Experiment and Modeling of Simultaneous Creep, Plasticity and Transformation of High Temperature Shape Memory Alloys During Cyclic Actuation

NASA Technical Reports Server (NTRS)

Kumar, Parikshith K.; Desai, Uri; Chatzigeorgiou, George; Lagoudas, Dimitris C.; Monroe, James; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glen

2010-01-01

The present work is focused on studying the cycling actuation behavior of HTSMAs undergoing simultaneous creep and transformation. For the thermomechanical testing, a high temperature test setup was assembled on a MTS frame with the capability to test up to temperatures of 600 C. Constant stress thermal cycling tests were conducted to establish the actuation characteristics and the phase diagram for the chosen HTSMA. Additionally, creep tests were conducted at constant stress levels at different test temperatures to characterize the creep behavior of the alloy over the operational range. A thermodynamic constitutive model is developed and extended to take into account a) the effect of multiple thermal cycling on the generation of plastic strains due to transformation (TRIP strains) and b) both primary and secondary creep effects. The model calibration is based on the test results. The creep tests and the uniaxial tests are used to identify the viscoplastic behavior of the material. The parameters for the SMA properties, regarding the transformation and transformation induced plastic strain evolutions, are obtained from the material phase diagram and the thermomechanical tests. The model is validated by predicting the material behavior at different thermomechanical test conditions.

A Comparison of the Irradiation Creep Behavior of Several Graphites

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

Burchell, Timothy D; Windes, Will

2016-01-01

Graphite creep strain data from the irradiation creep capsule Advanced Graphite Creep-1 (AGC-1) are reported. This capsule was the first (prototype) of a series of five or six capsules planned as part of the AGC experiment, which was designed to fully characterize the effects of neutron irradiation and the radiation creep behavior of current nuclear graphite. The creep strain data and analysis are reported for the six graphite grades incorporated in the capsule. The AGC-1 capsule was irradiated in the Advanced Test Reactor at Idaho National Laboratory (INL) at approximately 700 C and to a peak dose of 7 dpamore » (displacements per atom). The specimen s final dose, temperature, and stress conditions have been reported by INL and were used during this analysis. The derived creep coefficients (K) were calculated for each grade and were found to compare well to literature data for the creep coefficient, even under the wide range of AGC-1 specimen temperatures. Comparisons were made between AGC-1 data and historical grade data for creep coefficients.« less

Computational simulation of the creep-rupture process in filamentary composite materials

NASA Technical Reports Server (NTRS)

Slattery, Kerry T.; Hackett, Robert M.

1991-01-01

A computational simulation of the internal damage accumulation which causes the creep-rupture phenomenon in filamentary composite materials is developed. The creep-rupture process involves complex interactions between several damage mechanisms. A statistically-based computational simulation using a time-differencing approach is employed to model these progressive interactions. The finite element method is used to calculate the internal stresses. The fibers are modeled as a series of bar elements which are connected transversely by matrix elements. Flaws are distributed randomly throughout the elements in the model. Load is applied, and the properties of the individual elements are updated at the end of each time step as a function of the stress history. The simulation is continued until failure occurs. Several cases, with different initial flaw dispersions, are run to establish a statistical distribution of the time-to-failure. The calculations are performed on a supercomputer. The simulation results compare favorably with the results of creep-rupture experiments conducted at the Lawrence Livermore National Laboratory.

NASALife-Component Fatigue and Creep Life Prediction Program and Illustrative Examples

NASA Technical Reports Server (NTRS)

Murthy, Pappu L. N.; Mital, Subodh K.; Gyekenyesi, John Z.

2005-01-01

NASALife is a life prediction program for propulsion system components made of ceramic matrix composites (CMC) under cyclic thermo-mechanical loading and creep rupture conditions. Although, the primary focus was for CMC components the underlying methodologies are equally applicable to other material systems as well. The program references data for low cycle fatigue (LCF), creep rupture, and static material properties as part of the life prediction process. Multiaxial stresses are accommodated by Von Mises based methods and a Walker model is used to address mean stress effects. Varying loads are reduced by the Rainflow counting method. Lastly, damage due to cyclic loading (Miner s rule) and creep are combined to determine the total damage per mission and the number of missions the component can survive before failure are calculated. Illustration of code usage is provided through example problem of a CMC turbine stator vane made of melt-infiltrated, silicon carbide fiber-reinforced, silicon carbide matrix composite (MI SiC/SiC)

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

Oleinikov, A. I., E-mail: a.i.oleinikov@mail.ru; Bormotin, K. S., E-mail: cvmi@knastu.ru

It is shown that inverse problems of steady-state creep bending of plates in both the geometrically linear and nonlinear formulations can be represented in a variational formulation. Steady-state values of the obtained functionals corresponding to the solutions of the problems of inelastic deformation and springback are determined by applying a finite element procedure to the functionals. Optimal laws of creep deformation are formulated using the criterion of minimizing damage in the functionals of the inverse problems. The formulated problems are reduced to the problems solved by the finite element method using MSC.Marc software. Currently, forming of light metals poses tremendousmore » challenges due to their low ductility at room temperature and their unusual deformation characteristics at hot-cold work: strong asymmetry between tensile and compressive behavior, and a very pronounced anisotropy. We used the constitutive models of steady-state creep of initially transverse isotropy structural materials the kind of the stress state has influence. The paper gives basics of the developed computer-aided system of design, modeling, and electronic simulation targeting the processes of manufacture of wing integral panels. The modeling results can be used to calculate the die tooling, determine the panel processibility, and control panel rejection in the course of forming.« less

The inverse problems of wing panel manufacture processes

NASA Astrophysics Data System (ADS)

Oleinikov, A. I.; Bormotin, K. S.

2013-12-01

It is shown that inverse problems of steady-state creep bending of plates in both the geometrically linear and nonlinear formulations can be represented in a variational formulation. Steady-state values of the obtained functionals corresponding to the solutions of the problems of inelastic deformation and springback are determined by applying a finite element procedure to the functionals. Optimal laws of creep deformation are formulated using the criterion of minimizing damage in the functionals of the inverse problems. The formulated problems are reduced to the problems solved by the finite element method using MSC.Marc software. Currently, forming of light metals poses tremendous challenges due to their low ductility at room temperature and their unusual deformation characteristics at hot-cold work: strong asymmetry between tensile and compressive behavior, and a very pronounced anisotropy. We used the constitutive models of steady-state creep of initially transverse isotropy structural materials the kind of the stress state has influence. The paper gives basics of the developed computer-aided system of design, modeling, and electronic simulation targeting the processes of manufacture of wing integral panels. The modeling results can be used to calculate the die tooling, determine the panel processibility, and control panel rejection in the course of forming.

Creep model of unsaturated sliding zone soils and long-term deformation analysis of landslides

NASA Astrophysics Data System (ADS)

Zou, Liangchao; Wang, Shimei; Zhang, Yeming

2015-04-01

Sliding zone soil is a special soil layer formed in the development of a landslide. Its creep behavior plays a significant role in long-term deformation of landslides. Due to rainfall infiltration and reservoir water level fluctuation, the soils in the slide zone are often in unsaturated state. Therefore, the investigation of creep behaviors of the unsaturated sliding zone soils is of great importance for understanding the mechanism of the long-term deformation of a landslide in reservoir areas. In this study, the full-process creep curves of the unsaturated soils in the sliding zone in different net confining pressure, matric suctions and stress levels were obtained from a large number of laboratory triaxial creep tests. A nonlinear creep model for unsaturated soils and its three-dimensional form was then deduced based on the component model theory and unsaturated soil mechanics. This creep model was validated with laboratory creep data. The results show that this creep model can effectively and accurately describe the nonlinear creep behaviors of the unsaturated sliding zone soils. In order to apply this creep model to predict the long-term deformation process of landslides, a numerical model for simulating the coupled seepage and creep deformation of unsaturated sliding zone soils was developed based on this creep model through the finite element method (FEM). By using this numerical model, we simulated the deformation process of the Shuping landslide located in the Three Gorges reservoir area, under the cycling reservoir water level fluctuation during one year. The simulation results of creep displacement were then compared with the field deformation monitoring data, showing a good agreement in trend. The results show that the creeping deformations of landslides have strong connections with the changes of reservoir water level. The creep model of unsaturated sliding zone soils and the findings obtained by numerical simulations in this study are conducive to reveal the mechanisms of the dynamic process of landslide deformation, and serve as an important basis for the prediction and evaluation of landslides.

Modeling creep behavior of fiber composites

NASA Technical Reports Server (NTRS)

Chen, J. L.; Sun, C. T.

1988-01-01

A micromechanical model for the creep behavior of fiber composites is developed based on a typical cell consisting of a fiber and the surrounding matrix. The fiber is assumed to be linearly elastic and the matrix nonlinearly viscous. The creep strain rate in the matrix is assumed to be a function of stress. The nominal stress-strain relations are derived in the form of differential equations which are solved numerically for off-axis specimens under uniaxial loading. A potential function and the associated effective stress and effective creep strain rates are introduced to simplify the orthotropic relations.

The High Temperature Tensile and Creep Behaviors of High Entropy Superalloy.

PubMed

Tsao, Te-Kang; Yeh, An-Chou; Kuo, Chen-Ming; Kakehi, Koji; Murakami, Hideyuki; Yeh, Jien-Wei; Jian, Sheng-Rui

2017-10-04

This article presents the high temperature tensile and creep behaviors of a novel high entropy alloy (HEA). The microstructure of this HEA resembles that of advanced superalloys with a high entropy FCC matrix and L1 2 ordered precipitates, so it is also named as "high entropy superalloy (HESA)". The tensile yield strengths of HESA surpass those of the reported HEAs from room temperature to elevated temperatures; furthermore, its creep resistance at 982 °C can be compared to those of some Ni-based superalloys. Analysis on experimental results indicate that HESA could be strengthened by the low stacking-fault energy of the matrix, high anti-phase boundary energy of the strengthening precipitate, and thermally stable microstructure. Positive misfit between FCC matrix and precipitate has yielded parallel raft microstructure during creep at 982 °C, and the creep curves of HESA were dominated by tertiary creep behavior. To the best of authors' knowledge, this article is the first to present the elevated temperature tensile creep study on full scale specimens of a high entropy alloy, and the potential of HESA for high temperature structural application is discussed.

Ratcheting in a nonlinear viscoelastic adhesive

NASA Astrophysics Data System (ADS)

Lemme, David; Smith, Lloyd

2017-11-01

Uniaxial time-dependent creep and cycled stress behavior of a standard and toughened film adhesive were studied experimentally. Both adhesives exhibited progressive accumulation of strain from an applied cycled stress. Creep tests were fit to a viscoelastic power law model at three different applied stresses which showed nonlinear response in both adhesives. A third order nonlinear power law model with a permanent strain component was used to describe the creep behavior of both adhesives and to predict creep recovery and the accumulation of strain due to cycled stress. Permanent strain was observed at high stress but only up to 3% of the maximum strain. Creep recovery was under predicted by the nonlinear model, while cycled stress showed less than 3% difference for the first cycle but then over predicted the response above 1000 cycles by 4-14% at high stress. The results demonstrate the complex response observed with structural adhesives, and the need for further analytical advancements to describe their behavior.

Report on FY15 Alloy 617 SMT Creep-Fatigue Test Results

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

Wang, Yanli; Jetter, Robert I.; Baird, Seth T.

For the temperature range of 990-950C, Alloy 617 is a candidate IHX structural material for high temperature gas reactors (HTGRs) because of its high temperature creep properties. Also, its superior strength over a broad temperature range also offers advantages for certain component applications. In order for the designers to be able to use Alloy 617 for these high temperature components, Alloy 617 has to be approved for use in Section III (the nuclear section) of the ASME (American Society of Mechanical Engineers) Boiler and Pressure Vessel Code. A plan has been developed to propose a Code Case for use ofmore » Alloy 617 at elevated temperature in Section III of the ASME Code by September 2015. There has not been a new high temperature material approved for use in Section III for almost 20 years. The Alloy 617 Code Case effort would lead the way to establish a path for Code qualification of new high temperature materials of interest to other advanced SMRs. Creep-fatigue at elevated temperatures is the most damaging structural failure mode. In the past 40 years significant efforts have been devoted to the elevated temperature Code rule development in Section III, Subsection NH* of the ASME Boiler and Pressure Vessel Code, to ascertain conservative structural designs to prevent creep-fatigue failure. The current Subsection NH creep-fatigue procedure was established by the steps of (1) analytically obtaining a detailed stress-strain history, (2) comparing the stress and strain components to cyclic test results deconstructed into stress and strain quantities, and (3) recombining the results to obtain a damage function in the form of the so-called creep-fatigue damage-diagram. The deconstruction and recombination present difficulties in evaluation of test data and determination of cyclic damage in design. The uncertainties in these steps lead to the use of overly conservative design factors in the current creep-fatigue procedure. In addition, and of major significance to the viability of the Alloy 617 Code Case, the use of the current elastic analysis based rules in Subsection NH for the evaluation of strain limits (a precursor for the creep-fatigue rules) and the creep-fatigue rules themselves have been deemed inappropriate for Alloy 617 at temperatures above 650C (Corum and Brass, 1991). The rationale for this exclusion is that at higher temperatures it is not feasible to decouple plasticity and creep, which is the basis for the current simplified rules. This temperature, 650C, is well below the temperature range of interest for this material for the High Temperature Gas Cooled Reactor (HTGR) as well as the VHTR. The only current alternative is, thus, a full inelastic analysis which requires sophisticated material models which have not yet been formulated and verified. To address the prohibition on the use of current methods at very high temperatures, proposed Code rules have been developed which are based on the use of elastic-perfectly plastic (E-PP) analysis methods and which are expected to be applicable to very high temperatures. To provide data to implement the proposed rules and to verify their application, a series of tests have been initiated. One test concept, the Simplified Model Test (SMT), takes into account the stress and strain redistribution in real structures by including representative follow-up characteristics in the test specimen. The correlation parameter between test and design is the elastically calculated strain, and the dependent test variable is the observed cycles to failure. Although the initial priority for the SMT approach is to generate data to support validation of the E-PP Code Case for evaluation of creep-fatigue damage, the broader goal of the SMT approach is to develop a methodology for evaluation of creep fatigue damage which is simpler to implement than the current complex rules and applicable to the full temperature range from ambient conditions to the very high temperature creep regime of 900-950C. Also, guidance has been received from ASME Code committees that the proposed EPP methodology for evaluation of creep-fatigue damage should be extended to the other Subsection NH materials to the extent feasible. Thus, the scope of testing has been expanded to include SS304H and SS316H. This report describes the SMT approach and the development of testing capability to conduct SMT experiments on Alloy 617 and 304H and 316H and stainless steels. These SMT specimen data are also representative of component loading conditions and have been used as part of the verification of the proposed elastic-perfectly plastic Code Cases. Results from the SMT tests on both Alloy 617 and SS316H were compared to the predictions from the EPP Creep-Fatigue Code Case. Two different comparisons were made; one based on design life equal to the test duration and the other with an acceptable design life determined from the EPP Code Case procedure. The latter approach permits the determination of...« less

Mechanical and time-dependent behavior of wood-plastic composites subjected to tension and compression

Treesearch

Scott E. Hamel; John C. Hermanson; Steven M. Cramer

2012-01-01

The thermoplastics within wood—plastic composites (WPCs) are known to experience significant time-dependent deformation or creep. In some formulations, creep deformation can be twice as much as the initial quasi-static strain in as little as 4 days. While extensive work has been done on the creep behavior of pure polymers, little information is available on the...

Creep Deformation of Allvac 718Plus

DOE PAGES

Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam

2014-11-11

The creep deformation behavior of Allvac 718Plus was studied over the temperature range 650° to 732°C at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature stress regime this alloy exhibits Class M type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys this gamma prime strengthened superalloy does not exhibit steady state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics aremore » common amongst the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non Nb bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.« less

The Application of Strain Range Partitioning Method to Torsional Creep-Fatigue Interaction

NASA Technical Reports Server (NTRS)

Zamrik, S. Y.

1975-01-01

The method of strain range partitioning was applied to a series of torsional fatigue tests conducted on tubular 304 stainless steel specimens at 1200 F. Creep strain was superimposed on cycling strain, and the resulting strain range was partitioned into four components; completely reversed plastic shear strain, plastic shear strain followed by creep strain, creep strain followed by plastic strain and completely reversed creep strain. Each strain component was related to the cyclic life of the material. The damaging effects of the individual strain components were expressed by a linear life fraction rule. The plastic shear strain component showed the least detrimental factor when compared to creep strain reversed by plastic strain. In the latter case, a reduction of torsional fatigue life in the order of magnitude of 1.5 was observed.

The influence of temperature on brittle creep in sandstones

NASA Astrophysics Data System (ADS)

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.

2009-04-01

The characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of the Earth's upper crust. The presence of water promotes time-dependent deformation through environment-dependent stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure stress. Here we report results from an experimental study of the influence of an elevated temperature on time-dependent brittle creep in water-saturated samples of Darley Dale (initial porosity of 13%), Bentheim (23%) and Crab Orchard (4%) sandstones. We present results from both conventional creep experiments (or ‘static fatigue' tests) and stress-stepping creep experiments performed under 20°C and 75°C and an effective confining pressure of 30 MPa (50 MPa confining pressure and a 20 MPa pore fluid pressure). The evolution of crack damage was monitored throughout each experiment by measuring the three proxies for damage (1) axial strain (2) pore volume change and (3) the output of AE energy. Conventional creep experiments have demonstrated that, for any given applied differential stress, the time-to-failure is dramatically reduced and the creep strain rate is significantly increased by application of an elevated temperature. Stress-stepping creep experiments have allowed us to investigate the influence of temperature in detail. Results from these experiments show that the creep strain rate for Darley Dale and Bentheim sandstones increases by approximately 3 orders of magnitude, and for Crab Orchard sandstone increases by approximately 2 orders of magnitude, as temperature is increased from 20°C to 75°C at a fixed effective differential stress. We discuss these results in the context of the different mineralogical and microstructural properties of the three rock types and the micro-mechanical and chemical processes operating on them.

Effect of Steam Environment on Creep Behavior of Nextel720/Alumina-Mullite Ceramic Matrix Composite at Elevated Temperature

DTIC Science & Technology

2009-03-01

specimens achieving creep run-out of 100 h. Presence of v steam caused larger creep strains and the higher stress levels decreased the creep life ...tested at the same stress levels in other environments. He reported that environment did not appear to have a significant influence on the creep life of...MPa) Elastic Modulus (GPa) Creep Strain (%) Creep Life (h) 6* Air 1100 65.2 109 0.2 >100 7* Air 1100 64.7 131 0.23 >100 8 Steam 1100 62.9

Synergistic Effects of Physical Aging and Damage on Long-Term Behavior of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Brinson, L. Cate

1999-01-01

The research consisted of two major parts, first modeling and simulation of the combined effects of aging and damage on polymer composites and secondly an experimental phase examining composite response at elevated temperatures, again activating both aging and damage. For the simulation, a damage model for polymeric composite laminates operating at elevated temperatures was developed. Viscoelastic behavior of the material is accounted for via the correspondence principle and a variational approach is adopted to compute the temporal stresses within the laminate. Also, the effect of physical aging on ply level stress and on overall laminate behavior is included. An important feature of the model is that damage evolution predictions for viscoelastic laminates can be made. This allows us to track the mechanical response of the laminate up to large load levels though within the confines of linear viscoelastic constitutive behavior. An experimental investigation of microcracking and physical aging effects in polymer matrix composites was also pursued. The goal of the study was to assess the impact of aging on damage accumulation, in ten-ns of microcracking, and the impact of damage on aging and viscoelastic behavior. The testing was performed both at room and elevated temperatures on [+/- 45/903](sub s) and [02/903](sub s) laminates, both containing a set of 90 deg plies centrally located to facilitate investigation of microcracking. Edge replication and X-ray-radiography were utilized to quantify damage. Sequenced creep tests were performed to characterize viscoelastic and aging parameters. Results indicate that while the aging times studied have limited ]Influence on damage evolution, elevated temperature and viscoelastic effects have a profound effect on the damage mode seen. Some results are counterintuitive, including the lower strain to failure for elevated temperature tests and the catastrophic failure mode observed for the [+/- 45/9O3](sub s), specimens. The fracture toughness for transverse cracks increases with increasing temperature for both systems: transverse cracking was completely absent prior to failure in [+/- 45/903](sub s), and was suppressed for [02/903](sub s). No significant effect of damage on aging or viscoelastic parameters was observed.

Thermal and Irradiation Creep Behavior of a Titanium Aluminide in Advanced Nuclear Plant Environments

NASA Astrophysics Data System (ADS)

Magnusson, Per; Chen, Jiachao; Hoffelner, Wolfgang

2009-12-01

Titanium aluminides are well-accepted elevated temperature materials. In conventional applications, their poor oxidation resistance limits the maximum operating temperature. Advanced reactors operate in nonoxidizing environments. This could enlarge the applicability of these materials to higher temperatures. The behavior of a cast gamma-alpha-2 TiAl was investigated under thermal and irradiation conditions. Irradiation creep was studied in beam using helium implantation. Dog-bone samples of dimensions 10 × 2 × 0.2 mm3 were investigated in a temperature range of 300 °C to 500 °C under irradiation, and significant creep strains were detected. At temperatures above 500 °C, thermal creep becomes the predominant mechanism. Thermal creep was investigated at temperatures up to 900 °C without irradiation with samples of the same geometry. The results are compared with other materials considered for advanced fission applications. These are a ferritic oxide-dispersion-strengthened material (PM2000) and the nickel-base superalloy IN617. A better thermal creep behavior than IN617 was found in the entire temperature range. Up to 900 °C, the expected 104 hour stress rupture properties exceeded even those of the ODS alloy. The irradiation creep performance of the titanium aluminide was comparable with the ODS steels. For IN617, no irradiation creep experiments were performed due to the expected low irradiation resistance (swelling, helium embrittlement) of nickel-base alloys.

Nanoindentation creep behavior of human enamel.

PubMed

He, Li-Hong; Swain, Michael V

2009-11-01

In this study, the indentation creep behavior of human enamel was investigated with a nanoindentation system and a Berkovich indenter at a force of 250 mN with one-step loading and unloading method. A constant hold period of 900 s was incorporated into each test at the maximum load as well at 5 mN minimum load during unloading. The indentation creep at the maximum load and creep recovery at the minimum load was described with a double exponential function and compared with other classic viscoelastic models (Debye/Maxwell and Kohlrausch-Williams-Watts). Indentation creep rate sensitivity, m, of human enamel was measured for the first time with a value of approximately 0.012. Enamel displayed both viscoelastic and viscoplastic behavior similar to that of bone. These results indicate that, associated with entrapment of particulates between teeth under functional loading and sliding wear conditions, the enamel may inelastically deform but recover upon its release. This behavior may be important in explaining the excellent wear resistance, antifatigue, and crack resistant abilities of natural tooth structure. (c) 2008 Wiley Periodicals, Inc.

Cyclic Creep and Recovery Behavior of Nextel(Trademark) 720/Alumina Ceramic Matrix Composite at 1200deg C in Air and in Steam Environments

DTIC Science & Technology

2007-09-01

steam. The creep and recovery periods ranged from 3 min to 30 h. The laboratory air tests significantly exceeded the life of the monotonic creep ...orders of magnitude improvement in the creep life and rate. The presence of steam greatly reduced the performance of the material. The results in...steam. Mehrman also reported that prior fatigue subsequently improved in air but creep performance but in steam creep performance remained poor

Effect of Environment on Creep Behavior of an Oxide/Oxide CFCC with 45 deg. Fiber Orientation

DTIC Science & Technology

2006-06-01

MPa, the elastic modulus (E) was 45 GPa, and failure strain was 0.265%. The creep -rupture results showed a decrease in creep life with increasing...failure and increased creep life . A qualitative spectral analysis provided evidence of silicon species migration from the mullite phase of the...N720/AS in 0/90˚ and ±45˚ orientation at 1100°C. Shows that high creep rates generally correspond to a short creep life .................... 17

The role of cobalt on the creep of Waspaloy

NASA Technical Reports Server (NTRS)

Jarrett, R. N.; Chin, L.; Tien, J. K.

1984-01-01

Cobalt was systematically replaced with nickel in Waspaloy (which normally contains 13% Co) to determine the effects of cobalt on the creep behavior of this alloy. Effects of cobalt were found to be minimal on tensile strengths and microstructure. The creep resistance and the stress rupture resistance determined in the range from 704 to 760 C (1300 to 1400 C) were found to decrease as cobalt was removed from the standard alloy at all stresses and temperatures. Roughly a ten-fold drop in rupture life and a corresponding increase in minimum creep rate were found under all test conditions. Both the apparent creep activation energy and the matrix contribution to creep resistance were found to increase with cobalt. These creep effects are attributed to cobalt lowering the stacking fault energy of the alloy matrix. The creep resistance loss due to the removal of cobalt is shown to be restored by slightly increasing the gamma' volume fraction. Results are compared to a previous study on Udimet 700, a higher strength, higher gamma' volume fraction alloy with similar phase chemistry, in which cobalt did not affect creep resistance. An explanation for this difference in behavior based on interparticle spacing and cross-slip is presented.

Creep and precipitation behaviors of AL6XN austenitic steel at elevated temperatures

NASA Astrophysics Data System (ADS)

Meng, L. J.; Sun, J.; Xing, H.

2012-08-01

Creep behaviors of the solution-treated AL6XN austenitic stainless steel have been investigated at 873-1023 K and 120-260 MPa. The results showed that the creep stress exponent and activation energy of the AL6XN steel are 5 and 395.4 kJ/mol, respectively in the power-law breakdown regime. TEM observations revealed that dislocations distributed homogenously in grains. The creep deformation mechanism is mainly attributed to viscous dislocation glide. Precipitates in the steel after creep deformation were additionally analyzed by TEM, and the results showed that there are four different types of precipitates, such as M23C6, M6C, σ phase and Laves phase. The M23C6 carbides were observed at grain boundaries in the steel after creep at 873 K. The M6C, σ phase and Laves phase precipitates were found when the creep temperature increases to 923-1023 K. Although the AL6XN steel exhibited low steady state creep rates, a high volume fraction of brittle precipitates of σ and Laves phases reduced the creep lifetime of the steel at elevated temperatures.

Effects of Thermal Treatment on Tensile Creep and Stress-Rupture Behavior of Hi-Nicalon SiC Fibers

NASA Technical Reports Server (NTRS)

Yun, H. M.; Goldsby, J. C.; Dicarlo, J. A.

1995-01-01

Tensile creep and stress-rupture studies were conducted on Hi-Nicalon SiC fibers at 1200 and 1400 C in argon and air. Examined were as-received fibers as well as fibers annealed from 1400 to 1800 C for 1 hour in argon before testing. The creep and rupture results for these annealed fibers were compared to those of the as-received fibers to determine the effects of annealing temperature, test temperature, and test environment. Argon anneals up to 1500 C degrade room temperature strength of Hi-Nicalon fibers, but improve fiber creep resistance in argon or air by as much as 100% with no significant degradation in rupture strength. Argon anneals above 1500 C continue to improve fiber creep resistance when tested in argon, but significantly degrade creep resistance and rupture strength when tested in air. Decrease in creep resistance in air is greater at 1200 C than at 1400 C. Mechanisms are suggested for the observed behavior.

Time-Dependent Behaviors of Granite: Loading-Rate Dependence, Creep, and Relaxation

NASA Astrophysics Data System (ADS)

Hashiba, K.; Fukui, K.

2016-07-01

To assess the long-term stability of underground structures, it is important to understand the time-dependent behaviors of rocks, such as their loading-rate dependence, creep, and relaxation. However, there have been fewer studies on crystalline rocks than on tuff, mudstone, and rock salt, because the high strength of crystalline rocks makes the detection of their time-dependent behaviors much more difficult. Moreover, studies on the relaxation, temporal change of stress and strain (TCSS) conditions, and relations between various time-dependent behaviors are scarce for not only granites, but also other rocks. In this study, previous reports on the time-dependent behaviors of granites were reviewed and various laboratory tests were conducted using Toki granite. These tests included an alternating-loading-rate test, creep test, relaxation test, and TCSS test. The results showed that the degree of time dependence of Toki granite is similar to other granites, and that the TCSS resembles the stress-relaxation curve and creep-strain curve. A viscoelastic constitutive model, proposed in a previous study, was modified to investigate the relations between the time-dependent behaviors in the pre- and post-peak regions. The modified model reproduced the stress-strain curve, creep, relaxation, and the results of the TCSS test. Based on a comparison of the results of the laboratory tests and numerical simulations, close relations between the time-dependent behaviors were revealed quantitatively.

Generation of long time creep data on refractory alloys at elevated temperatures

NASA Technical Reports Server (NTRS)

Sheffler, K. D.

1970-01-01

Creep tests were conducted on two tantalum alloys (ASTAR 811C and T-111 alloy), on a molybdenum alloy (TZM), and on CVD tungsten. The T-111 alloy 1% creep life data have been subjected to Manson's station function analysis, and the progress on this analysis is described. In another test program, the behavior of T-111 alloy with continuously varying temperatures and stresses has been studied. The results indicated that the previously described analysis predicts the observed creep behavior with reasonable accuracy. In addition to the T-111 test program, conventional 1% creep life data have been obtained for ASTAR 811C alloy. Previously observed effects of heat treatment on the creep strength of this material have been discussed and a model involving carbide strengthening primarily at the grain boundaries, rather than in a classical dispersion hardening mechanism, has been proposed to explain the observed results.

Creep and Stress-strain Behavior After Creep from Sic Fiber Reinforced, Melt-infiltrated Sic Matrix Composites

NASA Technical Reports Server (NTRS)

Morscher, Gregory N.; Pujar, Vijay

2004-01-01

Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated Si were subjected to creep at 1315 C for a number of different stress conditions, This study is aimed at understanding the time-dependent creep behavior of CMCs for desired use-conditions, and also more importantly, how the stress-strain response changes as a result of the time-temperature-stress history of the crept material. For the specimens that did not rupture, fast fracture experiments were performed at 1315 C or at room temperature immediately following tensile creep. In many cases, the stress-strain response and the resulting matrix cracking stress of the composite change due to stress-redistribution between composite constituents during tensile creep. The paper will discuss these results and its implications on applications of these materials for turbine engine components.

The effects of physical aging at elevated temperatures on the viscoelastic creep on IM7/K3B

NASA Technical Reports Server (NTRS)

Gates, Thomas S.; Feldman, Mark

1994-01-01

Physical aging at elevated temperature of the advanced composite IM7/K3B was investigated through the use of creep compliance tests. Testing consisted of short term isothermal, creep/recovery with the creep segments performed at constant load. The matrix dominated transverse tensile and in-plane shear behavior were measured at temperatures ranging from 200 to 230 C. Through the use of time based shifting procedures, the aging shift factors, shift rates and momentary master curve parameters were found at each temperature. These material parameters were used as input to a predictive methodology, which was based upon effective time theory and linear viscoelasticity combined with classical lamination theory. Long term creep compliance test data was compared to predictions to verify the method. The model was then used to predict the long term creep behavior for several general laminates.

Creep behavior of bone cement: a method for time extrapolation using time-temperature equivalence.

PubMed

Morgan, R L; Farrar, D F; Rose, J; Forster, H; Morgan, I

2003-04-01

The clinical lifetime of poly(methyl methacrylate) (PMMA) bone cement is considerably longer than the time over which it is convenient to perform creep testing. Consequently, it is desirable to be able to predict the long term creep behavior of bone cement from the results of short term testing. A simple method is described for prediction of long term creep using the principle of time-temperature equivalence in polymers. The use of the method is illustrated using a commercial acrylic bone cement. A creep strain of approximately 0.6% is predicted after 400 days under a constant flexural stress of 2 MPa. The temperature range and stress levels over which it is appropriate to perform testing are described. Finally, the effects of physical aging on the accuracy of the method are discussed and creep data from aged cement are reported.

Normalized coffin-manson plot in terms of a new life function based on stress relaxation under creep-fatigue conditions

NASA Astrophysics Data System (ADS)

Jeong, Chang Yeol; Nam, Soo Woo; Lim, Jong Dae

2003-04-01

A new life prediction function based on a model formulated in terms of stress relaxation during hold time under creep-fatigue conditions is proposed. From the idea that reduction in fatigue life with hold is due to the creep effect of stress relaxation that results in additional energy dissipation in the hysteresis loop, it is suggested that the relaxed stress range may be a creep-fatigue damage function. Creep-fatigue data from the present and other investigators are used to check the validity of the proposed life prediction equation. It is shown that the data satisfy the applicability of the life relation model. Accordingly, using this life prediction model, one may realize that all the Coffin-Manson plots at various levels of hold time in strain-controlled creep-fatigue tests can be normalized to make one straight line.

Phase Transformation and Creep Behavior in Ti50Pd30Ni20 High Temperature Shape Memory Alloy in Compression

NASA Technical Reports Server (NTRS)

Kumar, Parikshith K.; Desai, Uri; Monroe, James; Lagoudas, Dimitris C.; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glenn

2010-01-01

The creep behavior and the phase transformation of Ti50Pd30Ni20 High Temperature Shape Memory Alloy (HTSMA) is investigated by standard creep tests and thermomechanical tests. Ingots of the alloy are induction melted, extruded at high temperature, from which cylindrical specimens are cut and surface polished. A custom high temperature test setup is assembled to conduct the thermomechanical tests. Following preliminary monotonic tests, standard creep tests and thermally induced phase transformation tests are conducted on the specimen. The creep test results suggest that over the operating temperatures and stresses of this alloy, the microstructural mechanisms responsible for creep change. At lower stresses and temperatures, the primary creep mechanism is a mixture of dislocation glide and dislocation creep. As the stress and temperature increase, the mechanism shifts to predominantly dislocation creep. If the operational stress or temperature is raised even further, the mechanism shifts to diffusion creep. The thermally induced phase transformation tests show that actuator performance can be affected by rate independent irrecoverable strain (transformation induced plasticity + retained martensite) as well as creep. The rate of heating and cooling can adversely impact the actuators performance. While the rate independent irrecoverable strain is readily apparent early in the actuators life, viscoplastic strain continues to accumulate over the lifespan of the HTSMA. Thus, in order to get full actuation out of the HTSMA, the heating and cooling rates must be sufficiently high enough to avoid creep.

Creep fatigue life prediction for engine hot section materials (isotropic)

NASA Technical Reports Server (NTRS)

Moreno, Vito; Nissley, David; Lin, Li-Sen Jim

1985-01-01

The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.

The development of methods for the prediction of primary creep behavior in metals

NASA Technical Reports Server (NTRS)

Zerwekh, R. P.

1978-01-01

The applicability of a thermodynamic constitutive theory of deformation to the prediction of primary creep and creep strain relaxation behavior in metals is examined. Constitutive equations derived from the theory are subjected to a parametric analysis in order to determine the influence of several parameters on the curve forms generated by the equations. A computer program is developed which enables the solution of a generalized constitutive equation using experimental data as input. Several metals were tested to form a data base of primary creep and relaxation behavior. The extent to which these materials conformed to the constitutive equation showed wide variability, with the alloy Ti-6Al-4V exhibiting the most consistent results. Accordingly, most of the analysis is concentrated upon data from that alloy, although creep and relaxation data from all the materials tested are presented. Experimental methods are outlined as well as some variations in methods of analysis. Various theoretical and practical implications of the work are discussed.

Physical aging effects on the compressive linear viscoelastic creep of IM7/K3B composite

NASA Technical Reports Server (NTRS)

Veazie, David R.; Gates, Thomas S.

1995-01-01

An experimental study was undertaken to establish the viscoelastic behavior of 1M7/K3B composite in compression at elevated temperature. Creep compliance, strain recovery and the effects of physical aging on the time dependent response was measured for uniaxial loading at several isothermal conditions below the glass transition temperature (T(g)). The IM7/K3B composite is a graphite reinforced thermoplastic polyimide with a T(g) of approximately 240 C. In a composite, the two matrix dominated compliance terms associated with time dependent behavior occur in the transverse and shear directions. Linear viscoelasticity was used to characterize the creep/recovery behavior and superposition techniques were used to establish the physical aging related material constants. Creep strain was converted to compliance and measured as a function of test time and aging time. Results included creep compliance master curves, physical aging shift factors and shift rates. The description of the unique experimental techniques required for compressive testing is also given.

Simulated acid rain alters litter decomposition and enhances the allelopathic potential of the invasive plant Wedelia trilobata (Creeping Daisy)

USDA-ARS?s Scientific Manuscript database

Invasive species and acid rain cause global environmental problems. Limited information exists, however, concerning the effects of acid rain on the invasiveness of these plants. For example, creeping daisy, an invasive exotic allelopathic weed, has caused great damage in southern China where acid ra...

Irradiation creep of candidate materials for advanced nuclear plants

NASA Astrophysics Data System (ADS)

Chen, J.; Jung, P.; Hoffelner, W.

2013-10-01

In the present paper, irradiation creep results of an intermetallic TiAl alloy and two ferritic oxide dispersion strengthened (ODS) steels are summarized. In situ irradiation creep measurements were performed using homogeneous implantation with α- and p-particles to maximum doses of 0.8 dpa at displacement damage rates of 2-8 × 10-6 dpa/s. The strains of miniaturized flat dog-bone specimens were monitored under uniaxial tensile stresses ranging from 20 to 400 MPa at temperatures of 573, 673 and 773 K, respectively. The effects of material composition, ODS particle size, and bombarding particle on the irradiation creep compliance was studied and results are compared to literature data. Evolution of microstructure during helium implantation was investigated in detail by TEM and is discussed with respect to irradiation creep models.

Microstructural effects on constitutive and fatigue fracture behavior of TinSilverCopper solder

NASA Astrophysics Data System (ADS)

Tucker, Jonathon P.

As microelectronic package construction becomes more diverse and complex, the need for accurate, geometry-independent material constitutive and failure models increases. Evaluations of packages based on accelerated environmental tests (such as accelerated thermal cycling or power cycling) only provide package-dependent reliability information. In addition, extrapolations of such test data to life predictions under field conditions are often empirical. Besides geometry, accelerated environmental test data must account for microstructural factors such as alloy composition or isothermal aging condition, resulting in expensive experimental variation. In this work, displacement-controlled, creep, and fatigue lap shear tests are conducted on specially designed SnAgCu test specimens with microstructures representative to those found in commercial microelectronic packages. The data are used to develop constitutive and fatigue fracture material models capable of describing deformation and fracture behavior for the relevant temperature and strain rate ranges. Furthermore, insight is provided into the microstructural variation of solder joints and the subsequent effect on material behavior. These models are appropriate for application to packages of any geometrical construction. The first focus of the thesis is on Pb-mixed SnAgCu solder alloys. During the transition from Pb-containing solders to Pb-free solders, joints composed of a mixture of SnPb and SnAgCu often result from either mixed assemblies or rework. Three alloys of 1, 5 and 20 weight percent Pb were selected so as to represent reasonable ranges of Pb contamination expected from different 63Sn37Pb components mixed with Sn3.0Ag0.5Cu. Displacement-controlled (constant strain rate) and creep tests were performed at temperatures of 25°C, 75°C, and 125°C using a double lap shear test setup that ensures a nearly homogeneous state of plastic strain at the joint interface. Rate-dependent constitutive models for Pb-contaminated SnAgCu solder alloys ranging from the traditional time-hardening creep model to the viscoplastic Anand model are described. The second focus of the thesis is on fatigue damage accumulation in SnAgCu solder alloys. While, typical fatigue fracture models are empirical, recently a non-empirical model termed Maximum Entropy Fracture Model (MEFM) was proposed. MEFM is a thermodynamically consistent and information theory inspired damage accumulation theory for ductile solids. This model has been validated recently for Sn3.8Ag0.7Cu solder alloy, and uses a single damage accumulation parameter to relate the probability of fracture to accumulated entropic dissipation. Isothermal cycling fatigue tests on Sn3.0Ag0.5Cu and mixed SnPb/Sn3.0Ag0.5Cu solder alloys at varying strain rates and temperatures are conducted using a custom-built microscale mechanical tester capable of submicron displacement resolution. MEFM is applied here in conjunction with the Anand viscoplasticity model to predict the softening occurring over successive cycles as a result of damage accumulation. The damage accumulation parameters for Sn3.0Ag0.5Cu in different aged states are related to a microstructural parameter which quantitatively describes the state of coarsening. In addition, damage accumulation parameters for the three mixed solder alloys are reported. This approach allows for a non-empirical prediction of both constitutive and fracture behavior of packages of different geometries and different microstructural states under thermo-mechanical fatigue. Approaches to solder joint reliability predictions from materials science and mechanics perspectives differ dramatically. Materials science methods identify key failure mechanisms, but most models cannot predict failure. In contrast, mechanics approaches often provide estimates of joint lifetime, but fail to provide insight into microstructural influences. This work attempts to connect the two fields by relating constitutive behavior and fatigue fracture models for different alloys and aging conditions to one or more microstructural parameters.

Creep deformation and rupture behavior of CLAM steel at 823 K and 873 K

NASA Astrophysics Data System (ADS)

Zhong, Boyu; Huang, Bo; Li, Chunjing; Liu, Shaojun; Xu, Gang; Zhao, Yanyun; Huang, Qunying

2014-12-01

China Low Activation Martensitic (CLAM) steel is selected as the candidate structural material in Fusion Design Study (FDS) series fusion reactor conceptual designs. The creep property of CLAM steel has been studied in this paper. Creep tests have been carried out at 823 K and 873 K over a stress range of 150-230 MPa. The creep curves showed three creep regimes, primary creep, steady-state creep and tertiary creep. The relationship between minimum creep rate (ε˙min) and the applied stress (σ) could be described by Norton power law, and the stress exponent n was decreased with the increase of the creep temperature. The creep mechanism was analyzed with the fractographes of the rupture specimens which were examined by scanning electron microscopy (SEM). The coarsening of precipitates observed with transmission electron microscope (TEM) indicated the microstructural degradation after creep test.

Finite Element Analysis of Plastic Deformation During Impression Creep

NASA Astrophysics Data System (ADS)

Naveena; Ganesh Kumar, J.; Mathew, M. D.

2015-04-01

Finite element (FE) analysis of plastic deformation associated with impression creep deformation of 316LN stainless steel was carried out. An axisymmetric FE model of 10 × 10 × 10 mm specimen with 1-mm-diameter rigid cylindrical flat punch was developed. FE simulation of impression creep deformation was performed by assuming elastic-plastic-power-law creep deformation behavior. Evolution of the stress with time under the punch during elastic, plastic, and creep processes was analyzed. The onset of plastic deformation was found to occur at a nominal stress about 1.12 times the yield stress of the material. The size of the developed plastic zone was predicted to be about three times the radius of the punch. The material flow behavior and the pile-up on specimen surface have been modeled.

Creep of Posidonia Shale at Elevated Pressure and Temperature

NASA Astrophysics Data System (ADS)

Rybacki, E.; Herrmann, J.; Wirth, R.; Dresen, G.

2017-12-01

The economic production of gas and oil from shales requires repeated hydraulic fracturing operations to stimulate these tight reservoir rocks. Besides simple depletion, the often observed decay of production rate with time may arise from creep-induced fracture closure. We examined experimentally the creep behavior of an immature carbonate-rich Posidonia shale, subjected to constant stress conditions at temperatures between 50 and 200 °C and confining pressures of 50-200 MPa, simulating elevated in situ depth conditions. Samples showed transient creep in the semibrittle regime with high deformation rates at high differential stress, high temperature and low confinement. Strain was mainly accommodated by deformation of the weak organic matter and phyllosilicates and by pore space reduction. The primary decelerating creep phase observed at relatively low stress can be described by an empirical power law relation between strain and time, where the fitted parameters vary with temperature, pressure and stress. Our results suggest that healing of hydraulic fractures at low stresses by creep-induced proppant embedment is unlikely within a creep period of several years. At higher differential stress, as may be expected in situ at contact areas due to stress concentrations, the shale showed secondary creep, followed by tertiary creep until failure. In this regime, microcrack propagation and coalescence may be assisted by stress corrosion. Secondary creep rates were also described by a power law, predicting faster fracture closure rates than for primary creep, likely contributing to production rate decline. Comparison of our data with published primary creep data on other shales suggests that the long-term creep behavior of shales can be correlated with their brittleness estimated from composition. Low creep strain is supported by a high fraction of strong minerals that can build up a load-bearing framework.

An Abnormal Increase of Fatigue Life with Dwell Time during Creep-Fatigue Deformation for Directionally Solidified Ni-Based Superalloy DZ445

NASA Astrophysics Data System (ADS)

Ding, Biao; Ren, Weili; Deng, Kang; Li, Haitao; Liang, Yongchun

2018-03-01

The paper investigated the creep-fatigue behavior for directionally solidified nickel-based superalloy DZ445 at 900 °C. It is found that the fatigue life shows an abnormal increase when the dwell time exceeds a critical value during creep-fatigue deformation. The area of hysteresis loop and fractograph explain the phenomenon quite well. The shortest life corresponds to the maximal area of hysteresis loop, i. e. the maximum energy to be consumed during the creep-fatigue cycle. The fractographic observation of failed samples further supports the abnormal behavior of fatigue life.

Mechanism-Based Modeling for Low Cycle Fatigue of Cast Austenitic Steel

NASA Astrophysics Data System (ADS)

Wu, Xijia; Quan, Guangchun; Sloss, Clayton

2017-09-01

A mechanism-based approach—the integrated creep-fatigue theory (ICFT)—is used to model low cycle fatigue behavior of 1.4848 cast austenitic steel over the temperature range from room temperature (RT) to 1173 K (900 °C) and the strain rate range from of 2 × 10-4 to 2 × 10-2 s-1. The ICFT formulates the material's constitutive equation based on the physical strain decomposition into mechanism strains, and the associated damage accumulation consisting of crack nucleation and propagation in coalescence with internally distributed damage. At room temperature, the material behavior is controlled by plasticity, resulting in a rate-independent and cyclically stable behavior. The material exhibits significant cyclic hardening at intermediate temperatures, 673 K to 873 K (400 °C to 600 °C), with negative strain rate sensitivity, due to dynamic strain aging. At high temperatures >1073 K (800 °C), time-dependent deformation is manifested with positive rate sensitivity as commonly seen in metallic materials at high temperature. The ICFT quantitatively delineates the contribution of each mechanism in damage accumulation, and predicts the fatigue life as a result of synergistic interaction of the above identified mechanisms. The model descriptions agree well with the experimental and fractographic observations.

Creep to inertia dominated stick-slip behavior in sliding friction modulated by tilted non-uniform loading

NASA Astrophysics Data System (ADS)

Tian, Pengyi; Tao, Dashuai; Yin, Wei; Zhang, Xiangjun; Meng, Yonggang; Tian, Yu

2016-09-01

Comprehension of stick-slip motion is very important for understanding tribological principles. The transition from creep-dominated to inertia-dominated stick-slip as the increase of sliding velocity has been described by researchers. However, the associated micro-contact behavior during this transition has not been fully disclosed yet. In this study, we investigated the stick-slip behaviors of two polymethyl methacrylate blocks actively modulated from the creep-dominated to inertia-dominated dynamics through a non-uniform loading along the interface by slightly tilting the angle of the two blocks. Increasing the tilt angle increases the critical transition velocity from creep-dominated to inertia-dominated stick-slip behaviors. Results from finite element simulation disclosed that a positive tilt angle led to a higher normal stress and a higher temperature on blocks at the opposite side of the crack initiating edge, which enhanced the creep of asperities during sliding friction. Acoustic emission (AE) during the stick-slip has also been measured, which is closely related to the different rupture modes regulated by the distribution of the ratio of shear to normal stress along the sliding interface. This study provided a more comprehensive understanding of the effect of tilted non-uniform loading on the local stress ratio, the local temperature, and the stick-slip behaviors.

Creep to inertia dominated stick-slip behavior in sliding friction modulated by tilted non-uniform loading.

PubMed

Tian, Pengyi; Tao, Dashuai; Yin, Wei; Zhang, Xiangjun; Meng, Yonggang; Tian, Yu

2016-09-19

Comprehension of stick-slip motion is very important for understanding tribological principles. The transition from creep-dominated to inertia-dominated stick-slip as the increase of sliding velocity has been described by researchers. However, the associated micro-contact behavior during this transition has not been fully disclosed yet. In this study, we investigated the stick-slip behaviors of two polymethyl methacrylate blocks actively modulated from the creep-dominated to inertia-dominated dynamics through a non-uniform loading along the interface by slightly tilting the angle of the two blocks. Increasing the tilt angle increases the critical transition velocity from creep-dominated to inertia-dominated stick-slip behaviors. Results from finite element simulation disclosed that a positive tilt angle led to a higher normal stress and a higher temperature on blocks at the opposite side of the crack initiating edge, which enhanced the creep of asperities during sliding friction. Acoustic emission (AE) during the stick-slip has also been measured, which is closely related to the different rupture modes regulated by the distribution of the ratio of shear to normal stress along the sliding interface. This study provided a more comprehensive understanding of the effect of tilted non-uniform loading on the local stress ratio, the local temperature, and the stick-slip behaviors.

Creep to inertia dominated stick-slip behavior in sliding friction modulated by tilted non-uniform loading

PubMed Central

Tian, Pengyi; Tao, Dashuai; Yin, Wei; Zhang, Xiangjun; Meng, Yonggang; Tian, Yu

2016-01-01

Comprehension of stick-slip motion is very important for understanding tribological principles. The transition from creep-dominated to inertia-dominated stick-slip as the increase of sliding velocity has been described by researchers. However, the associated micro-contact behavior during this transition has not been fully disclosed yet. In this study, we investigated the stick-slip behaviors of two polymethyl methacrylate blocks actively modulated from the creep-dominated to inertia-dominated dynamics through a non-uniform loading along the interface by slightly tilting the angle of the two blocks. Increasing the tilt angle increases the critical transition velocity from creep-dominated to inertia-dominated stick-slip behaviors. Results from finite element simulation disclosed that a positive tilt angle led to a higher normal stress and a higher temperature on blocks at the opposite side of the crack initiating edge, which enhanced the creep of asperities during sliding friction. Acoustic emission (AE) during the stick-slip has also been measured, which is closely related to the different rupture modes regulated by the distribution of the ratio of shear to normal stress along the sliding interface. This study provided a more comprehensive understanding of the effect of tilted non-uniform loading on the local stress ratio, the local temperature, and the stick-slip behaviors. PMID:27641908

Further Developments in Modeling Creep Effects Within Structural SiC/SiC Components

NASA Technical Reports Server (NTRS)

Lang, Jerry; DiCarlo, James A.

2008-01-01

Anticipating the implementation of advanced SiC/SiC composites into turbine section components of future aero-propulsion engines, the primary objective of this on-going study is to develop physics-based analytical and finite-element modeling tools to predict the effects of constituent creep on SiC/SiC component service life. A second objective is to understand how to possibly manipulate constituent materials and processes in order to minimize these effects. Focusing on SiC/SiC components experiencing through-thickness stress gradients (e.g., airfoil leading edge), prior NASA creep modeling studies showed that detrimental residual stress effects can develop globally within the component walls which can increase the risk of matrix cracking. These studies assumed that the SiC/SiC composites behaved as isotropic viscoelastic continuum materials with creep behavior that was linear and symmetric with stress and that the creep parameters could be obtained from creep data as experimentally measured in-plane in the fiber direction of advanced thin-walled 2D SiC/SiC panels. The present study expands on those prior efforts by including constituent behavior with non-linear stress dependencies in order to predict such key creep-related SiC/SiC properties as time-dependent matrix stress, constituent creep and content effects on composite creep rates and rupture times, and stresses on fiber and matrix during and after creep.

Flexural creep behaviour of jute polypropylene composites

NASA Astrophysics Data System (ADS)

Chandekar, Harichandra; Chaudhari, Vikas

2016-09-01

Present study is about the flexural creep behaviour of jute fabric reinforced polypropylene (Jute-PP) composites. The PP sheet and alkali treated jute fabric is stacked alternately and hot pressed in compression molding machine to get Jute-PP composite laminate. The flexural creep study is carried out on dynamic mechanical analyzer. The creep behaviour of the composite is modeled using four-parameter Burgers model. Short-term accelerated creep testing is conducted which is later used to predict long term creep behaviour. The feasibility of the construction of a master curve using the time-temperature superposition (TTS) principle to predict long term creep behavior of unreinforced PP and Jute-PP composite is investigated.

Creep and fracture of a model yoghurt

NASA Astrophysics Data System (ADS)

Manneville, Sebastien; Leocmach, Mathieu; Perge, Christophe; Divoux, Thibaut

2014-11-01

Biomaterials such as protein or polysaccharide gels are known to behave qualitatively as soft solids and to rupture under an external load. Combining optical and ultrasonic imaging to shear rheology we show that the failure scenario of a model yoghurt, namely a casein gel, is reminiscent of brittle solids: after a primary creep regime characterized by a macroscopically homogeneous deformation and a power-law behavior which exponent is fully accounted for by linear viscoelasticity, fractures nucleate and grow logarithmically perpendicularly to shear, up to the sudden rupture of the gel. A single equation accounting for those two successive processes nicely captures the full rheological response. The failure time follows a decreasing power-law with the applied shear stress, similar to the Basquin law of fatigue for solids. These results are in excellent agreement with recent fiber-bundle models that include damage accumulation on elastic fibers and exemplify protein gels as model, brittle-like soft solids. Work funded by the European Research Council under Grant Agreement No. 258803.

Transient creep and semibrittle behavior of crystalline rocks

USGS Publications Warehouse

Carter, N.L.; Kirby, S.H.

1978-01-01

We review transient creep and semibrittle behavior of crystalline solids. The results are expected to be pertinent to crystalline rocks undergoing deformation in the depth range 5 to 20 km, corresponding to depths of focus of many major earthquakes. Transient creep data for crystalline rocks at elevated temperatures are analyzed but are poorly understood because of lack of information on the deformation processes which, at low to moderate pressure, are likely to be semibrittle in nature. Activation energies for transient creep at high effective confining pressure are much higher than those found for atmospheric pressure tests in which thermally-activated microfracturing probably dominates the creep rate. Empirical transient creep equations are extrapolated at 200?? to 600??C, stresses from 0.1 to 1.0 kbar, to times ranging from 3.17??102 to 3.17??108 years. At the higher temperatures, appreciable transient creep strains may take place but the physical significance of the results is in question because the flow mechanisms have not been determined. The purpose of this paper is to stimulate careful research on this important topic. ?? 1978 Birkha??user Verlag.

Interrelation of creep and relaxation: a modeling approach for ligaments.

PubMed

Lakes, R S; Vanderby, R

1999-12-01

Experimental data (Thornton et al., 1997) show that relaxation proceeds more rapidly (a greater slope on a log-log scale) than creep in ligament, a fact not explained by linear viscoelasticity. An interrelation between creep and relaxation is therefore developed for ligaments based on a single-integral nonlinear superposition model. This interrelation differs from the convolution relation obtained by Laplace transforms for linear materials. We demonstrate via continuum concepts of nonlinear viscoelasticity that such a difference in rate between creep and relaxation phenomenologically occurs when the nonlinearity is of a strain-stiffening type, i.e., the stress-strain curve is concave up as observed in ligament. We also show that it is inconsistent to assume a Fung-type constitutive law (Fung, 1972) for both creep and relaxation. Using the published data of Thornton et al. (1997), the nonlinear interrelation developed herein predicts creep behavior from relaxation data well (R > or = 0.998). Although data are limited and the causal mechanisms associated with viscoelastic tissue behavior are complex, continuum concepts demonstrated here appear capable of interrelating creep and relaxation with fidelity.

Creep properties of Pb-free solder joints

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

Song, H.G.; Morris Jr., J.W.; Hua, F.

2002-04-01

Describes the creep behavior of three Sn-rich solders that have become candidates for use in Pb-free solder joints: Sn-3.5Ag, Sn-3Ag-0.5Cu and Sn-0.7Cu. The three solders show the same general behavior when tested in thin joints between Cu and Ni/Au metallized pads at temperatures between 60 and 130 C. Their steady-state creep rates are separated into two regimes with different stress exponents(n). The low-stress exponents range from {approx}3-6, while the high-stress exponents are anomalously high (7-12). Strikingly, the high-stress exponent has a strong temperature dependence near room temperature, increasing significantly as the temperature drops from 95 to 60 C. The anomalousmore » creep behavior of the solders appears to be due to the dominant Sn constituent. Joints of pure Sn have stress exponents, n, that change with stress and temperature almost exactly like those of the Sn-rich solder joints. Research on creep in bulk samples of pure Sn suggests that the anomalous temperature dependence of the stress exponent may show a change in the dominant mechanism of creep. Whatever its source, it has the consequence that conventional constitutive relations for steady-state creep must be used with caution in treating Sn-rich solder joints, and qualification tests that are intended to verify performance should be carefully designed.« less

Viscous Creep in Dry Unconsolidated Gulf of Mexico Shale

NASA Astrophysics Data System (ADS)

Chang, C.; Zoback, M. D.

2002-12-01

We conducted laboratory experiments to investigate creep characteristics of dry unconsolidated shale recovered from the pathfinder well, Gulf of Mexico (GOM). We subjected jacketed cylindrical specimens (25.4 mm diameter) to hydrostatic pressure that increased from 10 to 50 MPa in steps of 5 MPa. We kept the pressure constant in each step for at least 6 hours and measured axial and lateral strains (provided by LVDTs) and ultrasonic velocities (provided by seismic-wave transducers). The dry shale exhibited pronounced creep strain at all pressure levels, indicating that the dry frame of the shale possesses an intrinsic viscous property. Interestingly, the creep behavior of the shale is different above and below 30 MPa confining pressure. Above 30 MPa, the amount of creep strain in 6 hours is nearly constant with equal pressurization steps, indicating a linear viscous rheology. Below 30 MPa, the amount of creep increases linearly as pressure is raised in constant incremental steps, suggesting that the creep deformation accelerates as pressure increases within this pressure range. Thus, the general creep behavior of the GOM shale is characterized by a bilinear dependence on pressure magnitude. This creep characteristic is quite different from that observed in unconsolidated reservoir sands (Hagin and Zoback, 2002), which exhibited nearly constant amount of creep regardless of the pressure magnitude for equal increasing steps of pressure. The shale exhibits a lack of creep (and nearly negligible strain recovery) when unloaded, suggesting that the creep strain is irrecoverable and can be considered viscoplastic deformation. SEM observations show that the major mechanism of compaction of the dry shale appears to be packing of clay and a progressive collapse of pore (void) spaces. Creep compaction is considerably more significant than compaction that occurs instantaneously, indicating that the process of shale compaction is largely time-dependent.

Observations on the relationship of structure to the mechanical properties of thin TD-NiCr sheet

NASA Technical Reports Server (NTRS)

Whittenberger, J. D.

1976-01-01

A study of the relationship between structure and mechanical properties of thin TD-NiCr sheet indicated that the elevated temperature tensile, stress-rupture, and creep strength properties are dependent on grain aspect ratio and sheet thickness. In general, the strength properties increase with increasing grain aspect ratio and sheet thickness. Tensile testing revealed an absence of ductility at elevated temperatures (not less than 1144 K). Significant creep damage as determined by subsequent tensile testing at room temperature occurs after very small amounts (less than 0.1%) of prior creep deformation over the temperature range 1144-1477 K. A threshold stress for creep appears to exist. Creep exposure below the threshold stress at T not less than 1366 K results in almost full retention of room temperature tensile properties.

Dynamic responses of concrete-filled steel tubular member under axial compression considering creep effect

NASA Astrophysics Data System (ADS)

Jiang, X. T.; Wang, Y. D.; Dai, C. H.; Ding, M.

2017-08-01

The finite element model of concrete-filled steel tubular member was established by the numerical analysis software considering material nonlinearity to analyze concrete creep effect on the dynamic responses of the member under axial compression and lateral impact. In the model, the constitutive model of core concrete is the plastic damage model, that of steel is the Von Mises yield criterion and kinematic hardening model, and the creep effect at different ages is equivalent to the change of concrete elastic modulus. Then the dynamic responses of concrete-filled steel tubular member considering creep effects was simulated, and the effects of creep on contact time, impact load, deflection, stress and strain were discussed. The fruits provide a scientific basis for the design of the impact resistance of concrete filled steel tubular members.

Modeling of Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Ferguson, B. L.; Petrus, G. J.; Krauss, T. M.

1992-01-01

The project examined the effectiveness of studying the creep behavior of thermal barrier coating system through the use of a general purpose, large strain finite element program, NIKE2D. Constitutive models implemented in this code were applied to simulate thermal-elastic and creep behavior. Four separate ceramic-bond coat interface geometries were examined in combination with a variety of constitutive models and material properties. The reason for focusing attention on the ceramic-bond coat interface is that prior studies have shown that cracking occurs in the ceramic near interface features which act as stress concentration points. The model conditions examined include: (1) two bond coat coefficient of thermal expansion curves; (2) the creep coefficient and creep exponent of the bond coat for steady state creep; (3) the interface geometry; and (4) the material model employed to represent the bond coat, ceramic, and superalloy base.

Creep and fatigue behavior of a novel 2-component paste-like formulation of acrylic bone cements.

PubMed

Köster, Ulrike; Jaeger, Raimund; Bardts, Mareike; Wahnes, Christian; Büchner, Hubert; Kühn, Klaus-Dieter; Vogt, Sebastian

2013-06-01

The fatigue and creep performance of two novel acrylic bone cement formulations (one bone cement without antibiotics, one with antibiotics) was compared to the performance of clinically used bone cements (Osteopal V, Palacos R, Simplex P, SmartSet GHV, Palacos R+G and CMW1 with Gentamicin). The preparation of the novel bone cement formulations involves the mixing of two paste-like substances in a static mixer integrated into the cartridge which is used to apply the bone cement. The fatigue performance of the two novel bone cement formulations is comparable to the performance of the reference bone cements. The creep compliance of the bone cements is significantly influenced by the effects of physical ageing. The model parameters of Struik's creep law are used to compare the creep behavior of different bone cements. The novel 2-component paste-like bone cement formulations are in the group of bone cements which exhibit a higher creep resistance.

Creep substructure formation in sodium chloride single crystals in the power law and exponential creep regimes

NASA Technical Reports Server (NTRS)

Raj, S. V.; Pharr, G. M.

1989-01-01

Creep tests conducted on NaCl single crystals in the temperature range from 373 to 1023 K show that true steady state creep is obtained only above 873 K when the ratio of the applied stress to the shear modulus is less than or equal to 0.0001. Under other stress and temperature conditions, corresponding to both power law and exponential creep, the creep rate decreases monotonically with increasing strain. The transition from power law to exponential creep is shown to be associated with increases in the dislocation density, the cell boundary width, and the aspect ratio of the subgrains along the primary slip planes. The relation between dislocation structure and creep behavior is also assessed.

Tensile and creep rupture behavior of P/M processed Nb-base alloy, WC-3009

NASA Technical Reports Server (NTRS)

Hebsur, Mohan G.; Titran, Robert H.

1988-01-01

Due to its high strength at temperatures up to 1600 K, fabrication of niobium base alloy WC-3009 (Nb30Hf9W) by traditional methods is difficult. Powder metallurgy (P/M) processing offers an attractive fabrication alternative for this high strength alloy. Spherical powders of WC-3009 produced by electron beam atomizing (EBA) process were successfully consolidated into a one inch diameter rod by vacuum hot pressing and swaging techniques. Tensile strength of the fully dense P/M material at 300-1590 K were similar to the arc-melted material. Creep rupture tests in vacuum indicated that WC-3009 exhibits a class 1 solid solution (glide controlled) creep behavior in the 1480 to 1590 K temperature range and stress range of 14 to 70 MPa. The creep behavior was correlated with temperature and stress using a power law relationship. The calculated stress exponent n, was about 3.2 and the apparent activation energy, Q, was about 270 kJ/mol. The large creep ductility exhibited by WC-3009 was attributed to its high strain rate sensitivity.

The Mechanical Properties and Modeling of Creep Behavior of UHMWPE/Nano-HA Composites

NASA Astrophysics Data System (ADS)

Li, Fan; Gao, Lilan; Gao, Hong; Cui, Yun

2017-09-01

Composites with different levels of hydroxyapatite (HA) content and ultra-high molecular weight polyethylene (UHMWPE) were prepared in this work. Mechanical properties of the composites were examined here, and to evaluate the effect of HA particles on the time-dependent behavior of the pure matrix, the creep and recovery performance of composites at various stress levels were also researched. As expected, the addition of HA influenced the time-dependent response of the UHMWPE and the effect had a strong dependence on the HA content. The creep and recovery strain of the composites significantly decreased with increasing HA content, and tensile properties were also impaired, which was due to the concentration of HA fillers. The mechanism and effect of HA dispersed into the UHMWPE matrix were examined by scanning electron microscopy. Additionally, since variations in the adjusted parameters revealed the impact of HA on the creep behavior of the UHMWPE matrix, Findley's model was employed. The results indicated that the analytical model was accurate for the prediction of creep of the pure matrix and its composites.

Mechanism-based modeling of solute strengthening: application to thermal creep in Zr alloy

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

Tome, Carlos; Wen, Wei; Capolungo, Laurent

2017-08-01

This report focuses on the development of a physics-based thermal creep model aiming to predict the behavior of Zr alloy under reactor accident condition. The current models used for this kind of simulations are mostly empirical in nature, based generally on fits to the experimental steady-state creep rates under different temperature and stress conditions, which has the following limitations. First, reactor accident conditions, such as RIA and LOCA, usually take place in short times and involve only the primary, not the steady-state creep behavior stage. Moreover, the empirical models cannot cover the conditions from normal operation to accident environments. Formore » example, Kombaiah and Murty [1,2] recently reported a transition between the low (n~4) and high (n~9) power law creep regimes in Zr alloys depending on the applied stress. Capturing such a behavior requires an accurate description of the mechanisms involved in the process. Therefore, a mechanism-based model that accounts for the evolution with time of microstructure is more appropriate and reliable for this kind of simulation.« less

Experimental characterization and numerical modelling of polymeric film damage, constituting the stratospheric super pressurized balloons

NASA Astrophysics Data System (ADS)

Chaabane, Makram; Chaabane, Makram; Dalverny, Olivier; Deramecourt, Arnaud; Mistou, Sébastien

The super-pressure balloons developed by CNES are a great challenge in scientific ballooning. Whatever the balloon type considered (spherical, pumpkin...), it is necessary to have good knowledge of the mechanical behavior of the envelope regarding to the flight level and the lifespan of the balloon. It appears during the working stages of the super pressure balloons that these last can exploded prematurely in the course of the first hours of flight. For this reason CNES and LGP are carrying out research programs about experimentations and modelling in order to predict a good stability of the balloons flight and guarantee a life time in adequacy with the technical requirement. This study deals with multilayered polymeric film damage which induce balloons failure. These experimental and numerical study aims, are a better understanding and predicting of the damage mechanisms bringing the premature explosion of balloons. The following damages phenomena have different origins. The firsts are simple and triple wrinkles owed during the process and the stocking stages of the balloons. The second damage phenomenon is associated to the creep of the polymeric film during the flight of the balloon. The first experimental results we present in this paper, concern the mechanical characterization of three different damage phenomena. The severe damage induced by the wrinkles of the film involves a significant loss of mechanical properties. In a second part the theoretical study, concerns the choice and the development of a non linear viscoelastic coupled damage behavior model in a finite element code.

Matrix dominated stress/strain behavior in polymeric composites: Effects of hold time, nonlinearity and rate dependency

NASA Technical Reports Server (NTRS)

Gates, Thomas S.

1992-01-01

In order to understand matrix dominated behavior in laminated polymer matrix composites, an elastic/viscoplastic constitutive model was developed and used to predict stress strain behavior of off-axis and angle-ply symmetric laminates under in-plane, tensile axial loading. The model was validated for short duration tests at elevated temperatures. Short term stress relaxation and short term creep, strain rate sensitivity, and material nonlinearity were accounted for. The testing times were extended for longer durations, and periods of creep and stress relaxation were used to investigate the ability of the model to account for long term behavior. The model generally underestimated the total change in strain and stress for both long term creep and long term relaxation respectively.

Creep behavior of soil nail walls in high plasticity index (PI) soils : technical report.

DOT National Transportation Integrated Search

2017-04-01

An aspect of particular concern in the Geotechnical Engineering Circular No. 7: Soil Nail Walls (i.e., the soil : nail wall manual and construction guidelines) is the creep behavior of soil nail systems in high-plasticity : clays. This research proje...

Detection and quantification of creep strain using process compensated resonance testing (PCRT) sorting modules trained with modeled resonance spectra

NASA Astrophysics Data System (ADS)

Heffernan, Julieanne; Biedermann, Eric; Mayes, Alexander; Livings, Richard; Jauriqui, Leanne; Goodlet, Brent; Aldrin, John C.; Mazdiyasni, Siamack

2018-04-01

Process Compensated Resonant Testing (PCRT) is a full-body nondestructive testing (NDT) method that measures the resonance frequencies of a part and correlates them to the part's material and/or damage state. PCRT testing is used in the automotive, aerospace, and power generation industries via automated PASS/FAIL inspections to distinguish parts with nominal process variation from those with the defect(s) of interest. Traditional PCRT tests are created through the statistical analysis of populations of "good" and "bad" parts. However, gathering a statistically significant number of parts can be costly and time-consuming, and the availability of defective parts may be limited. This work uses virtual databases of good and bad parts to create two targeted PCRT inspections for single crystal (SX) nickel-based superalloy turbine blades. Using finite element (FE) models, populations were modeled to include variations in geometric dimensions, material properties, crystallographic orientation, and creep damage. Model results were verified by comparing the frequency variation in the modeled populations with the measured frequency variations of several physical blade populations. Additionally, creep modeling results were verified through the experimental evaluation of coupon geometries. A virtual database of resonance spectra was created from the model data. The virtual database was used to create PCRT inspections to detect crystallographic defects and creep strain. Quantification of creep strain values using the PCRT inspection results was also demonstrated.

Investigation of creep by use of closed loop servo-hydraulic test system

NASA Technical Reports Server (NTRS)

Wu, H. C.; Yao, J. C.

1981-01-01

Creep tests were conducted by means of a closed loop servo-controlled materials test system. These tests are different from the conventional creep tests in that the strain history prior to creep may be carefully monitored. Tests were performed for aluminum alloy 6061-0 at 150 C and monitored by a PDP 11/04 minicomputer at a preset constant plastic-strain rate prehistory. The results show that the plastic-strain rate prior to creep plays a significant role in creep behavior. The endochronic theory of viscoplasticity was applied to describe the observed creep curves. The concepts of intrinsic time and strain rate sensitivity function are employed and modified according to the present observation.

Numerical analysis of the creeping behavior of the S. Andrea di Perarolo secondary landslide (Italian Eastern Alps)

NASA Astrophysics Data System (ADS)

Cioli, C.; Genevois, R.; Iafelice, M.; Zorzi, L.

2012-04-01

The S. Andrea landslide is a complex secondary phenomenon characterized by continuous movements causing a very high hazard condition for the near Perarolo di Cadore village (Italian Eastern Alps). A significant amount of geological and geotechnical investigations has been carried out in the past allowing the detection of the basal sliding surface. In specific, the sliding surface coincides with the contact between the bedrock and the overlying mass of an old landslides, involving a volume of about 180.000 cubic meters. A numerical approach has been adopted to analyze the stability of slope. This method is able to simulate the formation and development of shear zones as areas of strain localization in the model. Indeed, the S. Andrea landslide has been, then, investigated using FLAC, a two-dimensional explicit finite difference program, particularly useful in case of slopes with complex geometry. In order to build up a suitable model, variation of geological, hydrogeological and geotechnical parameters have been identified from the interpretation of all available data. In a preliminary stage, a Mohr-Coulomb plasticity model has been adopted except for the bedrock, which was characterized by an isotropic elastic model. Groundwater flow condition has been performed evaluating the change in pore pressure coupled to the mechanical deformation calculation. Numerical results show that this model cannot simulate real displacement behavior of the slope mainly due to both the complex material behavior and lithological heterogeneity, and due to geotechnical spatial complexity of different soils and mechanical parameters. It has been assumed that it was necessary to improve the model in the light of a time dependent behavior of existing soils. An elastic-viscoplastic model has been then used to reproduce the observed creeping behavior, and only in viscoplastic region time effects have been considered. Discussion of results points out on: i) the evolution of the ``mechanical damage'' within the moving mass; ii) the identification of possible causes of the displacements recorded in the field; iii) the utility of the computational approach for the creeping response of the soil slopes under constant load conditions and for two dimensional applications.

Modeling Creep Effects within SiC/SiC Turbine Components

NASA Technical Reports Server (NTRS)

DiCarlo, J. A.; Lang, J.

2008-01-01

Anticipating the implementation of advanced SiC/SiC ceramic composites into the hot section components of future gas turbine engines, the primary objective of this on-going study is to develop physics-based analytical and finite-element modeling tools to predict the effects of constituent creep on SiC/SiC component service life. A second objective is to understand how to possibly select and manipulate constituent materials, processes, and geometries in order to minimize these effects. In initial studies aimed at SiC/SiC components experiencing through-thickness stress gradients, creep models were developed that allowed an understanding of detrimental residual stress effects that can develop globally within the component walls. It was assumed that the SiC/SiC composites behaved as isotropic visco-elastic materials with temperature-dependent creep behavior as experimentally measured in-plane in the fiber direction of advanced thin-walled 2D SiC/SiC panels. The creep models and their key results are discussed assuming state-of-the-art SiC/SiC materials within a simple cylindrical thin-walled tubular structure, which is currently being employed to model creep-related effects for turbine airfoil leading edges subjected to through-thickness thermal stress gradients. Improvements in the creep models are also presented which focus on constituent behavior with more realistic non-linear stress dependencies in order to predict such key creep-related SiC/SiC properties as time-dependent matrix stress, constituent creep and content effects on composite creep rates and rupture times, and stresses on fiber and matrix during and after creep.

Mechanisms of high-temperature, solid-state flow in minerals and ceramics and their bearing on the creep behavior of the mantle

USGS Publications Warehouse

Kirby, S.H.; Raleigh, C.B.

1973-01-01

The problem of applying laboratory silicate-flow data to the mantle, where conditions can be vastly different, is approached through a critical review of high-temperature flow mechanisms in ceramics and their relation to empirical flow laws. The intimate association of solid-state diffusion and high-temperature creep in pure metals is found to apply to ceramics as well. It is shown that in ceramics of moderate grain size, compared on the basis of self-diffusivity and elastic modulus, normalized creep rates compare remarkably well. This comparison is paralleled by the near universal occurrence of similar creep-induced structures, and it is thought that the derived empirical flow laws can be associated with dislocation creep. Creep data in fine-grained ceramics, on the other hand, are found to compare poorly with theories involving the stress-directed diffusion of point defects and have not been successfully correlated by self-diffusion rates. We conclude that these fine-grained materials creep primarily by a quasi-viscous grain-boundary sliding mechanism which is unlikely to predominate in the earth's deep interior. Creep predictions for the mantle reveal that under most conditions the empirical dislocation creep behavior predominates over the mechanisms involving the stress-directed diffusion of point defects. The probable role of polymorphic transformations in the transition zone is also discussed. ?? 1973.

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

Asamoto, Shingo, E-mail: asamoto@mail.saitama-u.ac.j; Ohtsuka, Ayumu; Kuwahara, Yuta

In this paper, the effects of actual environmental actions on shrinkage, creep and shrinkage cracking of concrete are studied comprehensively. Prismatic specimens of plain concrete were exposed to three sets of artificial outdoor conditions with or without solar radiation and rain to examine the shrinkage. For the purpose of studying shrinkage cracking behavior, prismatic concrete specimens with reinforcing steel were also subjected to the above conditions at the same time. The shrinkage behavior is described focusing on the effects of solar radiation and rain based on the moisture loss. The significant environment actions to induce shrinkage cracks are investigated frommore » viewpoints of the amount of the shrinkage and the tensile strength. Finally, specific compressive creep behavior according to solar radiation and rainfall is discussed. It is found that rain can greatly inhibit the progresses of concrete shrinkage and creep while solar radiation is likely to promote shrinkage cracking and creep.« less

A thermodynamic approach to nonlinear ultrasonics for material state awareness and prognosis

NASA Astrophysics Data System (ADS)

Chillara, Vamshi Krishna

2017-11-01

We develop a thermodynamic framework for modeling nonlinear ultrasonic damage sensing and prognosis in materials undergoing progressive damage. The framework is based on the internal variable approach and relies on the construction of a pseudo-elastic strain energy function that captures the energetics associated with the damage progression. The pseudo-elastic strain energy function is composed of two energy functions—one that describes how a material stores energy in an elastic fashion and the other describes how material dissipates energy or stores it in an inelastic fashion. Experimental motivation for the choice of the above two functionals is discussed and some specific choices pertaining to damage progression during fatigue and creep are presented. The thermodynamic framework is employed to model the nonlinear response of material undergoing stress relaxation and creep-like degradation. For each of the above cases, evolution of the nonlinearity parameter with damage as well as with macroscopic measurables like accumulated plastic strain is obtained.

Out-of-pile creep behavior of uranium carbide

NASA Technical Reports Server (NTRS)

Wright, T. R.; Seltzer, M. S.

1974-01-01

Compression creep tests were investigated on various UC-based fuel materials having a variation in both density and composition. Specimens were prepared by casting and by hot pressing. Steady-state creep rates were measured under vacuum at 1400 to 1800 C in the stress range 500-4000 psi.

Irradiation Creep in Graphite

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

Ubic, Rick; Butt, Darryl; Windes, William

2014-03-13

An understanding of the underlying mechanisms of irradiation creep in graphite material is required to correctly interpret experimental data, explain micromechanical modeling results, and predict whole-core behavior. This project will focus on experimental microscopic data to demonstrate the mechanism of irradiation creep. High-resolution transmission electron microscopy should be able to image both the dislocations in graphite and the irradiation-induced interstitial clusters that pin those dislocations. The team will first prepare and characterize nanoscale samples of virgin nuclear graphite in a transmission electron microscope. Additional samples will be irradiated to varying degrees at the Advanced Test Reactor (ATR) facility and similarlymore » characterized. Researchers will record microstructures and crystal defects and suggest a mechanism for irradiation creep based on the results. In addition, the purchase of a tensile holder for a transmission electron microscope will allow, for the first time, in situ observation of creep behavior on the microstructure and crystallographic defects.« less

Constitutive Model for Anisotropic Creep Behaviors of Single-Crystal Ni-Base Superalloys in the Low-Temperature, High-Stress Regime (Postprint)

DTIC Science & Technology

2012-01-19

specific dislocation reactions. Rae et al .[4,5,7] proposed micromechanisms for primary creep caused by SF shearing of c0 precipitates by ah112i...near the [0 0 1] was done by Matan et al .[3] They proposed a phenomenological creep model, which was adopted from Gilman’s dislocation density model...the original loading orientation). MacLachlan et al .[18 21] proposed a series of creep models for anisotropic creep of single-crystal superalloys. Their

High-temperature creep properties and life predictions for T91 and T92 steels

NASA Astrophysics Data System (ADS)

Pan, J. P.; Tu, S. H.; Sun, G. L.; Zhu, X. W.; Tan, L. J.; Hu, B.

2018-01-01

9-11%Cr heat-resistant steels are widely used in high-temperature and high-pressure boilers of advanced power plants. In the current paper, high-temperature creep behaviors of T91 and T92 steels have been investigated. Creep tests were performed for both steels at varied temperatures. The creep mechanisms of T91 and T92 steels were elucidated by analyzing the creep rupture data of the two steels. In addition, Manson-Haferd model was employed to predict the creep life of T91 and T92 steels, the results of which indicate that the Manson-Haferd model works well for the two steels.

A new uniformly valid asymptotic integration algorithm for elasto-plastic creep and unified viscoplastic theories including continuum damage

NASA Technical Reports Server (NTRS)

Chulya, Abhisak; Walker, Kevin P.

1991-01-01

A new scheme to integrate a system of stiff differential equations for both the elasto-plastic creep and the unified viscoplastic theories is presented. The method has high stability, allows large time increments, and is implicit and iterative. It is suitable for use with continuum damage theories. The scheme was incorporated into MARC, a commercial finite element code through a user subroutine called HYPELA. Results from numerical problems under complex loading histories are presented for both small and large scale analysis. To demonstrate the scheme's accuracy and efficiency, comparisons to a self-adaptive forward Euler method are made.

Creep fatigue life prediction for engine hot section materials (isotropic): Fourth year progress review

NASA Technical Reports Server (NTRS)

Nelson, Richard S.; Schoendorf, John F.

1986-01-01

As gas turbine technology continues to advance, the need for advanced life prediction methods for hot section components is becoming more and more evident. The complex local strain and temperature histories at critical locations must be accurately interpreted to account for the effects of various damage mechanisms (such as fatigue, creep, and oxidation) and their possible interactions. As part of the overall NASA HOST effort, this program is designed to investigate these fundamental damage processes, identify modeling strategies, and develop practical models which can be used to guide the early design and development of new engines and to increase the durability of existing engines.

A new uniformly valid asymptotic integration algorithm for elasto-plastic-creep and unified viscoplastic theories including continuum damage

NASA Technical Reports Server (NTRS)

Chulya, A.; Walker, K. P.

1989-01-01

A new scheme to integrate a system of stiff differential equations for both the elasto-plastic creep and the unified viscoplastic theories is presented. The method has high stability, allows large time increments, and is implicit and iterative. It is suitable for use with continuum damage theories. The scheme was incorporated into MARC, a commercial finite element code through a user subroutine called HYPELA. Results from numerical problems under complex loading histories are presented for both small and large scale analysis. To demonstrate the scheme's accuracy and efficiency, comparisons to a self-adaptive forward Euler method are made.

Creep of oxide dispersion strengthened materials /with special reference to T-D nichrome/

NASA Technical Reports Server (NTRS)

Lin, J.; Sherby, O. D.

1981-01-01

Analyses of oxide dispersion strengthened (ODS) alloys shows that their characteristics are mainly due to the creep behavior of the matrix material. Diffusion-controlled slip creep is established as the rate-controlling process in the alloys investigated, with the glide and climb of edge dislocations associated with the subgrain structure as barriers being the specific rate-controlling step. It is found that the stable subgrain size in ODS alloys is usually associated with the spacing between particles 500-1000 A in size, and that their creep behavior is distinguished from that of the matrix material by the existence of a threshold stress that is not well defined microscopically but appears to be related to particles of less than 500 A size.

High temperature behavior of B2-based ruthenium aluminide systems

NASA Astrophysics Data System (ADS)

Cao, Fang

Ru-modified NiAl-based bond coats have the potential to improve the durability of Superalloy-Thermal Barrier Coating systems (TBCs) for advanced gas turbine engines. A fundamental understanding of the high temperature mechanical behavior across the Ni-Al-Ru B2 phase field can provide direction for the development of these new bond coats for TBCs. The purpose of this study has been to describe the fundamental processes of creep deformation in single phase B2 Ru-Al-Ni ternary alloys which would form the basis for the bond coats. To accomplish this, five ternary alloys with compositions located within the B2 field across the NiAl-RuAl phase region were fabricated and investigated. Special emphasis was placed on characterizing creep deformation and describing the operative creep mechanisms in these alloys. At room temperature, brittle failure was observed in the Ni-rich alloys in compression, while improved strength and ductility were displayed in two Ru-rich ternary alloys at temperatures up to 700°C. Exceptional creep strength was observed in these alloys, as compared to other high melting temperature B2 intermetallics. A continuous increase of the melting temperature and creep resistance with the increasing of the Ru/Ni ratio in these alloys was observed. Post-creep dislocation analyses identified the presence of <100> and <110> edge dislocations in the Ni-rich alloys, while uniformly distributed jogged <100> screw dislocations predominated in the Ru-rich ternary alloys. A transition of the creep mechanism from viscous glide controlled to jogged screw motion in these Ru-Al-Ni ternary B2 alloys with increasing Ru/Ni ratio is demonstrated by the characteristics of the creep deformation process, stress change creep tests, post-creep dislocation analyses, and numerical modeling. Additionally, the knowledge of the cyclic oxidation behavior of ruthenium aluminide-based alloy is essential, as many high-temperature applications for which this intermetallic might be utilized undergo repeated severe thermal cycling. Thus the second portion of this thesis focuses on the characterization of the cyclic oxidation properties of RuAl-based alloys. The cyclic oxidation behavior of six RuAl-based alloys was studied in air over the temperature range of 1000°C to 1300°C. Oxidation kinetics have been shown to be influenced by microstructure as well as the addition of platinum.

Damage Assessment of Creep Tested and Thermally Aged Metallic Alloys Using Acousto-Ultrasonics

NASA Technical Reports Server (NTRS)

Gyekenyesi, Andrew L.; Kautz, Harold E.; Baaklini, George Y.

2001-01-01

In recent years emphasis has been placed on the early detection of material changes experienced in turbine powerplant components. During the scheduled overhaul of a turbine, the current techniques of examination of various hot section components aim to find flaws such as cracks, wear, and erosion, as well as excessive deformations. Thus far, these localized damage modes have been detected with satisfactory results. However, the techniques used to find these flaws provide no information on life until the flaws are actually detected. Major improvements in damage assessment, safety, as well as more accurate life prediction could be achieved if nondestructive evaluation (NDE) techniques could be utilized to sense material changes that occur prior to the localized defects mentioned. Because of elevated temperatures and excessive stresses, turbine components may experience creep behavior. As a result, it is desirable to monitor and access the current condition of such components. Research at the NASA Glenn Research Center involves developing and utilizing an NDE technique that discloses distributed material changes that occur prior to the localized damage detected by the current methods of inspection. In a recent study, creep processes in a nickel-base alloy were the life-limiting condition of interest, and the NDE technique was acousto-ultrasonics (AU). AU is an NDE technique that utilizes two ultrasonic transducers to interrogate the condition of a test specimen. The sending transducer introduces an ultrasonic pulse at a point on the surface of the specimen while a receiving transducer detects the signal after it has passed through the material. The goal of the method is to correlate certain parameters of the detected waveform to characteristics of the material between the two transducers. Here, the waveform parameter of interest is the attenuation due to internal damping for which information is being garnered from the frequency domain. The parameters utilized to indirectly quantify the attenuation are the ultrasonic decay rate as well as various moments of the frequency power spectrum. A new, user-friendly, graphical interface AU system was developed at NASA Glenn. This system is an all-inclusive, multifunction system that controls the sending and receiving ultrasonic transducers as well as all posttest signal analysis. The system's postprocessing software calculates the multiple parameters used to study the material of interest.

Characterization of C/Enhanced SiC Composite During Creep-Rupture Tests Using an Ultrasonic Guided Wave Scan System

NASA Technical Reports Server (NTRS)

Roth, Don J.; Verrilli, Michael J.; Martin, Richard E.; Cosgriff, Laura M.

2004-01-01

An ultrasonic guided wave scan system was used to nondestructively monitor damage over time and position in a C/enhanced SiC sample that was creep tested to failure at 1200 C in air at a stress of 69 MPa (10 ksi). The use of the guided wave scan system for mapping evolving oxidation profiles (via porosity gradients resulting from oxidation) along the sample length and predicting failure location was explored. The creep-rupture tests were interrupted for ultrasonic evaluation every two hours until failure at approx. 17.5 cumulative hours.

Creep-induced anisotropy in covalent adaptable network polymers.

PubMed

Hanzon, Drew W; He, Xu; Yang, Hua; Shi, Qian; Yu, Kai

2017-10-11

Anisotropic polymers with aligned macromolecule chains exhibit directional strengthening of mechanical and physical properties. However, manipulating the orientation of polymer chains in a fully cured thermoset is almost impossible due to its permanently crosslinked nature. In this paper, we demonstrate that rearrangeable networks with bond exchange reactions (BERs) can be utilized to tailor the anisotropic mechanical properties of thermosetting polymers. When a constant force is maintained at BER activated temperatures, the malleable thermoset creeps in the direction of stress, and macromolecule chains align themselves in the same direction. The aligned polymer chains result in an anisotropic network with a stiffer mechanical behavior in the direction of creep, while with a more compliant behavior in the transverse direction. The degree of network anisotropy is proportional to the amount of creep strain. A multi-length scale constitutive model is developed to study the creep-induced anisotropy of thermosetting polymers. The model connects the micro-scale BER kinetics, orientation of polymer chains, and directional mechanical properties of network polymers. Without any fitting parameters, it is able to predict the evolution of creep strain at different temperatures and anisotropic stress-strain behaviors of CANs after creep. Predictions on the chain orientation are verified by molecular dynamics (MD) simulation. Based on parametric studies, it is shown that the influences of creep time and temperature on the network anisotropy can be generalized into a single parameter, and the evolution of directional modulus follows an Arrhenius type time-temperature superposition principle (TTSP). The presented work provides a facile approach to transform isotropic thermosets into anisotropic ones using simple heating, and their directional properties can be readily tailored by the processing conditions.

Transient rolling friction model for discrete element simulations of sphere assemblies

NASA Astrophysics Data System (ADS)

Kuhn, Matthew R.

2014-03-01

The rolling resistance between a pair of contacting particles can be modeled with two mechanisms. The first mechanism, already widely addressed in the DEM literature, involves a contact moment between the particles. The second mechanism involves a reduction of the tangential contact force, but without a contact moment. This type of rotational resistance, termed creep-friction, is the subject of the paper. Within the creep-friction literature, the term “creep” does not mean a viscous mechanism, but rather connotes a slight slip that accompanies rolling. Two extremes of particle motions bound the range of creep-friction behaviors: a pure tangential translation is modeled as a Cattaneo-Mindlin interaction, whereas prolonged steady-state rolling corresponds to the traditional wheel-rail problem described by Carter, Poritsky, and others. DEM simulations, however, are dominated by the transient creep-friction rolling conditions that lie between these two extremes. A simplified model is proposed for the three-dimensional transient creep-friction rolling of two spheres. The model is an extension of the work of Dahlberg and Alfredsson, who studied the two-dimensional interactions of disks. The proposed model is applied to two different systems: a pair of spheres and a large dense assembly of spheres. Although creep-friction can reduce the tangential contact force that would otherwise be predicted with Cattaneo-Mindlin theory, a significant force reduction occurs only when the rate of rolling is much greater than the rate of translational sliding and only after a sustained period of rolling. When applied to the deviatoric loading of an assembly of spheres, the proposed creep-friction model has minimal effect on macroscopic strength or stiffness. At the micro-scale of individual contacts, creep-friction does have a modest influence on the incremental contact behavior, although the aggregate effect on the assembly's behavior is minimal.

Creep strain and creep-life prediction for alloy 718 using the omega method

NASA Astrophysics Data System (ADS)

Yeom, Jong-Taek; Kim, Jong-Yup; Na, Young-Sang; Park, Nho-Kwang

2003-12-01

The creep behavior of Alloy 718 was investigated in relation to the MPCs omega (Ω) method. To evaluate the creep model and determine material parameters, constant load creep tests were performed at different initial stresses in a temperature range between 550°C and 700°C. The imaginary initial strain rate ɛ limits^. _0 and omega (Ω), considered to be important variables in the model, were expressed as a function of initial stress and temperature. For these variables, power-law and hyperbolic sine-law equations were used as constitutive equations for the creep of Alloy 718. To consider the effect of γ″ coarsening leading to a radical drop of tensile strength and creep strength at temperatures above 650°C, different material constants at the temperatures above 650°C were applied. The reliability of the models was investigated in relation to the creep curve and creep life.

Low-Temperature Fault Creep: Strong vs. Weak, Steady vs. Episodic

NASA Astrophysics Data System (ADS)

Wang, K.; Gao, X.

2017-12-01

Unless we understand how faults creep, we do not fully understand how they produce earthquakes. However, most of the physics and geology of low-temperature creep is not known. There are two end-member types of low-temperature creep: weak creep of smooth faults and strong creep of rough faults, with a spectrum of intermediate modes in between. Most conceptual and numerical models deal with weak creep, assuming a very smooth fault with a gouge typically weakened by hydrous minerals (Harris, 2017). Less understood is strong creep. For subduction zones, strong creep appears to be common and is often associated with the subduction of large geometrical irregularities such as seamounts and aseismic ridges (Wang and Bilek, 2014). These irregularities generate fracture systems as they push against the resistance of brittle rocks. The resultant heterogeneous stress and structural environment makes it very difficult to lock the fault. The geodetically observed creep under such conditions is accomplished by the complex deformation of a 3D damage zone. Strong-creeping faults dissipate more heat than faults that produce great earthquakes (Gao and Wang, 2014). Although an integrated frictional strength of the fault is still a useful concept, the creeping mechanism is very different from frictional slip of a velocity-strengthening smooth fault. Cataclasis and pressure-solution creep in the fracture systems must be important processes in strong creep. Strong creep is necessarily non-steady and produces small and medium earthquakes. Strong creep of a megathrust can also promote the occurrence of a very special type of weak creep - episodic slow slip around the mantle wedge corner accompanied with tremor (ETS). An example is Hikurangi, where strong creep causes the frictional-viscous transition along the plate interface to occur much shallower than the mantle wedge corner, a necessary condition for ETS (Gao and Wang, 2017). Gao and Wang (2014), Strength of stick-slip and creeping subduction megathrusts from heat flow observations, Science. Gao and Wang (2017), Rheological separation of the megathrust seismogenic zone and Episodic Tremor and Slip, Nature. Harris (2017), Large earthquakes and creeping faults, Rev. Geophys. Wang and Bilek (2014), Fault creep caused by subduction of rough seafloor relief, Tectonophysics.

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.

Large earthquakes and creeping faults

USGS Publications Warehouse

Harris, Ruth A.

2017-01-01

Faults are ubiquitous throughout the Earth's crust. The majority are silent for decades to centuries, until they suddenly rupture and produce earthquakes. With a focus on shallow continental active-tectonic regions, this paper reviews a subset of faults that have a different behavior. These unusual faults slowly creep for long periods of time and produce many small earthquakes. The presence of fault creep and the related microseismicity helps illuminate faults that might not otherwise be located in fine detail, but there is also the question of how creeping faults contribute to seismic hazard. It appears that well-recorded creeping fault earthquakes of up to magnitude 6.6 that have occurred in shallow continental regions produce similar fault-surface rupture areas and similar peak ground shaking as their locked fault counterparts of the same earthquake magnitude. The behavior of much larger earthquakes on shallow creeping continental faults is less well known, because there is a dearth of comprehensive observations. Computational simulations provide an opportunity to fill the gaps in our understanding, particularly of the dynamic processes that occur during large earthquake rupture and arrest.

FEM simulation of the die compaction of pharmaceutical products: influence of visco-elastic phenomena and comparison with experiments.

PubMed

Diarra, Harona; Mazel, Vincent; Busignies, Virginie; Tchoreloff, Pierre

2013-09-10

This work studies the influence of visco-elastic behavior in the finite element method (FEM) modeling of die compaction of pharmaceutical products and how such a visco-elastic behavior may improve the agreement between experimental and simulated compression curves. The modeling of the process was conducted on a pharmaceutical excipient, microcrystalline cellulose (MCC), by using Drucker-Prager cap model coupled with creep behavior in Abaqus(®) software. The experimental data were obtained on a compaction simulator (STYLCAM 200R). The elastic deformation of the press was determined by performing experimental tests on a calibration disk and was introduced in the simulation. Numerical optimization was performed to characterize creep parameters. The use of creep behavior in the simulations clearly improved the agreement between the numerical and experimental compression curves (stresses, thickness), mainly during the unloading part of the compaction cycle. For the first time, it was possible to reproduce numerically the fact that the minimum tablet thickness is not obtained at the maximum compression stress. This study proves that creep behavior must be taken into account when modeling the compaction of pharmaceutical products using FEM methods. Copyright © 2013 Elsevier B.V. All rights reserved.

Creep Deformation and Rupture Behavior of Single- and Dual-Pass 316LN Stainless-Steel-Activated TIG Weld Joints

NASA Astrophysics Data System (ADS)

Vijayanand, V. D.; Vasudevan, M.; Ganesan, V.; Parameswaran, P.; Laha, K.; Bhaduri, A. K.

2016-06-01

Creep deformation and rupture behavior of single-pass and dual-pass 316LN stainless steel (SS) weld joints fabricated by an autogenous activated tungsten inert gas welding process have been assessed by performing metallography, hardness, and conventional and impression creep tests. The fusion zone of the single-pass joint consisted of columnar zones adjacent to base metals with a central equiaxed zone, which have been modified extensively by the thermal cycle of the second pass in the dual-pass joint. The equiaxed zone in the single-pass joint, as well as in the second pass of the dual-pass joint, displayed the lowest hardness in the joints. In the dual-pass joint, the equiaxed zone of the first pass had hardness comparable to the columnar zone. The hardness variations in the joints influenced the creep deformation. The equiaxed and columnar zone in the first pass of the dual-pass joint was more creep resistant than that of the second pass. Both joints possessed lower creep rupture life than the base metal. However, the creep rupture life of the dual-pass joint was about twofolds more than that of the single-pass joint. Creep failure in the single-pass joint occurred in the central equiaxed fusion zone, whereas creep cavitation that originated in the second pass was blocked at the weld pass interface. The additional interface and strength variation between two passes in the dual-pass joint provides more restraint to creep deformation and crack propagation in the fusion zone, resulting in an increase in the creep rupture life of the dual-pass joint over the single-pass joint. Furthermore, the differences in content, morphology, and distribution of delta ferrite in the fusion zone of the joints favors more creep cavitation resistance in the dual-pass joint over the single-pass joint with the enhancement of creep rupture life.

Time-dependent brittle deformation (creep) at Mt. Etna volcano

NASA Astrophysics Data System (ADS)

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.; Bell, A. F.; Main, I. G.

2009-04-01

Mt. Etna is the largest and most active volcano in Europe. Time-dependent weakening mechanisms, leading to slow fracturing, have been shown to act during pre-eruptive patterns of flank eruptions at Mt. Etna volcano. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts one of the biggest hydrogeologic reservoirs of Sicily (Ogniben, 1966). The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as ‘brittle creep'. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short-term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data not only demonstrates that basalt creeps in the brittle regime but also that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Furthermore, stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time-to-failure properties of the basaltic volcanic pile.

Creep rupture testing of carbon fiber-reinforced epoxy composites

NASA Astrophysics Data System (ADS)

Burton, Kathryn Anne

Carbon fiber is becoming more prevalent in everyday life. As such, it is necessary to have a thorough understanding of, not solely general mechanical properties, but of long-term material behavior. Creep rupture testing of carbon fiber is very difficult due to high strength and low strain to rupture properties. Past efforts have included testing upon strands, single tows and overwrapped pressure vessels. In this study, 1 inch wide, [0°/90°]s laminated composite specimens were constructed from fabric supplied by T.D. Williamson Inc. Specimen fabrication methods and gripping techniques were investigated and a method was developed to collect long term creep rupture behavior data. An Instron 1321 servo-hydraulic material testing machine was used to execute static strength and short term creep rupture tests. A hanging dead-weight apparatus was designed to perform long-term creep rupture testing. The testing apparatus, specimens, and specimen grips functioned well. Collected data exhibited a power law distribution and therefore, a linear trend upon a log strength-log time plot. Statistical analysis indicated the material exhibited slow degradation behavior, similar to previous studies, and could maintain a 50 year carrying capacity at 62% of static strength, approximately 45.7 ksi.

Analysis of the Mechanical Behavior, Creep Resistance and Uniaxial Fatigue Strength of Martensitic Steel X46Cr13

PubMed Central

Brnic, Josip; Krscanski, Sanjin; Lanc, Domagoj; Brcic, Marino; Turkalj, Goran; Canadija, Marko; Niu, Jitai

2017-01-01

The article deals with the analysis of the mechanical behavior at different temperatures, uniaxial creep and uniaxial fatigue of martensitic steel X46Cr13 (1.4034, AISI 420). For the purpose of considering the aforementioned mechanical behavior, as well as determining the appropriate resistance to creep and fatigue strength levels, numerous uniaxial tests were carried out. Tests related to mechanical properties performed at different temperatures are presented in the form of engineering stress-strain diagrams. Short-time creep tests performed at different temperatures and different stress levels are presented in the form of creep curves. Fatigue tests carried out at stress ratios R=0.25 and R=−1 are shown in the form of S–N (fatigue) diagrams. The finite fatigue regime for each of the mentioned stress ratios is modeled by an inclined log line, while the infinite fatigue regime is modeled by a horizontal line, which represents the fatigue limit of the material and previously was calculated by the modified staircase method. Finally, the fracture toughness has been calculated based on the Charpy V-notch impact energy. PMID:28772749

Viscoelastic Response of the Titanium Alloy Ti-6-4: Experimental Identification of Time- and Rate-Dependent Reversible and Irreversible Deformation Regions

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.; Arnold, Steven M.

2014-01-01

In support of an effort on damage prognosis, the viscoelastic behavior of Ti-6Al-4V (Ti-6-4) was investigated. This report documents the experimental characterization of this titanium alloy. Various uniaxial tests were conducted to low load levels over the temperature range of 20 to 538 C to define tensile, creep, and relaxation behavior. A range of strain rates (6x10(exp -7) to 0.001/s) were used to document rate effects. All tests were designed to include an unloading portion, followed by a hold time at temperature to allow recovery to occur either at zero stress or strain. The titanium alloy was found to exhibit viscoelastic behavior below the "yield" point and over the entire range of temperatures (although at lower temperatures the magnitude is extremely small). These experimental data will be used for future characterization of a viscoelastic model.

Accelerated Creep Testing of High Strength Aramid Webbing

NASA Technical Reports Server (NTRS)

Jones, Thomas C.; Doggett, William R.; Stnfield, Clarence E.; Valverde, Omar

2012-01-01

A series of preliminary accelerated creep tests were performed on four variants of 12K and 24K lbf rated Vectran webbing to help develop an accelerated creep test methodology and analysis capability for high strength aramid webbings. The variants included pristine, aged, folded and stitched samples. This class of webbings is used in the restraint layer of habitable, inflatable space structures, for which the lifetime properties are currently not well characterized. The Stepped Isothermal Method was used to accelerate the creep life of the webbings and a novel stereo photogrammetry system was used to measure the full-field strains. A custom MATLAB code is described, and used to reduce the strain data to produce master creep curves for the test samples. Initial results show good correlation between replicates; however, it is clear that a larger number of samples are needed to build confidence in the consistency of the results. It is noted that local fiber breaks affect the creep response in a similar manner to increasing the load, thus raising the creep rate and reducing the time to creep failure. The stitched webbings produced the highest variance between replicates, due to the combination of higher local stresses and thread-on-fiber damage. Large variability in the strength of the webbings is also shown to have an impact on the range of predicted creep life.

Low cycle fatigue of PM/HIP astroloy

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

Choe, S.J.; Stoloff, N.S.; Duquette, D.J.

Low cycle fatigue and creep-fatigue-environment interactions of PM/HIP Astrology were studied at 650 C and 725 C. Total strain range was varied from 1.5% to 2.7% at a frequency of 0.3Hz. Creep-fatigue tests were performed with 2 min. or 5 min. tensile hold times. All tests were run in high purity argon in an attempt to minimize environmental effects. Employing a tensile hold was more damaging than raising temperature by 75 C. Slopes of Coffin-Manson plots were nearly independent of temperature and hold time. Raising temperature from 650 C to 725 C did not change the transgranular (TG) crack propagationmore » mode, whereas employing hold times caused TG+IG propagation. All samples displayed multiple fracture origins associated with inclusions located at the specimen surface; pre-existing pores did not affect fatigue crack initiation. Examination of secondary cracks showed no apparent creep damage. Oxidation in high purity argon appeared to be the major factor in LCF life degradation due to hold times.« less

Study of Damage and Fracture Toughness Due to Influence of Creep and Fatigue of Commercially Pure Copper by Monotonic and Cyclic Indentation

NASA Astrophysics Data System (ADS)

Ghosh, Sabita; Prakash, Raghu V.

2013-01-01

Fracture toughness is the ability of a component containing a flow to resist fracture. In the current study, the Ball indentation (BI) test technique, which is well acknowledged as an alternative approach to evaluate mechanical properties of materials due to its semi-nondestructive, fast, and high accurate qualities is used to estimate damage and the fracture toughness for copper samples subjected to varying levels of creep and fatigue. The indentation fracture toughness shows the degradation of Cu samples when they are subjected to different creep conditions. Axial fatigue cycling increases the strength at the mid-gauge section compared to other regions of the samples due to initial strain hardening. The advancement of indentation depth with indentation fatigue cycles experiences transient stage, i.e., jump in indentation depth has been observed, which may be an indication of failure and followed by a steady state with almost constant depth propagation with indentation cycles.

Biaxial Thermal Creep of Alloy 617 and Alloy 230 for VHTR Applications

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

Mo, Kun; Lv, Wei; Tung, Hsiao-Ming

2016-05-18

In this study, we employed pressurized creep tubes to investigate the biaxial thermal creep behavior of Inconel 617 (alloy 617) and Haynes 230 (alloy 230). Both alloys are considered to he the primary candidate structural materials for very high-temperature reactors (VITITRs) due to their exceptional high-temperature mechanical properties. The current creep experiments were conducted at 900 degrees C for the effective stress range of 15-35 MPa. For both alloys, complete creep strain development with primary, secondary, and tertiary regimes was observed in all the studied conditions. Tertiary creep was found to he dominant over the entire creep lives of bothmore » alloys. With increasing applied creep stress, the fraction of the secondary creep regime decreases. The nucleation, diffusion, and coarsening of creep voids and carbides on grain boundaries were found to be the main reasons for the limited secondary regime and were also found to be the major causes of creep fracture. The creep curves computed using the adjusted creep equation of the form epsilon= cosh 1(1 rt) + P-sigma ntm agree well with the experimental results for both alloys at die temperatures of 850-950 degrees C.« less

Assessment of surface relief and short cracks under cyclic creep in a type 316LN austenitic stainless steel

NASA Astrophysics Data System (ADS)

Sarkar, Aritra; Nagesha, A.; Parameswaran, P.; Sandhya, R.; Laha, K.

2015-12-01

Formation of surface relief and short cracks under cyclic creep (stress-controlled fatigue) in type 316LN stainless steel was studied at temperatures ranging from ambient to 923 K using scanning electron microscopy technique. The surface topography and crack distribution behaviour under cyclic creep were found to be strong functions of testing temperature due to the difference in strain accumulation. At 823 K, surface relief mainly consisted of fine slip markings due to negligible accumulation of strain as a consequence of dynamic strain ageing (DSA) which led to an increase in the cyclic life. Persistent slip markings (PSM) with distinct extrusions containing minute cracks were seen to prevail in the temperature range 873-923 K, indicating a higher slip activity causing higher strain accumulation in the absence of DSA. Besides, a large number of secondary cracks (both transgranular and intergranular) which were partially accentuated by severe oxidation, were observed. Extensive cavitation-induced grain boundary cracking took place at 923 K, which coalesced with PSM-induced transgranular cracks resulting in failure dominated by creep that in turn led to a drastic reduction in cyclic life. Investigations on the influence of stress rate were also carried out which underlined the presence of DSA at 823 K. At 923 K, lowering the stress rate caused further strengthening of the contribution from creep damage marked by a shift in the damage mechanism from cyclic slip to diffusion.

Creep Behavior of ABS Polymer in Temperature-Humidity Conditions

NASA Astrophysics Data System (ADS)

An, Teagen; Selvaraj, Ramya; Hong, Seokmoo; Kim, Naksoo

2017-04-01

Acrylonitrile-Butadiene-Styrene (ABS), also known as a thermoplastic polymer, is extensively utilized for manufacturing home appliances products as it possess impressive mechanical properties, such as, resistance and toughness. However, the aforementioned properties are affected by operating temperature and atmosphere humidity due to the viscoelasticity property of an ABS polymer material. Moreover, the prediction of optimum working conditions are the little challenging task as it influences the final properties of product. This present study aims to develop the finite element (FE) models for predicting the creep behavior of an ABS polymeric material. In addition, the material constants, which represent the creep properties of an ABS polymer material, were predicted with the help of an interpolation function. Furthermore, a comparative study has been made with experiment and simulation results to verify the accuracy of developed FE model. The results showed that the predicted value from FE model could agree well with experimental data as well it can replicate the actual creep behavior flawlessly.

The effect of grain orientation on nanoindentation behavior of model austenitic alloy Fe-20Cr-25Ni

DOE PAGES

Chen, Tianyi; Tan, Lizhen; Lu, Zizhe; ...

2017-07-26

Instrumented nanoindentation was used in this paper to investigate the hardness, elastic modulus, and creep behavior of an austenitic Fe-20Cr-25Ni model alloy at room temperature, with the indented grain orientation being the variant. The samples indented close to the {111} surfaces exhibited the highest hardness and modulus. However, nanoindentation creep tests showed the greatest tendency for creep in the {111} indented samples, compared with the samples indented close to the {001} and {101} surfaces. Scanning electron microscopy and cross-sectional transmission electron microscopy revealed slip bands and dislocations in all samples. The slip band patterns on the indented surfaces were influencedmore » by the grain orientations. Deformation twinning was observed only under the {001} indented surfaces. Finally, microstructural analysis and molecular dynamics modeling correlated the anisotropic nanoindentation-creep behavior with the different dislocation substructures formed during indentation, which resulted from the dislocation reactions of certain active slip systems that are determined by the indented grain orientations.« less

High-Temperature Creep Degradation of the AM1/NiAlPt/EBPVD YSZ System

NASA Astrophysics Data System (ADS)

Riallant, Fanny; Cormier, Jonathan; Longuet, Arnaud; Milhet, Xavier; Mendez, José

2014-01-01

The failure mechanisms of a NiAlPt/electron beam physical vapor deposition yttria-stabilized-zirconia thermal barrier coating system deposited on the AM1 single crystalline substrate have been investigated under pure creep conditions in the temperature range from 1273 K to 1373 K (1000 °C to 1100 °C) and for durations up to 1000 hours. Doubly tapered specimens were used allowing for the analysis of different stress states and different accumulated viscoplastic strains for a given creep condition. Under such experiments, two kinds of damage mechanisms were observed. Under low applied stress conditions ( i.e., long creep tests), microcracking is localized in the vicinity of the thermally grown oxide (TGO). Under high applied stress conditions, an unconventional failure mechanism at the substrate/bond coat interface is observed because of large creep strains and fast creep deformation, hence leading to a limited TGO growth. This unconventional failure mechanism is observed although the interfacial bond coat/top coat TGO thickening is accelerated by the mechanical applied stress beyond a given stress threshold.

Tensile strength and creep behaviour of austenitic stainless steel type 18Cr - 12Ni with niobium additions at 700°C

NASA Astrophysics Data System (ADS)

Sordi, V. L.; Bueno, L. O.

2010-07-01

The effect of niobium additions up to 2.36 wt% on the creep behavior of a series of seven extra low carbon 18Cr-12Ni austenitic stainless steels at 700°C has been investigated. Grain size and hardness measurements, hot tensile tests and constant stress creep tests from 90 to 180 MPa were carried out for each alloy, in the solution treated condition at 1050, 1200 and 1300°C followed by quench in water. The mechanical behavior at high temperature was related to the amount of NbC precipitation occurring during the tests. Solid solution and intermetallic compound effects were also considered. Creep data analysis was done to determine the parameters of the creep power-law equation dot epsilon = A.σn and the Monkman-Grant relation dot epsilon.tmR = K. Niobium-carbide precipitation in these steels reduces the secondary stage dependence of strain rate with applied stress, resulting in n-values which indicate the possibility of operation of various creep mechanisms. The creep strength during the secondary stage is primarily controlled by the amount of NbC available for precipitation. However, the rupture times increase progressively with niobium content, as the amount of undissolved carbide particles in grain boundaries and the Laves phase precipitation increase.

Algorithms for elasto-plastic-creep postbuckling

NASA Technical Reports Server (NTRS)

Padovan, J.; Tovichakchaikul, S.

1984-01-01

This paper considers the development of an improved constrained time stepping scheme which can efficiently and stably handle the pre-post-buckling behavior of general structure subject to high temperature environments. Due to the generality of the scheme, the combined influence of elastic-plastic behavior can be handled in addition to time dependent creep effects. This includes structural problems exhibiting indefinite tangent properties. To illustrate the capability of the procedure, several benchmark problems employing finite element analyses are presented. These demonstrate the numerical efficiency and stability of the scheme. Additionally, the potential influence of complex creep histories on the buckling characteristics is considered.

Primary creep deformation behaviors related with lamellar interface in TiAl alloy

NASA Astrophysics Data System (ADS)

Cho, Han Seo; Nam, Soo Woo; Kim, Young-Won

1998-02-01

Constant tensile stress creep tests under the condition of 760 816°C/172 276 MPa in an air environment are conducted, and the microstructural evolution during primary creep deformation at the creep condition of 816°C/172 MPa was observed by transmission electron microscopy (TEM) for the lamellar structured Ti-45. 5Al-2Cr-2.6Nb-0.17W-0.lB-0.2C-0.15Si (at.%) alloy. The amount of creep strain deformed during primary creep stage is considered to be the summation of the strains occurred by gliding of initial dislocations and of newly generated dislocations. Creep rate controlling process within the primary stage seems to be shifting from the initial dislocation climb controlled to the generation of the new dislocations by the phase transformation of 2 to as creep strain increases.

Creep of Refractory Fibers and Modeling of Metal and Ceramic Matrix Composite Creep Behavior

NASA Technical Reports Server (NTRS)

Tewari, S.N.

1995-01-01

Our concentration during this research was on the following subprograms. (1) Ultra high vacuum creep tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires, temperature range from 1100 K to 1500 K, creep time of 1 to 500 hours. (2) High temperature vacuum tensile tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires. (3) Air and vacuum tensile creep tests on polycrystalline and single crystal alumina fibers, such as alumina-mullite Nextel fiber, yttrium aluminum ganet (YAG) and Saphikon, temperature range from 1150 K to 1470 K, creep time of 2 to 200 hours. (4) Microstructural evaluation of crept fibers, TEM study on the crept metal wires, SEM study on the fracture surface of ceramic fibers. (5) Metal Matrix Composite creep models, based on the fiber creep properties and fiber-matrix interface zone formation.

Recovery from nonlinear creep provides a window into physics of polymer glasses

NASA Astrophysics Data System (ADS)

Caruthers, James; Medvedev, Grigori

Creep under constant applied stress is one of the most basic mechanical experiments, where it exhibits extremely rich relaxation behavior for polymer glasses. As many as five distinct stages of nonlinear creep are observed, where the rate of creep dramatically slows down, accelerates and then slows down again. Modeling efforts to-date has primarily focused on predicting the intricacies of the nonlinear creep curve. We argue that as much attention should be paid to the creep recovery response, when the stress is removed. The experimental creep recovery curve is smooth, where the rate of recovery is initially quite rapid and then progressively decreases. In contrast, the majority of the traditional constitutive models predict recovery curves that are much too abrupt. A recently developed stochastic constitutive model that takes into account the dynamic heterogeneity of glasses produces a smooth creep recovery response that is consistent with experiment.

Tensile creep behavior of polycrystalline alumina fibers

NASA Technical Reports Server (NTRS)

Yun, H. M.; Goldsby, J. C.

1993-01-01

Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

Geometry and Material Constraint Effects on Creep Crack Growth Behavior in Welded Joints

NASA Astrophysics Data System (ADS)

Li, Y.; Wang, G. Z.; Xuan, F. Z.; Tu, S. T.

2017-02-01

In this work, the geometry and material constraint effects on creep crack growth (CCG) and behavior in welded joints were investigated. The CCG paths and rates of two kinds of specimen geometry (C(T) and M(T)) with initial cracks located at soft HAZ (heat-affected zone with lower creep strength) and different material mismatches were simulated. The effect of constraint on creep crack initiation (CCI) time was discussed. The results show that there exists interaction between geometry and material constraints in terms of their effects on CCG rate and CCI time of welded joints. Under the condition of low geometry constraint, the effect of material constraint on CCG rate and CCI time becomes more obvious. Higher material constraint can promote CCG due to the formation of higher stress triaxiality around crack tip. Higher geometry constraint can increase CCG rate and reduce CCI time of welded joints. Both geometry and material constraints should be considered in creep life assessment and design for high-temperature welded components.

Creep anomaly in electrospun fibers made of globular proteins

NASA Astrophysics Data System (ADS)

Regev, Omri; Arinstein, Arkadii; Zussman, Eyal

2013-12-01

The anomalous responses of electrospun nanofibers and film fabricated of unfolded bovine serum albumin (BSA) under constant stress (creep) is observed. In contrast to typical creep behavior of viscoelastic materials demonstrating (after immediate elastic response) a time-dependent elongation, in case of low applied stresses (<1 MPa) the immediate elastic response of BSA samples is followed by gradual contraction up to 2%. Under higher stresses (2-6 MPa) the contraction phase changes into elongation; and in case of stresses above 7 MPa only elongation was observed, with no initial contraction. The anomalous creep behavior was not observed when the BSA samples were subjected to additional creep cycles independently on the stress level. The above anomaly, which was not observed before either for viscoelastic solids or for polymers, is related to specific protein features, namely, to the ability to fold. We hypothesize that the phenomenon is caused by folding of BSA macromolecules into dry molten globule states, feasible after cross-linked bonds break up, resulting from the applied external force.

Mechanical behavior of high strength ceramic fibers at high temperatures

NASA Technical Reports Server (NTRS)

Tressler, R. E.; Pysher, D. J.

1991-01-01

The mechanical behavior of commercially available and developmental ceramic fibers, both oxide and nonoxide, has been experimentally studied at expected use temperatures. In addition, these properties have been compared to results from the literature. Tensile strengths were measured for three SiC-based and three oxide ceramic fibers for temperatures from 25 C to 1400 C. The SiC-based fibers were stronger but less stiff than the oxide fibers at room temperature and retained more of both strength and stiffness to high temperatures. Extensive creep and creep-rupture experiments have been performed on those fibers from this group which had the best strengths above 1200 C in both single filament tests and tests of fiber bundles. The creep rates for the oxides are on the order of two orders of magnitude faster than the polymer derived nonoxide fibers. The most creep resistant filaments available are single crystal c-axis sapphire filaments. Large diameter CVD fabricated SiC fibers are the most creep and rupture resistant nonoxide polycrystalline fibers tested to date.

Mechanical rejuvenation in bulk metallic glass induced by thermo-mechanical creep

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

Tong, Yang; Dmowski, W.; Bei, Hongbin

Using high energy X-ray diffraction we studied the temperature, stress, and time effect on structural changes in a Zr-based bulk metallic glass induced by thermo-mechanical creep. Pair distribution functions obtained from two-dimensional diffraction patterns show that thermo-mechanical creep induces structural disordering, but only when the stress beyond a threshold is applied. A similar threshold behavior was observed for anelastic strain. We conclude that anelastic creep strain induces rejuvenation, whereas plastic strain does not.

Creep-Rupture Data Analysis - Engineering Application of Regression Techniques. Ph.D. Thesis - North Carolina State Univ.

NASA Technical Reports Server (NTRS)

Rummler, D. R.

1976-01-01

The results are presented of investigations to apply regression techniques to the development of methodology for creep-rupture data analysis. Regression analysis techniques are applied to the explicit description of the creep behavior of materials for space shuttle thermal protection systems. A regression analysis technique is compared with five parametric methods for analyzing three simulated and twenty real data sets, and a computer program for the evaluation of creep-rupture data is presented.

Mechanical rejuvenation in bulk metallic glass induced by thermo-mechanical creep

DOE PAGES

Tong, Yang; Dmowski, W.; Bei, Hongbin; ...

2018-02-16

Using high energy X-ray diffraction we studied the temperature, stress, and time effect on structural changes in a Zr-based bulk metallic glass induced by thermo-mechanical creep. Pair distribution functions obtained from two-dimensional diffraction patterns show that thermo-mechanical creep induces structural disordering, but only when the stress beyond a threshold is applied. A similar threshold behavior was observed for anelastic strain. We conclude that anelastic creep strain induces rejuvenation, whereas plastic strain does not.

Continuous fiber-reinforced titanium aluminide composites

NASA Technical Reports Server (NTRS)

Mackay, R. A.; Brindley, P. K.; Froes, F. H.

1991-01-01

An account is given of the fabrication techniques, microstructural characteristics, and mechanical behavior of a lightweight, high service temperature SiC-reinforced alpha-2 Ti-14Al-21Nb intermetallic-matrix composite. Fabrication techniques under investigation to improve the low-temperature ductility and environmental resistance of this material system, while reducing manufacturing costs to competitive levels, encompass powder-cloth processing, foil-fiber-foil processing, and thermal-spray processing. Attention is given to composite microstructure problems associated with fiber distribution and fiber-matrix interfaces, as well as with mismatches of thermal-expansion coefficient; major improvements are noted to be required in tensile properties, thermal cycling effects, mechanical damage, creep, and environmental effects.

Aseismic creep along the North Anatolian Fault quantified by coupling microstructural strain and chemical analyses

NASA Astrophysics Data System (ADS)

Kaduri, Maor; Gratier, Jean-Pierre; Renard, François; Çakir, Ziyadin; Lasserre, Cécile

2017-04-01

In the last decade aseismic creep has been noted as one of the key processes along tectonic plate boundaries. It contributes to the energy budget during the seismic cycle, delaying or triggering the occurrence of large earthquakes. Several major continental active faults show spatial alternation of creeping and locked segments. A great challenge is to understand which parameters control the transition from seismic to aseismic deformation in fault zones, such as the lithology, the degree of deformation from damage rocks to gouge, and the stress driven fault architecture transformations at all scales. The present study focuses on the North Anatolian Fault (Turkey) and characterizes the mechanisms responsible for the partition between seismic and aseismic deformation. Strain values were calculated using various methods, e.g. Fry, R-φs from microstructural measurements in gouge and damage samples collected on more than 30 outcrops along the fault. Maps of mineral composition were reconstructed from microprobe measurements of gouge and damage rock microstructure, in order to calculate the relative mass changes due to stress driven processes during deformation. Strain values were extracted, in addition to the geometrical properties of grain orientation and size distribution. Our data cover subsamples in the damage zones that were protected from deformation and are reminiscent of the host rock microstructure and composition, and subsamples that were highly deformed and recorded both seismic and aseismic deformations. Increase of strain value is linked to the evolution of the orientation of the grains from random to sheared sub-parallel and may be related to various parameters: (1) relative mass transfer increase with increasing strain indicating how stress driven mass transfer processes control aseismic creep evolution with time; (2) measured strain is strongly related with the initial lithology and with the evolution of mineral composition: monomineralic rocks are stronger (less deformed) than polymineralic ones; (3) strain measurements allow to evaluate the cumulated geological displacement accommodated by aseismic creep and the relative ratio between seismic and aseismic displacement for each section of an active fault. These relations allow to quantify more accurately the aseismic creep processes and their evolution with time along the North Anatolian Fault which are controlled by a superposition of two kinds of mechanisms: (1) stress driven mass transfer (pressure solution and metamorphism) that control local and regional mass transfer and associated rheology evolution and (2) grain boundary sliding along weak mineral interfaces (initially weak minerals or more often transformed by deformation-related reactions).

Creep avalanches on San Andreas Fault and their underlying mechanism from 19 years of InSAR and seismicity

NASA Astrophysics Data System (ADS)

Khoshmanesh, M.; Shirzaei, M.

2017-12-01

Recent seismic and geodetic observations indicate that interseismic creep rate varies in both time and space. The spatial extent of creep determines the earthquake potential, while its temporal evolution, known as slow slip events (SSE), may trigger earthquakes. Although the conditions promoting fault creep are well-established, the mechanism for initiating self-sustaining and sometimes cyclic creep events is enigmatic. Here we investigate a time series of 19 years of surface deformation measured by radar interferometry between 1992 and 2011 along the Central San Andreas Fault (CSAF) to constrain the temporal evolution of creep. We show that the creep rate along the CSAF has a sporadic behavior, quantified with a Gumbel-like probability distribution characterized by longer tail toward the extreme positive rates, which is signature of burst-like creep dynamics. Defining creep avalanches as clusters of isolated creep with rates exceeding the shearing rate of tectonic plates, we investigate the statistical properties of their size and length. We show that, similar to the frequency-magnitude distribution of seismic events, the distribution of potency estimated for creep avalanches along the CSAF follows a power law, dictated by the distribution of their along-strike lengths. We further show that an ensemble of concurrent creep avalanches which aseismically rupture isolated fault compartments form the semi-periodic SSEs observed along the CSAF. Using a rate and state friction model, we show that normal stress is temporally variable on the fault, and support this using seismic observations. We propose that, through a self-sustaining fault-valve behavior, compaction induced elevation of pore pressure within hydraulically isolated fault compartments, and subsequent frictional dilation is the cause for the observed episodic SSEs. We further suggest that the 2004 Parkfield Mw6 earthquake may have been triggered by the SSE on adjacent creeping segment, which increased Coulomb failure stress up to 0.45 bar/yr. While creeping segments are suggested to act as barriers and arrest rupture, our study implies that SSEs on these zones may trigger seismic events on adjacent locked parts.

The effect of sheet processing on the microstructure, tensile, and creep behavior of INCONEL alloy 718

NASA Astrophysics Data System (ADS)

Boehlert, C. J.; Dickmann, D. S.; Eisinger, Ny. N. C.

2006-01-01

The grain size, grain boundary character distribution (GBCD), creep, and tensile behavior of INCONEL alloy 718 (IN 718) were characterized to identify processing-microstructure-property relationships. The alloy was sequentially cold rolled (CR) to 0, 10, 20, 30, 40, 60, and 80 pct followed by annealing at temperatures between 954 °C and 1050 °C and the traditional aging schedule used for this alloy. In addition, this alloy can be superplastically formed (IN 718SPF) to a significantly finer grain size and the corresponding microstructure and mechanical behavior were evaluated. The creep behavior was evaluated in the applied stress (σ a ) range of 300 to 758 MPa and the temperature range of 638 °C to 670 °C. Constant-load tensile creep experiments were used to measure the values of the steady-state creep rate and the consecutive load reduction method was used to determine the values of backstress (σ0). The values for the effective stress exponent and activation energy suggested that the transition between the rate-controlling creep mechanisms was dependent on effective stresses (σ e =σ a σ0) and the transition occurred at σ e ≅ 135 MPa. The 10 to 40 pct CR samples exhibited the greatest 650 °C strength, while IN 718SPF exhibited the greatest room-temperature (RT) tensile strength (>1550 MPa) and ductility (ɛ f >16 pct). After the 954 °C annealing treatment, the 20 pct CR and 30 pct CR microstructures exhibited the most attractive combination of elevated-temperature tensile and creep strength, while the most severely cold-rolled materials exhibited the poorest elevated-temperature properties. After the 1050 °C annealing treatment, the IN 718SPF material exhibited the greatest backstress and best creep resistance. Electron backscattered diffraction was performed to identify the GBCD as a function of CR and annealing. The data indicated that annealing above 1010 °C increased the grain size and resulted in a greater fraction of twin boundaries, which in turn increased the fraction of coincident site lattice boundaries. This result is discussed in light of the potential to grain boundary engineer this alloy.

Prediction and verification of creep behavior in metallic materials and components, for the space shuttle thermal protection system. Volume 1, phase 1: Cyclic materials creep predictions

NASA Technical Reports Server (NTRS)

Davis, J. W.; Cramer, B. A.

1974-01-01

Cyclic creep response was investigated and design methods applicable to thermal protection system structures were developed. The steady-state (constant temperature and load) and cyclic creep response characteristics of four alloys were studied. Steady-state creep data were gathered through a literature survey to establish reference data bases. These data bases were used to develop empirical equations describing creep as a function of time, temperature, and stress and as a basis of comparison for test data. Steady-state creep tests and tensile cyclic tests were conducted. The following factors were investigated: material thickness and rolling direction; material cyclic creep response under varying loads and temperatures; constant stress and temperature cycles representing flight conditions; changing stresses present in a creeping beam as a result of stress redistribution; and complex stress and temperature profiles representative of space shuttle orbiter trajectories. A computer program was written, applying creep hardening theories and empirical equations for creep, to aid in analysis of test data. Results are considered applicable to a variety of structures which are cyclicly exposed to creep producing thermal environments.

Creep Behavior of Passive Bovine Extraocular Muscle

PubMed Central

Yoo, Lawrence; Kim, Hansang; Shin, Andrew; Gupta, Vijay; Demer, Joseph L.

2011-01-01

This paper characterized bovine extraocular muscles (EOMs) using creep, which represents long-term stretching induced by a constant force. After preliminary optimization of testing conditions, 20 fresh EOM samples were subjected to four different loading rates of 1.67, 3.33, 8.33, and 16.67%/s, after which creep was observed for 1,500 s. A published quasilinear viscoelastic (QLV) relaxation function was transformed to a creep function that was compared with data. Repeatable creep was observed for each loading rate and was similar among all six anatomical EOMs. The mean creep coefficient after 1,500 seconds for a wide range of initial loading rates was at 1.37 ± 0.03 (standard deviation, SD). The creep function derived from the relaxation-based QLV model agreed with observed creep to within 2.7% following 16.67%/s ramp loading. Measured creep agrees closely with a derived QLV model of EOM relaxation, validating a previous QLV model for characterization of EOM biomechanics. PMID:22131809

Life Modeling and Design Analysis for Ceramic Matrix Composite Materials

NASA Technical Reports Server (NTRS)

2005-01-01

The primary research efforts focused on characterizing and modeling static failure, environmental durability, and creep-rupture behavior of two classes of ceramic matrix composites (CMC), silicon carbide fibers in a silicon carbide matrix (SiC/SiC) and carbon fibers in a silicon carbide matrix (C/SiC). An engineering life prediction model (Probabilistic Residual Strength model) has been developed specifically for CMCs. The model uses residual strength as the damage metric for evaluating remaining life and is posed probabilistically in order to account for the stochastic nature of the material s response. In support of the modeling effort, extensive testing of C/SiC in partial pressures of oxygen has been performed. This includes creep testing, tensile testing, half life and residual tensile strength testing. C/SiC is proposed for airframe and propulsion applications in advanced reusable launch vehicles. Figures 1 and 2 illustrate the models predictive capabilities as well as the manner in which experimental tests are being selected in such a manner as to ensure sufficient data is available to aid in model validation.

The high temperature creep behavior of oxides and oxide fibers

NASA Technical Reports Server (NTRS)

Jones, Linda E.; Tressler, Richard E.

1991-01-01

A thorough review of the literature was conducted on the high-temperature creep behavior of single and polycrystalline oxides which potentially could serve as fiber reinforcements in ceramics or metal matrix applications. Sapphire when oriented with the basal plane perpendicular to the fiber axis (c-axis oriented) is highly creep resistant at temperatures in excess of 1600 C and applied loads of 100 MPa and higher. Pyramidal slip is preferentially activated in sapphire under these conditions and steady-state creep rates in the range of 10(exp -7) to 10 (exp -8)/s were reported. Data on the creep resistance of polycrystalline beryllia suggest that C-axiz oriented single crystal beryllia may be a viable candidate as a fiber reinforcement material; however, the issure of fabricability and moisture sensitivity must be addressed for this material. Yttrium aluminum garnet (YAG) also appears to be a fiber candidate material having a high resistance to creep which is due to it's complex crystal structure and high Peierl resistance. The high creep resistance of garnet suggests that there may be other complex ternary oxides such as single crystal mullite which may also be candidate materials for fiber reinforcements. Finally, CVD and single crystal SiC, although not oxides, do possess a high resistance to creep in the temperature range between 1550 and 1850 C and under stresses of 110 to 220 MPa. From a review of the literature, it appears that for high creep resistant applications sapphire, silicon carbide, yttrium aluminum garnet, mullite, and beryllia are desirable candidate materials which require further investigation.

Mechanical Behavior of Low Porosity Carbonate Rock: From Brittle Creep to Ductile Creep.

NASA Astrophysics Data System (ADS)

Nicolas, A.; Fortin, J.; Gueguen, Y.

2014-12-01

Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this study, we focus on the mechanical behavior of a 14.7% porosity white Tavel (France) carbonate rock (>98% calcite). The samples were deformed in a triaxial cell at effective confining pressures ranging from 0 MPa to 85 MPa at room temperature and 70°C. Experiments were carried under dry and water saturated conditions in order to explore the role played by the pore fluids. Two types of experiments have been carried out: (1) a first series in order to investigate the rupture envelopes, and (2) a second series with creep experiments. During the experiments, elastic wave velocities (P and S) were measured to infer crack density evolution. Permeability was also measured during creep experiments. Our results show two different mechanical behaviors: (1) brittle behavior is observed at low confining pressures, whereas (2) ductile behavior is observed at higher confining pressures. During creep experiments, these two behaviors have a different signature in term of elastic wave velocities and permeability changes, due to two different mechanisms: development of micro-cracks at low confining pressures and competition between cracks and microplasticity at high confining pressure. The attached figure is a summary of 20 triaxial experiments performed on Tavel limestone under different conditions. Stress states C',C* and C*' and brittle strength are shown in the P-Q space: (a) 20°C and dry, (b) 20°C and water saturated samples, (c) 70°C dry and (d) summary of all the experiments. Three regimes of inelastic and failure modes are observed: brittle failure, shear-enhanced compaction and dilatant cataclastic flow.

Creep Behavior of Near-Stoichiometric Polycrystalline Binary NiAl

NASA Technical Reports Server (NTRS)

Raj, S. V.

2002-01-01

New and published constant load creep and constant engineering strain rate data on near-stoichiometric binary NiAl in the intermediate temperature range 700 to 1300 K are reviewed. Both normal and inverse primary creep curves are observed depending on stress and temperature. Other characteristics relating to creep of NiAl involving grain size, stress and temperature dependence are critically examined and discussed. At stresses below 25 MPa and temperatures above 1000 K, a new grain boundary sliding mechanism was observed with n approx. 2, Qc approx. 100 kJ/ mol and a grain size exponent of about 2. It is demonstrated that Coble creep and accommodated grain boundary sliding models fail to predict the experimental creep rates by several orders of magnitude.

Simulation of finite-strain inelastic phenomena governed by creep and plasticity

NASA Astrophysics Data System (ADS)

Li, Zhen; Bloomfield, Max O.; Oberai, Assad A.

2017-11-01

Inelastic mechanical behavior plays an important role in many applications in science and engineering. Phenomenologically, this behavior is often modeled as plasticity or creep. Plasticity is used to represent the rate-independent component of inelastic deformation and creep is used to represent the rate-dependent component. In several applications, especially those at elevated temperatures and stresses, these processes occur simultaneously. In order to model these process, we develop a rate-objective, finite-deformation constitutive model for plasticity and creep. The plastic component of this model is based on rate-independent J_2 plasticity, and the creep component is based on a thermally activated Norton model. We describe the implementation of this model within a finite element formulation, and present a radial return mapping algorithm for it. This approach reduces the additional complexity of modeling plasticity and creep, over thermoelasticity, to just solving one nonlinear scalar equation at each quadrature point. We implement this algorithm within a multiphysics finite element code and evaluate the consistent tangent through automatic differentiation. We verify and validate the implementation, apply it to modeling the evolution of stresses in the flip chip manufacturing process, and test its parallel strong-scaling performance.

A phenomenological creep model for nickel-base single crystal superalloys at intermediate temperatures

NASA Astrophysics Data System (ADS)

Gao, Siwen; Wollgramm, Philip; Eggeler, Gunther; Ma, Anxin; Schreuer, Jürgen; Hartmaier, Alexander

2018-07-01

For the purpose of good reproduction and prediction of creep deformation of nickel-base single crystal superalloys at intermediate temperatures, a phenomenological creep model is developed, which accounts for the typical γ/γ‧ microstructure and the individual thermally activated elementary deformation processes in different phases. The internal stresses from γ/γ‧ lattice mismatch and deformation heterogeneity are introduced through an efficient method. The strain hardening, the Orowan stress, the softening effect due to dislocation climb along γ/γ‧ interfaces and the formation of < 112> dislocation ribbons, and the Kear–Wilsdorf-lock effect as key factors in the main flow rules are formulated properly. By taking the cube slip in < 110> \\{100\\} slip systems and < 112> \\{111\\} twinning mechanisms into account, the creep behavior for [110] and [111] loading directions are well captured. Without specific interaction and evolution of dislocations, the simulations of this model achieve a good agreement with experimental creep results and reproduce temperature, stress and crystallographic orientation dependences. It can also be used as the constitutive relation at material points in finite element calculations with complex boundary conditions in various components of superalloys to predict creep behavior and local stress distributions.

Microstructural Evolution and Mechanical Properties of Ti-22Al-25Nb (At.%) Orthorhombic Alloy with Three Typical Microstructures

NASA Astrophysics Data System (ADS)

Wang, Wei; Zeng, Weidong; Liu, Yantao; Xie, Guoxin; Liang, Xiaobo

2018-01-01

Microstructural evolution, tensile and creep behavior of Ti-22Al-25Nb (at.%) orthorhombic alloy with three typical microstructures were investigated. The three typical microstructures were obtained by different solution and age treatment temperatures and analyzed by the BSE technique. The tensile strengths of the alloy at room temperature and 650 °C were investigated. The creep behaviors of the three typical microstructures were also studied at 650 °C/150 MPa for 100 h in air. The phase transformation mechanisms in creep deformation were also found. The experimental results showed that the formations of the three typical microstructures were decided by the isothermal forging and heat treatment. It was supposed that the high-temperature solution treatment might be dominant for the volume fraction and diameter of the equiaxed particles. While the double age treatment would lead to lamellar O phases. Due to grain refinement strengthening, the equiaxed microstructure presented the best tensile strength and ductility. The fully lamellar microstructure had the best creep resistance than that of other microstructures. In this paper, the phenomenon of creep-induced α 2 phase decomposition was occurred during creep deformation of the equiaxed microstructure.

Moving singularity creep crack growth analysis with the /Delta T/c and C/asterisk/ integrals. [path-independent vector and energy rate line integrals

NASA Technical Reports Server (NTRS)

Stonesifer, R. B.; Atluri, S. N.

1982-01-01

The physical meaning of (Delta T)c and its applicability to creep crack growth are reviewed. Numerical evaluation of (Delta T)c and C(asterisk) is discussed with results being given for compact specimen and strip geometries. A moving crack-tip singularity, creep crack growth simulation procedure is described and demonstrated. The results of several crack growth simulation analyses indicate that creep crack growth in 304 stainless steel occurs under essentially steady-state conditions. Based on this result, a simple methodology for predicting creep crack growth behavior is summarized.

Creep modeling for life evaluation and strengthening mechanism of tungsten alloyed 9-12% Cr steels

NASA Astrophysics Data System (ADS)

Park, Kyu-Seop; Bae, Dong-Sik; Lee, Sung-Keun; Lee, Goo-Hyun; Kim, Jung-Ho; Endo, Takao

2006-10-01

Recently, high strength tungsten (W) alloyed steels have been developed for use in power plants with higher steam conditions for environmental reasons as well as the improvement of thermal efficiency resulting in lower fuel costs. In order to establish a creep modeling of high strength martensitic steel and to understand the basic role of W in tungsten alloyed 9-12Cr steels, conventional martensitic steels (X20CrMoV121, X20CrMoWV121, and Mod9Cr-1Mo) and tungsten alloyed steels (NF616 and HCM12A) were employed for creep tests and creep behavior analyses by the Ω method. The proposed creep model, which takes into account both primary and tertiary creep, satisfactorily described the creep curves and accurately predicted creep life, as martensitic steel undergoes a relatively large amount of primary creep, up to nearly 30%, over its normal life. The tungsten alloyed steels exhibited a smaller minimum creep rate and a larger stress exponent compared to the conventional steels. In addition, in tungsten alloyed steel, the Ω value features strong stress dependence such that creep life is prolonged at lower stresses due to high Ω values. The importance of the Ω value from the standpoint of creep strengthening in primary and tertiary creep is discussed.

Creep Burst Testing of a Woven Inflatable Module

NASA Technical Reports Server (NTRS)

Selig, Molly M.; Valle, Gerard D.; James, George H.; Oliveras, Ovidio M.; Jones, Thomas C.; Doggett, William R.

2015-01-01

A woven Vectran inflatable module 88 inches in diameter and 10 feet long was tested at the NASA Johnson Space Center until failure from creep. The module was pressurized pneumatically to an internal pressure of 145 psig, and was held at pressure until burst. The external environment remained at standard atmospheric temperature and pressure. The module burst occurred after 49 minutes at the target pressure. The test article pressure and temperature were monitored, and video footage of the burst was captured at 60 FPS. Photogrammetry was used to obtain strain measurements of some of the webbing. Accelerometers on the test article measured the dynamic response. This paper discusses the test article, test setup, predictions, observations, photogrammetry technique and strain results, structural dynamics methods and quick-look results, and a comparison of the module level creep behavior to the strap level creep behavior.

Creep-rupture behavior of candidate Stirling engine alloys after long-term aging at 760 deg C in low-pressure hydrogen

NASA Technical Reports Server (NTRS)

Titran, R. H.

1984-01-01

Nine candidate Stirling automotive engine alloys were aged at 760 C for 3500 hr in low pressure hydrogen or argon to determine the resulting effects on mechanical behavior. Candidate heater head tube alloys were CG-27, W545, 12RN72, INCONEL-718, and HS-188 while candidate cast cylinder-regenerator housing alloys were SA-F11, CRM-6D, XF-818, and HS-31. Aging per se is detrimental to the creep rupture and tensile strengths of the iron base alloys. The presence of hydrogen does not significantly contribute to strength degradation. Based percent highway driving cycle; CG-27 has adequate 3500 hr - 870 C creep rupture strength and SA-Fll, CRM-6D, and XF-818 have adequate 3500 hr - 775 C creep rupture strength.

A Nonlinear Viscoelastic Model for Ceramics at High Temperatures

NASA Technical Reports Server (NTRS)

Powers, Lynn M.; Panoskaltsis, Vassilis P.; Gasparini, Dario A.; Choi, Sung R.

2002-01-01

High-temperature creep behavior of ceramics is characterized by nonlinear time-dependent responses, asymmetric behavior in tension and compression, and nucleation and coalescence of voids leading to creep rupture. Moreover, creep rupture experiments show considerable scatter or randomness in fatigue lives of nominally equal specimens. To capture the nonlinear, asymmetric time-dependent behavior, the standard linear viscoelastic solid model is modified. Nonlinearity and asymmetry are introduced in the volumetric components by using a nonlinear function similar to a hyperbolic sine function but modified to model asymmetry. The nonlinear viscoelastic model is implemented in an ABAQUS user material subroutine. To model the random formation and coalescence of voids, each element is assigned a failure strain sampled from a lognormal distribution. An element is deleted when its volumetric strain exceeds its failure strain. Element deletion has been implemented within ABAQUS. Temporal increases in strains produce a sequential loss of elements (a model for void nucleation and growth), which in turn leads to failure. Nonlinear viscoelastic model parameters are determined from uniaxial tensile and compressive creep experiments on silicon nitride. The model is then used to predict the deformation of four-point bending and ball-on-ring specimens. Simulation is used to predict statistical moments of creep rupture lives. Numerical simulation results compare well with results of experiments of four-point bending specimens. The analytical model is intended to be used to predict the creep rupture lives of ceramic parts in arbitrary stress conditions.

Effect of resin variables on the creep behavior of high density hardwood composite panels

Treesearch

R.C. Tang; Jianhua Pu; C.Y Hse

1993-01-01

The flexural creep behavior of oriented strandboards (OSB) fabricated with mixed high, density hardwood flakes was investigated. Three types of adhesives, liquid phenolic-formaldehyde (LPF), melamine modified urea-formaldehyde (MUF), and LPF (face)/MUF (core) were chosen in this investigation. The resin contents (RC) used were 3.5 percent and 5.0 percent. The flakes...

Contribution a la caracterisation des betons endommages par des methodes de l'acoustique non lineaire. Application a la reaction alcalis-silice

NASA Astrophysics Data System (ADS)

Kodjo, Apedovi

The aim of this thesis is to contribute to the non-destructive characterization of concrete materials damaged by alkali-silica reaction (ASR). For this purpose, some nonlinear characterization techniques have been developed, as well as a nonlinear resonance test device. In order to optimize the sensitivity of the test device, the excitation module and signal processing have been improved. The nonlinear tests were conducted on seven samples of concrete damaged by ASR, three samples of concrete damaged by heat, three concrete samples damaged mechanically and three sound concrete samples. Since, nonlinear behaviour of the material is often attribute to its micro-defects hysteretic behaviour, it was shown at first that concrete damaged by ASR exhibits an hysteresis behaviour. To conduct this study, an acoustoelastic test was set, and then nonlinear resonance test device was used for characterizing sound concrete and concrete damaged by ASR. It was shown that the nonlinear technique can be used for characterizing the material without knowing its initial state, and also for detecting early damage in the reactive material. Studies were also carried out on the effect of moisture regarding the nonlinear parameters; they allowed understanding the low values of nonlinear parameters measured on concrete samples that were kept in high moisture conditions. In order to find a specific characteristic of damage caused by ASR, the viscosity of ASR gel was used. An approach, based on static creep analysis, performed on the material, while applying the nonlinear resonance technique. The spring-damping model of Maxwell was used for the interpretation of the results. Then, the creep time was analysed on samples damaged by ASR. It appears that the ASR gel increases the creep time. Finally, the limitations of the nonlinear resonance technique for in situ application have been explained and a new applicable nonlinear technique was initiated. This technique use an external source such as a mass for making non-linearity behaviour in the material, while an ultrasound wave is investigating the medium. Keywords. Concrete, Alkali-silica reaction, Nonlinear acoustics, Nonlinearity, Hysteresis, Damage diagnostics.

Time-dependent brittle deformation at Mt. Etna volcano

NASA Astrophysics Data System (ADS)

Baud, Patrick; Heap, Michael; Meredith, Philip; Vinciguerra, Sergio; Bell, Andrew; Main, Ian

2010-05-01

Time-dependent weakening mechanisms, leading to slow fracturing, are likely to act during the build up to flank eruptions at Mt. Etna volcano and are potentially a primary control on pre-eruptive patterns of seismicity and deformation. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts a large water reservoir (Ogniben, 1966). The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as ‘brittle creep'. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short-term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data not only demonstrates that basalt creeps in the brittle regime but also that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Furthermore, stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations and inverse seismicity plots using our experimental AE data. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time-to-failure properties of the basaltic volcanic pile.

Power-law creep behavior of a semiflexible chain.

PubMed

Majumdar, Arnab; Suki, Béla; Rosenblatt, Noah; Alencar, Adriano M; Stamenović, Dimitrije

2008-10-01

Rheological properties of adherent cells are essential for their physiological functions, and microrheological measurements on living cells have shown that their viscoelastic responses follow a weak power law over a wide range of time scales. This power law is also influenced by mechanical prestress borne by the cytoskeleton, suggesting that cytoskeletal prestress determines the cell's viscoelasticity, but the biophysical origins of this behavior are largely unknown. We have recently developed a stochastic two-dimensional model of an elastically joined chain that links the power-law rheology to the prestress. Here we use a similar approach to study the creep response of a prestressed three-dimensional elastically jointed chain as a viscoelastic model of semiflexible polymers that comprise the prestressed cytoskeletal lattice. Using a Monte Carlo based algorithm, we show that numerical simulations of the chain's creep behavior closely correspond to the behavior observed experimentally in living cells. The power-law creep behavior results from a finite-speed propagation of free energy from the chain's end points toward the center of the chain in response to an externally applied stretching force. The property that links the power law to the prestress is the chain's stiffening with increasing prestress, which originates from entropic and enthalpic contributions. These results indicate that the essential features of cellular rheology can be explained by the viscoelastic behaviors of individual semiflexible polymers of the cytoskeleton.

Process compensated resonance testing modeling for damage evolution and uncertainty quantification

NASA Astrophysics Data System (ADS)

Biedermann, Eric; Heffernan, Julieanne; Mayes, Alexander; Gatewood, Garrett; Jauriqui, Leanne; Goodlet, Brent; Pollock, Tresa; Torbet, Chris; Aldrin, John C.; Mazdiyasni, Siamack

2017-02-01

Process Compensated Resonance Testing (PCRT) is a nondestructive evaluation (NDE) method based on the fundamentals of Resonant Ultrasound Spectroscopy (RUS). PCRT is used for material characterization, defect detection, process control and life monitoring of critical gas turbine engine and aircraft components. Forward modeling and model inversion for PCRT have the potential to greatly increase the method's material characterization capability while reducing its dependence on compiling a large population of physical resonance measurements. This paper presents progress on forward modeling studies for damage mechanisms and defects in common to structural materials for gas turbine engines. Finite element method (FEM) models of single crystal (SX) Ni-based superalloy Mar-M247 dog bones and Ti-6Al-4V cylindrical bars were created, and FEM modal analyses calculated the resonance frequencies for the samples in their baseline condition. Then the frequency effects of superalloy creep (high-temperature plastic deformation) and macroscopic texture (preferred crystallographic orientation of grains detrimental to fatigue properties) were evaluated. A PCRT sorting module for creep damage in Mar-M247 was trained with a virtual database made entirely of modeled design points. The sorting module demonstrated successful discrimination of design points with as little as 1% creep strain in the gauge section from a population of acceptable design points with a range of material and geometric variation. The resonance frequency effects of macro-scale texture in Ti-6Al-4V were quantified with forward models of cylinder samples. FEM-based model inversion was demonstrated for Mar-M247 bulk material properties and variations in crystallographic orientation. PCRT uncertainty quantification (UQ) was performed using Monte Carlo studies for Mar-M247 that quantified the overall uncertainty in resonance frequencies resulting from coupled variation in geometry, material properties, crystallographic orientation and creep damage. A model calibration process was also developed that evaluates inversion fitting to differences from a designated reference sample rather than absolute property values, yielding a reduction in fit error.

Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

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

Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

The research built upon a prior investigation to develop a unified constitutive model for design-­by-­analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-­fatigue and creep-­ratcheting tests were conducted on the nickel-­base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-­controlled cycling,more » are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-­fatigue and creep-­ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-­fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-­ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched application of the harmonic generation method to tubular mechanical test specimens and pipes for nondestructive evaluation. Tubular specimens and pipes act as waveguides, thus we applied the acoustic harmonic generation method to guided waves in both plates and shells. Magnetostrictive transducers were used to generate and receive guided wave modes in the shell sample and the received signals were processed to show the sensitivity of higher harmonic generation to microstructure evolution. Modeling was initiated to correlate higher harmonic generation with the microstructure that will lead to development of a life prediction model that is informed by the nonlinear acoustics measurements.« less

Finite Element Creep-Fatigue Analysis of a Welded Furnace Roll for Identifying Failure Root Cause

NASA Astrophysics Data System (ADS)

Yang, Y. P.; Mohr, W. C.

2015-11-01

Creep-fatigue induced failures are often observed in engineering components operating under high temperature and cyclic loading. Understanding the creep-fatigue damage process and identifying failure root cause are very important for preventing such failures and improving the lifetime of engineering components. Finite element analyses including a heat transfer analysis and a creep-fatigue analysis were conducted to model the cyclic thermal and mechanical process of a furnace roll in a continuous hot-dip coating line. Typically, the roll has a short life, <1 year, which has been a problem for a long time. The failure occurred in the weld joining an end bell to a roll shell and resulted in the complete 360° separation of the end bell from the roll shell. The heat transfer analysis was conducted to predict the temperature history of the roll by modeling heat convection from hot air inside the furnace. The creep-fatigue analysis was performed by inputting the predicted temperature history and applying mechanical loads. The analysis results showed that the failure was resulted from a creep-fatigue mechanism rather than a creep mechanism. The difference of material properties between the filler metal and the base metal is the root cause for the roll failure, which induces higher creep strain and stress in the interface between the weld and the HAZ.

Relationships between sliding behavior and internal geometry of laboratory fault zones and some creeping and locked strike-slip faults of California

USGS Publications Warehouse

Moore, Diane E.; Byerlee, J.

1992-01-01

Moore, D.E. and Byerlee, J., 1992. Relationships between sliding behavior and internal geometry of laboratory fault zones and some creeping and locked strike-slip faults of California. In: T. Mikumo, K. Aki, M. Ohnaka, L.J. Ruff and P.K.P. Spudich (Editors), Earthquake Source Physics and Earthquake Precursors. Tectonophysics, 211: 305-316. In order to relate fault geometries to sliding behavior, maps of recently active breaks within the Hayward fault of central California, which is characterized by fault creep, have been examined and compared to maps of the San Andreas fault. The patterns of recent breaks of the Hayward fault are consistent with those found within the creeping section of the San Andreas, and they appear to have plausible physical explanations in the findings of laboratory experiments. The distinguishing geometric features of the examined locked and creeping faults are: (1) P-type second-order traces predominate over R(Riedel)-type traces in creeping sections; and (2) R-type second-order traces make smaller angles to the local fault strike in creeping sections than they do in locked sections. Two different maps of the Hayward fault gave similar results, supporting the inference that the patterns identified are basic characteristics of the fault rather than artifacts of a particular mapping procedure. P shears predominate over R shears under laboratory conditions that allow dilation within the fault zone. In our own experiments, P-shear development was favored by the generation of excess pore-fluid pressures. We propose that creep in California faults also is the result of fluid overpressures that are maintained in a low-permeability gouge zone and that significantly lower effective stresses, thus helping to stabilize slip and producing high values of the ratio P/R. Small R-trace angles may also be an indicator of low effective stresses, but the evidence for this is not conclusive because other factors can also affect the size of the angles. ?? 1992.

A contribution to the modeling of metal plasticity and fracture: From continuum to discrete descriptions

NASA Astrophysics Data System (ADS)

Keralavarma, Shyam Mohan

The objective of this dissertation is to further the understanding of inelastic behavior in metallic materials. Despite the increasing use of polymeric composites in aircraft structures, high specific strength metals continue to be used in key components such as airframe, fuselage, wings, landing gear and hot engine parts. Design of metallic structures subjected to thermomechanical extremes in aerospace, automotive and nuclear applications requires consideration of the plasticity, creep and fracture behavior of these materials. Consideration of inelasticity and damage processes is also important in the design of metallic components used in functional applications such as thin films, flexible electronics and micro electro mechanical systems. Fracture mechanics has been largely successful in modeling damage and failure phenomena in a host of engineering materials. In the context of ductile metals, the Gurson void growth model remains one of the most successful and widely used models. However, some well documented limitations of the model in quantitative prediction of the fracture strains and failure modes at low triaxialities may be traceable to the limited representation of the damage microstructure in the model. In the first part of this dissertation, we develop an extended continuum model of void growth that takes into account details of the material microstructure such as the texture of the plastically deforming matrix and the evolution of the void shape. The need for such an extension is motivated by a detailed investigation of the effects of the two types of anisotropy on the materials' effective response using finite element analysis. The model is derived using the Hill--Mandel homogenization theory and an approximate limit analysis of a porous representative volume element. Comparisons with several numerical studies are presented towards a partial validation of the analytical model. Inelastic phenomena such as plasticity and creep result from the collective behavior of a large number of nano and micro scale defects such as dislocations, vacancies and grain boundaries. Continuum models relate macroscopically observable quantities such as stress and strain by coarse graining the discrete defect microstructure. While continuum models provide a good approximation for the effective behavior of bulk materials, several deviations have been observed in experiments at small scales such as an intrinsic size dependence of the material strength. Discrete dislocation dynamics (DD) is a mesoscale method for obtaining the mechanical response of a material by direct simulation of the motion and interactions of dislocations. The model incorporates an intrinsic length scale in the dislocation Burgers vector and potentially allows for size dependent mechanical behavior to emerge naturally from the dynamics of the dislocation ensemble. In the second part of this dissertation, a simplified twodimensional DD model is employed to study several phenomena of practical interest such as strain hardening under homogeneous deformation, growth of microvoids in a crystalline matrix and creep of single crystals at elevated temperatures. These studies have been enabled by several recent enhancements to the existing two-dimensional DD framework described in Chapter V. The main contributions from this research are: (i) development of a fully anisotropic continuum model of void growth for use in ductile fracture simulations and (ii) enhancing the capabilities of an existing two-dimensional DD framework for large scale simulations in complex domains and at elevated temperatures.

Plate-tectonic boundary formation by grain-damage and pinning

NASA Astrophysics Data System (ADS)

Bercovici, David

2015-04-01

Shear weakening in the lithosphere is an essential ingredient for understanding how and why plate tectonics is generated from mantle convection on terrestrial planets. I present continued work on a theoretical model for lithospheric shear-localization and plate generation through damage, grain evolution and Zener pinning in two-phase (polycrystalline) lithospheric rocks. Grain size evolves through the competition between coarsening, which drives grain-growth, with damage, which drives grain reduction. The interface between phases controls Zener pinning, which impedes grain growth. Damage to the interface enhances the Zener pinning effect, which then reduces grain-size, forcing the rheology into the grain-size-dependent diffusion creep regime. This process thus allows damage and rheological weakening to co-exist, providing a necessary shear-localizing feedback. Moreover, because pinning inhibits grain-growth it promotes shear-zone longevity and plate-boundary inheritance. This theory has been applied recently to the emergence of plate tectonics in the Archean by transient subduction and accumulation of plate boundaries over 1Gyr, as well as to rapid slab detachment and abrupt tectonic changes. New work explores the saturation of interface damage at low interface curvature (e.g., because it is associated with larger grains that take up more of the damage, and/or because interface area is reduced). This effect allows three possible equilibrium grain-sizes for a given stress; a small-grain-size high-shear state in diffusion creep, a large grain-size low shear state in dislocation creep, and an intermediate state (often near the deformation map phase-boundary). The low and high grain-size states are stable, while the intermediate one is unstable. This implies that a material deformed at a given stress can acquire two stable deformation regimes, a low- and high- shear state; these are indicative of plate-like flows, i.e, the coexistence of both slowly deforming plates and rapidly deforming plate boundaries.

Composite strengthening. [of nonferrous, fiber reinforced alloys

NASA Technical Reports Server (NTRS)

Stoloff, N. S.

1976-01-01

The mechanical behavior of unidirectionally reinforced metals is examined, with particular attention to fabrication techniques for artificial composites and eutectic alloys and to principles of fiber reinforcement. The properties of artificial composites are discussed in terms of strength of fiber composites, strength of ribbon-reinforced composites, crack initiation, crack propagation, and creep behavior. The properties of eutectic composites are examined relative to tensile strength, compressive strength, fracture, high-temperature strength, and fatigue. In the case of artificial composites, parallelism of fibers, good bonding between fibers and matrix, and freedom of fibers from damage are all necessary to ensure superior performance. For many eutectic systems there are stringent boundary conditions relative to melt purity and superheat, atmosphere control, temperature gradient, and growth rate in order to provide near-perfect alignment of the reinforcements with a minimum of growth defects.

Creep-rupture behavior of iron superalloys in high-pressure hydrogen

NASA Technical Reports Server (NTRS)

Bhattacharyya, S.; Peterman, W.

1984-01-01

The creep-rupture properties of five iron-base and one cobalt-base high temperature alloys were investigated to assess the feasibility of using the alloys as construction materials in a Stirling engine. The alloys were heat treated and hardness measurements were taken. Typical microstructures of the alloys are shown. The creep-rupture properties of the alloys were determined at 760 and 815 C in 15.0 MPa H2 for 200 to 1000 hours. Plots of rupture life versus stress for the six superalloys are presented along with creep strain-time plots.

Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system. Volume 3, phase 3: Full size heat shield data correlation and design criteria. [reentry

NASA Technical Reports Server (NTRS)

Cramer, B. A.; Davis, J. W.

1975-01-01

Analysis methods for predicting cyclic creep deflection in stiffened metal panel structures, were applied to full size panels. Results were compared with measured deflections from cyclic tests of thin gage L605, Rene' 41, and TDNiCr full size corrugation stiffened panels. A design criteria was then formulated for metallic thermal protection panels subjected to creep. A computer program was developed to calculate creep deflections.

A variational theorem for creep with applications to plates and columns

NASA Technical Reports Server (NTRS)

Sanders, J Lyell, Jr; Mccomb, Harvey G , Jr; Schlechte, Floyd R

1958-01-01

A variational theorem is presented for a body undergoing creep. Solutions to problems of the creep behavior of plates, columns, beams, and shells can be obtained by means of the direct methods of the calculus of variations in conjunction with the stated theorem. The application of the theorem is illustrated for plates and columns by the solution of two sample problems.

The Physical Mechanism of Frictional Aging Revealed by Nanoindentation Creep

NASA Astrophysics Data System (ADS)

Thom, C.; Carpick, R. W.; Goldsby, D. L.

2017-12-01

A classical observation from rock friction experiments is that friction increases linearly with the logarithm of the time of stationary contact, a phenomenon sometimes referred to as aging. Aging is most often attributed to an increase in the real area of contact due to asperity creep. However, recent atomic force microscopy (AFM) experiments and molecular dynamics simulations suggest that time-dependent siloxane (Si—O—Si) bonding gives rise to aging in silica-silica contacts in the absence of plastic deformation. Determining whether an increase in contact `quantity' (due to creep), contact `quality' (due to chemical bonding), or another unknown mechanism causes aging is a challenging experimental task, despite its importance for developing a physical basis for rate and state friction laws. An intriguing observation is that aging is absent in friction experiments on quartz rocks and gouge at humidities <5% and returns upon exposure of the test specimens to humid air. This behavior has been attributed to the effects of water on asperity creep (via hydrolytic weakening) or on the adhesive strength of contacts. To discern between these possibilities, we have conducted nanoindentation experiments on single crystals of quartz to measure their indentation hardness and creep behavior at humidities of 2% to 50%, and in vacuum. Samples were loaded at 1000 mN/s to a peak load of 15, 40, or 400 mN, which was then held constant for 10 s. After the peak load is reached, the tip sinks into the material with time due to creep of the indentation contact. Our experiments reveal that there is no effect of varying humidity on either indentation hardness or indentation creep behavior over the full range of humidities investigated. If asperity creep were the dominant mechanism of frictional aging for quartz in the experiments cited above, then significant increases in hardness and decreases in the growth rate of indentation contacts at low humidities is expected, in stark contrast with our nanoindentation data. Our experiments indicate that asperity creep cannot be the cause of aging in quartz rocks, and suggest that chemical bonding may instead be the dominant mechanism of frictional aging.

Comparative Analyses of Creep Models of a Solid Propellant

NASA Astrophysics Data System (ADS)

Zhang, J. B.; Lu, B. J.; Gong, S. F.; Zhao, S. P.

2018-05-01

The creep experiments of a solid propellant samples under five different stresses are carried out at 293.15 K and 323.15 K. In order to express the creep properties of this solid propellant, the viscoelastic model i.e. three Parameters solid, three Parameters fluid, four Parameters solid, four Parameters fluid and exponential model are involved. On the basis of the principle of least squares fitting, and different stress of all the parameters for the models, the nonlinear fitting procedure can be used to analyze the creep properties. The study shows that the four Parameters solid model can best express the behavior of creep properties of the propellant samples. However, the three Parameters solid and exponential model cannot very well reflect the initial value of the creep process, while the modified four Parameters models are found to agree well with the acceleration characteristics of the creep process.

Tensile and Compressive Constitutive Response of 316 Stainless Steel at Elevated Temperatures

NASA Technical Reports Server (NTRS)

Manson, S. S.; Muralidharan, U.; Halford, G. R.

1983-01-01

Creep rate in compression is lower by factors of 2 to 10 than in tension if the microstructure of the two specimens is the same and are tested at equal temperatures and equal but opposite stresses. Such behavior is characteristic for monotonic creep and conditions involving cyclic creep. In the latter case creep rate in both tension and compression progressively increases from cycle to cycle, rendering questionable the possibility of expressing a time stabilized constitutive relationship. The difference in creep rates in tension and compression is considerably reduced if the tension specimen is first subjected to cycles of tensile creep (reversed by compressive plasticity), while the compression specimen is first subjected to cycles of compressive creep (reversed by tensile plasticity). In both cases, the test temperature is the same and the stresses are equal and opposite. Such reduction is a reflection of differences in microstructure of the specimens resulting from different prior mechanical history.

Tensile and Creep Testing of Sanicro 25 Using Miniature Specimens

PubMed Central

Dymáček, Petr; Jarý, Milan; Dobeš, Ferdinand; Kloc, Luboš

2018-01-01

Tensile and creep properties of new austenitic steel Sanicro 25 at room temperature and operating temperature 700 °C were investigated by testing on miniature specimens. The results were correlated with testing on conventional specimens. Very good agreement of results was obtained, namely in yield and ultimate strength, as well as short-term creep properties. Although the creep rupture time was found to be systematically shorter and creep ductility lower in the miniature test, the minimum creep rates were comparable. The analysis of the fracture surfaces revealed similar ductile fracture morphology for both specimen geometries. One exception was found in a small area near the miniature specimen edge that was cut by electro discharge machining, where an influence of the steel fracture behavior at elevated temperature was identified. PMID:29337867

Development of Engineering Data on Advanced Composite Materials

DTIC Science & Technology

1982-02-01

otherwise as in any manner licensing the holder or any other person or corporation, or conveying any rights or permission to manufacture, use, or sell any...4.1 T300/V378A 138 4.5 HyE 1076J 168 4.6 G-160/6535-1 200 4.7 COMPARATIVE ENVIRONMENTAL BEHAVIOR 231 5 CONCLUSIONS 236 REFERENCES 240 APPENDICES A...Fiber Orientation 62 17 Tensile Creep Behavior of Unidirectional T300/AFRSOO Composite Laminates: 0* Fiber Orientation 64 18 Tensile Creep Behavior of

Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system

NASA Technical Reports Server (NTRS)

Davis, J. W.; Cramer, B. A.

1976-01-01

A method of analysis was developed for predicting permanent cyclic creep deflections in stiffened panel structures. This method uses creep equations based on cyclic tensile creep tests and a computer program to predict panel deflections as a function of mission cycle. Four materials were investigated - a titanium alloy (Ti-6Al-4V), a cobalt alloy (L605), and two nickel alloys (Rene'41 and TDNiCr). Steady-state and cyclic creep response data were obtained by testing tensile specimens fabricated from thin gage sheet (0.025 and 0.63 cm nominal). Steady-state and cyclic creep equations were developed which describe creep as a function of time, temperature and load. Tests were also performed on subsize (6.35 x 30.5 cm) rib and corrugation stiffened panels. These tests were used to correlate creep responses between elemental specimens and panels. The panel response was analyzed by use of a specially written computer program.

Creep and dynamic viscoelastic behavior of endodontic fiber-reinforced composite posts.

PubMed

Papadogiannis, D; Lakes, R S; Palaghias, G; Papadogiannis, Y

2009-10-01

Fiber-reinforced composite (FRC) posts have gained much interest recently and understanding of their viscoelastic properties is important as they can be used in stress-bearing posterior restorations. The aim of this study was to evaluate the creep behavior and the viscoelastic properties of four commercial FRC posts under different temperatures and different storage conditions. The FRC posts tested were Glassix, C-Post, Carbonite and Snowlight. For the creep measurements a constant load below the proportional limit of the posts was applied and the angular deformation of the specimens was recorded. The viscoelastic parameters were determined by using dynamic torsional loading under four different conditions. All materials were susceptible to creep and exhibited linear viscoelastic behavior. Residual strain was observed in all FRC posts. The viscoelastic properties were affected by the increase of temperature and water storage (p<0.001) resulting in their decline. Carbon fiber posts exhibited better performance than glass fiber posts. FRC posts exhibit permanent strains under regular masticatory stresses that can be generated in the oral cavity. Their properties are susceptible to changes in temperature, while direct contact with water also affects them deleteriously.

Investigation on the Flexural Creep Stiffness Behavior of PC-ABS Material Processed by Fused Deposition Modeling Using Response Surface Definitive Screening Design

NASA Astrophysics Data System (ADS)

Mohamed, Omar Ahmed; Masood, Syed Hasan; Bhowmik, Jahar Lal

2017-03-01

The resistance of polymeric materials to time-dependent plastic deformation is an important requirement of the fused deposition modeling (FDM) design process, its processed products, and their application for long-term loading, durability, and reliability. The creep performance of the material and part processed by FDM is the fundamental criterion for many applications with strict dimensional stability requirements, including medical implants, electrical and electronic products, and various automotive applications. Herein, the effect of FDM fabrication conditions on the flexural creep stiffness behavior of polycarbonate-acrylonitrile-butadiene-styrene processed parts was investigated. A relatively new class of experimental design called "definitive screening design" was adopted for this investigation. The effects of process variables on flexural creep stiffness behavior were monitored, and the best suited quadratic polynomial model with high coefficient of determination ( R 2) value was developed. This study highlights the value of response surface definitive screening design in optimizing properties for the products and materials, and it demonstrates its role and potential application in material processing and additive manufacturing.

Creep behavior of sweetgum OSB: effect of load level and relative humidity

Treesearch

J.H. Pu; R.C. Tang; Chung-Yun Hse

1994-01-01

Flexural creep behavior of laboratory-fabricated sweetgum oriented strandboard (OSB). under constnat (65% and 95%) and cyclic (65% 95% at a 96-hr. frequency) relative humidity (RH) conditions at 75 F (23.9 C) is presented. Two levels (4.5% and 6.5%) of resin content (RC) of phenol-formaldehyde were used in fabricating the test panels. Two load levels (20% and...

Experimental Plan for EDF Energy Creep Rabbit Graphite Irradiations- Rev. 2 (replaces Rev. 0 ORNL/TM/2013/49).

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

Burchell, Timothy D

2014-07-01

The experimental results obtained here will assist in the development and validation of future models of irradiation induced creep of graphite by providing the following data: Inert creep stain data from low to lifetime AGR fluence Inert creep-property data (especially CTE) from low to lifetime AGR fluence Effect of oxidation on creep modulus (by indirect comparison with experiment 1 and direct comparison with experiment 3 NB. Experiment 1 and 3 are not covered here) Data to develop a mechanistic understanding, including oAppropriate creep modulus (including pinning and high dose effects on structure) oInvestigation of CTE-creep strain behavior under inert conditionsmore » oInformation on the effect of applied stress/creep strain on crystallite orientation (requires XRD) oEffect of creep strain on micro-porosity (requires tomography & microscopy) This document describes the experimental work planned to meet the requirements of project technical specification [1] and EDF Energy requests for additional Pre-IE work. The PIE work is described in detail in this revision (Section 8 and 9).« less

Interactions between creep, fatigue and strain aging in two refractory alloys

NASA Technical Reports Server (NTRS)

Sheffler, K. D.

1972-01-01

The application of low-amplitude, high-frequency fatigue vibrations during creep testing of two strain-aging refractory alloys (molybdenum-base TZC and tantalum-base T-111) significantly reduced the creep strength of these materials. This strength reduction caused dramatic increases in both the first stage creep strain and the second stage creep rate. The magnitude of the creep rate acceleration varied directly with both frequency and A ratio (ratio of alternating to mean stress), and also varied with temperature, being greatest in the range where the strain-aging phenomenon was most prominent. It was concluded that the creep rate acceleration resulted from a negative strain rate sensitivity which is associated with the strain aging phenomenon in these materials. (A negative rate sensitivity causes flow stress to decrease with increasing strain rate, instead of increasing as in normal materials). By combining two analytical expressions which are normally used to describe creep and strain aging behavior, an expression was developed which correctly described the influence of temperature, frequency, and A ratio on the TZC creep rate acceleration.

The effect of solute additions on the steady-state creep behavior of dispersion-strengthened aluminum.

NASA Technical Reports Server (NTRS)

Reynolds, G. H.; Lenel, F. V.; Ansell, G. S.

1971-01-01

The effect of solute additions on the steady-state creep behavior of coarse-grained dispersion-strengthened aluminum alloys was studied. Recrystallized dispersion-strengthened solid solutions were found to have stress and temperature sensitivities quite unlike those observed in single-phase solid solutions having the same composition and grain size. The addition of magnesium or copper to the matrix of a recrystallized dispersion-strengthened aluminum causes a decrease in the steady-state creep rate which is much smaller than that caused by similar amounts of solute in single-phase solid solutions. All alloys exhibited essentially a 4.0 power stress exponent in agreement with the model of Ansell and Weertman. The activation energy for steady-state creep in dispersion-strengthened Al-Mg alloys, as well as the stress dependence, was in agreement with the physical model of dislocation climb over the dispersed particles.

1300 K Creep Behavior of [001] Oriented Ni-49Al-1Hf (at.%) Single Crystals

NASA Technical Reports Server (NTRS)

Whittenberger, J. Daniel; Locci, I. E.; Darolia, Ram; Bowman, R.

1999-01-01

A study of the 1300 K compressive and tensile creep properties of [001]-oriented NiAl-1Hf (D209) single crystals has been undertaken. Neither post homogenization cooling treatment, minor chemical variations within an ingot or from ingot-to-ingot, nor testing procedure had a significant effect on mechanical behavior; however a heat treatment which dissolved the initial G-phase precipitates and promoted formation of Heusler particles led to a strength reduction. Little primary creep was found utilizing direct measurement of strain, and a misorientation of 18 deg from the [001] did not reduce the creep strength. The effects of heat treatments on properties and a comparison of the flow stress-strain rate data to those predicted by the Jaswon-Cottrell solid solution hardening model indicate that the 1300 K strength in NiAl-1Hf single crystals is mainly due to precipitation hardening mechanisms.

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

Chen, Tianyi; Tan, Lizhen; Lu, Zizhe

Instrumented nanoindentation was used in this paper to investigate the hardness, elastic modulus, and creep behavior of an austenitic Fe-20Cr-25Ni model alloy at room temperature, with the indented grain orientation being the variant. The samples indented close to the {111} surfaces exhibited the highest hardness and modulus. However, nanoindentation creep tests showed the greatest tendency for creep in the {111} indented samples, compared with the samples indented close to the {001} and {101} surfaces. Scanning electron microscopy and cross-sectional transmission electron microscopy revealed slip bands and dislocations in all samples. The slip band patterns on the indented surfaces were influencedmore » by the grain orientations. Deformation twinning was observed only under the {001} indented surfaces. Finally, microstructural analysis and molecular dynamics modeling correlated the anisotropic nanoindentation-creep behavior with the different dislocation substructures formed during indentation, which resulted from the dislocation reactions of certain active slip systems that are determined by the indented grain orientations.« less

Effect of fiber-matrix adhesion on the creep behavior of CF/PPS composites: temperature and physical aging characterization

NASA Astrophysics Data System (ADS)

Motta Dias, M. H.; Jansen, K. M. B.; Luinge, J. W.; Bersee, H. E. N.; Benedictus, R.

2016-06-01

The influence of fiber-matrix adhesion on the linear viscoelastic creep behavior of `as received' and `surface modified' carbon fibers (AR-CF and SM-CF, respectively) reinforced polyphenylene sulfide (PPS) composite materials was investigated. Short-term tensile creep tests were performed on ±45° specimens under six different isothermal conditions, 40, 50, 60, 65, 70 and 75 °C. Physical aging effects were evaluated on both systems using the short-term test method established by Struik. The results showed that the shapes of the curves were affected neither by physical aging nor by the test temperature, allowing then superposition to be made. A unified model was proposed with a single physical aging and temperature-dependent shift factor, a_{T,te}. It was suggested that the surface treatment carried out in SM-CF/PPS had two major effects on the creep response of CF/PPS composites at a reference temperature of 40 °C: a lowering of the initial compliance of about 25 % and a slowing down of the creep response of about 1.1 decade.

Modeling Long-term Creep Performance for Welded Nickel-base Superalloy Structures for Power Generation Systems

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

Shen, Chen

2015-01-01

We report here a constitutive model for predicting long-term creep strain evolution in’ strengthened Ni-base superalloys. Dislocation climb-bypassing’, typical in intermediate’ volume fraction (~20%) alloys, is considered as the primary deformation mechanism. Dislocation shearing’ to anti-phase boundary (APB) faults and diffusional creep are also considered for high-stress and high-temperature low-stress conditions, respectively. Additional damage mechanism is taken into account for rapid increase in tertiary creep strain. The model has been applied to Alloy 282, and calibrated in a temperature range of 1375-1450°F, and stress range of 15-45ksi. The model parameters and a MATLAB code are provided. This report is preparedmore » by Monica Soare and Chen Shen at GE Global Research. Technical discussions with Dr. Vito Cedro are greatly appreciated. This work was supported by DOE program DE-FE0005859« less

The creep and intergranular cracking behavior of Ni-Cr-Fe-C alloys in 360{degree}C water

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

Angeliu, T.M.; Paraventi, D.J.; Was, G.S.

1995-09-01

Mechanical testing of controlled-purity Ni-xCr-9Fe-yC alloys at 360 C revealed an environmental enhancement in IG cracking and time-dependent deformation in high purity and primary water over that exhibited in argon. Dimples on the IG facets indicate a creep void nucleation and growth failure mode. IG cracking was primarily located at the interior of the specimen and not necessarily linked to direct contact with the environment. Controlled potential CERT experiments showed increases in IG cracking as the applied potential decreased, suggesting that hydrogen is detrimental to the mechanical properties. It is proposed that the environment, through the presence of hydrogen, enhancesmore » IG cracking by enhancing the matrix dislocation mobility. This is based on observations that dislocation-controlled creep controls the IG cracking of controlled-purity Ni-xCr-9Fe-yC in argon at 360 C and grain boundary cavitation and sliding results that show the environmental enhancement of the creep rate is primarily due to an increase in matrix plastic deformation. However, controlled potential CLT experiments did not exhibit a change in the creep rate as the applied potential decreased. While this does not clearly support hydrogen assisted creep, the material may already be saturated with hydrogen at these applied potentials and thus no effect was realized. Chromium and carbon decrease the IG cracking in high purity and primary water by increasing the creep resistance. The surface film does not play a significant role in the creep or IG cracking behavior under the conditions investigated.« less

Creep and intergranular cracking behavior of nickel-chromium-iron-carbon alloys in 360 C water

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

Angeliu, T.M.; Paraventi, D.J.; Was, G.S.

1995-11-01

Mechanical testing of controlled-purity Ni-x% Cr-9% Fe-y% C alloys at 360 C revealed an environmental enhancement in intergranular (IG) cracking and time-dependent deformation in high-purity (HP) and primary water (PW) over that exhibited in argon. Dimples on the IG facets indicated a creep void nucleation and growth failure mode. IG cracking was located primarily in the interior of the specimen and was not necessarily linked to the environment. Controlled-potential constant extension rate tensile (CERT) experiments showed increases in IG cracking as the applied potential decreased, suggesting that hydrogen was detrimental to the mechanical properties. It was proposed that the environment,more » through the presence of hydrogen, enhanced IG cracking by enhancing the matrix dislocation mobility. This conclusion was based on observations that dislocation creep controlled IG cracking of controlled-purity Ni-x% Cr-9% Fe-y% C in argon at 360 C. Grain-boundary cavitation (GBC) and sliding (GBS) results showed environmental enhancement of the creep rate primarily resulted from an increase in matrix plastic deformation. However, controlled-potential constant load tensile (CLT) experiments did not indicate a change in the creep rate as the applied potential decreased. While this result did not support hydrogen-assisted creep, the material already may have been saturated with hydrogen at these applied potentials, and thus, no effect was realized. Chromium and carbon decreased IG cracking in HP and PW by increasing the creep resistance. The surface film did not play a significant role in the creep or IG cracking behavior under the conditions investigated.« less

Cyclic Deformation, Damage, and Effects of Environment in the Ni3Al Ordered Alloy at Elevated Temperature

DTIC Science & Technology

1991-03-29

restricts atomic mobility leading to slower diffusion and perhaps better creep resistance. Ordered intermetallics such as aluminides and silicides are...evaluation of the mechanical properties of these materials (specifically creep , oxidation and fatigue) must be evaluated before implementation in...rate by an order of magnitude (frcm 0.001/s to 0.01/s) doubled the fatigue life at a given plastic strain range. When tested in vacuum environments

Creep Behavior of High-Strength Concrete Subjected to Elevated Temperatures.

PubMed

Yoon, Minho; Kim, Gyuyong; Kim, Youngsun; Lee, Taegyu; Choe, Gyeongcheol; Hwang, Euichul; Nam, Jeongsoo

2017-07-11

Strain is generated in concrete subjected to elevated temperatures owing to the influence of factors such as thermal expansion and design load. Such strains resulting from elevated temperatures and load can significantly influence the stability of a structure during and after a fire. In addition, the lower the water-to-binder (W-B) ratio and the smaller the quantity of aggregates in high-strength concrete, the more likely it is for unstable strain to occur. Hence, in this study, the compressive strength, elastic modulus, and creep behavior were evaluated at target temperatures of 100, 200, 300, 500, and 800 °C for high-strength concretes with W-B ratios of 30%, 26%, and 23%. The loading conditions were set as non-loading and 0.33f cu . It was found that as the compressive strength of the concrete increased, the mechanical characteristics deteriorated and transient creep increased. Furthermore, when the point at which creep strain occurred at elevated temperatures after the occurrence of transient creep was considered, greater shrinkage strain occurred as the compressive strength of the concrete increased. At a heating temperature of 800 °C, the 80 and 100 MPa test specimens showed creep failure within a shrinkage strain range similar to the strain at the maximum load.

Creep Behavior of High-Strength Concrete Subjected to Elevated Temperatures

PubMed Central

Yoon, Minho; Kim, Gyuyong; Kim, Youngsun; Lee, Taegyu; Choe, Gyeongcheol; Hwang, Euichul; Nam, Jeongsoo

2017-01-01

Strain is generated in concrete subjected to elevated temperatures owing to the influence of factors such as thermal expansion and design load. Such strains resulting from elevated temperatures and load can significantly influence the stability of a structure during and after a fire. In addition, the lower the water-to-binder (W–B) ratio and the smaller the quantity of aggregates in high-strength concrete, the more likely it is for unstable strain to occur. Hence, in this study, the compressive strength, elastic modulus, and creep behavior were evaluated at target temperatures of 100, 200, 300, 500, and 800 °C for high-strength concretes with W–B ratios of 30%, 26%, and 23%. The loading conditions were set as non-loading and 0.33fcu. It was found that as the compressive strength of the concrete increased, the mechanical characteristics deteriorated and transient creep increased. Furthermore, when the point at which creep strain occurred at elevated temperatures after the occurrence of transient creep was considered, greater shrinkage strain occurred as the compressive strength of the concrete increased. At a heating temperature of 800 °C, the 80 and 100 MPa test specimens showed creep failure within a shrinkage strain range similar to the strain at the maximum load. PMID:28773144

Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part I; Isothermal Creep

NASA Technical Reports Server (NTRS)

Raj, S. V.; Noebe, R. D.

2013-01-01

This two-part paper is the first published report on the long term, low temperature creep of hot-extruded near-stoichiometric NiTi. Constant load tensile creep tests were conducted on hot-extruded near-stoichiometric NiTi at 300, 373 and 473 K under initial applied stresses varying between 200 and 350 MPa as long as 15 months. These temperatures corresponded to the martensitic, two-phase and austenitic phase regions, respectively. Normal primary creep lasting several months was observed under all conditions indicating dislocation activity. Although steady-state creep was not observed under these conditions, the estimated creep rates varied between 10(exp -10) and 10(exp -9)/s. The creep behavior of the two phases showed significant differences. The martensitic phase exhibited a large strain on loading followed by a primary creep region accumulating a small amount of strain over a period of several months. The loading strain was attributed to the detwinning of the martensitic phase whereas the subsequent strain accumulation was attributed to dislocation glide-controlled creep. An "incubation period" was observed before the occurrence of detwinning. In contrast, the austenitic phase exhibited a relatively smaller loading strain followed by a primary creep region, where the creep strain continued to increase over several months. It is concluded that the creep of the austenitic phase occurs by a dislocation glide-controlled creep mechanism as well as by the nucleation and growth of deformation twins.

Flexural creep behavior of epoxy/cotton composite materials before and after saline absorption for orthopedics applications

NASA Astrophysics Data System (ADS)

Kontaxis, L. C.; Georgali, A.; Portan, D. V.; Papanicolaou, G. C.

2018-02-01

In the present study, epoxy resin-non-woven cotton fibers fabric composite plates were manufactured by using the vacuum infusion technique. Next, flexural creep-recovery experiments were performed in order to study the viscoelastic behavior of both the neat resin and the composite material manufactured under both dry and wet conditions. A low cost, mechanically operated flexural creep testing machine was designed and manufactured according to ASTM standards, for providing an economical means of performing flexural creep experiments. Initially, specimens were immersed in physiological saline for different periods of time at constant temperature of 37°C and subsequently tested under flexural creep conditions in order to study the effect of saline absorption on the creep-recovery behavior of the composites. The specific environmental conditions were chosen such as to simulate the real conditions existed into the human body. The combined effect of applied stress, time of immersion, creep time and amount of saline absorbed on the overall flexural viscoelastic behavior of composites was studied. The maximum amount of saline absorbed by the composites was 3.2%, which is double the saline intake of pure resin. It is believed that the 1.5% extra saline was absorbed into the now formed interphase between the matrix and the hydrophobic cotton fibers. It was observed that the creep strain increases as the immersion time increases. This is believed to occur because of the cumulative effect of absorbed saline from the fibers, the matrix, as well as from the fiber-matrix interphase resulting in the fiber matrix debonding and easier relaxation of the macromolecules at higher moisture contents leading to larger deformations at longer times. However, it should be noted that the strain levels of the epoxy resin/cotton fibers fabric composites, never surpassed those of the pure resin, indicating that the fabric successfully reinforces the composite even under the immersion of the latter in saline. Finally, experimental results were fitted using Burger's model and a detailed analysis of the model and the variation of the four characteristic parameters describing the model with time of immersion is given. Several interesting results were derived which are useful for the future application of the cotton - epoxy composites in medical applications such as in orthopedics.

Biomechanical study using fuzzy systems to quantify collagen fiber recruitment and predict creep of the rabbit medial collateral ligament.

PubMed

Ali, A F; Taha, M M Reda; Thornton, G M; Shrive, N G; Frank, C B

2005-06-01

In normal daily activities, ligaments are subjected to repeated loads, and respond to this environment with creep and fatigue. While progressive recruitment of the collagen fibers is responsible for the toe region of the ligament stress-strain curve, recruitment also represents an elegant feature to help ligaments resist creep. The use of artificial intelligence techniques in computational modeling allows a large number of parameters and their interactions to be incorporated beyond the capacity of classical mathematical models. The objective of the work described here is to demonstrate a tool for modeling creep of the rabbit medial collateral ligament that can incorporate the different parameters while quantifying the effect of collagen fiber recruitment during creep. An intelligent algorithm was developed to predict ligament creep. The modeling is performed in two steps: first, the ill-defined fiber recruitment is quantified using the fuzzy logic. Second, this fiber recruitment is incorporated along with creep stress and creep time to model creep using an adaptive neurofuzzy inference system. The model was trained and tested using an experimental database including creep tests and crimp image analysis. The model confirms that quantification of fiber recruitment is important for accurate prediction of ligament creep behavior at physiological loads.

Studies on Creep Deformation and Rupture Behavior of 316LN SS Multi-Pass Weld Joints Fabricated with Two Different Electrode Sizes

NASA Astrophysics Data System (ADS)

Vijayanand, V. D.; Kumar, J. Ganesh; Parida, P. K.; Ganesan, V.; Laha, K.

2017-02-01

Effect of electrode size on creep deformation and rupture behavior has been assessed by carrying out creep tests at 923 K (650 °C) over the stress range 140 to 225 MPa on 316LN stainless steel weld joints fabricated employing 2.5 and 4 mm diameter electrodes. The multi-pass welding technique not only changes the morphology of delta ferrite from vermicular to globular in the previous weld bead region near to the weld bead interface, but also subjects the region to thermo-mechanical heat treatment to generate appreciable strength gradient. Electron backscatter diffraction analysis revealed significant localized strain gradients in regions adjoining the weld pass interface for the joint fabricated with large electrode size. Larger electrode diameter joint exhibited higher creep rupture strength than the smaller diameter electrode joint. However, both the joints had lower creep rupture strength than the base metal. Failure in the joints was associated with microstructural instability in the fusion zone, and the vermicular delta ferrite zone was more prone to creep cavitation. Larger electrode diameter joint was found to be more resistant to failure caused by creep cavitation than the smaller diameter electrode joint. This has been attributed to the larger strength gradient between the beads and significant separation between the cavity prone vermicular delta ferrite zones which hindered the cavity growth. Close proximity of cavitated zones in smaller electrode joint facilitated their faster coalescence leading to more reduction in creep rupture strength. Failure location in the joints was found to depend on the electrode size and applied stress. The change in failure location has been assessed on performing finite element analysis of stress distribution across the joint on incorporating tensile and creep strengths of different constituents of joints, estimated by ball indentation and impression creep testing techniques.

Creep Properties of the As-Cast Al-A319 Alloy: T4 and T7 Heat Treatment Effects

NASA Astrophysics Data System (ADS)

Erfanian-Naziftoosi, Hamid R.; Rincón, Ernesto J.; López, Hugo F.

2016-08-01

In this work, the creep behavior of a commercial Al-A319 alloy was investigated in the temperature range of 413 K to 533 K (140 °C to 260 °C). Tensile creep specimens in the as-cast condition and after heat treating by solid solution (T4) and by aging (T7) were tested in a stress range varying from 60 to 170 MPa. It was found that steady-state creep strain rate was significantly low in the T7 condition when compared with either the T4 or as-cast alloy conditions. As a result, the time to failure behavior considerably increased. The experimentally determined creep exponents measured from the stress-strain curves were 4 for the as-cast alloy, 7.5 in the solid solution, and 9.5 after aging. In particular, after solid solution a grain substructure was found to develop which indicated that creep in a constant subgrain structure was active, thus accounting for the n exponent of 7.5. In the aged condition, a stress threshold is considered to account for the power law creep exponent n of 9.5. Moreover, It was found that the creep activation energy values were rather similar for the alloys in the as-cast (134 kJ/mol) and T4 (146 kJ/mol) conditions. These values are close to the one corresponding to pure Al self-diffusion (143 kJ/mol). In the aged alloy, the apparent creep activation energy (202 kJ/mol) exceeded that corresponding to Al self-diffusion. This deviation in activation energy is attributed to the effect of temperature on the alloy elastic modulus. Microstructural observations using transmission electron microscopy provided further support for the various dislocation-microstructure interactions exhibited by the alloy under the investigated creep conditions and implemented heat treatments.

Creep behavior of sweetgum OSB: Effect of load level and relative humidity

Treesearch

J.H. Pu; R.C. Tang; Chung-Yun Hse

1994-01-01

flexural creep behavior of laboratory-fabricated sweetgum oriented strandboard (0SB), under constant (65% and 95%) and cyclic (65% ↔ 95% at a 96-hr. frequency) relative humidity (RH) conditions at 75°F(23.9°C) is presented. Two levels (4.5% and 6.5%) of resin content (RC) of phenol-formaldehyde were used in fabricating the test panels. Two load levels (20%...

Alloying effect on the room temperature creep characteristics of a Ti-Zr-Be bulk metallic glass

NASA Astrophysics Data System (ADS)

Gong, Pan; Wang, Sibo; Li, Fangwei; Wang, Xinyun

2018-02-01

The effect of alloying elements (e.g. Fe, Al, and Ni) on the room temperature creep behavior of a lightweight Ti41Zr25Be34 bulk metallic glass (BMG) was investigated via nanoindentation tests. The generalized Kelvin model was adopted to describe the creep curves. The strain rate sensitivity m has been derived as a measure of the creep resistance. The compliance spectrum and retardation spectrum were also derived. The results show that the creep resistance of Ti41Zr25Be34 alloy can be obviously improved with the addition of alloying elements, and the most effective element is found to be Al. The mechanism for enhancing the creep resistance was discussed in terms of the scale variation of the shear transformation zone induced by alloying.

Oscillatory rheology and creep behavior of barley β-D-glucan concentrate dough: effect of particle size, temperature, and water content.

PubMed

Ahmed, Jasim; Thomas, Linu; Al-Attar, Hasan

2015-01-01

Small amplitude oscillatory rheology and creep behavior of β-glucan concentrate (BGC) dough were studied as function of particle size (74, 105, 149, 297, and 595 μm), BGC particle-to-water ratio (1:4, 1:5, and 1:6), and temperature (25, 40, 55, 70, and 85 °C). The color intensity and protein content increased with decreasing particle size by creating more surface areas. The water holding capacity (WHC) and sediment volume fraction increased with increasing particle size from 74 to 595 μm, which directly influences the mechanical rigidity and viscoelasticity of the dough. The dough exhibited predominating solid-like behavior (elastic modulus, G' > viscous modulus, G″). A discrete retardation spectrum is employed to the creep data to obtain retardation time and compliance parameters, which varied significantly with particle size and the process temperature. Creep tests exhibited more pronounced effect on dough behavior compared to oscillatory measurement. The protein denaturation temperature was insignificantly increased with particle fractions from 107 to 110 °C. All those information could be helpful to identify the particle size range and WHC of BGC that could be useful to produce a β-d-glucan enriched designed food. © 2014 Institute of Food Technologists®

A Study on Soil Movement Characteristics and Monitoring of Land creeping in the Republic of Korea

NASA Astrophysics Data System (ADS)

Kang, M.; Lee, C.; Woo, C.; Kim, D.; Seo, J.; Kim, K.

2017-12-01

In South Korea, `Landslide' is general phenomenon that the soil is saturated by rainfall and the soil is rapidly falling down at top soil. Landslide Sediment-related disaster is mainly composed of shallow landslide and debris flow in South Korea. However, land creeping is also occurring due to climate change and mountain development. Land creeping is a phenomenon in which a part of the soil layer moves due to the influence of groundwater and external impacts in the mountain slope. It is difficult to detect the phenomenon because the moving speed is very slow and it occurs even without the effect of rainfall. In case land creeping occurs, the damage appears on a large scale. Therefore, it is important to analyze the cause of the occurrence and to cope with it promptly. This study was conducted to investigation soil characteristics and cracks monitoring in order to understand the characteristics and causes of land creeping in South Korea. The crack of land creeping was found in 5ea and the total extension was about 121m. The width and depth range of the crack are each 0.2 0.5m, 0.25 0.45m. Geology, engineering and geomorphological characteristics of the ground were considered. As a result, the land creeping occurred to following reasons; (1) Characteristics of bed rock(anorthosite), (2) Relatively high groundwater level, (3) Maintenance of lower slope when reservoir build, (4) Stratum structure of thinly plied layer. In addition, stability analysis was carried out through the precision ground survey. As a result, instability was found in all sections except for some sections. The method of countermeasures was decided by opinions of field experts. As a result, a monitoring method was suggested in order to understand the change of tension cracks. Therefore, real-time monitoring of landslide early detection system is being implemented. NIFS `unmanned remote monitoring system detects the occurrence of landslides using sensor data and provides early warning information. In order to reduce damage of residents near the hazardous area, the system was introduces centered on places where it is difficult to install landslide control structures like debris control dam. Currently, the system is installed at 2 locations in the land creeping area. Monitoring is being continuously carried out to obtain useful measurement data.

Life Assessment for Cr-Mo Steel Dissimilar Joints by Various Filler Metals Using Accelerated Creep Testing

NASA Astrophysics Data System (ADS)

Petchsang, S.; Phung-on, I.; Poopat, B.

2016-12-01

Accelerated creep rupture tests were performed on T22/T91 dissimilar metal joints to determine the fracture location and rupture time of different weldments. Four configurations of deposited filler metal were tested using gas tungsten arc welding to estimate the service life for Cr-Mo steel dissimilar joints at elevated temperatures in power plants. Results indicated that failure in all configurations occurred in the tempered original microstructure and tempered austenite transformation products (martensite or bainite structure) as type IV cracking at the intercritical area of the heat-affected zone (ICHAZ) for both T22 and T91 sides rather than as a consequence of the different filler metals. Creep damage occurred with the formation of precipitations and microvoids. The correlation between applied stress and the Larson-Miller parameter (PLM) was determined to predict the service life of each material configuration. Calculated time-to-failure based on the PLM and test results for both temperature and applied stress parameters gave a reasonable fit. The dissimilar joints exhibited lower creep rupture compared to the base material indicating creep degradation of the weldment.

Materials for a Stirling engine heater head

NASA Technical Reports Server (NTRS)

Noble, J. E.; Lehmann, G. A.; Emigh, S. G.

1990-01-01

Work done on the 25-kW advanced Stirling conversion system (ASCS) terrestrial solar program in establishing criteria and selecting materials for the engine heater head and heater tubes is described. Various mechanisms contributing to incompatibility between materials are identified and discussed. Large thermal gradients, coupled with requirements for long life (60,000 h at temperature) and a large number of heatup and cooldown cycles (20,000) drive the design from a structural standpoint. The pressurized cylinder is checked for creep rupture, localized yielding, reverse plasticity, creep and fatigue damage, and creep ratcheting, in addition to the basic requirements for bust and proof pressure. In general, creep rupture and creep and fatigue interaction are the dominant factors in the design. A wide range of materials for the heater head and tubes was evaluated. Factors involved in the assessment were strength and effect on engine efficiency, reliability, and cost. A preliminary selection of Inconel 713LC for the heater head is based on acceptable structural properties but driven mainly by low cost. The criteria for failure, the structural analysis, and the material characteristics with basis for selection are discussed.

Numerical Experiments on Ductile Fracture in Granites

NASA Astrophysics Data System (ADS)

Regenauer-Lieb, K.; Weinberg, R. F.

2006-12-01

Ceramics and, by analogy rocks, are brittle at low temperatures, however, at high temperature and high pressure a second ductile mode of fracture based on dislocation and/or diffusion processes predominates. For ceramics 0.5-0.7 times the melting temperature suffice to create creep/ductile fracture which occurs typically after long time of deformation 104-1010 s (1). Ductile creep fractures make up for the low stress by profiting from accumulated strain and diffusion during slow creep deformation. Creep fractures typically nucleate on grain or phase boundaries, rigid or soft inclusions. Ultimately, the localized inhomogeneous damaged zone, begin to spread laterally and coalesce to create or follow a propagating shear band. The creep fracture sequence of crack nucleation, growth and coalescence relies on a mechanism of self-organization of fluids into a shear band during deformation and converts macroscopically to the crack like propagation of localized shear zones. Numerical experiments are used to test the ductile fracture hypothesis for the segregation and transfer of melts in granites. Ref: (1) C. Ghandi, M. F. Ashby, Acta Metallurgica 27, 1565 (1979).

Time-dependent Brittle Deformation in Etna Basalt

NASA Astrophysics Data System (ADS)

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.; Bell, A. F.; Main, I. G.

2008-12-01

Mt Etna is the largest and most active volcano in Europe. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts one of the biggest hydrogeologic reservoirs of Sicily (Ogniben, 1966). Pre-eruptive patterns of flank eruptions, closely monitored by means of ground deformation and seismicity, revealed the slow development of fracture systems at different altitudes, marked by repeated bursts of seismicity and accelerating/decelerating deformation patterns acting over the scale of months to days. The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as 'brittle creep'. Stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short- term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data demonstrate that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time- to-failure properties of the basaltic volcanic pile.

Effects of anisotropy and irradiation on the deformation behavior of Zircaloy 2. Final report

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

Pelloux, R.M.; Ballinger, R.; Lucas, G.

1979-01-01

An experimental program investigated the effects of texture anisotropy and irradiation on the mechanical behavior of Zircaloy-2. Short time and time dependent mechanical behavior were considered. Irradiation effects were simulated through the use of 4.75 MeV protons. The temperature ranges investigated were 298/sup 0/K and 573 to 673/sup 0/K. Both cold worked-stress relieved and annealed material were used in this experimental program. Short time yield behavior of different crystallographic textures was determined by uniaxial and plane strain tests in the temperature range 298/sup 0/K and 573 to 673/sup 0/K. Monotonic flow loci were constructed for each texture. Yield behavior ismore » a strong function of the crystallographic texture number f at all temperatures investigated. The rotation of texture with increasing plastic strain was investigated as a function of initial texture at 298/sup 0/K and 623/sup 0/K. The rate of texture rotation df/epsilon/sub p/ was found to be a unique function of the initial texture for plastic strains less than 0.08. Time dependent mechanical behavior was investigated in the range 573 to 673/sup 0/K using constant load creep and stress relaxation tests. The tensile creep strength is proportional to the resolved fraction of basal poles in the test direction. In variable stress and temperature tests, the time-hardening rule was found to be inapplicable. The strain-hardening rule was applied with success to data obtained at temperatures less than or equal to 648/sup 0/K. Irradiation creep tests were conducted in vacuum at 598/sup 0/K and 102 to 241 MPa on 80..mu..m thick Zircaloy-2 foil specimens in both the recrystallized and cold worked-stress relieved condition. In the irradiation creep tests irradiation hardening and enhanced irradiation creep were observed. Radiation hardening effects were significant in annealed material but were attenuated in cold worked-stress relieved material.« less

Creep deformation at crack tips in elastic-viscoplastic solids

NASA Astrophysics Data System (ADS)

Riedel, H.

1981-02-01

THE EVALUATION of crack growth tests under creep conditions must be based on the stress analysis of a cracked body taking into account elastic, plastic and creep deformation. In addition to the well-known analysis of a cracked body creeping in secondary (steady-state) creep, the stress field at the tip of a stationary crack is calculated for primary (strain-hardening) or tertiary (strain-softening) creep of the whole specimen. For the special hardening creep-law considered, a path-independent integral C∗h, can be defined which correlates the near-tip field to the applied load. It is also shown how, after sudden load application, creep strains develop in the initially elastic or, for a higher load level, plastic body. Characteristic times are derived to distinguish between short times when the creep-zones, in which creep strains are concentrated, are still small, and long times when the whole specimen creeps extensively in primary and finally in secondary and tertiary creep. Comparing the creep-zone sizes with the specimen dimensions or comparing the characteristic times with the test duration, one can decide which deformation mechanism prevails in the bulk of the specimen and which load parameter enters into the near-tip stress field and determines crack growth behavior. The governing load parameter is the stress intensity factor K 1 if the bulk of the specimen is predominantly elastic and it is the J-integral in a fully-plastic situation when large creep strains are still confined to a small zone. The C∗h-integral applies if the bulk of the specimen deforms in primary or tertiary creep, and C∗ is the relevant load parameter for predominantly secondary creep of the whole specimen.

Crack networks in damaged glass

NASA Astrophysics Data System (ADS)

Mallet, Celine; Fortin, Jerome; Gueguen, Yves

2013-04-01

We investigate how cracks develop and propagate in synthetic glass samples. Cracks are introduced in glass by a thermal shock of 300oC. Crack network is documented from optical and electronic microscopy on these samples that have been submitted to a thermal shock only. Samples are cylinder of 80 mm length and 40 mm diameter. Sections were cut along the cylinder axis and perpendicular to it. Using SEM, crack lengths and apertures can be measured. Optical microscopy allows to get the crack distribution over the entire sample. The sample average crack length is 3 mm. The average aperture is 6 ± 3μm. There is however a clear difference between the sample core, where the crack network has approximatively a transverse isotrope symmetry and the outer ring, where cracks are smaller and more numerous. By measuring before and after the thermal treatment the radial P and S wave velocities in room conditions, we can determine the total crack density which is 0.24. Thermally cracked samples, as described above, were submitted to creep tests. Constant axial stress and lateral stress were applied. Several experiments were performed at different stress values. Samples are saturated for 48 hours (to get an homogeneous pore fluid distribution), the axial stress is increased up to 80% of the sample strength. Stress step tests were performed in order to get creep data. The evolution of strain (axial and radial strain) is measured using strain gages, gap sensors (for the global axial strain) and pore volume change (for the volumetric strain). Creep data are interpreted as evidence of sub-critical crack growth in the cracked glass samples. The above microstructural observations are used, together with a crack propagation model, to account for the creep behavior. Assuming that (i) the observed volumetric strain rate is due to crack propagation and (ii) crack aspect ratio is constant we calculate the creep rate. We obtain some value on the crack propagation during a 24 hours of constant stress test. At each of these test, crack propagate of 0.3 to 0.4 mm. From the initial average crack length of 3 mm, the crack reach the size of 5.8 mm at the end of a complete creep test (with 8 constant stress step of 24 hours).

Elevated temperature mechanical properties and residual tensile properties of two cast superalloys and several nickel-base oxide dispersion strengthened alloys

NASA Technical Reports Server (NTRS)

Whittenberger, J. D.

1981-01-01

The elevated temperature tensile, stress-rupture and creep properties and residual tensile properties after creep straining have been determined for two cast superalloys and several wrought Ni-16Cr-4Al-yttria oxide dispersion strengthened (ODS) alloys. The creep behavior of the ODS alloys is similar to that of previously studied ODS nickel alloys. In general, the longitudinal direction is stronger than the long transverse direction, and creep is at least partially due to a diffusional creep mechanism as dispersoid-free zones were observed after creep-rupture testing. The tensile properties of the nickel-base superalloy B-1900 and cobalt-base superalloy MAR-M509 are not degraded by prior elevated temperature creep straining (at least up to 1 pct) between 1144 and 1366 K. On the other hand, the room temperature tensile properties of ODS nickel-base alloys can be reduced by prior creep strains of 0.5 pct or less between 1144 and 1477 K, with the long transverse direction being more susceptible to degradation than the longitudinal direction.

Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system. Volume 2: Phase 2 subsize panel cyclic creep predictions

NASA Technical Reports Server (NTRS)

Cramer, B. A.; Davis, J. W.

1975-01-01

A method for predicting permanent cyclic creep deflections in stiffened panel structures was developed. The resulting computer program may be applied to either the time-hardening or strain-hardening theories of creep accumulation. Iterative techniques were used to determine structural rotations, creep strains, and stresses as a function of time. Deflections were determined by numerical integration of structural rotations along the panel length. The analytical approach was developed for analyzing thin-gage entry vehicle metallic-thermal-protection system panels subjected to cyclic bending loads at high temperatures, but may be applied to any panel subjected to bending loads. Predicted panel creep deflections were compared with results from cyclic tests of subsize corrugation and rib-stiffened panels. Empirical equations were developed for each material based on correlation with tensile cyclic creep data and both the subsize panels and tensile specimens were fabricated from the same sheet material. For Vol. 1, see N75-21431.

Tensile and compressive constitutive response of 316 stainless steel at elevated temperatures

NASA Technical Reports Server (NTRS)

Manson, S. S.; Muralidharan, U.; Halford, G. R.

1982-01-01

It is demonstrated that creep rate of 316 SS is lower by factors of 2 to 10 in compression than in tension if the microstructure is the same and tests are conducted at identical temperatures and equal but opposite stresses. Such behavior was observed for both monotonic creep and conditions involving cyclic creep. In the latter case creep rate in both tension and compression progressively increases from cycle to cycle, rendering questionable the possibility of expressing a time-stabilized constitutive relationship. The difference in creep rates in tension and compression is considerably reduced if the tension specimen is first subjected to cycles of tensile creep (reversed by compressive plasticity), while the compression specimen is first subjected to cycles of compressive creep (reversed by tensile plasticity). In both cases, the test temperature is the same and the stresses are equal and opposite. Such reduction is a reflection of differences in microstructure of the specimens resulting from different prior mechanical history.

Pure climb creep mechanism drives flow in Earth’s lower mantle

PubMed Central

Boioli, Francesca; Carrez, Philippe; Cordier, Patrick; Devincre, Benoit; Gouriet, Karine; Hirel, Pierre; Kraych, Antoine; Ritterbex, Sebastian

2017-01-01

At high pressure prevailing in the lower mantle, lattice friction opposed to dislocation glide becomes very high, as reported in recent experimental and theoretical studies. We examine the consequences of this high resistance to plastic shear exhibited by ringwoodite and bridgmanite on creep mechanisms under mantle conditions. To evaluate the consequences of this effect, we model dislocation creep by dislocation dynamics. The calculation yields to an original dominant creep behavior for lower mantle silicates where strain is produced by dislocation climb, which is very different from what can be activated under high stresses under laboratory conditions. This mechanism, named pure climb creep, is grain-size–insensitive and produces no crystal preferred orientation. In comparison to the previous considered diffusion creep mechanism, it is also a more efficient strain-producing mechanism for grain sizes larger than ca. 0.1 mm. The specificities of pure climb creep well match the seismic anisotropy observed of Earth’s lower mantle. PMID:28345037

A 12 year EDF study of concrete creep under uniaxial and biaxial loading

DOE PAGES

Charpin, Laurent; Le Pape, Yann; Coustabeau, Eric; ...

2017-11-04

This paper presents a 12-year-long creep and shrinkage experimental campaign on cylindrical and prismatic concrete samples under uniaxial and biaxial stress, respectively. The motivation for the study is the need for predicting the delayed strains and the pre-stress loss of concrete containment buildings of nuclear power plants. Two subjects are central in this regard: the creep strain's long-term evolution and the creep Poisson's ratio. A greater understanding of these areas is necessary to ensure reliable predictions of the long-term behavior of the concrete containment buildings.Long-term basic creep appears to evolve as a logarithm function of time in the range ofmore » 3 to 10 years of testing. Similar trends are observed for drying creep, autogenous shrinkage, and drying shrinkage testing, which suggests that all delayed strains obtained using different loading and drying conditions originate from a common mechanism.The creep Poisson's ratio derived from the biaxial tests is approximately constant over time for both the basic and drying creep tests (creep strains corrected by the shrinkage strain).It is also shown that the biaxial non-drying samples undergo a significant increase in Young's modulus after 10 years.« less

Nanogranular origin of concrete creep.

PubMed

Vandamme, Matthieu; Ulm, Franz-Josef

2009-06-30

Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium-silicate-hydrates (C-S-H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C-S-H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C-S-H forms: low density, high density, ultra-high density. We demonstrate that the creep rate ( approximately 1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years.

A 12 year EDF study of concrete creep under uniaxial and biaxial loading

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

Charpin, Laurent; Le Pape, Yann; Coustabeau, Eric

This paper presents a 12-year-long creep and shrinkage experimental campaign on cylindrical and prismatic concrete samples under uniaxial and biaxial stress, respectively. The motivation for the study is the need for predicting the delayed strains and the pre-stress loss of concrete containment buildings of nuclear power plants. Two subjects are central in this regard: the creep strain's long-term evolution and the creep Poisson's ratio. A greater understanding of these areas is necessary to ensure reliable predictions of the long-term behavior of the concrete containment buildings.Long-term basic creep appears to evolve as a logarithm function of time in the range ofmore » 3 to 10 years of testing. Similar trends are observed for drying creep, autogenous shrinkage, and drying shrinkage testing, which suggests that all delayed strains obtained using different loading and drying conditions originate from a common mechanism.The creep Poisson's ratio derived from the biaxial tests is approximately constant over time for both the basic and drying creep tests (creep strains corrected by the shrinkage strain).It is also shown that the biaxial non-drying samples undergo a significant increase in Young's modulus after 10 years.« less

Nanogranular origin of concrete creep

PubMed Central

Vandamme, Matthieu; Ulm, Franz-Josef

2009-01-01

Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium–silicate–hydrates (C–S–H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C–S–H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C–S–H forms: low density, high density, ultra-high density. We demonstrate that the creep rate (≈1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years. PMID:19541652

Material Parameters for Creep Rupture of Austenitic Stainless Steel Foils

NASA Astrophysics Data System (ADS)

Osman, H.; Borhana, A.; Tamin, M. N.

2014-08-01

Creep rupture properties of austenitic stainless steel foil, 347SS, used in compact recuperators have been evaluated at 700 °C in the stress range of 54-221 MPa to establish the baseline behavior for its extended use. Creep curves of the foil show that the primary creep stage is brief and creep life is dominated by tertiary creep deformation with rupture lives in the range of 10-2000 h. Results are compared with properties of bulk specimens tested at 98 and 162 MPa. Thin foil 347SS specimens were found to have higher creep rates and higher rupture ductility than their bulk specimen counterparts. Power law relationship was obtained between the minimum creep rate and the applied stress with stress exponent value, n = 5.7. The value of the stress exponent is indicative of the rate-controlling deformation mechanism associated with dislocation creep. Nucleation of voids mainly occurred at second-phase particles (chromium-rich M23C6 carbides) that are present in the metal matrix by decohesion of the particle-matrix interface. The improvement in strength is attributed to the precipitation of fine niobium carbides in the matrix that act as obstacles to the movement of dislocations.

Mechanical Properties for Advanced Engine Materials

DTIC Science & Technology

1992-04-01

electric potential differences, fractography , and model verification. 2.1.2 Creep This investigation [Khobaib] studied the creep behavior of SCS-6/Ti-24AI-1...dependent behavior [Bushnell; Hunsaker et al.] into an in-house code, MAGNA [Brockman], was more cost effective than obtaining, learning , and modifying a new...the applicability of Eqn. (13) to disks with deep notches. These results correlated well with Eqn. (13) as shown in Fig. 4.4.3.-1 and confirmed its

Creep Behavior of Hafnia and Ytterbium Silicate Environmental Barrier Coating Systems on SiC/SiC Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Ghosn, Louis J.; Harder, Bryan

2011-01-01

Environmental barrier coatings will play a crucial role in future advanced gas turbine engines because of their ability to significantly extend the temperature capability and stability of SiC/SiC ceramic matrix composite (CMC) engine components, thus improving the engine performance. In order to develop high performance, robust coating systems for engine components, appropriate test approaches simulating operating temperature gradient and stress environments for evaluating the critical coating properties must be established. In this paper, thermal gradient mechanical testing approaches for evaluating creep and fatigue behavior of environmental barrier coated SiC/SiC CMC systems will be described. The creep and fatigue behavior of Hafnia and ytterbium silicate environmental barrier coatings on SiC/SiC CMC systems will be reported in simulated environmental exposure conditions. The coating failure mechanisms will also be discussed under the heat flux and stress conditions.

Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Fox, Dennis S.; Miller, Robert A.; Ghosn, Louis J.; Kalluri, Sreeramesh

2004-01-01

The development of advanced high performance constant-volume-combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz) in conjunction with the mechanical fatigue loads (10 Hz). The mechanical high cycle fatigue (HCF) testing of some laser pre-exposed specimens has also been conducted under a frequency of 100 Hz to determine the laser surface damage effect. The test results have indicated that material surface oxidation and creep-enhanced fatigue is an important mechanism for the surface crack initiation and propagation under the simulated CVCCE engine conditions.

Rate-based structural health monitoring using permanently installed sensors

PubMed Central

2017-01-01

Permanently installed sensors are becoming increasingly ubiquitous, facilitating very frequent in situ measurements and consequently improved monitoring of ‘trends’ in the observed system behaviour. It is proposed that this newly available data may be used to provide prior warning and forecasting of critical events, particularly system failure. Numerous damage mechanisms are examples of positive feedback; they are ‘self-accelerating’ with an increasing rate of damage towards failure. The positive feedback leads to a common time-response behaviour which may be described by an empirical relation allowing prediction of the time to criticality. This study focuses on Structural Health Monitoring of engineering components; failure times are projected well in advance of failure for fatigue, creep crack growth and volumetric creep damage experiments. The proposed methodology provides a widely applicable framework for using newly available near-continuous data from permanently installed sensors to predict time until failure in a range of application areas including engineering, geophysics and medicine. PMID:28989308

Characterizing the effect of creep on stress corrosion cracking of cold worked Alloy 690 in supercritical water environment

NASA Astrophysics Data System (ADS)

Zhang, Lefu; Chen, Kai; Du, Donghai; Gao, Wenhua; Andresen, Peter L.; Guo, Xianglong

2017-08-01

The effect of creep on stress corrosion cracking (SCC) was studied by measuring crack growth rates (CGRs) of 30% cold worked (CW) Alloy 690 in supercritical water (SCW) and inert gas environments at temperatures ranging from 450 °C to 550 °C. The SCC crack growth rate under SCW environments can be regarded as the cracking induced by the combined effect of corrosion and creep, while the CGR in inert gas environment can be taken as the portion of creep induced cracking. Results showed that the CW Alloy 690 sustained high susceptibility to intergranular (IG) cracking, and creep played a dominant role in the SCC crack growth behavior, contributing more than 80% of the total crack growth rate at each testing temperature. The temperature dependence of creep induced CGRs follows an Arrhenius dependency, with an apparent activation energy (QE) of about 225 kJ/mol.

Creep rupture strength of activated-TIG welded 316L(N) stainless steel

NASA Astrophysics Data System (ADS)

Sakthivel, T.; Vasudevan, M.; Laha, K.; Parameswaran, P.; Chandravathi, K. S.; Mathew, M. D.; Bhaduri, A. K.

2011-06-01

316L(N) stainless steel plates were joined using activated-tungsten inert gas (A-TIG) welding and conventional TIG welding process. Creep rupture behavior of 316L(N) base metal, and weld joints made by A-TIG and conventional TIG welding process were investigated at 923 K over a stress range of 160-280 MPa. Creep test results showed that the enhancement in creep rupture strength of weld joint fabricated by A-TIG welding process over conventional TIG welding process. Both the weld joints fractured in the weld metal. Microstructural observation showed lower δ-ferrite content, alignment of columnar grain with δ-ferrite along applied stress direction and less strength disparity between columnar and equiaxed grains of weld metal in A-TIG joint than in MP-TIG joint. These had been attributed to initiate less creep cavitation in weld metal of A-TIG joint leading to improvement in creep rupture strength.

Effects of Aging-Time Reference on the Long Term Behavior of the IM7/K3B Composite

NASA Technical Reports Server (NTRS)

Veazie, David R.; Gates, Thomas S.

1998-01-01

An analytical study was undertaken to investigate the effects of the time-based shift reference on the long term behavior of the graphite reinforced thermoplastic polyimide composite IM7/K3B at elevated temperature. Creep compliance and the effects of physical aging on the time dependent response was measured for uniaxial loading at several isothermal conditions below the glass transition temperature (T(sub g). Two matrix dominated loading modes, shear and transverse, were investigated in tension and compression. The momentary sequenced creep/aging curves were collapsed through a horizontal (time) shift using the shortest, middle and longest aging time curve as the reference curve. Linear viscoelasticity was used to characterize the creep/recovery behavior and superposition techniques were used to establish the physical aging related material constants. The use of effective time expressions in a laminated plate model allowed for the prediction of long term creep compliance. The effect of using different reference curves with time/aging-time superposition was most sensitive to the physical aging shift rate at lower test temperatures. Depending on the loading mode, the reference curve used can result in a more accurate long term prediction, especially at lower test temperatures.

Durability and Damage Development in Woven Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Haque, A.; Rahman, M.; Tyson, O. Z.; Jeelani, S.; Verrilli, Michael J. (Technical Monitor)

2001-01-01

Damage development in woven SiC/SiNC ceramic matrix composites (CMC's) under tensile and cyclic loading both at room and elevated temperatures have been investigated for the exhaust nozzle of high-efficient turbine engines. The ultimate strength, failure strain, proportional limit and modulus data at a temperature range of 23 to 1250 C are generated. The tensile strength of SiC/SiNC woven composites have been observed to increase with increased temperatures up to 1000 C. The stress/strain plot shows a pseudo-yield point at 25 percent of the failure strain (epsilon(sub r)) which indicates damage initiation in the form of matrix cracking. The evolution of damage beyond 0.25 epsilon(sub f), both at room and elevated temperature comprises multiple matrix cracking, interfacial debonding, and fiber pullout. Although the nature of the stress/strain plot shows damage-tolerant behavior under static loading both at room and elevated temperature, the life expectancy of SiC/SiNC composites degrades significantly under cyclic loading at elevated temperature. This is mostly due to the interactions of fatigue damage caused by the mechanically induced plastic strain and the damage developed by the creep strain. The in situ damage evolutions are monitored by acoustic event parameters, ultrasonic C-scan and stiffness degradation. Rate equations for modulus degradation and fatigue life prediction of ceramic matrix composites both at room and elevated temperatures are developed. These rate equations are observed to show reasonable agreement with experimental results.

Constitutive Behavior of Mixed Sn-Pb/Sn-3.0Ag-0.5Cu Solder Alloys

NASA Astrophysics Data System (ADS)

Tucker, J. P.; Chan, D. K.; Subbarayan, G.; Handwerker, C. A.

2012-03-01

During the transition from Pb-containing solders to Pb-free solders, joints composed of a mixture of Sn-Pb and Sn-Ag-Cu often result from either mixed assemblies or rework. Comprehensive characterization of the mechanical behavior of these mixed solder alloys resulting in a deformationally complete constitutive description is necessary to predict failure of mixed alloy solder joints. Three alloys with 1 wt.%, 5 wt.%, and 20 wt.% Pb were selected so as to represent reasonable ranges of Pb contamination expected from different 63Sn-37Pb components mixed with Sn-3.0Ag-0.5Cu. Creep and displacement-controlled tests were performed on specially designed assemblies at temperatures of 25°C, 75°C, and 125°C using a double lap shear test setup that ensures a nearly homogeneous state of plastic strain at the joint interface. The observed changes in creep and tensile behavior with Pb additions were related to phase equilibria and microstructure differences observed through differential scanning calorimetric and scanning electron microscopic cross-sectional analysis. As Pb content increased, the steady-state creep strain rates increased, and primary creep decreased. Even 1 wt.% Pb addition was sufficient to induce substantially large creep strains relative to the Sn-3.0Ag-0.5Cu alloy. We describe rate-dependent constitutive models for Pb-contaminated Sn-Ag-Cu solder alloys, ranging from the traditional time-hardening creep model to the viscoplastic Anand model. We illustrate the utility of these constitutive models by examining the inelastic response of a chip-scale package (CSP) under thermomechanical loading through finite-element analysis. The models predict that, as Pb content increases, total inelastic dissipation decreases.

Superplastic Creep of Metal Nanowires From Rate-Dependent Plasticity Transition

DOE PAGES

Tao, Weiwei; Cao, Penghui; Park, Harold S.

2018-04-30

Understanding the time-dependent mechanical behavior of nanomaterials such as nanowires is essential to predict their reliability in nanomechanical devices. This understanding is typically obtained using creep tests, which are the most fundamental loading mechanism by which the time dependent deformation of materials is characterized. However, due to existing challenges facing both experimentalists and theorists, the time dependent mechanical response of nanowires is not well-understood. Here, we use atomistic simulations that can access experimental time scales to examine the creep of single-crystal face-centered cubic metal (Cu, Ag, Pt) nanowires. Here, we report that both Cu and Ag nanowires show significantly increasedmore » ductility and superplasticity under low creep stresses, where the superplasticity is driven by a rate-dependent transition in defect nucleation from twinning to trailing partial dislocations at the micro- or millisecond time scale. The transition in the deformation mechanism also governs a corresponding transition in the stress-dependent creep time at the microsecond (Ag) and millisecond (Cu) time scales. Overall, this work demonstrates the necessity of accessing time scales that far exceed those seen in conventional atomistic modeling for accurate insights into the time-dependent mechanical behavior and properties of nanomaterials.« less

Superplastic Creep of Metal Nanowires from Rate-Dependent Plasticity Transition.

PubMed

Tao, Weiwei; Cao, Penghui; Park, Harold S

2018-05-22

Understanding the time-dependent mechanical behavior of nanomaterials such as nanowires is essential to predict their reliability in nanomechanical devices. This understanding is typically obtained using creep tests, which are the most fundamental loading mechanism by which the time-dependent deformation of materials is characterized. However, due to existing challenges facing both experimentalists and theorists, the time-dependent mechanical response of nanowires is not well-understood. Here, we use atomistic simulations that can access experimental time scales to examine the creep of single-crystal face-centered cubic metal (Cu, Ag, Pt) nanowires. We report that both Cu and Ag nanowires show significantly increased ductility and superplasticity under low creep stresses, where the superplasticity is driven by a rate-dependent transition in defect nucleation from twinning to trailing partial dislocations at the micro- or millisecond time scale. The transition in the deformation mechanism also governs a corresponding transition in the stress-dependent creep time at the microsecond (Ag) and millisecond (Cu) time scales. Overall, this work demonstrates the necessity of accessing time scales that far exceed those seen in conventional atomistic modeling for accurate insights into the time-dependent mechanical behavior and properties of nanomaterials.

Superplastic Creep of Metal Nanowires From Rate-Dependent Plasticity Transition

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

Tao, Weiwei; Cao, Penghui; Park, Harold S.

Understanding the time-dependent mechanical behavior of nanomaterials such as nanowires is essential to predict their reliability in nanomechanical devices. This understanding is typically obtained using creep tests, which are the most fundamental loading mechanism by which the time dependent deformation of materials is characterized. However, due to existing challenges facing both experimentalists and theorists, the time dependent mechanical response of nanowires is not well-understood. Here, we use atomistic simulations that can access experimental time scales to examine the creep of single-crystal face-centered cubic metal (Cu, Ag, Pt) nanowires. Here, we report that both Cu and Ag nanowires show significantly increasedmore » ductility and superplasticity under low creep stresses, where the superplasticity is driven by a rate-dependent transition in defect nucleation from twinning to trailing partial dislocations at the micro- or millisecond time scale. The transition in the deformation mechanism also governs a corresponding transition in the stress-dependent creep time at the microsecond (Ag) and millisecond (Cu) time scales. Overall, this work demonstrates the necessity of accessing time scales that far exceed those seen in conventional atomistic modeling for accurate insights into the time-dependent mechanical behavior and properties of nanomaterials.« less

A physics-based crystallographic modeling framework for describing the thermal creep behavior of Fe-Cr alloys

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

Wen, Wei; Capolungo, Laurent; Patra, Anirban

This Report addresses the Milestone M2MS-16LA0501032 of NEAMS Program (“Develop hardening model for FeCrAl cladding), with a deadline of 09/30/2016. Here we report a constitutive law for thermal creep of FeCrAl. This Report adds to and complements the one for Milestone M3MS-16LA0501034 (“Interface hardening models with MOOSE-BISON”), where we presented a hardening law for irradiated FeCrAl. The last component of our polycrystal-based constitutive behavior, namely, an irradiation creep model for FeCrAl, will be developed as part of the FY17 Milestones, and the three regimes will be coupled and interfaced with MOOSE-BISON.

Creep-rupture behavior of iron superalloys in high pressure hydrogen

NASA Technical Reports Server (NTRS)

Bhattacharyya, S.

1981-01-01

Two cast alloys (CRM-6D and XF-818) and four sheet alloys (A-26, Incoloy 800H, N-155, and 19-9DL) in the thickness range of 0.79 to 0.99 mm were evaluated for use in the Stirling engine. The creep rupture behavior of these iron base high temperature alloys is being determined in air for 10 hr to 3,00 hr, and in 20.7 MPa (3,000 psi) H2 for 10 to 300 hr at temperatures of 650 deg to 925 deg. Material procurement, preparation and air creep rupture testing are described and existing data is analyzed. Systems for the high pressure hydrogen testing are discussed. Statistical analysis of temperature-compensated rupture data for each alloy is included.

Technical evaluation report of the Specialists Meeting on Characterization of Low Cycle High Temperature Fatigue by the Strainrange Partitioning Method

NASA Technical Reports Server (NTRS)

Drapier, J. M.; Hirschberg, M. H.

1979-01-01

The ability of the Strainrange Partitioning Method SRP was evaluated to correlate the creep-fatigue behavior of gas turbine materials and to predict the creep fatigue life of laboratory specimens subjected to complex cycling conditions. A reference body of high temperature creep fatigue data which can be used in the evaluation of other SRP and low cycle high temperature fatigue predictive techniques was provided.

The Effects of Small Deformation on Creep and Stress Rupture Behavior of ODS Superalloys.

DTIC Science & Technology

1983-01-07

effects or shock loading effects. During this project year, we modified several Satec high temperature static creep test machines to obtain the required...loading control. Figure 14 is a schematic represen- tation of our cyclic creep test system. The system retains features of the Satec machine such as...and almost completely while, if the stress is held at the initial level for longer periods, dislocation will es - cape the strengthening interactions

Preliminary Development of a Unified Viscoplastic Constitutive Model for Alloy 617 with Special Reference to Long Term Creep Behavior

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

Sham, Sam; Walker, Kevin P.

The expected service life of the Next Generation Nuclear Plant is 60 years. Structural analyses of the Intermediate Heat Exchanger (IHX) will require the development of unified viscoplastic constitutive models that address the material behavior of Alloy 617, a construction material of choice, over a wide range of strain rates. Many unified constitutive models employ a yield stress state variable which is used to account for cyclic hardening and softening of the material. For low stress values below the yield stress state variable these constitutive models predict that no inelastic deformation takes place which is contrary to experimental results. Themore » ability to model creep deformation at low stresses for the IHX application is very important as the IHX operational stresses are restricted to very small values due to the low creep strengths at elevated temperatures and long design lifetime. This paper presents some preliminary work in modeling the unified viscoplastic constitutive behavior of Alloy 617 which accounts for the long term, low stress, creep behavior and the hysteretic behavior of the material at elevated temperatures. The preliminary model is presented in one-dimensional form for ease of understanding, but the intent of the present work is to produce a three-dimensional model suitable for inclusion in the user subroutines UMAT and USERPL of the ABAQUS and ANSYS nonlinear finite element codes. Further experiments and constitutive modeling efforts are planned to model the material behavior of Alloy 617 in more detail.« less

Interconversion of dynamic modulus to creep compliance and relaxation modulus : numerical modeling and laboratory validation - final report.

DOT National Transportation Integrated Search

2016-09-01

Viscoelastic material functions such as time domain functions, such as, relaxation modulus and creep compliance, : or frequency domain function, such as, complex modulus can be used to characterize the linear viscoelastic behavior : of asphalt concre...

Low strain, long life creep fatigue of AF2-1DA and INCO 718

NASA Technical Reports Server (NTRS)

Thakker, A. B.; Cowles, B. A.

1983-01-01

Two aircraft turbine disk alloys, GATORIZED AF2-DA and INCO 718 were evaluated for their low strain long life creep-fatigue behavior. Static (tensile and creep rupture) and cyclic properties of both alloys were characterized. The cntrolled strain LCF tests were conducted at 760 C (1400 F) and 649 C (1200 F) for AF2-1DA and INCO 718, respectively. Hold times were varied for tensile, compressive and tensile/compressive strain dwell (relaxation) tests. Stress (creep) hold behavior of AF2-1DA was also evaluated. Generally, INCO 718 exhibited more pronounced reduction in cyclic life due to hold than AF2-1DA. The percent reduction in life for both alloys for strain dwell tests was greater at low strain ranges (longer life regime). Changing hold time from 0 to 0.5, 2.0 and 15.0 min. resulted in corresponding reductions in life. The continuous cycle and cyclic/dwell initiation failure mechanism was predominantly transgranular for AF2-1DA and intergranular for INCO 718.

High temperature tensile and creep behaviour of low pressure plasma-sprayed Ni-Co-Cr-Al-Y coating alloy

NASA Technical Reports Server (NTRS)

Hebsur, M. G.; Miner, R. V.

1986-01-01

The high temperature tensile and creep behavior of low pressure plasma-sprayed plates of a typical Ni-Co-Cr-Al-Y alloy has been studied. From room temperature to 800 K, the Ni-Co-Cr-Al-Y alloy studied has nearly a constant low ductility and a high strength. At higher temperatures, it becomes weak and highly ductile. At and above 1123 K, the behavior is highly dependent on strain rate and exhibits classic superplastic characteristics with a high ductility at intermediate strain rates and a strain rate sensitivity of about 0.5. At either higher or lower strain rates, the ductility decreases and the strain rate sensitivities are about 0.2. In the superplastic deformation range, the activation energy for creep is 120 + or - 20 kJ/mol, suggesting a diffusion-aided grain boundary sliding mechanism. Outside the superplastic range, the activation energy for creep is calculated to be 290 + or - 20 kJ/mol.

Creep and fracture of dispersion-strengthened materials

NASA Technical Reports Server (NTRS)

Raj, Sai V.

1991-01-01

The creep and fracture of dispersion strengthened materials is reviewed. A compilation of creep data on several alloys showed that the reported values of the stress exponent for creep varied between 3.5 and 100. The activation energy for creep exceeded that for lattice self diffusion in the matrix in the case of some materials and a threshold stress behavior was generally reported in these instances. The threshold stress is shown to be dependent on the interparticle spacing and it is significantly affected by the initial microstructure. The effect of particle size and the nature of the dispersoid on the threshold stress is not well understood at the present time. In general, most studies indicate that the microstructure after creep is similar to that before testing and very few dislocations are usually observed. It is shown that the stress acting on a dispersoid due to a rapidly moving dislocation can exceed the particle yield strength of the G sub p/1000, where G sub p is the shear modulus of the dispersoid. The case when the particle deforms is examined and it is suggested that the dislocation creep threshold stress of the alloy is equal to the yield strength of the dispersoid under these conditions. These results indicate that the possibility that the dispersoid creep threshold stress is determined by either the particle yield strength or the stress required to detach a dislocation from the dispersoid matrix interface. The conditions under which the threshold stress is influenced by one or the other mechanism are discussed and it is shown that the particle yield strength is important until the extent of dislocation core relaxation at the dispersoid matrix interface exceeds about 25 pct. depending on the nature of the particle matrix combination. Finally, the effect of grain boundaries and grain morphology on the creep and fracture behavior of dispersoid strengthened alloys is examined.

Effect of Hf-Rich Particles on the Creep Life of a High-strength Nial Single Crystal Alloy

NASA Technical Reports Server (NTRS)

Garg, A.; Raj, S. V.; Darolia, R.

1995-01-01

Additions of small amounts of Hf and Si to NiAl single crystals significantly improve their high-temperature strength and creep properties. However, if large Hf-rich dendritic particles formed during casting of the alloyed single crystals are not dissolved completely during homogenization heat treatment, a large variation in creep rupture life can occur. This behavior, observed in five samples of a Hf containing NiAl single crystal alloy tested at 1144 K under an initial stress of 241.4 MPa, is described in detail highlighting the role of interdendritic Hf-rich particles in limiting creep rupture life.

Creep Strength Behavior of Boron Added P91 Steel and its Weld in the Temperature Range of 600-650°C

NASA Astrophysics Data System (ADS)

Swaminathan, J.; Das, C. R.; Baral, Jayashree; Phaniraj, C.; Ghosh, R. N.; Albert, S. K.; Bhaduri, A. K.

One of the promising ways for mitigation of Type IV cracking — a failure by cracking at the intercritical /fine grained heat affected zone, a life limiting problem in advanced 9-12 Cr ferritic steel weld like that of P91 is through modification of alloy composition by addition of boron. Addition of boron was observed to improve the microstructure at the weld zone and hence the creep strength. In the present work, boron (100 ppm with controlled nitrogen) added P91 steel after normalizing at 1050°C and 1150°C and tempered at 760°C were studied for the creep behavior in the base metal and welded condition in the temperature range of 600-650°C. Creep strength was characterized in terms of stress and temperature dependence of creep rate and rupture time. Weld creep life was reduced compared to the base metal with rupture occurring at the ICHAZ (Type IV crack). However at longer time (at lower stress levels) exposure creep crack moves from weld metal to HAZ (Type II crack). Rupture life was found to superior for the base and weld in the boron containing steel when higher normalizing temperature is used. Estimation of 105 h was attempted based on short term rupture data available and weld strength factors were calculated. Observed values are better for P91BH condition than the values for P91BLcondition as well as those available for P91 in open literature

Analysis of pellet cladding interaction and creep of U 3SIi2 fuel for use in light water reactors

NASA Astrophysics Data System (ADS)

Metzger, Kathryn E.

Following the accident at the Fukushima plant, enhancing the accident tolerance of the light water reactor (LWR) fleet became a topic of serious discussion. Under the direction of congress, the DOE office of Nuclear Energy added accident tolerant fuel development as a primary component to the existing Advanced Fuels Program. The DOE defines accident tolerant fuels as fuels that "in comparison with the standard UO2- Zircaloy system currently used by the nuclear industry, can tolerate loss of active cooling in the reactor core for a considerably longer time period (depending on the LWR system and accident scenario) while maintaining or improving the fuel performance during normal operations, operational transients, as well as design-basis and beyond design-basis events." To be economically viable, proposed accident tolerant fuels and claddings should be backward compatible with LWR designs, provide significant operating cost improvements such as power uprates, increased fuel burnup, or increased cycle length. In terms of safety, an alternative fuel pellet must have resistance to water corrosion comparable to UO2, thermal conductivity equal to or larger than that of UO2, and a melting temperature that allows the material to remain solid under power reactor conditions. Among the candidates, U3Si2 has a number of advantageous thermophysical properties, including; high density, high thermal conductivity at room temperature, and a high melting temperature. These properties support its use as an accident tolerant fuel while its high uranium density is capable of supporting uprates to the LWR fleet. This research characterizes U3Si2 pellets and analyzes U3Si2 under light water reactor conditions using the fuel performance code BISON. While some thermophysical properties for U3Si2 have been found in the literature, the irradiation behavior is sparse and limited to experience with dispersion fuels. Accordingly, the creep behavior for U3Si2 has been unknown, making it difficult to predict fuel-cladding mechanical behavior. This information is essential for designing accident tolerant fuel systems where ceramic claddings, like silicon carbide (SiC) are proposed. This research provides a model for both the thermal and irradiation creep behavior for U3Si2. This body of research is comprised of both experimental and modeling components. Characterization of the fuel microstructure includes; optical microscopy with pore and grain size analysis, helium pycnometry for density determination, mercury intrusion porosimetry, compositional analysis in the form of XRD, second phase identification using EDX, electrical resistance measurement via four point probe, determination of hardness and toughness through Vickers indentation testing, and determination of elastic properties using the impulse excitation method. Post-sintering grain size data allowed for the determination of grain boundary activation energy and diffusion coefficients, which were used to develop creep models. This was extended to lattice and irradiation enhanced diffusion in order to develop a U3Si2 creep model over thermal and irradiation creep regimes. In addition to the creep model, thermal and swelling behavior models for U3Si2 were implemented into the BISON fuel performance code. A series of simulations evaluated the performance and behavior of U3Si2 under typical light water reactor conditions with advanced SiC ceramic cladding. Simulation results show that fuel creep relieves stress in the ceramic cladding and postpones the. moment of fuel-clad contact. However, the stress reduction to the cladding is minimal because the fuel creep rate is low while the swelling rate is high. Future work should include the investigation of monolithic U3Si2 irradiation swelling since the current model relies upon the swelling data of U3Si2 particles in a metallic dispersion fuel. Additionally, planned thermal creep testing at the University of South Carolina can provide confirmation of the U3Si2 creep model contained herein.

Finite element analysis of history-dependent damage in time-dependent fracture mechanics

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

Krishnaswamy, P.; Brust, F.W.; Ghadiali, N.D.

1993-11-01

The demands for structural systems to perform reliably under both severe and changing operating conditions continue to increase. Under these conditions time-dependent straining and history-dependent damage become extremely important. This work focuses on studying creep crack growth using finite element (FE) analysis. Two important issues, namely, (1) the use of history-dependent constitutive laws, and (2) the use of various fracture parameters in predicting creep crack growth, have both been addressed in this work. The constitutive model used here is the one developed by Murakami and Ohno and is based on the concept of a creep hardening surface. An implicit FEmore » algorithm for this model was first developed and verified for simple geometries and loading configurations. The numerical methodology developed here has been used to model stationary and growing cracks in CT specimens. Various fracture parameters such as the C[sub 1], C[sup *], T[sup *], J were used to compare the numerical predictions with experimental results available in the literature. A comparison of the values of these parameters as a function of time has been made for both stationary and growing cracks. The merit of using each of these parameters has also been discussed.« less

Generation of plate tectonics with two-phase grain-damage and pinning: Source-sink model and toroidal flow

NASA Astrophysics Data System (ADS)

Bercovici, David; Ricard, Yanick

2013-03-01

The grain-damage and pinning mechanism of Bercovici and Ricard (2012) for lithospheric shear-localization is employed in two-dimensional flow calculations to test its ability to generate toroidal (strike-slip) motion and influence plate evolution. This mechanism posits that damage to the interface between phases in a polycrystalline material like peridotite (composed primarily of olivine and pyroxene) increases the number of small Zener pinning surfaces, which then constrain mineral grains to ever smaller sizes, regardless of creep mechanism. This effect allows a self-softening feedback in which damage and grain-reduction can co-exist with a grain-size dependent diffusion creep rheology; moreover, grain growth and weak-zone healing are greatly impeded by Zener pinning thereby leading to long-lived relic weak zones. The fluid dynamical calculations employ source-sink driven flow as a proxy for convective poloidal flow (upwelling/downwelling and divergent/convergent motion), and the coupling of this flow with non-linear rheological mechanisms excites toroidal or strike-slip motion. The numerical experiments show that pure dislocation-creep rheology, and grain-damage without Zener pinning (as occurs in a single-phase assemblages) permit only weak localization and toroidal flow; however, the full grain-damage with pinning readily allows focussed localization and intense, plate-like toroidal motion and strike-slip deformation. Rapid plate motion changes are also tested with abrupt rotations of the source-sink field after a plate-like configuration is developed; the post-rotation flow and material property fields retain memory of the original configuration for extensive periods, leading to suboptimally aligned plate boundaries (e.g., strike-slip margins non-parallel to plate motion), oblique subduction, and highly localized, weak and long lived acute plate-boundary junctions such as at what is observed at the Aleutian-Kurile intersection. The grain-damage and pinning theory therefore readily satisfies key plate-tectonic metrics of localized toroidal motion and plate-boundary inheritance, and thus provides a predictive theory for the generation of plate tectonics on Earth and other planets.

Non-isothermal elastoviscoplastic snap-through and creep buckling of shallow arches

NASA Technical Reports Server (NTRS)

Simitses, G. J.; Riff, R.

1987-01-01

The problem of buckling of shallow arches under transient thermomechanical loads is investigated. The analysis is based on nonlinear geometric and constitutive relations, and is expressed in a rate form. The material constitutive equations are capable of reproducing all non-isothermal, elasto-viscoplastic characteristics. The solution scheme is capable of predicting response which includes pre and postbuckling with creep and plastic effects. The solution procedure is demonstrated through several examples which include both creep and snap-through behavior.

Creeping Guanxian-Anxian Fault ruptured in the 2008 Mw 7.9 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

He, X.; Li, H.; Wang, H.; Zhang, L.; Si, J.

2017-12-01

Crustal active faults can slide either steadily by aseismic creep, or abruptly by earthquake rupture. Creep can relax continuously the stress and reduce the occurrence of large earthquakes. Identifying the behaviors of active faults plays a crucial role in predicting and preventing earthquake disasters. Based on multi-scale structural analyses for fault rocks from the GAF surface rupture zone and the Wenchuan Earthquake Fault Zone Science Drilling borehole 3P, we detect the analogous "mylonite structures" develop pervasively in GAF fault rocks. Such specious "ductile deformations", showing intensive foliation, spindly clasts, tailing structure, "boudin structure", "augen structure" and S-C fabrics, are actually formed in brittle faulting, which indicates the creeping behavior of the GAF. Furthermore, some special structures hint the creeping mechanism. The cracks and veins developed in fractured clasts imply pressure and fluid control in the faulting. Under the effect of fluid, clasts are dissolved in pressing direction, and solutions are transferred to stress vacancy area at both ends of clasts and deposit to regenerate clay minerals. The clasts thus present spindly shape and are surrounded by orientational clay minerals constituting continuous foliation structure. The clay minerals are dominated by phyllosilicates that can weaken faults and promote pressure solution. Therefore, pressure solution creep and phyllosilicates weakening reasonably interpret the creeping of GAF. Additionally, GPS velocity data show slip rates of the GAF are respectively 1.5 and 12 mm/yr during 1998-2008 and 2009-2011, which also indicate the GAF is in creeping during interseismic period. According to analysis on aftershocks distribution and P-wave velocity with depth and geological section in the Longmenshan thrust belt, we suggest the GAF is creeping in shallow (<10 km) and locked in deep (10-20 km). Comprehensive research shows stress propagated from the west was concentrated near the Yingxiu-Beichuan Fault (YBF) and GAF zones. As stress accumulation reached the limit, the YBF and GAF zones were simultaneously ruptured in 2008 Mw 7.9 Wenchuan earthquake, but the rupture area of the GAF was relatively small due to the presence of shallow creep that relaxed the partial stress.

A simple model for indentation creep

NASA Astrophysics Data System (ADS)

Ginder, Ryan S.; Nix, William D.; Pharr, George M.

2018-03-01

A simple model for indentation creep is developed that allows one to directly convert creep parameters measured in indentation tests to those observed in uniaxial tests through simple closed-form relationships. The model is based on the expansion of a spherical cavity in a power law creeping material modified to account for indentation loading in a manner similar to that developed by Johnson for elastic-plastic indentation (Johnson, 1970). Although only approximate in nature, the simple mathematical form of the new model makes it useful for general estimation purposes or in the development of other deformation models in which a simple closed-form expression for the indentation creep rate is desirable. Comparison to a more rigorous analysis which uses finite element simulation for numerical evaluation shows that the new model predicts uniaxial creep rates within a factor of 2.5, and usually much better than this, for materials creeping with stress exponents in the range 1 ≤ n ≤ 7. The predictive capabilities of the model are evaluated by comparing it to the more rigorous analysis and several sets of experimental data in which both the indentation and uniaxial creep behavior have been measured independently.

Simulation-Based Extreme Value Marked Correlations in Fatigue of Advanced Engineering Alloys (PREPRINT)

DTIC Science & Technology

2010-04-01

000 the response of damage dependent processes like fatigue crack formation, a framework is needed that accounts for the extreme value life...many different damage processes (e.g. fatigue, creep, fracture). In this work, multiple material volumes for both IN100 and Ti-6Al-4V are simulated via...polycrystalline P/M Ni-base superalloy IN100 Typically, fatigue damage formation in polycrystalline superalloys has been linked to the existence of

In situ nonlinear ultrasonic technique for monitoring microcracking in concrete subjected to creep and cyclic loading.

PubMed

Kim, Gun; Loreto, Giovanni; Kim, Jin-Yeon; Kurtis, Kimberly E; Wall, James J; Jacobs, Laurence J

2018-08-01

This research conducts in situ nonlinear ultrasonic (NLU) measurements for real time monitoring of load-induced damage in concrete. For the in situ measurements on a cylindrical specimen under sustained load, a previously developed second harmonic generation (SHG) technique with non-contact detection is adapted to a cylindrical specimen geometry. This new setup is validated by demonstrating that the measured nonlinear Rayleigh wave signals are equivalent to those in a flat half space, and thus the acoustic nonlinearity parameter, β can be defined and interpreted in the same way. Both the acoustic nonlinearity parameter and strain are measured to quantitatively assess the early-age damage in a set of concrete specimens subjected to either 25 days of creep, or 11 cycles of cyclic loading at room temperature. The experimental results show that the acoustic nonlinearity parameter is sensitive to early-stage microcrack formation under both loading conditions - the measured β can be directly linked to the accumulated microscale damage. This paper demonstrates the potential of NLU for the in situ monitoring of mechanical load-induced microscale damage in concrete components. Copyright © 2018 Elsevier B.V. All rights reserved.

Role of back stress in the creep behavior of particle strengthened alloys

NASA Technical Reports Server (NTRS)

Purushothaman, S.; Tien, J. K.

1978-01-01

Recent developments in the interpolation of high-temperature steady-state creep results have introduced the concept that the stress dependence of the creep rate should be in terms of the effective stress referred to as the applied stress minus a back stress. This paper reports on back stresses taken from data on a gamma-prime-strengthened wrought nickel-base superalloy, an oxide dispersion-strengthened ODS nickel-base solid solution alloy, and an ODS nickel-base superalloy. The effect of air versus vacuum environments and the effect of dynamic changes in the strengthening microstructures on the magnitude of the back stress are assessed. The role of modulus normalization and the back stress correction in determining the true creep activation energy are examined. It is shown that the high values of the apparent stress exponent 'n' of the steady-state creep equation can be easily explained through a relationship between n, the true stress exponent of steady-state creep, and the stress which when subtracted from the applied stress results in the effective driving stress acting on the mobile dislocations during creep.

A Critical Review of the Development of Several Viscoplastic Constitutive Theories.

DTIC Science & Technology

1987-09-15

20, 1241 -1251 (1949). [14] E. Krempl and P. Hewelt, "The Constant Volume Hypothesis for the Inelastic Deformation of Metals in the Small Strain Range...Analytical Representation of the Creep Strain-Time Behavior of Commercially Heat Treated Alloy 718," ORNL /TM-6232, 1978. 71 .r w *~ *U* ~ ~ V.WJW -9...Analytical Representation of the Creep Strain-Time Behavior of Commercially Heat Treated Alloy 718," ORNL /TM 6232, 1978. (67 M.A. Eisenberg and C.F

On numerical integration and computer implementation of viscoplastic models

NASA Technical Reports Server (NTRS)

Chang, T. Y.; Chang, J. P.; Thompson, R. L.

1985-01-01

Due to the stringent design requirement for aerospace or nuclear structural components, considerable research interests have been generated on the development of constitutive models for representing the inelastic behavior of metals at elevated temperatures. In particular, a class of unified theories (or viscoplastic constitutive models) have been proposed to simulate material responses such as cyclic plasticity, rate sensitivity, creep deformations, strain hardening or softening, etc. This approach differs from the conventional creep and plasticity theory in that both the creep and plastic deformations are treated as unified time-dependent quantities. Although most of viscoplastic models give better material behavior representation, the associated constitutive differential equations have stiff regimes which present numerical difficulties in time-dependent analysis. In this connection, appropriate solution algorithm must be developed for viscoplastic analysis via finite element method.

Indentation creep behaviors of amorphous Cu-based composite alloys

NASA Astrophysics Data System (ADS)

Song, Defeng; Ma, Xiangdong; Qian, Linfang

2018-04-01

This work reports the indentation creep behaviors of two Si2Zr3/amorphous Cu-based composite alloys utilizing nanoindentation technique. By analysis with Kelvin model, the retardation spectra of alloys at different positions, detached and attached regions to the intermetallics, were deduced. For the indentation of detached regions to Si2Zr3 intermetallics in both alloys, very similarity in creep displacement can be observed and retardation spectra show a distinct disparity in the second retardation peak. For the indentation of detached regions, the second retardation spectra also display distinct disparity. At both positions, the retardation spectra suggest that Si elements may lead to the relatively dense structure in the amorphous matrix and to form excessive Si2Zr3 intermetallics which may deteriorate the plastic deformation of current Cu-based composite alloys.

Strengthening behavior of beta phase in lamellar microstructure of TiAl alloys

NASA Astrophysics Data System (ADS)

Zhu, Hanliang; Seo, D. Y.; Maruyama, K.

2010-01-01

β phase can be introduced to TiAl alloys by the additions of β stabilizing elements such as Cr, Nb, W, and Mo. The β phase has a body-centered cubic lattice structure and is softer than the α2 and γ phases in TiAl alloys at elevated temperatures, and hence is thought to have a detrimental effect on creep strength. However, fine β precipitates can be formed at lamellar interfaces by proper heat treatment conditions and the β interfacial precipitate improves the creep resistance of fully lamellar TiAl alloys, since the phase interface of γ/β retards the motion of dislocations during creep. This paper reviews recent research on high-temperature strengthening behavior of the β phase in fully lamellar TiAl alloys.

Modeling the viscoplastic behavior of Inconel 718 at 1200 F

NASA Technical Reports Server (NTRS)

Abdel-Kader, M. S.; Eftis, J.; Jones, D. L.

1988-01-01

A large number of tests, including tensile, creep, fatigue, and creep-fatigue were performed to characterize the mechanical properties of Inconel 718 (a nickel based superalloy) at 1200 F, the operating temperature for turbine blades. In addition, a few attempts were made to model the behavior of Inconel 718 at 1200 F using viscoplastic theories. The Chaboche theory of viscoplasticity can model a wide variety of mechanical behavior, including monotonic, sustained, and cyclic responses of homogeneous, initially-isotropic, strain hardening (or softening) materials. It is shown how the Chaboche theory can be used to model the viscoplastic behavior of Inconel 718 at 1200 F. First, an algorithm was developed to systematically determine the material parameters of the Chaboche theory from uniaxial tensile, creep, and cyclic data. The algorithm is general and can be used in conjunction with similar high temperature materials. A sensitivity study was then performed and an optimal set of Chaboche's parameters were obtained. This study has also indicated the role of each parameter in modeling the response to different loading conditions.

Interim analysis of long time creep behavior of columbium C-103 alloy

NASA Technical Reports Server (NTRS)

Klopp, W. D.; Titran, R. H.

1976-01-01

Analysis of 16 long time creep tests on columbium C-103 alloy (Cb-10Hf-1Ti-0.7Zr) indicates that the calculated stresses to give 1 percent creep strain in 100,000 hours at 1,255 K (1800 F) are 7.93 and 8.96 MPa (1,150 and 1,300 psi) for fine grained and course grained materials, respectively. The apparent activation energy and stress dependence for creep of this alloy are approximately 315 KJ/gmol (75,300 cal/gmol) and 2.51, respectively, based on Dorn-Sherby types of relations. However, the 90 percent confidence limits on these values are wide because of the limited data currently available.

Spatial and temporal variations in creep rate along the El Pilar fault at the Caribbean-South American plate boundary (Venezuela), from InSAR

NASA Astrophysics Data System (ADS)

Pousse Beltran, Léa.; Pathier, Erwan; Jouanne, François; Vassallo, Riccardo; Reinoza, Carlos; Audemard, Franck; Doin, Marie Pierre; Volat, Matthieu

2016-11-01

In eastern Venezuela, the Caribbean-South American plate boundary follows the El Pilar fault system. Previous studies based on three GPS campaigns (2003-2005-2013) demonstrated that the El Pilar fault accommodates the whole relative displacement between the two tectonic plates (20 mm/yr) and proposed that 50-60% of the slip is aseismic. In order to quantify the possible variations of the aseismic creep in time and space, we conducted an interferometric synthetic aperture radar (InSAR) time series analysis, using the (NSBAS) New Small BAseline Subset method, on 18 images from the Advanced Land Observing Satellite (ALOS-1) satellite spanning the 2007-2011 period. During this 3.5 year period, InSAR observations show that aseismic slip decreases eastward along the fault: the creep rate of the western segment reaches 25.3 ± 9.4 mm/yr on average, compared to 13.4 ± 6.9 mm/yr on average for the eastern segment. This is interpreted, through slip distribution models, as being related to coupled and uncoupled areas between the surface and 20 km in depth. InSAR observations also show significant temporal creep rate variations (accelerations) during the considered time span along the western segment. The transient behavior of the creep is not consistent with typical postseismic afterslip following the 1997 Ms 6.8 earthquake. The creep is thus interpreted as persistent aseismic slip during an interseismic period, which has a pulse- or transient-like behavior.

DaDyn-RS: a tool for the time-dependent simulation of damage, fluid pressure and long-term instability in alpine rock slopes

NASA Astrophysics Data System (ADS)

Riva, Federico; Agliardi, Federico; Amitrano, David; Crosta, Giovanni B.

2017-04-01

Large mountain slopes in alpine environments undergo a complex long-term evolution from glacial to postglacial environments, through a transient period of paraglacial readjustment. During and after this transition, the interplay among rock strength, topographic relief, and morpho-climatic drivers varying in space and time can lead to the development of different types of slope instability, from sudden catastrophic failures to large, slow, long-lasting yet potentially catastrophic rockslides. Understanding the long-term evolution of large rock slopes requires accounting for the time-dependence of deglaciation unloading, permeability and fluid pressure distribution, displacements and failure mechanisms. In turn, this is related to a convincing description of rock mass damage processes and to their transition from a sub-critical (progressive failure) to a critical (catastrophic failure) character. Although mechanisms of damage occurrence in rocks have been extensively studied in the laboratory, the description of time-dependent damage under gravitational load and variable external actions remains difficult. In this perspective, starting from a time-dependent model conceived for laboratory rock deformation, we developed Dadyn-RS, a tool to simulate the long-term evolution of real, large rock slopes. Dadyn-RS is a 2D, FEM model programmed in Matlab, which combines damage and time-to-failure laws to reproduce both diffused damage and strain localization meanwhile tracking long-term slope displacements from primary to tertiary creep stages. We implemented in the model the ability to account for rock mass heterogeneity and property upscaling, time-dependent deglaciation, as well as damage-dependent fluid pressure occurrence and stress corrosion. We first tested DaDyn-RS performance on synthetic case studies, to investigate the effect of the different model parameters on the mechanisms and timing of long-term slope behavior. The model reproduces complex interactions between topography, deglaciation rate, mechanical properties and fluid pressure occurrence, resulting in different kinematics, damage patterns and timing of slope instabilities. We assessed the role of groundwater on slope damage and deformation mechanisms by introducing time-dependent pressure cycling within simulations. Then, we applied DaDyn-RS to real slopes located in the Italian Central Alps, affected by an active rockslide and a Deep Seated Gravitational Slope Deformation, respectively. From Last Glacial Maximum to present conditions, our model allows reproducing in an explicitly time-dependent framework the progressive development of damage-induced permeability, strain localization and shear band differentiation at different times between the Lateglacial period and the Mid-Holocene climatic transition. Different mechanisms and timings characterize different styles of slope deformations, consistently with available dating constraints. DaDyn-RS is able to account for different long-term slope dynamics, from slow creep to the delayed transition to fast-moving rockslides.

Variations in creep rate along the Hayward Fault, California, interpreted as changes in depth of creep

USGS Publications Warehouse

Simpson, R.W.; Lienkaemper, J.J.; Galehouse, J.S.

2001-01-01

Variations ill surface creep rate along the Hayward fault are modeled as changes in locking depth using 3D boundary elements. Model creep is driven by screw dislocations at 12 km depth under the Hayward and other regional faults. Inferred depth to locking varies along strike from 4-12 km. (12 km implies no locking.) Our models require locked patches under the central Hayward fault, consistent with a M6.8 earthquake in 1868, but the geometry and extent of locking under the north and south ends depend critically on assumptions regarding continuity and creep behavior of the fault at its ends. For the northern onshore part of the fault, our models contain 1.4-1.7 times more stored moment than the model of Bu??rgmann et al. [2000]; 45-57% of this stored moment resides in creeping areas. It is important for seismic hazard estimation to know how much of this moment is released coseismically or as aseismic afterslip.

Creep of Ni(3)Al in the temperature regime of anomalous flow behavior

NASA Astrophysics Data System (ADS)

Uchic, Michael David

Much attention has been paid to understanding the dynamics of dislocation motion and substructure formation in Ni3Al in the anomalous flow regime. However, most of the experimental work that has been performed in the lowest temperatures of the anomalous flow regime has been under constant-strain-rate conditions. An alternative and perhaps more fundamental way to probe the plastic behavior of materials is a monotonic creep test, in which the stress and temperature are held constant while the time-dependent strain is measured. The aim of this study is to use constant-stress experiments to further explore the plastic flow anomaly in L12 alloys at low temperatures. Tension creep experiments have been carried out on <123> oriented single crystals of Ni75Al24Ta1 at temperatures between 293 and 473 K. We have observed primary creep leading to exhaustion at all temperatures and stresses, with creep rates declining faster than predicted by the logarithmic creep law. The total strain and creep strain have an anomalous dependence on temperature, which is consistent with the flow stress anomaly. We have also observed other unusual behavior in our creep experiments; for example, the reinitiation of plastic flow at low temperatures after a modest increment in applied stress shows a sigmoidal response, i.e., there is a significant time delay before the plastic strain rate accelerates to a maximum value. We also examined the ability to reinitiate plastic flow in samples that have been crept to exhaustion by simply lowering the test temperature. In addition, we have also performed conventional constant-displacement-rate experiments in the same temperature range. From these experiments, we have discovered that unlike most metals, Ni3Al displays a negative dependence of the work hardening rate (WHR) with increasing strain rate. For tests at intermediate temperatures (373 and 423 K), the WHRs of crystals tested at moderately high strain rates (10-2 s-1) are half the WHRs of crystals tested at conventional strain rates (10 -5 s-1), and this anomalous dependence has also been shown to be reversible with changes in strain rate. The implications of all results are discussed in light of our efforts to model plastic deformation in these alloys.

Permeability and of the San Andreas Fault core and damage zone from SAFOD drill core

NASA Astrophysics Data System (ADS)

Rathbun, A. P.; Fry, M.; Kitajima, H.; Song, I.; Carpenter, B. M.; Marone, C.; Saffer, D. M.

2012-12-01

Quantifying fault-rock permeability is important toward understanding both the regional hydrologic behavior of fault zones, and poro-elastic processes that may affect faulting and earthquake mechanics by mediating effective stress. These include persistent fluid overpressures hypothesized to reduce fault strength, as well as dynamic processes that may occur during earthquake slip, including thermal pressurization and dilatancy hardening. To date, studies of permeability on fault rocks and gouge from plate-boundary strike-slip faults have mainly focused on samples from surface outcrops. We report on permeability tests conducted on the host rock, damage zone, and a major actively creeping fault strand (Central Deformation Zone, CDZ) of the San Andreas Fault (SAF), obtained from coring across the active SAF at ~2.7 km depth as part of SAFOD Phase III. We quantify permeability on subsamples oriented both perpendicular and parallel to the coring axis, which is nearly perpendicular to the SAF plane, to evaluate permeability anisotropy. The fault strand samples were obtained from the CDZ, which accommodates significant creep, and hosts ~90% of the observed casing deformation measured between drilling phases. The CDZ is 2.6 m thick with a matrix grain size < 10 μm and ~5% vol. clasts, and contains ~80% clay, of which ~90% is smectite. We also tested damage zone samples taken from adjacent core sections within a few m on either side of the CDZ. Permeability experiments were conducted in a triaxial vessel, on samples 25.4 mm in diameter and ~20-35 mm in length. We conducted measurements under isotropic stress conditions, at effective stress (Pc') of ~5-70 MPa. We measure permeability using a constant head flow-through technique. At the highest Pc', low permeability of the CDZ and damage zone necessitates using a step loading transient method and is in good agreement with permeabilities obtained from flow-through experiments. We quantify compression behavior by monitoring the volumetric and axial strain in response to changes in effective stress. Permeability of the CDZ is systematically lower than that of the damage zone or wall rock, and decreases from 2x10 -19m 2 at 5 MPa effective stress to 5x10-21 m 2 at 65 MPa. Some damage zone samples exhibit permeabilities as low as the CDZ, but most values are ~10-30 times higher. For both the damage zone and CDZ, permeability anisotropy is negligible. Volumetric compressibility (mv) decreases from ~1x10-9 Pa-1 to ~1x10-10 Pa-1 and hydraulic diffusivity decreases from ~2x10-7 m2/s to 1.7x10-8 m2/s over a range of effective stresses from 10 to 65 MPa. Our results are consistent with published geochemical data from SAFOD mud gas monitoring, and from inferred pore pressures during drilling [Zoback et al., 2010], which together suggest that the fault has a low permeability and is a barrier to regional fluid flow along. Our results also demonstrate that the diffusivity of the fault core of CDZ is sufficiently low to result in effectively undrained behavior over timescales of minutes to hours, thus facilitating dynamic hydrologic processes that may impact fault slip, including thermal pressurization and dilatancy hardening.

Generation of plate tectonics via grain-damage and pinning

NASA Astrophysics Data System (ADS)

Bercovici, D.; Ricard, Y. R.

2012-12-01

Weakening and shear localization in the lithosphere are essential ingredients for understanding how and whether plate tectonics is generated from mantle convection on terrestrial planets. The grain-damage and pinning mechanism of Bercovici & Ricard (2012) for lithospheric shear--localization proposes that damage to the interface between phases in a polycrystalline material like peridotite (composed primarily of olivine and pyroxene) increases the number of small Zener pinning surfaces that constrain mineral grains to ever smaller sizes regardless of creep mechanism. This effect allows a self-softening feedback in which damage and grain-reduction can co-exist with a grain-size dependent diffusion creep rheology; moreoever, grain growth and weak-zone healing are greatly impeded by Zener pinning thereby leading to long-lived relic weak zones. This mechanism is employed in two-dimensional flow calculations to test its ability to generate toroidal (strike-slip) motion from convective type flow and to influence plate evolution. The fluid dynamical calculations employ source-sink driven flow as a proxy for convective poloidal flow (upwelling/downwelling and divergent/convergent motion), and the coupling of this flow with non-linear rheological mechanisms excites toroidal or strike-slip motion. The numerical experiments show that pure dislocation-creep rheology, and grain-damage without Zener pinning (as occurs in a single-phase assemblages) permit only weak localization and toroidal flow; however, the full grain-damage with pinning readily allows focussed localization and intense, plate-like toroidal motion and strike-slip deformation. Rapid plate motion changes are also tested with abrupt rotations of the source-sink field after a plate-like configuration is developed; the post-rotation flow and material property fields are found to never recover or lose memory of the original configuration, leading to suboptimally aligned plate boundaries (e.g., strike-slip margins non-parallel to plate motion), oblique subduction and highly localized, weak and long lived acute plate-boundary junctions such as at the Aleution-Kurile intersection. The grain-damage and pinning theory therefore readily satisfies key plate-tectonic metrics of localized toroidal motion and plate-boundary inheritance, and thus provides a predictive theory for the generation of plate tectonics on Earth and other planets. References: Bercovici, D., Ricard, Y., 2012. Mechanisms for the generation of plate tectonics by two-phase grain-damage and pinning. Phys. Earth Planet. Int. 202-203, 27--55.

Creep-fatigue modelling in structural steels using empirical and constitutive creep methods implemented in a strip-yield model

NASA Astrophysics Data System (ADS)

Andrews, Benjamin J.

The phenomena of creep and fatigue have each been thoroughly studied. More recently, attempts have been made to predict the damage evolution in engineering materials due to combined creep and fatigue loading, but these formulations have been strictly empirical and have not been used successfully outside of a narrow set of conditions. This work proposes a new creep-fatigue crack growth model based on constitutive creep equations (adjusted to experimental data) and Paris law fatigue crack growth. Predictions from this model are compared to experimental data in two steels: modified 9Cr-1Mo steel and AISI 316L stainless steel. Modified 9Cr-1Mo steel is a high-strength steel used in the construction of pressure vessels and piping for nuclear and conventional power plants, especially for high temperature applications. Creep-fatigue and pure creep experimental data from the literature are compared to model predictions, and they show good agreement. Material constants for the constitutive creep model are obtained for AISI 316L stainless steel, an alloy steel widely used for temperature and corrosion resistance for such components as exhaust manifolds, furnace parts, heat exchangers and jet engine parts. Model predictions are compared to pure creep experimental data, with satisfactory results. Assumptions and constraints inherent in the implementation of the present model are examined. They include: spatial discretization, similitude, plane stress constraint and linear elasticity. It is shown that the implementation of the present model had a non-trivial impact on the model solutions in 316L stainless steel, especially the spatial discretization. Based on these studies, the following conclusions are drawn: 1. The constitutive creep model consistently performs better than the Nikbin, Smith and Webster (NSW) model for predicting creep and creep-fatigue crack extension. 2. Given a database of uniaxial creep test data, a constitutive material model such as the one developed for modified 9Cr-1Mo can be developed for other materials. 3. Due to the assumptions used to develop the strip-yield model, model predictions are expected to show some scatter, especially in some situations. Several areas of future research are proposed from these conclusions: 1. Alternative methods for predicting fatigue crack growth, especially a constitutive fatigue crack growth model, 2. Continued development of new material models and refinement the existing ones, and 3. Implementation of the present creep-fatigue model as a user-defined subroutine in a finite element solver.

Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part 2; Effect of Thermal Cycling

NASA Technical Reports Server (NTRS)

Raj, S. V.; Noebe, R. D.

2013-01-01

This paper is the first report on the effect prior low temperature creep on the thermal cycling behavior of NiTi. The isothermal low temperature creep behavior of near-stoichiometric NiTi between 300 and 473 K was discussed in Part I. The effect of temperature cycling on its creep behavior is reported in the present paper (Part II). Temperature cycling tests were conducted between either 300 or 373 K and 473 K under a constant applied stress of either 250 or 350 MPa with hold times lasting at each temperature varying between 300 and 700 h. Each specimen was pre-crept either at 300 or at 473 K for several months under an identical applied stress as that used in the subsequent thermal cycling tests. Irrespective of the initial pre-crept microstructures, the specimens exhibited a considerable increase in strain with each thermal cycle so that the total strain continued to build-up to 15 to 20 percent after only 5 cycles. Creep strains were immeasurably small during the hold periods. It is demonstrated that the strains in the austenite and martensite are linearly correlated. Interestingly, the differential irrecoverable strain, in the material measured in either phase decreases with increasing number of cycles, similar to the well-known Manson-Coffin relation in low cycle fatigue. Both phases are shown to undergo strain hardening due to the development of residual stresses. Plots of true creep rate against absolute temperature showed distinct peaks and valleys during the cool-down and heat-up portions of the thermal cycles, respectively. Transformation temperatures determined from the creep data revealed that the austenitic start and finish temperatures were more sensitive to the pre-crept martensitic phase than to the pre-crept austenitic phase. The results are discussed in terms of a phenomenological model, where it is suggested that thermal cycling between the austenitic and martensitic phase temperatures or vice versa results in the deformation of the austenite and a corresponding development of a back stress due to a significant increase in the dislocation density during thermal cycling.

Thermomechanical fatigue life prediction for several solders

NASA Astrophysics Data System (ADS)

Wen, Shengmin

Since solder connections operate at high homologous temperature, solders are high temperature materials. This feature makes their mechanical behavior and fatigue phenomena unique. Based on experimental findings, a physical damage mechanism is introduced for solders. The mechanism views the damage process as a series of independent local damage events characterized by the failure of individual grains, while the structural damage is the eventual percolation result of such local events. Fine's dislocation energy density concept and Mura's microcrack initiation theory are adopted to derive the fatigue formula for an individual grain. A physical damage metric is introduced to describe the material with damage. A unified creep and plasticity constitutive model is adopted to simulate the mechanical behavior of solders. The model is cast into a continuum damage mechanics framework to simulate material with damage. The model gives good agreement with the experimental results of 96.5Pb-3.5Sn and 96.5Sn-3.5Ag solders under uniaxial strain-controlled cyclic loading. The model is convenient for implementation into commercial computational packages. Also presented is a fatigue theory with its failure criterion for solders based on physical damage mechanism. By introducing grain orientation into the fatigue formula, an m-N curve (m is Schmid factor) at constant loading condition is suggested for fatigue of grains with different orientations. A solder structure is defined as fatigued when the damage metric reaches a critical threshold, since at this threshold the failed grains may form a cluster and percolate through the structure according to percolation theory. Fatigue data of 96.5Pb-3.5Sn solder bulk specimens under various uniaxial tension tests were analyzed. Results show that the theory gives consistent predictions under broad conditions, while inelastic strain theory does not. The theory is anisotropic with no size limitation to its application, which could be suitable for anisotropic small-scale (micron or nano scale) solder joints. More importantly, the theory is materials science based so that the parameters of the fatigue formula can be worked out by testing of bulk specimens while the formula can be applicable to small-scale structures. The theory suggests metallurgical control in the manufacturing process to optimize the fatigue life of solder structures.

Thermal, creep-recovery and viscoelastic behavior of high density polyethylene/hydroxyapatite nano particles for bone substitutes: effects of gamma radiation.

PubMed

Alothman, Othman Y; Fouad, H; Al-Zahrani, S M; Eshra, Ayman; Al Rez, Mohammed Fayez; Ansari, S G

2014-08-28

High Density Polyethylene (HDPE) is one of the most often used polymers in biomedical applications. The limitations of HDPE are its visco-elastic behavior, low modulus and poor bioactivity. To improve HDPE properties, HA nanoparticles can be added to form polymer composite that can be used as alternatives to metals for bone substitutes and orthopaedic implant applications. In our previous work (BioMedical Engineering OnLine 2013), different ratios of HDPE/HA nanocomposites were prepared using melt blending in a co-rotating intermeshing twin screw extruder. The accelerated aging effects on the tensile properties and torsional viscoelastic behavior (storage modulus (G') and Loss modulus (G")) at 80°C of irradiated and non-irradiated HDPE/HA was investigated. Also the thermal behavior of HDPE/HA were studied. In this study, the effects of gamma irradiation on the tensile viscoelastic behavior (storage modulus (E') and Loss modulus (E")) at 25°C examined for HDPE/HA nanocomposites at different frequencies using Dynamic Mechanical Analysis (DMA). The DMA was also used to analyze creep-recovery and relaxation properties of the nanocomposites. To analyze the thermal behavior of the HDPE/HA nanocomposite, Differential Scanning Calorimetry (DSC) was used. The microscopic examination of the cryogenically fractured surface revealed a reasonable distribution of HA nanoparticles in the HDPE matrix. The DMA showed that the tensile storage and loss modulus increases with increasing the HA nanoparticles ratio and the test frequency. The creep-recovery behavior improves with increasing the HA nanoparticle content. Finally, the results indicated that the crystallinity, viscoelastic, creep recovery and relaxation behavior of HDPE nanocomposite improved due to gamma irradiation. Based on the experimental results, it is found that prepared HDPE nanocomposite properties improved due to the addition of HA nanoparticles and irradiation. So, the prepared HDPE/HA nanocomposite appears to have fairly good comprehensive properties that make it a good candidate as bone substitute.

Quantitative energy-filtered TEM imaging of interfaces

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

Bentley, J.; Kenik, E.A.; Siangchaew, K.

Quantitative elemental mapping by inner shell core-loss energy-filtered transmission electron microscopy (TEM) with a Gatan Imaging Filter (GIF) interfaced to a Philips CM30 TEM operated with a LaB{sub 6} filament at 300 kV has been applied to interfaces in a range of materials. In sensitized type 304L stainless steel aged 15 h at 600{degrees}C, grain-boundary Cr depletion occurs between Cr-rich intergranular M{sub 23}C{sub 6} particles. Images of net Cr L{sub 23} intensity show segregation profiles that agree quantitatively with focused-probe spectrum-line measurements recorded with a Gatan PEELS on a Philips EM400T/FEG (0.8 nA in 2-nm-diam probe) of the same regions.more » Rare-earth oxide additives that are used for the liquid-phase sintering of Si{sub 3}N{sub 4} generate second phases of complex composition at grain boundaries and edges. These grain boundary phases often control corrosion, crack growth and creep damage behavior. High resolution imaging has been widely and with focused probes can be compromised by beam damage, but elemental mapping by EFTEM appears not to cause appreciable beam damage.« less

Tension and Compression Creep Apparatus for wood-Plastic Composites

Treesearch

Scott E. Hamel; John C. Hermanson; Steven M. Cramer

2011-01-01

Design of structural members made of wood-plastic composites (WPC) is not possible without accurate test data for tension and compression. The viscoelastic behavior of these materials means that these data are required for both the quasi-static stress-strain response, and the long-term creep response. Their relative incompressibility causes inherent difficulties in...

Effect of moderate magnetic annealing on the microstructure, quasi-static and viscoelastic mechanical behavior of a structural epoxy

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

Tehrani, Mehran; Al-Haik, Marwan; Garmestani, Hamid

2012-01-01

In this study the effect of moderate magnetic fields on the microstructure of a structural epoxy system was investigated. The changes in the microstructure have been quantitatively investigated using wide angle x-ray diffraction (WAXD) and pole figure analysis. The mechanical properties (modulus, hardness and strain rate sensitivity parameter) of the epoxy system annealed in the magnetic field were probed with the aid of instrumented nanoindentation and the results are compared to the reference epoxy sample. To further examine the creep response of the magnetically annealed and reference samples, short 45 min duration creep tests were carried out. An equivalent tomore » the macro scale creep compliance was calculated using the aforementioned nano-creep data. Using the continuous complex compliance (CCC) analysis, the phase lag angle, tan (δ), between the displacement and applied force in an oscillatory nanoindentation test was measured for both neat and magnetically annealed systems through which the effect of low magnetic fields on the viscoelastic properties of the epoxy was invoked. The comparison of the creep strain rate sensitivity parameter , A/d(0), from short term(80 ), creep tests and the creep compliance J(t) from the long term(2700 s) creep tests with the tan(δ) suggests that former parameter is a more useful comparative creep parameter than the creep compliance. The results of this investigation reveal that under low magnetic fields both the quasi-static and viscoelastic mechanical properties of the epoxy have been improved.« less

Damage mechanisms in alloy 800H under creep-fatigue conditions

NASA Astrophysics Data System (ADS)

Mu, Z.; Bothe, K.; Gerold, V.

1994-05-01

The interaction between fatigue damage (i.e., fatigue crack propagation) and internal grain boundary damage (i.e., cavity formation at grain boundaries) has been studied for the Alloy 800H at 750 C for constant plastic strain ranges but different experimental conditions. Most experiments were performed at constant ranges of alternating tensile/compression stresses. Symmetrical as well as asymmetrical tests (with larger compression stresses) were performed. In comparison to the former tests, asymmetrical tests led to shorter cyclic lifetimes mainly due to cavity formation which was not observed for symmetrical tests. It could be shown that a fast compressive and a slow tensile half cycle (at large compressive and low tensile stresses) are ideal conditions for the nucleation and growth of cavities. Based on quantitative measurements of the cavity density from interrupted fatigue tests, a physical model is presented which can predict the number of cycles to failure. This cycle number is determined only by fatigue crack growth which is controlled by (1) athermal plastic deformation, (2) creep deformation and (3) rate enhancement by cavitation.

Creep deformation in near-γ TiAl: Part 1. the influence of microstructure on creep deformation in Ti-49Al-1V

NASA Astrophysics Data System (ADS)

Worth, Brian D.; Jones, J. Wayne; Allison, John E.

1995-11-01

The influence of microstructure on creep deformation was examined in the near-y TiAl alloy Ti-49A1-1V. Specifically, microstructures with varying volume fractions of lamellar constituent were produced through thermomechanical processing. Creep studies were conducted on these various microstructures under constant load in air at temperatures between 760 °C and 870 °C and at stresses ranging from 50 to 200 MPa. Microstructure significantly influences the creep behavior of this alloy, with a fully lamellar microstructure yielding the highest creep resistance of the microstructures examined. Creep resistance is dependent on the volume fraction of lamellar constituent, with the lowest creep resistance observed at intermediate lamellar volume fractions. Examination of the creep deformation structure revealed planar slip of dislocations in the equiaxed y microstructure, while subboundary formation was observed in the duplex microstructure. The decrease in creep resistance of the duplex microstructure, compared with the equiaxed y microstructure, is attributed to an increase in dislocation mobility within the equiaxed y constituent, that results from partitioning of oxygen from the γ phase to the α2 phase. Dislocation motion in the fully lamellar microstructure was confined to the individual lamellae, with no evidence of shearing of γ/γ or γ/α2 interfaces. This suggests that the high creep resistance of the fully lamellar microstructure is a result of the fine spacing of the lamellar structure, which results in a decreased effective slip length for dislocation motion over that found in the duplex and equiaxed y microstructures.

The Combined Influence of Molecular Weight and Temperature on the Aging and Viscoelastic Response of a Glassy Thermoplastic Polyimide

NASA Technical Reports Server (NTRS)

Nicholson, Lee M.; Whitley, Karen S.; Gates, Thomas S.

2000-01-01

The effect of molecular weight on the viscoelastic performance of an advanced polymer (LaRC-SI) was investigated through the use of creep compliance tests. Testing consisted of short-term isothermal creep and recovery with the creep segments performed under constant load. The tests were conducted at three temperatures below the glass transition temperature of five materials of different molecular weight. Through the use of time-aging-time superposition procedures, the material constants, material master curves and aging-related parameters were evaluated at each temperature for a given molecular weight. The time-temperature superposition technique helped to describe the effect of temperature on the timescale of the viscoelastic response of each molecular weight. It was shown that the low molecular weight materials have higher creep compliance and creep rate, and are more sensitive to temperature than the high molecular weight materials. Furthermore, a critical molecular weight transition was observed to occur at a weight-average molecular weight of M (bar) (sub w) 25000 g/mol below which, the temperature sensitivity of the time-temperature superposition shift factor increases rapidly. The short-term creep compliance data were used in association with Struik's effective time theory to predict the long-term creep compliance behavior for the different molecular weights. At long timescales, physical aging serves to significantly decrease the creep compliance and creep rate of all the materials tested.

Creep of Heat-Resistant Composites of an Oxide-Fiber/Ni-Matrix Family

NASA Astrophysics Data System (ADS)

Mileiko, S. T.

2001-09-01

A creep model of a composite with a creeping matrix and initially continuous elastic brittle fibers is developed. The model accounts for the fiber fragmentation in the stage of unsteady creep of the composite, which ends with a steady-state creep, where a minimum possible average length of the fiber is achieved. The model makes it possible to analyze the creep rate of the composite in relation to such parameters of its structure as the statistic characteristics of the fiber strength, the creep characteristics of the matrix, and the strength of the fiber-matrix interface, the latter being of fundamental importance. A comparison between the calculation results and the experimental ones obtained on composites with a Ni-matrix and monocrystalline and eutectic oxide fibers as well as on sapphire fiber/TiAl-matrix composites shows that the model is applicable to the computer simulation of the creep behavior of heat-resistant composites and to the optimization of the structure of such composites. By combining the experimental data with calculation results, it is possible to evaluate the heat resistance of composites and the potential of oxide-fiber/Ni-matrix composites. The composite specimens obtained and tested to date reveal their high creep resistance up to a temperature of 1150°C. The maximum operating temperature of the composites can be considerably raised by strengthening the fiber-matrix interface.

Long Term Displacement Data of Woven Fabric Webbings Under Constant Load for Inflatable Structures

NASA Technical Reports Server (NTRS)

Kenner, Winfred S.; Jones, Thomas C.; Doggett, William R.; Lucy, Melvin H.; Grondin, Trevor A.; Whitley, Karen S.; Duncan, Quinton; Plant, James V.

2014-01-01

Inflatable modules for space applications offer weight and launch volume savings relative to current metallic modules. Limited data exist on the creep behavior of the restraint layer of inflatable modules. Long-term displacement and strain data of two high strength woven fabric webbings, Kevlar and Vectran, under constant load is presented. The creep behavior of webbings is required by designers to help determine service life parameters of inflatable modules. Four groups of different webbings with different loads were defined for this study. Group 1 consisted of 4K Kevlar webbings loaded to 33% ultimate tensile strength and 6K Vectran webbings loaded to 27% ultimate tensile strength, group 2 consisted of 6K Kevlar webbings loaded to 40% and 43% ultimate tensile strength, and 6K Vectran webbings loaded to 50% ultimate tensile strength, group 3 consisted of 6K Kevlar webbings loaded to 52% ultimate tensile strength and 6K Vectran webbings loaded to 60% ultimate tensile strength, and group 4 consisted of 12.5K Kevlar webbings loaded to 22% ultimate tensile strength, and 12.5K Vectran webbings loaded to 22% ultimate tensile strength. The uniquely designed test facility, hardware, displacement measuring devices, and test data are presented. Test data indicate that immediately after loading all webbings stretch an inch or more, however as time increases displacement values significantly decrease to fall within a range of several hundredth of an inch over the remainder of test period. Webbings in group 1 exhibit near constant displacements and strains over a 17-month period. Data acquisition was suspended after the 17th month, however webbings continue to sustain load without any local webbing damage as of the 21st month of testing. Webbings in group 2 exhibit a combination of initial constant displacement and subsequent increases in displacement rates over a 16-month period. Webbings in group 3 exhibit steady increases in displacement rates leading to webbing failure over a 3-month period. Five of six webbings experienced local damage and subsequent failure in group 3. Data from group 4 indicates increasing webbing displacements over a 7-month period. All webbings in groups 1, 2, and 4 remain suspended without any local damage as of the writing of this paper. Variations in facility temperatures over test period seem to have had limited effect on long-term webbing displacement data.

Strengthening Mechanisms, Creep and Fatigue Processes in Dispersion Hardened Niobium Alloy

DTIC Science & Technology

1991-05-01

WORK UNIT BOLLING AFB DC 20332-6448 ELEMENT No. NO. NO. NO ATTN: DR. ALAN H. ROSENSTEIN 61102F 2306 Al 1 1 TITLE tilnciude Security CluAifIcatlonI 12... Mughrabi , volume editor, in the series "Materials Science and Technology" by VCH Verlagsgesellshaft mbH, Germany. 4. CREEP BEHAVIOR OF Nb-1%Zr AT...Meeting, Japan Institute of Metals, Sendia, Japan, 1990. 6. CREEP AND AGING RESPONSE OF A RAPIDLY SOLIDIFIED Al -Fe-V-Si ALLOY, R. J. Lewis and J. C

Biaxial Creep Specimen Fabrication

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

JL Bump; RF Luther

This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Navalmore » Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments.« less

Quasi-static and ratcheting properties of trabecular bone under uniaxial and cyclic compression.

PubMed

Gao, Li-Lan; Wei, Chao-Lei; Zhang, Chun-Qiu; Gao, Hong; Yang, Nan; Dong, Li-Min

2017-08-01

The quasi-static and ratcheting properties of trabecular bone were investigated by experiments and theoretical predictions. The creep tests with different stress levels were completed and it is found that both the creep strain and creep compliance increase rapidly at first and then increase slowly as the creep time goes by. With increase of compressive stress the creep strain increases and the creep compliance decreases. The uniaxial compressive tests show that the applied stress rate makes remarkable influence on the compressive behaviors of trabecular bone. The Young's modulus of trabecular bone increases with increase of stress rate. The stress-strain hysteresis loops of trabecular bone under cyclic load change from sparse to dense with increase of number of cycles, which agrees with the change trend of ratcheting strain. The ratcheting strain rate rapidly decreases at first, and then exhibits a relatively stable and small value after 50cycles. Both the ratcheting strain and ratcheting strain rate increase with increase of stress amplitude or with decrease of stress rate. The creep model and the nonlinear viscoelastic constitutive model of trabecular bone were proposed and used to predict its creep property and rate-dependent compressive property. The results show that there are good agreements between the experimental data and predictions. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of Silane Coupling Agent on the Creep Behavior and Mechanical Properties of Carbon Fibers/Acrylonitrile Butadiene Rubber Composites.

PubMed

Choi, Woong-Ki; Park, Gil-Young; Kim, Byoung-Shuk; Seo, Min-Kang

2018-09-01

In this study, we investigated the effect of the silane coupling agent on the relationship between the surface free energy of carbon fibers (CFs) and the mechanical strength of CFs/acrylonitrile butadiene rubber (NBR) composites. Moreover, the creep behavior of the CF/NBR composites at surface energetic point of view were studied. The specific component of the surface free energy of the carbon fibers was found to increase upon grafting of the silane coupling agent, resulting in an increase in the tensile strength of the CF/NBR composites. On the other hand, the compressive creep strength was found to follow a slightly different trend. These results indicate the possible formation of a complex interpenetrating polymer network depending on the molecular size of the organic functional groups of the silane coupling agent.

Unified Static and Dynamic Recrystallization Model for the Minerals of Earth's Mantle Using Internal State Variable Model

NASA Astrophysics Data System (ADS)

Cho, H. E.; Horstemeyer, M. F.; Baumgardner, J. R.

2017-12-01

In this study, we present an internal state variable (ISV) constitutive model developed to model static and dynamic recrystallization and grain size progression in a unified manner. This method accurately captures temperature, pressure and strain rate effect on the recrystallization and grain size. Because this ISV approach treats dislocation density, volume fraction of recrystallization and grain size as internal variables, this model can simultaneously track their history during the deformation with unprecedented realism. Based on this deformation history, this method can capture realistic mechanical properties such as stress-strain behavior in the relationship of microstructure-mechanical property. Also, both the transient grain size during the deformation and the steady-state grain size of dynamic recrystallization can be predicted from the history variable of recrystallization volume fraction. Furthermore, because this model has a capability to simultaneously handle plasticity and creep behaviors (unified creep-plasticity), the mechanisms (static recovery (or diffusion creep), dynamic recovery (or dislocation creep) and hardening) related to dislocation dynamics can also be captured. To model these comprehensive mechanical behaviors, the mathematical formulation of this model includes elasticity to evaluate yield stress, work hardening in treating plasticity, creep, as well as the unified recrystallization and grain size progression. Because pressure sensitivity is especially important for the mantle minerals, we developed a yield function combining Drucker-Prager shear failure and von Mises yield surfaces to model the pressure dependent yield stress, while using pressure dependent work hardening and creep terms. Using these formulations, we calibrated against experimental data of the minerals acquired from the literature. Additionally, we also calibrated experimental data for metals to show the general applicability of our model. Understanding of realistic mantle dynamics can only be acquired once the various deformation regimes and mechanisms are comprehensively modeled. The results of this study demonstrate that this ISV model is a good modeling candidate to help reveal the realistic dynamics of the Earth's mantle.

Creep behavior for advanced polycrystalline SiC fibers

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

Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

1997-04-01

A bend stress relaxation (BSR) test has been utilized to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Qualitative, S-shaped 1hr BSR curves were compared for three selected advanced SiC fiber types and standard Nicalon CG fiber. The temperature corresponding to the middle of the S-curve (where the BSR parameter m = 0.5) is a measure of a fiber`s thermal stability as well as it creep resistance. In order of decreasing thermal creep resistance, the measured transition temperatures were Nicalon S (1450{degrees}C), Sylramic (1420{degrees}C), Hi-Nicalon (1230{degrees}C) and Nicalonmore » CG (1110{degrees}C).« less

Assessing the Effects of Radiation Damage on Ni-base Alloys for the Prometheus Space Reactor System

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

T. Angeliu

2006-01-19

Ni-base alloys were considered for the Prometheus space reactor pressure vessel with operational parameters of {approx}900 K for 15 years and fluences up to 160 x 10{sup 20} n/cm{sup 2} (E > 0.1 MeV). This paper reviews the effects of irradiation on the behavior of Ni-base alloys and shows that radiation-induced swelling and creep are minor considerations compared to significant embrittlement with neutron ,exposure. While the mechanism responsible for radiation-induced embrittlement is not fully understood, it is likely a combination of helium embrittlement and solute segregation that can be highly dependent on the alloy composition and exposure conditions. Transmutation calculationsmore » show that detrimental helium levels would be expected at the end of life for the inner safety rod vessel (thimble) and possibly the outer pressure vessel, primarily from high energy (E > 1 MeV) n,{alpha} reactions with {sup 58}Ni. Helium from {sup 10}B is significant only for the outer vessel due to the proximity of the outer vessel to the Be0 control elements. Recommendations for further assessments of the material behavior and methods to minimize the effects of radiation damage through alloy design are provided.« less

Elevated temperature mechanical behavior of monolithic and SiC whisker-reinforced silicon nitrides

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.; Choi, Sung R.; Sanders, William A.; Fox, Dennis S.

1991-01-01

The mechanical behavior of a 30 volume percent SiC whisker reinforced silicon nitride and a similar monolithic silicon nitride were measured at several temperatures. Measurements included strength, fracture toughness, crack growth resistance, dynamic fatigue susceptibility, post oxidation strength, and creep rate. Strength controlling defects were determined with fractographic analysis. The addition of SiC whiskers to silicon nitride did not substantially improve the strength, fracture toughness, or crack growth resistance. However, the fatigue resistance, post oxidation strength, and creep resistance were diminished by the whisker addition.

Compressive creep behavior of alloys based on B2 FeAl

NASA Technical Reports Server (NTRS)

Mantravadi, N.; Vedula, K.; Gaydosh, D.; Titran, R. H.

1986-01-01

Alloys based on FeAl are attractive alternate materials for environmental resistance at intermediate temperatures. Addition of small amounts of Nb, Hf, Ta, Mo, Zr, and B were shown to improve the compressive creep of this alloy at 1100 K. Boron, in particular, was found to have a synergistic effect along with Zr in providing properties substantially better than the binary alloy. This improvement seems to be related to the higher activation energy found for this alloy, suggesting a modification in the diffusion behavior due to the alloying additions.

Compressive creep behavior of alloys based on B2 FeAl

NASA Technical Reports Server (NTRS)

Mantravadi, N.; Vedula, K.; Gaydosh, D.; Titran, R. H.

1987-01-01

Alloys based on FeAl are attractive alternative materials for environmental resistance at intermediate temperatures. Addition of small amounts of Nb, Hf, Ta, Mo, Zr, and B were shown to improve the compressive creep of this alloy at 1100 K. Boron, in particular, was found to have a synergistic effect along with Zr in providing properties substantially better than the binary alloy. This improvement seems to be related to the higher activation energy found for this alloy, suggesting a modification in the diffusion behavior due to the alloying additions.

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

Wereszczak, A.A.; Ferber, M.K.; Kirkland, T.P.

Several yttria-fluxed, hot-isostatically pressed (HIPed) silicon nitrides have been tensile creep tested at temperatures representative of gas turbine engines. Creep and oxidation assisted damage mechanisms concurrently evolve when these materials are tested at high temperatures and low stresses (i.e., long exposure times at temperature). Atmospheric creep testing results in creation of oxygen and yttrium gradients across the radial dimension. High concentrations of oxygen and yttrium coincide with dense populations of lenticular-shaped cavities near the surface of crept specimens. The center of the tensile specimens was devoid of oxygen or yttrium; in addition, lenticular cavities were rare. The gradient in lenticular-cavitymore » concentration is coincident with the oxygen and yttrium gradients. Stress corrosion cracking (SCC) also occurs in these HIPed silicon nitrides when they are subjected to stress at high temperatures in ambient air. The size of this damage zone increases when the temperature is higher and/or the applied stress is lower. Stress-corrosion cracking initiates at the surface of the tensile specimen and advances radially inwards. What nucleates SCC has not yet been identified, but it is believed to result from a stress-concentrator (e.g., machining damage) at the surface and its growth is a result of coalescence of microcracks and cavities. The higher concentration of oxygen and yttrium in the grain boundaries near the specimen`s surface lessens the local high temperature mechanical integrity; this is believed to be associated with the growth of the SCC zone. This SCC zone continues to grow in size during tensile loading until it reaches a critical size which causes fracture.« less

Reliability and Creep/Fatigue Analysis of a CMC Component

NASA Technical Reports Server (NTRS)

Murthy, Pappu L. N.; Mital, Subodh K.; Gyekenyesi, John Z.; Gyekenyesi, John P.

2007-01-01

High temperature ceramic matrix composites (CMC) are being explored as viable candidate materials for hot section gas turbine components. These advanced composites can potentially lead to reduced weight and enable higher operating temperatures requiring less cooling; thus leading to increased engine efficiencies. There is a need for convenient design tools that can accommodate various loading conditions and material data with their associated uncertainties to estimate the minimum predicted life as well as the failure probabilities of a structural component. This paper presents a review of the life prediction and probabilistic analyses performed for a CMC turbine stator vane. A computer code, NASALife, is used to predict the life of a 2-D woven silicon carbide fiber reinforced silicon carbide matrix (SiC/SiC) turbine stator vane due to a mission cycle which induces low cycle fatigue and creep. The output from this program includes damage from creep loading, damage due to cyclic loading and the combined damage due to the given loading cycle. Results indicate that the trends predicted by NASALife are as expected for the loading conditions used for this study. In addition, a combination of woven composite micromechanics, finite element structural analysis and Fast Probability Integration (FPI) techniques has been used to evaluate the maximum stress and its probabilistic distribution in a CMC turbine stator vane. Input variables causing scatter are identified and ranked based upon their sensitivity magnitude. Results indicate that reducing the scatter in proportional limit strength of the vane material has the greatest effect in improving the overall reliability of the CMC vane.

Creep of plain weave polymer matrix composites

NASA Astrophysics Data System (ADS)

Gupta, Abhishek

Polymer matrix composites are increasingly used in various industrial sectors to reduce structural weight and improve performance. Woven (also known as textile) composites are one class of polymer matrix composites with increasing market share mostly due to their lightweight, their flexibility to form into desired shape, their mechanical properties and toughness. Due to the viscoelasticity of the polymer matrix, time-dependent degradation in modulus (creep) and strength (creep rupture) are two of the major mechanical properties required by engineers to design a structure reliably when using these materials. Unfortunately, creep and creep rupture of woven composites have received little attention by the research community and thus, there is a dire need to generate additional knowledge and prediction models, given the increasing market share of woven composites in load bearing structural applications. Currently, available creep models are limited in scope and have not been validated for any loading orientation and time period beyond the experimental time window. In this thesis, an analytical creep model, namely the Modified Equivalent Laminate Model (MELM), was developed to predict tensile creep of plain weave composites for any orientation of the load with respect to the orientation of the fill and warp fibers, using creep of unidirectional composites. The ability of the model to predict creep for any orientation of the load is a "first" in this area. The model was validated using an extensive experimental involving the tensile creep of plain weave composites under varying loading orientation and service conditions. Plain weave epoxy (F263)/ carbon fiber (T300) composite, currently used in aerospace applications, was procured as fabrics from Hexcel Corporation. Creep tests were conducted under two loading conditions: on-axis loading (0°) and off-axis loading (45°). Constant load creep, in the temperature range of 80-240°C and stress range of 1-70% UTS of the composites, was experimentally evaluated for time periods ranging from 1--120 hours under both loading conditions. The composite showed increase in creep with increase in temperature and stress. Creep of composite increased with increase in angle of loading, from 1% under on-axis loading to 31% under off-axis loading, within the tested time window. The experimental creep data for plain weave composites were superposed using TTSP (Time Temperature Superposition Principle) to obtain a master curve of experimental data extending to several years and was compared with model predictions to validate the model. The experimental and model results were found in good agreement within an error range of +/-1-3% under both loading conditions. A parametric study was also conducted to understand the effect of microstructure of plain weave composites on its on-axis and off-axis creep. Generation of knowledge in this area is also "first". Additionally, this thesis generated knowledge on time-dependent damage m woven composites and its effect on creep and tensile properties and their prediction.

3D discrete dislocation dynamics study of creep behavior in Ni-base single crystal superalloys by a combined dislocation climb and vacancy diffusion model

NASA Astrophysics Data System (ADS)

Gao, Siwen; Fivel, Marc; Ma, Anxin; Hartmaier, Alexander

2017-05-01

A three-dimensional (3D) discrete dislocation dynamics (DDD) creep model is developed to investigate creep behavior under uniaxial tensile stress along the crystallographic [001] direction in Ni-base single crystal superalloys, which takes explicitly account of dislocation glide, climb and vacancy diffusion, but neglects phase transformation like rafting of γ‧ precipitates. The vacancy diffusion model takes internal stresses by dislocations and mismatch strains into account and it is coupled to the dislocation dynamics model in a numerically efficient way. This model is helpful for understanding the fundamental creep mechanisms in superalloys and clarifying the effects of dislocation glide and climb on creep deformation. In cases where the precipitate cutting rarely occurs, e.g. due to the high anti-phase boundary energy and the lack of superdislocations, the dislocation glide in the γ matrix and the dislocation climb along the γ/γ‧ interface dominate plastic deformation. The simulation results show that a high temperature or a high stress both promote dislocation motion and multiplication, so as to cause a large creep strain. Dislocation climb accelerated by high temperature only produces a small plastic strain, but relaxes the hardening caused by the filling γ channels and lets dislocations further glide and multiply. The strongest variation of vacancy concentration occurs in the horizontal channels, where more mixed dislocations exit and tend to climb. The increasing internal stresses due to the increasing dislocation density are easily overcome by dislocations under a high external stress that leads to a long-term dislocation glide accompanied by multiplication.

Effect of Double Aging Heat Treatment on the Short-Term Creep Behavior of the Inconel 718

NASA Astrophysics Data System (ADS)

Caliari, Felipe Rocha; Candioto, Kátia Cristiane Gandolpho; Couto, Antônio Augusto; Nunes, Carlos Ângelo; Reis, Danieli Aparecida Pereira

2016-06-01

This research studies the effect of double aging heat treatment on the short-term creep behavior of the superalloy Inconel 718. The superalloy, received in the solution treated state, was subjected to an aging treatment which comprises a solid solution at 1095 °C for 1 h, a first aging step of 955 °C for 1 h, then aged at 720 and 620 °C, 8 h each step. Creep tests at constant load mode, under temperatures of 650, 675, 700 °C and stress of 510, 625 and 700 MPa, were performed before and after heat treatment. The results indicate that after the double aging heat treatment creep resistance is increased, influenced by the presence of precipitates γ' and γ″ and its interaction with the dislocations, by grain size growth (from 8.20 to 7.23 ASTM) and the increase of hardness by approximately 98%. Creep parameters of primary and secondary stages have been determined. There is a breakdown relationship between dot{\\upvarepsilon }_{{s}} and stress at 650 °C of Inconel 718 as received, around 600 MPa. By considering the internal stress values, effective stress exponent, effective activation energy, and TEM images of Inconel 718 double aged, it is suggested that the creep mechanism is controlled by the interaction of dislocations with precipitates. The fracture mechanism of Inconel 718 as received is transgranular (coalescence of dimples) and mixed (transgranular-intergranular), whereas the Inconel 718 double aged condition crept surfaces evidenced the intergranular fracture mechanism.

Multi-asperity models of slow slip and tremor

NASA Astrophysics Data System (ADS)

Ampuero, Jean Paul; Luo, Yingdi; Lengline, Olivier; Inbal, Asaf

2016-04-01

Field observations of exhumed faults indicate that fault zones can comprise mixtures of materials with different dominant deformation mechanisms, including contrasts in strength, frictional stability and hydrothermal transport properties. Computational modeling helps quantify the potential effects of fault zone heterogeneity on fault slip styles from seismic to aseismic slip, including slow slip and tremor phenomena, foreshocks sequences and swarms, high- and low-frequency radiation during large earthquakes. We will summarize results of ongoing modeling studies of slow slip and tremor in which fault zone structure comprises a collection of frictionally unstable patches capable of seismic slip (tremorgenic asperities) embedded in a frictionally stable matrix hosting aseismic transient slips. Such models are consistent with the current view that tremors result from repeated shear failure of multiple asperities as Low Frequency Earthquakes (LFEs). The collective behavior of asperities embedded in creeping faults generate a rich spectrum of tremor migration patterns, as observed in natural faults, whose seismicity rate, recurrence time and migration speed can be mechanically related to the underlying transient slow slip rate. Tremor activity and slow slip also responds to periodic loadings induced by tides or surface waves, and models relate tremor tidal sensitivity to frictional properties, fluid pressure and creep rate. The overall behavior of a heterogeneous fault is affected by structural parameters, such as the ratio of stable to unstable materials, but also by time-dependent variables, such as pore pressure and loading rate. Some behaviors are well predicted by homogenization theory based on spatially-averaged frictional properties, but others are somewhat unexpected, such as seismic slip behavior found in asperities that are much smaller than their nucleation size. Two end-member regimes are obtained in rate-and-state models with velocity-weakening asperities embedded in a matrix with either (A) velocity-strengthening friction or (B) a transition from velocity-weakening to velocity-strengthening at increasing slip velocity. The most conventional regime is tremor driven by slow slip. However, if the interaction between asperities mediated by intervening transient creep is strong enough, a regime of slow slip driven by tremors emerges. These two regimes lead to different statistics of inter-event times of LFE sequences, which we confront to observations from LFE catalogs in Mexico, Cascadia and Parkfield. These models also suggest that the depth dependence of tremor and slow slip behavior, for instance their shorter recurrence time and weaker amplitude with increasing depth, are not necessarily related to depth dependent size distribution of asperities, but could be due to depth-dependence of the properties of the intervening creep materials. Simplified fracture mechanics models illustrate how the resistance of the fault zone matrix can control the effective distance of interaction between asperities, and lead to transitions between Gutenberg-Richter to size-bounded (exponential) frequency-magnitude distributions. Structural fault zone properties such as the thickness of the damage zone can also introduce characteristic length scales that may affect the size distribution of tremors. Earthquake cycle simulations on heterogeneous faults also provide insight into the conditions that allow asperities to generate foreshock activity and high-frequency radiation during large earthquakes.

Flexural creep of structural flakeboards under cyclic humidity

Treesearch

M.C. Yeh; R.C. Tang; Chung-Yun Hse

1990-01-01

Flexural creep behavior of randomly oriented structural flakeboards under cyclic humidity is presented. Specimens fabricated with 5 and 7 percent phenol-formaldehyde resin were subjected to constant concentrated load in bending under slow and fast cyclic relative humidity (RH) between 65 and 95 percent for 100 days. The temperature was set at a constant 75°F through...

Anomalous creep in Sn-rich solder joints

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

Song, Ho Geon; Morris Jr., John W.; Hua, Fay

2002-03-15

This paper discusses the creep behavior of example Sn-rich solders that have become candidates for use in Pb-free solder joints. The specific solders discussed are Sn-3.5Ag, Sn-3Ag-0.5Cu, Sn-0.7Cu and Sn-10In-3.1Ag, used in thin joints between Cu and Ni-Au metallized pads.

Damage mechanisms in bithermal and thermomechanical fatigue of Haynes 188

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Halford, Gary R.

1992-01-01

Post failure fractographic and metallographic studies were conducted on Haynes 188 specimens fatigued under bithermal and thermomechanical loading conditions between 316 and 760 C. Bithermal fatigue specimens examined included those tested under high strain rate in-phase and out-phase, tensile creep in-phase, and compressive creep out-of-phase loading conditions. Specimens tested under in-phase and out-of-phase thermomechanical fatigue were also examined. The nature of failure mode (transgrandular versus intergranular), the topography of the fracture surface, and the roles of oxidation and metallurgical changes were studied for each type of bithermal and thermomechanical test.

Effect of Cross-linking Density on Creep and Recovery Behavior in Epoxy-Based Shape Memory Polymers (SMEPs) for Structural Applications

NASA Astrophysics Data System (ADS)

Rao, Kavitha V.; Ananthapadmanabha, G. S.; Dayananda, G. N.

2016-12-01

Epoxy-based shape memory polymers (SMEPs) are gaining importance in the area of aerospace structures due to their high strength and stiffness which is a primary requirement for an SMEP in structural applications. The understanding of viscoelastic behavior of SMEPs is very essential to assess their shape memory effect. In the present work, three types of SMEPs with varying cross-linking densities were developed by curing an aromatic epoxy resin with aliphatic amines. Glass transition temperature ( T g) was measured for these SMEPs using advanced rheometric expansion system, and from the T g measurements, a range of temperatures from glassy to rubbery regimes were chosen. At selected temperatures, creep-recovery tests were performed in order to evaluate the viscoelastic behavior of SMEPs and also to investigate the effect of temperature on creep-recovery. Further, a three-parameter viscoelastic model (Zener) was used to fit the data obtained from experiments. Model parameters like moduli of the springs and viscosity of the dashpot were evaluated by curve fitting. Results revealed that Zener model was well suited to describe the viscoelastic behavior of SMEPs as a function of test temperatures.

Analyses of Small Punch Creep Deformation Behavior of 316LN Stainless Steel Having Different Nitrogen Contents

NASA Astrophysics Data System (ADS)

Ganesh Kumar, J.; Laha, K.; Ganesan, V.; Prasad Reddy, G. V.

2018-05-01

The small punch creep (SPC) behavior of 316LN stainless steel (SS) containing 0.07, 0.11 and 0.14 wt.% nitrogen has been investigated at 923 K. The transient and tertiary SPC deformation of 316LN SS with various nitrogen contents have been analyzed according to the equation proposed for SPC deflection, δ = δ0 + δT (1 - e^{ - κ t} ) + \\dot{δ }s t + δ3 e^{[ φ( {t - tr } )} ]. The relationships among the rate of exhaustion of transient creep ( κ), steady-state deflection rate (\\dot{δ }s) and the rate of acceleration of tertiary creep ( φ) revealed the interrelationships among the three stages of SPC curve. The first-order reaction rate theory was found to be applicable to SPC deformation throughout the transient as well as tertiary region, in all the investigated steels. The initial and final creep deflection rates were decreased, whereas time to attain steady-state deflection rate increased with the increase in nitrogen content. By increasing the nitrogen content in 316LN SS from 0.07 to 0.14 wt.%, each stage of SPC was prolonged, and consequently, the values of κ, \\dot{δ }s and φ were lowered. Using the above parameters, the master curves for both transient and tertiary SPC deflections were constructed for 316LN SS containing different nitrogen contents.

Analyses of Small Punch Creep Deformation Behavior of 316LN Stainless Steel Having Different Nitrogen Contents

NASA Astrophysics Data System (ADS)

Ganesh Kumar, J.; Laha, K.; Ganesan, V.; Prasad Reddy, G. V.

2018-04-01

The small punch creep (SPC) behavior of 316LN stainless steel (SS) containing 0.07, 0.11 and 0.14 wt.% nitrogen has been investigated at 923 K. The transient and tertiary SPC deformation of 316LN SS with various nitrogen contents have been analyzed according to the equation proposed for SPC deflection, δ = δ0 + δT (1 - e^{ - κ t} ) + \\dot{δ }s t + δ3 e^[ φ( t - tr ) ]. The relationships among the rate of exhaustion of transient creep (κ), steady-state deflection rate (\\dot{δ }s ) and the rate of acceleration of tertiary creep (φ) revealed the interrelationships among the three stages of SPC curve. The first-order reaction rate theory was found to be applicable to SPC deformation throughout the transient as well as tertiary region, in all the investigated steels. The initial and final creep deflection rates were decreased, whereas time to attain steady-state deflection rate increased with the increase in nitrogen content. By increasing the nitrogen content in 316LN SS from 0.07 to 0.14 wt.%, each stage of SPC was prolonged, and consequently, the values of κ, \\dot{δ }s and φ were lowered. Using the above parameters, the master curves for both transient and tertiary SPC deflections were constructed for 316LN SS containing different nitrogen contents.

Mechanical Interferometry Imaging for Creep Modeling of the Cornea

PubMed Central

Yoo, Lawrence; Reed, Jason; Gimzewski, James K.

2011-01-01

Purpose. A novel nanoindentation technique was used to biomechanically characterize each of three main layers of the cornea by using Hertzian viscoelastic formulation of creep, the deformation resulting from sustained-force application. Methods. The nanoindentation method known as mechanical interferometry imaging (MII) with <1-nm displacement precision was used to observe indentation of bovine corneal epithelium, endothelium, and stroma by a spherical ferrous probe in a calibrated magnetic field. For each specimen, creep testing was performed using two different forces for 200 seconds. Measurements for single force were used to build a quantitative Hertzian model that was then used to predict creep behavior for another imposed force. Results. For all three layers, displacement measurements were highly repeatable and were well predicted by Hertzian models. Although short- and long-term stiffnesses of the endothelium were highest of the three layers at 339.2 and 20.2 kPa, respectively, both stromal stiffnesses were lowest at 100.4 and 3.6 kPa, respectively. Stiffnesses for the epithelium were intermediate at 264.6 and 12.2 kPa, respectively. Conclusions. Precise, repeatable measurements of corneal creep behavior can be conveniently obtained using MII at mechanical scale as small as one cell thickness. When interpreted in analytical context of Hertzian viscoelasticity, MII technique proved to be a powerful tool for biomechanical characterization of time-dependent biomechanics of corneal regions. PMID:21969299

Correlation of creep rate with microstructural changes during high temperature creep

NASA Technical Reports Server (NTRS)

Young, C. T.; Sommers, B. R.; Lytton, J. L.

1977-01-01

Creep tests were conducted on Haynes 188 cobalt-base alloy and alpha titanium. The tests on Haynes 188 were conducted at 1600 F and 1800 F for stresses from 3 to 20 ksi, and the as-received, mill-annealed results were compared to specimens given 5%, 10%, and 15% room temperature prestrains and then annealed one hour at 1800 F. The tests on alpha titanium were performed at 7,250 and 10,000 psi at 500 C. One creep test was done at 527 C and 10,000 psi to provide information on kinetics. Results for annealed titanium were compared to specimens given 10% and 20% room temperature prestrains followed by 100 hours recovery at 550 C. Electron microscopy was used to relate dislocation and precipitate structure to the creep behavior of the two materials. The results on Haynes 188 alloy reveal that the time to reach 0.5% creep strain at 1600 F increases with increasing prestrain for exposure times less than 1,000 hours, the increase at 15% prestrain being more than a factor of ten.

Environmental Durability and Stress Rupture of EBC/CMCs

NASA Technical Reports Server (NTRS)

Appleby, Matthew; Morscher, Gregory N.; Zhu, Dongming

2012-01-01

This research focuses on the strength and creep performance of SiC fiber-reinforced SiC ceramic matrix composite (CMC) environmental barrier coating (EBC) systems under complex simulated engine environments. Tensile-strength and stress-rupture testing was conducted to illustrate the material properties under isothermal and thermal gradient conditions. To determine material durability, further testing was conducted under exposure to thermal cycling, thermal gradients and simulated combustion environments. Emphasis is placed on experimental techniques as well as implementation of non-destructive evaluation, including modal acoustic emission and electrical resistivity monitoring, to characterize strength degradation and damage mechanisms. Currently, little is known about the behavior of EBC-CMCs under these conditions; consequently, this work will prove invaluable in the development of structural components for use in high temperature applications.

Opposite rheological properties of neuronal microcompartments predict axonal vulnerability in brain injury.

PubMed

Grevesse, Thomas; Dabiri, Borna E; Parker, Kevin Kit; Gabriele, Sylvain

2015-03-30

Although pathological changes in axonal morphology have emerged as important features of traumatic brain injury (TBI), the mechanical vulnerability of the axonal microcompartment relative to the cell body is not well understood. We hypothesized that soma and neurite microcompartments exhibit distinct mechanical behaviors, rendering axons more sensitive to a mechanical injury. In order to test this assumption, we combined protein micropatterns with magnetic tweezer rheology to probe the viscoelastic properties of neuronal microcompartments. Creep experiments revealed two opposite rheological behaviors within cortical neurons: the cell body was soft and characterized by a solid-like response, whereas the neurite compartment was stiffer and viscous-like. By using pharmacological agents, we demonstrated that the nucleus is responsible for the solid-like behavior and the stress-stiffening response of the soma, whereas neurofilaments have a predominant contribution in the viscous behavior of the neurite. Furthermore, we found that the neurite is a mechanosensitive compartment that becomes softer and adopts a pronounced viscous state on soft matrices. Together, these findings highlight the importance of the regionalization of mechanical and rigidity-sensing properties within neuron microcompartments in the preferential damage of axons during traumatic brain injury and into potential mechanisms of axonal outgrowth after injury.

Opposite rheological properties of neuronal microcompartments predict axonal vulnerability in brain injury

NASA Astrophysics Data System (ADS)

Grevesse, Thomas; Dabiri, Borna E.; Parker, Kevin Kit; Gabriele, Sylvain

2015-03-01

Although pathological changes in axonal morphology have emerged as important features of traumatic brain injury (TBI), the mechanical vulnerability of the axonal microcompartment relative to the cell body is not well understood. We hypothesized that soma and neurite microcompartments exhibit distinct mechanical behaviors, rendering axons more sensitive to a mechanical injury. In order to test this assumption, we combined protein micropatterns with magnetic tweezer rheology to probe the viscoelastic properties of neuronal microcompartments. Creep experiments revealed two opposite rheological behaviors within cortical neurons: the cell body was soft and characterized by a solid-like response, whereas the neurite compartment was stiffer and viscous-like. By using pharmacological agents, we demonstrated that the nucleus is responsible for the solid-like behavior and the stress-stiffening response of the soma, whereas neurofilaments have a predominant contribution in the viscous behavior of the neurite. Furthermore, we found that the neurite is a mechanosensitive compartment that becomes softer and adopts a pronounced viscous state on soft matrices. Together, these findings highlight the importance of the regionalization of mechanical and rigidity-sensing properties within neuron microcompartments in the preferential damage of axons during traumatic brain injury and into potential mechanisms of axonal outgrowth after injury.

Creep, creep-rupture tests of Al-surface-alloyed T91 steel in liquid lead bismuth at 500 and 550 °C

NASA Astrophysics Data System (ADS)

Weisenburger, A.; Jianu, A.; An, W.; Fetzer, R.; Del Giacco, Mattia; Heinzel, A.; Müller, G.; Markov, V. G.; Kasthanov, A. D.

2012-12-01

Surface layers made of FeCrAl alloys on T91 steel have shown their capability as corrosion protection barriers in lead bismuth. Pulsed electron beam treatment improves the density and more over the adherence of such layers. After the treatment of previously deposited coatings a surface graded material is achieved with a metallic bonded interface. Creep-rupture tests of T91 in lead-alloy at 550 °C reveal significant reduced creep strength of non-modified T91 test specimens. Oxide scales protecting the steels from attacks of the liquid metal will crack at a certain strain leading to a direct contact between the steel and the liquid metal. The negative influence of the lead-alloy on the creep behavior of non-modified T91 is stress dependent, but below a threshold stress value of 120 MPa at 550 °C this influence becomes almost negligible. At 500 °C and stress values of 200 MPa and 220 MPa the creep rates are comparable between them and significantly lower than creep rates at 180 MPa of original T91 in air at 550 °C. No signs of LBE influence are detected. The surface modified specimens tested at high stress levels instead had creep-rupture times similar to T91 (original state) tested in air. The thin oxide layers formed on the surface modified steel samples are less susceptible to crack formation and therefore to lead-alloy enhanced creep.

Creep-Fatigue Behavior of Alloy 617 at 850 and 950°C, Revision 2

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

Carroll, L.; Carroll, M.

Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests including hold times up to 9000 s at maximum tensile strain were conducted at 850 and 950 degrees C. At both temperatures, the fatigue resistance decreased when a hold time was added at peak tensile strain. The magnitude of this effect depended on the specific mechanisms and whether they resulted in a change in fracture mode from transgranular in pure fatigue to intergranular in creep-fatiguemore » for a particular temperature and strain range combination. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep-fatigue resistance at 950 degrees C but did continue to degrade the lifetimes at 850 degrees C.« less

Universal slow dynamics in granular solids

PubMed

TenCate; Smith; Guyer

2000-07-31

Experimental properties of a new form of creep dynamics are reported, as manifest in a variety of sandstones, limestone, and concrete. The creep is a recovery behavior, following the sharp drop in elastic modulus induced either by nonlinear acoustic straining or rapid temperature change. The extent of modulus recovery is universally proportional to the logarithm of the time after source discontinuation in all samples studied, over a scaling regime covering at least 10(3) s. Comparison of acoustically and thermally induced creep suggests a single origin based on internal strain, which breaks the symmetry of the inducing source.

Creep-rupture behavior of a developmental cast-iron-base alloy for use up to 800 deg C

NASA Technical Reports Server (NTRS)

Titran, Robert H.; Scheuermann, Coulson M.

1987-01-01

A promising iron-base cast alloy is being developed as part of the DOE/NASA Stirling Engine Systems Project under contract DEN 3-282 with the United Technologies Research Center. This report presents the results of a study at the Lewis Research Center of the alloy's creep-rupture properties. The alloy was tested under a variety of conditions and was found to exhibit the normal 3-stage creep response. The alloy compared favorably with others being used or under consideration for the automotive Stirling engine cylinder/regenerator housing.

In Situ Optical Creep Observation of Joint-Scale Tin-Silver-Copper Solder Shear Samples

NASA Astrophysics Data System (ADS)

Herkommer, Dominik; Reid, Michael; Punch, Jeff

2009-10-01

In this paper the creep behavior of lead-free 96.5Sn-3.0Ag-0.5Cu solder is evaluated. A series of creep tests at different stress/temperature and strain rate/temperature pairs has been conducted. The tests were observed in situ with a high-magnification camera system. Optical observation results are presented from selected tests, showing the occurrence of surface effects such as shear bands, voiding, and rumpling. From these observations the main deformation mechanisms were derived and compiled in terms of their dependence on the test conditions.

VORTEX CREEP AGAINST TOROIDAL FLUX LINES, CRUSTAL ENTRAINMENT, AND PULSAR GLITCHES

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

Gügercinoğlu, Erbil; Alpar, M. Ali, E-mail: egugercinoglu@gmail.com, E-mail: alpar@sabanciuniv.edu

2014-06-10

A region of toroidally oriented quantized flux lines must exist in the proton superconductor in the core of the neutron star. This region will be a site of vortex pinning and creep. Entrainment of the neutron superfluid with the crustal lattice leads to a requirement of superfluid moment of inertia associated with vortex creep in excess of the available crustal moment of inertia. This will bring about constraints on the equation of state. The toroidal flux region provides the moment of inertia necessary to complement the crust superfluid with postglitch relaxation behavior fitting the observations.

A potential drop strain sensor for in-situ power station creep monitoring

NASA Astrophysics Data System (ADS)

Corcoran, Joseph; Cawley, Peter; Nagy, Peter B.

2014-02-01

Creep is a high temperature damage mechanism of interest to the power industry and at present lacks a satisfactory inspection technique. Existing material inspection techniques are extremely laborious while strain measurements rely on often infrequent off-load measurements. A quasi-DC directional potential drop technique has been suggested that is able to suppress the effects of permeability and is primarily sensitive to changes in resistivity and also the geometry that will develop through strain. The change in creep related resistivity is shown by an equivalent effective resistivity approach to be small at <2% change when compared to the >100% change in transfer resistance that occurs due to strain as observed in laboratory tests. A biaxial inversion is then presented and demonstrated on in-lab samples showing good performance. The result is a sensor that performs as a very robust high temperature strain gauge.

Creep-Fatigue Failure Diagnosis

PubMed Central

Holdsworth, Stuart

2015-01-01

Failure diagnosis invariably involves consideration of both associated material condition and the results of a mechanical analysis of prior operating history. This Review focuses on these aspects with particular reference to creep-fatigue failure diagnosis. Creep-fatigue cracking can be due to a spectrum of loading conditions ranging from pure cyclic to mainly steady loading with infrequent off-load transients. These require a range of mechanical analysis approaches, a number of which are reviewed. The microstructural information revealing material condition can vary with alloy class. In practice, the detail of the consequent cracking mechanism(s) can be camouflaged by oxidation at high temperatures, although the presence of oxide on fracture surfaces can be used to date events leading to failure. Routine laboratory specimen post-test examination is strongly recommended to characterise the detail of deformation and damage accumulation under known and well-controlled loading conditions to improve the effectiveness and efficiency of failure diagnosis. PMID:28793676

Simulation of irradiation creep

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

Reiley, T.C.; Jung, P.

1977-01-01

The results to date in the area of radiation enhanced deformation using beams of light ions to simulate fast neutron displacement damage are reviewed. A comparison is made between these results and those of in-reactor experiments. Particular attention is given to the displacement rate calculations for light ions and the electronic energy losses and their effect on the displacement cross section. Differences in the displacement processes for light ions and neutrons which may effect the irradiation creep process are discussed. The experimental constraints and potential problem areas associated with these experiments are compared to the advantages of simulation. Support experimentsmore » on the effect of thickness on thermal creep are presented. A brief description of the experiments in progress is presented for the following laboratories: HEDL, NRL, ORNL, PNL, U. of Lowell/MIT in the United States, AERE Harwell in the United Kingdom, CEN Saclay in France, GRK Karlsruhe and KFA Julich in West Germany.« less

Creep/Stress Rupture Behavior of 3D Woven SiC/SiC Composites with Sylramic-iBN, Super Sylramic-iBN and Hi-Nicalon-S Fibers at 2700F in Air

NASA Technical Reports Server (NTRS)

Bhatt, R. T.

2017-01-01

To determine the influence of fiber types on creep durability, 3D SiC/SiC CMCs were fabricated with Sylramic-iBN, super Sylramic-iBN and Hi-Nicalon-S fibers and the composite specimens were then tested under isothermal tensile creep at 14820C at 69, 103 and 138 MPa for up to 300hrs in air. The failed specimens were examined by scanning electron microscopy (SEM) and computed tomography (CT) for fracture mode analysis. The creep data of these composites are compared with those of other SiC/SiC composites in the literature. The results of this study will be presented.

Modeling Creep Effects in Advanced SiC/SiC Composites

NASA Technical Reports Server (NTRS)

Lang, Jerry; DiCarlo, James

2006-01-01

Because advanced SiC/SiC composites are projected to be used for aerospace components with large thermal gradients at high temperatures, efforts are on-going at NASA Glenn to develop approaches for modeling the anticipated creep behavior of these materials and its subsequent effects on such key composite properties as internal residual stress, proportional limit stress, ultimate tensile strength, and rupture life. Based primarily on in-plane creep data for 2D panels, this presentation describes initial modeling progress at applied composite stresses below matrix cracking for some high performance SiC/SiC composite systems recently developed at NASA. Studies are described to develop creep and rupture models using empirical, mechanical analog, and mechanistic approaches, and to implement them into finite element codes for improved component design and life modeling

Irradiation effect on mechanical properties in structural materials of fast breeder reactor plant

NASA Astrophysics Data System (ADS)

Nagae, Yuji; Takaya, Shigeru; Wakai, Eiichi; Aoto, Kazumi

2011-07-01

The effects of displacement per atom (dpa) level, helium content, and the ratio of helium content to dpa level on the tensile and creep properties have been investigated in the assumed irradiation damage range of FBR structural materials. The assumed irradiation damage range is up to about 1 dpa and about 30 appm for helium content. Austenitic stainless steel and high-chromium martensitic steel are considered as FBR structural materials. As a result, it is shown that the dpa level is a promising index for evaluating neutron irradiation damage.

Special Considerations for Qualifying Thin Films for Supper Pressure Pumpkin Ultra Long Duration Balloon (ULDB) Missions

NASA Astrophysics Data System (ADS)

Said, M.

Pumpkin type super pressure balloons require much less stringent mechanical requirements on the envelope film material when compared to spherical super pressure type balloons. However, since suitable thin films are typically viscoelastic in nature, their creep characteristics must be fully characterized and must not exceed specific and predetermined design limits. Proper assessment of materials limits to meet these design limits requires creep-load-temperature data that characterizes the performance of the material over a time that exceeds the duration of the design service life by some specified margin. Contrary to the behavior of materials with purely elastic response, visco-elastic materials such as these considered for the ULDB design, change their geometry under sustained loading over time. This change is usually reflected by exhibiting a significant visco-elastic component over the service life of the mission. For that regime of large visco-elastic response, where the material is highly nonlinear, a certain load-temperature threshold can be reached where the creep is limited by an asymptote that depends on both the temperature and load level. Such creep is recoverable, although the recovery period may be much longer than the 100 day design service life of the ULDB structure plus the factor of safety required for the design. For a typical flight, the most significant creep occurs at the highest temperature, which also produces the highest internal pressure. At mid- latitudes a significant portion of the service life is spent at night, i.e. at low temperature and low load; for the ULDB film, this nighttime contribution to creep is insignificant in comparison to any daytime contribution. By contrast, flight exposure in an Antarctic summer is at an almost constant high temperature and corresponding high pressure. This response behavior must be sufficiently characterized to serve the needs of the structural design and performance predictions of the vehicle in service. In this work, a special emphasis will be given to the creep and dynamic characteristics of selected coextruded films and their dependence on the loading level and temperature. Preliminary testing has suggested t at the creep behavior of theh coextruded linear low density resin films is highly dependent on temperature and that the dynamic response depends on the make up of the composite film. In addition, the paper will, in general, highlight the process of qualify ing thin films for the pumpkin class of super pressure balloons.

Creep Behavior of Structural Insulated Panels (SIPS): Results from a Pilot Study

Treesearch

Dwight McDonald; Marshall Begel; C. Adam Senalik; Robert Ross; Thomas D. Skaggs; Borjen Yeh; Thomas Williamson

2014-01-01

Structural insulated panels (SIPs) have been recognized as construction materials in the International Residential Code (IRC) since 2009. Although most SIPs are used in wall applications, they can also be used as roof or floor panels that are subjected to long-term transverse loading, for which SIP creep performance may be critical in design. However, limited...

Viscoelastic and fatigue properties of model methacrylate-based dentin adhesives

PubMed Central

Singh, Viraj; Misra, Anil; Marangos, Orestes; Park, Jonggu; Ye, Qiang; Kieweg, Sarah L.; Spencer, Paulette

2013-01-01

The objective of the current study is to characterize the viscoelastic and fatigue properties of model methacrylate-based dentin adhesives under dry and wet conditions. Static, creep, and fatigue tests were performed on cylindrical samples in a 3-point bending clamp. Static results showed that the apparent elastic modulus of the model adhesive varied from 2.56 to 3.53 GPa in the dry condition, and from 1.04 to 1.62 GPa in the wet condition, depending upon the rate of loading. Significant differences were also found for the creep behavior of the model adhesive under dry and wet conditions. A linear viscoelastic model was developed by fitting the adhesive creep behavior. The developed model with 5 Kelvin Voigt elements predicted the apparent elastic moduli measured in the static tests. The model was then utilized to interpret the fatigue test results. It was found that the failure under cyclic loading can be due to creep or fatigue, which has implications for the failure criterion that are applied for these types of tests. Finally, it was found that the adhesive samples tested under dry conditions were more durable than those tested under wet conditions. PMID:20848661

Crystal viscoplasticity model for the creep-fatigue interactions in single-crystal Ni-base superalloy CMSX-8

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

Estrada Rodas, Ernesto A.; Neu, Richard W.

A crystal viscoplasticity (CVP) model for the creep-fatigue interactions of nickel-base superalloy CMSX-8 is proposed. At the microstructure scale of relevance, the superalloys are a composite material comprised of a γ phase and a γ' strengthening phase with unique deformation mechanisms that are highly dependent on temperature. Considering the differences in the deformation of the individual material phases is paramount to predicting the deformation behavior of superalloys at a wide range of temperatures. In this work, we account for the relevant deformation mechanisms that take place in both material phases by utilizing two additive strain rates to model the deformationmore » on each material phase. The model is capable of representing the creep-fatigue interactions in single-crystal superalloys for realistic 3-dimensional components in an Abaqus User Material Subroutine (UMAT). Using a set of material parameters calibrated to superalloy CMSX-8, the model predicts creep-fatigue, fatigue and thermomechanical fatigue behavior of this single-crystal superalloy. In conclusion, a sensitivity study of the material parameters is done to explore the effect on the deformation due to changes in the material parameters relevant to the microstructure.« less

Crystal viscoplasticity model for the creep-fatigue interactions in single-crystal Ni-base superalloy CMSX-8

DOE PAGES

Estrada Rodas, Ernesto A.; Neu, Richard W.

2017-09-11

A crystal viscoplasticity (CVP) model for the creep-fatigue interactions of nickel-base superalloy CMSX-8 is proposed. At the microstructure scale of relevance, the superalloys are a composite material comprised of a γ phase and a γ' strengthening phase with unique deformation mechanisms that are highly dependent on temperature. Considering the differences in the deformation of the individual material phases is paramount to predicting the deformation behavior of superalloys at a wide range of temperatures. In this work, we account for the relevant deformation mechanisms that take place in both material phases by utilizing two additive strain rates to model the deformationmore » on each material phase. The model is capable of representing the creep-fatigue interactions in single-crystal superalloys for realistic 3-dimensional components in an Abaqus User Material Subroutine (UMAT). Using a set of material parameters calibrated to superalloy CMSX-8, the model predicts creep-fatigue, fatigue and thermomechanical fatigue behavior of this single-crystal superalloy. In conclusion, a sensitivity study of the material parameters is done to explore the effect on the deformation due to changes in the material parameters relevant to the microstructure.« less

Creep and shrinkage effects on integral abutment bridges

NASA Astrophysics Data System (ADS)

Munuswamy, Sivakumar

Integral abutment bridges provide bridge engineers an economical design alternative to traditional bridges with expansion joints owing to the benefits, arising from elimination of expensive joints installation and reduced maintenance cost. The superstructure for integral abutment bridges is cast integrally with abutments. Time-dependent effects of creep, shrinkage of concrete, relaxation of prestressing steel, temperature gradient, restraints provided by abutment foundation and backfill and statical indeterminacy of the structure introduce time-dependent variations in the redundant forces. An analytical model and numerical procedure to predict instantaneous linear behavior and non-linear time dependent long-term behavior of continuous composite superstructure are developed in which the redundant forces in the integral abutment bridges are derived considering the time-dependent effects. The redistributions of moments due to time-dependent effects have been considered in the analysis. The analysis includes nonlinearity due to cracking of the concrete, as well as the time-dependent deformations. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) models for creep and shrinkage are considered in modeling the time dependent material behavior. The variations in the material property of the cross-section corresponding to the constituent materials are incorporated and age-adjusted effective modulus method with relaxation procedure is followed to include the creep behavior of concrete. The partial restraint provided by the abutment-pile-soil system is modeled using discrete spring stiffness as translational and rotational degrees of freedom. Numerical simulation of the behavior is carried out on continuous composite integral abutment bridges and the deformations and stresses due to time-dependent effects due to typical sustained loads are computed. The results from the analytical model are compared with the published laboratory experimental and field data. The behavior of the laterally loaded piles supporting the integral abutments is evaluated and presented in terms of the lateral deflection, bending moment, shear force and stress along the pile depth.

A composite viscoelastic model for incorporating grain boundary sliding and transient diffusion creep; correlating creep and attenuation responses for materials with a fine grain size

NASA Astrophysics Data System (ADS)

Sundberg, Marshall; Cooper, Reid F.

2010-07-01

A new viscoelastic creep function that incorporates both the effects of elastically-accommodated grain boundary sliding (GBS) and transient diffusion creep is proposed. It is demonstrated that this model can simultaneously describe both the transient microcreep curves and the shear attenuation/modulus dispersion in a fine-grained (d ∼ 5 µm) peridotite (olivine + 39 vol. % orthopyroxene) specimen. Low-frequency shear attenuation, ? , and modulus dispersion, G(ω), spectra were measured in a one-atmosphere reciprocating torsion apparatus at temperatures of 1200 ≤ T ≤ 1300°C and frequencies of 10-2.25 ≤ f ≤ 100 Hz. Reciprocating tests were complemented by a series of small stress (τ ∼ 90 kPa) microcreep experiments at the same temperatures. In contrast to previous models where the parameters of viscoelastic models are derived by fitting the Laplace transform of the creep function to measured attenuation spectra, the parameters are derived solely from the fit of the creep function to the experimental microcreep curves using different published expressions for the relaxation strength of elastically-accommodated GBS. This approach may allow future studies to better link the large dataset of steady-state creep response to the dynamic attenuation behavior.

Creep analysis of silicone for podiatry applications.

PubMed

Janeiro-Arocas, Julia; Tarrío-Saavedra, Javier; López-Beceiro, Jorge; Naya, Salvador; López-Canosa, Adrián; Heredia-García, Nicolás; Artiaga, Ramón

2016-10-01

This work shows an effective methodology to characterize the creep-recovery behavior of silicones before their application in podiatry. The aim is to characterize, model and compare the creep-recovery properties of different types of silicone used in podiatry orthotics. Creep-recovery phenomena of silicones used in podiatry orthotics is characterized by dynamic mechanical analysis (DMA). Silicones provided by Herbitas are compared by observing their viscoelastic properties by Functional Data Analysis (FDA) and nonlinear regression. The relationship between strain and time is modeled by fixed and mixed effects nonlinear regression to compare easily and intuitively podiatry silicones. Functional ANOVA and Kohlrausch-Willians-Watts (KWW) model with fixed and mixed effects allows us to compare different silicones observing the values of fitting parameters and their physical meaning. The differences between silicones are related to the variations of breadth of creep-recovery time distribution and instantaneous deformation-permanent strain. Nevertheless, the mean creep-relaxation time is the same for all the studied silicones. Silicones used in palliative orthoses have higher instantaneous deformation-permanent strain and narrower creep-recovery distribution. The proposed methodology based on DMA, FDA and nonlinear regression is an useful tool to characterize and choose the proper silicone for each podiatry application according to their viscoelastic properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

Significantly enhanced creep resistance of low volume fraction in-situ TiBw/Ti6Al4V composites by architectured network reinforcements

PubMed Central

Wang, S.; Huang, L. J.; Geng, L.; Scarpa, F.; Jiao, Y.; Peng, H. X.

2017-01-01

We present a new class of TiBw/Ti6Al4V composites with a network reinforcement architecture that exhibits a significant creep resistance compared to monolithic Ti6Al4V alloys. Creep tests performed at temperatures between 773 K and 923 K and stress range of 100 MPa-300 MPa indicate both a significant improvement of the composites creep resistance due to the network architecture made by the TiB whiskers (TiBw), and a decrease of the steady-state creep rates by augmenting the local volume fractions of TiBw in the network region. The deformation behavior is driven by a diffusion-controlled dislocation climb process. Moreover, the activation energies of these composites are significantly higher than that of Ti6Al4V alloys, indicating a higher creep resistance. The increase of the activation energy can be attributed to the TiBw architecture that severely impedes the movements of dislocation and grain boundary sliding and provides a tailoring of the stress transfer. These micromechanical mechanisms lead to a remarkable improvement of the creep resistance of these networked TiBw/Ti6Al4V composites featuring the special networked architecture. PMID:28094350

Damage Characterization in SiC/SiC Composites using Electrical Resistance

NASA Technical Reports Server (NTRS)

Smith, Craig E.; Xia, Zhenhai

2011-01-01

SiC/SiC ceramic matrix composites (CMCs) under creep-rupture loading accumulate damage by means of local matrix cracks that typically form near a stress concentration, such as a 90o fiber tow or large matrix pore, and grow over time. Such damage is difficult to detect through conventional techniques. Electrical resistance changes can be correlated with matrix cracking to provide a means of damage detection. Sylramic-iBN fiber-reinforced SiC composites with both melt infiltrated (MI) and chemical vapor infiltrated (CVI) matrix types are compared here. Results for both systems exhibit an increase in resistance prior to fracture, which can be detected either in situ or post-damage.

Age hardening and creep resistance of cast Al–Cu alloy modified by praseodymium

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

Bai, Zhihao; Qiu, Feng; Wu, Xiaoxue

The effects of praseodymium on age hardening behavior and creep resistance of cast Al–Cu alloy were investigated. The results indicated that praseodymium facilitated the formation of the θ′ precipitates during the age process and improved the hardness of the Al–Cu alloy. Besides, praseodymium resulted in the formation of the Al{sub 11}Pr{sub 3} phase in the grain boundaries and among the dendrites of the modified alloy. Because of the good thermal stability of Al{sub 11}Pr{sub 3} phase, it inhibits grain boundary migration and dislocation movement during the creep process, which contributes to the improvement in the creep resistance of the modifiedmore » alloy at elevated temperatures. - Highlights: • Pr addition enhances the hardness and creep resistance of the Al–Cu alloy. • Pr addition facilitates the formation of the θ′ precipitates. • Pr addition results in the formation of the Al11Pr3 phase in the Al–Cu alloy.« less

Environmental effects on long term behavior of composite laminates

NASA Astrophysics Data System (ADS)

Singhal, S. N.; Chamis, C. C.

Model equations are presented for approximate methods simulating the long-term behavior of composite materials and structures in hot/humid service environments. These equations allow laminate property upgradings with time, and can account for the effects of service environments on creep response. These methodologies are illustrated for various individual and coupled temperature/moisture, longitudinal/transverse, and composite material type cases. Creep deformation is noted to rise dramatically for cases of matrix-borne, but not of fiber-borne, loading in hot, humid environments; the coupled influence of temperature and moisture is greater than a mere combination of their individual influences.

Environmental effects on long term behavior of composite laminates

NASA Technical Reports Server (NTRS)

Singhal, S. N.; Chamis, C. C.

1992-01-01

Model equations are presented for approximate methods simulating the long-term behavior of composite materials and structures in hot/humid service environments. These equations allow laminate property upgradings with time, and can account for the effects of service environments on creep response. These methodologies are illustrated for various individual and coupled temperature/moisture, longitudinal/transverse, and composite material type cases. Creep deformation is noted to rise dramatically for cases of matrix-borne, but not of fiber-borne, loading in hot, humid environments; the coupled influence of temperature and moisture is greater than a mere combination of their individual influences.

Thermal barrier coating life prediction model development, phase 1

NASA Technical Reports Server (NTRS)

Demasi, Jeanine T.; Ortiz, Milton

1989-01-01

The objective of this program was to establish a methodology to predict thermal barrier coating (TBC) life on gas turbine engine components. The approach involved experimental life measurement coupled with analytical modeling of relevant degradation modes. Evaluation of experimental and flight service components indicate the predominant failure mode to be thermomechanical spallation of the ceramic coating layer resulting from propagation of a dominant near interface crack. Examination of fractionally exposed specimens indicated that dominant crack formation results from progressive structural damage in the form of subcritical microcrack link-up. Tests conducted to isolate important life drivers have shown MCrAlY oxidation to significantly affect the rate of damage accumulation. Mechanical property testing has shown the plasma deposited ceramic to exhibit a non-linear stress-strain response, creep and fatigue. The fatigue based life prediction model developed accounts for the unusual ceramic behavior and also incorporates an experimentally determined oxide rate model. The model predicts the growth of this oxide scale to influence the intensity of the mechanic driving force, resulting from cyclic strains and stresses caused by thermally induced and externally imposed mechanical loads.

Using surface creep rate to infer fraction locked for sections of the San Andreas fault system in northern California from alignment array and GPS data

USGS Publications Warehouse

Lienkaemper, James J.; McFarland, Forrest S.; Simpson, Robert W.; Caskey, S. John

2014-01-01

Surface creep rate, observed along five branches of the dextral San Andreas fault system in northern California, varies considerably from one section to the next, indicating that so too may the depth at which the faults are locked. We model locking on 29 fault sections using each section’s mean long‐term creep rate and the consensus values of fault width and geologic slip rate. Surface creep rate observations from 111 short‐range alignment and trilateration arrays and 48 near‐fault, Global Positioning System station pairs are used to estimate depth of creep, assuming an elastic half‐space model and adjusting depth of creep iteratively by trial and error to match the creep observations along fault sections. Fault sections are delineated either by geometric discontinuities between them or by distinctly different creeping behaviors. We remove transient rate changes associated with five large (M≥5.5) regional earthquakes. Estimates of fraction locked, the ratio of moment accumulation rate to loading rate, on each section of the fault system provide a uniform means to inform source parameters relevant to seismic‐hazard assessment. From its mean creep rates, we infer the main branch (the San Andreas fault) ranges from only 20%±10% locked on its central creeping section to 99%–100% on the north coast. From mean accumulation rates, we infer that four urban faults appear to have accumulated enough seismic moment to produce major earthquakes: the northern Calaveras (M 6.8), Hayward (M 6.8), Rodgers Creek (M 7.1), and Green Valley (M 7.1). The latter three faults are nearing or past their mean recurrence interval.

Microstructure and Mechanical Properties of Extruded Gamma Met PX

NASA Technical Reports Server (NTRS)

Draper, S. L.; Das, G.; Locci, I.; Whittenberger, J. D.; Lerch, B. A.; Kestler, H.

2003-01-01

A gamma TiAl alloy with a high Nb content is being assessed as a compressor blade material. The microstructure and mechanical properties of extruded Ti-45Al-X(Nb,B,C) (at %) were evaluated in both an as-extruded condition and after a lamellar heat treatment. Tensile behavior of both as-extruded and lamellar heat treated specimens was studied in the temperature range of RT to 926 C. In general, the yield stress and ultimate tensile strength reached relatively high values at room temperature and decreased with increasing deformation temperature. The fatigue strength of both microstructures was characterized at 650 C and compared to a baseline TiAl alloy and to a Ni-base superalloy. Tensile and fatigue specimens were also exposed to 800 C for 200 h in air to evaluate the alloy's environmental resistance. A decrease in ductility was observed at room temperature due to the 800 C exposure but the 650 C fatigue properties were unaffected. Compressive and tensile creep testing between 727 and 1027 C revealed that the creep deformation was reproducible and predictable. Creep strengths reached superalloy-like levels at fast strain rates and lower temperatures but deformation at slower strain rates and/or higher temperature indicated significant weakening for the as-extruded condition. At high temperatures and low stresses, the lamellar microstructure had improved creep properties when compared to the as-extruded material. Microstructural evolution during heat treatment, identification of various phases, and the effect of microstructure on the tensile, fatigue, and creep behaviors is discussed.

Microstructure and Mechanical Properties of Extruded Gamma Microstructure Met PX

NASA Technical Reports Server (NTRS)

Draper, S. L.; Das, G.; Locci, J.; Whittenberger, J. D.; Lerch, B. A.; Kestler, H.

2003-01-01

A gamma TiAl alloy with a high Nb content is being assessed as a compressor blade material. The microstructure and mechanical properties of extruded Ti-45Al-X(Nb,B,C) (at.%) were evaluated in both an as-extruded condition and after a lamellar heat treatment. Tensile behavior of both as-extruded and lamellar heat treated specimens was studied in the temperature range of RT to 926 C. In general, the yield stress and ultimate tensile strength reached relatively high values at room temperature and decreased with increasing deformation temperature. The fatigue strength of both microstructures was characterized at 650 C and compared to a baseline TiAl alloy and to a Ni-base superalloy. Tensile and fatigue specimens were also exposed to 800 C for 200 h in air to evaluate the alloy's environmental resistance. A decrease in ductility was observed at room temperature due to the 800 C. exposure but the 650 C fatigue properties were unaffected. Compressive and tensile creep testing between 727 and 1027 C revealed that the creep deformation was reproducible and predictable. Creep strengths reached superalloy-like levels at fast strain rates and lower temperatures but deformation at slower strain rates and/or higher temperature indicated significant weakening for the as-extruded condition. At high temperatures and low stresses, the lamellar microstructure had improved creep properties when compared to the as-extruded material. Microstructural evolution during heat treatment, identification of various phases, and the effect of microstructure on the tensile, fatigue, and creep behaviors is discussed.

A Novel Creep-Fatigue Life Prediction Model for P92 Steel on the Basis of Cyclic Strain Energy Density

NASA Astrophysics Data System (ADS)

Ji, Dongmei; Ren, Jianxing; Zhang, Lai-Chang

2016-11-01

A novel creep-fatigue life prediction model was deduced based on an expression of the strain energy density in this study. In order to obtain the expression of the strain energy density, the load-controlled creep-fatigue (CF) tests of P92 steel at 873 K were carried out. Cyclic strain of P92 steel under CF load was divided into elastic strain, applying and unloading plastic strain, creep strain, and anelastic strain. Analysis of cyclic strain indicates that the damage process of P92 steel under CF load consists of three stages, similar to pure creep. According to the characteristics of the strains above, an expression was defined to describe the strain energy density for each cycle. The strain energy density at stable stage is inversely proportional to the total strain energy density dissipated by P92 steel. However, the total strain energy densities under different test conditions are proportional to the fatigue life. Therefore, the expression of the strain energy density at stable stage was chosen to predict the fatigue life. The CF experimental data on P92 steel were employed to verify the rationality of the novel model. The model obtained from the load-controlled CF test of P92 steel with short holding time could predict the fatigue life of P92 steel with long holding time.

Special considerations for qualifying thin films for super pressure pumpkin ultra long duration balloon missions

NASA Astrophysics Data System (ADS)

Said, Magdi A.

2004-01-01

The assessment of creep and dynamic response behaviors on materials intended for ultra long duration balloon (ULDB) applications is essential. The first provides needed information for design and fabrication. The second ensures that the film is sufficiently tough to survive the dynamic events during launch and ascent. Characterization and assessment of these two important parameters are discussed in this paper. Visco-elastic behavior of materials in a loaded structure, such as the ULDB film change their geometry significantly over time under load causing possible changes in the load path and the stress distribution. These changes must be held in check to satisfy the functional requirements of the structure over its service life. Typically, the balloon experiences during its service life various environmental conditions each with a different creep response. These are characterized by a simplified load temperature history for the purpose of lifetime response assessment. At mid-latitudes a significant portion of the service life is spent at night, i.e., at low temperature and low load; for the ULDB film this night-time contribution to creep is negligible. By contrast, flight exposure in an Antarctic summer is at an almost constant high temperature and corresponding high pressure. This paper presents the creep behavior of the ULDB film as a function of load, temperature, and time along with an overview of its implementation in the design. In addition, it presents a quantitative assessment on the toughness of the material under dynamic "Snatch" loading.

Power-law creep and residual stresses in carbopol microgels

NASA Astrophysics Data System (ADS)

Lidon, Pierre; Manneville, Sebastien

We report on the interplay between creep and residual stresses in carbopol microgels. When a constant shear stress σ is applied below the yield stress σc, the strain is shown to increase as a power law of time, γ (t) =γ0 +(t / τ) α , with and exponent α ~= 0 . 38 that is strongly reminiscent of Andrade creep in hard solids. For applied shear stresses lower than some characteristic value of about σc / 10 , the microgels experience a more complex creep behavior that we link to the existence of residual stresses and to weak aging of the system after preshear. The influence of the preshear protocol, of boundary conditions and of microgel concentration on residual stresses is investigated. We discuss our results in light of previous works on colloidal glasses and other soft glassy systems.

EVALUATION OF SPECIFICATION RANGES FOR CREEP STRENGTH ENHANCED FERRITIC STEELS

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

Shingledecker, John P; Santella, Michael L; Wilson, Keely A

2008-01-01

Creep Strength Enhanced Ferritic Steels (CSEF) such as Gr. 91, 911, 92, and 122 require a fully martensitic structure for optimum properties, mainly good creep strength. However, broad chemical compositional ranges are specified for these steel grades which can strongly influence the microstructures obtained. In this study, we have produced chemical compositions within the specification ranges for these alloys which intentionally cause the formation of ferrite or substantially alter the lower intercritical temperatures (A1) so as to affect the phase transformation behavior during tempering. Thermodynamic modeling, thermo-mechanical simulation, tensile testing, creep testing, and microstructural analysis were used to evaluate thesemore » materials. The results show the usefulness of thermodynamic calculations for setting rational chemical composition ranges for CSEF steels to control the critical temperatures, set heat-treatment temperature limits, and eliminate the formation of ferrite.« less

Unified Viscoplastic Behavior of Metal Matrix Composites

NASA Technical Reports Server (NTRS)

Arnold, S. M.; Robinson, D. N.; Bartolotta, P. A.

1992-01-01

The need for unified constitutive models was recognized more than a decade ago in the results of phenomenological tests on monolithic metals that exhibited strong creep-plasticity interaction. Recently, metallic alloys have been combined to form high-temperature ductile/ductile composite materials, raising the natural question of whether these metallic composites exhibit the same phenomenological features as their monolithic constituents. This question is addressed in the context of a limited, yet definite (to illustrate creep/plasticity interaction) set of experimental data on the model metal matrix composite (MMC) system W/Kanthal. Furthermore, it is demonstrated that a unified viscoplastic representation, extended for unidirectional composites and correlated to W/Kanthal, can accurately predict the observed longitudinal composite creep/plasticity interaction response and strain rate dependency. Finally, the predicted influence of fiber orientation on the creep response of W/Kanthal is illustrated.

Use of multiscale zirconium alloy deformation models in nuclear fuel behavior analysis

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

Montgomery, Robert; Tomé, Carlos; Liu, Wenfeng

Accurate prediction of cladding mechanical behavior is a key aspect of modeling nuclear fuel behavior, especially for conditions of pellet-cladding interaction (PCI), reactivity-initiated accidents (RIA), and loss of coolant accidents (LOCA). Current approaches to fuel performance modeling rely on empirical models for cladding creep, growth and plastic deformation, which are limited to the materials and conditions for which the models were developed. CASL has endeavored to improve upon this approach by incorporating a microstructurally-based, atomistically-informed, zirconium alloy mechanical deformation analysis capability into the BISON-CASL engineering scale fuel performance code. Specifically, the viscoplastic self-consistent (VPSC) polycrystal plasticity modeling approach, developed bymore » Lebensohn and Tome´ [2], has been coupled with BISON-CASL to represent the mechanistic material processes controlling the deformation behavior of the cladding. A critical component of VPSC is the representation of the crystallographic orientation of the grains within the matrix material and the ability to account for the role of texture on deformation. The multiscale modeling of cladding deformation mechanisms allowed by VPSC far exceed the functionality of typical semi-empirical constitutive models employed in nuclear fuel behavior codes to model irradiation growth and creep, thermal creep, or plasticity. This paper describes the implementation of an interface between VPSC and BISON-CASL and provides initial results utilizing the coupled functionality.« less

A geomechanical model of a sinkhole formation

NASA Astrophysics Data System (ADS)

Danchiv, Alexandru; Zamfirescu, Florian; Mocuta, Marius; Popa, Iulian; Zlibut, Alexandru; Huggenberger, Peter; Zechner, Eric; Dresmann, Horst; Scheidler, Stefan; Wiesmeier, Stefan

2016-04-01

On December 2010 a sinkhole was suddenly formed close to the eastern flank of Ocna-Mures salt dome. Soon after the collapse the sinkhole was filled with brine forming a salt lake called Plus Lake. The total volume of sinkhole of about 100000 m3 remained constant since February 2011. The Ocna Mures salt dome is situated on the western border of the Transylvanian basin (Romania) and has been exploited for a long time. The ceilings of some shallow mine chambers are now collapsed and filled with brine. Along the eastern flank of the salt dome there is a disturbed zone due to diapirism. Its presence is suggested by the strong fragmentation of rock in the boreholes drilled along the salt-sterile contact, as it resulted from the low values of RQD index. The sinkhole is probably due to a pressure increase along the diapir flank. The causes of this sudden increase of pressure are not well known. Most probably it is due to the damage of the tubing of a flank borehole as mentioned in a technical report of the exploiting company. The injected fresh water expelled through the breaches of the damaged borehole and, due to the high pressure flushed up the crushed material of the disturbed zone. In order to better understand the setting up of the Plus Lake joint research efforts were performed by teams from Bucharest and Basel Universities since 2013. For the geomechanical approach a numerical model was performed using the Flac 7.0 code. In a first stage the creep behavior of salt was analyzed considering a Norton creep law. It resulted that after 100 years the salt reached equilibrium, the creep could be neglected and in a first approximation mechanical equilibrium could be analyzed considering only an elasto-plastic behavior of both the salt and the sterile. For both the salt and the surrounding sedimentary rocks the Mohr-Coulomb criterion was considered. The properties of sterile rocks were estimated following the GSI system. Due to poor rock quality the strength parameters have very low values, with a cohesion within a range from 0.167 to 0.46 MPa and a friction angle in a range between 1.05 and 4.5 degrees. As a result the global safety factor is strongly diminished, to values close to 1. In this case the rock mass exceeds the limit for equilibrium and will collapse. Also the maximum shear strain rate is concentrated in a narrow zone which delineates a disequilibrium prism, which according to the velocity vectors is sliding to the old mine chambers. Thus, after the collapse of the prism the rock mass will enter into the old mine chambers and the expelled brine will form the Plus Lake.

Creep analysis of solid oxide fuel cell with bonded compliant seal design

NASA Astrophysics Data System (ADS)

Jiang, Wenchun; Zhang, Yucai; Luo, Yun; Gong, J. M.; Tu, S. T.

2013-12-01

Solid oxide fuel cell (SOFC) requires good sealant because it works in harsh conditions (high temperature, thermal cycle, oxidative and reducing gas environments). Bonded compliant seal (BCS) is a new sealing method for planar SOFC. It uses a thin foil metal to bond the window frame and cell, achieving the seal between window frame and cell. At high temperature, a comprehensive evaluation of its creep strength is essential for the adoption of BCS design. In order to characterize the creep behavior, the creep induced by thermal stresses in SOFC with BCS design is simulated by finite element method. The results show that the foil is compressed and large thermal stresses are generated. The initial peak thermal stress is located in the thin foil because the foil acts as a spring stores the thermal stresses by elastic and plastic deformation in itself. Serving at high temperature, initial thermal displacement is partially recovered because of the creep relaxation, which becomes a new discovered advantage for BCS design. It predicts that the failures are likely to happen in the middle of the cell edge and BNi-2 filler metal, because the maximum residual displacement and creep strain are located.

Investigation of Tensile Creep of a Normal Strength Overlay Concrete.

PubMed

Drexel, Martin; Theiner, Yvonne; Hofstetter, Günter

2018-06-12

The present contribution deals with the experimental investigation of the time-dependent behavior of a typical overlay concrete subjected to tensile stresses. The latter develop in concrete overlays, which are placed on existing concrete structures as a strengthening measure, due to the shrinkage of the young overlay concrete, which is restrained by the substrate concrete. Since the tensile stresses are reduced by creep, creep in tension is investigated on sealed and unsealed specimens, loaded at different concrete ages. The creep tests as well as the companion shrinkage tests are performed in a climatic chamber at constant temperature and constant relative humidity. Since shrinkage depends on the change of moisture content, the evolution of the mass water content is determined at the center of each specimen by means of an electrolytic resistivity-based system. Together with the experimental results for compressive creep from a previous study, a consistent set of time-dependent material data, determined for the same composition of the concrete mixture and on identical specimens, is now available. It consists of the hygral and mechanical properties, creep and shrinkage strains for both sealed and drying conditions, the respective compliance functions, and the mass water contents in sealed and unsealed, loaded and load-free specimens.

Effects of Heat-Treated Wood Particles on the Physico-Mechanical Properties and Extended Creep Behavior of Wood/Recycled-HDPE Composites Using the Time-Temperature Superposition Principle.

PubMed

Yang, Teng-Chun; Chien, Yi-Chi; Wu, Tung-Lin; Hung, Ke-Chang; Wu, Jyh-Horng

2017-03-30

This study investigated the effectiveness of heat-treated wood particles for improving the physico-mechanical properties and creep performance of wood/recycled-HDPE composites. The results reveal that the composites with heat-treated wood particles had significantly decreased moisture content, water absorption, and thickness swelling, while no improvements of the flexural properties or the wood screw holding strength were observed, except for the internal bond strength. Additionally, creep tests were conducted at a series of elevated temperatures using the time-temperature superposition principle (TTSP), and the TTSP-predicted creep compliance curves fit well with the experimental data. The creep resistance values of composites with heat-treated wood particles were greater than those having untreated wood particles due to the hydrophobic character of the treated wood particles and improved interfacial compatibility between the wood particles and polymer matrix. At a reference temperature of 20 °C, the improvement of creep resistance ( ICR ) of composites with heat-treated wood particles reached approximately 30% over a 30-year period, and it increased significantly with increasing reference temperature.

Effects of Heat-Treated Wood Particles on the Physico-Mechanical Properties and Extended Creep Behavior of Wood/Recycled-HDPE Composites Using the Time–Temperature Superposition Principle

PubMed Central

Yang, Teng-Chun; Chien, Yi-Chi; Wu, Tung-Lin; Hung, Ke-Chang; Wu, Jyh-Horng

2017-01-01

This study investigated the effectiveness of heat-treated wood particles for improving the physico-mechanical properties and creep performance of wood/recycled-HDPE composites. The results reveal that the composites with heat-treated wood particles had significantly decreased moisture content, water absorption, and thickness swelling, while no improvements of the flexural properties or the wood screw holding strength were observed, except for the internal bond strength. Additionally, creep tests were conducted at a series of elevated temperatures using the time–temperature superposition principle (TTSP), and the TTSP-predicted creep compliance curves fit well with the experimental data. The creep resistance values of composites with heat-treated wood particles were greater than those having untreated wood particles due to the hydrophobic character of the treated wood particles and improved interfacial compatibility between the wood particles and polymer matrix. At a reference temperature of 20 °C, the improvement of creep resistance (ICR) of composites with heat-treated wood particles reached approximately 30% over a 30-year period, and it increased significantly with increasing reference temperature. PMID:28772726

Input Correlations for Irradiation Creep of FeCrAl and SiC Based on In-Pile Halden Test Results

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

Terrani, K. A.; Karlsen, T. M.; Yamamoto, Yukinori

2016-05-01

Swelling and creep behavior of wrought FeCrAl alloys and CVD-SiC, two candidate accident tolerant fuel cladding materials, are being examined using in-pile tests at the Halden reactor. The outcome of these tests are material property correlations that are inputs into fuel performance analysis tools. The results are discussed and compared with what is available in literature from irradiation experiments in other reactors or out-of-pile tests. Specific recommendation on what correlations should be used for swelling, thermal, and irradiation creep for each material are provided in this document.

Constrained Self-adaptive Solutions Procedures for Structure Subject to High Temperature Elastic-plastic Creep Effects

NASA Technical Reports Server (NTRS)

Padovan, J.; Tovichakchaikul, S.

1983-01-01

This paper will develop a new solution strategy which can handle elastic-plastic-creep problems in an inherently stable manner. This is achieved by introducing a new constrained time stepping algorithm which will enable the solution of creep initiated pre/postbuckling behavior where indefinite tangent stiffnesses are encountered. Due to the generality of the scheme, both monotone and cyclic loading histories can be handled. The presentation will give a thorough overview of current solution schemes and their short comings, the development of constrained time stepping algorithms as well as illustrate the results of several numerical experiments which benchmark the new procedure.

Damage Characterization of EBC-SiCSiC Ceramic Matrix Composites Under Imposed Thermal Gradient Testing

NASA Technical Reports Server (NTRS)

Appleby, Matthew P.; Morscher, Gregory N.; Zhu, Dongming

2014-01-01

Due to their high temperature capabilities, Ceramic Matrix Composite (CMC) components are being developed for use in hot-section aerospace engine applications. Harsh engine environments have led to the development of Environmental Barrier Coatings (EBCs) for silicon-based CMCs to further increase thermal and environmental capabilities. This study aims at understanding the damage mechanisms associated with these materials under simulated operating conditions. A high heat-flux laser testing rig capable of imposing large through-thickness thermal gradients by means of controlled laser beam heating and back-side air cooling is used. Tests are performed on uncoated composites, as well as CMC substrates that have been coated with state-of-the-art ceramic EBC systems. Results show that the use of the EBCs may help increase temperature capability and creep resistance by reducing the effects of stressed oxidation and environmental degradation. Also, the ability of electrical resistance (ER) and acoustic emission (AE) measurements to monitor material condition and damage state during high temperature testing is shown; suggesting their usefulness as a valuable health monitoring technique. Micromechanics models are used to describe the localized stress state of the composite system, which is utilized along with ER modeling concepts to develop an electromechanical model capable of characterizing material behavior.

Life prediction technologies for aeronautical propulsion systems

NASA Technical Reports Server (NTRS)

Mcgaw, Michael A.

1987-01-01

Fatigue and fracture problems continue to occur in aeronautical gas turbine engines. Components whose useful life is limited by these failure modes include turbine hot-section blades, vanes and disks. Safety considerations dictate that catastrophic failures be avoided, while economic considerations dictate that noncatastrophic failures occur as infrequently as possible. The design decision is therefore in making the tradeoff between engine performance and durability. The NASA Lewis Research Center has contributed to the aeropropulsion industry in the areas of life prediction technology for 30 years, developing creep and fatigue life prediction methodologies for hot-section materials. Emphasis is placed on the development of methods capable of handling both thermal and mechanical fatigue under severe environments. Recent accomplishments include the development of more accurate creep-fatigue life prediction methods such as the total strain version of Lewis' Strainrange Partitioning (SRP) and the HOST-developed Cyclic Damage Accumulation (CDA) model. Other examples include the Double Damage Curve Approach (DDCA), which provides greatly improved accuracy for cumulative fatigue design rules.

Creeping flashover characteristics improvement of nanofluid/pressboard system with TiO2 nanoparticles

NASA Astrophysics Data System (ADS)

Huang, Meng; Wang, Lei; Ge, Yang; Lv, Yu-zhen; Qi, Bo; Li, Cheng-rong

2018-03-01

Creeping flashover easily occurs at the interface between oil and pressboard in transformer and thus results in outage of power transmission system. Investigations have shown that creeping flashover characteristics at oil/pressboard interface can be improved by the addition of TiO2 nanoparticles, but the mechanism is still not thoroughly known. In this work, creeping flashover performance at nanofluid/pressboard interface modified by different sizes of nanoparticles were studied and the mechanism was presented as well. Nanofluids with the same concentration but with different sizes of TiO2 nanoparticles were prepared, and pressboards impregnated with them were prepared as well. After that, their creeping flashover characteristics were measured and compared. Nanoparticle's size affected the creeping flashover performance along oil/pressboard greatly under both AC and lightning impulse voltages. The highest creeping flashover voltage can be enhanced by as high as 12.2% and 32.0% respectively. The underlying electric field distribution and charge transportation behaviors were analyzed to demonstrate the influence of nanoparticle's size. By the addition of nanoparticles with a smaller size, the dielectric constant of nanofluid was increased closer to that of the pressboard, thus they were matched better. Moreover, charge was easier to dissipate from the oil/pressboard interface and electric field distortion at the interface was consequently reduced. Therefore, the electric field was more like a uniform field and the forward development of flashover was more difficult, leading to a better performance of creeping flashover of oil-impregnated pressboard.

Electrical Resistance of SiC/SiC Ceramic Matrix Composites for Damage Detection and Life-Prediction

NASA Technical Reports Server (NTRS)

Smith, Craig; Morscher, Gregory; Xia, Zhenhai

2009-01-01

Ceramic matrix composites (CMC) are suitable for high temperature structural applications such as turbine airfoils and hypersonic thermal protection systems due to their low density high thermal conductivity. The employment of these materials in such applications is limited by the ability to accurately monitor and predict damage evolution. Current nondestructive methods such as ultrasound, x-ray, and thermal imaging are limited in their ability to quantify small scale, transverse, in-plane, matrix cracks developed over long-time creep and fatigue conditions. CMC is a multifunctional material in which the damage is coupled with the material s electrical resistance, providing the possibility of real-time information about the damage state through monitoring of resistance. Here, resistance measurement of SiC/SiC composites under mechanical load at both room temperature monotonic and high temperature creep conditions, coupled with a modal acoustic emission technique, can relate the effects of temperature, strain, matrix cracks, fiber breaks, and oxidation to the change in electrical resistance. A multiscale model can in turn be developed for life prediction of in-service composites, based on electrical resistance methods. Results of tensile mechanical testing of SiC/SiC composites at room and high temperatures will be discussed. Data relating electrical resistivity to composite constituent content, fiber architecture, temperature, matrix crack formation, and oxidation will be explained, along with progress in modeling such properties.

Erythrocyte Membrane Failure by Electromechanical Stress.

PubMed

Du, E; Qiang, Yuhao; Liu, Jia

2018-01-01

We envision that electrodeformation of biological cells through dielectrophoresis as a new technique to elucidate the mechanistic details underlying membrane failure by electrical and mechanical stresses. Here we demonstrate the full control of cellular uniaxial deformation and tensile recovery in biological cells via amplitude-modified electric field at radio frequency by an interdigitated electrode array in microfluidics. Transient creep and cyclic experiments were performed on individually tracked human erythrocytes. Observations of the viscoelastic-to-viscoplastic deformation behavior and the localized plastic deformations in erythrocyte membranes suggest that electromechanical stress results in irreversible membrane failure. Examples of membrane failure can be separated into different groups according to the loading scenarios: mechanical stiffening, physical damage, morphological transformation from discocyte to echinocyte, and whole cell lysis. These results show that this technique can be potentially utilized to explore membrane failure in erythrocytes affected by other pathophysiological processes.

Structural Benchmark Testing for Stirling Convertor Heater Heads

NASA Technical Reports Server (NTRS)

Krause, David L.; Kalluri, Sreeramesh; Bowman, Randy R.

2007-01-01

The National Aeronautics and Space Administration (NASA) has identified high efficiency Stirling technology for potential use on long duration Space Science missions such as Mars rovers, deep space missions, and lunar applications. For the long life times required, a structurally significant design limit for the Stirling convertor heater head is creep deformation induced even under relatively low stress levels at high material temperatures. Conventional investigations of creep behavior adequately rely on experimental results from uniaxial creep specimens, and much creep data is available for the proposed Inconel-718 (IN-718) and MarM-247 nickel-based superalloy materials of construction. However, very little experimental creep information is available that directly applies to the atypical thin walls, the specific microstructures, and the low stress levels. In addition, the geometry and loading conditions apply multiaxial stress states on the heater head components, far from the conditions of uniaxial testing. For these reasons, experimental benchmark testing is underway to aid in accurately assessing the durability of Stirling heater heads. The investigation supplements uniaxial creep testing with pneumatic testing of heater head test articles at elevated temperatures and with stress levels ranging from one to seven times design stresses. This paper presents experimental methods, results, post-test microstructural analyses, and conclusions for both accelerated and non-accelerated tests. The Stirling projects use the results to calibrate deterministic and probabilistic analytical creep models of the heater heads to predict their life times.

Accelerated Life Structural Benchmark Testing for a Stirling Convertor Heater Head

NASA Technical Reports Server (NTRS)

Krause, David L.; Kantzos, Pete T.

2006-01-01

For proposed long-duration NASA Space Science missions, the Department of Energy, Lockheed Martin, Infinia Corporation, and NASA Glenn Research Center are developing a high-efficiency, 110 W Stirling Radioisotope Generator (SRG110). A structurally significant limit state for the SRG110 heater head component is creep deformation induced at high material temperature and low stress level. Conventional investigations of creep behavior adequately rely on experimental results from uniaxial creep specimens, and a wealth of creep data is available for the Inconel 718 material of construction. However, the specified atypical thin heater head material is fine-grained with a heat treatment that limits precipitate growth, and little creep property data for this microstructure is available in the literature. In addition, the geometry and loading conditions apply a multiaxial stress state on the component, far from the conditions of uniaxial testing. For these reasons, an extensive experimental investigation is ongoing to aid in accurately assessing the durability of the SRG110 heater head. This investigation supplements uniaxial creep testing with pneumatic testing of heater head-like pressure vessels at design temperature with stress levels ranging from approximately the design stress to several times that. This paper presents experimental results, post-test microstructural analyses, and conclusions for four higher-stress, accelerated life tests. Analysts are using these results to calibrate deterministic and probabilistic analytical creep models of the SRG110 heater head.

Creep performance of oxide ceramic fiber materials at elevated temperature in air and in steam

NASA Astrophysics Data System (ADS)

Armani, Clinton J.

Structural aerospace components that operate in severe conditions, such as extreme temperatures and detrimental environments, require structural materials that have superior long-term mechanical properties and that are thermochemically stable over a broad range of service temperatures and environments. Ceramic matrix composites (CMCs) capable of excellent mechanical performance in harsh environments are prime candidates for such applications. Oxide ceramic materials have been used as constituents in CMCs. However, recent studies have shown that high-temperature mechanical performance of oxide-oxide CMCs deteriorate in a steam-rich environment. The degradation of strength at elevated temperature in steam has been attributed to the environmentally assisted subcritical crack growth in the oxide fibers. Furthermore, oxide-oxide CMCs have shown significant increases in steady-state creep rates in steam. The present research investigated the effects of steam on the high-temperature creep and monotonic tension performance of several oxide ceramic materials. Experimental facilities were designed and configured, and experimental methods were developed to explore the influence of steam on the mechanical behaviors of ceramic fiber tows and of ceramic bulk materials under temperatures in the 1100--1300°C range. The effects of steam on creep behavior of Nextel(TM)610 and Nextel(TM)720 fiber tows were examined. Creep rates at elevated temperatures in air and in steam were obtained for both types of fibers. Relationships between creep rates and applied stresses were modeled and underlying creep mechanisms were identified. For both types of fiber tows, a creep life prediction analysis was performed using linear elastic fracture mechanics and a power-law crack velocity model. These results have not been previously reported and have critical design implications for CMC components operating in steam or near the recommended design limits. Predictions were assessed and validated via comparisons with experimental results. Additionally, the utility of the Monkman-Grant relationship to predicting creep-rupture life of the fiber tows at elevated temperature in air and in steam was demonstrated. Furthermore, the effects of steam on the compressive creep performance of bulk ceramic materials were also studied. Performance of fine grained, polycrystalline alumina (Al2O3) was investigated at 1100 and 1300°C in air and in steam. To evaluate the effect of silica doping during material processing both undoped and silica doped polycrystalline alumina specimens were tested. Finally, compressive creep performance of yttrium aluminum garnet (YAG, Y3Al5O12) was evaluated at 1300°C in air and in steam. Both undoped and silica doped YAG specimens were included in the study. YAG is being considered as the next-generation oxide fiber material. However, before considerable funding and effort are invested in a fiber development program, it is necessary to evaluate the creep performance of YAG at elevated temperature in steam. Results of this research demonstrated that both the undoped YAG and the silica doped YAG exhibited exceptional creep resistance at 1300°C in steam for grain sizes ˜1 microm. These results supplement the other promising features of YAG that make it a strong candidate material for the next generation ceramic fiber.

Fracture Mechanisms For SiC Fibers And SiC/SiC Composites Under Stress-Rupture Conditions at High Temperatures

NASA Technical Reports Server (NTRS)

DiCarlo, James A.; Yun, Hee Mann; Hurst, Janet B.; Viterna, L. (Technical Monitor)

2002-01-01

The successful application of SiC/SiC ceramic matrix composites as high-temperature structural materials depends strongly on maximizing the fracture or rupture life of the load-bearing fiber and matrix constituents. Using high-temperature data measured under stress-rupture test conditions, this study examines in a mechanistic manner the effects of various intrinsic and extrinsic factors on the creep and fracture behavior of a variety of SiC fiber types. It is shown that although some fiber types fracture during a large primary creep stage, the fiber creep rate just prior to fracture plays a key role in determining fiber rupture time (Monkman-Grant theory). If it is assumed that SiC matrices rupture in a similar manner as fibers with the same microstructures, one can develop simple mechanistic models to analyze and optimize the stress-rupture behavior of SiC/SiC composites for applied stresses that are initially below matrix cracking.

Relaxation of creep strain in paper

NASA Astrophysics Data System (ADS)

Mustalahti, Mika; Rosti, Jari; Koivisto, Juha; Alava, Mikko J.

2010-07-01

In disordered, viscoelastic or viscoplastic materials a sample response exhibits a recovery phenomenon after the removal of a constant load or after creep. We study experimentally the recovery in paper, a quasi-two-dimensional system with intrinsic structural disorder. The deformation is measured by using the digital image correlation (DIC) method. By the DIC we obtain accurate displacement data and the spatial fields of deformation and recovered strains. The averaged results are first compared to several heuristic models for viscoelastic polymer materials in particular. The most important experimental quantity is the permanent creep strain, and we analyze whether it is non-zero by fitting the empirical models of viscoelasticity. We then present in more detail the spatial recovery behavior results from DIC, and show that they indicate a power-law-type relaxation. We outline results on variation from sample to sample and collective, spatial fluctuations in the recovery behavior. An interpretation is provided for the relaxation in the general context of glassy, interacting systems with barriers.

Creep-rupture reliability analysis

NASA Technical Reports Server (NTRS)

Peralta-Duran, A.; Wirsching, P. H.

1984-01-01

A probabilistic approach to the correlation and extrapolation of creep-rupture data is presented. Time temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson-Miller and on the Manson-Haferd parameters, but it can be applied to any of the TTP's. A method is developed for evaluating material dependent constants for TTP's. It is shown that optimized constants can provide a significant improvement in the correlation of the data, thereby reducing modelling error. Attempts were made to quantify the performance of the proposed method in predicting long term behavior. Uncertainty in predicting long term behavior from short term tests was derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state of the art reliability methods to the design of components under creep.

Monotonic, Creep-Rupture, and Fatigue Behavior of Carbon Fiber Reinforced Silicon Carbide (C/SiC) at an Elevated Temperature

DTIC Science & Technology

2004-03-01

elevated temperature of 550 C. Cyclic loading of C/SiC was investigated at frequencies of 375 Hz , 10 Hz, 1 Hz, and 0.1 Hz. Creep-Rupture tests and tests that...is reduced when frequency of fatigue is increased. At high frequency fatigue (10Hz to 375 Hz ), C/SiC composites have longer cycle lives and time lives

Predicting the viscosity of solids using steady-state creep behavior of the fibrous composites semi-theoretically

NASA Astrophysics Data System (ADS)

Monfared, Vahid

A semi-analytical formulation is presented for obtaining the viscosity of solids (such as metals) using the steady state creep model of the short-fiber composites. For achieving this aim, fluid mechanics theory is used for determining the viscosity. Sometimes, obtaining the viscosity is experimentally difficult and intricate. So, the present model may be beneficial to obtain the viscosity of metals.

Effects of thermomechanical processing on tensile and long-time creep behavior of Nb-1 percent Zr-0.1 percent C sheet

NASA Technical Reports Server (NTRS)

Titran, Robert H.; Uz, Mehmet

1994-01-01

Effects of thermomechanical processing on the mechanical properties of Nb-1 wt. percent Zr-0.1 wt. percent C, a candidate alloy for use in advanced space power systems, were investigated. Sheet bars were cold rolled into 1-mm thick sheets following single, double, or triple extrusion operations at 1900 K. All the creep and tensile specimens were given a two-step heat treatment 1 hr at 1755 K + 2 hr 1475 K prior to testing. Tensile properties were determined at 300 as well as at 1350 K. Microhardness measurements were made on cold rolled, heat treated, and crept samples. Creep tests were carried out at 1350 K and 34.5 MPa for times of about 10,000 to 19,000 hr. The results show that the number of extrusions had some effects on both the microhardness and tensile properties. However, the long-time creep behavior of the samples were comparable, and all were found to have adequate properties to meet the design requirements of advanced power systems regardless of thermomechanical history. The results are discussed in correlation with processing and microstructure, and further compared to the results obtained from the testing of Nb-1 wt. percent Zr and Nb-1 wt. percent Zr-0.06 wt. percent C alloys.

Predicting knee replacement damage in a simulator machine using a computational model with a consistent wear factor.

PubMed

Zhao, Dong; Sakoda, Hideyuki; Sawyer, W Gregory; Banks, Scott A; Fregly, Benjamin J

2008-02-01

Wear of ultrahigh molecular weight polyethylene remains a primary factor limiting the longevity of total knee replacements (TKRs). However, wear testing on a simulator machine is time consuming and expensive, making it impractical for iterative design purposes. The objectives of this paper were first, to evaluate whether a computational model using a wear factor consistent with the TKR material pair can predict accurate TKR damage measured in a simulator machine, and second, to investigate how choice of surface evolution method (fixed or variable step) and material model (linear or nonlinear) affect the prediction. An iterative computational damage model was constructed for a commercial knee implant in an AMTI simulator machine. The damage model combined a dynamic contact model with a surface evolution model to predict how wear plus creep progressively alter tibial insert geometry over multiple simulations. The computational framework was validated by predicting wear in a cylinder-on-plate system for which an analytical solution was derived. The implant damage model was evaluated for 5 million cycles of simulated gait using damage measurements made on the same implant in an AMTI machine. Using a pin-on-plate wear factor for the same material pair as the implant, the model predicted tibial insert wear volume to within 2% error and damage depths and areas to within 18% and 10% error, respectively. Choice of material model had little influence, while inclusion of surface evolution affected damage depth and area but not wear volume predictions. Surface evolution method was important only during the initial cycles, where variable step was needed to capture rapid geometry changes due to the creep. Overall, our results indicate that accurate TKR damage predictions can be made with a computational model using a constant wear factor obtained from pin-on-plate tests for the same material pair, and furthermore, that surface evolution method matters only during the initial "break in" period of the simulation.

Development of advanced high strength tantalum base alloys. Phase 3: Influence of metallurgical condition on the mechanical properties of ASTAR-811C sheet

NASA Technical Reports Server (NTRS)

Ammon, R. L.; Buckman, R. W., Jr.; Harrod, D. L.

1972-01-01

Metallurgical condition was shown to have a significant effect on the creep properties of ASTAR-811C (Ta-8W-1Re-0.7Hf-0.025C) sheet. Cold worked material exhibited creep rates 30 times higher than solution annealed material and 10 times greater than for recrystallized material. Both grain size and the carbide morphology changes as the final annealing temperature was raised from 3000 F to 3600 F. However, the lowest creep rates were achieved for material which retained the high temperature form of the Ta2C precipitate. Samples with GTA weldments had essentially identical properties as recrystallized base metal. Cooling rates from 3600 F of 5, 50, and 800 F deg/min. had little effect on the 2000 and 2400 F creep behavior of ASTAR-811C.

Constitutive Modeling of the Thermomechanical Behavior of Rock Salt

NASA Astrophysics Data System (ADS)

Hampel, A.

2016-12-01

For the safe disposal of heat-generating high-level radioactive waste in rock salt formations, highly reliable numerical simulations of the thermomechanical and hydraulic behavior of the host rock have to be performed. Today, the huge progress in computer technology has enabled experts to calculate large and detailed computer models of underground repositories. However, the big ad­van­ces in computer technology are only beneficial when the applied material models and modeling procedures also meet very high demands. They result from the fact that the evaluation of the long-term integrity of the geological barrier requires an extra­polation of a highly nonlinear deforma­tion behavior to up to 1 million years, while the underlying experimental investigations in the laboratory or in situ have a duration of only days, weeks or at most some years. Several advanced constitutive models were developed and continuously improved to describe the dependences of various deformation phenomena in rock salt on in-situ relevant boundary conditions: transient and steady-state creep, evolution of damage and dilatancy in the DRZ, failure, post-failure behavior, residual strength, damage and dilatancy reduction, and healing. In a joint project series between 2004 and 2016, fundamental features of the advanced models were investigated and compared in detail with benchmark calculations. The study included procedures for the determination of characteristic salt-type-specific model parameter values and for the performance of numerical calculations of underground structures. Based on the results of this work and on specific laboratory investigations, the rock mechanical modeling is currently developed further in a common research project of experts from Germany and the United States. In this presentation, an overview about the work and results of the project series is given and the current joint research project WEIMOS is introduced.

THE CREEP BEHAVIOUR OF THE MAGNESIUM-ZIRCONIUM ALLOY ZA AT 400 AND 450 C IN CARBON DIOXIDE CONTAINING /approximately equals/200 PPM MOISTURE

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

Kent, R.P.; Wells, T.C.

1963-03-01

The creep behavior of the magnesium-zirconium alloy ZA was studied in tests of up to 5600 hr duration at 400 deg C and up to 12 600 hr duration at 450 deg C, in an atmosphere of carbon dioxide containing approximately 200 ppm water. The accompanying microstructural changes were observed by optical and electron microscopy. The alloy is stronger at 450 deg C than at 400 deg C and additional strengthening obtains from prestraining at 250 deg C prior to creep-testing. In stress rupture tests at 200 deg C subsequent to creep-testing, the time to rupture and the rupture ductilitymore » are lower in specimens previously tested at 450 deg C than in those tested at 400 deg C. The increase in creep strength at 450 deg C, and subsequent loss of ductility, are attributed principally to the precipitation of a zirconium-rich phase, tentatively identified as epsilon - zirconium hydride, which forms both intragranularly (as ribbons and thin hexagonal plates) and as intergranular particles. (auth)« less

Robust Rocket Engine Concept

NASA Technical Reports Server (NTRS)

Lorenzo, Carl F.

1995-01-01

The potential for a revolutionary step in the durability of reusable rocket engines is made possible by the combination of several emerging technologies. The recent creation and analytical demonstration of life extending (or damage mitigating) control technology enables rapid rocket engine transients with minimum fatigue and creep damage. This technology has been further enhanced by the formulation of very simple but conservative continuum damage models. These new ideas when combined with recent advances in multidisciplinary optimization provide the potential for a large (revolutionary) step in reusable rocket engine durability. This concept has been named the robust rocket engine concept (RREC) and is the basic contribution of this paper. The concept also includes consideration of design innovations to minimize critical point damage.

Study of Creep of Alumina-Forming Austenitic Stainless Steel for High-Temperature Energy Applications

NASA Astrophysics Data System (ADS)

Afonina, Natalie Petrovna

To withstand the high temperature (>700°C) and pressure demands of steam turbines and boilers used for energy applications, metal alloys must be economically viable and have the necessary material properties, such as high-temperature creep strength, oxidation and corrosion resistance, to withstand such conditions. One promising class of alloys potentially capable of withstanding the rigors of aggressive environments, are alumina-forming austenitic stainless steels (AFAs) alloyed with aluminum to improve corrosion and oxidation resistance. The effect of aging on the microstructure, high temperature constant-stress creep behavior and mechanical properties of the AFA-type alloy Fe-20Cr-30Ni-2Nb-5Al (at.%) were investigated in this study. The alloy's microstructural evolution with increased aging time was observed prior to creep testing. As aging time increased, the alloy exhibited increasing quantities of fine Fe2Nb Laves phase dispersions, with a precipitate-free zone appearing in samples with higher aging times. The presence of the L1 2 phase gamma'-Ni3Al precipitate was detected in the alloy's matrix at 760°C. A constant-stress creep rig was designed, built and its operation validated. Constant-stress creep tests were performed at 760°C and 35MPa, and the effects of different aging conditions on creep rate were investigated. Specimens aged for 240 h exhibited the highest creep rate by a factor of 5, with the homogenized sample having the second highest rate. Samples aged for 2.4 h and 24 h exhibited similar low secondary creep rates. Creep tests conducted at 700oC exhibited a significantly lower creep rate compared to those at 760oC. Microstructural analysis was performed on crept samples to explore high temperature straining properties. The quantity and size of Fe2Nb Laves phase and NiAl particles increased in the matrix and on grain boundaries with longer aging time. High temperature tensile tests were performed and compared to room temperature results. The high temperature results were significantly lower when compared to room temperature values. Higher creep rates were correlated with lower yield strengths.

Mechanical Performance of Ferritic Martensitic Steels for High Dose Applications in Advanced Nuclear Reactors

NASA Astrophysics Data System (ADS)

Anderoglu, Osman; Byun, Thak Sang; Toloczko, Mychailo; Maloy, Stuart A.

2013-01-01

Ferritic/martensitic (F/M) steels are considered for core applications and pressure vessels in Generation IV reactors as well as first walls and blankets for fusion reactors. There are significant scientific data on testing and industrial experience in making this class of alloys worldwide. This experience makes F/M steels an attractive candidate. In this article, tensile behavior, fracture toughness and impact property, and creep behavior of the F/M steels under neutron irradiations to high doses with a focus on high Cr content (8 to 12) are reviewed. Tensile properties are very sensitive to irradiation temperature. Increase in yield and tensile strength (hardening) is accompanied with a loss of ductility and starts at very low doses under irradiation. The degradation of mechanical properties is most pronounced at <0.3 T M ( T M is melting temperature) and up to 10 dpa (displacement per atom). Ferritic/martensitic steels exhibit a high fracture toughness after irradiation at all temperatures even below 673 K (400 °C), except when tested at room temperature after irradiations below 673 K (400 °C), which shows a significant reduction in fracture toughness. Creep studies showed that for the range of expected stresses in a reactor environment, the stress exponent is expected to be approximately one and the steady state creep rate in the absence of swelling is usually better than austenitic stainless steels both in terms of the creep rate and the temperature sensitivity of creep. In short, F/M steels show excellent promise for high dose applications in nuclear reactors.