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Sample records for ii fracture mechanics

  1. Fracture of Sn-Ag-Cu Solder Joints on Cu Substrates. II: Fracture Mechanism Map

    NASA Astrophysics Data System (ADS)

    Kumar, P.; Huang, Z.; Dutta, I.; Sidhu, R.; Renavikar, M.; Mahajan, R.

    2012-02-01

    A methodology to construct fracture mechanism maps for Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates has been developed. The map, which delineates the operative mechanisms of fracture along with corresponding joint fracture toughness values, is plotted in a space described by two microstructure-dependent parameters, with the abscissa describing the interfacial intermetallic compound (IMC) and the ordinate representing the strain-rate-dependent solder yield strength. The plot space encompasses the three major mechanisms by which joints fail, namely (i) cohesive fracture of solder, (ii) cleavage fracture of interfacial intermetallic compounds (IMC), and (iii) fracture of the solder-IMC interface. Line contours of constant fracture toughness values, as well as constant fraction of each of the above mechanisms, are indicated on the plots. The plots are generated by experimentally quantifying the dependence of the operative fracture mechanism(s) on the two microstructure-dependent parameters (IMC geometry and solder yield strength) as functions of strain rate, reflow parameters, and post-reflow aging. Separate maps are presented for nominally mode I and equi-mixed mode loading conditions (loading angle ϕ = 0° and 45°, respectively). The maps allow rapid assessment of the operative fracture mechanism(s) along with estimation of the expected joint fracture toughness value for a given loading condition (strain rate and loading angle) and joint microstructure without conducting actual tests, and may serve as a tool for both prediction and microstructure design.

  2. Fracture Mechanics

    DTIC Science & Technology

    1974-01-31

    2219 -T851 aluminum (fractures at low stresses). The parameter KF is alloy compact specimens 1 2 and demonstrate consistent a function of specimen...Congress of 20. Walker, E. K., "The Effect of Stress Ratio Applied Mechanics, 1924. During Crack Propagation and Fatigue for 2024-T3 and 7015- T6 Aluminum ...34Stress- Corrosion Cracking in 12. Kaufman, J. G., and Nelson, F. G., "More Ti-6A1-4V Titanium Alloy in Nitrogen Tetroxide," on Specimen Size Effect in 2219

  3. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part II. Fatigue crack growth rate

    NASA Astrophysics Data System (ADS)

    Margolin, B.; Minkin, A.; Smirnov, V.; Sorokin, A.; Shvetsova, V.; Potapova, V.

    2016-11-01

    The experimental data on the fatigue crack growth rate (FCGR) have been obtained for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various radiation swelling. The performed study of the fracture mechanisms for cracked specimens under cyclic loading has explained why radiation swelling affects weakly FCGR unlike its effect on fracture toughness. Mechanical modeling of fatigue crack growth has been carried out and the dependencies for prediction of FCGR in irradiated austenitic steel with and with no swelling are proposed and verified with the obtained experimental results. As input data for these dependencies, FCGR for unirradiated steel and the tensile mechanical properties for unirradiated and irradiated steels are used.

  4. Mechanics of tungsten blistering II: Analytical treatment and fracture mechanical assessment

    NASA Astrophysics Data System (ADS)

    Li, Muyuan; You, Jeong-Ha

    2015-10-01

    Since a decade the blistering of pure tungsten under hydrogen implantation has been one of the major research topics in relation to the plasma-wall interaction of tungsten-armored first wall. Overall blistering may reduce the erosion lifetime of the wall. Mature blisters grown by high internal pressure are likely to burst leading to exfoliation of the surface. Therefore, the control and suppression of blistering is an important concern for sustainable operation of the tungsten-armored plasma-facing components. In this context, a quantitative assessment of the mechanical conditions for blister bulging and growth is an important concern. In this article a theoretical framework is presented to describe the bulging deformation of tungsten blisters and to estimate the mechanical driving force of blister growth. The validity of the analytical formulations based on the theory of elastic plates is evaluated with the help of finite element analysis. Plastic strains and J-integral values at the blister boundary edge are assessed by means of numerical simulation. Extensive parametric studies were performed for a range of blister geometry (cap aspect ratio), gas pressure, yield stress and hardening rate. The characteristic features of the blistering mechanics are discussed and the cracking energy is quantitatively estimated for the various combinations of parameters.

  5. Fracture mechanics expert system

    NASA Technical Reports Server (NTRS)

    Powers, E.; Elfer, N.; Casadaban, C.

    1992-01-01

    Attention is given to fracture mechanics, an analytical method used extensively in the National Space Transportation System to conservatively predict the remaining service life of an article when a flaw or a material defect is detected. These analyses are performed on hardware containing material defects that have been detected by various nondestructive inspection techniques. An expert system being developed to streamline the process so that hardware dispositions may be obtained in a timely and consistent manner is discussed. The expert system reduces the potential for errors due to the manual transcription between the various software programs involved in completing a fracture mechanics analysis. NEXPERT Object, the expert system development shell selected for this purpose, allows the various software programs used in fracture mechanics analyses to be accessed and manipulated from the same platform.

  6. Phase Field Fracture Mechanics.

    SciTech Connect

    Robertson, Brett Anthony

    2015-11-01

    For this assignment, a newer technique of fracture mechanics using a phase field approach, will be examined and compared with experimental data for a bend test and a tension test. The software being used is Sierra Solid Mechanics, an implicit/explicit finite element code developed at Sandia National Labs in Albuquerque, New Mexico. The bend test experimental data was also obtained at Sandia Labs while the tension test data was found in a report online from Purdue University.

  7. Fracture mechanics validity limits

    NASA Technical Reports Server (NTRS)

    Lambert, Dennis M.; Ernst, Hugo A.

    1994-01-01

    Fracture behavior is characteristics of a dramatic loss of strength compared to elastic deformation behavior. Fracture parameters have been developed and exhibit a range within which each is valid for predicting growth. Each is limited by the assumptions made in its development: all are defined within a specific context. For example, the stress intensity parameters, K, and the crack driving force, G, are derived using an assumption of linear elasticity. To use K or G, the zone of plasticity must be small as compared to the physical dimensions of the object being loaded. This insures an elastic response, and in this context, K and G will work well. Rice's J-integral has been used beyond the limits imposed on K and G. J requires an assumption of nonlinear elasticity, which is not characteristic of real material behavior, but is thought to be a reasonable approximation if unloading is kept to a minimum. As well, the constraint cannot change dramatically (typically, the crack extension is limited to ten-percent of the initial remaining ligament length). Rice, et al investigated the properties required of J-type parameters, J(sub x), and showed that the time rate, dJ(sub x)/dt, must not be a function of the crack extension rate, da/dt. Ernst devised the modified-J parameter, J(sub M), that meets this criterion. J(sub M) correlates fracture data to much higher crack growth than does J. Ultimately, a limit of the validity of J(sub M) is anticipated, and this has been estimated to be at a crack extension of about 40-percent of the initial remaining ligament length. None of the various parameters can be expected to describe fracture in an environment of gross plasticity, in which case the process is better described by deformation parameters, e.g., stress and strain. In the current study, various schemes to identify the onset of the plasticity-dominated behavior, i.e., the end of fracture mechanics validity, are presented. Each validity limit parameter is developed in

  8. Linear elastic fracture mechanics primer

    NASA Technical Reports Server (NTRS)

    Wilson, Christopher D.

    1992-01-01

    This primer is intended to remove the blackbox perception of fracture mechanics computer software by structural engineers. The fundamental concepts of linear elastic fracture mechanics are presented with emphasis on the practical application of fracture mechanics to real problems. Numerous rules of thumb are provided. Recommended texts for additional reading, and a discussion of the significance of fracture mechanics in structural design are given. Griffith's criterion for crack extension, Irwin's elastic stress field near the crack tip, and the influence of small-scale plasticity are discussed. Common stress intensities factor solutions and methods for determining them are included. Fracture toughness and subcritical crack growth are discussed. The application of fracture mechanics to damage tolerance and fracture control is discussed. Several example problems and a practice set of problems are given.

  9. Mechanisms of intergranular fracture

    SciTech Connect

    Farkas, D.

    1999-08-01

    The authors present a study of the atomistic mechanisms of crack propagation along grain boundaries in metals and alloys. The failure behavior showing cleavage crack growth and/or crack-tip dislocation emission is demonstrated using atomistic simulations for an embedded-atom model. The simulations follow the quasi-equilibrium growth of a crack as the stress intensity applied increases. Dislocations emitted from crack tips normally blunt the crack and inhibit cleavage, inducing ductile behavior. When the emitted dislocations stay near the crack tip (sessile dislocations), they do blunt the crack but brittle cleavage can occur after the emission of a sufficient number of dislocations. The fracture process occurs as a combination of dislocation emission/micro-cleavage portions that are controlled by the local atomistic structure of the grain boundary. The grain boundary is shown to be a region where dislocation emission is easier, a mechanism that competes with the lower cohesive strength of the boundary region.

  10. Mechanics of Hydraulic Fractures

    NASA Astrophysics Data System (ADS)

    Detournay, Emmanuel

    2016-01-01

    Hydraulic fractures represent a particular class of tensile fractures that propagate in solid media under pre-existing compressive stresses as a result of internal pressurization by an injected viscous fluid. The main application of engineered hydraulic fractures is the stimulation of oil and gas wells to increase production. Several physical processes affect the propagation of these fractures, including the flow of viscous fluid, creation of solid surfaces, and leak-off of fracturing fluid. The interplay and the competition between these processes lead to multiple length scales and timescales in the system, which reveal the shifting influence of the far-field stress, viscous dissipation, fracture energy, and leak-off as the fracture propagates.

  11. Geometrically Frustrated Fracture Mechanics

    NASA Astrophysics Data System (ADS)

    Mitchell, Noah; Koning, Vinzenz; Vitelli, Vincenzo; Irvine, William T. M.

    2015-03-01

    When a flat elastic sheet is forced to conform to a surface with Gaussian curvature, stresses arise in the sheet. The mismatch between initial and final metrics gives rise to new fracture behavior which cannot be achieved by boundary loading alone. Using experiments of PDMS sheets frustrated on 3D-printed surfaces and a linearized analytical model, we demonstrate the ability of curvature to govern the sheets' fracture phenomenology. In this talk, we first show that curvature can both stimulate and suppress fracture initiation, depending on the position and orientation of the initial slit. Secondly, we show that curvature can steer the path of a crack as it propagates through the material. Lastly, the curvature can arrest cracks which would otherwise continue to propagate.

  12. Fracture toughness of polycrystalline ceramics in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, Dileep; Shetty, Dinesh K.

    1989-01-01

    The present investigation of the fracture of alumina and zirconia polycrystalline ceramic specimens of precracked-disk type, in diametral compression, evaluated fracture toughness in pure mode I, combined mode I/mode II, and pure mode II, depending on the alignment of the center crack relative to the loading diameter. The mixed-mode fracture-toughness envelope thus obtained exhibits significant deviation to higher fracture toughness in mode II, relative to the predictions of linear elastic fracture mechanics theory. Crack-surface resistance due to grain-interlocking and abrasion are identified as the primary sources of increased fracture resistance in mode II loading of the polycrystalline ceramics.

  13. Modelling the graphite fracture mechanisms

    SciTech Connect

    Jacquemoud, C.; Marie, S.; Nedelec, M.

    2012-07-01

    In order to define a design criterion for graphite components, it is important to identify the physical phenomena responsible for the graphite fracture, to include them in a more effective modelling. In a first step, a large panel of experiments have been realised in order to build up an important database; results of tensile tests, 3 and 4 point bending tests on smooth and notched specimens have been analysed and have demonstrated an important geometry related effects on the behavior up to fracture. Then, first simulations with an elastic or an elastoplastic bilinear constitutive law have not made it possible to simulate the experimental fracture stress variations with the specimen geometry, the fracture mechanisms of the graphite being at the microstructural scale. That is the reason why a specific F.E. model of the graphite structure has been developed in which every graphite grain has been meshed independently, the crack initiation along the basal plane of the particles as well as the crack propagation and coalescence have been modelled too. This specific model has been used to test two different approaches for fracture initiation: a critical stress criterion and two criteria of fracture mechanic type. They are all based on crystallographic considerations as a global critical stress criterion gave unsatisfactory results. The criteria of fracture mechanic type being extremely unstable and unable to represent the graphite global behaviour up to the final collapse, the critical stress criterion has been preferred to predict the results of the large range of available experiments, on both smooth and notched specimens. In so doing, the experimental observations have been correctly simulated: the geometry related effects on the experimental fracture stress dispersion, the specimen volume effects on the macroscopic fracture stress and the crack propagation at a constant stress intensity factor. In addition, the parameters of the criterion have been related to

  14. Fracture mechanics of cellular glass

    NASA Technical Reports Server (NTRS)

    Zwissler, J. G.; Adams, M. A.

    1981-01-01

    The fracture mechanics of cellular glasses (for the structural substrate of mirrored glass for solr concentrator reflecting panels) are discussed. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials were developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region 1 may be slower, by orders of magnitude, than that found in dense glasses.

  15. Fracture mechanics and corrosion fatigue.

    NASA Technical Reports Server (NTRS)

    Mcevily, A. J.; Wei, R. P.

    1972-01-01

    Review of the current state-of-the-art in fracture mechanics, particularly in relation to the study of problems in environment-enhanced fatigue crack growth. The usefulness of this approach in developing understanding of the mechanisms for environmental embrittlement and its engineering utility are discussed. After a brief review of the evolution of the fracture mechanics approach and the study of environmental effects on the fatigue behavior of materials, a study is made of the response of materials to fatigue and corrosion fatigue, the modeling of the mechanisms of the fatigue process is considered, and the application of knowledge of fatigue crack growth to the prediction of the high cycle life of unnotched specimens is illustrated.

  16. Some recent theoretical and experimental developments in fracture mechanics

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Eftis, J.; Hones, D. L.

    1978-01-01

    Recent theoretical and experimental developments in four distinct areas of fracture mechanics research are described. These are as follows: experimental comparisons of different nonlinear fracture toughness measures, including the nonlinear energy, R curve, COD and J integral methods; the singular elastic crack-tip stress and displacement equations and the validity of the proposition of their general adequacy as indicated, for example, by the biaxially loaded infinite sheet with a flat crack; the thermodynamic nature of surface energy induced by propagating cracks in relation to a general continuum thermodynamic description of brittle fracture; and analytical and experimental aspects of Mode II fracture, with experimental data for certain aluminum, steel and titanium alloys.

  17. (Fracture mechanics of inhomogeneous materials)

    SciTech Connect

    Bass, B.R.

    1990-10-01

    Discussions were held with Japanese researchers concerning (1) the Elastic-Plastic Fracture Mechanics in Inhomogeneous Materials and Structures (EPI) Program, and (2) ongoing large-scale pressurized- thermal-shock (PTS) experiments in Japan. In the EPI Program, major activities in the current fiscal year include round-robin analyses of measured data from inhomogeneous base metal/weld metal compact- tension (CT) specimens fabricated from welded plates of A533 grade B class 1 steel. The round-robin task involves participants from nine research organizations in Japan and is scheduled for completion by the end of 1990. Additional experiments will be performed on crack growth in inhomogeneous CT specimens and three-point bend (3PB) specimens 10 mm thick. The data will be compared with that generated previously from 19-mm-thick-specimens. A new type of inhomogeneous surface-cracked specimen will be tested this year, with ratio of crack depth to surface length (a/c) satisfying 0.2 {le} (a/c) {le} 0. 8 and using a 3PB type of applied load. Plans are under way to fabricate a new welded plate of A533 grade B class 1 steel (from a different heat than that currently being tested) in order to provide an expanded fracture-toughness data base. Other topics concerning fracture-prevention issues in reactor pressure vessels were discussed with each of the host organizations, including an overview of ongoing work in the Heavy-Section Steel Technology (HSST) Program.

  18. Fracture mechanics of cellular glass

    SciTech Connect

    Zwissler, J.G.; Adams, M.A.

    1981-02-01

    Cellular glasses are prime candidate materials for the structural substrate of mirrored glass for solar concentrator reflecting panels. These materials are brittle, however, and susceptible to mechanical failure from slow crack growth caused by a stress corrosion mechanism. The results are detailed of one part of a program established to develop improved cellular glasses and to characterize the behavior of these and commercially available materials. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials are developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region I may be slower, by orders of magnitude, than that found in dense glasses.

  19. Mechanical Coal-Face Fracturer

    NASA Technical Reports Server (NTRS)

    Collins, E. R., Jr.

    1984-01-01

    Radial points on proposed drill bit take advantage of natural fracture planes of coal. Radial fracture points retracted during drilling and impacted by piston to fracture coal once drilling halts. Group of bits attached to array of pneumatic drivers to fracture large areas of coal face.

  20. Compendium of fracture mechanics problems

    NASA Technical Reports Server (NTRS)

    Stallworth, R.; Wilson, C.; Meyers, C.

    1990-01-01

    Fracture mechanics analysis results are presented from the following structures/components analyzed at Marshall Space Flight Center (MSFC) between 1982 and 1989: space shuttle main engine (SSME), Hubble Space Telescope (HST), external tank attach ring, B-1 stand LOX inner tank, and solid rocket booster (SRB). Results from the SSME high pressure fuel turbopump (HPFTP) second stage blade parametric analysis determine a critical flaw size for a wide variety of stress intensity values. The engine 0212 failure analysis was a time dependent fracture life assessment. Results indicated that the disk ruptured due to an overspeed condition. Results also indicated that very small flaws in the curvic coupling area could propagate and lead to failure under normal operating conditions. It was strongly recommended that a nondestructive evaluation inspection schedule be implemented. The main ring of the HST, scheduled to launch in 1990, was analyzed by safe-life and fail-safe analyses. First safe-life inspection criteria curves for the ring inner and outer skins and the fore and aft channels were derived. Afterwards the skins and channels were determined to be fail-safe by analysis. A conservative safe-life analysis was done on the 270 redesign external tank attach ring. Results from the analysis were used to determine the nondestructive evaluation technique required.

  1. Entablature: fracture types and mechanisms

    NASA Astrophysics Data System (ADS)

    Forbes, A. E. S.; Blake, S.; Tuffen, H.

    2014-05-01

    Entablature is the term used to describe zones or tiers of irregular jointing in basaltic lava flows. It is thought to form when water from rivers dammed by the lava inundates the lava flow surface, and during lava-meltwater interaction in subglacial settings. A number of different fracture types are described in entablature outcrops from the Búrfell lava and older lava flows in Þjórsárdalur, southwest Iceland. These are: striae-bearing, column-bounding fractures and pseudopillow fracture systems that themselves consist of two different fracture types—master fractures with dimpled surface textures and subsidiary fractures with curved striae. The interaction of pseudopillow fracture systems and columnar jointing in the entablature produces the chevron fracture patterns that are commonly observed in entablature. Cube-jointing is a more densely fractured version of entablature, which likely forms when more coolant enters the hot lava. The entablature tiers display closely spaced striae and dendritic crystal shapes which indicate rapid cooling. Master fracture surfaces show a thin band with an evolved composition at the fracture surface; mineral textures in this band also show evidence of quenching of this material. This is interpreted as gas-driven filter pressing of late-stage residual melt that is drawn into an area of low pressure immediately preceding or during master fracture formation by ductile extensional fracture of hot, partially crystallised lava. This melt is then quenched by an influx of water and/or steam when the master fracture fully opens. Our findings suggest that master fractures are the main conduit for coolant entering the lava flow during entablature formation.

  2. Chemical and Mechanical Alteration of Fractured Caprock Under Reactive Flow

    NASA Astrophysics Data System (ADS)

    Elkhoury, J. E.; Ameli, P.; Detwiler, R. L.

    2013-12-01

    Permeability evolution of fractures depends on chemical and mechanical processes. Stress perturbations lead to mechanical deformation and fracture propagation that can increase formation permeability. Chemical disequilibrium between fluids and resident minerals leads to dissolution and precipitation that further alter fracture porosity and permeability. The ability to predict whether these coupled chemical and mechanical processes will enhance or diminish fracture permeability remains elusive. Here, we present results from reactive-transport experiments in fractured anhydrite cores, with significant alteration of the rock matrix, where only the flow rate differed. For high flow rate, the transformation of anhydrite to gypsum occurred uniformly within the fracture leading to compaction and a two-order-of-magnitude decrease in permeability. For low flow rate, rock-fluid reactions proceeded to near equilibrium within the fracture with preferential flow paths persisting over the 6-month duration of the experiment and a negligible change in permeability. Anticipating such permeability evolution is critical for successful geologic CO2 sequestration and waste injection. Additionally, reactive alteration of the porous matrix bounding fractures will influence the strength of earthquake fault zones. Comparison of the aperture field before (a) and after (b) the reactive flow-through experiment at low flow rate. a) Aperture field from optical profilometry measurements of the fracture surfaces. b) Inferred aperture from x-ray computed tomography scans. Color scale I (blue) denotes mainly unaltered regions of the fracture and/or aperture < 200 μm. Color scale II (green/yellow) denotes reacted regions of the fracture surfaces and the matrix adjacent to the fracture. Persistent flow paths are clearly observed in panel (b) (color scale III corresponds to aperture > 200 μm) leading to negligible change in permeability after a 6-month run.

  3. Combined mode I and mode II fracture of monolithic ceramics

    NASA Technical Reports Server (NTRS)

    Tikare, Veena; Choi, Sung R.

    1993-01-01

    The mode I, mode II, and combined mode I-mode II fracture behaviors of a coarse-grained silicon nitride, a fine-grained silicon nitride, and an alumina were investigated. These ceramics were fractured from two types of fracture initiating flaws: small surface flaws and large single edge precracks. The small surface flaws were introduced by Knoop indentation in flexural samples at various angles to the tensile stress direction and fractured in four-point bending. The samples with large precracks were fractured in the asymmetric four-point-bend geometry. The mixed-mode fracture toughness values obtained from the two flaw configurations were in good agreement with each other. All three ceramics displayed very similar mixed-mode fracture behavior, although their microstructures were not similar. Comparison of experimental data to mixed-mode fracture theories revealed that the minimum strain energy density theory best described the mixed-mode fracture behavior of all three ceramics.

  4. Mode II Interlaminar Fracture Toughness and Fatigue Characterization of a Graphite Epoxy Composite Material

    NASA Technical Reports Server (NTRS)

    O'Brien, T. Kevin; Johnston, William M.; Toland, Gregory J.

    2010-01-01

    Mode II interlaminar fracture toughness and delamination onset and growth characterization data were generated for IM7/8552 graphite epoxy composite materials from two suppliers for use in fracture mechanics analyses. Both the fracture toughness testing and the fatigue testing were conducted using the End-notched Flexure (ENF) test. The ENF test for mode II fracture toughness is currently under review by ASTM as a potential standard test method. This current draft ASTM protocol was used as a guide to conduct the tests on the IM7/8552 material. This report summarizes the test approach, methods, procedures and results of this characterization effort.

  5. Microstructural effects on fracture toughness of polycrystalline ceramics in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, D.; Shetty, D. K.

    1988-01-01

    Fracture toughness of polycrystalline alumina and ceria partially-stabilized tetragonal zirconia (CeO2-TZP) ceramics were assessed in combined mode I and mode II loading using precracked disk specimens in diametral compression. Stress states ranging from pure mode I, combined mode I and mode II, and pure mode II were obtained by aligning the center crack at specific angles relative to the loading diameter. The resulting mixed-mode fracture toughness envelope showed significant deviation to higher fracture toughness in mode II relative to the predictions of the linear elastic fracture mechanics theory. Critical comparison with corresponding results on soda-lime glass and fracture surface observations showed that crack surface resistance arising from grain interlocking and abrasion was the main source of the increased fracture toughness in mode II loading of the polycrystalline ceramics. The normalized fracture toughness for pure mode II loading, (KII/KIc), increased with increasing grain size for the CeO2-TZP ceramics. Quantitative fractography confirmed an increased percentage of transgranular fracture of the grains in mode II loading.

  6. Fracture mechanism of a thermal barrier coating

    NASA Astrophysics Data System (ADS)

    Samoilenko, V. M.; Ravilov, R. G.; Drevnyak, V. V.; Petrova, M. A.

    2016-06-01

    The fracture mechanism of the thermal barrier coating of gas turbine blades is studied. The causes of the fracture of the ceramic layer are discussed and the possible ways to increase the fatigue life of the thermal barrier coating are considered.

  7. Fracture Mechanics of Delamination. Initiation and Growth.

    DTIC Science & Technology

    1982-01-01

    transverse cracking, delamina- tion, x- radiography , fracture mechanics, strain energy release rate, finite element, initiation and growth criteria...Battelle Columbus Laboratories, Metals and Ceramics Information Center, 505 King Avenue, Columbus, OH 43201. . . .1 Bell Aerospace Company, Buffalo , NY

  8. Fracture mechanism of borated stainless steel

    SciTech Connect

    He, J.Y.; Soliman, S.E.; Baratta, A.J.; Balliett, T.A.

    2000-05-01

    The mechanical properties and fracture mechanism of irradiated and unirradiated boron containing Type 304 stainless steel are studied. Four different batches with different boron weight percentages are used. One of these batches was manufactured by a conventional wrought technique, while the others were manufactured by a powder metallurgy technique. The irradiated specimens were subjected to a fluence level of 5 x 10{sup 19} or 1 {times} 10{sup 21} n/m{sup 2}. The mechanical and fracture tests were performed at temperatures of 233, 298, and 533 K. No significant effects on the mechanical properties or fracture behavior were observed as a result of neutron irradiation and/or temperature. The ductility and toughness of the borated steel were found to decrease with increasing boron content. The effect of boride on void nucleation and linkage was found to play an important role in the fracture behavior of borated steel.

  9. A Hierarchical Approach to Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Saether, Erik; Taasan, Shlomo

    2004-01-01

    Recent research conducted under NASA LaRC's Creativity and Innovation Program has led to the development of an initial approach for a hierarchical fracture mechanics. This methodology unites failure mechanisms occurring at different length scales and provides a framework for a physics-based theory of fracture. At the nanoscale, parametric molecular dynamic simulations are used to compute the energy associated with atomic level failure mechanisms. This information is used in a mesoscale percolation model of defect coalescence to obtain statistics of fracture paths and energies through Monte Carlo simulations. The mathematical structure of predicted crack paths is described using concepts of fractal geometry. The non-integer fractal dimension relates geometric and energy measures between meso- and macroscales. For illustration, a fractal-based continuum strain energy release rate is derived for inter- and transgranular fracture in polycrystalline metals.

  10. Fracture mechanics of snow avalanches

    NASA Astrophysics Data System (ADS)

    Åström, J. A.; Timonen, J.

    2001-07-01

    Dense snow avalanches are analyzed by modeling the snow slab as an elastic and brittle plate, attached by static friction to the underlying ground. The grade of heterogeneity in the local fracture (slip) thresholds, and the ratio of the average substrate slip threshold to the average slab fracture threshold, are the decisive parameters for avalanche dynamics. For a strong pack of snow there appears a stable precursor of local slips when the frictional contacts are weakened (equivalent to rising temperature), which eventually trigger a catastrophic crack growth that suddenly releases the entire slab. In the opposite limit of very high slip thresholds, the slab simply melts when the temperature is increased. In the intermediate regime, and for a homogeneous slab, the model display features typical of real snow avalanches. The model also suggests an explanation to why avalanches are impossible to forecast reliably based on precursor observations. This explanation may as well be applicable to other catastrophic rupture phenomena such as earthquakes.

  11. Rabotnov damageparameter and description of delayed fracture: Results, current status, application to fracture mechanics, and prospects

    NASA Astrophysics Data System (ADS)

    Stepanova, L. V.; Igonin, S. A.

    2015-03-01

    This paper presents a review of studies of delayed fracture and fracture mechanics problems in which the hypotheses and ideas of Yu. N. Rabotnov and L. M. Kachanov on the mechanisms of delayed fracture under creep conditions are extended to describe fracture processes using scalar and tensor measures of damage. The results of current research in the theory of elasticity, the mathematical theory of plasticity and creep, the mechanics of composites, and linear and nonlinear fracture mechanics, with material damage taken into account.

  12. Crack branching in carbon steel. Fracture mechanisms

    NASA Astrophysics Data System (ADS)

    Syromyatnikova, A. S.; Alekseev, A. A.; Levin, A. I.; Lyglaev, A. V.

    2010-04-01

    The fracture surfaces of pressure vessels made of carbon steel that form during crack branching propagation are examined by fractography. Crack branching is found to occur at a crack velocity higher than a certain critical value V > V c . In this case, the material volume that is involved in fracture and depends on the elastoplastic properties of the material and the sample width has no time to dissipate the energy released upon crack motion via the damage mechanisms intrinsic in the material under given deformation conditions (in our case, via cracking according to intragranular cleavage).

  13. Size Effects in Linear Elastic Fracture Mechanics

    DTIC Science & Technology

    1988-01-01

    Recent Theoretical and Experimental Developments in Fracture Mechanics", Fracture 1977, 1 (1977) 695-723. 40 S. Mindess and J. S. Nadeau," Effect of Notch...0.4 1.42 b 2.0 0.80 b Mindess and Nadeau [40], 1.0 3.98 0.86 b Mortar, 3PB 8.03 0.80 b 12.0 0.82 b 16.0 0.84 b 20.0 0.83 b Concrete, 3PB 1.0 3.54 1.08

  14. A review of fracture mechanics life technology

    NASA Technical Reports Server (NTRS)

    Besuner, P. M.; Harris, D. O.; Thomas, J. M.

    1986-01-01

    Lifetime prediction technology for structural components subjected to cyclic loads is examined. The central objectives of the project are: (1) to report the current state of the art, and (2) recommend future development of fracture mechanics-based analytical tools for modeling subcritical fatigue crack growth in structures. Of special interest is the ability to apply these tools to practical engineering problems and the developmental steps necessary to bring vital technologies to this stage. The authors conducted a survey of published literature and numerous discussions with experts in the field of fracture mechanics life technology. One of the key points made is that fracture mechanics analyses of crack growth often involve consideration of fatigue and fracture under extreme conditions. Therefore, inaccuracies in predicting component lifetime will be dominated by inaccuracies in environment and fatigue crack growth relations, stress intensity factor solutions, and methods used to model given loads and stresses. Suggestions made for reducing these inaccuracies include development of improved models of subcritical crack growth, research efforts aimed at better characterizing residual and assembly stresses that can be introduced during fabrication, and more widespread and uniform use of the best existing methods.

  15. Fracture mechanics; Proceedings of the Seventeenth National Symposium, Albany, NY, August 7-9, 1984

    NASA Technical Reports Server (NTRS)

    Underwood, J. M. (Editor); Chait, R. (Editor); Smith, C. W. (Editor); Wilhem, D. P. (Editor); Andrews, W. A. (Editor); Newman, J. C. (Editor)

    1986-01-01

    The present conference gives attention to topics in the application of fracture mechanics, subcritical crack growth phenomena, fracture testing methods, ductile fracture behavior, and fracture mechanisms and their analysis. Specific papers treat the resistance curve approach to composite materials characterization, fracture toughness in ductile iron and cast steel, hold-time effects in elevated temperature fatigue crack propagation, creep crack growth under nonsteady conditions, viscoplastic fatigue in a superalloy at elevated temperatures, fracture testing with arc bend specimens, one-point bend impact test application, and a compact mode II fracture specimen. Also discussed are the computation of stable crack growth using the J-integral, the use of plastic energy dissipation to characterize crack growth, the extension of surface cracks under cyclic loading, the minimum time criterion for crack instability in structural materials, dynamic crack propagation and branching under biaxial loading, and boundary layer effects in cracked bodies.

  16. Applications of advanced fracture mechanics to fuselage

    NASA Astrophysics Data System (ADS)

    Kanninen, M. F.; O'Donoghue, P. E.; Green, S. T.; Leung, C. P.; Roy, S.; Burnside, O. H.

    Multi-site damage (MSD) in the form of cracking at rivet holes in lap splice joints has been identified as a serious threat to the integrity of commercial aircraft nearing their design life targets. Consequently, to assure the safety of aircraft that have accumulated large numbers of flights, flight hours and years in service requires requires inspection procedures that are based on the possibility that MSD may be present. For inspections of aircraft components to be properly focused on me defect sizes that are critical for structural integrity, fracture analyses are needed. The current methods are essentially those of linear elastic fracture mechanics (LEFM) which are strictly valid only for cracks that extend in a quasi-static manner under small-scale crack tip plasticity conditions. While LEFM is very likely to be appropriate for subcritical crack growth, quantifying the conditions for fracture instability and subsequent propagation may require advanced fracture mechanics techniques. The specific focus in this paper was to identify the conditions in which inelastic-dynamic effects occur in (1) the linking up Of local damage in a lap splice joint to form a major crack, and (2) large-scale fuselage failure by a rapidly occurring fluid structure interaction process.

  17. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part I. Ductility and fracture toughness

    NASA Astrophysics Data System (ADS)

    Margolin, B.; Sorokin, A.; Shvetsova, V.; Minkin, A.; Potapova, V.; Smirnov, V.

    2016-11-01

    The radiation swelling effect on the fracture properties of irradiated austenitic steels under static loading has been studied and analyzed from the mechanical and physical viewpoints. Experimental data on the stress-strain curves, fracture strain, fracture toughness and fracture mechanisms have been represented for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various swelling. Some phenomena in mechanical behaviour of irradiated austenitic steels have been revealed and explained as follows: a sharp decrease of fracture toughness with swelling growth; untypical large increase of fracture toughness with decrease of the test temperature; some increase of fracture toughness after preliminary cyclic loading. Role of channel deformation and channel fracture has been clarified in the properties of irradiated austenitic steel and different tendencies to channel deformation have been shown and explained for the same austenitic steel irradiated at different temperatures and neutron doses.

  18. Fracture Mechanisms in Iron and Nickel Aluminides

    DTIC Science & Technology

    1988-08-15

    ITmc rE co"i 41 ) 0) Final Report I Contract N00014-84-K-0276 FRACTURE MECHANISMS IN IRON AND NICKEL ALUMINIDES covering the period 1/3/84 - 31/5/88...THIS PAGE ABSTRACT -he high cycle fatigue ( HCF ) resistance of several boron-doped Ni3AI alloys has been determined over a range of test temperatures...were transgranular in the Ni-rich alloys and intergranular or interdendritic in Ni-26%A).. HCF lives decreased sharply at temperatures above 500dC

  19. Analogy between fluid cavitation and fracture mechanics

    NASA Technical Reports Server (NTRS)

    Hendricks, R. C.; Mullen, R. L.; Braun, M. J.

    1983-01-01

    When the stresses imposed on a fluid are sufficiently large, rupture or cavitation can occur. Such conditions can exist in many two-phase flow applications, such as the choked flows, which can occur in seals and bearings. Nonspherical bubbles with large aspect ratios have been observed in fluids under rapid acceleration and high shear fields. These bubbles are geometrically similar to fracture surface patterns (Griffith crack model) existing in solids. Analogies between crack growth in solid and fluid cavitation are proposed and supported by analysis and observation (photographs). Healing phenomena (void condensation), well accepted in fluid mechanics, have been observed in some polymers and hypothesized in solid mechanics. By drawing on the strengths of the theories of solid mechanics and cavitation, a more complete unified theory can be developed.

  20. Fracture mechanics parameters for small fatigue cracks

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1992-01-01

    This paper presents a review of some common small-crack test specimens, the underlying causes of the small-crack effect, and the fracture-mechanics parameters that have been used to correlate or predict their growth behavior. This review concentrates on continuum mechanics concepts and on the nonlinear behavior of small cracks. The paper reviews some stress-intensity factor solutions for small-crack test specimens and develops some simple elastic-plastic J integral and cyclic J integral expressions that include the influence of crack-closure. These parameters were applied to small-crack growth data on two aluminum alloys, and a fatigue life prediction methodology is demonstrated. For these materials, the crack-closure transient from the plastic wake was found to be the major factor in causing the small-crack effect.

  1. Mechanics of fracture - Fundamentals and some recent developments

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Subramonian, N.; Lee, J. D.

    1979-01-01

    An overview is presented of the fundamental aspects of and recent developments in fracture mechanics. Reference is made to linear elastic fracture mechanics including the state of stresses and displacements in the vicinity of cracks, effects of crack geometry and orientation on stress intensity factors, energy balance of Griffith, Irwin's stress intensity concept, and linear elastic fracture mechanics testing for fracture toughness. Other aspects of this paper include the non-linear behavior of materials and their influence on fracture mechanics parameters, consideration of viscoelasticity and plasticity, non-linear fracture toughness parameters as C.O.D., R-curve and J-integral, and a non-linear energy method, proposed by Liebowitz. Finite element methods applied to fracture mechanics problems are indicated. Also, consideration has been given to slow crack growth, dynamic effects on K(IC), Sih's criterion for fracture, Lee and Liebowitz's criterion relating crack growth with plastic energy, and applications of fracture mechanics to aircraft design. Suggestions are offered for future research efforts to be undertaken in fracture mechanics.

  2. Patterns and perspectives in applied fracture mechanics

    SciTech Connect

    Merkle, J.G.

    1994-12-31

    This lecture begins with a overview of applied fracture mechanics pertinent to safety of pressure vessels. It then progresses to a chronological panorama of experimental and analytical results. To be useful and dependable in safety analysis of real structures, new analysis developments must be physically realistic, which means that they must accurately describe physical cause and effect. Consequently, before mathematical modeling can begin, cause and effect must be established from experimental data. This can be difficult and time consuming, but worth the effort. Accordingly, the theme of this paper is that the search for patterns is constant and vital. This theme is illustrated by the development of small, single-specimen, fracture toughness testing techniques. It is also illustrated by the development, based on two different published large-strain, elastic-plastic, three-dimensional finite-element analyses, of a hypothesis concerning three-dimensional loss of constraint. When a generalization of Irwin`s thickness-normalized plastic-zone parameter, reaches a value close to 2{pi}, the through-thickness contraction strain at the apex of the near-tip logarithmic-spiral slip-line region becomes the dominant negative strain accommodating crack opening. Because slip lines passing from the midplane to the stress-free side surfaces do not have to curve, once these slip lines are established, stresses near the crack tip are only elevated by strain hardening and constraint becomes significantly relaxed. This hypothesis, based on published three-dimensional elastic-plastic analyses, provides a potentially valuable means for gaining additional insight into constraint effects on fracture toughness by considering the roles played by the plastic strains as well as the stresses that develop near a crack tip.

  3. Mechanisms for fast flow in unsaturated fractured rock

    SciTech Connect

    Tokunaga, Tetsu K.; Wan, Jiamin

    1998-03-01

    Although fractures in rock are well-recognized as pathways for fast percolation of water, the possibility that fast flow could occur along unsaturated fracture pathways is commonly not considered in vadose zone hydrology. In this study, two mechanisms for fast flow along unsaturated fractures were investigated, film flow and surface zone flow. The importance of fracture surface roughness was demonstrated through experiments conducted on ceramic blocks having simple surface topographies. Those experiments showed that film flow on fracture surfaces is largely due to flow along continuous surface channels which become water-filled at near-zero matric (capillary) potentials. The second mechanism, surface zone flow, is important when the permeability of the rock along fractures (fracture skin) is significantly greater than that of the bulk rock matrix. Surface zone fast flow was demonstrated through water imbibition (sorptivity) experiments. These mechanisms help explain observations of rapid solute transport in unsaturated subsurface environments.

  4. Mechanical stratigraphic controls on natural fracture spacing and penetration

    NASA Astrophysics Data System (ADS)

    McGinnis, Ronald N.; Ferrill, David A.; Morris, Alan P.; Smart, Kevin J.; Lehrmann, Daniel

    2017-02-01

    Fine-grained low permeability sedimentary rocks, such as shale and mudrock, have drawn attention as unconventional hydrocarbon reservoirs. Fracturing - both natural and induced - is extremely important for increasing permeability in otherwise low-permeability rock. We analyze natural extension fracture networks within a complete measured outcrop section of the Ernst Member of the Boquillas Formation in Big Bend National Park, west Texas. Results of bed-center, dip-parallel scanline surveys demonstrate nearly identical fracture strikes and slight variation in dip between mudrock, chalk, and limestone beds. Fracture spacing tends to increase proportional to bed thickness in limestone and chalk beds; however, dramatic differences in fracture spacing are observed in mudrock. A direct relationship is observed between fracture spacing/thickness ratio and rock competence. Vertical fracture penetrations measured from the middle of chalk and limestone beds generally extend to and often beyond bed boundaries into the vertically adjacent mudrock beds. In contrast, fractures in the mudrock beds rarely penetrate beyond the bed boundaries into the adjacent carbonate beds. Consequently, natural bed-perpendicular fracture connectivity through the mechanically layered sequence generally is poor. Fracture connectivity strongly influences permeability architecture, and fracture prediction should consider thin bed-scale control on fracture heights and the strong lithologic control on fracture spacing.

  5. [Bone fracture and the healing mechanisms. The mechanical stress for fracture healing in view of distraction osteogenesis].

    PubMed

    Yukata, Kiminori; Takahashi, Mitsuhiko; Yasui, Natsuo

    2009-05-01

    It is generally accepted that moderate mechanical stress influences the course of fracture healing. A flexible fixation of the fractured site can induce fracture callus formation, whereas an unstable fixation can lead to a nonunion. The relationship between mechanical stress and the process of bone regeneration or healing remains incompletely understood. Distraction osteogenesis is a surgical technique that, using appropriate mechanical tension-stress, does not break the callus but rather it stimulates and maintains osteogenesis. The common principles of distraction osteogenesis are osteotomy and slow progressive distraction by an external fixation device. Interest in bone regeneration associated with mechanical stress might lead to better understanding of the fracture healing process.

  6. Mechanics and fracture of hybrid material interface bond

    NASA Astrophysics Data System (ADS)

    Wang, Jialai

    Considering current and future applications of hybrid materials and structures in civil engineering, the strength and durability of interface bond between the conventional materials and composites are critical to development of such products. Conventional methods mostly used for analysis of isotropic materials may not be well suitable or accurate enough for a system made of anisotropic materials with relatively low shear stiffness. A need exists for developing more accurate and explicit analytical solutions for hybrid material interface analysis and related novel experimental characterization techniques. In this study, a combined analytical and experimental approach to characterize hybrid material interface bond is developed. Using a shear deformable plate theory and an elastic interface model, a mechanics approach for interface analysis of hybrid material bond under general loading is first proposed. The resulting closed-form solution of interface stress distribution is used to compute strain energy release rate (SERB) and stress intensity factor (SIF) of the interface with or without adhesive bond. This approach is then extended to delamination of composite structures under generic loading conditions. Second, novel experimental approaches for characterization of hybrid material bonded interfaces are presented. To account for the crack tip deformations, a tapered beam on elastic foundation (TBEF) is developed. Based on the TBEF model, analysis and design of two novel fracture specimens, Tapered Double Cantilever Beam (TDCB) and Tapered End Notched Flexure (TENF), are proposed, and they are effectively used in fracture toughness tests of bonded interface under Mode-I and Mode-II loadings, respectively. A constant compliance rate change over certain crack length range is achieved for the TDCB and TENF specimens, and it alleviates the necessity of experimental compliance calibration tests. The fracture toughness data obtained from the experiments are useful to

  7. Effects of pulp capping materials on fracture resistance of Class II composite restorations

    PubMed Central

    Kucukyilmaz, Ebru; Yasa, Bilal; Akcay, Merve; Savas, Selcuk; Kavrik, Fevzi

    2015-01-01

    Objective: The aim of this study was to investigate the effect of cavity design and the type of pulp capping materials on the fracture resistance of Class II composite restorations. Materials and Methods: Sixty freshly extracted, sound molar teeth were selected for the study. A dovetail cavity on the mesio-occlusal and a slot cavity on disto-occlusal surfaces of each tooth were prepared, and the teeth were divided 4 groups which one of them as a control group. The pulp capping materials (TheraCal LC, Calcimol LC, Dycal) applied on pulpo-axial wall of each cavity, and the restoration was completed with composite resin. The teeth were subjected to a compressive load in a universal mechanical testing machine. The surfaces of the tooth and restoration were examined under a stereomicroscope. The data were analyzed using factorial analysis of variance and Tukey's test. Results: For pulp capping materials, the highest fracture load (931.15 ± 203.81 N) and the lowest fracture load (832.28 ± 245.75 N) were calculated for Control and Dycal group, respectively. However, there were no statistically significant differences among all groups (P > 0.05). The fracture load of the dovetail groups was significantly higher than those of the slot cavity groups (P < 0.05). Conclusion: Dovetail cavity design shows better fracture resistance in Class II composite restorations, independent of used or not used pulp capping materials. PMID:26038653

  8. Elastic - Plastic Fracture Mechanics. A Critical Review. Part 1

    DTIC Science & Technology

    1990-04-01

    STATE UNIVERSITY OF NEW YORK MICS COMMITTEE MARITIME COLLE GE Dr. William Sandberg Dr. W. R. Porter AMERICAN IRON AND STEEL INSTITUTE WELDING RESEARCH... welded steel structures. Fundamental concepts and underlying assumptions are described. Standardized test methods and recent developments are reviewed...fracture mechanics, as applied to welded steel structures. First, the fundamental concepts and underlying assumptions of fracture mechanics are described

  9. Solution-adaptive finite element method in computational fracture mechanics

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Bass, J. M.; Spradley, L. W.

    1993-01-01

    Some recent results obtained using solution-adaptive finite element method in linear elastic two-dimensional fracture mechanics problems are presented. The focus is on the basic issue of adaptive finite element method for validating the applications of new methodology to fracture mechanics problems by computing demonstration problems and comparing the stress intensity factors to analytical results.

  10. Mixed-mode Mechanism of Hydraulic Fracture Segmentation

    NASA Astrophysics Data System (ADS)

    Hurt, R. S.; Germanovich, L.; Wu, R.

    2006-12-01

    Mixed-mode I+III loading is one of the primary causes of fracture front segmentation. Although such segmented fractures have been observed both in nature and laboratory, we are not aware of direct laboratory experiments on the mode III mechanism of segmentation of hydraulically induced fractures. In this work, we developed a laboratory technique and a theoretical model for studying not only the effect of mode III loading on the onset of hydraulic fracture segmentation, but also the effect of segmentation on the subsequent growth of hydraulic fractures. In quasi-brittle materials, even a small mode III component may cause fracture segmentation due to a tensile stress field induced near the fracture front [Rice, 1968]. Previously, this has been confirmed in experiments with non-hydraulic fractures [Knauss, 1970; Cooke and Pollard, 1996]. In one occasion, quasi-hydraulic fractures propagated in fast, uncontrollable manner [Sommer, 1969]. This is why, we focused on controlled hydraulic fractures with a rather small KIII/KI ratio (1-10 %). For mixed mode I+III experiments, we used transparent, cylindrical PMMA samples with circular internal fractures perpendicular to the sample axis. Fracture orientation was controlled by thermoelastic stresses induced in each sample by preheating it before creating a fracture. In order to apply mode III loading to the initial fracture, a constant torque was applied to the specimen while fluid was injected into the fracture at a constant rate to pressurize it and to induce mode I loading. The velocity of fracture propagation was constrained by controlling the rate of fluid injection. In spite of a small magnitude of the mode III component, we observed segmented fracture fronts in all tested samples. The segments had similar dimensions and shape elongated around the perimeter of the initial fracture. When the fractures were further pressurized by injecting additional fluid into the sample, second-order segments developed along the fronts

  11. Patient-reported outcome following nonsurgical management of type II odontoid process fractures in adults

    PubMed Central

    Fam, Maged D; Zeineddine, Hussein A; Nassir, Rafiq Muhammed; Bhatt, Pragnesh; Kamel, Mahmoud H

    2017-01-01

    Background: Transverse (type II) odontoid process fracture is among the most commonly encountered cervical spine fractures. Nonsurgical management through external immobilization is occasionally preferred to surgical management but is criticized for its higher rates of failure and lower patient satisfaction. Our aim is to analyze patient-reported outcomes in patients who underwent nonsurgical treatment for type II odontoid fractures. Methods: We identified patients >18-year-old who underwent external immobilization as a treatment for isolated type II odontoid fracture between 2007 and 2012. We collected demographic parameters, clinical presentation, mode of injury, imaging studies and modality and duration of treatment (soft collar, halo-vest, or both). Patients were contacted by telephone to participate in a 15-min survey addressing their recovery including their subjective rate of return to preinjury level of functioning. Results: Fifteen patients met the inclusion/exclusion criteria and participated in our survey. Patients were followed up for an average of 19 months after injury. Overall mean age was 61 years. Injury followed a mechanical fall or a road traffic accident in 11 and 4 cases, respectively. External immobilization was achieved by halo vest only in nine patients, soft collar only in two patients (13%), and through a sequential combination in the remaining 4 (27%). This was deployed for a mean of 7.8 months. Radiological studies at the last follow-up showed bony healing (27%), fibrous nonunion (60%), and persistent instability (13%). Patients reported gradual recovery of function throughout the 1st year after injury with levels above 70% of preinjury functioning achieved by 13% of patients at 6 months, 33% at 9 months, and 47% at 12 months. Overall satisfaction with nonsurgical management was 68%. Conclusion: In selected patients with type II odontoid fractures, external immobilization represents a good option with acceptable course of recovery. PMID

  12. Hinged external fixation for Regan-Morrey type I and II fractures and fracture-dislocations.

    PubMed

    Castelli, Alberto; D'amico, Salvatore; Combi, Alberto; Benazzo, Francesco

    2016-06-01

    Elbow fracture-dislocation is always demanding to manage due to the considerable soft-tissue swelling or damage involved, which can make an early open approach and ligamentous reconstruction impossible. The purpose of this study was to evaluate the role of elbow hinged external fixation (HEF) as a definitive treatment in patients with elbow dislocations associated with Regan-Morrey (R-M) type I and II coronoid fractures and soft-tissue damage. We treated 11 patients between 2010 and 2012 with HEF. Instability tests and standard X-ray examinations were performed before surgery and 1-3 to 3-6 months after surgery, respectively. All patients underwent a preoperative CT scan. Outcomes were assessed with a functional assessment scale (Mayo Elbow Performance Score, MEPS) that included 4 parameters: pain, ROM, stability, and function. The results were good or excellent in all 11 patients, and no patient complained of residual instability. Radiographic examination showed bone metaplasia involving the anterior and medial sides of the joint in 5 patients. HEF presented several advantages: it improves elbow stability and it avoids long and demanding surgery in particular in cases with large soft tissue damage. We therefore consider elbow HEF to be a viable option for treating R-M type I and II fracture-dislocations.

  13. Fracture Mechanics for Composites: State of the Art and Challenges

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald; Krueger, Ronald

    2006-01-01

    Interlaminar fracture mechanics has proven useful for characterizing the onset of delaminations in composites and has been used with limited success primarily to investigate onset in fracture toughness specimens and laboratory size coupon type specimens. Future acceptance of the methodology by industry and certification authorities however, requires the successful demonstration of the methodology on the structural level. In this paper, the state-of-the-art in fracture toughness characterization, and interlaminar fracture mechanics analysis tools are described. To demonstrate the application on the structural level, a panel was selected which is reinforced with stringers. Full implementation of interlaminar fracture mechanics in design however remains a challenge and requires a continuing development effort of codes to calculate energy release rates and advancements in delamination onset and growth criteria under mixed mode conditions.

  14. On the Role of Dimensionless Elastic Fracture Mechanics.

    DTIC Science & Technology

    1985-07-03

    INDIVIDUAL 22b. TELEPHONE NUMBER 122c. OFFICE SYMS L David A. Glasgow, MAJOR, ’"F ’NA, I DD FORM 1473,83 APR EDTION OF 1 𔃻IB OBSOLETE. unclassified I 5 11...fracture are available in the literature and address various aspects of its consequences, e.g. Goodier in Fracture, Vol. I. The aspect of concern here...various aspects of its consequences, e.g. Goodier in Fracture, Vol. II. The aspect of concern here is the size de- pendence implied by the approach

  15. Fracture Mechanisms of Layer-By-Layer Polyurethane/Poly(Acrylic Acid) Nanocomposite

    NASA Astrophysics Data System (ADS)

    Kheng, Eugene R.

    A layer-by-layer(LBL) manufactured material is examined in detail in this thesis. Improvements are made to the method of its manufacture. Efforts are made to understand its fracture mechanisms and take advantage of these fracture mechanisms in the absorption of impact energy. A novel series of experiments has been performed on LBL manufactured thin films to demonstrate their unique fracture mechanisms. Polyurethane/Poly(Acrylic Acid) (PU/PAA) and PU/PAA/(PU/Clay)5 nanocomposite films readily undergo Interlaminar mode II fracture, because of the relatively weak elctrostatic bonds between monolayers. Tensile tests performed while under observation by a scanning electron microscope demonstrate the tendency of these nanocomposite films to undergo interlaminar mode II fracture even when loads are applied in the plane of nanocomposite film. It is concluded that these mechanisms of energy dissipation are responsible for the enhanced toughness of these films when used as layers between glass blocks in the prevention of impact damage to the glass. A novel automated manufacturing facility has been designed and built to deposit large sheets of Layer-by-Layer nanocomposite film. These large sheets are incorporated into a borosillicate glass composite in order to compare the ballistic characteristics of LBL PU based nanocomposite films to a single cast layer of polyurethane. It is demonstrated that shear fracture is the mode of failure in the blocks containing the nanocomposite film. The shear fracture surface in the nanocomposite after it has undergone a ballistic impact is characterized. Additional experiments are performed to characterize the interlaminar fracture stresses and toughnesses of the nanocomposite LBL layers, to assist in the implementation of a numerical crack band model that describes the nanocomposite film. The computational model predicts the failure of the ballistic nanocomposite samples, and the predicted V50 velocity is found to be in good agreement with

  16. Adaptive Finite-Element Computation In Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Bass, J. M.; Spradley, L. W.

    1995-01-01

    Report discusses recent progress in use of solution-adaptive finite-element computational methods to solve two-dimensional problems in linear elastic fracture mechanics. Method also shown extensible to three-dimensional problems.

  17. A nonlinear high temperature fracture mechanics basis for strainrange partitioning

    NASA Technical Reports Server (NTRS)

    Kitamura, Takayuki; Halford, Gary R.

    1989-01-01

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

  18. Ship Fracture Mechanisms Investigation. Part 1

    DTIC Science & Technology

    1987-01-01

    the spar deck, but is belcw the nominal yield for mild steel of 32,000 psi. 3-13 Initiation Site Arrest Down- Toward Ship’s bottom Up- Toward Figure 3...hatch. The deck material in the vicinity of fracture was 46mm (1.81 inch)"EH33" normalized steel . Description of the Circumstances at the Time of...finally installing "CS" normalized steel doubler plate over the existing deck plate at the hatch corners. This repair fractured in the spring of 1976

  19. Multiscale rotational mechanism of fracture propagation in geomaterials

    NASA Astrophysics Data System (ADS)

    Dyskin, Arcady; Pasternak, Elena; Esin, Maxim

    2015-10-01

    We consider rotational mechanism of macrocrack propagation based on breakage of the bonds between mutually rotating grains. The mechanism is multiscale with the macroscopic scale corresponding to the macrocrack, the next, smaller scale corresponding to the grain rotations and the smallest scale corresponding to the microcracks formed in the bonds whose propagation causes the bond breakage. The bond breakage is initiated by their bending or twisting caused by the corresponding moments. The sign of the moments only affects the side of the bond where the microfracturing starts. The independence of the microfracturing of the sign of the moment stresses provides a unified way of describing such apparently different types of fractures as tensile (Mode I) cracks, compaction bands (Mode I anticracks) and shear bands (Mode II and III). Modelling of this mechanism is based on the Cosserat theory. The bending/twisting moments are controlled by the corresponding components of moment stress. In the cases, when the Cosserat characteristic lengths are comparable with the grain sizes, the Cosserat theory is reduced to the couple-stress theory. It is found that the stress exhibits the square root singularity that coincides with the conventional ones, while the moment stress has singularity of the power -3/2. The J-integral, however, reflects only stress singularities, while the moment stress singularities do not contribute to the energy release rate. Subsequently, the energy criterion of macrofracture propagation can be based on the conventional J-integral and is not affected by the strong moment stress singularity.

  20. Size effect law and fracture mechanics of the triggering of dry snow slab avalanches

    NASA Astrophysics Data System (ADS)

    Bažant, ZdeněK. P.; Zi, Goangseup; McClung, David

    2003-02-01

    A size effect law for fracture triggering in dry snow slabs of high enough length-to-thickness ratio is formulated, based on simplified one-dimensional analysis by equivalent linear elastic fracture mechanics. Viscoelastic effects during fracture are neglected. The derived law, which is analogous to Bažant's energetic size effect law developed for concrete and later for sea ice, fiber composites, rocks, and ceramics, is shown to agree with two-dimensional finite element analysis of mode II cohesive crack model with a finite residual shear stress. Fitting the proposed size effect law to fracture data for various slab thicknesses permits identifying the material fracture parameters. The value of preexisting shear stress in a thin weak zone of finite length is shown to have significant effect. There exists a certain critical snow depth, depending on the preexisting stress value, below which the size effect disappears. Practical applications require considering that the material properties (particularly the mode II fracture toughness or fracture energy) at the snow slab base are not constant but depend strongly on the slab thickness. This means that one must distinguish the material size effect from the structural size effect, and the combined size effect law must be obtained by introducing into the structural size effect law dependence of its parameters on snow thickness. The thickness dependence of these parameters can be obtained by matching the combined law to avalanche observations. Matching Perla's field data on 116 avalanches suggests that the mode II fracture toughness is approximately proportional to 1.8 power of snow thickness.

  1. In Vitro Fracture of Human Cortical Bone: Local Fracture Criteria and Toughening Mechanisms

    SciTech Connect

    Nalla, R; Stolken, J; Kinney, J; Ritchie, R

    2004-08-18

    A micro-mechanistic understanding of bone fracture that encompasses how cracks interact with the underlying microstructure and defines their local failure mode is lacking, despite extensive research on the response of bone to a variety of factors like aging, loading, and/or disease. Micro-mechanical models for fracture incorporating such local failure criteria have been widely developed for metallic and ceramic materials systems; however, few such deliberations have been undertaken for the fracture of bone. In fact, although the fracture event in mineralized tissues such as bone is commonly believed to be locally strain controlled, until recently there has been little experimental evidence to support this widely held belief. In the present study, a series of in vitro experiments involving a double-notch bend test geometry are performed in order to shed further light on the nature of the local cracking events that precede catastrophic fracture in bone and to define their relationship to the microstructure. Specifically, crack-microstructure interactions are examined to determine the salient toughening mechanisms in human cortical bone and to characterize how these may affect the anisotropy in fracture properties. Based on preliminary micro-mechanical models of these processes, in particular crack deflection and uncracked ligament bridging, the relative importance of these toughening mechanisms is established.

  2. Elastic-plastic fracture mechanics technology

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr. (Editor); Loss, F. J. (Editor)

    1985-01-01

    Among the topics discussed are: fracture analysis methods evaluation; instability prediction using the K sub R-curve approach; and the deformation failure assessment diagram. Consideration is also given to: instability prediction based on the modified J, J sub M-resistance curve approach; and stable crack growth and instability prediction on the V by means of the V sub R-curve method.

  3. Multiescalar studies of fracturing mechanisms in fluvial-lacustrine basins

    NASA Astrophysics Data System (ADS)

    Carreon-Freyre, D.; Cerca, M.; Hidalgo, C.; Hernandez-Marin, M.

    2007-05-01

    Fracturing of clayey fluvial and lacustrine deposits has become a major problem in several cities of central Mexico. The available data reveals the coexistence of several factors determining fracturing at different scales. As main factors we analyze the variation in compressibility of sediments causing differential deformation and withdrawal of groundwater causing a drop in pore pressure. Compressibility depends on consolidation, a term that in soil mechanics refers to the expulsion of interstitial water, and provokes volume decrease and land subsidence. Although major volume decrease occurs in the vertical scale, consolidation of silty clayey materials generates also horizontal tensile stresses. Considering that this factor can be determining to the generation of fractures, the deformational conditions of clayey, silty and sandy sequences is analyzed integrating their stratigraphy and mechanical characteristics. A particular emphasis is made in the mineralogical heterogeneity of the clay fraction that can be related to compressibility variations and can generate micro-fracturing by differential deformation. As study case we analyze the mechanical and geological properties of two sedimentary sequences with contrasting hydraulic and mechanical behavior. Our results show that the paleoenvironmental history of sediments can be used to determine a specific type of fracturing. Thus, the fracturing in fluvial lacustrine deposits is not a random phenomenon but is highly dependent of the geological properties of materials.

  4. Electron radiation effects on Mode II interlaminar fracture toughness of GFRP and CFRP composites

    SciTech Connect

    Takeda, N.; Tohdoh, M.; Takahashi, K.

    1989-01-01

    The degradation properties of epoxy-based fiber-reinforced-plastics (FRP) composites irradiated by high-energy electrons were studied using the Mode II interlaminar fracture toughness G/sub IIc/, measured by end-notched flexure tests. The radiation-induced degradation mechanisms were investigated through G/sub IIc/ and the scanning electron micrographs of fracture surfaces. For GFRP, the significant decrease in G/sub IIc/ was found. Debonding of glass fibers and epoxy matrix (or degradation of silane coupling agents) plays an important role in degradation in addition to resin degradation. Thus, the improvement of the radiation resistance of fiber-resin interfaces as well as matrix itself is of supreme importance in order to increase the radiation resistance of GFRP. For CFRP, on the other hand, no degradation in fiber-resin interfaces was found and the slight decrease in G/sub IIc/ seems to be due to the resin degradation. 18 references, 6 figures.

  5. Advances in the fracture mechanics of cortical bone.

    PubMed

    Bonfield, W

    1987-01-01

    As cortical bone is a semi-brittle solid, its fracture is dependent not only on the magnitude of the applied stress, but also on the nature of any intrinsic or introduced cracks. Consequently a variety of fracture mechanics techniques have been utilised to evaluate the fracture toughness of cortical bone, including the single edge notched, centre notched cylindrical and compact tension methods, and values have been established for the critical stress intensity factor (Kc) and the critical strain energy release rate (Gc). The Kc and Gc values obtained depend on the orientation of the cortical bone, as well as on bone density, the velocity of crack propagation and specimen geometry. The significance of these fracture mechanics parameters for cortical bone is critically reviewed.

  6. Fracture prediction for the proximal femur using finite element models: Part II--Nonlinear analysis.

    PubMed

    Lotz, J C; Cheal, E J; Hayes, W C

    1991-11-01

    In Part I we reported the results of linear finite element models of the proximal femur generated using geometric and constitutive data collected with quantitative computed tomography. These models demonstrated excellent agreement with in vitro studies when used to predict ultimate failure loads. In Part II, we report our extension of those finite element models to include nonlinear behavior of the trabecular and cortical bone. A highly nonlinear material law, originally designed for representing concrete, was used for trabecular bone, while a bilinear material law was used for cortical bone. We found excellent agreement between the model predictions and in vitro fracture data for both the onset of bone yielding and bone fracture. For bone yielding, the model predictions were within 2 percent for a load which simulated one-legged stance and 1 percent for a load which simulated a fall. For bone fracture, the model predictions were within 1 percent and 17 percent, respectively. The models also demonstrated different fracture mechanisms for the two different loading configurations. For one-legged stance, failure within the primary compressive trabeculae at the subcapital region occurred first, leading to load transfer and, ultimately, failure of the surrounding cortical shell. However, for a fall, failure of the cortical and trabecular bone occurred simultaneously within the intertrochanteric region. These results support our previous findings that the strength of the subcapital region is primarily due to trabecular bone whereas the strength of the intertrochanteric region is primarily due to cortical bone.

  7. Interaction of hydraulic and buckling mechanisms in blowout fractures.

    PubMed

    Nagasao, Tomohisa; Miyamoto, Junpei; Jiang, Hua; Tamaki, Tamotsu; Kaneko, Tsuyoshi

    2010-04-01

    The etiology of blowout fractures is generally attributed to 2 mechanisms--increase in the pressure of the orbital contents (the hydraulic mechanism) and direct transmission of impacts on the orbital walls (the buckling mechanism). The present study aims to elucidate whether or not an interaction exists between these 2 mechanisms. We performed a simulation experiment using 10 Computer-Aided-Design skull models. We applied destructive energy to the orbits of the 10 models in 3 different ways. First, to simulate pure hydraulic mechanism, energy was applied solely on the internal walls of the orbit. Second, to simulate pure buckling mechanism, energy was applied solely on the inferior rim of the orbit. Third, to simulate the combined effect of the hydraulic and buckling mechanisms, energy was applied both on the internal wall of the orbit and inferior rim of the orbit. After applying the energy, we calculated the areas of the regions where fracture occurred in the models. Thereafter, we compared the areas among the 3 energy application patterns. When the hydraulic and buckling mechanisms work simultaneously, fracture occurs on wider areas of the orbital walls than when each of these mechanisms works separately. The hydraulic and buckling mechanisms interact, enhancing each other's effect. This information should be taken into consideration when we examine patients in whom blowout fracture is suspected.

  8. Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs

    PubMed Central

    Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

    2015-01-01

    Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing. PMID:25966285

  9. Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs.

    PubMed

    Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

    2015-01-01

    Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing.

  10. Fixation of unstable type II clavicle fractures with distal clavicle plate and suture button.

    PubMed

    Johnston, Peter S; Sears, Benjamin W; Lazarus, Mark R; Frieman, Barbara G

    2014-11-01

    This article reports on a technique to treat unstable type II distal clavicle fractures using fracture-specific plates and coracoclavicular augmentation with a suture button. Six patients with clinically unstable type II distal clavicle fractures underwent treatment using the above technique. All fractures demonstrated radiographic union at 9.6 (8.4-11.6) weeks with a mean follow-up of 15.6 (12.4-22.3) months. American Shoulder and Elbow Surgeons, Penn Shoulder Score, and Single Assessment Numeric Evaluation scores were 97.97 (98.33-100), 96.4 (91-99), and 95 (90-100), respectively. One patient required implant removal. Fracture-specific plating with suture-button augmentation for type II distal clavicle fractures provides reliable rates of union without absolute requirement for implant removal.

  11. Toughness of carbon nanotubes conforms to classic fracture mechanics.

    PubMed

    Yang, Lin; Greenfeld, Israel; Wagner, H Daniel

    2016-02-01

    Defects in crystalline structure are commonly believed to degrade the ideal strength of carbon nanotubes. However, the fracture mechanisms induced by such defects, as well as the validity of solid mechanics theories at the nanoscale, are still under debate. We show that the fracture toughness of single-walled nanotubes (SWNTs) conforms to the classic theory of fracture mechanics, even for the smallest possible vacancy defect (~2 Å). By simulating tension of SWNTs containing common types of defects, we demonstrate how stress concentration at the defect boundary leads to brittle (unstable) fracturing at a relatively low strain, degrading the ideal strength of SWNTs by up to 60%. We find that, owing to the SWNT's truss-like structure, defects at this scale are not sharp and stress concentrations are finite and low. Moreover, stress concentration, a geometric property at the macroscale, is interrelated with the SWNT fracture toughness, a material property. The resulting SWNT fracture toughness is 2.7 MPa m(0.5), typical of moderately brittle materials and applicable also to graphene.

  12. Toughness of carbon nanotubes conforms to classic fracture mechanics

    PubMed Central

    Yang, Lin; Greenfeld, Israel; Wagner, H. Daniel

    2016-01-01

    Defects in crystalline structure are commonly believed to degrade the ideal strength of carbon nanotubes. However, the fracture mechanisms induced by such defects, as well as the validity of solid mechanics theories at the nanoscale, are still under debate. We show that the fracture toughness of single-walled nanotubes (SWNTs) conforms to the classic theory of fracture mechanics, even for the smallest possible vacancy defect (~2 Å). By simulating tension of SWNTs containing common types of defects, we demonstrate how stress concentration at the defect boundary leads to brittle (unstable) fracturing at a relatively low strain, degrading the ideal strength of SWNTs by up to 60%. We find that, owing to the SWNT’s truss-like structure, defects at this scale are not sharp and stress concentrations are finite and low. Moreover, stress concentration, a geometric property at the macroscale, is interrelated with the SWNT fracture toughness, a material property. The resulting SWNT fracture toughness is 2.7 MPa m0.5, typical of moderately brittle materials and applicable also to graphene. PMID:26989774

  13. RSRM nozzle actuator bracket/lug fracture mechanics qualification test

    NASA Technical Reports Server (NTRS)

    Kelley, Peggy

    1993-01-01

    This is the final report for the actuator bracket/lug fracture mechanics qualification test. The test plan (CTP-0071) outlined a two-phase test program designed to answer questions about the fracture criticality of the redesigned solid rocket motor (RSRM) nozzle actuator bracket. An analysis conducted using the NASA/FLAGRO fracture mechanics computer program indicated that the actuator bracket might be a fracture critical component. In the NASA/FLAGRO analysis, a simple lug model was used to represent the actuator bracket. It was calculated that the bracket would fracture if subjected to an actuator stall load in the presence of a 0.10 in. corner crack at the actuator attachment hole. The 0.10 in. crack size corresponds to the nondestructive inspection detectability limit for the actuator bracket. The inspection method used is the dye penetrant method. The actuator stall load (103,424 lb) is the maximum load which the actuator bracket is required to withstand during motor operation. This testing was designed to establish the accuracy of the analytical model and to directly determine whether the actuator bracket is capable of meeting fracture mechanics safe-life requirements.

  14. Fracture mechanics life analytical methods verification testing

    NASA Technical Reports Server (NTRS)

    Favenesi, J. A.; Clemons, T. G.; Riddell, W. T.; Ingraffea, A. R.; Wawrzynek, P. A.

    1994-01-01

    The objective was to evaluate NASCRAC (trademark) version 2.0, a second generation fracture analysis code, for verification and validity. NASCRAC was evaluated using a combination of comparisons to the literature, closed-form solutions, numerical analyses, and tests. Several limitations and minor errors were detected. Additionally, a number of major flaws were discovered. These major flaws were generally due to application of a specific method or theory, not due to programming logic. Results are presented for the following program capabilities: K versus a, J versus a, crack opening area, life calculation due to fatigue crack growth, tolerable crack size, proof test logic, tearing instability, creep crack growth, crack transitioning, crack retardation due to overloads, and elastic-plastic stress redistribution. It is concluded that the code is an acceptable fracture tool for K solutions of simplified geometries, for a limited number of J and crack opening area solutions, and for fatigue crack propagation with the Paris equation and constant amplitude loads when the Paris equation is applicable.

  15. Relating Cohesive Zone Model to Linear Elastic Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Wang, John T.

    2010-01-01

    The conditions required for a cohesive zone model (CZM) to predict a failure load of a cracked structure similar to that obtained by a linear elastic fracture mechanics (LEFM) analysis are investigated in this paper. This study clarifies why many different phenomenological cohesive laws can produce similar fracture predictions. Analytical results for five cohesive zone models are obtained, using five different cohesive laws that have the same cohesive work rate (CWR-area under the traction-separation curve) but different maximum tractions. The effect of the maximum traction on the predicted cohesive zone length and the remote applied load at fracture is presented. Similar to the small scale yielding condition for an LEFM analysis to be valid. the cohesive zone length also needs to be much smaller than the crack length. This is a necessary condition for a CZM to obtain a fracture prediction equivalent to an LEFM result.

  16. Fracture mechanics criteria for turbine engine hot section components

    NASA Technical Reports Server (NTRS)

    Meyers, G. J.

    1982-01-01

    The application of several fracture mechanics data correlation parameters to predicting the crack propagation life of turbine engine hot section components was evaluated. An engine survey was conducted to determine the locations where conventional fracture mechanics approaches may not be adequate to characterize cracking behavior. Both linear and nonlinear fracture mechanics analyses of a cracked annular combustor liner configuration were performed. Isothermal and variable temperature crack propagation tests were performed on Hastelloy X combustor liner material. The crack growth data was reduced using the stress intensity factor, the strain intensity factor, the J integral, crack opening displacement, and Tomkins' model. The parameter which showed the most effectiveness in correlation high temperature and variable temperature Hastelloy X crack growth data was crack opening displacement.

  17. Fracture mechanics analysis of a high-pressure hydrogen facility compressor

    NASA Technical Reports Server (NTRS)

    Vroman, G. A.

    1974-01-01

    The investigation and analysis of a high-pressure hydrogen facility compressor is chronicled, and a life prediction based on fracture mechanics is presented. Crack growth rates in SA 105 Gr II steel are developed for the condition of sustained loading, using a hypothesis of hydrogen embrittlement associated with plastic zone reverse yielding. The resultant formula is compared with test data obtained from laboratory specimens.

  18. In-plane response and mode II fracture response of Z-pin woven laminates

    NASA Astrophysics Data System (ADS)

    Huang, Hseng-Ji

    Textile composites are proven to be an attractive choice over traditional pre-preg based composites because of reduced manufacturing costs and improved transverse mechanical properties. However, similar to traditional pre-preg composites, 2D laminates consisting of multiple layers of laminae still suffer from delamination under impact or transverse loads. Z-pin (carbon fiber of small diameter inserted in the thickness direction-z) composites are a means to provide higher through-thethickness stiffness and strength that 2D woven composites lack. In this thesis, The influences of Z-pin density and Z-pin diameter on the response of Z-pin under in-plane loads (compression) and transverse loads (mode II fracture) are examined. Both experiments and numerical simulations were performed to address the problems. Compression tests were conducted first and failure mechanism in each loading scenario was identified, through optical and mechanical measurements, during and after the tests. This was followed by the development of different numerical models of varying degree of sophistication, which include in-plane 2D models, (used to study fiber distortion and damage due to Z-pin insertion), multi-layer 2D models, (used to provide an inexpensive multi-layer model to study the effect of phase difference due to stacking consolidation), and multi-layer-multi-cell models (used to provide a full 3D multi-layer and multi-representative unit cell description). The second part of this thesis investigates the mode II fracture response under static and dynamic loading. Discrete Cohesive Zone Model (DCZM) was adopted to obtain the fracture toughness in conjunction with experimental data. In dynamic test, a crack advance gage (CAG) was designed to capture the exact time when the crack begins to propagate. By use of these CAGs, the corresponding crack propagation speed between different CAGs can be computed accordingly. These observations are supplemented through high speed optical images

  19. Equine cortical bone exhibits rising R-curve fracture mechanics.

    PubMed

    Malik, C L; Stover, S M; Martin, R B; Gibeling, J C

    2003-02-01

    Previous studies of the fracture properties of cortical bone have suggested that the fracture toughness increases with crack length, which is indicative of rising R-curve behavior. Based on this indirect evidence and the similarity of bone to ceramic matrix composites, we hypothesized that bone would exhibit rising R-curve behavior in the transverse orientation and that the characteristics of the R-curves would be regionally dependent within the cortex due to variations in bone microstructure and toughening mechanisms. To test these hypotheses, we conducted R-curve experiments on specimens from equine third metacarpal bones using standard fracture mechanics testing methods. Compact type specimens from the dorsal and lateral regions in the middle of the diaphysis were oriented for crack propagation transverse to the longitudinal axis of the bone. The test results demonstrate that equine cortical bone exhibits rising R-curve behavior during transverse crack propagation as hypothesized. Statistical analyses of the crack growth initiation toughness, K0, the peak toughness, Kpeak, and the crack extension at peak toughness, deltaa, revealed significant regional differences in these characteristics. Specifically, the lateral cortex displayed higher crack growth initiation and peak toughnesses. The dorsal cortex exhibited greater crack extension at the peak of crack growth resistance. Scanning electron microscopy revealed osteon pullout on fracture surfaces from the dorsal cortex and but not in the lateral cortex. Taken together, the significant differences in R-curves and the SEM fractography indicate that the fracture mechanisms acting in equine cortical bone are regionally dependent.

  20. Fracture mechanics evaluation for at typical PWR primary coolant pipe

    SciTech Connect

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

    1997-04-01

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

  1. Measurements of residual stress in fracture mechanics coupons

    SciTech Connect

    Prime, Michael B; Hill, Michael R; Nav Dalen, John E

    2010-01-01

    This paper describes measurements of residual stress in coupons used for fracture mechanics testing. The primary objective of the measurements is to quantify the distribution of residual stress acting to open (and/or close) the crack across the crack plane. The slitting method and the contour method are two destructive residual stress measurement methods particularly capable of addressing that objective, and these were applied to measure residual stress in a set of identically prepared compact tension (C(T)) coupons. Comparison of the results of the two measurement methods provides some useful observations. Results from fracture mechanics tests of residual stress bearing coupons and fracture analysis, based on linear superposition of applied and residual stresses, show consistent behavior of coupons having various levels of residual stress.

  2. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

    Clougherty, E. V.; Pober, R. L.; Kaufman, L.

    1972-01-01

    Significant results were obtained in fabrication studies of the role of metallic additives of Zr, Ti, Ni, Fe and Cr on the densification of ZrB2. All elemental additions lower the processing temperatures required to effect full densification of ZrB2. Each addition effects enhanced densification by a clearly distinguishable and different mechanism and the resulting fabricated materials are different. A significant improvement in strength and fracture toughness was obtained for the ZrB2/Ti composition. Mechanical characterization studies for the ZrB2/SiC/C composites and the new ZrB2/Metal materials produced data relevant to the effect of impacting load on measured impact energies, a specimen configuration for which controlled fracture could occur in a suitably hard testing apparatus, and fracture strength data. Controlled fracture--indicative of measurable fracture toughness--was obtained for the ZrB2-SiC-C composite, and a ZrB2/Ti composite fabricated from ZrB2 with an addition of 30 weight per cent Ti. The increased strength and toughness of the ZrB2/Ti composite is consistent with the presence of a significantly large amount of a fine grained acicular phase formed by reaction of Ti with ZrB2 during processing.

  3. Probabilistic fracture mechanics and optimum fracture control of the solid rocket motor case of the shuttle

    NASA Technical Reports Server (NTRS)

    Hanagud, S.; Uppaluri, B.

    1977-01-01

    Development of a procedure for the reliability analysis of the solid rocket motor case of the space shuttle is described. The analysis is based on probabilistic fracture mechanics and consideration of a probability distribution for the initial flaw sizes. The reliability analysis can be used to select design variables, such as the thickness of the SRM case, projected design life and proof factor, on the basis of minimum expected cost and specified reliability bounds. Effects of fracture control plans such as the non-destructive inspections and the material erosion between missions can also be considered in the developed methodology for selection of design variables. The reliability-based procedure can be easily modified to consider other similar structures and different fracture control plans.

  4. Fracture mechanics applied to the machining of brittle materials

    SciTech Connect

    Hiatt, G.D.; Strenkowski, J.S.

    1988-12-01

    Research has begun on incorporating fracture mechanics into a model of the orthogonal cutting of brittle materials. Residual stresses are calculated for the machined material by a combination of Eulerian and Lagrangian finite element models and then used in the calculation of stress intensity factors by the Green`s Function Method.

  5. The fracture properties and toughening mechanisms of bone and dentin

    NASA Astrophysics Data System (ADS)

    Koester, Kurt John

    The mechanical properties of bone and dentin and in particular their fracture properties, are the subject of intense research. The relevance of these properties is increasing as our population ages and fracture incidence impacts the lives of a greater portion of the population. A robust framework is needed to understand the fracture properties of bone and dentin to guide researchers as they attempt to characterize the effects of aging, disease, and pharmaceutical treatments on the properties of these mineralized tissues. In the present work, this framework is provided and applied to human bone, human dentin, and animal bone. In situ electron microscopy was also used to identify the salient toughening mechanisms in bone and dentin. It was found that bone and dentin are extrinsically toughened materials and consequently their fracture properties are best characterized utilizing a crack-growth resistance approach. A description of the different mechanical measurements commonly employed when using small animal models (rats and mice) to evaluate the influence of drug therapies on bone fragility is provided. A study where these properties were measured for a large population of wild-type rats and mice was also conducted. Given my findings, it was determined that for the most complete understanding of small animal bone it was necessary to measure strength and toughness. Strength measurements probe the flaw distribution and toughness measurements to evaluate the resistance to facture in the presence of a single dominant worst-case flaw.

  6. Hydraulic Fracture Extending into Network in Shale: Reviewing Influence Factors and Their Mechanism

    PubMed Central

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design. PMID:25032240

  7. Hydraulic fracture extending into network in shale: reviewing influence factors and their mechanism.

    PubMed

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design.

  8. Fracture mechanics analysis of composite microcracking - Experimental results in fatigue

    NASA Technical Reports Server (NTRS)

    Nairn, J. A.; Liu, S.

    1990-01-01

    The Nairn (1989) variational mechanics analysis, which yields the energy release rate of a microcrack's formation between two existing microcracks, has proven useful in the fracture mechanics interpretation of cross-ply laminates' microcracking. Attention is presently given to the application of this energy release rate analysis to a fracture mechanics-based interpretation of microcrack formation during fatigue loading, for the case of fatigue experiments on three layups of Avimid K/IM6 laminates and four layups of Fiberite 934/T300 laminates. The single master Paris-law plot onto which the data from all layups of a given material system fall is claimed to offer a complete characterization of that system's microcrack-formation resistance during fatigue loading.

  9. Fracture control methods for space vehicles. Volume 2: Assessment of fracture mechanics technology for space shuttle applications

    NASA Technical Reports Server (NTRS)

    Ehret, R. M.

    1974-01-01

    The concepts explored in a state of the art review of those engineering fracture mechanics considered most applicable to the space shuttle vehicle include fracture toughness, precritical flaw growth, failure mechanisms, inspection methods (including proof test logic), and crack growth predictive analysis techniques.

  10. Deformation and fracture of Macadamia nuts Part 2: Microstructure and fracture mechanics analysis of nutshell

    NASA Astrophysics Data System (ADS)

    Wang, Chun-Hui; Mai, Yiu-Wing

    A study of the microstructure and mechanical properties of Macadamia nutshells subjected to various heat treatments is given in Part 2 of this paper. It is found that the nutshell has a three-dimensional, close-packed, cell structure. The cells have a diameter to length ratio of about 1 to 3, and the orientation of the cells is reasonably isotropic with no apparent variation with either position or direction. The material behaves in a very brittle manner under tension and compression. Based on the elastic stress analysis of a nut under diametrical compression and the mechanical properties of the shell, it is shown that cracks that cause the final fracture are initiated from the inner surface beneath the loading point. A theoretical model is proposed and predictions of the fracture load for Macadamia nuts are in good agreement with experimental results.

  11. Elastic plastic fracture mechanics methodology for surface cracks

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A.; Lambert, D. M.

    1994-01-01

    The Elastic Plastic Fracture Mechanics Methodology has evolved significantly in the last several years. Nevertheless, some of these concepts need to be extended further before the whole methodology can be safely applied to structural parts. Specifically, there is a need to include the effect of constraint in the characterization of material resistance to crack growth and also to extend these methods to the case of 3D defects. As a consequence, this project was started as a 36 month research program with the general objective of developing an elastic plastic fracture mechanics methodology to assess the structural reliability of pressure vessels and other parts of interest to NASA which may contain flaws. The project is divided into three tasks that deal with (1) constraint and thickness effects, (2) three-dimensional cracks, and (3) the Leak-Before-Burst (LBB) criterion. This report period (March 1994 to August 1994) is a continuation of attempts to characterize three dimensional aspects of fracture present in 'two dimensional' or planar configuration specimens (Chapter Two), especially, the determination of, and use of, crack face separation data. Also, included, are a variety of fracture resistance testing results (J(m)R-curve format) and a discussion regarding two materials of NASA interest (6061-T651 Aluminum alloy and 1N718-STA1 nickel-base super alloy) involving a bases for like constraint in terms of ligament dimensions, and their comparison to the resulting J(m)R-curves (Chapter Two).

  12. Physeal fractures of the distal tibia and fibula (Salter-Harris Type I, II, III, and IV fractures).

    PubMed

    Podeszwa, David A; Mubarak, Scott J

    2012-06-01

    Physeal fractures of the distal tibia and fibula are common and can be seen at any age, although most are seen in the adolescent. An understanding of the unique anatomy of the skeletally immature ankle in relation to the mechanism of injury will help one understand the injury patterns seen in this population. A thorough clinical exam is critical to the diagnosis and treatment of these injuries and the avoidance of potentially catastrophic complications. Nondisplaced physeal fractures of the distal tibia and fibula can be safely treated nonoperatively. Displaced fractures should undergo a gentle reduction with appropriate anesthesia while multiple reduction attempts should be avoided. Gapping of the physis >3 mm after reduction should raise the suspicion of entrapped periosteum that will increase the risk of premature physeal closure. Open reduction of displaced Salter-Harris type III and IV fractures is critical to maintain joint congruity and minimize the risk of physeal arrest.

  13. [Bone fracture and the healing mechanisms. Pathophysiology and classification of osteoporotic fractures].

    PubMed

    Kishimoto, Hideaki

    2009-05-01

    Bone provides momentary strength and fatigue strength, and bone strength decreases with age. In elderly men and women with fragile bones osteoporotic fractures frequently occur. Fragility fracture occurs as a consequence of the decrease in momentary strength, and fragility fracture is one of the pathological fractures. In patients with the decrease in fatigue strength, insufficiency fractures frequently occurs. Insufficiency fracture is the same term as stress or fatigue fracture.

  14. Mechanical Stability and Reversible Fracture of Vault Particles

    PubMed Central

    Llauró, Aida; Guerra, Pablo; Irigoyen, Nerea; Rodríguez, José F.; Verdaguer, Núria; de Pablo, Pedro J.

    2014-01-01

    Vaults are the largest ribonucleoprotein particles found in eukaryotic cells, with an unclear cellular function and promising applications as vehicles for drug delivery. In this article, we examine the local stiffness of individual vaults and probe their structural stability with atomic force microscopy under physiological conditions. Our data show that the barrel, the central part of the vault, governs both the stiffness and mechanical strength of these particles. In addition, we induce single-protein fractures in the barrel shell and monitor their temporal evolution. Our high-resolution atomic force microscopy topographies show that these fractures occur along the contacts between two major vault proteins and disappear over time. This unprecedented systematic self-healing mechanism, which enables these particles to reversibly adapt to certain geometric constraints, might help vaults safely pass through the nuclear pore complex and potentiate their role as self-reparable nanocontainers. PMID:24507609

  15. RNA polymerase II transcription: structure and mechanism.

    PubMed

    Liu, Xin; Bushnell, David A; Kornberg, Roger D

    2013-01-01

    A minimal RNA polymerase II (pol II) transcription system comprises the polymerase and five general transcription factors (GTFs) TFIIB, -D, -E, -F, and -H. The addition of Mediator enables a response to regulatory factors. The GTFs are required for promoter recognition and the initiation of transcription. Following initiation, pol II alone is capable of RNA transcript elongation and of proofreading. Structural studies reviewed here reveal roles of GTFs in the initiation process and shed light on the transcription elongation mechanism. This article is part of a Special Issue entitled: RNA Polymerase II Transcript Elongation.

  16. Stress Fracture Etiology as Dependent on Mechanically Induced Fluid Flow

    DTIC Science & Technology

    2004-08-01

    Martin, M . B. Schaffler, and C. H . Turner. Bone microdamage and skeletal fragility in osteoporotic and stress fractures. J.Bone Miner.Res. 12:6...ulnae (Adams et al., 1995). Endosteal and periosteal were labeled weekly using tetracycline solution (15 ing- new bone formation, as well as...Transport mechanism operating Huiskes, R.. Weinans, H ., Grootenboer, H.J., Dalstra, M ., Fudala. B., between blood supply and osteocytes in long bones

  17. Micro and Macro Mechanics of Fracture in Ceramics.

    DTIC Science & Technology

    1982-10-30

    originates from resistant second phase particles in the path of a propagating crack. The crack tends to bow between the particles, causing the stress...increases until the fracture toughness of the particle is reached, whereupon crack advance ensues. The penetrability (or resistance ) of the second phase... resistance interfaces. Crack deflection has been associated with improved mechanical properties; I-3 however, the specific quantitative relation between the

  18. Fracture and Stress Evolution on Europa: New Insights Into Fracture Interpretation and Ice Thickness Estimates Using Fracture Mechanics Analyses

    NASA Technical Reports Server (NTRS)

    Kattenhorn, Simon

    2004-01-01

    The work completed during the funding period has provided many important insights into fracturing behavior in Europa's ice shell. It has been determined that fracturing through time is likely to have been controlled by the effects of nonsynchronous rotation stresses and that as much as 720 deg of said rotation may have occurred during the visible geologic history. It has been determined that there are at least two distinct styles of strike-slip faulting and that their mutual evolutionary styles are likely to have been different, with one involving a significant dilational component during shear motion. It has been determined that secondary fracturing in perturbed stress fields adjacent to older structures such as faults is a prevalent process on Europa. It has been determined that cycloidal ridges are likely to experience shear stresses along the existing segment portions as they propagate, which affects propagation direction and ultimately induces tailcracking at the segment tip than then initiates a new cycle of cycloid segment growth. Finally, it has been established that mechanical methods (e.g., flexure analysis) can be used to determine the elastic thickness of the ice shell, which, although probably only several km thick, is likely to be spatially variable, being thinner under bands but thicker under ridged plains terrain.

  19. Results of fracture mechanics tests on PNC SUS 304 plate

    SciTech Connect

    Mills, W.J.; James, L.A.; Blackburn, L.D.

    1985-08-01

    PNC provided SUS 304 plate to be irradiated in FFTF at about 400/sup 0/C to a target fluence of 5 x 10/sup 21/ n/cm/sup 2/ (E > 0.1 MeV). The actual irradiation included two basically different exposure levels to assure that information would be available for the exposure of interest. After irradiation, tensile properties, fatigue-crack growth rates and J-integral fracture toughness response were determined. These same properties were also measured for the unirradiated material so radiation damage effects could be characterized. This report presents the results of this program. It is expected that these results would be applicable for detailed fracture analysis of reactor components. Recent advances in elastic-plastic fracture mechanics enable reasonably accurate predictions of failure conditions for flawed stainless steel components. Extensive research has focused on the development of J-integral-based engineering approach for assessing the load carrying capacity of low-strength, high-toughness structural materials. Furthermore, Kanninen, et al., have demonstrated that J-integral concepts can accurately predict the fracture response for full-scale cracked structures manufactured from Type 304 stainless steel.

  20. Wide-range displacement expressions for standard fracture mechanics specimens

    NASA Technical Reports Server (NTRS)

    Kapp, J. A.; Gross, B.; Leger, G. S.

    1985-01-01

    Wide-range algebraic expressions for the displacement of cracked fracture mechanics specimens are developed. For each specimen two equations are given: one for the displacement as a function of crack length, the other for crack length as a function of displacement. All the specimens that appear in ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399) are represented in addition to the crack mouth displacement for a pure bending specimen. For the compact tension sample and the disk-shaped compact tension sample, the displacement at the crack mouth and at the load line are both considered. Only the crack mouth displacements for the arc-shaped tension samples are presented. The agreement between the displacements or crack lengths predicted by the various equations and the corresponding numerical data from which they were developed are nominally about 3 percent or better. These expressions should be useful in all types of fracture testing including fracture toughness, K-resistance, and fatigue crack growth.

  1. State-of-the-art report on piping fracture mechanics

    SciTech Connect

    Wilkowski, G.M.; Olson, R.J.; Scott, P.M.

    1998-01-01

    This report is an in-depth summary of the state-of-the-art in nuclear piping fracture mechanics. It represents the culmination of 20 years of work done primarily in the US, but also attempts to include important aspects from other international efforts. Although the focus of this work was for the nuclear industry, the technology is also applicable in many cases to fossil plants, petrochemical/refinery plants, and the oil and gas industry. In compiling this detailed summary report, all of the equations and details of the analysis procedure or experimental results are not necessarily included. Rather, the report describes the important aspects and limitations, tells the reader where he can go for further information, and more importantly, describes the accuracy of the models. Nevertheless, the report still contains over 150 equations and over 400 references. The main sections of this report describe: (1) the evolution of piping fracture mechanics history relative to the developments of the nuclear industry, (2) technical developments in stress analyses, material property aspects, and fracture mechanics analyses, (3) unresolved issues and technically evolving areas, and (4) a summary of conclusions of major developments to date.

  2. Elasto-plastic fracture mechanics of crack growth in soil

    NASA Astrophysics Data System (ADS)

    Hallett, P. D.; Newson, T. A.

    2003-04-01

    A predominant variable in soil structure formation and degradation is crack propagation. Empirical models exist to predict fracture but these do not describe the underlying physical processes. Theoretical fracture mechanics models have been applied to soil, but most are not applicable when soil is in a wet, plastic state. Since the onset of crack formation in soil tends to occur in this condition, physically sound elasto-plastic fracture mechanics approaches are long overdue. We address this weakness by applying a new elasto-plastic fracture mechanics approach to describe crack formation in plastic soil. Samples are fractured using a deep-notch (modified 4-point) bend test, with data on load transmission, sample bending, crack growth, and crack mouth opening collected to assess the crack opening angle (COA), the crack tip opening angle (CTOA) and the plastic energy dissipation rate (Dpl). These are all material properties that can be used directly to predict and describe crack propagation. CTOA will be used to discuss the results here, although a full description of the other parameters will be provided in the conference presentation. It provides a powerful parameter for describing soil cracking since CTOA is induced by soil shrinkage (an easily measured parameter) and can be used to describe elasto-plastic fracture in finite element modelling packages. The test variables we have studied to date are clay platelet orientation, soil texture, clay mineralogy, and pore water salinity. All samples were formed by consolidating a soil slurry with a 120 kPa vertical stress. Tests on pure kaolinite showed that platelet orientation did not affect CTOA which was 0.23 ± 0.02 for both conditions. Soil texture did have a marked influence, however, with silica sand:kaolinite mixes of 20:80 and 40:60 reducing CTOA to 0.14 ± 0.02 and 0.12 ± 0.01 respectively. These lower values of CTOA indicate that less strain is required to induce fracture when the amount of clay is lowered

  3. Mechanical Properties for Fracture Analysis of Mild Steel Storage Tasks

    SciTech Connect

    Sindelar, R.L.

    1999-03-03

    Mechanical properties of 1950's vintage, A285 Grade B carbon steels have been compiled for elastic-plastic fracture mechanics analysis of storage tanks (Lam and Sindelar, 1999). The properties are from standard Charpy V-notch (CVN), 0.4T planform Compact Tension (C(T)), and Tensile (T) specimens machined from archival steel from large water piping. The piping and storage tanks were constructed in the 1950s from semi-killed, hot-rolled carbon steel plate specified as A285 Grade B. Evaluation of potential aging mechanisms at both service conditions shows no loss in fracture resistance of the steel in either case.Site and literature data show that the A285, Grade B steel, at and above approximately 70 degrees Fahrenheit, is in the upper transition to upper shelf region for absorbed energy and is not subject to cleavage cracking or a brittle fracture mode. Furthermore, the tank sidewalls are 1/2 or 5/8-inch thick, and therefore, the J-resistance (JR) curve that characterizes material resistance to stable crack extension under elastic-plastic deformation best defines the material fracture toughness. The JR curves for several heats of A285, Grade B steel tested at 40 degrees Fahrenheit, a temperature near the average ductile-to-brittle (DBTT) transition temperature (CVN {at} 15 ft-lb), are presented. This data is applicable to evaluate flaw stability of the storage tanks that are operated above 70 degrees Fahrenheit since, even at 40 degrees Fahrenheit, crack advance is observed to proceed by ductile tearing.

  4. Physeal fractures, part II: fate of interposed periosteum in a physeal fracture.

    PubMed

    Gruber, Helen E; Phieffer, Laura S; Wattenbarger, J Michael

    2002-01-01

    This study describes the histologic features of periosteum interposed into a physeal fracture of the rat proximal tibia. Periosteum was introduced into a physeal fracture in two groups of animals: those with an intact physis after fracture, and those with the medial half of the physis surgically ablated. Specimens of the proximal tibia underwent histologic analysis at 2, 4, 6, 10, and 21 days after fracture to determine the histologic features of interposed periosteum in a physeal fracture. In animals with an intact physis, interposed periosteum underwent one of two fates: it was degraded by giant cells in the fracture plane, which allowed cellular infiltration, or if the periosteum was closely surrounded by physeal cartilage, the physis grew around it and appeared to force it toward the metaphysis. In animals whose physis received surgical ablation, physeal bar formation was always present, with poor organization of the remaining lateral growth plate. Histologic evidence from this study also underscores the fact that physeal bar formation occurs from the migration of osteoblasts and osteoclasts along vertical septa.

  5. Mechanical and fracture behavior of calcium phosphate cements

    NASA Astrophysics Data System (ADS)

    Jew, Victoria Chou

    Apatite-based calcium phosphate cements are currently employed to a limited extent in the biomedical and dental fields. They present significant potential for a much broader range of applications, particularly as a bone mineral substitute for fracture fixation. Specifically, hydroxyapatite (HA) is known for its biocompatibility and non-immunogenicity, attributed to its similarity to the mineral phase of natural bone. The advantages of a cement-based HA include injectability, greater resorbability and osteoconductivity compared to sintered HA, and an isothermal cement-forming reaction that avoids necrosis during cement setting. Although apatite cements demonstrate good compressive strength, tensile properties are very weak compared to natural bone. Applications involving normal weight-bearing require better structural integrity than apatite cements currently provide. A more thorough understanding of fracture behavior can elucidate failure mechanisms and is essential for the design of targeted strengthening methods. This study investigated a hydroxyapatite cement using a fracture mechanics approach, focusing on subcritical crack growth properties. Subcritical crack growth can lead to much lower load-bearing ability than critical strength values predict. Experiments show that HA cement is susceptible to crack growth under both cyclic fatigue-crack growth and stress corrosion cracking conditions, but only environmental, not mechanical, mechanisms contribute to crack extension. This appears to be the first evidence ever presented of stress corrosion crack growth behavior in calcium phosphate cements. Stress corrosion cracking was examined for a range of environmental conditions. Variations in pH have surprisingly little effect. Behavior in water at elevated temperature (50°C) is altered compared to water at ambient temperature (22°C), but only for crack-growth velocities below 10-7 m/s. However, fracture resistance of dried HA cement in air increases significantly

  6. Compensating Mechanisms That Minimize Flux Variability Through Unsaturated Fractures

    NASA Astrophysics Data System (ADS)

    Nimmo, J. R.; Su, G. W.

    2001-12-01

    Fast flow in fractures and macropores is a major cause of discrepancy between measurements and unsaturated flow models. Most models treat preferential flow as diffuse Darcy-Richards flow, so it is important to ascertain whether the mechanisms of unsaturated fracture flow accord with Darcy's law. The key issue is whether water flux is directly proportional to driving force with a proportionality factor, the hydraulic conductivity (K), that is independent of flux and force. We consider flow in a partially water-filled fracture with continuously supplied (e.g. ponded) water, responding to a change in driving force such as a change in tilt angle with respect to gravity. Four general flow modes, alone or in combination, can account for the dominant portion of the flow for these conditions, as shown by the experimental studies of Su and others (1999) and Tokunaga and Wan (1997). (1) Film flow occurs within a sheet or film that contacts a wall of the fracture. (2) Connected rivulet flow occurs when a rivulet that bridges across the fracture aperture by capillary force is consistently connected across the domain of interest from the inflow point to the outflow point. (3) Snapping rivulet flow occurs if the rivulet sometimes but not always extends continuously across the domain. (4) Pulsating-blob flow occurs in isolated blobs that bridge across the fracture aperture and move across the domain of interest without ever extending completely between the inflow and outflow points. Where fractures are large enough that the air-water interfaces are free to change shape or position in response to an externally applied change, each flow mode has its own characteristic relation between force and flow rate. This contrasts with the air-water interfaces commonly visualized in fine-textured media, in which the interface is constrained to a particular shape and position by capillarity and adsorption, so that the consistent geometry of the effective flow conduits leads to Darcian flow. In

  7. [Bone fracture and the healing mechanisms. Fragility fracture and bone quality].

    PubMed

    Mawatari, Taro; Iwamoto, Yukihide

    2009-05-01

    Fracture occurs in bone having less than normal elastic resistance without any violence. Numerous terms have been used to classify various types of fractures from low trauma events; "fragility fracture", "stress fracture", "insufficiency fracture", "fatigue fracture", "pathologic fracture", etc. The definitions of these terms and clinical characteristics of these fractures are discussed. Also state-of-the-art bone quality assessments; Finite element analysis of clinical CT scans, assessments of the Microdamage, and the Cross-links of Collagen are introduced in this review.

  8. Measurement of residual stresses using fracture mechanics weight functions

    SciTech Connect

    Fan, Y.

    2000-10-01

    A residual stress measurement method has been developed to quantify through-the-thickness residual stresses. Accurate measurement of residual stresses is crucial for many engineering structures. Fabrication processes such as welding and machining generate residual stresses that are difficult to predict. Residual stresses affect the integrity of structures through promoting failures due to brittle fracture, fatigue, stress corrosion cracking, and wear. In this work, the weight function theory of fracture mechanics is used to measure residual stresses. The weight function theory is an important development in computational fracture mechanics. Stress intensity factors for arbitrary stress distribution on the crack faces can be accurately and efficiently computed for predicting crack growth. This paper demonstrates that the weight functions are equally useful in measuring residual stresses. In this method, an artificial crack is created by a thin cut in a structure containing residual stresses. The cut relieves the residual stresses normal to the crack-face and allows the relieved residual stresses to deform the structure. Strain gages placed adjacent to the cut measure the relieved strains corresponding to incrementally increasing depths of the cut. The weight functions of the cracked body relate the measured strains to the residual stresses normal to the cut within the structure. The procedure details, such as numerical integration of the singular functions in applying the weight function method, will be discussed.

  9. Some basic fracture mechanics concepts in functionally graded materials

    NASA Astrophysics Data System (ADS)

    Jin, Z.-H.; Batra, R. C.

    1996-08-01

    In this paper, the crack-tip fields in a general nonhomogeneous material are summarized. The fracture toughness and R-curve of functionally graded materials (FGMs) are studied based on the crack-bridging concept and a rule of mixtures. It is shown that the fracture toughness is significantly increased when a crack grows from the ceramic-rich region into the metal-rich region in an alumina-nickel FGM. By applying the concept of the toughening mechanism to the study of the strength behavior of FGMs, it is found that the residual strength of the alumina-nickel FGM with an edge crack on the ceramic side is quite notch insensitive.

  10. Teriparatide anabolic therapy as potential treatment of type II dens non-union fractures

    PubMed Central

    Pola, Enrico; Pambianco, Virginia; Colangelo, Debora; Formica, Virginia M; Autore, Giovanni; Nasto, Luigi A

    2017-01-01

    Odontoid fractures account for 5% to 15% of all cervical spine injuries and 1% to 2% of all spine fractures. Type II fractures are the most common fracture pattern in elderly patients. Treatment (rigid and non-rigid immobilization, anterior screw fixation of the odontoid and posterior C1-C2 fusion) remains controversial and represents a unique challenge for the treating surgeon. The aims of treatment in the elderly is to quickly restore pre-injury function while decreasing morbidity and mortality associated with inactivity, immobilization with rigid collar and prolonged hospitalization. Conservative treatment of type II odontoid fractures is associated with relatively high rates of non-union and in a few cases delayed instability. Options for treatment of symptomatic non-unions include surgical fixation or prolonged rigid immobilization. In this report we present the case of a 73-year-old woman with post-traumatic odontoid non-union successfully treated with Teriparatide systemic anabolic therapy. Complete fusion and resolution of the symptoms was achieved 12 wk after the onset of the treatment. Several animal and clinical studies have confirmed the potential role of Teriparatide in enhancing fracture healing. Our case suggests that Teriparatide may have a role in improving fusion rates of C2 fractures in elderly patients. PMID:28144584

  11. Mechanical design optimization of bioabsorbable fixation devices for bone fractures.

    PubMed

    Lovald, Scott T; Khraishi, Tariq; Wagner, Jon; Baack, Bret

    2009-03-01

    Bioabsorbable bone plates can eliminate the necessity for a permanent implant when used to fixate fractures of the human mandible. They are currently not in widespread use because of the low strength of the materials and the requisite large volume of the resulting bone plate. The aim of the current study was to discover a minimally invasive bioabsorbable bone plate design that can provide the same mechanical stability as a standard titanium bone plate. A finite element model of a mandible with a fracture in the body region is subjected to bite loads that are common to patients postsurgery. The model is used first to determine benchmark stress and strain values for a titanium plate. These values are then set as the limits within which the bioabsorbable bone plate must comply. The model is then modified to consider a bone plate made of the polymer poly-L/DL-lactide 70/30. An optimization routine is run to determine the smallest volume of bioabsorbable bone plate that can perform and a titanium bone plate when fixating fractures of this considered type. Two design parameters are varied for the bone plate design during the optimization analysis. The analysis determined that a strut style poly-L-lactide-co-DL-lactide plate of 690 mm2 can provide as much mechanical stability as a similar titanium design structure of 172 mm2. The model has determined a bioabsorbable bone plate design that is as strong as a titanium plate when fixating fractures of the load-bearing mandible. This is an intriguing outcome, considering that the polymer material has only 6% of the stiffness of titanium.

  12. Imaging appearance of entrapped periosteum within a distal femoral Salter-Harris II fracture.

    PubMed

    Chen, Johnathan; Abel, Mark F; Fox, Michael G

    2015-10-01

    Salter Harris II fractures of the distal femur are associated with a high incidence of complications, especially premature physeal closure. Many risk factors for this high rate of premature physeal closure have been proposed. More recently, entrapment of periosteum within the physis has been suggested as an additional predisposing factor for premature physeal closure. The radiographic diagnosis of entrapped soft tissues, including periosteum, can be suggested in the setting of a Salter-Harris II fracture when the fracture does not reduce and physeal widening >3 mm remains. We report a patient who sustained a distal femoral Salter-Harris II fracture following a valgus injury. The patient had persistent distal medial physeal widening >5 mm following attempted reduction. A subsequent MRI revealed a torn periosteum entrapped within the distal femoral physis. Following removal of the periosteum, the patient developed a leg length discrepancy which required physiodesis of the contralateral distal femur. We present this case to raise awareness of the importance of having a high index of suspicion of periosteal entrapment in the setting of Salter-Harris II fractures since most consider entrapped periosteum an indication for surgery.

  13. Uncommon Variant of Type II Monteggia Fracture with Concomitant Distal Humeral Fracture

    PubMed Central

    Matta, Jihad F.; El Rassi, George S.; Abd El Nour, Hicham G.; El Asmar, Rachel

    2015-01-01

    Monteggia fracture-dislocation, a common injury sustained by pediatric population, is a rare entity in adults. It was first observed by Giovanni Battista Monteggia and later classified by Bado into 4 groups. The term “Monteggia equivalent or variant” was introduced to describe certain injuries with similar radiographic pattern and biomechanism of injury. Since then various types and their variants have been described in the literature. We present a complex fracture pattern in a 55-year-old male not previously described in the literature along with its treatment modality and favorable outcome. PMID:26550509

  14. Improvement of the mode II interface fracture toughness of glass fiber reinforced plastics/aluminum laminates through vapor grown carbon fiber interleaves

    PubMed Central

    Ning, Huiming; Li, Yuan; Hu, Ning; Cao, Yanping; Yan, Cheng; Azuma, Takesi; Peng, Xianghe; Wu, Liangke; Li, Jinhua; Li, Leilei

    2014-01-01

    The effects of acid treatment, vapor grown carbon fiber (VGCF) interlayer and the angle, i.e., 0° and 90°, between the rolling stripes of an aluminum (Al) plate and the fiber direction of glass fiber reinforced plastics (GFRP) on the mode II interlaminar mechanical properties of GFRP/Al laminates were investigated. The experimental results of an end notched flexure test demonstrate that the acid treatment and the proper addition of VGCF can effectively improve the critical load and mode II fracture toughness of GFRP/Al laminates. The specimens with acid treatment and 10 g m−2 VGCF addition possess the highest mode II fracture toughness, i.e., 269% and 385% increases in the 0° and 90° specimens, respectively compared to those corresponding pristine ones. Due to the induced anisotropy by the rolling stripes on the aluminum plate, the 90° specimens possess 15.3%–73.6% higher mode II fracture toughness compared to the 0° specimens. The improvement mechanisms were explored by the observation of crack propagation path and fracture surface with optical, laser scanning and scanning electron microscopies. Moreover, finite element analyses were carried out based on the cohesive zone model to verify the experimental fracture toughness and to predict the interface shear strength between the aluminum plates and GFRP laminates. PMID:27877680

  15. Improvement of the mode II interface fracture toughness of glass fiber reinforced plastics/aluminum laminates through vapor grown carbon fiber interleaves.

    PubMed

    Ning, Huiming; Li, Yuan; Hu, Ning; Cao, Yanping; Yan, Cheng; Azuma, Takesi; Peng, Xianghe; Wu, Liangke; Li, Jinhua; Li, Leilei

    2014-06-01

    The effects of acid treatment, vapor grown carbon fiber (VGCF) interlayer and the angle, i.e., 0° and 90°, between the rolling stripes of an aluminum (Al) plate and the fiber direction of glass fiber reinforced plastics (GFRP) on the mode II interlaminar mechanical properties of GFRP/Al laminates were investigated. The experimental results of an end notched flexure test demonstrate that the acid treatment and the proper addition of VGCF can effectively improve the critical load and mode II fracture toughness of GFRP/Al laminates. The specimens with acid treatment and 10 g m(-2) VGCF addition possess the highest mode II fracture toughness, i.e., 269% and 385% increases in the 0° and 90° specimens, respectively compared to those corresponding pristine ones. Due to the induced anisotropy by the rolling stripes on the aluminum plate, the 90° specimens possess 15.3%-73.6% higher mode II fracture toughness compared to the 0° specimens. The improvement mechanisms were explored by the observation of crack propagation path and fracture surface with optical, laser scanning and scanning electron microscopies. Moreover, finite element analyses were carried out based on the cohesive zone model to verify the experimental fracture toughness and to predict the interface shear strength between the aluminum plates and GFRP laminates.

  16. Improvement of the mode II interface fracture toughness of glass fiber reinforced plastics/aluminum laminates through vapor grown carbon fiber interleaves

    NASA Astrophysics Data System (ADS)

    Ning, Huiming; Li, Yuan; Hu, Ning; Cao, Yanping; Yan, Cheng; Azuma, Takesi; Peng, Xianghe; Wu, Liangke; Li, Jinhua; Li, Leilei

    2014-06-01

    The effects of acid treatment, vapor grown carbon fiber (VGCF) interlayer and the angle, i.e., 0° and 90°, between the rolling stripes of an aluminum (Al) plate and the fiber direction of glass fiber reinforced plastics (GFRP) on the mode II interlaminar mechanical properties of GFRP/Al laminates were investigated. The experimental results of an end notched flexure test demonstrate that the acid treatment and the proper addition of VGCF can effectively improve the critical load and mode II fracture toughness of GFRP/Al laminates. The specimens with acid treatment and 10 g m-2 VGCF addition possess the highest mode II fracture toughness, i.e., 269% and 385% increases in the 0° and 90° specimens, respectively compared to those corresponding pristine ones. Due to the induced anisotropy by the rolling stripes on the aluminum plate, the 90° specimens possess 15.3%-73.6% higher mode II fracture toughness compared to the 0° specimens. The improvement mechanisms were explored by the observation of crack propagation path and fracture surface with optical, laser scanning and scanning electron microscopies. Moreover, finite element analyses were carried out based on the cohesive zone model to verify the experimental fracture toughness and to predict the interface shear strength between the aluminum plates and GFRP laminates.

  17. Mechanical degradation of fuel cell membranes under fatigue fracture tests

    NASA Astrophysics Data System (ADS)

    Khorasany, Ramin M. H.; Sadeghi Alavijeh, Alireza; Kjeang, Erik; Wang, G. G.; Rajapakse, R. K. N. D.

    2015-01-01

    The effects of cyclic stresses on the fatigue and mechanical stability of perfluorosulfonic acid (PFSA) membranes are experimentally investigated under standard fuel cell conditions. The experiments are conducted ex-situ by subjecting membrane specimens to cyclic uniaxial tension at controlled temperature and relative humidity. The fatigue lifetime is measured in terms of the number of cycles until ultimate fracture. The results indicate that the membrane fatigue lifetime is a strong function of the applied stress, temperature, and relative humidity. The fatigue life increases exponentially with reduced stresses in all cases. The effect of temperature is found to be more significant than that of humidity, with reduced fatigue life at high temperatures. The maximum membrane strain at fracture is determined to decrease exponentially with increasing membrane lifetime. At a given fatigue life, a membrane exposed to fuel cell conditions is shown to accommodate more plastic strain before fracture than one exposed to room conditions. Overall, the proposed ex-situ membrane fatigue experiment can be utilized to benchmark the fatigue lifetime of new materials in a fraction of the time and cost associated with conventional in-situ accelerated stress testing methods.

  18. Combined Mode I and Mode II Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    The mode I, mode II, and combined mode I-mode II fracture behavior of ZrO2- 8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. Precracks were introduced in test specimens using the single-edge-v-notched beam (SEVNB) method incorporated with final diamond polishing to achieve sharp crack tips. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of K(sub I)/K(sub II) were also determined. The mixed-mode fracture behaviors of the coating material were compared with those of monolithic advanced ceramics determined previously. The mixed-mode fracture behavior of the plasma-sprayed thermal barrier coating material was predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

  19. Fracture resistance of premolars with bonded class II amalgams.

    PubMed

    Dias de Souza, Grace Mendonça; Pereira, Gisele Damiana Silveira; Dias, Carlos Tadeu Santos; Paulillo, Luis Alexandre Maffei Sartini

    2002-01-01

    This study evaluated the fracture resistance of maxillary premolars with MOD cavity preparation and simulated periodontal ligament. The teeth were restored with silver amalgam (G1), Scotchbond Multi-Purpose Plus and silver amalgam (G2) and Panavia F and silver amalgam (G3). After restorations were made, the specimens were stored at 37 degrees C for 24 hours at 100% humidity and submitted to the compression test in the Universal Testing Machine (Instron). The statistical analysis of the results (ANOVA and Tukey Test) revealed that the fracture resistance of group 2 (G2=105.720 kgF) was superior to those of groups 1 (G1=72.433 kgF) and 3 (G3=80.505 kgF) that did not differ between them.

  20. Survival Predictions of Ceramic Crowns Using Statistical Fracture Mechanics.

    PubMed

    Nasrin, S; Katsube, N; Seghi, R R; Rokhlin, S I

    2017-01-01

    This work establishes a survival probability methodology for interface-initiated fatigue failures of monolithic ceramic crowns under simulated masticatory loading. A complete 3-dimensional (3D) finite element analysis model of a minimally reduced molar crown was developed using commercially available hardware and software. Estimates of material surface flaw distributions and fatigue parameters for 3 reinforced glass-ceramics (fluormica [FM], leucite [LR], and lithium disilicate [LD]) and a dense sintered yttrium-stabilized zirconia (YZ) were obtained from the literature and incorporated into the model. Utilizing the proposed fracture mechanics-based model, crown survival probability as a function of loading cycles was obtained from simulations performed on the 4 ceramic materials utilizing identical crown geometries and loading conditions. The weaker ceramic materials (FM and LR) resulted in lower survival rates than the more recently developed higher-strength ceramic materials (LD and YZ). The simulated 10-y survival rate of crowns fabricated from YZ was only slightly better than those fabricated from LD. In addition, 2 of the model crown systems (FM and LD) were expanded to determine regional-dependent failure probabilities. This analysis predicted that the LD-based crowns were more likely to fail from fractures initiating from margin areas, whereas the FM-based crowns showed a slightly higher probability of failure from fractures initiating from the occlusal table below the contact areas. These 2 predicted fracture initiation locations have some agreement with reported fractographic analyses of failed crowns. In this model, we considered the maximum tensile stress tangential to the interfacial surface, as opposed to the more universally reported maximum principal stress, because it more directly impacts crack propagation. While the accuracy of these predictions needs to be experimentally verified, the model can provide a fundamental understanding of the

  1. Probabilistic/Fracture-Mechanics Model For Service Life

    NASA Technical Reports Server (NTRS)

    Watkins, T., Jr.; Annis, C. G., Jr.

    1991-01-01

    Computer program makes probabilistic estimates of lifetime of engine and components thereof. Developed to fill need for more accurate life-assessment technique that avoids errors in estimated lives and provides for statistical assessment of levels of risk created by engineering decisions in designing system. Implements mathematical model combining techniques of statistics, fatigue, fracture mechanics, nondestructive analysis, life-cycle cost analysis, and management of engine parts. Used to investigate effects of such engine-component life-controlling parameters as return-to-service intervals, stresses, capabilities for nondestructive evaluation, and qualities of materials.

  2. The method of lines in three dimensional fracture mechanics

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, J.; Berke, L.

    1980-01-01

    A review of recent developments in the calculation of design parameters for fracture mechanics by the method of lines (MOL) is presented. Three dimensional elastic and elasto-plastic formulations are examined and results from previous and current research activities are reported. The application of MOL to the appropriate partial differential equations of equilibrium leads to coupled sets of simultaneous ordinary differential equations. Solutions of these equations are obtained by the Peano-Baker and by the recurrance relations methods. The advantages and limitations of both solution methods from the computational standpoint are summarized.

  3. Salter-Harris II forearm fracture reduction and fixation using a buttress plate

    PubMed Central

    Barnes, Jonathan; Webb, Mark; Fearon, Paul v

    2014-01-01

    Distal radius fractures are common injuries in children. Those that affect the growth plate (physis) need to be managed carefully as inadequate management may lead to long-term deformity and a reduction in function. However, different management strategies all have drawbacks and controversy exists over how best to manage these cases. This is the case of a 13-year-old girl who presented with a Salter Harris II fracture, which was managed using a novel approach of utilising a T plate in a buttress mode to stabilise the fracture after anatomical reduction. This provided effective fracture fixation and should allow good bone healing without causing any iatrogenic growth plate damage and without fixing a plate across the physis, which may need removal in the future. PMID:24488665

  4. Application of probabilistic fracture mechanics to the PTS issue

    SciTech Connect

    Cheverton, R.D.; Ball, D.G.

    1985-01-01

    As a part of the NRC effort to obtain a resolution to the PWR PTS issue, a probabilistic approach has been applied that includes a probabilistic fracture-mechanics (PFM) analysis. The PFM analysis is performed with OCA-P, a computer code that performs thermal, stress and fracture-mechanics analyses and estimates the conditional probability of vessel failure, P(F/E), using Monte Carlo techniques. The stress intensity factor (K/sub I/) is calculated for two- and three-dimensional surface flaws using superposition techniques and influence coefficients. Importance-sampling techniques are used, as necessary, to limit to a reasonable value the number of vessels actually calculated. Analyses of three PWR plants indicate that (1) the critical initial flaw depth is very small (5 to 15 mm), (2) the benefit of warm prestressing and the role of crack arrest are transient dependent, (3) crack arrest does not occur for the dominant transients, and (4) the single largest uncertainty in the overall probabilistic analysis is the number of surface flaws per vessel. 30 refs., 6 figs., 4 tabs.

  5. Fracture mechanics parameters for failure prediction of composite resins.

    PubMed

    De Groot, R; Van Elst, H C; Peters, M C

    1988-06-01

    This study contains the first part of a research project in which the applicability of fracture mechanics parameters to predict failure of a restored tooth was investigated. Fracture mechanics parameters have been used in dental research before, but were restricted to comparative studies between various brands of composites. The critical values of the opening mode stress intensity factor (KI), its equivalents, the strain energy release rate (GI), and the J integral (JI), were measured with single-edge notched-bend (SENB) specimens of dental composite in a three-point bend test. The measured values of KIc for Silux (KIc = 0.99 +/- 0.03 MNm-3/2) and P-30 (KIc = 1.88 +/- 0.12 MNm-3/2), compared with values from the literature, show quantitative agreement. The J integral was computed by means of finite element analysis (FEA) on a two-dimensional model of the SENB specimens. The critical value of the J integral (measured with SENB specimens, notch depth-to-width ratio (a/W) = 1/2) was used to predict failure of specimens having an arbitrary geometry. In this study, failure was predicted for SENB specimens with notch depth-to-width ratio (a/W) = 1/4 and 3/4. The predicted deflection and load at failure correspond well with the measured deflection and load.

  6. Critically Stressed Fractures as Conduits: Mechanically-Chemically-Mediated Anisotropy of the Effective Permeability of Fractured Rock

    NASA Astrophysics Data System (ADS)

    Lang, P. S.; Nejati, M.; Paluszny, A.; Zimmerman, R. W.

    2015-12-01

    It has long been suggested that fractures that are critically oriented with respect to the in situ stress field are the most likely to be hydraulically conductive. This observation is revisited from the point of view of chemically mediated compaction processes, using numerical multi-physics, multi-scale simulations. Fracture contact is computed explicitly for discrete fracture networks, to find local displacements and contact tractions, which govern the initial permeability of the fractures. Subsequent flow simulations compute the full permeability tensor of the network. Local normal tractions then inform a series of transient reactive-transport, elastic-contact simulations at the grain scale that model the compaction of the fracture void space due to pressure-solution and free-face precipitation, assuming the pore-fluid in equilibrium concentration. The ensuing change of fracture transmissivity feeds back to the discrete fracture network model, wherein changes in the permeability tensor are evaluated. The eigenvectors of the initial permeability tensor reflect the higher permeability of fractures having shear/normal stress ratios near 0.6, which are characterized by relatively high permeability due to their combination of shear displacement and normal compression. The resulting preferred flow direction of the network becomes more pronounced over time as fractures that are subject to larger normal stresses experience stronger compaction, for two reasons. Firstly, larger normal traction over the surfaces provides a stronger drive for pressure solution at the contacting asperities. Secondly, these fractures are subject to smaller shear displacement. Their void space has less pronounced channels and is more sensitive to hydraulic sealing due to contact-zone percolation during the compaction process. It is concluded that mechanically-chemically mediated closure processes contribute to critically stressed fractures being likely hydraulic conduits.

  7. Coupled Flow and Mechanics in Porous and Fractured Media*

    NASA Astrophysics Data System (ADS)

    Martinez, M. J.; Newell, P.; Bishop, J.

    2012-12-01

    Numerical models describing subsurface flow through deformable porous materials are important for understanding and enabling energy security and climate security. Some applications of current interest come from such diverse areas as geologic sequestration of anthropogenic CO2, hydro-fracturing for stimulation of hydrocarbon reservoirs, and modeling electrochemistry-induced swelling of fluid-filled porous electrodes. Induced stress fields in any of these applications can lead to structural failure and fracture. The ultimate goal of this research is to model evolving faults and fracture networks and flow within the networks while coupling to flow and mechanics within the intact porous structure. We report here on a new computational capability for coupling of multiphase porous flow with geomechanics including assessment of over-pressure-induced structural damage. The geomechanics is coupled to the flow via the variation in the fluid pore pressures, whereas the flow problem is coupled to mechanics by the concomitant material strains which alter the pore volume (porosity field) and hence the permeability field. For linear elastic solid mechanics a monolithic coupling strategy is utilized. For nonlinear elastic/plastic and fractured media, a segregated coupling is presented. To facilitate coupling with disparate flow and mechanics time scales, the coupling strategy allows for different time steps in the flow solve compared to the mechanics solve. If time steps are synchronized, the controller allows user-specified intra-time-step iterations. The iterative coupling is dynamically controlled based on a norm measuring the degree of variation in the deformed porosity. The model is applied for evaluation of the integrity of jointed caprock systems during CO2 sequestration operations. Creation or reactivation of joints can lead to enhanced pathways for leakage. Similarly, over-pressures can induce flow along faults. Fluid flow rates in fractures are strongly dependent on the

  8. Mechanical evaluation of two canine iliac fracture fixation systems.

    PubMed

    Vangundy, T E; Hulse, D A; Nelson, J K; Boothe, H W

    1988-01-01

    Twenty-three canine pelves were tested bilaterally to determine the stiffness and strength of intact ilium and stabilized oblique iliac osteotomies that simulated a common clinical fracture. Fixation systems tested were three 4.0 mm cancellous screws inserted ventral to dorsal across the osteotomy site and one laterally placed five hole 3.5 mm dynamic compression plate. Specimens were mechanically tested to failure under torsional, axial, or axial plus bending loads. Lag screw fixation was stiffer and stronger than plate fixation in all testing modes. The differences were statistically significant (p less than .05) in the torsional and axial plus bending loading modes. Fatigue testing was performed on implanted specimens with low-level cyclic loading under axial plus bending loading conditions. Physiologic loading conditions failed to produce mechanical failure of either fixation system after 100,000 cycles.

  9. NASGRO(registered trademark): Fracture Mechanics and Fatigue Crack Growth Analysis Software

    NASA Technical Reports Server (NTRS)

    Forman, Royce; Shivakumar, V.; Mettu, Sambi; Beek, Joachim; Williams, Leonard; Yeh, Feng; McClung, Craig; Cardinal, Joe

    2004-01-01

    This viewgraph presentation describes NASGRO, which is a fracture mechanics and fatigue crack growth analysis software package that is used to reduce risk of fracture in Space Shuttles. The contents include: 1) Consequences of Fracture; 2) NASA Fracture Control Requirements; 3) NASGRO Reduces Risk; 4) NASGRO Use Inside NASA; 5) NASGRO Components: Crack Growth Module; 6) NASGRO Components:Material Property Module; 7) Typical NASGRO analysis: Crack growth or component life calculation; and 8) NASGRO Sample Application: Orbiter feedline flowliner crack analysis.

  10. Fracture Mechanics Modelling of an In Situ Concrete Spalling Experiment

    NASA Astrophysics Data System (ADS)

    Siren, Topias; Uotinen, Lauri; Rinne, Mikael; Shen, Baotang

    2015-07-01

    During the operation of nuclear waste disposal facilities, some sprayed concrete reinforced underground spaces will be in use for approximately 100 years. During this time of use, the local stress regime will be altered by the radioactive decay heat. The change in the stress state will impose high demands on sprayed concrete, as it may suffer stress damage or lose its adhesion to the rock surface. It is also unclear what kind of support pressure the sprayed concrete layer will apply to the rock. To investigate this, an in situ experiment is planned in the ONKALO underground rock characterization facility at Olkiluoto, Finland. A vertical experimental hole will be concreted, and the surrounding rock mass will be instrumented with heat sources, in order to simulate an increase in the surrounding stress field. The experiment is instrumented with an acoustic emission system for the observation of rock failure and temperature, as well as strain gauges to observe the thermo-mechanical interactive behaviour of the concrete and rock at several levels, in both rock and concrete. A thermo-mechanical fracture mechanics study is necessary for the prediction of the damage before the experiment, in order to plan the experiment and instrumentation, and for generating a proper prediction/outcome study due to the special nature of the in situ experiment. The prediction of acoustic emission patterns is made by Fracod 2D and the model later compared to the actual observed acoustic emissions. The fracture mechanics model will be compared to a COMSOL Multiphysics 3D model to study the geometrical effects along the hole axis.

  11. Outcomes of Nonoperative Treatment of Salter-Harris II Distal Radius Fractures

    PubMed Central

    Larsen, Meredith C.; Bohm, Kyle C.; Rizkala, Amir R.; Ward, Christina M.

    2016-01-01

    Background: Despite the frequent occurrence of these injuries, we know little about the natural history of Salter-Harris II (SH II) distal radius fractures. We conducted a systematic review of studies examining the radiographic and clinical outcomes of nonoperatively managed SH II distal radius fractures. Methods: Systematic searches of the MEDLINE and Cochrane computerized literature databases and manual searches of bibliographies were performed. We reviewed both descriptive and quantitative data. Results: Seven studies including 434 SH II fractures were reviewed. Two studies reported clinical outcomes based on patient age, but neither study described a statistical correlation between patient age and outcome. Two studies discussed the effect of age on radiographic outcome and reported higher rates of anatomic remodeling in children 10 years or younger. Two studies with long-term (average follow-up greater than 8 years) clinical results reported complication rates of 5%. Long-term follow-up of radiographic outcomes appeared in 4 studies with variable results. Five studies reported the frequency of premature physeal arrest after SH II fractures, with results ranging from 0% to 4.3%. Conclusions: Based on this review, no recommendations can be made as to what defines an acceptable reduction or which fractures would benefit from surgical intervention. Angular deformity seems to correct to an acceptable alignment in patients less than 10 years of age, but these younger patients seem to be at higher risk for symptomatic shortening if a growth arrest occurs. Redisplacement after reduction is fairly common, and other more severe complications such as pain, loss of motion, and nerve injury can occur. PMID:27418886

  12. Combined Mode I and Mode II Fracture of Plasma-Sprayed Thermal Barrier Coatings at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    The mode I, mode II, and combined mode I-mode II fracture behavior of ZrO2 - 8wt%Y2O3 thermal barrier coatings was determined in asymmetric flexure loading at both ambient and elevated temperatures. Precracks were introduced in test specimens using the single-edge-v-notched beam (SEVNB) method incorporated with final diamond polishing to achieve sharp crack tips. A fracture envelope of KI versus KII was determined for the coating material at ambient and elevated temperatures. Propagation angles of fracture as a function of KI/KII were also determined. The mixed-mode fracture behaviors of the coating material were compared with those of monolithic advanced ceramics determined previously. The mixed-mode fracture behavior of the plasma- sprayed thermal barrier coating material was predicted in terms of fracture envelope and propagation angle using mixed-mode fracture theories.

  13. Fracture mechanics of bone--the effects of density, specimen thickness and crack velocity on longitudinal fracture.

    PubMed

    Behiri, J C; Bonfield, W

    1984-01-01

    The fracture mechanics parameters of critical stress intensity factor (Kc) and critical strain energy release rate (Gc) for longitudinal fracture of bovine tibia cortical bone were determined by the compact tension method. It was demonstrated that, for a given bone density, Kc and Gc depended on the loading rate, and resultant crack velocity, with a maximum in fracture toughness (Kc approximately 6.3 MNm-3/2, Gc approximately 2900 Jm-2) at a crack velocity approximately 10(-3) ms-1. For a given loading rate, or crack velocity, an increase in bone density, in the range from 1.92 to 2.02 Mgm-3, produced increases in Kc and Gc, but a variation in specimen thickness (from 0.5 to 2 mm) had no effect on the measured fracture mechanics parameters.

  14. Probabilistic Fracture Mechanics and Optimum Fracture Control Analytical Procedures for a Reusable Solid Rocket Motor Case

    NASA Technical Reports Server (NTRS)

    Hanagud, S.; Uppaluri, B.

    1977-01-01

    A methodology for the reliability analysis of a reusable solid rocket motor case is discussed. The analysis is based on probabilistic fracture mechanics and probability distribution for initial flaw sizes. The developed reliability analysis is used to select the structural design variables of the solid rocket motor case on the basis of minimum expected cost and specified reliability bounds during the projected design life of the case. Effects of failure prevention plans such as nondestructive inspection and the material erosion between missions are also considered in the developed procedure for selection of design variables. The reliability-based procedure can be modified to consider other similar structures of reusable space vehicle systems with different failure prevention plans.

  15. Fracture and mechanical stratigraphy for Mississippian-Pennsylvanian age carbonates, Ozark Dome, NW Arkansas

    NASA Astrophysics Data System (ADS)

    Peppers, M.; Burberry, C. M.

    2014-12-01

    Identifying natural fracture patterns in an area gives a detailed look into the local tectonic history. Comparing those fractures to the mechanical properties of the rocks provides key insights into predicting fractures in the subsurface. The Ozark Dome is an ideal study area for fracture research due to multiple fracturing events resulting from the multi-stage deformation Ouachita Orogeny during the late Paleozoic. This study used field observations of lithology and fracture attributes over ~10 outcrops in the Mississppian-Pennsylvanian (360-298 ma) carbonate sequence of the Ozark Plateau. Outcrops were chosen having excellent lithological exposure up the sequence from the Boone to Atoka formations and with 3D representations of the fracture patterns. In all, the area investigated covered nearly 60 square miles. Fracture attributes collected included fracture intensity, length, and abutting relationships; and rock hardness data collected from a Schmidt Hammer. Data was analyzed using programs such as Stereonet and MOVE structural software that generated rose diagrams, structural cross sections, and products. Initial results indicate 4 main fracture orientations that resulted from at least 3 discrete phases of deformation during the Miss-Penn. Initial results also indicate that the present-day mechanical stratigraphy is not the same one that existed during the deformation phases. Work done at the Tiger Blvd. outcrops showed at least 2 distinct mechanical units. Fractures observed at the outcrop did not respect mechanical bed boundaries, and showed no relationship to the differences in mechanical properties observed. This study will aid in the interpretation of fractures in regards to mechanical stratigraphy, which allows for a better understanding of subsurface fracture prediction in carbonate sequences worldwide. Finally, the fracture work here will also help in elucidating the tectonic history of the field area during the Mississippian and Pennsylvanian.

  16. Fracture Mechanics Analysis of LH2 Feed Line Flow Liners

    NASA Technical Reports Server (NTRS)

    James, Mark A.; Dawicke, David S.; Brzowski, Matthew B.; Raju, Ivatury S.; Elliott, Kenny B.; Harris, Charles E.

    2006-01-01

    Inspections of the Space Shuttle Main Engine revealed fatigue cracks growing from slots in the flow liner of the liquid hydrogen (LH2) feed lines. During flight, the flow liners experience complex loading induced by flow of LH2 and the resonance characteristics of the structure. The flow liners are made of Inconel 718 and had previously not been considered a fracture critical component. However, fatigue failure of a flow liner could have catastrophic effect on the Shuttle engines. A fracture mechanics study was performed to determine if a damage tolerance approach to life management was possible and to determine the sensitivity to the load spectra, material properties, and crack size. The load spectra were derived separately from ground tests and material properties were obtained from coupon tests. The stress-intensity factors for the fatigue cracks were determined from a shell-dynamics approach that simulated the dominant resonant frequencies. Life predictions were obtained using the NASGRO life prediction code. The results indicated that adequate life could not be demonstrated for initial crack lengths of the size that could be detected by traditional NDE techniques.

  17. Elastic plastic fracture mechanics methodology for surface cracks

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A.; Boatwright, D. W.; Curtin, W. J.; Lambert, D. M.

    1993-01-01

    The Elastic Plastic Fracture Mechanics (EPFM) Methodology has evolved significantly in the last several years. Nevertheless, some of these concepts need to be extended further before the whole methodology can be safely applied to structural parts. Specifically, there is a need to include the effect of constraint in the characterization of material resistance to crack growth and also to extend these methods to the case of 3D defects. As a consequence, this project was started as a 36 month research program with the general objective of developing an EPFM methodology to assess the structural reliability of pressure vessels and other parts of interest to NASA containing defects. This report covers a computer modelling algorithm used to simulate the growth of a semi-elliptical surface crack; the presentation of a finite element investigation that compared the theoretical (HRR) stress field to that produced by elastic and elastic-plastic models; and experimental efforts to characterize three dimensional aspects of fracture present in 'two dimensional', or planar configuration specimens.

  18. Chemical and Mechanical Alteration of Fractures: Micro-Scale Simulations and Comparison to Experimental Results

    NASA Astrophysics Data System (ADS)

    Ameli, P.; Detwiler, R. L.; Elkhoury, J. E.; Morris, J. P.

    2012-12-01

    Fractures are often the main pathways for subsurface fluid flow especially in rocks with low matrix porosity. Therefore, the hydro-mechanical properties of fractures are of fundamental concern for subsurface CO2 sequestration, enhanced geothermal energy production, enhanced oil recovery, and nuclear waste disposal. Chemical and mechanical stresses induced during these applications may lead to significant alteration of the hydro-mechanical properties of fractures. Laboratory experiments aimed at understanding the chemo-hydro-mechanical response of fractures have shown a range of results that contradict simple conceptual models. For example, under conditions favoring mineral dissolution, where one would expect an overall increase in permeability and fracture aperture, permeability increases under some conditions and decreases under others. Recent experiments have attempted to link these core-scale observations to the relevant small-scale processes occurring within fractures. Results suggest that the loss of mechanical strength in asperities due to chemical alteration may cause non-uniform deformation and alteration of fracture apertures. However, it remains difficult to directly measure the coupled chemical and mechanical processes that lead to alteration of contacting fracture surfaces, which challenges our ability to predict the long-term evolution of the hydro-mechanical properties of fractures. Here, we present a computational model that uses micro-scale surface roughness and explicitly couples dissolution and elastic deformation to calculate local alterations in fracture aperture under chemical and mechanical stresses. Chemical alteration of the fracture surfaces is modeled using a depth-averaged algorithm of fracture flow and reactive transport. Then, we deform the resulting altered fracture-surfaces using an algorithm that calculates the elastic deformation. Nonuniform dissolution may cause the location of the resultant force between the two contacting

  19. Diameter of basalt columns derived from fracture mechanics bifurcation analysis.

    PubMed

    Bahr, H-A; Hofmann, M; Weiss, H-J; Bahr, U; Fischer, G; Balke, H

    2009-05-01

    The diameter of columnar joints forming in cooling basalt and drying starch increases with decreasing growth rate. This observation can be reproduced with a linear-elastic three-dimensional fracture mechanics bifurcation analysis, which has been done for a periodic array of hexagonal columnar joints by considering a bifurcation mode compatible with observations on drying starch. In order to be applicable to basalt columns, the analysis has been carried out with simplified stationary temperature fields. The critical diameter differs from the one derived with a two-dimensional model by a mere factor of 1/2. By taking into account the latent heat released at the solidification front, the results agree fairly well with observed column diameters.

  20. Simple spline-function equations for fracture mechanics calculations

    NASA Technical Reports Server (NTRS)

    Orange, T. W.

    1979-01-01

    The paper presents simple spline-function equations for fracture mechanics calculations. A spline function is a sequence of piecewise polynomials of degree n greater than 1 whose coefficients are such that the function and its first n-1 derivatives are continuous. Second-degree spline equations are presented for the compact, three point bend, and crack-line wedge-loaded specimens. Some expressions can be used directly, so that for a cyclic crack propagation test using a compact specimen, the equation given allows the cracklength to be calculated from the slope of the load-displacement curve. For an R-curve test, equations allow the crack length and stress intensity factor to be calculated from the displacement and the displacement ratio.

  1. Modification of fracture surfaces by dissolution. Part II

    SciTech Connect

    Johnson, B.

    1983-01-01

    This study focuses upon how and to what extent dissolution related fluid/rock interactions modify the morphology and roughness of surfaces on Sioux Quartzite. Dissolution experiments consisted of reacting small discs of Sioux Quartzite in sealed gold capsules containing either distilled water or 0.05 N to 4.0 N aqueous solutions of Na/sub 2/CO/sub 3/. Samples were reacted at 200/sup 0/C and 20 to 30 MPa fluid pressures for 2 to 5 days. Two markedly different starting surface textures were used: polished, optically flat surfaces and tensile fracture surfaces. An exploratory experiment also was performed to assess the occurrence of a pressure solution phenomenon on a polished quartzite surface at contact regions of indenting quartz sand grains. Scanning electron microscopy studies indicate progressive increases in the amount of dissolution produced significant changes of surface roughness for both initial surface textures. Surface roughness increased measurably, with the initially polished surfaces exhibiting the more dramatic changes. The pressure solution experiments did not produce definite results, but several surface features are suggestive of dissolution enhancement at load carrying contacts. 9 refs., 10 figs.

  2. Fracture-Based Mesh Size Requirements for Matrix Cracks in Continuum Damage Mechanics Models

    NASA Technical Reports Server (NTRS)

    Leone, Frank A.; Davila, Carlos G.; Mabson, Gerald E.; Ramnath, Madhavadas; Hyder, Imran

    2017-01-01

    This paper evaluates the ability of progressive damage analysis (PDA) finite element (FE) models to predict transverse matrix cracks in unidirectional composites. The results of the analyses are compared to closed-form linear elastic fracture mechanics (LEFM) solutions. Matrix cracks in fiber-reinforced composite materials subjected to mode I and mode II loading are studied using continuum damage mechanics and zero-thickness cohesive zone modeling approaches. The FE models used in this study are built parametrically so as to investigate several model input variables and the limits associated with matching the upper-bound LEFM solutions. Specifically, the sensitivity of the PDA FE model results to changes in strength and element size are investigated.

  3. A mechanism-based approach to modeling ductile fracture.

    SciTech Connect

    Bammann, Douglas J.; Hammi, Youssef; Antoun, Bonnie R.; Klein, Patrick A.; Foulk, James W., III; McFadden, Sam X.

    2004-01-01

    Ductile fracture in metals has been observed to result from the nucleation, growth, and coalescence of voids. The evolution of this damage is inherently history dependent, affected by how time-varying stresses drive the formation of defect structures in the material. At some critically damaged state, the softening response of the material leads to strain localization across a surface that, under continued loading, becomes the faces of a crack in the material. Modeling localization of strain requires introduction of a length scale to make the energy dissipated in the localized zone well-defined. In this work, a cohesive zone approach is used to describe the post-bifurcation evolution of material within the localized zone. The relations are developed within a thermodynamically consistent framework that incorporates temperature and rate-dependent evolution relationships motivated by dislocation mechanics. As such, we do not prescribe the evolution of tractions with opening displacements across the localized zone a priori. The evolution of tractions is itself an outcome of the solution of particular, initial boundary value problems. The stress and internal state of the material at the point of bifurcation provides the initial conditions for the subsequent evolution of the cohesive zone. The models we develop are motivated by in-situ scanning electron microscopy of three-point bending experiments using 6061-T6 aluminum and 304L stainless steel, The in situ observations of the initiation and evolution of fracture zones reveal the scale over which the failure mechanisms act. In addition, these observations are essential for motivating the micromechanically-based models of the decohesion process that incorporate the effects of loading mode mixity, temperature, and loading rate. The response of these new cohesive zone relations is demonstrated by modeling the three-point bending configuration used for the experiments. In addition, we survey other methods with the potential

  4. Atypical subtrochanteric femoral shaft fractures: role for mechanics and bone quality.

    PubMed

    van der Meulen, Marjolein C H; Boskey, Adele L

    2012-08-29

    Bisphosphonates are highly effective agents for reducing osteoporotic fractures in women and men, decreasing fracture incidence at the hip and spine up to 50%. In a small subset of patients, however, these agents have recently been associated with 'atypical femoral fractures' (AFFs) in the subtrochanteric region or the diaphysis. These fractures have several atypical characteristics, including occurrence with minimal trauma; younger age than typical osteoporotic fractures; occurrence at cortical, rather than cancellous sites; early radiographic appearance similar to that of a stress fracture; transverse fracture pattern rather than the familiar spiral or transverse-oblique morphologies; initiation on the lateral cortex; and high risk of fracture on the contralateral side, at the same location as the initial fracture. Fracture is a mechanical phenomenon that occurs when the loads applied to a structure such as a long bone exceed its load-bearing capacity, either due to a single catastrophic overload (traumatic failure) or as a result of accumulated damage and crack propagation at sub-failure loads (fatigue failure). The association of AFFs with no or minimal trauma suggests a fatigue-based mechanism that depends on cortical cross-sectional geometry and tissue material properties. In the case of AFFs, bisphosphonate treatment may alter cortical tissue properties, as these agents are known to alter bone remodeling. This review discusses the use of bisphosphonates, their effects on bone remodeling, mechanics and tissue composition, their significance as an effective therapy for osteoporosis, and why these agents may increase fracture risk in a small population of patients.

  5. Damage Tolerance Assessment Handbook. Volume 1. Introduction Fracture Mechanics Fatigue Crack Propagation

    DTIC Science & Technology

    1993-10-01

    Volume ,: Introduction NJ 08405 Fracture Mechanics Fatigue Crack Propagation Research and Special Programs Administration John A. Volpe National...Load-displacement plot [Adapted from John M. Barson/Stanley T. Rolfe, Fracture and Fatigue Control in Structures. Applications of Fracture Mechanics...Methods ASTM STP 527, American Society for Testing and Materials, Philadelphia, PA, 1973. 2-19. Ratwani, M.M. and Wilhem , DP. Develonment and EvaluAtion of

  6. On study of nonclassical problems of fracture and failure mechanics and related mechanisms

    NASA Astrophysics Data System (ADS)

    Guz, A. N.

    2009-01-01

    Nonclassical problems of fracture and failure mechanics that have been analyzed by the author and his collaborators at the S. P. Timoshenko Institute of Mechanics (Kiev, National Academy of Sciences of Ukraine) during the past forty years are considered in brief. The results of the analysis are presented in a form that would be quite informative for the majority of experts interested in various fundamental and applied aspects of fracture and failure problems including the identification of related mechanisms. This paper was prepared on invitation of the Editorial Board of the journal "Annals. The European Academy of Sciences" and may be considered as an Extended Pascal Medal Lecture (The 2007 Blaise Pascal Medal in Materials Sciences of the EAS)

  7. Combined Isolated Laugier's Fracture and Distal Radial Fracture: Management and Literature Review on the Mechanism of Injury

    PubMed Central

    Osman, Walid; Alaya, Zeineb; Naouar, Nader; Ben Ayeche, Mohamed

    2016-01-01

    Introduction. Isolated fracture of the trochlea is an uncommon condition requiring a particular mechanism of injury. Its association with a distal radial fracture is rare. We aimed through this case report to identify the injury mechanism and to assess surgical outcomes. Case Presentation. We report a 26-year-old female who was admitted to our department for elbow trauma following an accidental fall on her outstretched right hand with her elbow extended and supinated. On examination, the right elbow was swollen with tenderness over the anteromedial aspect of the distal humerus. The elbow range was restricted. Standard radiographs showed an intra-articular half-moon-shaped fragment lying proximal and anterior to the distal humerus. There was a comminuted articular fracture of the distal radius with an anterior displacement. A computed tomography revealed an isolated shear fracture of the trochlea without any associated lesion of the elbow. The patient was surgically managed. Anatomical reduction was achieved and the fracture was fixed with 2 Kirschner wires. The distal radial fracture was treated by open reduction and plate fixation. The postoperative course was uneventful with a good recovery. Conclusion. Knowledge of such entity would be useful to indicate the suitable surgical management and eventually to obtain good functional outcomes. PMID:28070435

  8. On the localization of fracture in highly constrained polymeric layer subjected to mode II loading

    SciTech Connect

    Chiang, M.Y.M.; Chai, H.

    1996-12-31

    The tight spatial constraints imposed on the interlayer by the relatively rigid substrates in adhesive bonding may impede the natural development and growth of damage sources such as voids, kinks and microcracks. This may lead to extensive nonlinear deformations and intense strain localization prior to fracture in ductile or brittle adhesive systems. Moreover, the localized deformation in the bond may be highly triaxial regardless of the nature of the far-field loading. Fracture criteria based on conventional linear elastic fracture mechanics and small-scale yielding condition may not be applicable on large strain. Therefore, the purpose of the authors work is to focus on the local deformation at the crack tip in an effort to demonstrate a fracture criterion, which is independent of the specimen geometry, for the situation in large (or small) plastic deformation.

  9. Impact of Injury Mechanisms on Patterns and Management of Facial Fractures.

    PubMed

    Greathouse, S Travis; Adkinson, Joshua M; Garza, Ramon; Gilstrap, Jarom; Miller, Nathan F; Eid, Sherrine M; Murphy, Robert X

    2015-07-01

    Mechanisms causing facial fractures have evolved over time and may be predictive of the types of injuries sustained. The objective of this study is to examine the impact of mechanisms of injury on the type and management of facial fractures at our Level 1 Trauma Center. The authors performed an Institutional Review Board-approved review of our network's trauma registry from 2006 to 2010, documenting age, sex, mechanism, Injury Severity Score, Glasgow Coma Scale, facial fracture patterns (nasal, maxillary/malar, orbital, mandible), and reconstructions. Mechanism rates were compared using a Pearson χ2 test. The database identified 23,318 patients, including 1686 patients with facial fractures and a subset of 1505 patients sustaining 2094 fractures by motor vehicle collision (MVC), fall, or assault. Nasal fractures were the most common injuries sustained by all mechanisms. MVCs were most likely to cause nasal and malar/maxillary fractures (P < 0.01). Falls were the least likely and assaults the most likely to cause mandible fractures (P < 0.001), the most common injury leading to surgical intervention (P < 0.001). Although not statistically significant, fractures sustained in MVCs were the most likely overall to undergo surgical intervention. Age, number of fractures, and alcohol level were statistically significant variables associated with operative management. Age and number of fractures sustained were associated with operative intervention. Although there is a statistically significant correlation between mechanism of injury and type of facial fracture sustained, none of the mechanisms evaluated herein are statistically associated with surgical intervention. Clinical Question/Level of Evidence: Therapeutic, III.

  10. Mixed-mode I+II fracture characterization of human cortical bone using the Single Leg Bending test.

    PubMed

    Silva, F G A; de Moura, M F S F; Dourado, N; Xavier, J; Pereira, F A M; Morais, J J L; Dias, M I R

    2016-02-01

    Mixed-mode I+II fracture characterization of human cortical bone was analyzed in this work. A miniaturized version of the Single Leg Bending test (SLB) was used owing to its simplicity. A power law criterion was verified to accurately describe the material fracture envelop under mixed-mode I+II loading. The crack tip opening displacements measured by digital image correlation were used in a direct method to determine the cohesive law mimicking fracture behavior of cortical bone. Cohesive zone modeling was used for the sake of validation. Several fracture quantities were compared with the experimental results and the good agreement observed proves the appropriateness of the proposed procedure for fracture characterization of human bone under mixed-mode I+II loading.

  11. Atlanto-axial dislocation complicating a type II odontoid fracture. Reduction and final fixation.

    PubMed

    Riouallon, G; Pascal-Moussellard, H

    2014-05-01

    A case of traumatic posterolateral C1-C2 dislocation associated with odontoid fracture is reported. This is a rare case of traumatic posterolateral C1-C2 dislocation associated with odontoid fracture. Its management is discussed. A traumatic dislocation of atlanto-axial joint associated with an odontoid fracture remains a rare injury. No case of posterior dislocation has been reported so far in the literature with this type of management. The case is of a 25 year-old-man with a primary atlanto-axial posterolateral dislocation associated with a type II displaced odontoid fracture without any neurological complication. The patient underwent gentle traction during 24 hours with a halo frame. An incomplete reduction was achieved. Two days later, a complete reduction was obtained thanks to a preoperative manual traction maintained by a Mayfield (R) modified skull clamp. Anterior C1-C2 fixation was performed according to Vaccaro's technique. The patient wore a cervical collar and underwent physiotherapy during three months. To our best knowledge, this case represents the first traumatic atlanto-axial dislocation associated with an odontoid fracture which was treated through retropaharyngeal approach. This had been rendered possible thanks to the final reduction maneuver in extension.

  12. Mode II interlaminar fracture toughness of carbon fabric composite laminates with carbon nanotube oriented by magnet

    NASA Astrophysics Data System (ADS)

    Xu, Xinguang; Zhou, Zhenggang

    2017-03-01

    Inspired by the residual iron nanoparticles wrapped in the CNTs tips, we developed a method to induce efficient orientation of multiwalled CNTs bundles by relatively low magnetic fields. Laminates were fabricated to investigate the effect of magnet oriented CNTs on GIIC properties. Microstructure anisotropy of nanotube bundles demonstrated the orientation of CNT bundles by magnet. Furthermore, the application of magnet increased mode II interlaminar fracture toughness by 29% compared to plain laminates.

  13. Buckling and hydraulic mechanisms in orbital blowout fractures: fact or fiction?

    PubMed

    Ahmad, Fateh; Kirkpatrick, Niall A; Lyne, Jonathan; Urdang, Michael; Waterhouse, Norman

    2006-05-01

    Since the first description of orbital blowout fractures, there has been much confusion as to their etiology. Two principal mechanisms have been proposed to explain their production, the buckling and the hydraulic mechanisms caused, respectively, by trauma to the orbital rim and the globe of the eye. The aim of this study was to evaluate both mechanisms qualitatively and quantitatively. Our protocol used intact cadavers, quantifiable intraocular pressure, variable and quantifiable force, and quantifiable bone strain distribution with strain gauge analysis. One orbit of each cadaver was used to simulate each of the two mechanisms, allowing direct comparison. Fractures produced by the buckling mechanism were limited to the anterior part of the orbital floor, with strain readings reaching up to 3756 microepsilon. Posteriorly, strain did not exceed 221 microepsilon. In contrast, hydraulic-type fractures were much larger, involving anterior and posterior parts of the floor as well as the medial wall of the orbit. Here, strain exceeded 3756 microepsilon in both parts of the floor. Furthermore, we have demonstrated that the average energy required to fracture the orbital floor by the buckling mechanism is 1.54 J, whereas an average energy of 1.22 J is needed to produce this fracture by the hydraulic mechanism. Our results suggest that efforts to establish one or another mechanism as the primary etiology are misplaced. Both mechanisms produce orbital blowout fractures, with different and specific characteristics. We believe this provides the basis for our reclassification of such fractures.

  14. Mechanical and petrophysical study of fractured shale materials

    NASA Astrophysics Data System (ADS)

    Bonnelye, A.; Schubnel, A.; David, C.; Henry, P.; Guglielmi, Y.; Gout, C.; Dick, P.

    2015-12-01

    Mechanical and physical properties of shales are of major importance for upper crustal fault hydro-mechanical behavior. In particular, relationships between applied stress, textural anisotropy and transport properties. These relations can be investigated in the laboratory and here, was used shales from Tournemire (southern France). Triaxial tests were performed in order to determine the elasto-plastic yield envelope on 3 sets of samples with 3various bedding orientations (0°, 45°, and 90°). For each set, experiments were carried out at increasing confining pressures (2.5, 5, 10, 20, 40, 80MPa). They were performed under nominally drained conditions, at strain rates ranging between 5x10-7 s-1 - 1x10-5 s-1up to failure. During each experiment, P and S wave elastic velocities were continuously measured, in order to monitor the evolution of elastic anisotropy. Results show that the orientation of principal stress relative to bedding plays an important role on the brittle strength. Minimum strength is observed for samples deformed at 45° to bedding. Strength anisotropy increases both with confining pressure and strain rate. We interpret this result as the cohesive strength (and fracture toughness) being strain rate dependent. Although brittle failure and stress drops were systematically observed, deformation remained aseismic. This confirms that shales are good lithological candidates for shallow aseismic creep and slow slip events. Brittle failure was preceded by the development of P wave anisotropy, due to both crack growth and mineral re-orientation. Anisotropy variations were largest for samples deformed perpendicular to bedding, at the onset of rupture. Anisotropy reversal was observed at the highest confining pressures. For samples deformed parallel to bedding, the P wave anisotropy development is weaker. For both of these orientations, Thomsens parameters were inverted from the elastic wave data in order to quantify the evolution of elastic anisotropy. We

  15. Mechanical test and fractal analysis on anisotropic fracture of cortical bone

    NASA Astrophysics Data System (ADS)

    Yin, Dagang; Chen, Bin; Ye, Wei; Gou, Jihua; Fan, Jinghong

    2015-12-01

    The mechanical properties of the cortical bone of fresh bovine femora along three different directions are tested through four-point bending experiments. It is indicated that the fracture energy along the transversal direction of the bone is distinctly larger than those of the longitudinal and radial directions. The fracture surfaces of the three different directions are observed by scanning electron microscope (SEM). It is shown that the roughness of the fracture surface of the transversal direction is obviously larger than those of the fracture surfaces of the longitudinal and radial directions. It is also revealed that the osteons in the bone are perpendicular to the fracture surface of the transversal direction and parallel to the fracture surfaces of the longitudinal and radial directions. Based on these experimental results, the fractal dimensions of the fracture surfaces of different directions are calculated by box-counting method in MATLAB. The calculated results show that the fractal dimension of the fracture surface of the transversal direction is remarkably larger than those of the fracture surfaces of the longitudinal and radial directions. The fracture energies of different directions are also calculated based on their fractal models. It is denoted that the fracture energy of the transversal direction is remarkably larger than those of the longitudinal and radial directions. The calculated results are in good agreement with the tested results.

  16. Crack blunting, crack bridging and resistance-curve fracture mechanics in dentin: effect of hydration.

    PubMed

    Kruzic, J J; Nalla, R K; Kinney, J H; Ritchie, R O

    2003-12-01

    Few studies have focused on a description of the fracture toughness properties of dentin in terms of resistance-curve (R-curve) behavior, i.e., fracture resistance increasing with crack extension, particularly in light of the relevant toughening mechanisms involved. Accordingly, in the present study, fracture mechanics based experiments were conducted on elephant dentin in order to determine such R-curves, to identify the salient toughening mechanisms and to discern how hydration may affect their potency. Crack bridging by uncracked ligaments, observed directly by microscopy and X-ray tomography, was identified as a major toughening mechanism, with further experimental evidence provided by compliance-based experiments. In addition, with hydration, dentin was observed to display significant crack blunting leading to a higher overall fracture resistance than in the dehydrated material. The results of this work are deemed to be of importance from the perspective of modeling the fracture behavior of dentin and in predicting its failure in vivo.

  17. Fractures

    MedlinePlus

    A fracture is a break, usually in a bone. If the broken bone punctures the skin, it is called an open ... falls, or sports injuries. Other causes are low bone density and osteoporosis, which cause weakening of the ...

  18. Spartan Release Engagement Mechanism (REM) stress and fracture analysis

    NASA Technical Reports Server (NTRS)

    Marlowe, D. S.; West, E. J.

    1984-01-01

    The revised stress and fracture analysis of the Spartan REM hardware for current load conditions and mass properties is presented. The stress analysis was performed using a NASTRAN math model of the Spartan REM adapter, base, and payload. Appendix A contains the material properties, loads, and stress analysis of the hardware. The computer output and model description are in Appendix B. Factors of safety used in the stress analysis were 1.4 on tested items and 2.0 on all other items. Fracture analysis of the items considered fracture critical was accomplished using the MSFC Crack Growth Analysis code. Loads and stresses were obtaind from the stress analysis. The fracture analysis notes are located in Appendix A and the computer output in Appendix B. All items analyzed met design and fracture criteria.

  19. Fracture strength and elastic modulus as a function of porosity for hydroxyapatite and other brittle materials, Part II

    SciTech Connect

    Fan, Xiaofeng; Case, Eldon D; Ren, Fei; Shu, Yutian; Baumann, Melissa

    2012-01-01

    Part I of this paper discussed the Weibull modulus m, versus porosity P behavior of brittle materials, including HA. While the Weibull modulus m deals with the scatter in fracture strength data, this paper (Part II) focuses on two additional key mechanical properties of porous materials, namely the average fracture strength f , and Young s modulus E, for P in the interval from P zero to P PG (the porosity of the unfired compacts). The f versus P data for HA from this study and the literature data for alumina, yttria stabilized zirconia (YSZ) and silicon nitride are describedwell by functions of , where = 1 P/PG = the degree of densification. A similar function of applies to the E versus P behavior of HA from this study and data from the literature for alumina, titanium and YSZ. All of the data analyzed in this study (Part II) are based on partially and fully sintered powder compacts (excluding green powder compacts), thus the f / 0 versus and E /E0 versus relationships may apply only to such specimens.

  20. Fracture Mechanics Analyses for Interface Crack Problems - A Review

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald; Shivakumar, Kunigal; Raju, Ivatury S.

    2013-01-01

    Recent developments in fracture mechanics analyses of the interfacial crack problem are reviewed. The intent of the review is to renew the awareness of the oscillatory singularity at the crack tip of a bimaterial interface and the problems that occur when calculating mode mixity using numerical methods such as the finite element method in conjunction with the virtual crack closure technique. Established approaches to overcome the nonconvergence issue of the individual mode strain energy release rates are reviewed. In the recent literature many attempts to overcome the nonconvergence issue have been developed. Among the many approaches found only a few methods hold the promise of providing practical solutions. These are the resin interlayer method, the method that chooses the crack tip element size greater than the oscillation zone, the crack tip element method that is based on plate theory and the crack surface displacement extrapolation method. Each of the methods is validated on a very limited set of simple interface crack problems. However, their utility for a wide range of interfacial crack problems is yet to be established.

  1. Fracture-mechanics parameters of the composite-enamel bond.

    PubMed

    de Groot, R; van Elst, H C; Peters, M C

    1990-01-01

    In a previous study, the critical values of the opening mode stress intensity factor (K1), its equivalent, the strain energy-release rate (G1), and the J integral (J1) (in the elastic case being equal to that of G1) were determined for resin composite. In this study, the strength of the composite-tooth interface was investigated. The critical values of K1 and J1 were measured with single-edge notched-bend (SENB) specimens of resin composite bonded to enamel, with the notch at midspan at the bonded interface. Due to enamel's anisotropy, the values of Klc and Jlc to be used in a fracture-mechanics application for failure prediction of a structure depend on the enamel prism orientation relative to the adhesive interface. Where interfacial failure is to be expected, the following values for Jlc and Klc can be used: Silux, Jlc = 145 +/- 35 Jm-2 and Klc = 0.84 +/- 0.16 MNm-3/2; P-30, Jlc = 163 +/- 13 Jm-2 and Klc = 1.02 +/- 0.07 MNm-3/2. Where enamel failure is expected or where the failure mode cannot be predicted, the following values can be applied: Silux, Jlc = 89 +/- 15 Jm-2 and Klc = 0.84 +/- 0.16 MNm-3/2; P-30, Jlc = 89 +/- 15 Jm-2 and Klc = 0.75 +/- 0.10 MNm-3/2.

  2. Chemically- and mechanically-mediated influences on the transport and mechanical characteristics of rock fractures

    SciTech Connect

    Min, K.-B.; Rutqvist, J.; Elsworth, D.

    2009-02-01

    A model is presented to represent changes in the mechanical and transport characteristics of fractured rock that result from coupled mechanical and chemical effects. The specific influence is the elevation of dissolution rates on contacting asperities, which results in a stress- and temperature-dependent permanent closure. A model representing this pressure-dissolution-like behavior is adapted to define the threshold and resulting response in terms of fundamental thermodynamic properties of a contacting fracture. These relations are incorporated in a stress-stiffening model of fracture closure to define the stress- and temperature-dependency of aperture loss and behavior during stress and temperature cycling. These models compare well with laboratory and field experiments, representing both decoupled isobaric and isothermal responses. The model was applied to explore the impact of these responses on heated structures in rock. The result showed a reduction in ultimate induced stresses over the case where chemical effects were not incorporated, with permanent reduction in final stresses after cooling to ambient conditions. Similarly, permeabilities may be lower than they were in the case where chemical effects were not considered, with a net reduction apparent even after cooling to ambient temperature. These heretofore-neglected effects may have a correspondingly significant impact on the performance of heated structures in rock, such as repositories for the containment of radioactive wastes.

  3. Effects of Strain Rates on Mechanical Properties and Fracture Mechanism of DP780 Dual Phase Steel

    NASA Astrophysics Data System (ADS)

    Li, Shengci; Kang, Yonglin; Zhu, Guoming; Kuang, Shuang

    2015-06-01

    The mechanical properties of DP780 dual phase steel were measured by quasi-static and high-speed tensile tests at strain rates between 0.001 and 1000 s-1 at room temperature. The deformation and fracture mechanisms were analyzed by observation of the tensile fracture and microstructure near the fracture. Dynamic factor and feret ratio quantitative methods were applied to study the effect of strain rate on the microstructure and properties of DP780 steel. The constitutive relation was described by a modified Johnson-Cook and Zerilli-Armstrong model. The results showed that the strain rate sensitivity of yield strength is bigger than that of ultimate tensile strength; as strain rate increased, the formation of microcracks and voids at the ferrite/martensite interface can be alleviated; the strain rate effect is unevenly distributed in the plastic deformation region. Moreover, both models can effectively describe the experimental results, while the modified Zerilli-Armstrong model is more accurate because the strain-hardening rate of this model is independent of strain rate.

  4. Fracture mechanics; Proceedings of the 22nd National Symposium, Atlanta, GA, June 26-28, 1990. Vols. 1 & 2

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A. (Editor); Saxena, Ashok (Editor); Mcdowell, David L. (Editor); Atluri, Satya N. (Editor); Newman, James C., Jr. (Editor); Raju, Ivatury S. (Editor); Epstein, Jonathan S. (Editor)

    1992-01-01

    Current research on fracture mechanics is reviewed, focusing on ductile fracture; high-temperature and time-dependent fracture; 3D problems; interface fracture; microstructural aspects of fatigue and fracture; and fracture predictions and applications. Particular attention is given to the determination and comparison of crack resistance curves from wide plates and fracture mechanics specimens; a relationship between R-curves in contained and uncontained yield; the creep crack growth behavior of titanium alloy Ti-6242; a crack growth response in three heat resistant materials at elevated temperature; a crack-surface-contact model for determining effective-stress-intensity factors; interfacial dislocations in anisotropic bimaterials; an effect of intergranular crack branching on fracture toughness evaluation; the fracture toughness behavior of exservice chromium-molybdenum steels; the application of fracture mechanics to assess the significance of proof loading; and a load ratio method for estimating crack extension.

  5. Non-Linear Analysis of Mode II Fracture in the end Notched Flexure Beam

    NASA Astrophysics Data System (ADS)

    Rizov, V.

    2016-03-01

    Analysis is carried-out of fracture in the End Notched Flex- ure (ENF) beam configuration, taking into account the material nonlin- earity. For this purpose, the J-integral approach is applied. A non-linear model, based on the Classical beam theory is used. The mechanical be- haviour of the ENF configuration is described by the Ramberg-Osgood stress-strain curve. It is assumed that the material possesses the same properties in tension and compression. The influence is evaluated of the material constants in the Ramberg-Osgood stress-strain equation on the fracture behaviour. The effect of the crack length on the J-integral value is investigated, too. The analytical approach, developed in the present paper, is very useful for parametric analyses, since the simple formulae obtained capture the essentials of the non-linear fracture in the ENF con- figuration.

  6. Surgical treatment of intraarticular calcaneous fractures of sanders' types II and III. Systematic review

    PubMed Central

    Pelliccioni, Adriano Augusto Antoniazzi; Bittar, Cíntia Kelly; Zabeu, José Luis Amim

    2012-01-01

    Objective This paper aims to identify the most effective surgical technique for intraarticular calcaneal fractures of Sanders' types II and III. Methods Systematic review of comparative randomized clinical trials on surgical treatment of the intraarticular fractures of the calcaneus (Sanders types II and III) that used the questionnaire of the American Orthopaedic Foot and Ankle Society. The studies were identified and retrieved in the following databases - LILACS, MEDLINE/PubMed, Cochrane Library, SciELO, EMBASE, Science Direct, Scopus, Journals@Ovid, ISI Web of Knowledge, Evidence Based Medicine, besides consulting the references of studies accessed. The keywords used Boolean logic (AND and OR): "calcaneus fracture, calcaneous, calcaneal; surgical treatment, management; open reduction, minimally invasive, percutaneous reduction; internal fixation, external fixation. Results We identified only three randomized comparative trials. Each study compared a different technique (external fixation, percutaneous fixation with Kirchner wires and cannulated screws fixation) to the open reduction with internal fixation using plate and screws (considered the standard technique). Conclusion Comparing the series, percutaneous fixation using Kirschner wires presented the best results, however, evidence is insufficient to assert superiority of this treatment in comparison with other surgical techniques. PMID:24453579

  7. Effects of Temperature on Mode II Fracture Toughness of Multidirectional CFRP Laminates

    NASA Astrophysics Data System (ADS)

    Kim, Hyoung Soo; Wang, Wen Xue; Takao, Yoshihiro; Ben, Goichi

    End notched flexure (ENF) tests were performed to investigate the effects of temperature and fiber orientation on Mode II interlaminar fracture behavior, GIIC (GII at the crack initiation), of carbon fiber-reinforced epoxy composites, T800H/#3631. The values of GIIC for three kinds of laminates, [012//012], [22.5/-22.5/08/-22.5/22.5//-22.5/22.5/08/22.5/-22.5] and [45/-45/08/-45/45//-45/45/08/45/-45], with a pre-cracked interface, that is // in each laminate, were obtained at three temperatures, i.e. -100°C, 25°C and 150°C. It is shown that GIIC is obviously affected by the temperature and fiber orientation. The scanning electron microscope (SEM) observation was also carried out to investigate the fracture surface. SEM analysis suggested that the decreased Mode II interlaminar fracture toughness for all kinds of specimens at high temperature could be attributed to temperature-induced matrix property change or fiber-matrix interfacial weakening.

  8. A numerical model of hydro-thermo-mechanical coupling in a fractured rock mass

    SciTech Connect

    Bower, Kathleen Marie

    1996-06-01

    Coupled hydro-thermo-mechanical codes with the ability to model fractured materials are used for predicting groundwater flow behavior in fractured aquifers containing thermal sources. The potential applications of such a code include the analysis of groundwater behavior within a geothermal reservoir. The capability of modeling hydro-thermo systems with a dual porosity, fracture flow model has been previously developed in the finite element code, FEHM. FEHM has been modified to include stress coupling with the dual porosity feature. FEHM has been further developed to implicitly couple the dependence of fracture hydraulic conductivity on effective stress within two dimensional, saturated aquifers containing fracture systems. The cubic law for flow between parallel plates was used to model fracture permeability. The Bartin-Bandis relationship was used to determine the fracture aperture within the cubic law. The code used a Newton Raphson iteration to implicitly solve for six unknowns at each node. Results from a model of heat flow from a reservoir to the moving fluid in a single fracture compared well with analytic results. Results of a model showing the increase in fracture flow due to a single fracture opening under fluid pressure compared well with analytic results. A hot dry rock, geothermal reservoir was modeled with realistic time steps indicating that the modified FEHM code does successfully model coupled flow problems with no convergence problems.

  9. Biomechanical Assessment of Stabilization of Simulated Type II Odontoid Fracture with Case Study

    PubMed Central

    Daniel, Roy T.; Klocke, Noelle; Yandamuri, Soumya S.; Bobinski, Lukas; Duff, John M.; Bucklen, Brandon S.

    2017-01-01

    Study Design Researchers created a proper type II dens fracture (DF) and quantified a novel current posterior fixation technique with spacers at C1–C2. A clinical case study supplements this biomechanical analysis. Purpose Researchers explored their hypothesis that spacers combined with posterior instrumentation (PI) reduce range of motion significantly, possibly leading to better fusion outcomes. Overview of Literature Literature shows that the atlantoaxial joint is unique in allowing segmental rotary motion, enabling head turning. With no intervertebral discs at these joints, multiple ligaments bind the axis to the skull base and to the atlas; an intact odontoid (dens) enhances stability. The most common traumatic injury at these strong ligaments is a type II odontoid fracture. Methods Each of seven specimens (C0–C3) was tested on a custom-built six-degrees-of-freedom spine simulator with constructs of intact state, type II DF, C1–C2 PI, PI with joint capsulotomy (PIJC), PI with spacers (PIS) at C1–C2, and spacers alone (SA). A bending moment of 2.0 Nm (1.5°/sec) was applied in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). One-way analysis of variance with repeated measures was performed. Results DF increased motion to 320%, 429%, and 120% versus intact (FE, LB, and AR, respectively). PI significantly reduced motion to 41%, 21%, and 8%. PIJC showed negligible changes from PI. PIS reduced motion to 16%, 14%, and 3%. SA decreased motion to 64%, 24%, and 54%. Reduced motion facilitated solid fusion in an 89-year-old female patient within 1 year. Conclusions Type II odontoid fractures can lead to acute or chronic instability. Current fixation techniques use C1–C2 PI or an anterior dens screw. Addition of spacers alongside PI led to increased biomechanical rigidity over intact motion and may offer an alternative to established surgical fixation techniques. PMID:28243364

  10. An extension of fracture mechanics/technology to larger and smaller cracks/defects.

    PubMed

    Abé, Hiroyuki

    2009-01-01

    Fracture mechanics/technology is a key science and technology for the design and integrity assessment of the engineering structures. However, the conventional fracture mechanics has mostly targeted a limited size of cracks/defects, say of from several hundred microns to several tens of centimeters. The author and his group has tried to extend that limited size and establish a new version of fracture technology for very large cracks used in geothermal energy extraction and for very small cracks/defects or damage often appearing in the combination of mechanical and electronic components of engineering structures. Those new versions are reviewed in this paper.

  11. Cracked finite elements proposed for NASTRAN. [based on application of finite element method to fracture mechanics

    NASA Technical Reports Server (NTRS)

    Aberson, J. A.; Anderson, J. M.

    1973-01-01

    The recent introduction of special crack-tip singularity elements, usually referred to as cracked elements, has brought the power and flexibility of the finite-element method to bear much more effectively on fracture mechanics problems. This paper recalls the development of two cracked elements and presents the results of some applications proving their accuracy and economy. Judging from the available literature on numerical methods in fracture mechanics, it seems clear that the elements described have been used more extensively than any others in practical fracture mechanics applications.

  12. An extension of fracture mechanics/technology to larger and smaller cracks/defects

    PubMed Central

    Abé, Hiroyuki

    2009-01-01

    Fracture mechanics/technology is a key science and technology for the design and integrity assessment of the engineering structures. However, the conventional fracture mechanics has mostly targeted a limited size of cracks/defects, say of from several hundred microns to several tens of centimeters. The author and his group has tried to extend that limited size and establish a new version of fracture technology for very large cracks used in geothermal energy extraction and for very small cracks/defects or damage often appearing in the combination of mechanical and electronic components of engineering structures. Those new versions are reviewed in this paper. PMID:19907123

  13. Analysis of seismic sources for different mechanisms of fracture growth for microseismic monitoring applications

    SciTech Connect

    Duchkov, A. A.; Stefanov, Yu. P.

    2015-10-27

    We have developed and illustrated an approach for geomechanic modeling of elastic wave generation (microsiesmic event occurrence) during incremental fracture growth. We then derived properties of effective point seismic sources (radiation patterns) approximating obtained wavefields. These results establish connection between geomechanic models of hydraulic fracturing and microseismic monitoring. Thus, the results of the moment tensor inversion of microseismic data can be related to different geomechanic scenarios of hydraulic fracture growth. In future, the results can be used for calibrating hydrofrac models. We carried out a series of numerical simulations and made some observations about wave generation during fracture growth. In particular when the growing fracture hits pre-existing crack then it generates much stronger microseismic event compared to fracture growth in homogeneous medium (radiation pattern is very close to the theoretical dipole-type source mechanism)

  14. The peel test in experimental adhesive fracture mechanics

    NASA Technical Reports Server (NTRS)

    Anderson, G. P.; Devries, K. L.; Williams, M. L.

    1974-01-01

    Several testing methods have been proposed for obtaining critical energy release rate or adhesive fracture energy in bond systems. These tests include blister, cone, lap shear, and peel tests. Peel tests have been used for many years to compare relative strengths of different adhesives, different surface preparation techniques, etc. The present work demonstrates the potential use of the peel test for obtaining adhesive fracture energy values.

  15. Mechanisms and Management of Stress Fractures in Physically Active Persons

    PubMed Central

    Romani, William A.; Gieck, Joe H.; Perrin, David H.; Saliba, Ethan N.; Kahler, David M.

    2002-01-01

    Objective: To describe the anatomy of bone and the physiology of bone remodeling as a basis for the proper management of stress fractures in physically active people. Data Sources: We searched PubMed for the years 1965 through 2000 using the key words stress fracture, bone remodeling, epidemiology, and rehabilitation. Data Synthesis: Bone undergoes a normal remodeling process in physically active persons. Increased stress leads to an acceleration of this remodeling process, a subsequent weakening of bone, and a higher susceptibility to stress fracture. When a stress fracture is suspected, appropriate management of the injury should begin immediately. Effective management includes a cyclic process of activity and rest that is based on the remodeling process of bone. Conclusions/Recommendations: Bone continuously remodels itself to withstand the stresses involved with physical activity. Stress fractures occur as the result of increased remodeling and a subsequent weakening of the outer surface ofthe bone. Once a stress fracture is suspected, a cyclic management program that incorporates the physiology of bone remodeling should be initiated. The cyclic program should allow the physically active person to remove the source of the stress to the bone, maintain fitness, promote a safe return to activity, and permit the bone to heal properly. PMID:16558676

  16. Subcritical fracture propagation in rocks: An examination using the methods of fracture mechanics and non-destructive testing. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Swanson, P. L.

    1984-01-01

    An experimental investigation of tensile rock fracture is presented with an emphasis on characterizing time dependent crack growth using the methods of fracture mechanics. Subcritical fracture experiments were performed in moist air on glass and five different rock types at crack velocities using the double torsion technique. The experimental results suggest that subcritical fracture resistance in polycrystals is dominated by microstructural effects. Evidence for gross violations of the assumptions of linear elastic fracture mechanics and double torsion theory was found in the tests on rocks. In an effort to obtain a better understanding of the physical breakdown processes associated with rock fracture, a series of nondestructive evaluation tests were performed during subcritical fracture experiments on glass and granite. Comparison of the observed process zone shape with that expected on the basis of a critical normal principal tensile stress criterion shows that the zone is much more elongated in the crack propagation direction than predicted by the continuum based microcracking model alone.

  17. Applicability of Fracture Mechanics Methodology to Cracking and Fracture of Concrete.

    DTIC Science & Technology

    1986-02-01

    cracking and fracture. The publicized, annotated bibliography was the one by S. Mindess entitled "The Cracking and Fracture of Concrete: An Annotated...7 --- 109 157.0 Mindess , S.. J. S. Nadeau and J. M. Hay, Effects of Different Curing Conditions on Slow Crack Growth in Cement Paste, Cement and...Concrete Research. Vol. 4, 1974, pp. 953-965 158.0 Nadeau, J3. S.. S. Mindess and J3. MI. Hay, Slow Crack Growth in Cement Paste, Journal of the

  18. Commentary on the management of type II odontoid process fractures in octogenarians: Article by Graffeo et al. and Editorial by Falavigna (J Neurosurgery Spine August 19, 2016)

    PubMed Central

    Epstein, Nancy E.

    2016-01-01

    Background: Establishing a clear treatment paradigm for octogenarians with type II odontoid fractures in hampered by a literature replete with level III articles. Methods: In the study by Graffeo et al., the authors evaluated 111 patients over the age of 79 (average age: 87) with type II odontoid fractures undergoing nonoperative (94 patients) vs. operative intervention (17 total; 15 posterior and 2 anterior). They studied multiple variables and utilized several scales [abbreviated injury scale (AIS), injury severity score (ISS), and the Glasgow coma scale (GCS)] to determine the outcomes of nonoperative vs. operative management. Results: Graffeo et al. concluded that there were no significant differences between nonoperative and operative management for type II odontoid fractures in octogenarians. They found similar frequencies of additional cervical fractures, mechanisms of injury, GCS of 8 or under, AIS/ISS scores, and disposition to “nonhome” facilities. Furthermore, both appeared to have increased mortality rates at 1-year post injury; 13% during hospitalization, 26% within the first post-injury month, and 41% at 1 year. Conclusions: In the editorial by Falavigna, his major criticism of Graffeo's article was the marked disparity in the number of patients in the operative (17 patients) vs. the nonoperative group (94 patients), making it difficult to accept any conclusions as “significant”. He further noted that few prior studies provided level I evidence, and that most, like this one, were level III analyses that did not “significantly” advance our knowledge as to whether to treat octogenarians with type II odontoid fractures operatively vs. nonoperatively. PMID:28028444

  19. Nonsurgical treatment of Mason type II radial head fractures in athletes. A retrospective study

    PubMed Central

    GUZZINI, M.; VADALÀ, A.; AGRÒ, A.; DI SANZO, V.; PIRONI, D.; REDLER, A.; SERLORENZI, P.; PROIETTI, L.; CIVITENGA, C.; MAZZA, D.; LANZETTI, R.M.; FERRETTI, A.

    2016-01-01

    Objective The best treatment for moderately displaced radial head fractures (Mason type II) still remains controversial. In cases of isolated fractures, there is no evidence that a fragment displacement of ≥ 2 mm gives poor results in conservatively treated fractures. Patients and methods We retrospectively reviewed 52 patients (31M, 21F) affected by an isolated Mason type II fracture, treated with a long arm cast for two weeks between 2008 and 2013. All patients had practiced sports before being injured. They were all either bicyclists, or baseball, boxers, basketball, rugby, tennis or football players. The mean follow-up was 36 months. Elbow and forearm range of motion were measured. The Mayo Elbow Performance Score, the Broberg and Morrey rating system and the Disabilities of the Arm, Shoulder and Hand Score (DASH score) were analyzed. Follow-up radiographs were examined for evidence of consolidation, late displacement, early arthritis and non-unions. Results Flexion was slightly impaired in the injured limb when compared to the uninjured limb (137°± 6° versus 139°±5°) as were extension (–3°±6° versus 1°±4°, p < 0.05), supination (86°±6° versus 88°±3°), pronation (87°±4° versus 88°±6°) and valgus deviation (10°±4° versus 8°±3°, p < 0.05). 40 patients had no elbow complaints; 9 patients experienced occasional pain, 2 a mild instability of the elbow, and 4 a mild loss of grip strength. The DASH score was excellent in 48 patients (92.31%). In only 6 cases (11.53%) degenerative changes were greater in formerly injured elbows than in uninjured elbows. All patients returned to their previous sports activities. Conclusions Isolated Mason type II fractures can have a good or excellent mid-term functional outcome even when treated conservatively. PMID:28098055

  20. Integrity of the osteocyte bone cell network in osteoporotic fracture: Implications for mechanical load adaptation

    NASA Astrophysics Data System (ADS)

    Kuliwaba, J. S.; Truong, L.; Codrington, J. D.; Fazzalari, N. L.

    2010-06-01

    The human skeleton has the ability to modify its material composition and structure to accommodate loads through adaptive modelling and remodelling. The osteocyte cell network is now considered to be central to the regulation of skeletal homeostasis; however, very little is known of the integrity of the osteocyte cell network in osteoporotic fragility fracture. This study was designed to characterise osteocyte morphology, the extent of osteocyte cell apoptosis and expression of sclerostin protein (a negative regulator of bone formation) in trabecular bone from the intertrochanteric region of the proximal femur, for postmenopausal women with fragility hip fracture compared to age-matched women who had not sustained fragility fracture. Osteocyte morphology (osteocyte, empty lacunar, and total lacunar densities) and the degree of osteocyte apoptosis (percent caspase-3 positive osteocyte lacunae) were similar between the fracture patients and non-fracture women. The fragility hip fracture patients had a lower proportion of sclerostin-positive osteocyte lacunae in comparison to sclerostin-negative osteocyte lacunae, in contrast to similar percent sclerostin-positive/sclerostin-negative lacunae for non-fracture women. The unexpected finding of decreased sclerostin expression in trabecular bone osteocytes from fracture cases may be indicative of elevated bone turnover and under-mineralisation, characteristic of postmenopausal osteoporosis. Further, altered osteocytic expression of sclerostin may be involved in the mechano-responsiveness of bone. Optimal function of the osteocyte cell network is likely to be a critical determinant of bone strength, acting via mechanical load adaptation, and thus contributing to osteoporotic fracture risk.

  1. Mechanical behavior and fracture characteristics of off-axis fiber composites. 2: Theory and comparisons

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.

    1978-01-01

    The mechanical behavior and stresses inducing fracture modes of unidirectional high-modulus graphite-fiber/epoxy composites subjected to off-axis tensile loads were investigated theoretically. The investigation included the use of composite mechanics, combined-stress failure criteria, and finite-element stress analysis. The results are compared with experimental data and led to the formulation of criteria and convenient plotting procedures for identifying, characterizing, and quantifying these fracture modes.

  2. Fracture Mechanics Analyses of the Slip-Side Joggle Regions of Wing-Leading-Edge Panels

    NASA Technical Reports Server (NTRS)

    Raju, Ivatury S.; Knight, Norman F., Jr.; Song, Kyongchan; Phillips, Dawn R.

    2011-01-01

    The Space Shuttle wing-leading edge consists of panels that are made of reinforced carbon-carbon. Coating spallation was observed near the slip-side region of the panels that experience extreme heating. To understand this phenomenon, a root-cause investigation was conducted. As part of that investigation, fracture mechanics analyses of the slip-side joggle regions of the hot panels were conducted. This paper presents an overview of the fracture mechanics analyses.

  3. Effects of cement augmentation on the mechanical stability of multilevel spine after vertebral compression fracture

    PubMed Central

    Wang, Tian; Pelletier, Matthew H.; Walsh, William R.

    2016-01-01

    Background Studies on the effects of cement augmentation or vertebroplasty on multi-level spine after vertebral compression fractures are lacking. This paper seeks to establish a 3-vertebrae ovine model to determine the impact of compression fracture on spine biomechanics, and to discover if cement augmentation can restore mechanical stability to fractured spine. Methods Five lumbar spine segments (L1-L3) were obtained from 5-year-old female Merino sheep. Standardized wedge-compression fractures were generated in each L2 vertebra, and then augmented with polymethyl methacrylate (PMMA) cement mixed with 30% barium sulphate powder. Biomechanical pure moment testing in axial rotation (AR), flexion/extension (FE) and lateral bending (LB) was carried out in the intact, fractured and repaired states. Range of motion (ROM) and neutral zone (NZ) parameters were compared, and plain radiographs taken at every stage. Results Except for a significant increase in ROM between the intact and fractured states in AR between L1 and L2 (P<0.05), there were no other significant differences in ROM or NZ between the other groups. There was a trend towards an increase in ROM and NZ in all directions after fracture, but this did not reach significance. Normal biomechanics was only minimally restored after augmentation. Conclusions Results suggest that cement augmentation could not restore mechanical stability of fractured spine. Model-specific factors may have had a role in these findings. Caution should be exercised when applying these results to humans. PMID:27683707

  4. Variations in Fracturing Mechanisms Observed by Broadband Microseismic Monitoring of Hydraulic Treatment

    NASA Astrophysics Data System (ADS)

    Tang, Y.; Niu, F.; Chen, H.; Zuo, Q.

    2015-12-01

    Hydraulic fracturing is the key stimulation technology to improve unconventional hydrocarbon recovery nowadays. Stimulation increases permeability of tight formations by causing fractures at depth. It involves pumping high-pressure fluid into reservoir rocks to force the opening of cracks, which could allow oil and gas to flow freely. The progress of a fracturing operation must be monitored carefully as fracturing could activate existing faults, leading the fluid mixed with chemicals to propagate beyond the targeted treatment zone. In order to study dynamic processes involved in hydraulic fracturing, we deployed a small-scale seismic array consisting of 22 broadband seismographs at the surface above a hydraulic fracturing area to monitor the whole fracturing progress. We made continuous recording for 20 days, and detected a total of 961 microseismic events with relatively high signal-to-noise ratio (SNR) recordings. We found that these events occurred either during the fracturing operation or after the fluid pumping. Some of the events also do not seem to be directly induced by the pumping, based on their locations and sizes. We determined the focal mechanisms of all events using the P-wave polarity data, and found that both the microseismicity and their focal mechanisms exhibit significant spatial and temporal variations. This variability can be associated with the hydraulic treatment, pre-existing faults, as well as the evolving stress field during the treatment. We computed the Coulomb stress changes of the observed seismicity to seek its contribution to the observed seismic variability.

  5. A Fracture-Mechanical Model of Crack Growth and Interaction: Application to Pre-eruptive Seismicity

    NASA Astrophysics Data System (ADS)

    Matthews, C.; Sammonds, P.; Kilburn, C.

    2007-12-01

    A greater understanding of the physical processes occurring within a volcano is a key aspect in the success of eruption forecasting. By considering the role of fracture growth, interaction and coalescence in the formation of dykes and conduits as well as the source mechanism for observed seismicity we can create a more general, more applicable model for precursory seismicity. The frequency of volcano-tectonic earthquakes, created by fracturing of volcanic rock, often shows a short-term increase prior to eruption. Using fracture mechanics, the model presented here aims to determine the conditions necessary for the acceleration in fracture events which produces the observed pre-eruptive seismicity. By focusing on the cause of seismic events rather than simply the acceleration patterns observed, the model also highlights the distinction between an accelerating seismic sequence ending with an eruption and a short-term increase which returns to background levels with no activity occurring, an event also observed in the field and an important capability if false alarms are to be avoided. This 1-D model explores the effects of a surrounding stress field and the distribution of multi-scale cracks on the interaction and coalescence of these cracks to form an open pathway for magma ascent. Similarly to seismic observations in the field, and acoustic emissions data from the laboratory, exponential and hyperbolic accelerations in fracturing events are recorded. Crack distribution and inter-crack distance appears to be a significant controlling factor on the evolution of the fracture network, dominating over the effects of a remote stress field. The generality of the model and its basis on fundamental fracture mechanics results makes it applicable to studies of fracture networks in numerous situations. For example looking at the differences between high temperature fracture processes and purely brittle failure the model can be similarly applied to fracture dynamics in the

  6. How tough is bone? Application of elastic-plastic fracture mechanics to bone.

    PubMed

    Yan, Jiahau; Mecholsky, John J; Clifton, Kari B

    2007-02-01

    Bone, with a hierarchical structure that spans from the nano-scale to the macro-scale and a composite design composed of nano-sized mineral crystals embedded in an organic matrix, has been shown to have several toughening mechanisms that increases its toughness. These mechanisms can stop, slow, or deflect crack propagation and cause bone to have a moderate amount of apparent plastic deformation before fracture. In addition, bone contains a high volumetric percentage of organics and water that makes it behave nonlinearly before fracture. Many researchers used strength or critical stress intensity factor (fracture toughness) to characterize the mechanical property of bone. However, these parameters do not account for the energy spent in plastic deformation before bone fracture. To accurately describe the mechanical characteristics of bone, we applied elastic-plastic fracture mechanics to study bone's fracture toughness. The J integral, a parameter that estimates both the energies consumed in the elastic and plastic deformations, was used to quantify the total energy spent before bone fracture. Twenty cortical bone specimens were cut from the mid-diaphysis of bovine femurs. Ten of them were prepared to undergo transverse fracture and the other 10 were prepared to undergo longitudinal fracture. The specimens were prepared following the apparatus suggested in ASTM E1820 and tested in distilled water at 37 degrees C. The average J integral of the transverse-fractured specimens was found to be 6.6 kPa m, which is 187% greater than that of longitudinal-fractured specimens (2.3 kPa m). The energy spent in the plastic deformation of the longitudinal-fractured and transverse-fractured bovine specimens was found to be 3.6-4.1 times the energy spent in the elastic deformation. This study shows that the toughness of bone estimated using the J integral is much greater than the toughness measured using the critical stress intensity factor. We suggest that the J integral method is

  7. Multi-Scale Fracture Mechanics of 3-D Reinforced Composites

    DTIC Science & Technology

    2010-02-26

    technique and cohesive formulation for crack extension. A representative volume element (RVE) approach employed for homogenized stiffness and stress...the mesh-independent crack propagation technique and cohesive formulation for crack extension. A representative volume element (RVE) approach employed...technology for application and development of progressive fracture modeling, SCSAM is a technique for modeling complex multiple site initiation and

  8. The application of fracture mechanics to failure analysis of photovoltaic solar modules

    NASA Technical Reports Server (NTRS)

    Chen, C. P.; Leipold, M. H.

    1981-01-01

    Cracking of silicon solar cells and solar module transparent cover panels such as glass or polymethylmethacrylate (PMMA) is a major cause of photovoltaic solar module failure in field service. Silicon and cover materials are brittle, and cracking of these materials is expected to result from the extension of preexisting flaws under stress. Study of the cracking mechanisms is therefore an appropriate area for the application of fracture mechanics principles. In this study, fracture mechanics techniques were employed to identify the mode of crack propagation, to examine the fracture-initiating flaw, to estimate the nature and magnitude of fracture stress in the field, and to predict analytically the service lifetime. Recommendations for corrective actions are also made.

  9. Correlating laboratory observations of fracture mechanical properties to hydraulically-induced microseismicity in geothermal reservoirs.

    SciTech Connect

    Stephen L. Karner, Ph.D

    2006-02-01

    To date, microseismicity has provided an invaluable tool for delineating the fracture network produced by hydraulic stimulation of geothermal reservoirs. While the locations of microseismic events are of fundamental importance, there is a wealth of information that can be gleaned from the induced seismicity (e.g. fault plane solutions, seismic moment tensors, source characteristics). Closer scrutiny of the spatial and temporal evolution of seismic moment tensors can shed light on systematic characteristics of fractures in the geothermal reservoir. When related to observations from laboratory experiments, these systematic trends can be interpreted in terms of mechanical processes that most likely operate in the fracture network. This paper reports on mechanical properties that can be inferred from observations of microseismicity in geothermal systems. These properties lead to interpretations about fracture initiation, seismicity induced after hydraulic shut-in, spatial evolution of linked fractures, and temporal evolution of fracture strength. The correlations highlight the fact that a combination of temperature, stressing rate, time, and fluid-rock interactions can alter the mechanical and fluid transport properties of fractures in geothermal systems.

  10. A revisit to high-rate mode-II fracture characterization of composites with Kolsky bar techniques.

    SciTech Connect

    Lu, Wei-Yang; Song, Bo; Jin, Huiqing

    2010-03-01

    Nowadays composite materials have been extensively utilized in many military and industrial applications. For example, the newest Boeing 787 uses 50% composite (mostly carbon fiber reinforced plastic) in production. However, the weak delamination strength of fiber reinforced composites, when subjected to external impact such as ballistic impact, has been always potential serious threats to the safety of passengers. Dynamic fracture toughness is a critical indicator of the performance from delamination in such impact events. Quasi-static experimental techniques for fracture toughness have been well developed. For example, end notched flexure (ENF) technique, which is illustrated in Fig. 1, has become a typical method to determined mode-II fracture toughness for composites under quasi-static loading conditions. However, dynamic fracture characterization of composites has been challenging. This has resulted in conflictive and confusing conclusions in regard to strain rate effects on fracture toughness of composites.

  11. Molecular mechanisms of osteoporotic hip fractures in elderly women.

    PubMed

    Föger-Samwald, Ursula; Vekszler, György; Hörz-Schuch, Edith; Salem, Sylvia; Wipperich, Markus; Ritschl, Peter; Mousavi, Mehdi; Pietschmann, Peter

    2016-01-01

    A common manifestation of age-related bone loss and resultant osteoporosis are fractures of the hip. Age-related osteoporosis is thought to be determined by a number of intrinsic factors including genetics, hormonal changes, changes in levels of oxidative stress, or an inflammatory status associated with the aging process. The aim of this study was to investigate gene expression and bone architecture in bone samples derived from elderly osteoporotic women with hip fractures (OP) in comparison to bone samples from age matched women with osteoarthritis of the hip (OA). Femoral heads and adjacent neck tissue were collected from 10 women with low-trauma hip fractures (mean age 83±6) and consecutive surgical hip replacement. Ten bone samples from patients undergoing hip replacement due to osteoarthritis (mean age 80±5) served as controls. One half of each bone sample was subjected to gene expression analysis. The second half of each bone sample was analyzed by microcomputed tomography. From each half, samples from four different regions, the central and subcortical region of the femoral head and neck, were analyzed. We could show a significantly decreased expression of the osteoblast related genes RUNX2, Osterix, Sclerostin, WNT10B, and Osteocalcin, a significantly increased ratio of RANKL to Osteoprotegerin, and a significantly increased expression of the enzymes superoxide dismutase 2 (SOD2) and glutathione peroxidase GPX3, and of the inflammatory cytokine IL6 in bone samples from hip fracture patients compared to controls. Major microstructural changes in OP bone were seen in the neck and were characterized by a significant decrease of bone volume, trabecular number, and connectivity density and a significant increase of trabecular separation. In conclusion, our data give evidence for a decreased expression of osteoblast related genes and increased expression of osteoclast related genes. Furthermore, increased expression of SOD2 and GPX3 suggest increased

  12. Micro-mechanical analysis of damage growth and fracture in discontinuous fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Goree, James G.; Richardson, David E.

    1991-01-01

    An experimental verification is presented for a new two parameter fracture model based on the equivalent remote biaxial stresses (ERBS). A detailed comparison is made between the new theory and the constant K(sub IC) approach of linear elastic fracture mechanics (LEFM). Fracture is predicted through a failure curve representing the change in a variable fracture toughness K(sub IC) with the ERBS ratio B(sub E). The nonsingular term (T) in the series expansion of the near crack-tip transverse stress is included in the model. Experimental results for polymethyl methacrylate (PPMA) show that the theory can account for the effects of geometry on fracture toughness as well as indicate the initiation of crack branching. It is shown that the new criterion predicts failure for PMMA with a 95 percent confidence zone which is nearly three times smaller than that of the LEFM K(sub IC) approach.

  13. Biomechanical analysis of the mechanism of elbow fracture-dislocations by compression force.

    PubMed

    Wake, Hirofumi; Hashizume, Hiroyuki; Nishida, Keiichiro; Inoue, Hajime; Nagayama, Noriyuki

    2004-01-01

    Fracture-dislocations of the coronoid and olecranon were produced experimentally, and their onset mechanisms were analyzed to clarify the effects of compression force on the coronoid and olecranon. The study used two-dimensional finite element method (2D-FEM) simulations and static loading experiments. The latter applied axial force distally to 40 cadaveric elbows. Posterior fracture-dislocations occurred between 15 degrees of extension and 30 degrees of flexion, anterior or posterior fracture-dislocations at 60 degrees, and only anterior fracture-dislocations at 90 degrees. Injuries were mainly to anterior or posterior support structures. The 2D-FEM simulations showed that the stress concentration areas moved from the coronoid process to the olecranon as position changed from extension to flexion. The very high frequency of concurrent fracture-dislocations of radial head or neck in the current study indicated that the radial head may also function as a stabilizer in the anterior support system.

  14. On the mechanical interaction between a fluid-filled fracture and the earth's surface

    USGS Publications Warehouse

    Pollard, D.D.; Holzhausen, G.

    1979-01-01

    The mechanical interaction between a fluid-filled fracture (e.g., hydraulic fracture joint, or igneous dike) and the earth's surface is analyzed using a two-dimensional elastic solution for a slit of arbitrary inclination buried beneath a horizontal free surface and subjected to an arbitrary pressure distribution. The solution is obtained by iteratively superimposing two fundamental sets of analytical solutions. For uniform internal pressure the slit behaves essentially as if it were in an infinite region if the depth-to-center is three times greater than the half-length. For shallower slits interaction with the free surface is pronounced: stresses and displacements near the slit differ by more than 10% from values for the deeply buried slit. The following changes are noted as the depth-to-center decreases: 1. (1) the mode I stress intensity factor increases for both ends of the slit, but more rapidly at the upper end; 2. (2) the mode II stress-intensity factor is significantly different from zero (except for vertical slits) suggesting propagation out of the original plane of the slit; 3. (3) displacements of the slit wall are asymmetric such that the slit gaps open more widely near the upper end. Similar changes are noted if fluid density creates a linear pressure gradient that is smaller than the lithostatic gradient. Under such conditions natural fractures should propagate preferentially upward toward the earth's surface requiring less pressure as they grow in length. If deformation near the surface is of interest, the model should account explicitly for the free surface. Stresses and displacements at the free surface are not approximated very well by values calculated along a line in an infinite region, even when the slit is far from the line. As depth-to-center of a shallow pressurized slit decreases, the following changes are noted: 1. (1) displacements of the free surface increase to the same order of magnitude as the displacements of the slit walls, 2. (2

  15. E. coli RS2GFP Retention Mechanisms in Laboratory-Scale Fractured Rocks: A Statistical Model

    NASA Astrophysics Data System (ADS)

    Rodrigues, S. N.; Qu, J.; Dickson, S. E.

    2011-12-01

    With billions of gallons of groundwater being withdrawn every day in the US and Canada, it is imperative to understand the mechanisms which jeopardize this resource and the health of those who rely on it. Porous media aquifers have typically been considered to provide significant filtration of particulate matter (e.g. microorganisms), while the fractures in fractured rock aquifers and aquitards are considered to act as contaminant highways allowing a large fraction of pathogens to travel deep into an aquifer relatively quickly. Recent research results indicate that fractured rocks filter out more particulates than typically believed. The goal of the research presented here is to quantify the number of E. coli RS2GFP retained in a single, saturated, laboratory-scale fracture, and to relate the retention of E. coli RS2GFP to the aperture field characteristics and groundwater flow rate. To achieve this goal, physical experiments were conducted at the laboratory-scale to quantify the retention of E. coli RS2GFP through several single, saturated, dolomitic limestone fractures under a range of flow rates. These fractures were also cast with a transparent epoxy in order to visualize the transport mechanisms in the various different aperture fields. The E. coli RS2GFP is tagged with a green-fluorescent protein (GFP) that is used to obtain visualization data when excited by ultraviolet light. A series of experiments was conducted, each of which involved the release of a known number of E. coli RS2GFP at the upstream end of the fracture and measuring the effluent concentration profile. These experiments were conducted using both the natural rock and transparent cast of several different aperture fields, under a range of flow rates. The effects of different aperture field characteristics and flow rates on the retention of E. coli RS2GFP will be determined by conducting a statistical analysis of the retention data under different experimental conditions. The images captured

  16. Tensile fracture resistance mechanisms in brittle polycrystals: An ultrasonics and in situ microscopy investigation

    NASA Astrophysics Data System (ADS)

    Swanson, Peter L.

    1987-07-01

    A zone of distributed microcracking is often suggested to accompany tensile macrocrack propagation in rocks and ceramics. The microcracking is said to be largely responsible for (1) high values of fracture energy, (2) increasing resistance to fracture with crack extension and (3) the dependence of fracture mechanics data on the experimental setup. In the present paper, the material breakdown processes in imperfectly elastic Westerly granite are investigated using ultrasonic wave probing and in situ microscopy during mode I fracture experiments. These observations are compared with an in situ reflection/transmission microscopy investigation of mode I fracture in a near-ideal elastic polycrystalline alumina (Al2O3). As defined by the spatial distribution of longitudinal and surface wave attenuation in wedge-loaded double-cantilever beam specimens of Westerly granite, the fracture process zone is elongate in the direction of fracture propagation (15-40 mm long by 1-2 grain dimensions wide; grain size 0.75 mm). As revealed by in situ reflection microscopy, the ultrasonic wave energy is partially transmitted through the developing fracture surfaces via two sources of crack interface traction: (1) remnant islands of unfractured material left behind the advancing fracture front and (2) geometrical interlocking of the microstructurally rough fracture surfaces. A similar zone of crack flank tractions is found in the alumina (greater than 2000 μm long; grain size 20-100 μm). No evidence of a diffuse kidney-shaped cloud of microcracking distributed ahead of the main fracture tip (predicted by many fracture models) was found in either material. Instead, interface-localized microcracking was observed to operate at positions where the tractions, or restraining forces, are transmitted across the nascent fracture surfaces. Crack flank tractions shield the main crack tip from high levels of stress and are relieved by friction-induced microcracking and microcrack rupture of intact

  17. Mechanisms of orbital floor fractures: a clinical, experimental, and theoretical study.

    PubMed Central

    Bullock, J D; Warwar, R E; Ballal, D R; Ballal, R D

    1999-01-01

    PURPOSE: The purpose of this study was to investigate the two accepted mechanisms of the orbital blow-out fracture (the hydraulic and the buckling theories) from a clinical, experimental, and theoretical standpoint. METHODS: Clinical cases in which blow-out fractures resulted from both a pure hydraulic mechanism and a pure buckling mechanism are presented. Twenty-one intact orbital floors were obtained from human cadavers. A metal rod was dropped, experimentally, onto each specimen until a fracture was produced, and the energy required in each instance was calculated. A biomathematical model of the human bony orbit, depicted as a thin-walled truncated conical shell, was devised. Two previously published (by the National Aeronautics Space Administration) theoretical structural engineering formulas for the fracture of thin-walled truncated conical shells were used to predict the energy required to fracture the bone of the orbital floor via the hydraulic and buckling mechanisms. RESULTS: Experimentally, the mean energy required to fracture the bone of the human cadaver orbital floor directly was 78 millijoules (mj) (range, 29-127 mj). Using the engineering formula for the hydraulic theory, the predicted theoretical energy is 71 mj (range, 38-120 mj); for the buckling theory, the predicted theoretical energy is 68 mj (range, 40-106 mj). CONCLUSION: Through this study, we have experimentally determined the amount of energy required to fracture the bone of the human orbital floor directly and have provided support for each mechanism of the orbital blow-out fracture from a clinical and theoretical basis. Images FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5A FIGURE 5B FIGURE 5E FIGURE 5F PMID:10703119

  18. Evolution of Stiffness and Permeability in Fractures Subject to - and Mechanically-Activated Dissolution

    NASA Astrophysics Data System (ADS)

    Faoro, I.; Elsworth, D.; Candela, T.

    2013-12-01

    Strong feedbacks link thermal gradients (T), hydrologic flow (H), chemical alteration (C) and mechanical deformation (M) in fractured rock. These processes are strongly interconnected since one process effects the initiation and progress of another. Dissolution and precipitation of minerals are affected by temperature and stress, and can result in significant changes in permeability and solute transport characteristics. Understanding these couplings is important for oil, gas, and geothermal reservoir engineering and for waste disposal in underground repositories and reservoirs. In order to experimentally investigate the interactions between THCM processes in a natural stressed fracture, we report on heated ( up to 150C) flow-through experiments on fractured core samples of Westerly granite. These experiments are performed to examine the influence of thermally and mechanically activated dissolution on the mechanical (stress/strain) and transport (permeability) characteristics of fractures. The evolutions of both the permeability and stiffness of the sample are recorded as the experimental thermal conditions change and chemical alteration progresses. Furthermore efflux of dissolved mineral mass is measured periodically to provide a record of the net mass removal, to correlate this with observed changes in fracture aperture, defined by the flow test. During the experiments the fracture shows high hydraulic sensitivity to the changing conditions of stress and temperature. Significant variation of the effluent fluid chemistry is observed. We argue that the formation of clay (Kaolinite) is the main mechanism responsible for the permanent change in permeability recorded at higher confining stresses (40 MPa).

  19. A Mixed-Mode (I-II) Fracture Criterion for AS4/8552 Carbon/Epoxy Composite Laminate

    NASA Astrophysics Data System (ADS)

    Karnati, Sidharth Reddy

    A majority of aerospace structures are subjected to bending and stretching loads that introduce peel and shear stresses between the plies of a composite laminate. These two stress components cause a combination of mode I and II fracture modes in the matrix layer of the composite laminate. The most common failure mode in laminated composites is delamination that affects the structural integrity of composite structures. Damage tolerant designs of structures require two types of materials data: mixed-mode (I-II) delamination fracture toughness that predicts failure and delamination growth rate that predicts the life of the structural component. This research focuses determining mixed-mode (I-II) fracture toughness under a combination of mode I and mode II stress states and then a fracture criterion for AS4/8552 composite laminate, which is widely used in general aviation. The AS4/8552 prepreg was supplied by Hexcel Corporation and autoclave fabricated into a 20-ply unidirectional laminate with an artificial delamination by a Fluorinated Ethylene Propylene (FEP) film at the mid-plane. Standard split beam specimens were prepared and tested in double cantilever beam (DCB) and end notched flexure modes to determine mode I (GIC) and II (GIIC) fracture toughnesses, respectively. The DCB specimens were also tested in a modified mixed-mode bending apparatus at GIIm /GT ratios of 0.18, 0.37, 0.57 and 0.78, where GT is total and GIIm is the mode II component of energy release rates. The measured fracture toughness, GC, was found to follow the locus a power law equation. The equation was validated for the present and literature experimental data.

  20. Direct Observations of Fracture and the Damage Mechanics of Ceramics

    DTIC Science & Technology

    1988-10-31

    microplasticity up to the fracture load. d. It shculd have low enough strength in tension and compression to enable strength measurements at easily accessible...15jm. SEM examination of the grains after large amounts of deformation indicated that the grains are brittle without any evidence of microplasticity . In...and microplasticity in polycrystalline alumina", J.Mater.Sci., 12(1977)791-796. 93. J Lankford, "Compressive microfracture and indentation damage in A1

  1. Scaling of Crack Surfaces and Implications for Fracture Mechanics

    NASA Astrophysics Data System (ADS)

    Morel, Stéphane; Schmittbuhl, Jean; Bouchaud, Elisabeth; Valentin, Gérard

    2000-08-01

    The scaling laws describing the roughness development of crack surfaces are incorporated into the Griffith criterion. We show that, in the case of a Family-Vicsek scaling, the energy balance leads to a purely elastic brittle behavior. On the contrary, it appears that an anomalous scaling reflects an R-curve behavior associated with a size effect of the critical resistance to crack growth in agreement with the fracture process of heterogeneous brittle materials exhibiting a microcracking damage.

  2. Scaling of crack surfaces and implications for fracture mechanics

    PubMed

    Morel; Schmittbuhl; Bouchaud; Valentin

    2000-08-21

    The scaling laws describing the roughness development of crack surfaces are incorporated into the Griffith criterion. We show that, in the case of a Family-Vicsek scaling, the energy balance leads to a purely elastic brittle behavior. On the contrary, it appears that an anomalous scaling reflects an R-curve behavior associated with a size effect of the critical resistance to crack growth in agreement with the fracture process of heterogeneous brittle materials exhibiting a microcracking damage.

  3. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

    Kaufman, L.; Clougherty, E. V.; Nesor, H.

    1971-01-01

    Fracture energies of WC-6Co, Boride 5 (ZrB2+SiC), Boride 8(ZrB2+SiC+C) and Boride 8-M2(ZrB2+SiC+C) were measured by slow bend and impact tests of notched charpy bars. Cobalt bonded tungsten carbide exhibited impact energies of 0.76 ft-lb or 73.9 in-lb/square inch. Boride 5 and the Boride 8 exhibit impact energies one third and one quarter of that observed for WC-6Co comparing favorably with measurements for SiC and Si3N4. Slow bend-notched bar-fracture energies for WC-6Co were near 2.6 in-lb/square inch or 1/20 the impact energies. Slow bend energies for Boride 8-M2, Boride 8 and Boride 5 were 58%, 42% and 25% of the value observed for WC-6Co. Fractograph showed differences for WC-6Co where slow bend testing resulted in smooth transgranular cleavage while samples broken by impact exhibited intergranular failures. By contrast the boride fractures showed no distinction based on testing method. Fabrication studies were conducted to effect alteration of the boride composites by alloying and introduction of graphite cloth.

  4. Fracture mechanics analysis of the dentine-luting cement interface.

    PubMed

    Ryan, A K; Mitchell, C A; Orr, J F

    2002-01-01

    The objectives of this study were to determine the fracture toughness of adhesive interfaces between dentine and clinically relevant, thin layers of dental luting cements. Cements tested included a conventional glass-ionomer, F (Fuji 1), a resin-modified glass-ionomer, FP (Fuji Plus) and a compomer cement, D (DyractCem). Ten miniature short-bar chevron notch specimens were manufactured for each cement, each comprising a 40 microm thick chevron of lute, between two 1.5 mm thick blocks of bovine dentine, encased in resin composite. The interfacial K(IC) results (MN/m3/2) were median (range): F; 0.152 (0.14-0.16), FP; 0.306 (0.27-0.37), D; 0.351 (0.31-0.37). Non-parametric statistical analysis showed that the fracture toughness of F was significantly lower (p <0.05) than those of FP or D, and all were significantly lower than values for monolithic cement specimens. Scanning electron microscopy of the specimens suggested crack propagation along the interface. However, energy dispersive X-ray analysis indicated that failure was cohesive within the cement. It is concluded that the fracture toughness of luting cement was lowered by cement-dentine interactions.

  5. Fracture mechanisms of retrieved titanium screw thread in dental implant.

    PubMed

    Yokoyama, Ken'ichi; Ichikawa, Tetsuo; Murakami, Hiroki; Miyamoto, Youji; Asaoka, Kenzo

    2002-06-01

    Titanium and its alloy are increasingly attracting attention for use as biomaterials. However, delayed fracture of titanium dental implants has been reported, and factors affecting the acceleration of corrosion and fatigue have to be determined. The fractured surface of a retrieved titanium screw and metallurgical structures of a dental implant system were analyzed. The outer surface of the retrieved screw had a structure different from that of the as-received screw. It was confirmed that a shear crack initiated at the root of the thread and propagated into the inner section of the screw. Gas chromatography revealed that the retrieved screw had absorbed a higher amount of hydrogen than the as-received sample. The grain structure of a titanium screw, immersed in a solution known to induce hydrogen absorption, showed features similar to those of the retrieved screw. It was concluded that titanium in a biological environment absorbs hydrogen and this may be the reason for delayed fracture of a titanium implant.

  6. Fracture mechanics; Proceedings of the Nineteenth National Symposium, San Antonio, TX, June 30-July 2, 1986

    SciTech Connect

    Cruse, T.A.

    1988-01-01

    The papers contained in this volume provide an overview of current theoretical and experimental research in the field of fracture mechanics. Topics discussed include three-dimensional issues, computational and analytical issues, damage tolerance and fatigue, elastoplastic fracture, dynamic inelastic fracture, and crack arrest theory and applications. Papers are presented on approximate methods for analysis of dynamic crack growth and arrest, constraint-loss model for the growth of surface fatigue cracks, fatigue crack growth in aircraft main landing gear wheels, and near-threshold crack growth in nickel-base superalloys.

  7. The fracture mechanics of human bone: influence of disease and treatment

    PubMed Central

    Zimmermann, Elizabeth A; Busse, Björn; Ritchie, Robert O

    2015-01-01

    Aging and bone diseases are associated with increased fracture risk. It is therefore pertinent to seek an understanding of the origins of such disease-related deterioration in bone's mechanical properties. The mechanical integrity of bone derives from its hierarchical structure, which in healthy tissue is able to resist complex physiological loading patterns and tolerate damage. Indeed, the mechanisms through which bone derives its mechanical properties make fracture mechanics an ideal framework to study bone's mechanical resistance, where crack-growth resistance curves give a measure of the intrinsic resistance to the initiation of cracks and the extrinsic resistance to the growth of cracks. Recent research on healthy cortical bone has demonstrated how this hierarchical structure can develop intrinsic toughness at the collagen fibril scale mainly through sliding and sacrificial bonding mechanisms that promote plasticity. Furthermore, the bone-matrix structure develops extrinsic toughness at much larger micrometer length-scales, where the structural features are large enough to resist crack growth through crack-tip shielding mechanisms. Although healthy bone tissue can generally resist physiological loading environments, certain conditions such as aging and disease can significantly increase fracture risk. In simple terms, the reduced mechanical integrity originates from alterations to the hierarchical structure. Here, we review how human cortical bone resists fracture in healthy bone and how changes to the bone structure due to aging, osteoporosis, vitamin D deficiency and Paget's disease can affect the mechanical integrity of bone tissue. PMID:26380080

  8. Development and fracture mechanics data for 6Al-6V-2 Sn titanium alloy

    NASA Technical Reports Server (NTRS)

    Fiftal, C. F.; Beck, E. J.

    1974-01-01

    Fracture mechanics properties of 6Al-6V-2Sn titanium in the annealed, solution-treated, and aged condition are presented. Tensile, fracture toughness, cyclic flaw growth, and sustained-load threshold tests were conducted. Both surface flaw and compact tension-specimen geometries were employed. Temperatures and/or environments used were -65 F (220 K) air, ambient, 300 F (422 K) air, and room-temperature air containing 10 and 100% relative humidity.

  9. Modeling naturally fractured reservoirs: From experimental rock mechanics to flow simulation

    NASA Astrophysics Data System (ADS)

    Rijken, Margaretha Catharina Maria

    Fractures have a big impact on reservoir production but are inherently difficult to quantify. This study gives a robust and practical workflow to obtain a mechanically consistent naturally fractured reservoir model without direct sampling of the fracture network. The three tiers of the workflow are: (1) subcritical testing, (2) geomechanical modeling, and (3) flow modeling. Subcritical fracture index, a rock property, has been shown to influence fracture attributes such as length, spacing and connectivity. Subcritical tests show that the average subcritical index for sandstones in ambient air is around 62, whereas the average value for microstructurally comparable carbonates samples is 120. Thin-section analysis shows that an increase in cement content increases the subcritical index. Furthermore, sandstone samples containing more than 15% carbonate cement, sandstone samples containing more than 40% clay, and pure carbonate samples exhibit a large drop in subcritical index when the environment is changed from ambient air or oil to fresh water or brine. Geomechanical modeling has shown that the mechanical bed thickness has a large influence on fracture pattern characteristics and has the potential to overshadow fracture pattern changes due to strain level, strain anisotropy and subcritical index. Furthermore, an increase in strain anisotropy reduces the number of dominant through-going fracture sets and decreases the fracture spacing between the through-going fractures. This spacing variation not only influences the preferential drainage direction, it can also enhance the drainage efficiency, because more rock is exposed to the through-going fractures which are more likely to be intersected by a borehole. The level of detail provided by the geomechanical model greatly exceeds the level of detail normally used in reservoir simulation. Therefore, upscaling of the geomechanically generated fracture patterns is necessary for practical flow modeling. This study shows

  10. Damage mechanics approach to remove the constraint dependence of elastic-plastic fracture toughness

    NASA Astrophysics Data System (ADS)

    Wang, T.-J.; Kuang, Z.-B.

    1995-02-01

    It is now generally agreed that the applicability of a one-parameter J-based ductile fracture approach is limited to so-called high constraint crack geometries, and that the elastic-plastic fracture toughness J(Ic) is not a material constant but strongly specimen geometry constraint-dependent. In this paper, the constraint effect on elastic-plastic fracture toughness is investigated by use of a continuum damage mechanics approach. Based on a new local damage theory for ductile fracture (proposed by the author) which has a clear physical meaning and can describe both deformation and constraint effects on ductile fracture, a relationship is described between the conventional elastic-plastic fracture toughness, J(Ic), and crack tip constraint, characterized by crack tip stress triaxiality T. Then, a new parameter J(dc) (and associated criterion, J(d) = J(dc)) for ductile fracture is proposed. Experiments show that toughness variation with specimen geometry constraint changes can effectively be removed by use of the constraint correction procedure proposed in this paper, and that the new parameter J(dc) is a material constant independent of specimen geometry (constraint). This parameter can serve as a new parameter to differentiate the elastic-plastic fracture toughness of engineering materials, which provides a new approach for fracture assessments of structures. It is not necessary to determine which laboratory specimen matches the structural constraint; rather, any specimen geometry can be tested to measure the size-independent fracture toughness J(dc). The potential advantage is clear and the results are very encouraging.

  11. Mechanical behavior and fracture characteristics of off-axis fiber composites. 1: Experimental investigation. [at the Lewis Research Center

    NASA Technical Reports Server (NTRS)

    Sinclair, J. H.; Chamis, C. C.

    1977-01-01

    The mechanical behavior, fracture surfaces, and fracture modes of unidirectional high-modulus graphite-fiber/epoxy composites subjected to off-axis tensile loads were investigated experimentally. The investigation included the generation of stress-strain-to-fracture data and scanning electron microscope studies of the fractured surfaces. The results led to the identification of fracture modes and distinct fracture surface characteristics for off-axis tensile loading. The results also led to the formulation of critical for identifying and characterizing these fracture modes and their associated fracture surfaces. The results presented and discussed herein were used in the theoretical investigation and comparisons described in Part 2. These results should also provide a good foundation for identifying, characterizing, and quantifying fracture modes in both off-axis and angle-plied laminates.

  12. Mechanisms of angiotensin II natriuresis and antinatriuresis.

    PubMed

    Olsen, M E; Hall, J E; Montani, J P; Guyton, A C; Langford, H G; Cornell, J E

    1985-08-01

    The aim of this study was to determine the role of changes in renal arterial pressure (RAP), renal hemodynamics, and tubular reabsorption in mediating the natriuretic and antinatriuretic actions of angiotensin II (ANG II). In seven anesthetized dogs, endogenous ANG II formation was blocked with captopril, and ANG II was infused intravenously at rates of 5-1,215 ng X kg-1 X min-1 while RAP was either servo-controlled at the preinfusion level or permitted to increase. When RAP was servo-controlled, ANG II infusion at all rates from 5-1,215 ng X kg-1 X min-1 decreased urinary sodium excretion (UNaV) and fractional sodium excretion (FENa) while increasing fractional reabsorption of lithium (FRLi) (an index of proximal tubular fractional sodium reabsorption) and causing no change in calculated distal tubule fractional sodium reabsorption (FRDNa). When RAP was permitted to increase, ANG II infusion rates up to 45 ng X kg-1. min-1 also decreased UNaV and FENa while increasing FRLi and causing no change in FRDNa. However, at 135 ng X kg-1 X min-1 and above, UNaV and FENa increased while FRLi and FRDNa decreased when RAP was allowed to rise, even though renal blood flow and filtration fraction were not substantially different from the values observed when RAP was servo-controlled. Filtered sodium load was slightly higher when RAP was permitted to increase during ANG II infusion compared with when RAP was servo-controlled, although the differences were not statistically significant. Thus, even very large doses of ANG II cause antinatriuresis when RAP is prevented from increasing.(ABSTRACT TRUNCATED AT 250 WORDS)

  13. Association of microstructural and mechanical properties of cancellous bone and their fracture risk assessment tool scores

    PubMed Central

    Wu, Dengke; Li, Xin; Tao, Cheng; Dai, Ruchun; Ni, Jiangdong; Liao, Eryuan

    2015-01-01

    This study is to investigate the association between fracture probabilities determined by using the fracture risk assessment tool (FRAX) and the microstructure and mechanical properties of femoral bone trabecula in osteoporosis (OP) and osteoarthritis (OA) patients with hip replacements. By using FRAX, we evaluated fracture risks of the 102 patients with bone replacements. Using micro CT scanning, we obtained the analysis parameters of microstructural properties of cancellous bone. Through morphometric observations, fatigue tests and compression tests, we obtained parameters of mechanical properties of cancellous bones. Relevant Pearson analysis was performed to investigate the association between the fracture probability and the microstructure and mechanical properties of femoral bone trabecula in patients. Fifteen risk factors in FRAX were compared between OP and OA patients. FRAX hip fracture risk score and major osteoporotic in OP and OA patients were significantly different. FRAX was associated with tissue bone mineral density and volumetric bone mineral density. Our study suggests that the probabilities of major osteoporotic and hip fracture using FRAX is associated with bone mass but not with micro bone quality. PMID:26064297

  14. Updated Fatigue-Crack-Growth And Fracture-Mechanics Software

    NASA Technical Reports Server (NTRS)

    Forman, Royce G.; Shivakumar, Venkataraman; Newman, James C., Jr.

    1995-01-01

    NASA/FLAGRO 2.0 developed as analytical aid in predicting growth and stability of preexisting flaws and cracks in structural components of aerospace systems. Used for fracture-control analysis of space hardware. Organized into three modules to maximize efficiency in operation. Useful in: (1) crack-instability/crack-growth analysis, (2) processing raw crack-growth data from laboratory tests, and (3) boundary-element analysis to determine stresses and stress-intensity factors. Written in FORTRAN 77 and ANSI C.

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

    PubMed

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

    2014-11-01

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

  16. Flow visualization of flow into 8 point-source fractures II: The effect of fracture non-uniformity and fluid crosslinking

    SciTech Connect

    Clark, P.E.; Zhu, Q.

    1994-12-31

    Recently, the flow of fluids into a fracture from a point source has been the subject of several different papers. Cleary and Fonseca first suggested that convective transport should play a major role in the placement of proppant when the flow into a fracture was from a point source. Clark and Courington presented data showing that for non-viscosified fluids convection was the dominant mechanism of transport. However, they showed, that for uniform fractures, viscosifying the fluid made a large difference in the transport mechanism. In a later paper, Clark and Zhu presented data for nonuniform fractures and viscosified fluids weighted with either salt or silica flour that showed that the presence of minor non-uniformities serve to negate the effect of convection even more than viscosifying the fluids. In this work, the authors have extended the work presented in the previous two papers to high viscosity Newtonian fluids and crosslinked fluids. The experiments have all been done with various concentrations of silica flour to simulate added proppant. Both changing the nature of the non-uniformities and crosslinking the polymer solution have a profound affect on the flow into the fracture and the convective process.

  17. Salter-Harris type II fracture of the femoral bone in a 14-year-old boy – case report

    PubMed Central

    Kuleta-Bosak, Elżbieta; Bożek, Paweł; Kluczewska, Ewa; Tomaszewski, Ryszard; Machnik-Broncel, Joanna

    2010-01-01

    Summary Background: Distal femoral physis fractures with displacement are rare injuries seen in adolescents related with high incidence of complication. They may lead to premature physeal closure consequently, to growth arrest and bone deformity. Case Report: The case of a 14-year-old boy with Salter-Harris type II displaced fracture underwent surgery with open reduction has been described. CT examination with multiplanar reconstruction was used in pre-operative assessment of distal femur growth plate fracture. Conclusions: Knowledge of classification, prognosis and methods of treatment is necessary in accurate pre- and postoperative assessment of physial fractures in adolescents. CT and multiplanar reconstruction improve the understanding of patterns of injury, relative prevalence and accuracy of pre-operative planning. PMID:22802768

  18. Natural hydraulic fractures and the mechanical stratigraphy of shale-dominated strata

    NASA Astrophysics Data System (ADS)

    Imber, Jonathan; Armstrong, Howard; Atar, Elizabeth; Clancy, Sarah; Daniels, Susan; Grattage, Joshua; Herringshaw, Liam; Trabucho-Alexandre, João; Warren, Cassandra; Wille, Jascha; Yahaya, Liyana

    2016-04-01

    .2-4.3 fractures per m, consistent with field observations that this formation is more highly fractured than the Cleveland Ironstone Formation. Semi-quantitative estimates of the mineralogical "brittleness index" suggest the highly fractured, clay-rich Mulgrave Shale Member of the Whitby Mudstone Formation has a low brittleness. Our results are therefore inconsistent with the widely held assumption that natural fracture density is greatest within units characterised by a high brittleness index. We propose that stratigraphic variations in fracture densities are more likely to result from the different distributions of crack driving stresses; formations containing decimetre-scale, and most likely stiff, carbonate layers (such as the Cleveland Ironstone Formation) will have differing crack driving stresses compared with silt- and mudstone dominated successions (such as the Whitby Mudstone Formation). The high fracture density observed within the Mulgrave Shale Member is also consistent with propagation of natural hydraulic fractures driven by fluid overpressure caused by maturation of organic matter concentrated within this unit. The next step is to investigate the relative importance of maturation-driven overpressure v. mechanical heterogeneity by analysing the stratigraphic variations in fracture density within the underlying, organic-matter lean Redcar Mudstone Formation.

  19. Fracture mechanics in fiber reinforced composite materials, taking as examples B/A1 and CRFP

    NASA Technical Reports Server (NTRS)

    Peters, P. W. M.

    1982-01-01

    The validity of linear elastic fracture mechanics and other fracture criteria was investigated with laminates of boron fiber reinforced aluminum (R/A1) and of carbon fiber reinforced epoxide (CFRP). Cracks are assessed by fracture strength Kc or Kmax (critical or maximum value of the stress intensity factor). The Whitney and Nuismer point stress criterion and average stress criterion often show that Kmax of fiber composite materials increases with increasing crack length; however, for R/A1 and CFRP the curve showing fracture strength as a function of crack length is only applicable in a small domain. For R/A1, the reason is clearly the extension of the plastic zone (or the damage zone n the case of CFRP) which cannot be described with a stress intensity factor.

  20. Hydraulic and mechanical properties of natural fractures in low-permeability rock

    SciTech Connect

    Pyrack-Nolte, L.J.; Myer, L.R.; Cook, N.G.W.; Witherspoon, P.A.

    1987-01-01

    The results of a comprehensive laboratory study of the mechanical displacement, permeability, and void geometry of single rock fractures in a quartz monzonite are summarized and analyzed. A metal-injection technique was developed that provided quantitative data on the precise geometry of the void spaces between the fracture surfaces and the areas of contact at different stresses. At effective stresses of less than 20 MPa fluid flow was proportional to the mean fracture aperture raised to a power greater than 3. As stress was increased, contact area was increased and void spaces become interconnected by small tortuous channels that constitute the principal impediment to fluid flow. At effective stresses higher than 20 MPa, the mean fracture aperture continued to diminish with increasing stress, but this had little effect on flow because the small tortuous flow channels deformed little with increasing stress.

  1. The Mechanical Benefit of Medial Support Screws in Locking Plating of Proximal Humerus Fractures

    PubMed Central

    Liu, Yanjie; Pan, Yao; Zhang, Wei; Zhang, Changqing; Zeng, Bingfang; Chen, Yunfeng

    2014-01-01

    Background The purpose of this study was to evaluate the biomechanical advantages of medial support screws (MSSs) in the locking proximal humeral plate for treating proximal humerus fractures. Methods Thirty synthetic left humeri were randomly divided into 3 subgroups to establish two-part surgical neck fracture models of proximal humerus. All fractures were fixed with a locking proximal humerus plate. Group A was fixed with medial cortical support and no MSSs; Group B was fixed with 3 MSSs but without medial cortical support; Group C was fixed with neither medial cortical support nor MSSs. Axial compression, torsional stiffness, shear stiffness, and failure tests were performed. Results Constructs with medial support from cortical bone showed statistically higher axial and shear stiffness than other subgroups examined (P<0.0001). When the proximal humerus was not supported by medial cortical bone, locking plating with medial support screws exhibited higher axial and torsional stiffness than locking plating without medial support screws (P≤0.0207). Specimens with medial cortical bone failed primarily by fracture of the humeral shaft or humeral head. Specimens without medial cortical bone support failed primarily by significant plate bending at the fracture site followed by humeral head collapse or humeral head fracture. Conclusions Anatomic reduction with medial cortical support was the stiffest construct after a simulated two-part fracture. Significant biomechanical benefits of MSSs in locking plating of proximal humerus fractures were identified. The reconstruction of the medial column support for proximal humerus fractures helps to enhance mechanical stability of the humeral head and prevent implant failure. PMID:25084520

  2. Problems of dynamic fracture mechanics without contact of the crack faces

    NASA Astrophysics Data System (ADS)

    Guz', A. N.; Zozulya, V. V.

    1994-10-01

    In this, the first part of the survey we have discussed only certain aspects of dynamic fracture mechanics. The surveyed material has been selected with a preference for the most highly developed parts of the theory, specifically those elements which have direct bearing on the second part of the survey. We have also included information on the dynamic fracture mechanics of initially stressed materials, in the development of which one of the authors has been a major contributor. Since many problems of dynamic fracture mechanics have been overlooked in the survey, we have added supplementary references to the literature. Various aspects of the strength and fracture of materials under dynamic loading are set forth in [11, 12, 40, 57, 60, 73, 80, 83]. Criteria of the initiation, motion, branching, and arrest of cracks are discussed in [7, 9, 60, 102, 111, 113, 124]. Among the most interesting elements of dynamic fracture mechanics are the problems of crack propagation. Certain analytical results pertinent to this topic have been obtained in [43-45, 47, 67-72, 78, 87, 92, 96, 97].

  3. The effects of glass ionomer and flowable composite liners on the fracture resistance of open-sandwich class II restorations.

    PubMed

    Güray Efes, Begüm; Yaman, Batu Can; Gümüştaş, Burak; Tıryakı, Murat

    2013-01-01

    This in vitro study aimed to investigate the effects of glass-ionomer and flowable composite liners on the fracture resistance of Class II amalgam and composite restorations. Group 1 cavities were restored with amalgam and Group 4 cavities with nanofill composite after the application of a dentin-bonding agent. For the remaining groups, light-cured-glass-ionomer liner was used in a gingival floor proximal box (Groups 2, 5) or flowable composite was used as a liner (Groups 3, 6), the remainder of the cavity was restored with amalgam (Groups 2, 3) or composite (Groups 5, 6). The restorations were loaded in compression to failure. The data was analyzed using Tukey's multiple comparison test. The fracture resistance was significantly higher (p<0.05) in Group 3 than in all other groups, except Group 2 (p>0.05). Flowable composite, glass-ionomer liners increased the fracture resistance of open-sandwich Class II amalgam restorations.

  4. Relationship between microstructure, material distribution, and mechanical properties of sheep tibia during fracture healing process.

    PubMed

    Gao, Jiazi; Gong, He; Huang, Xing; Fang, Juan; Zhu, Dong; Fan, Yubo

    2013-01-01

    The aim of this study was to investigate the relationship between microstructural parameters, material distribution, and mechanical properties of sheep tibia at the apparent and tissue levels during the fracture healing process. Eighteen sheep underwent tibial osteotomy and were sacrificed at 4, 8, and 12 weeks. Radiographs and micro-computed tomography (micro-CT) scanning were taken for microstructural assessment, material distribution evaluation, and micro-finite element analysis. A displacement of 5% compressive strain on the longitudinal direction was applied to the micro-finite element model, and apparent and tissue-level mechanical properties were calculated. Principle component analysis and linear regression were used to establish the relationship between principle components (PCs) and mechanical parameters. Visible bony callus formation was observed throughout the healing process from radiographic assessment. Apparent mechanical property increased at 8 weeks, but tissue-level mechanical property did not increase significantly until 12 weeks. Three PCs were extracted from microstructural parameters and material distribution, which accounted for 87.592% of the total variation. The regression results showed a significant relationship between PCs and mechanical parameters (R>0.8, P<0.05). Results of this study show that microstructure and material distribution based on micro-CT imaging could efficiently predict bone strength and reflect the bone remodeling process during fracture healing, which provides a basis for exploring the fracture healing mechanism and may be used as an approach for fractured bone strength assessment.

  5. Fracture processes and mechanisms of crack growth resistance in human enamel

    NASA Astrophysics Data System (ADS)

    Bajaj, Devendra; Park, Saejin; Quinn, George D.; Arola, Dwayne

    2010-07-01

    Human enamel has a complex micro-structure that varies with distance from the tooth’s outer surface. But contributions from the microstructure to the fracture toughness and the mechanisms of crack growth resistance have not been explored in detail. In this investigation the apparent fracture toughness of human enamel and the mechanisms of crack growth resistance were evaluated using the indentation fracture approach and an incremental crack growth technique. Indentation cracks were introduced on polished surfaces of enamel at selected distances from the occlusal surface. In addition, an incremental crack growth approach using compact tension specimens was used to quantify the crack growth resistance as a Junction of distance from the occlusal surface. There were significant differences in the apparent toughness estimated using the two approaches, which was attributed to the active crack length and corresponding scale of the toughening mechanisms.

  6. Non-double-couple mechanisms of microearthquakes induced by hydraulic fracturing

    USGS Publications Warehouse

    Sileny, J.; Hill, D.P.; Eisner, L.; Cornet, F.H.

    2009-01-01

    We have inverted polarity and amplitude information of representative microearthquakes to investigate source mechanisms of seismicity induced by hydraulic fracturing in the Carthage Cotton Valley, east Texas, gas field. With vertical arrays of four and eight three-component geophones in two monitoring wells, respectively, we were able to reliably determine source mechanisms of the strongest events with the best signal-to-noise ratio. Our analysis indicates predominantly non-double-couple source mechanisms with positive volumetric component consistent with opening cracks oriented close to expected hydraulic fracture orientation. Our observations suggest the induced events are directly the result of opening cracks by fluid injection, in contrast to many previous studies where the seismicity is interpreted to be primarily shearing caused by pore pressure diffusion into the surrounding rock or associated with shear stresses created at the hydraulic fracture tip. Copyright 2009 by the American Geophysical Union.

  7. 1-stage primary arthroplasty of mechanically failed internally fixated of hip fractures with deep wound infection

    PubMed Central

    Klatte, Till O; O’Loughlin, Padraigh F; Citak, Mustafa; Rueger, Johannes M; Gehrke, Thorsten; Kendoff, Daniel

    2013-01-01

    Background and purpose Mechanically failed internal fixation following hip fracture is often treated by salvage arthroplasty. If deep wound infection is present, a 2-stage procedure is often used. We have used a 1-stage procedure in infected cases, and we now report the outcome. Patients and methods We reviewed 16 cases of deep wound infection after mechanically failed hip fracture fixation, treated between 1994 and 2010. In all patients, a joint prosthesis was implanted in a 1-stage procedure. Results After an average follow-up period of 12 (2–18) years, no reinfection was detected. In 4 cases, a hip dislocation occurred and 3 of these needed further surgery. Interpretation A 1-stage procedure for arthroplasty of an infected, mechanically failed hip fracture fixation is feasible and carries a low risk of infection. PMID:23799345

  8. Fracture characterization of human cortical bone under mode II loading using the end-notched flexure test.

    PubMed

    Silva, F G A; de Moura, M F S F; Dourado, N; Xavier, J; Pereira, F A M; Morais, J J L; Dias, M I R; Lourenço, P J; Judas, F M

    2016-10-25

    Fracture characterization of human cortical bone under mode II loading was analyzed using a miniaturized version of the end-notched flexure test. A data reduction scheme based on crack equivalent concept was employed to overcome uncertainties on crack length monitoring during the test. The crack tip shear displacement was experimentally measured using digital image correlation technique to determine the cohesive law that mimics bone fracture behavior under mode II loading. The developed procedure was validated by finite element analysis using cohesive zone modeling considering a trapezoidal with bilinear softening relationship. Experimental load-displacement curves, resistance curves and crack tip shear displacement versus applied displacement were used to validate the numerical procedure. The excellent agreement observed between the numerical and experimental results reveals the appropriateness of the proposed test and procedure to characterize human cortical bone fracture under mode II loading. The proposed methodology can be viewed as a novel valuable tool to be used in parametric and methodical clinical studies regarding features (e.g., age, diseases, drugs) influencing bone shear fracture under mode II loading.

  9. Fracture Mechanics Evaluation of B-1 Materials. Volume I. Text

    DTIC Science & Technology

    1976-10-01

    8.2.14 Weldments In Ti-6AI-4V, 9-4,.20 and PH13 -8Mo 8 -314 8.2.15 Comparison of All Aluminum Alloys 8 -359 8.2.16 Comparison of Steels and Inconel 718 8 ...Inconel 718 8 -299 tbru 8.2.13.7-3 8 -313 8.2.14.1.1-1 t•nru Comparison FCGR Curves on Weldments in 8 -319 thru 8.2.14.3.9-1 Ti-6A1-4V, PH13 -8Mo and 9-4...investigated. In addition, the fracture properties of welds in Ti-6A1-4V, PH13 -8Mo, and 9-4-.20 alloys and of diffusion bonds in Ti-6AI-hV were determined

  10. Elastic-plastic fracture mechanics of strength-mismatching

    SciTech Connect

    Parks, D.M.; Ganti, S.; McClintock, F.A.

    1996-12-31

    Approximate solutions to stress-fields are provided for a strength-mismatched interface crack in small-scale yielding (SSY) for non-hardening and low hardening materials. Variations of local deformation intensities, characterized by a J-type contour integral, are proposed. The softer material experiences a higher deformation intensity level, J{sub S}, while the harder material sees a much lower deformation intensity level, J{sub H}, compared to that obtained from the applied J near the respective homogeneous crack-tips. For a low hardening material, the stress fields are obtained by scaling from an elastic/perfectly-plastic problem, based on an effective mismatch, M{sub eff}, which is a function of mismatch, M, and the hardening exponent, n. Triaxial stress build-up is discussed quantitatively in terms of M. The influence of strength-mismatch on cleavage fracture is discussed using Weibull statistics.

  11. A numerical manifold method model for analyzing fully coupled hydro-mechanical processes in porous rock masses with discrete fractures

    NASA Astrophysics Data System (ADS)

    Hu, Mengsu; Rutqvist, Jonny; Wang, Yuan

    2017-04-01

    In this study, a numerical manifold method (NMM) model was developed for fully coupled analysis of hydro-mechanical (HM) processes in porous rock masses with discrete fractures. Using an NMM two-cover-mesh system of mathematical and physical covers, fractures are conveniently discretized by dividing the mathematical cover along fracture traces to physical cover, resulting in a discontinuous model on a non-conforming mesh. In this model, discrete fracture deformation (e.g. open and slip) and fracture fluid flow within a permeable and deformable porous rock matrix are rigorously considered. For porous rock, direct pore-volume coupling was modeled based on an energy-work scheme. For mechanical analysis of fractures, a fracture constitutive model for mechanically open states was introduced. For fluid flow in fractures, both along-fracture and normal-to-fracture fluid flow are modeled without introducing additional degrees of freedom. When the mechanical aperture of a fracture is changing, its hydraulic aperture and hydraulic conductivity is updated. At the same time, under the effect of coupled deformation and fluid flow, the contact state may dynamically change, and the corresponding contact constraint is updated each time step. Therefore, indirect coupling is realized under stringent considerations of coupled HM effects and fracture constitutive behavior transfer dynamically. To verify the new model, examples involving deformable porous media containing a single and two sets of fractures were designed, showing good accuracy. Last, the model was applied to analyze coupled HM behavior of fractured porous rock domains with complex fracture networks under effects of loading and injection.

  12. An Overview of Innovative Strategies for Fracture Mechanics at NASA Langley Research Center

    NASA Technical Reports Server (NTRS)

    Ransom, Jonathan B.; Glaessgen, Edward H.; Ratcliffe, James G.

    2010-01-01

    Engineering fracture mechanics has played a vital role in the development and certification of virtually every aerospace vehicle that has been developed since the mid-20th century. NASA Langley Research Center s Durability, Damage Tolerance and Reliability Branch has contributed to the development and implementation of many fracture mechanics methods aimed at predicting and characterizing damage in both metallic and composite materials. This paper presents a selection of computational, analytical and experimental strategies that have been developed by the branch for assessing damage growth under monotonic and cyclic loading and for characterizing the damage tolerance of aerospace structures

  13. Inorganic Reaction Mechanisms Part II: Homogeneous Catalysis

    ERIC Educational Resources Information Center

    Cooke, D. O.

    1976-01-01

    Suggests several mechanisms for catalysis by metal ion complexes. Discusses the principal factors of importance in these catalysis reactions and suggests reactions suitable for laboratory study. (MLH)

  14. Mechanism of histone survival during transcription by RNA polymerase II.

    PubMed

    Kulaeva, Olga I; Studitsky, Vasily M

    2010-01-01

    This work is related to and stems from our recent NSMB paper, "Mechanism of chromatin remodeling and recovery during passage of RNA polymerase II" (December 2009). Synopsis. Recent genomic studies from many laboratories have suggested that nucleosomes are not displaced from moderately transcribed genes. Furthermore, histones H3/H4 carrying the primary epigenetic marks are not displaced or exchanged (in contrast to H2A/H2B histones) during moderate transcription by RNA polymerase II (Pol II) in vivo. These exciting observations suggest that the large molecule of Pol II passes through chromatin structure without even transient displacement of H3/H4 histones. The most recent analysis of the RNA polymerase II (Pol II)-type mechanism of chromatin remodeling in vitro (described in our NSMB 2009 paper) suggests that nucleosome survival is tightly coupled with formation of a novel intermediate: a very small intranucleosomal DNA loop (Ø-loop) containing transcribing Pol II. In the submitted manuscript we critically evaluate one of the key predictions of this model: the lack of even transient displacement of histones H3/H4 during Pol II transcription in vitro. The data suggest that, indeed, histones H3/H4 are not displaced during Pol II transcription in vitro. These studies are directly connected with the observation in vivo on the lack of exchange of histones H3/H4 during Pol II transcription.

  15. Case histories involving fatigue and fracture mechanics; Proceedings of the Symposium, Charleston, SC, Mar. 21, 22, 1985

    NASA Technical Reports Server (NTRS)

    Hudson, C. Michael (Editor); Rich, Thomas P. (Editor)

    1986-01-01

    Papers are presented on cracking at nozzle corners in the nuclear pressure vessel industry, applied fracture mechanics for assessing defect significance in a crude oil pipeline, failure analysis of a large wind-tunnel compressor blade, analysis of a compressor-wheel failure, and preventing fracture by inspection and analysis. Consideration is also given to the fatigue crack growth predictions of welded aircraft structures containing flaws in the residual stress field, the fatigue and fracture mechanics analysis of a compression loaded aircraft structure, fracture of an aircraft horizontal stabilizer, fatigue life analysis of fuel tank skins under combined loads, and aircraft structural maintenance recommendations based on fracture mechanics analysis. Additional papers discuss an analysis of two metal-forming die failures, an analysis of a failed saw arbor, and the role of fracture mechanics in assessing the effect on fatigue life of design changes in welded fabrications.

  16. Evaluation of fracture strength of metal/epoxy joint by interface mechanics

    SciTech Connect

    Nakai, Yoshikazu

    1995-11-01

    Tension tests of metal/epoxy joints with or without interface cracks were conducted and fracture criteria of the joints were discussed based on interface mechanics. The variation of the fracture strength of each specimen was large, and the strength showed Gaussian distribution. The fracture strength of smooth specimens was lower for wider specimens, but the cumulative probability of fracture of smooth specimens was not controlled by the stress singularity parameter. In interface cracked specimens, the cracks were propagated either along the interface or in epoxy resin, depending on crack length. When cracks propagated along the interface, the cumulative probability of the fracture of the specimen was controlled by the real part of the complex stress intensity factor along the interface, K{sub 1}. When cracks kinked to epoxy resin, the angle was almost identical to that of the maximum tangential stress, {sigma}{sub {theta}max}. In this case, the cumulative probability of fracture was controlled by the value of K{sub {theta}max}.

  17. Auto Mechanics. Volume II. Instructional Units.

    ERIC Educational Resources Information Center

    Armstrong, Ivan J.

    To assist teachers and students in understanding the latest concepts and functions of the automobile, this curriculum guide treats both the skills and knowledge necessary for auto mechanics. Developed by an advisory committee of instructors and mechanics in the industry, this manual consists of the following four sections: engine rebuilding;…

  18. American Society of Biomechanics Journal of Biomechanics Award 2013: cortical bone tissue mechanical quality and biological mechanisms possibly underlying atypical fractures.

    PubMed

    Geissler, Joseph R; Bajaj, Devendra; Fritton, J Christopher

    2015-04-13

    The biomechanics literature contains many well-understood mechanisms behind typical fracture types that have important roles in treatment planning. The recent association of "atypical" fractures with long-term use of drugs designed to prevent osteoporosis has renewed interest in the effects of agents on bone tissue-level quality. While this class of fracture was recognized prior to the introduction of the anti-resorptive bisphosphonate drugs and recently likened to stress fractures, the mechanism(s) that lead to atypical fractures have not been definitively identified. Thus, a causal relationship between these drugs and atypical fracture has not been established. Physicians, bioengineers and others interested in the biomechanics of bone are working to improve fracture-prevention diagnostics, and the design of treatments to avoid this serious side-effect in the future. This review examines the mechanisms behind the bone tissue damage that may produce the atypical fracture pattern observed increasingly with long-term bisphosphonate use. Our recent findings and those of others reviewed support that the mechanisms behind normal, healthy excavation and tunnel filling by bone remodeling units within cortical tissue strengthen mechanical integrity. The ability of cortical bone to resist the damage induced during cyclic loading may be altered by the reduced remodeling and increased tissue age resulting from long-term bisphosphonate treatment. Development of assessments for such potential fractures would restore confidence in pharmaceutical treatments that have the potential to spare millions in our aging population from the morbidity and death that often follow bone fracture.

  19. Mechanisms and impact of damage resulting from hydraulic fracturing. Topical report, May 1995-July 1996

    SciTech Connect

    Penny, G.S.; Conway, M.W.; Almond, S.W.; Himes, R.; Nick, K.E.

    1996-08-01

    This topical report documents the mechanisms of formation damage following hydraulic fracturing and their impact upon gas well productivity. The categories of damage reviewed include absolute or matrix permeability damage, relative permeability alterations, the damage of natural fracture permeability mechanisms and proppant conductivity impairment. Case studies are reviewed in which attempts are made to mitigate each of the damage types. Industry surveys have been conducted to determine the perceptions of the industry on the topic of formation damage following hydraulic fracturing and to identify key formations in which formation damage is a problem. From this information, technical hurdles and new technology needs are identified and estimates are made of the benefits of developing and applying minimum formation damage technology.

  20. Hip fracture presenting as mechanical low back pain subsequent to a fall: a case study

    PubMed Central

    Gleberzon, Brian; Hyde, David

    2006-01-01

    This case chronicles the assessment and clinical management of a 54 year old female patient who presented with post traumatic lower back, hip and lower extremity pain, initially attributed to mechanical low back pain but ultimately diagnosed as a hip fracture. This case study illustrates a number of important issues germane to chiropractic care. These are; the importance of using different assessment procedures, combined with clinical experience, in order to differentiate between those patients with clinical conditions that are amenable to conservative care from those that are not; the usefulness of a tuning fork test as a clinical tool in differentiating between hip fracture and mechanical spinal pain syndromes and; the impact of falls and fractures among older Canadian patients. PMID:17549186

  1. Effect of root canal preparation, type of endodontic post and mechanical cycling on root fracture strength

    PubMed Central

    RIPPE, Marília Pivetta; SANTINI, Manuela Favarin; BIER, Carlos Alexandre Souza; BALDISSARA, Paolo; VALANDRO, Luiz Felipe

    2014-01-01

    Objective To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots. Material and Methods eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments), the type of intraradicular post (fiber posts- FRC and cast post and core- CPC) and the use of mechanical cycling (MC) as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom #2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45°, 37°C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45° device with 1 mm/ min cross-head speed until failure occurred. Results The 3-way ANOVA showed that the root canal preparation strategy (p<0.03) and post type (p<0.0001) affected the fracture strength results, while mechanical cycling (p=0.29) did not. Conclusion The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario. PMID:25025556

  2. Effects of chemical alteration on fracture mechanical properties in hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Callahan, O. A.; Eichhubl, P.; Olson, J. E.

    2015-12-01

    Fault and fracture networks often control the distribution of fluids and heat in hydrothermal and epithermal systems, and in related geothermal and mineral resources. Additional chemical influences on conduit evolution are well documented, with dissolution and precipitation of mineral species potentially changing the permeability of fault-facture networks. Less well understood are the impacts of chemical alteration on the mechanical properties governing fracture growth and fracture network geometry. We use double-torsion (DT) load relaxation tests under ambient air conditions to measure the mode-I fracture toughness (KIC) and subcritical fracture growth index (SCI) of variably altered rock samples obtained from outcrop in Dixie Valley, NV. Samples from southern Dixie Valley include 1) weakly altered granite, characterized by minor sericite in plagioclase, albitization and vacuolization of feldspars, and incomplete replacement of biotite with chlorite, and 2) granite from an area of locally intense propylitic alteration with chlorite-calcite-hematite-epidote assemblages. We also evaluated samples of completely silicified gabbro obtained from the Dixie Comstock epithermal gold deposit. In the weakly altered granite KIC and SCI are 1.3 ±0.2 MPam1/2 (n=8) and 59 ±25 (n=29), respectively. In the propylitic assemblage KIC is reduced to 0.6 ±0.1 MPam1/2 (n=11), and the SCI increased to 75 ±36 (n = 33). In both cases, the altered materials have lower fracture toughness and higher SCI than is reported for common geomechanical standards such as Westerly Granite (KIC ~1.7 MPam1/2; SCI ~48). Preliminary analysis of the silicified gabbro shows a significant increase in fracture toughness, 3.6 ±0.4 MPam1/2 (n=2), and SCI, 102 ±45 (n=19), compared to published values for gabbro (2.9 MPam1/2 and SCI = 32). These results suggest that mineralogical and textural changes associated with different alteration assemblages may result in spatially variable rates of fracture

  3. Advances in Fatigue and Fracture Mechanics Analyses for Aircraft Structures

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1999-01-01

    This paper reviews some of the advances that have been made in stress analyses of cracked aircraft components, in the understanding of the fatigue and fatigue-crack growth process, and in the prediction of residual strength of complex aircraft structures with widespread fatigue damage. Finite-element analyses of cracked structures are now used to determine accurate stress-intensity factors for cracks at structural details. Observations of small-crack behavior at open and rivet-loaded holes and the development of small-crack theory has lead to the prediction of stress-life behavior for components with stress concentrations under aircraft spectrum loading. Fatigue-crack growth under simulated aircraft spectra can now be predicted with the crack-closure concept. Residual strength of cracked panels with severe out-of-plane deformations (buckling) in the presence of stiffeners and multiple-site damage can be predicted with advanced elastic-plastic finite-element analyses and the critical crack-tip-opening angle (CTOA) fracture criterion. These advances are helping to assure continued safety of aircraft structures.

  4. Mechanical properties and fracture strength of cathodically polarized prestressing wire

    SciTech Connect

    Kiszowski, S.; Hartt, W.H.

    1996-11-01

    Constant extension rate testing experiments were performed upon prestressing steel wire specimens prepared from three lots of Grade 270 and one lot of Grade 250 material for the purpose of characterizing susceptibility to environmental cracking under conditions associated with cathodic protection of prestressed concrete components and structures. Smooth, notched (six different geometries) and pitted (four different geometries) specimens were tested in air and deaerated saturated Ca(OH){sub 2}-distilled water at potentials of {minus}0.90 and {minus}1.30 v (SCE) and strength and ductility properties characterized. Relatively low strength was recorded for steel specimens at {minus}09.90 v from material for which the weight percent chromium was relatively high (0.24 w/o compared to 0.02 w/o). Under conditions that are likely to be most relevant to service, fracture load correlated with the amount by which the local wire cross section area was reduced, either from a notch or pit, and was independent of depth of the irregularity and of root radius to the extent to which these were addressed. It was concluded that it may be unsafe to apply cathodically protection to prestressing wire, even in situations where potential is maintained in the regime where hydrogen embrittlement should not occur.

  5. Discrete fracture modeling of hydro-mechanical damage processes in geological systems

    NASA Astrophysics Data System (ADS)

    Kim, K.; Rutqvist, J.; Houseworth, J. E.; Birkholzer, J. T.

    2014-12-01

    This study presents a modeling approach for investigating coupled thermal-hydrological-mechanical (THM) behavior, including fracture development, within geomaterials and structures. In the model, the coupling procedure consists of an effective linkage between two codes: TOUGH2, a simulator of subsurface multiphase flow and mass transport based on the finite volume approach; and an implementation of the rigid-body-spring network (RBSN) method, a discrete (lattice) modeling approach to represent geomechanical behavior. One main advantage of linking these two codes is that they share the same geometrical mesh structure based on the Voronoi discretization, so that a straightforward representation of discrete fracture networks (DFN) is available for fluid flow processes. The capabilities of the TOUGH-RBSN model are demonstrated through simulations of hydraulic fracturing, where fluid pressure-induced fracturing and damage-assisted flow are well represented. The TOUGH-RBSN modeling methodology has been extended to enable treatment of geomaterials exhibiting anisotropic characteristics. In the RBSN approach, elastic spring coefficients and strength parameters are systematically formulated based on the principal bedding direction, which facilitate a straightforward representation of anisotropy. Uniaxial compression tests are simulated for a transversely isotropic material to validate the new modeling scheme. The model is also used to simulate excavation fracture damage for the HG-A microtunnel in the Opalinus Clay rock, located at the Mont Terri underground research laboratory (URL) near Saint-Ursanne, Switzerland. The Opalinus Clay has transversely isotropic material properties caused by natural features such as bedding, foliation, and flow structures. Preferential fracturing and tunnel breakouts were observed following excavation, which are believed to be strongly influenced by the mechanical anisotropy of the rock material. The simulation results are qualitatively

  6. Adaptive finite element methods for two-dimensional problems in computational fracture mechanics

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Bass, J. M.; Spradley, L. W.

    1994-01-01

    Some recent results obtained using solution-adaptive finite element methods in two-dimensional problems in linear elastic fracture mechanics are presented. The focus is on the basic issue of adaptive finite element methods for validating the new methodology by computing demonstration problems and comparing the stress intensity factors to analytical results.

  7. Structural Reliability of Ceramics at High Temperature: Mechanisms of Fracture and Fatigue Crack Growth

    SciTech Connect

    Reinhold H. Dauskardt

    2005-08-01

    Final report of our DOE funded research program. Aim of the research program was to provide a fundamental basis from which the mechanical reliability of layered structures may be understood, and to provide guidelines for the development of technologically relevant layered material structures with optimum resistance to fracture and subcritical debonding. Progress in the program to achieve these goals is described.

  8. Current concepts in the treatment of Anderson Type II odontoid fractures in the elderly in Germany, Austria and Switzerland.

    PubMed

    Löhrer, L; Raschke, M J; Thiesen, D; Hartensuer, R; Surke, C; Ochman, S; Vordemvenne, T

    2012-04-01

    Although currently there are many different recommendations and strategies in the therapy of odontoid fractures in the elderly, there are still no generally accepted guidelines for a structured and standardised treatment. Moreover, the current opinion of spine surgeons regarding the optimal treatment of odontoid fractures Type II of the elderly is unknown. In order to have an objective insight into the diverging strategies for the management of Anderson Type II odontoid fractures and form a basis for future comparisons, this study investigated the current concepts and preferences of orthopaedic, neuro- and trauma surgeons. Spine surgeons from 34 medical schools and 8 hospitals in Germany, 4 university hospitals in Austria and 5 in Switzerland were invited to participate in an online survey using a 12-item 1-sided questionnaire. A total of 44 interviewees from 34 medical institutions participated in the survey, consisting of trauma (50%), orthopaedic (20.5%) and neurosurgeons (27.3%). Out of these, 70.5% treated 1-20 fractures per year; 63.6% favoured the anterior screw fixation as therapy for Type II odontoid fractures, the open posterior Magerl transarticular C1/C2 fusion, the posterior Harms C1/C2 fusion, and conservative immobilisation by cervical orthosis was preferred by 9.1% in each case. 59.1% preferred the anterior odontoid screw fixation as an appropriate treatment of Anderson Type II odontoid fractures in the elderly. 79.5% chose cervical orthosis for postsurgical treatment. Following operative treatment, nonunion rates were reported to be <10% and <20% by 40.9% and 70% of the surgeons, respectively. 56.8% reported changing from primary conservative to secondary operative treatment in <10% of cases. The most favoured technique in revision surgery of nonunions was the open posterior Magerl transarticular fusion technique, chosen by 38.6% of respondents. 18.2% preferred the posterior Harms C1/C2 fusion technique, 11.4% the percutaneous posterior Magerl

  9. Interval coding. II. Dendrite-dependent mechanisms.

    PubMed

    Doiron, Brent; Oswald, Anne-Marie M; Maler, Leonard

    2007-04-01

    The rich temporal structure of neural spike trains provides multiple dimensions to code dynamic stimuli. Popular examples are spike trains from sensory cells where bursts and isolated spikes can serve distinct coding roles. In contrast to analyses of neural coding, the cellular mechanics of burst mechanisms are typically elucidated from the neural response to static input. Bridging the mechanics of bursting with coding of dynamic stimuli is an important step in establishing theories of neural coding. Electrosensory lateral line lobe (ELL) pyramidal neurons respond to static inputs with a complex dendrite-dependent burst mechanism. Here we show that in response to dynamic broadband stimuli, these bursts lack some of the electrophysiological characteristics observed in response to static inputs. A simple leaky integrate-and-fire (LIF)-style model with a dendrite-dependent depolarizing afterpotential (DAP) is sufficient to match both the output statistics and coding performance of experimental spike trains. We use this model to investigate a simplification of interval coding where the burst interspike interval (ISI) codes for the scale of a canonical upstroke rather than a multidimensional stimulus feature. Using this stimulus reduction, we compute a quantization of the burst ISIs and the upstroke scale to show that the mutual information rate of the interval code is maximized at a moderate DAP amplitude. The combination of a reduced description of ELL pyramidal cell bursting and a simplification of the interval code increases the generality of ELL burst codes to other sensory modalities.

  10. C2-fractures: part II. A morphometrical analysis of computerized atlantoaxial motion, anatomical alignment and related clinical outcomes.

    PubMed

    Koller, Heiko; Acosta, Frank; Forstner, Rosemarie; Zenner, Juliane; Resch, Herbert; Tauber, Mark; Lederer, Stefan; Auffarth, Alexander; Hitzl, Wolfgang

    2009-08-01

    Knowledge on the outcome of C2-fractures is founded on heterogenous samples with cross-sectional outcome assessment focusing on union rates, complications and technical concerns related to surgical treatment. Reproducible clinical and functional outcome assessments are scant. Validated generic and disease specific outcome measures were rarely applied. Therefore, the aim of the current study is to investigate the radiographic, functional and clinical outcome of a patient sample with C2-fractures. Out of a consecutive series of 121 patients with C2 fractures, 44 met strict inclusion criteria and 35 patients with C2-fractures treated either nonsurgically or surgically with motion-preserving techniques were surveyed. Outcome analysis included validated measures (SF-36, NPDI, CSOQ), and a functional CT-scanning protocol for the evaluation of C1-2 rotation and alignment. Mean follow-up was 64 months and mean age of patients was 52 years. Classification of C2-fractures at injury was performed using a detailed morphological description: 24 patients had odontoid fractures type II or III, 18 patients had fracture patterns involving the vertebral body and 11 included a dislocated or a burst lateral mass fracture. Thirty-one percent of patients were treated with a halo, 34% with a Philadelphia collar and 34% had anterior odontoid screw fixation. At follow-up mean atlantoaxial rotation in left and right head position was 20.2 degrees and 20.6 degrees, respectively. According to the classification system of posttreatment C2-alignment established by our group in part I of the C2-fracture study project, mean malunion score was 2.8 points. In 49% of patients the fractures healed in anatomical shape or with mild malalignment. In 51% fractures healed with moderate or severe malalignment. Self-rated outcome was excellent or good in 65% of patients and moderate or poor in 35%. The raw data of varying nuances allow for comparison in future benchmark studies and metaanalysis. Detailed

  11. Local Crack Branching as a Mechanism for Instability in Dynamic Fracture

    NASA Astrophysics Data System (ADS)

    Sharon, Eran; Gross, Steven P.; Fineberg, Jay

    1995-06-01

    The motion of a crack in dynamic fracture has been shown to be governed by a dynamical instability causing oscillations in its velocity and structure on the fracture surface. We present experimental evidence indicating that the mechanism for instability is attempted local crack branching. At the instability onset, a crack will locally change its topology and sprout small, microscopic side branches. The trajectories of these local branches are independent of the crack velocity and exhibit scaling behavior. A connection between microscopic and macroscopic crack branching is established.

  12. Fracture mechanics research at NASA related to the aging commercial transport fleet

    NASA Astrophysics Data System (ADS)

    Newman, James C., Jr.; Harris, Charles E.

    1992-07-01

    NASA is conducting the Airframe Structural Integrity Program in support of the aging commercial transport fleet. This interdisciplinary program is being worked in cooperation with the U.S. airframe manufacturers, airline operators, and the FAA. Advanced analysis methods are under development and an extensive testing program is under way to study fatigue crack growth and fracture in complex built-up shell structures. Innovative nondestructive examination technologies are also being developed to provide large area inspection capability to detect corrosion, disbonds, and cracks. Recent fracture mechanics results applicable to predicting the growth of cracks under monotonic and cyclic loading at rivets in fuselage lap-splice joints are reviewed.

  13. Identification of Fracture Toughness for Discrete Damage Mechanics Analysis of Glass-Epoxy Laminates

    NASA Astrophysics Data System (ADS)

    Barbero, E. J.; Cosso, F. A.; Martinez, X.

    2014-08-01

    A methodology for determination of the intralaminar fracture toughness is presented, based on fitting discrete damage mechanics (DDM) model predictions to available experimental data. DDM is constitutive model that, when incorporated into commercial finite element software via user material subroutines, is able to predict intralaminar transverse and shear damage initiation and evolution in terms of the fracture toughness of the composite. The applicability of the DDM model is studied by comparison to available experimental data for Glass-Epoxy laminates. Sensitivity of the DDM model to h- and p-refinement is studied. Also, the effect of in-situ correction of strength is highlighted.

  14. Establishing the Foundations of the Mechanics of Fracture of Materials Compressed Along Cracks (Review)

    NASA Astrophysics Data System (ADS)

    Guz, A. N.

    2014-01-01

    The basic results of establishing the foundations of the mechanics of fracture of homogeneous materials compressed along cracks and inhomogeneous (composite) materials compressed along interface cracks are analyzed. These results were obtained using elastic, plastic, and viscoelastic material models. This review consists of three parts. The first part discusses the basic concept that the start (onset) of fracture is the mechanism of local instability near the cracks located in a single plane or parallel planes. The fracture criterion and the basic problems arising in this division of fracture mechanics are also formulated. Two basic approaches to establishing the foundations of the mechanics of fracture of materials compressed along cracks are outlined. One approach, so-called beam approximation, is based on various applied theories of stability of thin-walled systems (including the Bernoulli, Kirchhoff-Love, Timoshenko-type hypotheses, etc.). This approach is essentially approximate and introduces an irreducible error into the calculated stresses. The other approach is based on the basic equations and methods of the three-dimensional linearized theory of stability of deformable bodies for finite and small subcritical strains. This approach does not introduce major errors typical for the former approach and allows obtaining results with accuracy acceptable for mechanics. The second part offers a brief analysis of the basic results obtained with the first approach and a more detailed analysis of the basic results obtained with the second approach, including the consideration of the exact solutions for interacting cracks in a single plane and in parallel planes and results for some structural materials. The third part reports new results for interacting cracks in very closely spaced (or coinciding, as an asymptotic case) planes. These results may be considered a transition from the second approach (three-dimensional linearized theory of elastic stability) to the

  15. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    NASA Astrophysics Data System (ADS)

    Lee, Seok Woo; Lee, Hyun-Wook; Ryu, Ill; Nix, William D.; Gao, Huajian; Cui, Yi

    2015-06-01

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Here, we demonstrate physical and mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated Si by lessening the tensile stress concentrations in Si structures. This study will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.

  16. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    SciTech Connect

    Lee, Seok Woo; Lee, Hyun -Wook; Ryu, Ill; Nix, William D.; Gao, Huajian; Cui, Yi

    2015-06-26

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Here, we demonstrate physical and mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated Si by lessening the tensile stress concentrations in Si structures. Lastly, this study will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.

  17. Fracture Mechanics Analysis of Stitched Stiffener-Skin Debonding

    NASA Technical Reports Server (NTRS)

    Glaessgen, E. H.; Raju, I. S.; Poe, C. C., Jr.

    1998-01-01

    An analysis based on plate finite elements and the virtual crack closure technique has been implemented to study the effect of stitching on mode I and mode II strain energy release rates for debond configurations. The stitches were modeled as discrete nonlinear fastener elements with a compliance determined by experiment. The axial and shear behavior of the stitches was considered, however, the two compliances and failure loads were assumed to be independent. Both a double cantilever beam (mode I) and a mixed mode skin-stiffener debond configuration were studied. In the double cantilever beam configurations, G(sub I) began to decrease once the debond had grown beyond the first row of stitches and was reduced to zero for long debonds. In the mixed-mode skin-stiffener configurations, G(sub I) showed a similar behavior as in the double cantilever beam configurations, however, G(sub u), continued to increase with increasing debond length.

  18. Role of large-scale slip in mode II fracture of bimaterial interface produced by diffusion bonding

    NASA Astrophysics Data System (ADS)

    Fox, M. R.; Ghosh, A. K.

    2001-08-01

    Bimaterial interfaces present in diffusion-bonded (and in-situ) composites are often not flat interfaces. The unevenness of the interface can result not only from interface reaction products but also from long-range waviness associated with the surfaces of the component phases bonded together. Experimental studies aimed at determining interface mechanical properties generally ignore the departure in the local stress due to waviness and assume a theoretically flat interface. Furthermore, the commonly used testing methods involving superimposed tension often renders the interface so extremely brittle that if microplastic effects were present it becomes impossible to perceive them. This article examines the role of waviness of the interface and microplastic effects on crack initiation. To do this, a test was selected that provides significant stability against crack growth by superimposing compressive stresses. Mode II interface fracture was studied for NiAl/Mo model laminates using a recently developed asymmetrically loaded shear (ALS) interface shear test. The ALS test may be viewed as opposite of the laminate bend test. In the bend test, shear at the interface is created via tension on one surface of the bend, while in the ALS test, shear is created by compression on one side of the interface relative to the other. Normal to the interface, near the crack tip, an initially compressive state is replaced by slight tension due to Poisson’s expansion of the unbonded part of the compressed beam.

  19. Coupled chemical alteration and mechanical deformation in fractures: Insights from laboratory-scale imaging

    NASA Astrophysics Data System (ADS)

    Detwiler, R. L.; Elkhoury, J. E.; Ameli, P.

    2012-12-01

    Perturbations from mechanical and chemical equilibrium can lead to significant alterations in fracture permeability and corresponding changes in fracture mechanical properties. Under conditions favoring mineral dissolution, alterations caused by chemical disequilibrium depend on the dimensionless Damkohler number (Da=kL/Vb, where k is an effective reaction rate, L is the length scale of the fracture, V is a mean flow velocity and b is the mean fracture aperture). At small values of Da, dissolution is relatively uniform throughout the fracture, whereas at high values of Da, instabilities in the reaction front lead to the formation of dissolution channels, and increased permeability at all values of Da. However, the addition of mechanical stresses can lead to contrasting behavior (i.e., either permeability increase or permeability decrease) due to the alteration of contact regions between the fracture surfaces. Quantifying the rates and relative impacts of different mechanisms in such experiments is necessary, particularly if we wish to use results to support predictions of field-scale behavior under different conditions. However, laboratory-scale experiments aimed at understanding coupled chemical and mechanical disequilibrium typically rely upon core-scale observations that provide insufficient details about the evolution of contacting asperities and the resulting stress induced deformation. We present results from a set of experiments in fractured cores through which we flowed reactive fluids. The cores were reservoir- and cap-rock (limestone and anhydrite, respectively) from the Weyburn CO2 sequestration project in Saskatchewan. In addition to differential pore pressures and effluent chemistry we measured the surface topography (+/- 1 μm) of each sample before and after each experiment at high spatial resolution (20 x 20 μm). We fabricated a jig for accurately aligning the halves of the core on the profilometer stage and developed and tested numerical routines

  20. Effect of CO2-induced reactions on the mechanical behaviour of fractured wellbore cement

    NASA Astrophysics Data System (ADS)

    Wolterbeek, Timotheus; Hangx, Suzanne; Spiers, Christopher

    2016-04-01

    Geomechanical damage, such as fracturing of wellbore cement, can severely impact well integrity in CO2 storage fields. Chemical reactions between the cement and CO2-bearing fluids may subsequently alter the cement's mechanical properties, either enhancing or inhibiting damage accumulation during ongoing changes in wellbore temperature and stress-state. To evaluate the potential for such effects, we performed triaxial compression tests on Class G Portland cement, conducted at down-hole temperature (80 ° C) and effective confining pressures ranging from 1 to 25 MPa. After deformation, samples displaying failure on localised shear fractures were reacted with CO2-H2O, and then subjected to a second triaxial test to assess changes in mechanical properties. Using results from the first phase of deformation, baseline yield and failure criteria were constructed for virgin cement. These delineate stress conditions where unreacted cement is most prone to dilatational (permeability-enhancing) failure. Once shear-fractures formed, later reaction with CO2 did not produce further geomechanical weakening. Instead, after six weeks of reaction, we observed up to 83% recovery of peak-strength and increased frictional strength (15-40%) in the post-failure regime, due to calcium carbonate precipitation in the fractures. As such, our results suggest more or less complete mechanical healing on timescales of the order of months.

  1. Critical Chemical-Mechanical Couplings that Define Permeability Modifications in Pressure-Sensitive Rock Fractures

    SciTech Connect

    Derek Elsworth; Abraham Grader; Susan Brantley

    2007-04-25

    This work examined and quantified processes controlling changes in the transport characteristics of natural fractures, subjected to coupled thermal-mechanical-chemical (TMC) effects. Specifically, it examined the effects of mineral dissolution and precipitation mediated by mechanical effects, using laboratory through-flow experiments concurrently imaged by X-ray CT. These were conducted on natural and artificial fractures in cores using water as the permeant. Fluid and mineral mass balances are recorded and are correlated with in-sample saturation, porosity and fracture aperture maps, acquired in real-time by X-ray CT-imaging at a maximum spatial resolution of 15-50 microns per pixel. Post-test, the samples were resin-impregnated, thin-sectioned, and examined by microscopy to define the characteristics of dissolution and precipitation. The test-concurrent X-ray imaging, mass balances, and measurements of permeability, together with the post-test microscopy, were used to define dissolution/precipitation processes, and to constrain process-based models. These models define and quantify key processes of pressure solution, free-face dissolution, and shear-dilation, and the influence of temperature, stress level, and chemistry on the rate of dissolution, its distribution in space and time, and its influence on the mechanical and transport properties of the fracture.

  2. Simulation of crack propagation in fiber-reinforced concrete by fracture mechanics

    SciTech Connect

    Zhang Jun; Li, Victor C

    2004-02-01

    Mode I crack propagation in fiber-reinforced concrete (FRC) is simulated by a fracture mechanics approach. A superposition method is applied to calculate the crack tip stress intensity factor. The model relies on the fracture toughness of hardened cement paste (K{sub IC}) and the crack bridging law, so-called stress-crack width ({sigma}-{delta}) relationship of the material, as the fundamental material parameters for model input. As two examples, experimental data from steel FRC beams under three-point bending load are analyzed with the present fracture mechanics model. A good agreement has been found between model predictions and experimental results in terms of flexural stress-crack mouth opening displacement (CMOD) diagrams. These analyses and comparisons confirm that the structural performance of concrete and FRC elements, such as beams in bending, can be predicted by the simple fracture mechanics model as long as the related material properties, K{sub IC} and ({sigma}-{delta}) relationship, are known.

  3. The 1/r1/r singularity in weakly nonlinear fracture mechanics

    NASA Astrophysics Data System (ADS)

    Bouchbinder, Eran; Livne, Ariel; Fineberg, Jay

    2009-09-01

    Material failure by crack propagation essentially involves a concentration of large displacement-gradients near a crack's tip, even at scales where no irreversible deformation and energy dissipation occurs. This physical situation provides the motivation for a systematic gradient expansion of general nonlinear elastic constitutive laws that goes beyond the first order displacement-gradient expansion that is the basis for linear elastic fracture mechanics (LEFM). A weakly nonlinear fracture mechanics theory was recently developed by considering displacement-gradients up to second order. The theory predicts that, at scales within a dynamic lengthscale ℓ from a crack's tip, significant logr displacements and 1/r displacement-gradient contributions arise. Whereas in LEFM the 1/r singularity generates an unbalanced force and must be discarded, we show that this singularity not only exists but is also necessary in the weakly nonlinear theory. The theory generates no spurious forces and is consistent with the notion of the autonomy of the near-tip nonlinear region. The J-integral in the weakly nonlinear theory is also shown to be path-independent, taking the same value as the linear elastic J-integral. Thus, the weakly nonlinear theory retains the key tenets of fracture mechanics, while providing excellent quantitative agreement with measurements near the tip of single propagating cracks. As ℓ is consistent with lengthscales that appear in crack tip instabilities, we suggest that this theory may serve as a promising starting point for resolving open questions in fracture dynamics.

  4. Deformation and Fracture Mechanisms of Bone and Nacre

    NASA Astrophysics Data System (ADS)

    Wang, Rizhi; Gupta, Himadri S.

    2011-08-01

    Bone and nacre are the most-known biological hard tissues to materials researchers. Although highly mineralized, both bone and nacre are amazingly tough and exhibit remarkable inelasticity, properties that are still beyond the reach of many modern ceramic materials. Very interestingly, the two hard tissues seem to have adopted totally different structural strategies for achieving mechanical robustness. Starting from a true nanocomposite of the mineralized collagen fibril and following up to seven levels of hierarchical organization, bone is built on a structure with extreme complexity. In contrast, nacre possesses a structure of surprising simplicity. Polygonal mineral tablets of micrometer size are carefully cemented together into a macroscopic wonder. A comparative analysis of the structure-property relations in bone and nacre helps us to unveil the underlying mechanisms of this puzzling phenomenon. In this review, we critically compare the various levels of structures and their mechanical contributions between bone and nacre, with a focus on inelasticity and the toughening process. We demonstrate that, although nacre and bone differ from each other in many aspects, they have adopted very similar deformation and toughening mechanisms.

  5. Application of a Fracture Methodology for Studying the Mechanics that Govern Failure of Aluminum Structures

    NASA Astrophysics Data System (ADS)

    Galanis, Konstantinos Panagiotis; Wierzbicki, Tomasz; Papazoglou, Vassilios John

    The existence of cracks besides the effect of structural degradation can cause partial or total failure of a structure. Usually, structures are designed to resist yielding, buckling and fatigue, but not fracture due to limited existing data on large scalemodels. As a result, robust methods and procedures to design structures against fracture have not been developed, although the industry is seeking to achieve more efficient concepts and designs with advanced safety and performance using optimized structural design. The rapidly increasing application of lightweight materials and thin-walled structures in several industries requires fundamental understanding of the mechanisms and mechanics of fracture that govern stiffened panels. A methodology consisting of the application of advanced fracture models, material calibration, and validation through component testing is provided that will increase the survivability envelope of new structures. This paper presents its application that will enable designers to evaluate critical areas within a structure with respect to crack initiation, propagation, optimum material usage, and computational cost. It is based on the effect of stiffening configurations on fracture of aluminum marine structures by studying the structural response of various stiffened plates, represented by small-scale compact tension (CT) and intermediate-scale specimens, which are compared with unstiffened plates. It is shown that mapping of crack patterns in stiffened plates is feasible. Numerical modeling and analyses of ductile fracture initiation and propagation on a precracked geometry using a commercial finite element code (ABAQUS), taking into account the behavior of simple uncracked material, has been performed showing a very good agreement with small and intermediate scale tests.

  6. Can Deterministic Mechanical Size Effects Contribute to Fracture and Microdamage Accumulation in Trabecular Bone?

    PubMed Central

    Siegmund, Thomas; Allen, Matthew R.; Burr, David B.

    2010-01-01

    Failure of bone under monotonic and cyclic loading is related to the bone mineral density, the quality of the bone matrix and the evolution of microcracks. The theory of linear elastic fracture mechanics has commonly been applied to describe fracture in bone. Evidence is presented that bone failure can be described through a non-linear theory of fracture. Thereby, deterministic size effects are introduced. Concepts of a non-linear theory are applied to discern how the interaction among bone matrix constituents (collagen and mineral), microcrack characteristics, and trabecular architecture can create distinctively differences in the fracture resistance at the bone tissue level. The nonlinear model is applied to interpret pre-clinical data concerning the effects of anti-osteoporotic agents on bone properties. The results show that bisphosphonate (BP) treatments that suppress bone remodeling will change trabecular bone in ways such that the size of the failure process zone relative to the trabecular thickness is reduced. Selective estrogen receptor modulators (SERMs) that suppress bone remodeling will change trabecular bone in ways such that the size of the failure process zone relative to the trabecular thickness is increased. The consequences of these changes are reflected in bone mechanical response and predictions are consistent with experimental observations in the animal model which show that BP treatment is associated with more brittle fracture and microcracks without altering the average length of the cracks, whereas SERM treatments lead to a more ductile fracture and mainly increase crack length with a smaller increase in microcrack density. The model suggests that BPs may be more effective in cases in which bone mass is very low, whereas SERMS may be more effective when milder osteoporotic symptoms are present. PMID:20398678

  7. Analysis of propagation mechanisms of stimulation-induced fractures in rocks

    NASA Astrophysics Data System (ADS)

    Krause, Michael; Renner, Joerg

    2016-04-01

    Effectivity of geothermal energy production depends crucially on the heat exchange between the penetrated hot rock and the circulating water. Hydraulic stimulation of rocks at depth intends to create a network of fractures that constitutes a large area for exchange. Two endmembers of stimulation products are typically considered, tensile hydro-fractures that propagate in direction of the largest principal stress and pre-existing faults that are sheared when fluid pressure reduces the effective normal stress acting on them. The understanding of the propagation mechanisms of fractures under in-situ conditions is still incomplete despite intensive research over the last decades. Wing-cracking has been suggested as a mechanism of fracture extension from pre-existent faults with finite length that are induced to shear. The initiation and extension of the wings is believed to be in tensile mode. Open questions concern the variability of the nominal material property controlling tensile fracture initiation and extension, the mode I facture toughness KIC, with in-situ conditions, e.g., its mean-stress dependence. We investigated the fracture-propagation mechanism in different rocks (sandstones and granites) under varying conditions mimicking those representative for geothermal systems. To determine KIC-values we performed 3-point bending experiments. We varied the confining pressure, the piston velocity, and the position of the chevron notch relative to the loading configuration. Additional triaxial experiments at a range of confining pressures were performed to study wing crack propagation from artificial flaws whose geometrical characteristics, i.e., length, width, and orientation relative to the axial load are varied. We monitored acoustic emissions to constrain the spacio-temporal evolution of the fracturing. We found a significant effect of the length of the artificial flaw and the confining pressure on wing-crack initiation but did not observe a systematic dependence

  8. Phenomenological and mechanics aspects of nondestructive evaluation and characterization by sound and ultrasound of material and fracture properties

    NASA Technical Reports Server (NTRS)

    Fu, L. S. W.

    1982-01-01

    Developments in fracture mechanics and elastic wave theory enhance the understanding of many physical phenomena in a mathematical context. Available literature in the material, and fracture characterization by NDT, and the related mathematical methods in mechanics that provide fundamental underlying principles for its interpretation and evaluation are reviewed. Information on the energy release mechanism of defects and the interaction of microstructures within the material is basic in the formulation of the mechanics problems that supply guidance for nondestructive evaluation (NDE).

  9. Recent finite element studies in plasticity and fracture mechanics

    NASA Technical Reports Server (NTRS)

    Rice, J. R.; Mcmeeking, R. M.; Parks, D. M.; Sorensen, E. P.

    1979-01-01

    The paper reviews recent work on fundamentals of elastic-plastic finite-element analysis and its applications to the mechanics of crack opening and growth in ductile solids. The presentation begins with a precise formulation of incremental equilibrium equations and their finite-element forms in a manner valid for deformations of arbitrary magnitude. Special features of computational procedures are outlined for accuracy in view of the near-incompressibility of elastic-plastic response. Applications to crack mechanics include the analysis of large plastic deformations at a progressively opening crack tip, the determination of J integral values and of limitations to J characterizations of the intensity of the crack tip field, and the determination of crack tip fields in stable crack growth.

  10. Direct Studies of Fracture Mechanisms in Metals at Highest Magnification.

    DTIC Science & Technology

    1982-05-01

    or even high purity and therefore will deform before and after void initiation according to recog- nized mechanisms of workhardening in pure metals...discussion it is clear that in precipitation hardened alloys material between voids must suffer extensive plastic deformation during neck formation and the...motion of dislocation groups and their specific behavior during plastic deformation to rupture at record- ing speeds of 30 frames per second. In order

  11. The mechanics of tessellations - bioinspired strategies for fracture resistance.

    PubMed

    Fratzl, Peter; Kolednik, Otmar; Fischer, F Dieter; Dean, Mason N

    2016-01-21

    Faced with a comparatively limited palette of minerals and organic polymers as building materials, evolution has arrived repeatedly on structural solutions that rely on clever geometric arrangements to avoid mechanical trade-offs in stiffness, strength and flexibility. In this tutorial review, we highlight the concept of tessellation, a structural motif that involves periodic soft and hard elements arranged in series and that appears in a vast array of invertebrate and vertebrate animal biomaterials. We start from basic mechanics principles on the effects of material heterogeneities in hypothetical structures, to derive common concepts from a diversity of natural examples of one-, two- and three-dimensional tilings/layerings. We show that the tessellation of a hard, continuous surface - its atomization into discrete elements connected by a softer phase - can theoretically result in maximization of material toughness, with little expense to stiffness or strength. Moreover, the arrangement of soft/flexible and hard/stiff elements into particular geometries can permit surprising functions, such as signal filtering or 'stretch and catch' responses, where the constrained flexibility of systems allows a built-in safety mechanism for ensuring that both compressive and tensile loads are managed well. Our analysis unites examples ranging from exoskeletal materials (fish scales, arthropod cuticle, turtle shell) to endoskeletal materials (bone, shark cartilage, sponge spicules) to attachment devices (mussel byssal threads), from both invertebrate and vertebrate animals, while spotlighting success and potential for bio-inspired manmade applications.

  12. Metal cutting simulation of 4340 steel using an accurate mechanical description of meterial strength and fracture

    SciTech Connect

    Maudlin, P.J.; Stout, M.G.

    1996-09-01

    Strength and fracture constitutive relationships containing strain rate dependence and thermal softening are important for accurate simulation of metal cutting. The mechanical behavior of a hardened 4340 steel was characterized using the von Mises yield function, the Mechanical Threshold Stress model and the Johnson- Cook fracture model. This constitutive description was implemented into the explicit Lagrangian FEM continuum-mechanics code EPIC, and orthogonal plane-strain metal cutting calculations were performed. Heat conduction and friction at the toolwork-piece interface were included in the simulations. These transient calculations were advanced in time until steady state machining behavior (force) was realized. Experimental cutting force data (cutting and thrust forces) were measured for a planning operation and compared to the calculations. 13 refs., 6 figs.

  13. Nonlinear fracture mechanics-based analysis of thin wall cylinders

    NASA Technical Reports Server (NTRS)

    Brust, Frederick W.; Leis, Brian N.; Forte, Thomas P.

    1994-01-01

    This paper presents a simple analysis technique to predict the crack initiation, growth, and rupture of large-radius, R, to thickness, t, ratio (thin wall) cylinders. The method is formulated to deal both with stable tearing as well as fatigue mechanisms in applications to both surface and through-wall axial cracks, including interacting surface cracks. The method can also account for time-dependent effects. Validation of the model is provided by comparisons of predictions to more than forty full scale experiments of thin wall cylinders pressurized to failure.

  14. First-order Description of the Mechanical Fracture Behavior of Fine-Grained Surficial Marine Sediments During Gas Bubble Growth

    DTIC Science & Technology

    2010-01-01

    10 F04O29 BARRY ET AL.: BUBBLE GROWTH BY FRACTURE P04029 Figure 3. Map of field site. Canard, Nova Scotia, Canada. appears to approximate the...Bottinger. and T. Dahm (2005), Buoyancy-driven fracture ascent: Experiments in layered gelatine. J. Volcano!. Geotherm . Res., 144. 273-285. doi...Journal Article 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE First-order description of the mechanical fracture behavior of fine-grained

  15. Understanding Irreversible Degradation of Nb3Sn Wires with Fundamental Fracture Mechanics

    SciTech Connect

    Zhai, Yuhu; Calzolaio, Ciro; Senatore, Carmine

    2014-08-01

    Irreversible performance degradation of advanced Nb3Sn superconducting wires subjected to transverse or axial mechanical loading is a critical issue for the design of large-scale fusion and accelerator magnets such as ITER and LHC. Recent SULTAN tests indicate that most cable-in-conduit conductors for ITER coils made of Nb3Sn wires processed by various fabrication techniques show similar performance degradation under cyclic loading. The irreversible degradation due to filament fracture and local strain accumulation in Nb3Sn wires cannot be described by the existing strand scaling law. Fracture mechanic modeling combined with X-ray diffraction imaging of filament micro-crack formation inside the wires under mechanical loading may reveal exciting insights to the wire degradation mechanisms. We apply fundamental fracture mechanics with a singularity approach to study influence of wire filament microstructure of initial void size and distribution to local stress concentration and potential crack propagation. We report impact of the scale and density of the void structure on stress concentration in the composite wire materials for crack initiation. These initial defects result in an irreversible degradation of the critical current beyond certain applied stress. We also discuss options to minimize stress concentration in the design of the material microstructure for enhanced wire performance for future applications.

  16. The Merging of Fatigue and Fracture Mechanics Concepts: A Historical Perspective

    NASA Technical Reports Server (NTRS)

    Newman, James C., Jr.

    1997-01-01

    The seventh Jerry L. Swedlow Memorial Lecture presents a review of some of the technical developments, that have occurred during the past 40 years, which have led to the merger of fatigue and fracture mechanics concepts. This review is made from the viewpoint of 'crack propagation.' As methods to observe the 'fatigue' process have improved, the formation of fatigue micro-cracks have been observed earlier in life and the measured crack sizes have become smaller. These observations suggest that fatigue damage can now be characterized by 'crack size.' In parallel, the crack-growth analysis methods, using stress-intensity factors, have also improved. But the effects of material inhomogeneities, crack-fracture mechanisms, and nonlinear behavior must now be included in these analyses. The discovery of crack-closure mechanisms, such as plasticity, roughness, and oxide/corrosion/fretting product debris, and the use of the effective stress-intensity factor range, has provided an engineering tool to predict small- and large-crack-growth rate behavior under service loading, conditions. These mechanisms have also provided a rationale for developing, new, damage-tolerant materials. This review suggests that small-crack growth behavior should be viewed as typical behavior, whereas large-crack threshold behavior should be viewed as the anomaly. Small-crack theory has unified 'fatigue' and 'fracture mechanics' concepts; and has bridged the cap between safe-life and durability/damage-tolerance design concepts.

  17. Fracture Mechanics Analyses of Subsurface Defects in Reinforced Carbon-Carbon Joggles Subjected to Thermo-Mechanical Loads

    NASA Technical Reports Server (NTRS)

    Knight, Norman F., Jr.; Raju, Ivatury S.; Song, Kyongchan

    2011-01-01

    Coating spallation events have been observed along the slip-side joggle region of the Space Shuttle Orbiter wing-leading-edge panels. One potential contributor to the spallation event is a pressure build up within subsurface voids or defects due to volatiles or water vapor entrapped during fabrication, refurbishment, or normal operational use. The influence of entrapped pressure on the thermo-mechanical fracture-mechanics response of reinforced carbon-carbon with subsurface defects is studied. Plane-strain simulations with embedded subsurface defects are performed to characterize the fracture mechanics response for a given defect length when subjected to combined elevated-temperature and subsurface-defect pressure loadings to simulate the unvented defect condition. Various subsurface defect locations of a fixed-length substrate defect are examined for elevated temperature conditions. Fracture mechanics results suggest that entrapped pressure combined with local elevated temperatures have the potential to cause subsurface defect growth and possibly contribute to further material separation or even spallation. For this anomaly to occur, several unusual circumstances would be required making such an outcome unlikely but plausible.

  18. Exploring particulate retention mechanisms through visualization of E. coli transport through a single, saturated fracture

    NASA Astrophysics Data System (ADS)

    Burke, M. G.; Dickson, S. E.; Schutten, M.

    2011-12-01

    Groundwater is an extremely valuable resource; a large body of work has been conducted towards remediating, tracking and reducing its contamination. Even so, there are large gaps within the current understanding of groundwater flow and contaminant transport, particularly within fractured media. Fractured media has the ability transport contaminants over longer distances in less time relative to porous media. Furthermore, colloids display unique transport characteristics in comparison to dissolved constituents, including the fact that they typically exhibit earlier initial arrival times. Of particular concern to human health are pathogenic microorganisms, which often originate from fecal contamination. Escherichia coli is a common indicator for fecal contamination; some strains are pathogenic, causing acute illness and sometimes death, in humans. A comprehensive understanding of the transport and retention of E. coli in fractured media will improve our ability to accurately assess whether a site is at risk of becoming contaminated by pathogenic microorganisms. Therefore, the goal of this work is to expand our mechanistic understanding particulate retention, specifically E. coli, in fractures, and the influence of flow rate on these mechanisms. In order to achieve this goal, clear epoxy casts were fabricated of two dolomitic limestone fractures retrieved from a quarry in Guelph, Ontario. Each aperture field was characterized through hydraulic and tracer tests, and measured directly using the light transmission technique. E. coli RS2-GFP, which is a non-pathogenic strain of E. coli that has been tagged with a green fluorescent protein, was injected into the cast under three separate specific discharges ranging from 5 - 30 m/d. These experiments were conducted on an ultraviolet light source, and a high resolution charged-couple device (CCD) camera was employed to take photos at regular intervals in order to capture the dominant flow paths and the areas of retention

  19. Mixed-mode fracture of ceramics

    SciTech Connect

    Petrovic, J.J.

    1985-01-01

    The mixed-mode fracture behavior of ceramic materials is of importance for monolithic ceramics in order to predict the onset of fracture under generalized loading conditions and for ceramic composites to describe crack deflection toughening mechanisms. Experimental data on surface flaw mixed-mode fracture in various ceramics indicate that the flaw-plane normal stress at fracture decreases with increasing in-flaw-plane shear stress, although present data exhibit a fairly wide range in details of this sigma - tau relationship. Fracture from large cracks suggests that Mode II has a greater effect on Mode I fracture than Mode III. A comparison of surface flaw and large crack mixed-mode I-II fracture responses indicated that surface flaw behavior is influenced by shear resistance effects.

  20. A mechanical model for predicting the probability of osteoporotic hip fractures based in DXA measurements and finite element simulation

    PubMed Central

    2012-01-01

    Background Osteoporotic hip fractures represent major cause of disability, loss of quality of life and even mortality among the elderly population. Decisions on drug therapy are based on the assessment of risk factors for fracture, from BMD measurements. The combination of biomechanical models with clinical studies could better estimate bone strength and supporting the specialists in their decision. Methods A model to assess the probability of fracture, based on the Damage and Fracture Mechanics has been developed, evaluating the mechanical magnitudes involved in the fracture process from clinical BMD measurements. The model is intended for simulating the degenerative process in the skeleton, with the consequent lost of bone mass and hence the decrease of its mechanical resistance which enables the fracture due to different traumatisms. Clinical studies were chosen, both in non-treatment conditions and receiving drug therapy, and fitted to specific patients according their actual BMD measures. The predictive model is applied in a FE simulation of the proximal femur. The fracture zone would be determined according loading scenario (sideway fall, impact, accidental loads, etc.), using the mechanical properties of bone obtained from the evolutionary model corresponding to the considered time. Results BMD evolution in untreated patients and in those under different treatments was analyzed. Evolutionary curves of fracture probability were obtained from the evolution of mechanical damage. The evolutionary curve of the untreated group of patients presented a marked increase of the fracture probability, while the curves of patients under drug treatment showed variable decreased risks, depending on the therapy type. Conclusion The FE model allowed to obtain detailed maps of damage and fracture probability, identifying high-risk local zones at femoral neck and intertrochanteric and subtrochanteric areas, which are the typical locations of osteoporotic hip fractures. The

  1. Geomechanical Simulation of Fluid-Driven Fractures

    SciTech Connect

    Makhnenko, R.; Nikolskiy, D.; Mogilevskaya, S.; Labuz, J.

    2012-11-30

    The project supported graduate students working on experimental and numerical modeling of rock fracture, with the following objectives: (a) perform laboratory testing of fluid-saturated rock; (b) develop predictive models for simulation of fracture; and (c) establish educational frameworks for geologic sequestration issues related to rock fracture. These objectives were achieved through (i) using a novel apparatus to produce faulting in a fluid-saturated rock; (ii) modeling fracture with a boundary element method; and (iii) developing curricula for training geoengineers in experimental mechanics, numerical modeling of fracture, and poroelasticity.

  2. Basic mechanism of transcription by RNA polymerase II

    PubMed Central

    Svetlov, Vladimir; Nudler, Evgeny

    2012-01-01

    RNA polymerase II-like enzymes carry out transcription of genomes in Eukaryota, Archaea, and some viruses. They also exhibit fundamental similarity to RNA polymerases from bacteria, chloroplasts, and mitochondria. In this review we take an inventory of recent studiesilluminating different steps of basic transcription mechanism, likely common for most multi-subunit RNA polymerases. Through the amalgamation of structural and computational chemistry data we attempt to highlight the most feasible reaction pathway for the two-metal nucleotidyl transfer mechanism, and to evaluate the way catalysis can be linked to translocation in the mechano-chemical cycle catalyzed by RNA polymerase II. PMID:22982365

  3. Fracture mechanics for the design of ceramic multilayer actuators

    NASA Astrophysics Data System (ADS)

    Hao, T. H.; Gong, X.; Suo, Z.

    1996-01-01

    In a multilayer actuator, each internal electrode terminates an edge inside the active ceramic. Around the edge, the nonuniform electric field generates an incompatible strain field, which, in its turn, generates stresses and may cause the ceramic to crack. The industry has been exploring alternative electrode configurations to alleviate the stress concentration. The effort has been empirical and benefited little from numerical simulations. An inherent difficulty is that the actuator ceramics have nonlinear electro-mechanical interactions, of which no unified mathematical description is now available. In this paper, we develop a crack nucleation model that includes essential features of this nonlinearity. The model applies to both paraelectrics and ferroelectrics. Attention is focused on situations where the small-scale saturation conditions prevail. That is, the driving voltage is low enough so that the bulk of the ceramics is linearly dielectric, except for a cylinder of a small radius around the electrode edge. Inside the cylinder, large strains result from electrostriction or polar rotation. We identify a parameter group that determines the cracking condition; details in the material description only affect a dimensionless coefficient. Everything else being fixed, a critical layer thickness exists, below which a multilayer actuator will not crack around its internal electrode edges. Merits and limitations of the small-scale saturation model are discussed. We analyze this model analytically for a paraelectric with perfect polarization saturation, and estimate the value of the dimensionless coefficient in the model.

  4. Probabilistic Fracture Mechanics Evaluation of Selected Passive Components – Technical Letter Report

    SciTech Connect

    Simonen, Fredric A.; Doctor, Steven R.; Gosselin, Stephen R.; Rudland, David L.; Xu, H.; Wilkowski, Gery M.; Lydell, Bengt O.

    2007-05-31

    This report addresses the potential application of probabilistic fracture mechanics computer codes to support the Proactive Materials Degradation Assessment (PMDA) program as a method to predict component failure probabilities. The present report describes probabilistic fracture mechanics calculations that were performed for selected components using the PRO-LOCA and PRAISE computer codes. The calculations address the failure mechanisms of stress corrosion cracking, intergranular stress corrosion cracking, and fatigue for components and operating conditions that are known to make particular components susceptible to cracking. It was demonstrated that the two codes can predict essentially the same failure probabilities if both codes start with the same fracture mechanics model and the same inputs to the model. Comparisons with field experience showed that both codes predict relatively high failure probabilities for components under operating conditions that have resulted in field failures. It was found that modeling assumptions and inputs tended to give higher calculated failure probabilities than those derived from data on field failures. Sensitivity calculations were performed to show that uncertainties in the probabilistic calculations were sufficiently large to explain the differences between predicted failure probabilities and field experience.

  5. Fracture mechanics correlation of boron/aluminum coupons containing stress risers

    NASA Technical Reports Server (NTRS)

    Adsit, N. R.; Waszczak, J. P.

    1975-01-01

    The mechanical behavior of boron/aluminum near stress risers has been studied and reported. This effort was directed toward defining the tensile behavior of both unidirectional and (0/ plus or minus 45) boron/aluminum using linear elastic fracture mechanics (LEFM). The material used was 5.6-mil boron in 6061 aluminum, consolidated using conventional diffusion bonding techniques. Mechanical properties are reported for both unidirectional and (0/ plus or minus 45) boron/aluminum, which serve as control data for the fracture mechanics predictions. Three different flawed specimen types were studied. In each case the series of specimens remained geometrically similar to eliminate variations in finite size correction factors. The fracture data from these tests were reduced using two techniques. They both used conventional LEFM methods, but the existence of a characteristic flaw was assumed in one case and not the other. Both the data and the physical behavior of the specimens support the characteristic flaw hypothesis. Cracks were observed growing slowly in the (0/ plus or minus 45) laminates, until a critical crack length was reached at which time catastrophic failure occurred.

  6. Fracture Mechanics Analyses of Reinforced Carbon-Carbon Wing-Leading-Edge Panels

    NASA Technical Reports Server (NTRS)

    Raju, Ivatury S.; Phillips, Dawn R.; Knight, Norman F., Jr.; Song, Kyongchan

    2010-01-01

    Fracture mechanics analyses of subsurface defects within the joggle regions of the Space Shuttle wing-leading-edge RCC panels are performed. A 2D plane strain idealized joggle finite element model is developed to study the fracture behavior of the panels for three distinct loading conditions - lift-off and ascent, on-orbit, and entry. For lift-off and ascent, an estimated bounding aerodynamic pressure load is used for the analyses, while for on-orbit and entry, thermo-mechanical analyses are performed using the extreme cold and hot temperatures experienced by the panels. In addition, a best estimate for the material stress-free temperature is used in the thermo-mechanical analyses. In the finite element models, the substrate and coating are modeled separately as two distinct materials. Subsurface defects are introduced at the coating-substrate interface and within the substrate. The objective of the fracture mechanics analyses is to evaluate the defect driving forces, which are characterized by the strain energy release rates, and determine if defects can become unstable for each of the loading conditions.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  8. A study of fracture mechanisms in ATD roller bearing

    NASA Technical Reports Server (NTRS)

    Zee, Ralph H.

    1990-01-01

    The purpose was to investigate how microstructures, especially anisotropy, affects internal stresses and the overall mechanical response of bearings. Samples with the stress axis along the aligned carbide direction possessed high modulus values compared to those with their axis perpendicular to the carbide stringers. The difference in the modulus was found to be more than a factor of two. A series of experiments was conducted on rolled samples to further investigate this effect; the two sets of results were consistent with each other. The degree of anisotropy of the microstructure in terms of the carbide and matrix orientations was determined using x-ray diffraction. The stress state determination was conducted using neutron diffraction. It was found that there was little variation in the distribution of the internal stresses amongst different samples, indicating that small changes in the processing and geometrical conditions did not result in significant variations in the internal stress. A nominal tensile hoop stress of 39 ksi was obtained for the inner raceway. Furthermore, during the course of the investigation, it was apparent that there was a need to determine the stress state induced by the shrink fitting process. Therefore, a series of experiments was conducted using strain gages to identify the stress distribution in a shrink fitting process in three different types of geometries. Correlations were obtained to estimate the highest stress values in the outer and inner groove geometry. A finite element program based on the ANSYS system was developed to compute the stress distribution in the inner raceway geometry. This analysis indicates that the highest tensile stress in the system occurs at the ID of the ring with a stress value of over 5 times that of the applied radial stress. Results from all these facets were correlated with one another. It appears that the material does not fail as a result of any one single factor, but results from a combination of

  9. The mechanics of delamination in fiber-reinforced composite materials. Part 2: Delamination behavior and fracture mechanics parameters

    NASA Technical Reports Server (NTRS)

    Wang, S. S.; Choi, I.

    1983-01-01

    Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extenstion. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined.

  10. Stress fracture of the hamate body and fourth metacarpal base following military style push-ups: an unusual trauma mechanism.

    PubMed

    Busche, Marc N; Knobloch, Karsten; Rosenthal, Herbert; Vogt, Peter M

    2008-12-01

    We report the case of a 19-year-old male soldier, who sustained stress fractures of the hamate body and fourth metacarpal base due to his daily knuckle push-up routine in the military. We introduce repetitive microtrauma due to daily knuckle push-ups as an unusual, but potential trauma mechanism for metacarpal and carpal stress fractures.

  11. Mechanisms of hydrogen-assisted fracture in austenitic stainless steel welds.

    SciTech Connect

    Balch, Dorian K.; Sofronis, Petros; Somerday, Brian P.; Novak, Paul

    2005-03-01

    The objective of this study was to quantify the hydrogen-assisted fracture susceptibility of gas-tungsten arc (GTA) welds in the nitrogen-strengthened, austenitic stainless steels 21Cr-6Ni-9Mn (21-6-9) and 22Cr-13Ni-5Mn (22-13-5). In addition, mechanisms of hydrogen-assisted fracture in the welds were identified using electron microscopy and finite-element modeling. Elastic-plastic fracture mechanics experiments were conducted on hydrogen-charged GTA welds at 25 C. Results showed that hydrogen dramatically lowered the fracture toughness from 412 kJ/m{sup 2} to 57 kJ/m{sup 2} in 21-6-9 welds and from 91 kJ/m{sup 2} to 26 kJ/m{sup 2} in 22-13-5 welds. Microscopy results suggested that hydrogen served two roles in the fracture of welds: it promoted the nucleation of microcracks along the dendritic structure and accelerated the link-up of microcracks by facilitating localized deformation. A continuum finite-element model was formulated to test the notion that hydrogen could facilitate localized deformation in the ligament between microcracks. On the assumption that hydrogen decreased local flow stress in accordance with the hydrogen-enhanced dislocation mobility argument, the finite-element results showed that deformation was localized in a narrow band between two parallel, overlapping microcracks. In contrast, in the absence of hydrogen, the finite-element results showed that deformation between microcracks was more uniformly distributed.

  12. Computational Investigation of Fundamental Mechanisms Contributing to Fracture Dissolution and the Evolution of Hypogene Karst Systems

    NASA Astrophysics Data System (ADS)

    Chaudhuri, A.; Rajaram, H.; Viswanathan, H. S.; Zyvoloski, G.; Stauffer, P. H.

    2009-12-01

    Hypogene karst systems evolve by dissolution resulting from the cooling of water flowing upward against the geothermal gradient in limestone formations. We present a comprehensive coupled-process model of fluid flow, heat transfer, reactive transport and buoyancy effects to investigate the origin of hypogene karst systems by fracture dissolution. Our model incorporates the temperature and pressure dependence of the solubility and dissolution kinetics of calcite. Our formulation inherently incorporates mechanisms such as “mixing corrosion” that have been implicated in the formation of hypogene cave systems. It also allows for rigorous representation of temperature-dependent fluid density and its consequences at various stages of karstification. The model is applied to investigate karstification over geological time scales in a network of faults/fractures that serves as a vertical conduit for upward flow. We considered two different conceptual hydrogeologic models. In the first model, the upward flow is controlled by a constant pressure gradient. In the second model, the flow is induced by topographic effects in a mountainous hydrologic system. During the very early stages of fracture growth, there is a positive feedback between fluid flow rate, heat transfer and dissolution. In this stage the dissolution rate is largely controlled by the retrograde solubility of calcite and aperture growth occurs throughout the fracture. For the first model, there is a period of slow continuous increase in the mass flow rate through the fracture, which is followed by an abrupt rapid increase. We refer to the time when this rapid increase occurs as the maturation time. For the second model of a mountainous hydrologic system, the fluid flux through the fracture remains nearly constant even though the fracture permeability and aperture increase. This is largely because the permeability of the country rock does not increase significantly. While this limits the fluid flux through the

  13. Unusual Mechanism of Injury Resulting in a Thoracic Chance Fracture in a Rodeo Athlete: A Case Report

    PubMed Central

    Boham, Mikaela; O'Connell, Kim

    2014-01-01

    Objective: To introduce the characteristics of a Chance fracture and increase awareness of the mechanism of injury that may occur during athletic activity. Background: A T12 Chance fracture was diagnosed in an 18-year-old male rodeo athlete. The rider was forced into extreme lumbothoracic hyperflexion when the horse bucked within the chute, pinning the rider's legs to his chest. Differential Diagnosis: Burst fracture, abdominal organ rupture, spinal dislocation, spinal cord injury, disk herniation, pars interarticularis fracture, spinal nerve injury, paralysis. Treatment: The patient underwent an open reduction and fixation of the thoracic fracture. Posterior stabilization was obtained with nonsegmental instrumentation. Allograft and autografts were used for posterolateral arthrodesis at T11–T12 and T12–L1. Uniqueness: Motor vehicle crashes with occupants wearing lap-type–only restraints account for nearly all previously reported Chance fractures. When only lap seatbelts are worn, the pelvis is stabilized, and the torso continues moving forward with impact. The stabilized body segment for this individual was reversed. Nearly 3 years after the initial surgery, fixation, and infection, the bareback rider has returned to full participation in rodeo. Conclusions: To our knowledge, this is the first reported diagnosis of a T12 Chance fracture in a rodeo athlete. When animals buck, athletes can be forced into hyperflexion, exposing them to Chance fractures. Therefore, anyone treating rodeo athletes must suspect possible spinal fracture when this mechanism is present and must treat all athletes with early conservative management and hospital referral. PMID:24520836

  14. Applications of FEM and BEM in two-dimensional fracture mechanics problems

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Steeve, B. E.; Swanson, G. R.

    1992-01-01

    A comparison of the finite element method (FEM) and boundary element method (BEM) for the solution of two-dimensional plane strain problems in fracture mechanics is presented in this paper. Stress intensity factors (SIF's) were calculated using both methods for elastic plates with either a single-edge crack or an inclined-edge crack. In particular, two currently available programs, ANSYS for finite element analysis and BEASY for boundary element analysis, were used.

  15. The effect of adhesive layer elasticity on the fracture mechanics of a blister test specimen

    NASA Technical Reports Server (NTRS)

    Updike, D. P.

    1975-01-01

    An analytical model of a blister type specimen for evaluating adhesive bond strength was developed. Plate theory with shear deformation was used to model the deformation of the plate, and elastic deformation of the adhesive layer is taken into account. It is shown that the inclusion of the elastic deformation of the adhesive layer can have a significant influence in the energy balance calculations of fracture mechanics.

  16. Condylar restoration after early TMJ fractures and functional appliance therapy. Part II: Muscle evaluation.

    PubMed

    Kahl-Nieke, B; Fischbach, R

    1999-01-01

    The aim of this study was to analyze and to describe the condition of the lateral pterygoid muscle during and after functional appliance therapy in children who had sustained condylar fractures. The treatment group consisted of 19 patients with an average age of 13.4 years, who had sustained a unilateral fracture at an average age of 8.4 years and had been treated functionally for 6 to 8 months. Muscle condition was assessed through axial soft tissue description. The volume and density of the lateral pterygoid muscle were measured in both groups and were compared on the basis of sex, age and fracture type. 74% of the patients in the follow-up group showed muscle differences of more than 10% between the 2 sides. In 2/3 of these patients the lateral pterygoid of the fracture side was 13 to 69% smaller. The volumes of the contralateral pterygoid muscles in the 2 patient groups differed by 10% on the basis of sex. Both in the treatment group and in the follow-up group the volume difference between the healthy and fractured side was as high as 70% depending on localization and type of fracture. Deep fractures and fractures with complete dislocation of the condyle evoked the most serious reduction in muscle volume.

  17. Criterion for mixed mode fracture in composite bonded joints

    NASA Technical Reports Server (NTRS)

    Mall, S.; Kochhar, N. K.

    1986-01-01

    A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite-epoxy composite adherends bonded with a toughened epoxy adhesive. The mode I, mode II and mixed mode I-II fracture energies of the tested adhesives were found to be equal to each other. The criterion for mixed mode fracture in composite bonded joints was found.

  18. Hydro-mechanical coupled simulation of hydraulic fracturing using the eXtended Finite Element Method (XFEM)

    NASA Astrophysics Data System (ADS)

    Youn, Dong Joon

    This thesis presents the development and validation of an advanced hydro-mechanical coupled finite element program analyzing hydraulic fracture propagation within unconventional hydrocarbon formations under various conditions. The realistic modeling of hydraulic fracturing is necessarily required to improve the understanding and efficiency of the stimulation technique. Such modeling remains highly challenging, however, due to factors including the complexity of fracture propagation mechanisms, the coupled behavior of fracture displacement and fluid pressure, the interactions between pre-existing natural and initiated hydraulic fractures and the formation heterogeneity of the target reservoir. In this research, an eXtended Finite Element Method (XFEM) scheme is developed allowing for representation of single or multiple fracture propagations without any need for re-meshing. Also, the coupled flows through the fracture are considered in the program to account for their influence on stresses and deformations along the hydraulic fracture. In this research, a sequential coupling scheme is applied to estimate fracture aperture and fluid pressure with the XFEM. Later, the coupled XFEM program is used to estimate wellbore bottomhole pressure during fracture propagation, and the pressure variations are analyzed to determine the geometry and performance of the hydraulic fracturing as pressure leak-off test. Finally, material heterogeneity is included into the XFEM program to check the effect of random formation property distributions to the hydraulic fracture geometry. Random field theory is used to create the random realization of the material heterogeneity with the consideration of mean, standard deviation, and property correlation length. These analyses lead to probabilistic information on the response of unconventional reservoirs and offer a more scientific approach regarding risk management for the unconventional reservoir stimulation. The new stochastic approach

  19. Fracture toughness testing and toughening mechanisms of some commercial cobalt-free hardfacing alloys

    SciTech Connect

    Cockeram, B.V.

    1998-04-27

    Hardfacing alloys are weld deposited to provide a wear resistant surface for structural base materials. Commercial low cobalt hardfacing alloys are being evaluated to reduce plant activation levels. Since hardfacing alloys typically must be resistant to cracking to assure adequate in service performance, fracture toughness is a critical material property. Fracture toughness (K{sub IC}) measurements of Fe base, Ni-base, and Co-base hardfacing were performed in accordance with ASTM E399-90 procedure in an effort to identify a tough cobalt-free alternative. Reduced scatter in K{sub IC} data was observed for the Fe base hardfacing, and the 95% lower bound K{sub IC} values were generally higher than the Ni-base Hardfacing alloys. Preliminary crack growth data obtained during precracking indicate that the Ni-base hardfacing possess better fatigue crack growth resistance. However, none of the Fe-base or Ni-base hardfacing have K{sub IC} values that are comparable to the reference Co-base hard facing. The test specimens were machined from thick (0.5 inches) weld deposits, and the microstructures of the test specimens are compared with the more prototypic, thinner deposits. Microstructural and fractographic examinations are used to characterize the fracture mechanisms and delineate the operative toughening mechanisms. Crack deflection and crack bridging toughening mechanisms are shown to be relevant for most of the commercial hardfacing.

  20. Resistance Against the Intrinsic Rate of Fracture Mechanics Parameters for Polymeric Materials Under Moderate Impact Loading

    NASA Astrophysics Data System (ADS)

    Lach, R.; Seidler, S.; Grellmann, W.

    2005-09-01

    This study contributes towards understanding crack toughness as resistance against the intrinsic rate of fracture mechanics parameters. Up to now only few investigations have been done under moderate impact loading conditions. Based on experimental investigations using the crack resistance (R) concept, it has been shown that the stop block method combined with the multiple-specimen technique is a unique method for polymers under impact loading conditions in comparison with different R-curve methods. Other methods for the determination of R curve such as the low-blow technique are normally not applicable for polymers due to their time-dependent mechanical properties. The crack-tip opening displacement (CTOD) rate is a measurement of the rate sensibility of stable fracture process depending on the type of deformation, which can provide deep insights into the micromechanics and activation mechanisms during the fracture processes. In the polymeric materials mostly investigated, one can understand the stable crack propagation with three-stage processes; crack-tip blunting/crack initiation, non-stationary stable crack growth and steady-state stable crack growth (an equilibrium state). In this stable crack propagation, the values of normalized CTOD rate converge rapidly to a ‘matrix’-specific threshold. The stop block method in the multiple-specimen technique assures the criteria of the time-independent strain field around the crack tip and constant crack speed therewith and the J-integral is a valid toughness parameter.

  1. American Society of Biomechanics Journal of Biomechanics Award 2013: Cortical bone tissue mechanical quality and biological mechanisms possibly underlying atypical fractures

    PubMed Central

    Geissler, Joseph R.; Bajaj, Devendra; Fritton, J. Christopher

    2015-01-01

    The biomechanics literature contains many well-understood mechanisms behind typical fracture types that have important roles in treatment planning. The recent association of “atypical” fractures with long-term use of drugs designed to prevent osteoporosis has renewed interest in the effects of agents on bone tissue-level quality. While this class of fracture was recognized prior to the introduction of the anti-resorptive bisphosphonate drugs and recently likened to stress fractures, the mechanism(s) that lead to atypical fractures have not been definitively identified. Thus, a causal relationship between these drugs and atypical fracture has not been established. Physicians, bioengineers and others interested in the biomechanics of bone are working to improve fracture-prevention diagnostics, and the design of treatments to avoid this serious side-effect in the future. This review examines the mechanisms behind the bone tissue damage that may produce the atypical fracture pattern observed increasingly with long-term bisphosphonate use. Our recent findings and those of others reviewed support that the mechanisms behind normal, healthy excavation and tunnel filling by bone remodeling units within cortical tissue strengthen mechanical integrity. The ability of cortical bone to resist the damage induced during cyclic loading may be altered by the reduced remodeling and increased tissue age resulting from long-term bisphosphonate treatment. Development of assessments for such potential fractures would restore confidence in pharmaceutical treatments that have the potential to spare millions in our aging population from the morbidity and death that often follow bone fracture. PMID:25683519

  2. Study of fracture mechanisms of short fiber reinforced AS composite by acoustic emission technique

    SciTech Connect

    Kida, Sotoaki; Suzuki, Megumu

    1995-11-01

    The fracture mechanisms of short fiber reinforced AS composites are studied by acoustic emission technique for examining the effects of fiber contents. The loads P{sub b} and P{sub c} which the damage mechanisms change are obtained at the inflection points of the total AE energy curve the energy gradient method. The damages are generated by fiber breaking at the load point of P{sub b} and P{sub c} in B material, and by the fiber breaking and the debonding between resin and fiber at the load points of P{sub b} and P{sub c} in C material.

  3. Computational implementation of the multi-mechanism deformation coupled fracture model for salt

    SciTech Connect

    Koteras, J.R.; Munson, D.E.

    1996-05-01

    The Multi-Mechanism Deformation (M-D) model for creep in rock salt has been used in three-dimensional computations for the Waste Isolation Pilot Plant (WIPP), a potential waste, repository. These computational studies are relied upon to make key predictions about long-term behavior of the repository. Recently, the M-D model was extended to include creep-induced damage. The extended model, the Multi-Mechanism Deformation Coupled Fracture (MDCF) model, is considerably more complicated than the M-D model and required a different technology from that of the M-D model for a computational implementation.

  4. A novel Lagrangian approach for the stable numerical simulation of fault and fracture mechanics

    SciTech Connect

    Franceschini, Andrea; Ferronato, Massimiliano Janna, Carlo; Teatini, Pietro

    2016-06-01

    The simulation of the mechanics of geological faults and fractures is of paramount importance in several applications, such as ensuring the safety of the underground storage of wastes and hydrocarbons or predicting the possible seismicity triggered by the production and injection of subsurface fluids. However, the stable numerical modeling of ground ruptures is still an open issue. The present work introduces a novel formulation based on the use of the Lagrange multipliers to prescribe the constraints on the contact surfaces. The variational formulation is modified in order to take into account the frictional work along the activated fault portion according to the principle of maximum plastic dissipation. The numerical model, developed in the framework of the Finite Element method, provides stable solutions with a fast convergence of the non-linear problem. The stabilizing properties of the proposed model are emphasized with the aid of a realistic numerical example dealing with the generation of ground fractures due to groundwater withdrawal in arid regions. - Highlights: • A numerical model is developed for the simulation of fault and fracture mechanics. • The model is implemented in the framework of the Finite Element method and with the aid of Lagrange multipliers. • The proposed formulation introduces a new contribution due to the frictional work on the portion of activated fault. • The resulting algorithm is highly non-linear as the portion of activated fault is itself unknown. • The numerical solution is validated against analytical results and proves to be stable also in realistic applications.

  5. Mechanical properties and fracture behaviour of polyimide (SINTIMID) at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Tschegg, E.; Humer, K.; Weber, H. W.

    In view of emerging applications in aeronautics, low temperature and nuclear fusion technology, the mechanical properties of plastics have to be tested both at cryogenic temperatures and under certain radiation environments. In the present paper measurements are reported of the elastic modulus, the ultimate tensile strength (UTS) and the failure strain of a polyimide (SINTIMID), which were carried out at room temperature, 77 and 4.2 K. In addition to this temperature dependence, the influence of sample size on the mechanical properties, as well as the fracture behaviour in mode I on cylindrical precracked samples with a circumferential notch, have been investigated. The results show an increase in both the elastic modulus and the UTS by 40 and 60%, respectively, on decreasing the temperature to 77 K, but no further change at lower temperatures. On the other hand, the failure strain decreases continuously (by ≈ 25%) down to 4.2 K, while the fracture toughness increases in a similar way (by ≈ 10%). No sample size dependence could be detected. These results will be discussed in conjunction with additional observations of the fracture behaviour made using optical and scanning electron microscopes.

  6. Relation between mechanical stiffness and vibration transmission of fracture callus: an experimental study on rabbit tibia.

    PubMed

    Akkus, O; Korkusuz, F; Akin, S; Akkas, N

    1998-01-01

    It has been suggested that the vibration transmission across a fracture is affected by the stages of healing of the fracture callus. This study aims to correlate the change in vibration transmission with mechanical stiffness of the callus measured by three-point bending. The right tibiae of male, three-month old local albino rabbits were osteotomized and stabilized by intramedullary fixation following open reduction. The intramedullary rods were removed on the 15th, 28th, 42nd and 90th days postoperatively and the tibiae were excised for vibration, three-point bending and bone mineral density analysis by quantitative computerized tomography (QCT). Optimum time for clinical weight bearing was determined by checking the convergence of the vibration parameters of the fractured tibia to those of the unfractured contralateral. The conclusions obtained from curvature analysis, based on vibration experiments, were in considerable correlation (Spearman's rank correlation coefficient r = 0.93, p = 0.003) with the conclusions obtained from the three-point bending test data which reflected the mechanical condition of the bone by direct means. However, no correlation between bone mineral density change and vibration transmission was noted.

  7. Fracture resistance curves and toughening mechanisms in polymer based dental composites.

    PubMed

    De Souza, J A; Goutianos, S; Skovgaard, M; Sørensen, B F

    2011-05-01

    The fracture resistance (R-curve behaviour) of two commercial dental composites (Filtek Z350(®) and Concept Advanced(®)) were studied using Double Cantilever Beam sandwich specimens loaded with pure bending moments to obtain stable crack growth. The experiments were conducted in an environmental scanning electron microscope to (a) accurately measure the applied energy-release rate for crack initiation, (b) measure the early (rising) part of the R-curve, and (c) provide direct microscopic evidence of the toughening mechanisms ahead of and/or in the wake of the crack tip. The two tested composites displayed distinctly different R-curve behaviours. The difference was related to different toughening mechanisms as the two composites had markedly different microstructures. Contrary to common experience, the composite with the finer microstructure (smaller particles), the Concept Advanced(®), showed significantly higher fracture resistance than the composite with the coarser microstructure. The fracture properties were related to the flexural strength of the dental composites. The method, thus, can provide useful insight into how the microstructure enhances toughness, which is necessary for the future development of such materials.

  8. Characterization of the Microstructure, Fracture, and Mechanical Properties of Aluminum Alloys 7085-O and 7175-T7452 Hollow Cylinder Extrusions

    NASA Astrophysics Data System (ADS)

    Benoit, Samuel G.; Chalivendra, Vijaya B.; Rice, Matthew A.; Doleski, Robert F.

    2016-09-01

    Microstructural, tensile, and fracture characterizations of cylindrically forged forms of aluminum alloys AA7085-O and AA7175-T7452 were performed. Mechanical and fracture properties were investigated along radial, circumferential, and longitudinal directions to determine directional dependency. American Society for Testing and Materials (ASTM) test methods (ASTM E8-04 and ASTM E1820) were employed for both the tensile and fracture characterizations, respectively. The tensile and fracture properties were related to microstructure in each direction. The strength, elongation at break, and ultimate tensile strength of AA7085-O were higher than those of AA7175-T7452. AA7175-T7452 alloy failed in a brittle manner during fracture studies. AA7085-O outperformed AA7175-T7452 on fracture energy in all of the orientations studied. Smaller grain sizes on the planes normal to circumferential and longitudinal directions showed improvement in both elongation at break and fracture energy values compared to those of radial direction. Scanning electron microscopy images demonstrated cleavage fracture in AA7175-T7452 and transgranular fracture in AA7085-O.

  9. Investigation of the fracture mechanism in Ti-5Al-2.5Sn at cryogenic temperatures

    NASA Technical Reports Server (NTRS)

    Vanstone, R. H.; Low, J. R., Jr.; Shannon, J. L., Jr.

    1977-01-01

    The influence of microstructure on the fracture mechanism and plane-strain fracture toughness of Ti-5Al-2.5Sn was studied through the use of fractography and metallographic sectioning techniques. One-inch thick plates of extra low interstitial (ELI) and normal interstitial Ti-5Al-2.5Sn were mill annealed at 815 C followed by either air or furnace cooling. These variations in composition and cooling rate resulted in differences in the volume fraction and internal structure of the iron-stabilized phase, and in the crystallographic texture and ordering of the alpha matrix. The tensile properties of these plates were determined at 20 K, 77 K, and 295 K. The air-cooled ELI plate was the toughest material evaluated.

  10. Molecular mechanisms controlling bone formation during fracture healing and distraction osteogenesis.

    PubMed

    Ai-Aql, Z S; Alagl, A S; Graves, D T; Gerstenfeld, L C; Einhorn, T A

    2008-02-01

    Fracture healing and distraction osteogenesis have important applications in orthopedic, maxillofacial, and periodontal treatment. In this review, the cellular and molecular mechanisms that regulate fracture repair are contrasted with bone regeneration that occurs during distraction osteogenesis. While both processes have many common features, unique differences are observed in the temporal appearance and expression of specific molecular factors that regulate each. The relative importance of inflammatory cytokines in normal and diabetic healing, the transforming growth factor beta superfamily of bone morphogenetic mediators, and the process of angiogenesis are discussed as they relate to bone repair. A complete summary of biological activities and functions of various bioactive factors may be found at COPE (Cytokines & Cells Online Pathfinder Encyclopedia), http://www.copewithcytokines.de/cope.cgi.

  11. A novel Lagrangian approach for the stable numerical simulation of fault and fracture mechanics

    NASA Astrophysics Data System (ADS)

    Franceschini, Andrea; Ferronato, Massimiliano; Janna, Carlo; Teatini, Pietro

    2016-06-01

    The simulation of the mechanics of geological faults and fractures is of paramount importance in several applications, such as ensuring the safety of the underground storage of wastes and hydrocarbons or predicting the possible seismicity triggered by the production and injection of subsurface fluids. However, the stable numerical modeling of ground ruptures is still an open issue. The present work introduces a novel formulation based on the use of the Lagrange multipliers to prescribe the constraints on the contact surfaces. The variational formulation is modified in order to take into account the frictional work along the activated fault portion according to the principle of maximum plastic dissipation. The numerical model, developed in the framework of the Finite Element method, provides stable solutions with a fast convergence of the non-linear problem. The stabilizing properties of the proposed model are emphasized with the aid of a realistic numerical example dealing with the generation of ground fractures due to groundwater withdrawal in arid regions.

  12. Mechanical Modeling of Foods Including Fracture and Simulation of Food Compression

    NASA Astrophysics Data System (ADS)

    Morimoto, Masamichi; Mizunuma, Hiroshi; Sonomura, Mitsuhiro; Kohyama, Kaoru; Ogoshi, Hiro

    2008-07-01

    The purposes of this research are to simulate the swallowing of foods, and to investigate the relationship between the rheological properties of foods and the swallowing. Here we proposed the mechanical modeling of foods, and simulated the compression test using the finite element method. A linear plasticity model was applied as the rheological model of the foods, and two types of computational elements were used to simulate the fracture behavior. The compression tests with a wedged plunger were simulated for tofu, banana, and biscuit, and were compared with the experimental results. Other than the homogeneous food model, the simulations were conducted for the multi-layer models. Reasonable agreements on the behaviors of compression and fracture were obtained between the simulations and the experiments including the reaction forces on the plunger.

  13. ADDITIONAL STRESS AND FRACTURE MECHANICS ANALYSES OF PRESSURIZED WATER REACTOR PRESSURE VESSEL NOZZLES

    SciTech Connect

    Walter, Matthew; Yin, Shengjun; Stevens, Gary; Sommerville, Daniel; Palm, Nathan; Heinecke, Carol

    2012-01-01

    In past years, the authors have undertaken various studies of nozzles in both boiling water reactors (BWRs) and pressurized water reactors (PWRs) located in the reactor pressure vessel (RPV) adjacent to the core beltline region. Those studies described stress and fracture mechanics analyses performed to assess various RPV nozzle geometries, which were selected based on their proximity to the core beltline region, i.e., those nozzle configurations that are located close enough to the core region such that they may receive sufficient fluence prior to end-of-life (EOL) to require evaluation of embrittlement as part of the RPV analyses associated with pressure-temperature (P-T) limits. In this paper, additional stress and fracture analyses are summarized that were performed for additional PWR nozzles with the following objectives: To expand the population of PWR nozzle configurations evaluated, which was limited in the previous work to just two nozzles (one inlet and one outlet nozzle). To model and understand differences in stress results obtained for an internal pressure load case using a two-dimensional (2-D) axi-symmetric finite element model (FEM) vs. a three-dimensional (3-D) FEM for these PWR nozzles. In particular, the ovalization (stress concentration) effect of two intersecting cylinders, which is typical of RPV nozzle configurations, was investigated. To investigate the applicability of previously recommended linear elastic fracture mechanics (LEFM) hand solutions for calculating the Mode I stress intensity factor for a postulated nozzle corner crack for pressure loading for these PWR nozzles. These analyses were performed to further expand earlier work completed to support potential revision and refinement of Title 10 to the U.S. Code of Federal Regulations (CFR), Part 50, Appendix G, Fracture Toughness Requirements, and are intended to supplement similar evaluation of nozzles presented at the 2008, 2009, and 2011 Pressure Vessels and Piping (PVP

  14. Dyke propagation and tensile fracturing at high temperature and pressure, insights from experimental rock mechanics.

    NASA Astrophysics Data System (ADS)

    Bakker, Richard; Benson, Philip; Vinciguerra, Sergio

    2014-05-01

    It is well known that magma ascends trough the crust by the process of dyking. To enable dyke emplacement, basement rocks typically fail in a mode 1 fracture, which acts as conduits for magma transport. An overpressure of the ascending magma will further open/widen the fracture and permit the fracture to propagate. In order to further understand the emplacement and arrest of dykes in the subsurface, analogue and numerical studies have been conducted. However, a number of assumptions regarding rock mechanical behaviour frequently has to be made as such data are very hard to directly measure at the pressure/temperature conditions of interest: high temperatures at relatively shallow depths. Such data are key to simulating the magma intrusion dynamics through the lithologies that underlie the volcanic edifice. Here we present a new laboratory setup, which allows us to investigate the tensile fracturing properties under both temperature and confining pressure, and the emplacement of molten material within the newly formed fracture. We have modified a traditional tri-axial test assembly setup to be able to use a Paterson type High Pressure, High Temperature deformation apparatus. Sample setup consists of cylindrical rock samples with a 22 mm diameter and a 8 mm bore at their centre, filled with a material chosen as such that it's in a liquid state at the experimental temperature and solid at room temperature to enable post-experiment analysis. The top and lower parts of the rock sample are fitted with plugs, sealing in the melt. The assembly is then placed between ceramic pistons to ensure there are no thermal gradients across the sample. The assembly is jacketed to ensure the confining medium (Ar) cannot enter the assembly. A piston is driven into the sample such that the inner conduit materials pressure is slowly increased. At some point a sufficient pressure difference between the inner and outer surfaces causes the sample to deform and fail in the tensile regime

  15. NESC-VII: Fracture Mechanics Analyses of WPS Experiments on Large-scale Cruciform Specimen

    SciTech Connect

    Yin, Shengjun; Williams, Paul T; Bass, Bennett Richard

    2011-01-01

    This paper describes numerical analyses performed to simulate warm pre-stress (WPS) experiments conducted with large-scale cruciform specimens within the Network for Evaluation of Structural Components (NESC-VII) project. NESC-VII is a European cooperative action in support of WPS application in reactor pressure vessel (RPV) integrity assessment. The project aims in evaluation of the influence of WPS when assessing the structural integrity of RPVs. Advanced fracture mechanics models will be developed and performed to validate experiments concerning the effect of different WPS scenarios on RPV components. The Oak Ridge National Laboratory (ORNL), USA contributes to the Work Package-2 (Analyses of WPS experiments) within the NESCVII network. A series of WPS type experiments on large-scale cruciform specimens have been conducted at CEA Saclay, France, within the framework of NESC VII project. This paper first describes NESC-VII feasibility test analyses conducted at ORNL. Very good agreement was achieved between AREVA NP SAS and ORNL. Further analyses were conducted to evaluate the NESC-VII WPS tests conducted under Load-Cool-Transient- Fracture (LCTF) and Load-Cool-Fracture (LCF) conditions. This objective of this work is to provide a definitive quantification of WPS effects when assessing the structural integrity of reactor pressure vessels. This information will be utilized to further validate, refine, and improve the WPS models that are being used in probabilistic fracture mechanics computer codes now in use by the NRC staff in their effort to develop risk-informed updates to Title 10 of the U.S. Code of Federal Regulations (CFR), Part 50, Appendix G.

  16. Quantifying mechanical properties in a murine fracture healing system using inverse modeling: preliminary work

    NASA Astrophysics Data System (ADS)

    Miga, Michael I.; Weis, Jared A.; Granero-Molto, Froilan; Spagnoli, Anna

    2010-03-01

    Understanding bone remodeling and mechanical property characteristics is important for assessing treatments to accelerate healing or in developing diagnostics to evaluate successful return to function. The murine system whereby mid-diaphaseal tibia fractures are imparted on the subject and fracture healing is assessed at different time points and under different therapeutic conditions is a particularly useful model to study. In this work, a novel inverse geometric nonlinear elasticity modeling framework is proposed that can reconstruct multiple mechanical properties from uniaxial testing data. To test this framework, the Lame' constants were reconstructed within the context of a murine cohort (n=6) where there were no differences in treatment post tibia fracture except that half of the mice were allowed to heal 4 days longer (10 day, and 14 day healing time point, respectively). The properties reconstructed were a shear modulus of G=511.2 +/- 295.6 kPa, and 833.3+/- 352.3 kPa for the 10 day, and 14 day time points respectively. The second Lame' constant reconstructed at λ=1002.9 +/-42.9 kPa, and 14893.7 +/- 863.3 kPa for the 10 day, and 14 day time points respectively. An unpaired Student t-test was used to test for statistically significant differences among the groups. While the shear modulus did not meet our criteria for significance, the second Lame' constant did at a value p<0.0001. Traditional metrics that are commonly used within the bone fracture healing research community were not found to be statistically significant.

  17. Unravelling the quenching mechanisms of a luminescent Ru(II) probe for Cu(II).

    PubMed

    Santos, André Ribeiro; Escudero, Daniel; González, Leticia; Orellana, Guillermo

    2015-03-01

    We have investigated the photophysical and photochemical features of a luminescent heteroleptic Ru(II)-polypyridyl probe and of its corresponding Ru(II)-Cu(II) dinuclear complex formed upon the analyte binding through extensive density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The molecular probe contains the tailored imidazo[4,5-f]-1,10-phenanthroline (IIP) ligand for simultaneously binding the Ru(II) core and the target metal ion in aqueous solution. We have rationalized the static photoluminescence quenching observed upon the Cu(II) coordination, on the grounds of distinct excited state deactivation mechanisms which are absent in the free Ru(II) complex probe. Additionally, the emission quenching found upon increasing the solution pH has also been investigated. When coordinated IIP deprotonates, the nature of the lowest excited state of its complex changes from (3)MLCT to (3)LLCT/(3)IL. The strong base-induced emission quenching can be understood in terms of both the energy-gap law, since the (3)LLCT/(3)IL states lie at a significantly lower energy than the (3)MLCT state increasing the contribution of non-radiative mechanisms, and the expected slower radiative rates from such (3)LLCT/(3)IL states. After Cu(II) binding, the lowest triplet excited state is similar to the analyte-free probe in both energy and electronic nature. However, Cu-centered non-radiative excited states, populated after photoinduced electron transfer and intersystem crossing processes, are responsible for the population drainage of the emissive state.

  18. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    DOE PAGES

    Lee, Seok Woo; Lee, Hyun -Wook; Ryu, Ill; ...

    2015-06-26

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Here, we demonstrate physical and mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics somore » that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated Si by lessening the tensile stress concentrations in Si structures. Lastly, this study will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.« less

  19. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    SciTech Connect

    Lee, Seok Woo; Lee, Hyun-Wook; Ryu, Ill; Nix, William D.; Gao, Huajian; Cui, Yi; /Stanford U., Materials Sci. Dept. /SLAC

    2015-06-01

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Herein, we demonstrate physical/mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515. SLAC-PUB-16300 2 lithiated Si by lessening the tensile stress concentrations in Si structures. This study will contribute to improved design of Si structures at the electrode level for high performance Li-ion batteries.

  20. Fracture mechanisms in dual phase steels based on the acicular ferrite + martensite/austenite microstructure

    NASA Astrophysics Data System (ADS)

    Poruks, Peter

    The fracture mechanisms of low carbon microalloyed plate steels based on the acicular ferrite + marten site/austenite microstructure (AF + M/A) are investigated. The final microstructure consists of a dispersed phase of submicron equi-axed martensite particles with a bainitic ferrite matrix. A series of plates with M/A volume fractions of 0.076--0.179 are studied. Brittle fracture is investigated by Instrumented Charpy impact testing of samples at -196°C and subsequent metallography. The M/A particles are identified as the crack nucleation sites and the cleavage fracture stress calculated to be 2400 MPa in a complete AF microstrucuture. This value is significantly larger than in steels that contain significant proportions of conventional bainite. Standard Charpy and Instrumented Charpy impact testing is conducted through a temperature range from -80 to + 22°C to study ductile fracture behaviour. The total absorbed energy is separated into energies of crack nucleation and of crack propagation. It is found that the energy of crack nucleation is weakly dependent on the volume fraction of M/A and completely independent of temperature over the range studied. The crack propagation energy varies significantly with both variables, decreasing with increased volume fraction of M/A and with decreasing temperature. The peak load in the instrumented Charpy data is used to calculate the dynamic fracture toughness, KId, which is found to be 105--120 MPa-m1/2. The void nucleation and void growth stages of ductile fracture are studied by metallographic examination of tensile bars. The sites of void nucleation are identified as inclusions and M/A particles. Voids nucleate at the M/A particles by decohesion of the particle-matrix interface. A constant void nucleation strain of epsilon = 0.90 +/- 0.05 is measured for all of the samples independent of the volume fraction of M/A. A stress-based criterion is used to predict void nucleation and the interface strength is determined to be

  1. Erwin Schroedinger and the rise of Wave mechanics. II. The creation of wave mechanics

    SciTech Connect

    Mehra, J.

    1987-12-01

    This article (Part II) deals with the creation of the theory of wave mechanics by Erwin Schroedinger in Zurich during the early months of 1926; he laid the foundations of this theory in his first two communications to Annalen der Physik. The background of Schroedinger's work on, and his actual creation of, wave mechanics are analyzed.

  2. Anomalous surface states modify the size-dependent mechanical properties and fracture of silica nanowires

    NASA Astrophysics Data System (ADS)

    Tang, Chun; Dávila, Lilian P.

    2014-10-01

    Molecular dynamics simulations of amorphous silica nanowires under tension were analyzed for size and surface stress effects on mechanical properties and for structural modifications via bond angle distributions. Their fracture behavior was also investigated beyond the elastic limit. The Young’s moduli of silica nanowires were predicted to be about 75-100 GPa, depending on the nanowire size. The ultimate strength was calculated to be ˜10 GPa, depending on the diameter, which is in excellent agreement with the experiments. The dependence of the Young’s modulus on nanowire diameter is explained in terms of surface compressive stress effects. The fracture behavior of nanowires was also found to be influenced by surface compressive stresses. Bond angle distribution analysis of various nanowires reveals significant compressive surface states, as evidenced by the appearance of a secondary peak in the Si-O-Si bond angle distribution at ˜97°, which is absent in bulk silica. The strain rate was found to have a negligible effect on the Young’s modulus of the silica nanowires, but it has a critical role in determining their fracture mode.

  3. Fracture Mechanisms of Zirconium Diboride Ultra-High Temperature Ceramics under Pulse Loading

    NASA Astrophysics Data System (ADS)

    Skripnyak, Vladimir V.; Bragov, Anatolii M.; Skripnyak, Vladimir A.; Lomunov, Andrei K.; Skripnyak, Evgeniya G.; Vaganova, Irina K.

    2015-06-01

    Mechanisms of failure in ultra-high temperature ceramics (UHTC) based on zirconium diboride under pulse loading were studied experimentally by the method of SHPB and theoretically using the multiscale simulation method. The obtained experimental and numerical data are evidence of the quasi-brittle fracture character of nanostructured zirconium diboride ceramics under compression and tension at high strain rates and the room temperatures. Damage of nanostructured porous zirconium diboride -based UHTC can be formed under stress pulse amplitude below the Hugoniot elastic limit. Fracture of nanostructured ultra-high temperature ceramics under pulse and shock-wave loadings is provided by fast processes of intercrystalline brittle fracture and relatively slow processes of quasi-brittle failure via growth and coalescence of microcracks. A decrease of the shear strength can be caused by nano-voids clusters in vicinity of triple junctions between ceramic matrix grains and ultrafine-grained ceramics. This research was supported by grants from ``The Tomsk State University Academic D.I. Mendeleev Fund Program'' and also N. I. Lobachevski State University of Nizhny Novgorod (Grant of post graduate mobility).

  4. Friction Stir-Welded Titanium Alloy Ti-6Al-4V: Microstructure, Mechanical and Fracture Properties

    NASA Astrophysics Data System (ADS)

    Sanders, D. G.; Edwards, P.; Cantrell, A. M.; Gangwar, K.; Ramulu, M.

    2015-05-01

    Friction stir welding (FSW) has been refined to create butt welds from two sheets of Ti-6Al-4V alloy to have an ultra-fine grain size. Weld specimen testing was completed for three different FSW process conditions: As welded, stress relieved, stress relieved and machined, and for the un-welded base material. The investigation includes macrostructure, microstructure, microhardness, tensile property testing, notched bar impact testing, and fracture toughness evaluations. All experiments were conducted in accordance with industry standard testing specifications. The microstructure in the weld nugget was found to consist of refined and distorted grains of alpha in a matrix of transformed beta containing acicular alpha. The enhanced fracture toughness of the welds is a result of increased hardness, which is attributed to an increase in alpha phase, increase in transformed beta in acicular alpha, and grain refinement during the weld process. The noted general trend in mechanical properties from as welded, to stress relieved, to stress relieved and machined conditions exhibited a decrease in ultimate tensile strength, and yield strength with a small increase in ductility and a significant increase in fracture toughness.

  5. Mechanical design of the CDF SVX II silicon vertex detector

    SciTech Connect

    Skarha, J.E.

    1994-08-01

    A next generation silicon vertex detector is planned at CDF for the 1998 Tevatron collider run with the Main Injector. The SVX II silicon vertex detector will allow high luminosity data-taking, enable online triggering of secondary vertex production, and greatly increase the acceptance for heavy flavor physics at CDF. The design specifications, geometric layout, and early mechanical prototyping work for this detector are discussed.

  6. Interlaminar fracture reinforcement under mode-II loading: Post-cure through-thickness reinforcement of graphite epoxy, unidirectional laminates

    NASA Astrophysics Data System (ADS)

    Jacobson, Joel B.

    A novel through-thickness reinforcement method proposed by S. Kravchenko et al., has been static tested under mode II loading using end notched flexure (ENF), unidirectional laminate specimens to determine the impact on the apparent critical fracture toughness (GIIc) for the material tested. Both experimental and numerical methods have been employed in an attempt to characterize and model these effects. Testing and analysis were conducted on two different specimen thickness, 2.34 mm and 3.54 mm nominally. ASTM D7905/7905M -- 14 was followed during the experimental portion of the thick specimens. Multiple reinforcing configurations using the proposed technique were experimentally tested including single, double, and quadruple rows of orthogonal, pultruded carbon/epoxy pins located within the crack and ahead of the crack (pristine material) to determine the effect on the apparent critical fracture toughness for each configuration. Both pre-cracked and no pre-cracked specimens were evaluated. The results of this study indicate that specimens pinned in the crack experienced the highest supportable reaction force such that the crack was completely arrested and most of the specimens failed in flexure. Pre-cracked specimens that were pinned in the body exhibited stable crack growth as well as a shadowing phenomenon. Both pins and the crack surface topography due to this phenomenon are attributed to the increased apparent fracture toughness for these specimens. Similar outcomes were observed through numerical simulations for the models simulated in this study.

  7. Experiments on fracture toughness of thick-wall cylinder for modes I, II, III

    SciTech Connect

    Saegusa, T.; Urabe, N.; Ito, C.; Shirai, K.; Kosaki, A.

    1999-07-01

    There have been few data on fracture toughness for Mode 2 and 3 as compared with those for Mode 1. Experimental data on fracture toughness of plates made of ductile cast iron (ASTM A874-89) and forged steel (ASME SA350 LF5 C1.1) were obtained at a temperature range from 77K to 293K for Mode 1, 2 and 3. The results showed: J{sub IC} < J{sub IIC} < J{sub IIIC}, and K{sub IC} < K{sub IIC} K{sub IIIC}. Integrity of a thick-wall cylinder with artificial flaw was demonstrated against brittle fracture at 233K for Mode 1, 2 and 3, which is one of the design requirements of containers shipping radioactive materials.

  8. Temporary space maintainers retained with composite resin. Part II: Fracture load in vitro.

    PubMed

    Grajower, R; Stern, N; Zamir, S T; Kohavi, D

    1981-01-01

    The average fracture load during occlusal loading of pontics which were bonded to natural abutment teeth in vitro was found to be 56.1, 57.5 and 74.2 kg for natural, acrylic resin, and Restodent pontics, respectively. Coating the roots of the abutment teeth with a thin layer of silicone rubber before embedding them in stone slightly reduced the strength of the fixed partial dentures. Thermocycling the specimens with coated roots caused a considerable decrease in strength to fracture loads of 33.0, 17.9, and 37.3 kg for natural, acrylic resin, and Restodent pontics, respectively. Fracture of the enamel of natural tooth pontics was observed in a few specimens. The superior strength of the fixed partial dentures with natural tooth and Restodent pontics would indicate that these pontics are superior for clinical trials rather than acrylic resin pontics.

  9. Materials characterization and fracture mechanics of a space grade dielectric silicone insulation

    NASA Technical Reports Server (NTRS)

    Abdel-Latif, A. I.; Tweedie, A. T.

    1982-01-01

    The present investigation is concerned with the DC 93-500 high voltage silicone insulation material employed to pot the gun and the collector end of a traveling wave tube (TWT) used on the Landsat D Satellite. The fracture mechanics behavior of the silicone resin was evaluated by measuring the slow crack velocity as a function of the opening mode of the stress intensity factor at +25 and -10 C, taking into account various uniaxial discrete strain values. It was found that the silicone resins slow crack growth is faster than that for a high voltage insulation polyurethane material at the same stress intensity factor value and room temperature.

  10. Use of holographic optical elements in speckle metrology. Part 3: application to fracture mechanics.

    PubMed

    Shakher, C; Yadav, H L

    1991-09-01

    In this work a two-hololens imaging system has been used to measure crack-mouth opening displacement and crack-tip opening displacement to determine the stress intensity factor K(1), the crack-tip plastic zone size r(p)(*) and the rotational factor r in a beam specimen having the central edge crack subjected to three-point bending using focused plane speckle photography. Experimental results are in good agreement with theoretical predictions. Current experimental investigations establish that low-cost holographic optics can be advantageously used in speckle metrology to solve complex problems of fracture mechanics.

  11. Fracture mechanics. [review of fatigue crack propagation and technology of constructing safe structures

    NASA Technical Reports Server (NTRS)

    Hardrath, H. F.

    1974-01-01

    Fracture mechanics is a rapidly emerging discipline for assessing the residual strength of structures containing flaws due to fatigue, corrosion or accidental damage and for anticipating the rate of which such flaws will propagate if not repaired. The discipline is also applicable in the design of structures with improved resistance to such flaws. The present state of the design art is reviewed using this technology to choose materials, to configure safe and efficient structures, to specify inspection procedures, to predict lives of flawed structures and to develop reliability of current and future airframes.

  12. Modeling mechanical degradation in lithium ion batteries during cycling: Solid electrolyte interphase fracture

    NASA Astrophysics Data System (ADS)

    Laresgoiti, Izaro; Käbitz, Stefan; Ecker, Madeleine; Sauer, Dirk Uwe

    2015-12-01

    During cycling, mechanical stresses can occur in the composite electrode, inside the active material, but also in the solid electrolyte interphase layer. A mechanical model is proposed based on a system made of a spherical graphite particle surrounded by the solid electrolyte interphase layer. During lithium intercalation or de-intercalation, stresses in the graphite are produced, governed by the diffusion induced stress phenomena and in the solid electrolyte interphase, driven by the graphite expansion. The stresses in both materials were simulated and a sensitivity analysis was performed to clarify the influence of principal parameters on both processes. Finally, assuming that the solid electrolyte interphase is the weakest material and therefore more prone to fracture than graphite, the experimental capacity fade during cycling was modeled based on its break and repair effect rather than on the fracture of the active material. The mechanical model of the solid electrolyte interphase was implemented in a single particle lithium ion battery model in order to reproduce capacity fade during battery lifetime. The model results were compared against cycle life aging experimental data, reproducing accurately the influence of the depth of discharge as well as the average state of charge on the capacity fade.

  13. A Review on Recent Contribution of Meshfree Methods to Structure and Fracture Mechanics Applications

    PubMed Central

    Daxini, S. D.; Prajapati, J. M.

    2014-01-01

    Meshfree methods are viewed as next generation computational techniques. With evident limitations of conventional grid based methods, like FEM, in dealing with problems of fracture mechanics, large deformation, and simulation of manufacturing processes, meshfree methods have gained much attention by researchers. A number of meshfree methods have been proposed till now for analyzing complex problems in various fields of engineering. Present work attempts to review recent developments and some earlier applications of well-known meshfree methods like EFG and MLPG to various types of structure mechanics and fracture mechanics applications like bending, buckling, free vibration analysis, sensitivity analysis and topology optimization, single and mixed mode crack problems, fatigue crack growth, and dynamic crack analysis and some typical applications like vibration of cracked structures, thermoelastic crack problems, and failure transition in impact problems. Due to complex nature of meshfree shape functions and evaluation of integrals in domain, meshless methods are computationally expensive as compared to conventional mesh based methods. Some improved versions of original meshfree methods and other techniques suggested by researchers to improve computational efficiency of meshfree methods are also reviewed here. PMID:24516359

  14. Modeling and additive manufacturing of bio-inspired composites with tunable fracture mechanical properties.

    PubMed

    Dimas, Leon S; Buehler, Markus J

    2014-07-07

    Flaws, imperfections and cracks are ubiquitous in material systems and are commonly the catalysts of catastrophic material failure. As stresses and strains tend to concentrate around cracks and imperfections, structures tend to fail far before large regions of material have ever been subjected to significant loading. Therefore, a major challenge in material design is to engineer systems that perform on par with pristine structures despite the presence of imperfections. In this work we integrate knowledge of biological systems with computational modeling and state of the art additive manufacturing to synthesize advanced composites with tunable fracture mechanical properties. Supported by extensive mesoscale computer simulations, we demonstrate the design and manufacturing of composites that exhibit deformation mechanisms characteristic of pristine systems, featuring flaw-tolerant properties. We analyze the results by directly comparing strain fields for the synthesized composites, obtained through digital image correlation (DIC), and the computationally tested composites. Moreover, we plot Ashby diagrams for the range of simulated and experimental composites. Our findings show good agreement between simulation and experiment, confirming that the proposed mechanisms have a significant potential for vastly improving the fracture response of composite materials. We elucidate the role of stiffness ratio variations of composite constituents as an important feature in determining the composite properties. Moreover, our work validates the predictive ability of our models, presenting them as useful tools for guiding further material design. This work enables the tailored design and manufacturing of composites assembled from inferior building blocks, that obtain optimal combinations of stiffness and toughness.

  15. Alteration of Fractured Rocks Due to Coupled Chemical and Mechanical Processes: High-Resolution Simulations and Experimental Observations

    NASA Astrophysics Data System (ADS)

    Ameli, Pasha

    Engineering activities such as enhanced geothermal energy production and improved oil recovery techniques are heavily dependent on the permeability of the subsurface, while others such as CO2 sequestration and nuclear waste disposal rely on the efficiency of rock formations as transport barriers. In either case fractures provide the main pathways for fluid flow and transport, especially in rocks with lower matrix porosity. Laboratory experiments aimed at quantifying the chemo-mechanical responses of fractures have shown a range of results, some of which contradict simple conceptual models. For example, under conditions favoring mineral dissolution, where one would expect an overall increase in permeability, experiments show that permeability increases under some conditions and decreases under others. Recent experiments have attempted to link these core-scale observations to the relevant small-scale processes occurring within fractures. Results suggest that the loss of mechanical strength in asperities due to chemical alteration may cause non-uniform deformation and alteration of fracture apertures. However, due to the lack of direct micro-scale measurements of the coupled chemical and mechanical processes that lead to alteration of contacting fracture surfaces, our ability to predict the long-term evolution of fractures is still limited. To explore the processes that control permeability evolution, I developed a computational model that uses micro-scale surface roughness and explicitly couples dissolution and elastic deformation to calculate local alterations in fracture aperture under chemical and mechanical stresses. A depth-averaged algorithm of fracture flow is used to model reactive transport and chemical alteration of the fracture surfaces. Then, I deform the resulting altered fracture-surfaces using an algorithm that calculates the elastic deformation. The results of the model are compared with flow-through experiments conducted on fractured limestone. The

  16. Mechanisms of defect complex formation and environmental-assisted fracture behavior of iron aluminides

    SciTech Connect

    Cooper, B.R.; Muratov, L.S.; Kang, B.S.J.; Li, K.Z.

    1997-12-01

    Iron aluminide has excellent corrosion resistance in high-temperature oxidizing-sulfidizing environments; however, there are problems at room and medium temperature with hydrogen embrittlement as related to exposure to moisture. In this research, a coordinated computational modeling/experimental study of mechanisms related to environmental-assisted fracture behavior of selected iron aluminides is being undertaken. The modeling and the experimental work will connect at the level of coordinated understanding of the mechanisms for hydrogen penetration and for loss of strength and susceptibility to fracture. The focus of the modeling component at this point is on the challenging question of accurately predicting the iron vacancy formation energy in Fe{sub 3}A{ell} and the subsequent tendency, if present, for vacancy clustering. The authors have successfully performed, on an ab initio basis, the first calculation of the vacancy formation energy in Fe{sub 3}A{ell}. These calculations include lattice relaxation effects which are quite large. This has significant implications for vacancy clustering effects with consequences to be explored for hydrogen diffusion. The experimental work at this stage has focused on the relationship of the choice and concentration of additives to the improvement of resistance to hydrogen embrittlement and hence to the fracture behavior. For this reason, comparative crack growth tests of FA-186, FA-187, and FA-189 iron aluminides (all with basic composition of Fe-28A{ell}-5Cr, at % with micro-alloying additives of Zr, C or B) under, air, oxygen, or water environment have been performed. These tests showed that the alloys are susceptible to room temperature hydrogen embrittlement in both B2 and DO{sub 3} conditions. Test results indicated that FA-187, and FA-189 are intrinsically more brittle than FA-186.

  17. Long-term cumulative survival and mechanical complications of single-tooth Ankylos Implants: focus on the abutment neck fractures

    PubMed Central

    2015-01-01

    PURPOSE To evaluate the cumulative survival rate (CSR) and mechanical complications of single-tooth Ankylos® implants. MATERIALS AND METHODS This was a retrospective clinical study that analyzed 450 single Ankylos® implants installed in 275 patients between December 2005 and December 2012. The main outcomes were survival results CSR and implant failure) and mechanical complications (screw loosening, fracture, and cumulative fracture rate [CFR]). The main outcomes were analyzed according to age, sex, implant length or diameter, bone graft, arch, and position. RESULTS The 8-year CSR was 96.9%. Thirteen (2.9%) implants failed because of early osseointegration failure in 3, marginal bone loss in 6, and abutment fracture in 4. Screw loosening occurred in 10 implants (2.2%), and 10 abutment fractures occurred. All abutment fractures were located in the neck, and concurrent screw fractures were observed. The CSR and rate of screw loosening did not differ significantly according to factors. The CFR was higher in middle-aged patients (5.3% vs 0.0% in younger and older patients); for teeth in a molar position (5.8% vs 0.0% for premolar or 1.1% for anterior position); and for larger-diameter implants (4.5% for 4.5 mm and 6.7% for 5.5 mm diameter vs 0.5% for 3.5 mm diameter) (all P<.05). CONCLUSION The Ankylos® implant is suitable for single-tooth restoration in Koreans. However, relatively frequent abutment fractures (2.2%) were observed and some fractures resulted in implant failures. Middle-aged patients, the molar position, and a large implant diameter were associated with a high incidence of abutment fracture. PMID:26813443

  18. Stimuli Responsive/Rheoreversible Hydraulic Fracturing Fluids for Enhanced Geothermal Energy Production (Part II)

    SciTech Connect

    Bonneville, Alain; Jung, Hun Bok; Shao, Hongbo; Kabilan, Senthil; Um, Wooyong; Carroll, Kenneth C.; Varga, Tamas; Suresh, Niraj; Stephens, Sean A.; Fernandez, Carlos A.

    2014-12-14

    We have used an environmentally friendly and recyclable hydraulic fracturing fluid - diluted aqueous solutions of polyallylamine or PAA – for reservoir stimulation in Enhanced Geothermal System (EGS). This fluid undergoes a controlled and large volume expansion with a simultaneous increase in viscosity triggered by CO2 at EGS temperatures. We are presenting here the results of laboratory-scale hydraulic fracturing experiment using the fluid on small cylindrical rock cores (1.59 cm in diameter and 5.08 cm in length) from the Coso geothermal field in California. Rock samples consisted of Mesozoic diorite metamorphosed to greenschist facies. The experiments were conducted on 5 samples for realistic ranges of pressures (up to 275 bar) and temperatures (up to 210 °C) for both the rock samples and the injected fluid. After fracturing, cores were subjected to a CO2 leakage test, injection of KI solution, and X-ray microtomography (XMT) scanning to examine the formation and distribution of fractures. The design and conduct of these experiments will be presented and discussed in details. Based on the obtained XMT images, Computational Fluid Dynamics (CFD) simulations were then performed to visualize hydraulic fractures and compute the bulk permeability. OpenFOAM (OpenCFD Ltd., Reading, UK), was used to solve the steady state simulation. The flow predictions, based upon the laminar, 3-D, incompressible Navier-Stokes equations for fluid mass and momentum, show the remarkable stimulation of the permeability in the core samples and demonstrate the efficiency of such a CO2 triggered fluid in EGS.

  19. A New Approximate Fracture Mechanics Analysis Methodology for Composites with a Crack or Hole

    NASA Technical Reports Server (NTRS)

    Tsai, H. C.; Arocho, A.

    1990-01-01

    A new approximate theory which links the inherent flaw concept with the theory of crack tip stress singularities at a bi-material interface was developed. Three assumptions were made: (1) the existence of inherent flaw (i.e., damage zone) at the tip of the crack, (2) a fracture of the filamentary composites initiates at a crack lying in the matrix material at the interface of the matrix/filament, and (3) the laminate fails whenever the principal load-carrying laminae fails. This third assumption implies that for a laminate consisting of 0 degree plies, cracks into matrix perpendicular to the 0 degree filaments are the triggering mechanism for the final failure. Based on this theory, a parameter bar K sub Q which is similar to the stress intensity factor for isotropic materials but with a different dimension was defined. Utilizing existing test data, it was found that bar K sub Q can be treated as a material constant. Based on this finding a fracture mechanics analysis methodology was developed. The analytical results are correlated well with test results. This new approximate theory can apply to both brittle and metal matrix composite laminates with crack or hole.

  20. Fracture mechanics models developed for piping reliability assessment in light water reactors: piping reliability project

    SciTech Connect

    Harris, D.O.; Lim, E.Y.; Dedhia, D.D.; Woo, H.H.; Chou, C.K.

    1982-06-01

    The efforts concentrated on modifications of the stratified Monte Carlo code called PRAISE (Piping Reliability Analysis Including Seismic Events) to make it more widely applicable to probabilistic fracture mechanics analysis of nuclear reactor piping. Pipe failures are considered to occur as the result of crack-like defects introduced during fabrication, that escape detection during inspections. The code modifications allow the following factors in addition to those considered in earlier work to be treated: other materials, failure criteria and subcritical crack growth characteristic; welding residual and vibratory stresses; and longitudinal welds (the original version considered only circumferential welds). The fracture mechanics background for the code modifications is included, and details of the modifications themselves provided. Additionally, an updated version of the PRAISE user's manual is included. The revised code, known as PRAISE-B was then applied to a variety of piping problems, including various size lines subject to stress corrosion cracking and vibratory stresses. Analyses including residual stresses and longitudinal welds were also performed.

  1. Laser Speckle Metrology Using Holo-Lens Imaging System And Its Application In Fracture Mechanics

    NASA Astrophysics Data System (ADS)

    Shakher, Chandra; Rao, G. Venkata; Lal Yadav, Heera; Gupta, B. N.

    1987-01-01

    It has already been shown 1,2 that by using proper recording and playback geometries, almost diffraction limited performance in speckle metrology can be achieved over the entire object field which can be imaged by two hololens configuration. Because of the complexities encountered in closed form or numerical solutions in the area of theoretical fracture mechanics, carefully controlled experiment which can provide more accurate data is essential for validating the theoretical results. Therefore use of holographic optics in fracture mechanics has an edge over conventional optics. This paper concentrates on the study of crack opening problem, in a beam specimen having central edge crack subjected to three point bending (Fig.1), using focused plane speckle photography and two holo-lens imaging configuration. Fig. 2 shows the schematic of the typical imaging system used in the experiment. The lenses used in the experiment were all recorded using di vering spherical and plane waves. The recording and play back geometries are discussed elsewhere (See Ref. 2).

  2. A mechanism for the production of ultrafine particles from concrete fracture.

    PubMed

    Jabbour, Nassib; Rohan Jayaratne, E; Johnson, Graham R; Alroe, Joel; Uhde, Erik; Salthammer, Tunga; Cravigan, Luke; Faghihi, Ehsan Majd; Kumar, Prashant; Morawska, Lidia

    2017-03-01

    While the crushing of concrete gives rise to large quantities of coarse dust, it is not widely recognized that this process also emits significant quantities of ultrafine particles. These particles impact not just the environments within construction activities but those in entire urban areas. The origin of these ultrafine particles is uncertain, as existing theories do not support their production by mechanical processes. We propose a hypothesis for this observation based on the volatilisation of materials at the concrete fracture interface. The results from this study confirm that mechanical methods can produce ultrafine particles (UFP) from concrete, and that the particles are volatile. The ultrafine mode was only observed during concrete fracture, producing particle size distributions with average count median diameters of 27, 39 and 49 nm for the three tested concrete samples. Further volatility measurements found that the particles were highly volatile, showing between 60 and 95% reduction in the volume fraction remaining by 125 °C. An analysis of the volatile fraction remaining found that different volatile material is responsible for the production of particles between the samples.

  3. Grain Size Effect of Commercial Pure Titanium Foils on Mechanical Properties, Fracture Behaviors and Constitutive Models

    NASA Astrophysics Data System (ADS)

    Daming, Nie; Zhen, Lu; Kaifeng, Zhang

    2017-02-01

    The constitutive models based on grain size effect are crucial for analyzing the deformation of metal foils. Previous investigations on the constitutive models concentrate on the foils whose thickness/average grain diameter (T/D) ratios are more than 3. In this study, the commercial pure titanium foils with thickness of 0.1 and 0.2 mm were employed as the experimental materials. The mechanical properties of foils with dimensions of nine different T/D ratios categorized into three ranges (T/D < 1, 1 ≤ T/D < 3, T/D ≥ 3)were tested. Meanwhile, the fracture behaviors and fracture mechanisms of the samples with different T/D ratios were compared and analyzed. Besides, three constitutive models incorporating the surface layer effect and grain boundary strengthening effect were established for the three T/D ratio ranges correspondingly. In these models, the thickness of the surface layers is set T for T/D < 1 foils, D for T/D > 3, and increases with D linearly in 1 ≤ T/D < 3. The results calculated by the three models were compared. The experiments indicate that those models are all in good agreement.

  4. Mechanisms of fracture of the free surface of shock-compressed metals

    SciTech Connect

    Mokhova, V. V. Mikhailov, A. L.; Til’kunov, A. V.; Orlov, N. I.; Kanunova, L. I.; Bragunets, V. A.; Tkachenko, M. I.; Simakov, V. G.; Sokolov, S. S.; Podurets, A. M.

    2015-12-15

    The mechanisms of the ejection of aluminum and copper microparticles from the free surfaces of these metals have been studied under conditions of the escape of a moderate-intensity shock wave from a sample. The free surfaces of samples contained 0.7–0.9 mm deep artificial wells and protrusions simulating (on a greater scale of 10: 1) the natural surface roughness retained upon mechanical processing. The pressure in a shock-wave pulse at the base of a protrusion was controlled within P = 5–20 GPa (i.e., below the melting region), and the variable duration of pressure pulses was 0.02, 0.2, and 1 μs. Analysis of the free surfaces of postloaded samples showed that, for certain loading and roughness parameters, the ejection of metal from vertices of protruding ridges or pyramids (as a result of the longitudinal fracture) was about ten times greater than the amount of metal ejected in the form of cumulative jets from wells. The amount of ejected metal and the size distribution of metal microparticles were quantitatively characterized using “soft collecting targets” and by measuring mass losses of samples upon fracture.

  5. Fracture mechanics based design for radioactive material transport packagings -- Historical review

    SciTech Connect

    Smith, J.A.; Salzbrenner, D.; Sorenson, K.; McConnell, P.

    1998-04-01

    The use of a fracture mechanics based design for the radioactive material transport (RAM) packagings has been the subject of extensive research for more than a decade. Sandia National Laboratories (SNL) has played an important role in the research and development of the application of this technology. Ductile iron has been internationally accepted as an exemplary material for the demonstration of a fracture mechanics based method of RAM packaging design and therefore is the subject of a large portion of the research discussed in this report. SNL`s extensive research and development program, funded primarily by the U. S. Department of Energy`s Office of Transportation, Energy Management and Analytical Services (EM-76) and in an auxiliary capacity, the office of Civilian Radioactive Waste Management, is summarized in this document along with a summary of the research conducted at other institutions throughout the world. In addition to the research and development work, code and standards development and regulatory positions are also discussed.

  6. Finite element analysis of surface cracks in the Wilkins Ice Shelf using fracture mechanics

    NASA Astrophysics Data System (ADS)

    Plate, Carolin; Müller, Ralf; Gross, Dietmar; Humbert, Angelika; Braun, Matthias

    2010-05-01

    Ice shelves, located between the warming atmosphere and the ocean, are sensitive elements of the climate system. The Wilkins Ice Shelf is situated in the south-western part of the Antarctic Peninsula, a well known hot spot of global warming. Recent break-up events exemplified the potential of disintegration of the ice shelf. A multi interdisciplinary project consisting of remote sensing, modeling of the ice dynamics and fracture mechanics intends to improve the understanding of the impacts of temperature increase on ice shelf stability. As a part of this project the aim of this presentation is to demonstrate the fracture mechanical approach using finite elements and configurational forces. For fracture mechanical purposes the material behavior of ice is treated as a brittle solid, and linear fracture mechanics is used. Crucial to all methods in linear fracture mechanics is the evaluation of the stress intensity factor K which is a measure for the load concentration at the crack tip and which depends on the geometry of the body and on the applied loading. The computed value of K can be compared to the critical stress intensity factor Kc, a material property obtained from experimental examinations, to judge whether a crack will propagate. One very effective procedure to obtain the stress intensity factor takes advantage of configurational forces, which can be easily obtained in the finite element analysis. An initial investigation is based on a 2-dimensional analysis of a single crack with a mode-I load type using a static plane strain model in the finite element analysis software COMSOL and additional routines to compute and evaluate the configurational forces. Analytical solutions of simple geometry and load cases are called on in comparison. The application to the Wilkins Ice Shelf follows by using material parameters, geometries and loading situations, which are obtained from literature values, remote sensing data analysis and modeling of the ice dynamics

  7. A predictive mechanical model for evaluating vertebral fracture probability in lumbar spine under different osteoporotic drug therapies.

    PubMed

    López, E; Ibarz, E; Herrera, A; Puértolas, S; Gabarre, S; Más, Y; Mateo, J; Gil-Albarova, J; Gracia, L

    2016-07-01

    Osteoporotic vertebral fractures represent a major cause of disability, loss of quality of life and even mortality among the elderly population. Decisions on drug therapy are based on the assessment of risk factors for fracture from bone mineral density (BMD) measurements. A previously developed model, based on the Damage and Fracture Mechanics, was applied for the evaluation of the mechanical magnitudes involved in the fracture process from clinical BMD measurements. BMD evolution in untreated patients and in patients with seven different treatments was analyzed from clinical studies in order to compare the variation in the risk of fracture. The predictive model was applied in a finite element simulation of the whole lumbar spine, obtaining detailed maps of damage and fracture probability, identifying high-risk local zones at vertebral body. For every vertebra, strontium ranelate exhibits the highest decrease, whereas minimum decrease is achieved with oral ibandronate. All the treatments manifest similar trends for every vertebra. Conversely, for the natural BMD evolution, as bone stiffness decreases, the mechanical damage and fracture probability show a significant increase (as it occurs in the natural history of BMD). Vertebral walls and external areas of vertebral end plates are the zones at greatest risk, in coincidence with the typical locations of osteoporotic fractures, characterized by a vertebral crushing due to the collapse of vertebral walls. This methodology could be applied for an individual patient, in order to obtain the trends corresponding to different treatments, in identifying at-risk individuals in early stages of osteoporosis and might be helpful for treatment decisions.

  8. Hydrologic mechanisms governing fluid flow in partially saturated, fractured, porous tuff at Yucca Mountain

    SciTech Connect

    Wang, J.S.Y.; Narasimhan, T.N.

    1984-10-01

    In contrast to the saturated zone where fluid moves rapidly along fractures, the fractures (with apertures large relative to the size of matrix pores) will desaturate first during drainage process and the bulk of fluid flow would be through interconnected pores in the matrix. Within a partially drained fracture, the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture. The residual liquid will be held by capillary force in regions around fracture contact areas where the apertures are small. Normal to the fracture surfaces, the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block. A general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions. Results are obtained from an aperture distribution model for fracture saturation, hydraulic conductivity, and effective matrix-fracture flow areas as functions of pressure. Drainage from a fractured tuff column is simulated. The parameters for the simulations are deduced from fracture surface characteristics, spacings and orientations based on core analyses, and from matrix characteristics curve based on laboratory measurements. From the cases simulated for the fractured, porous column with discrete vertical and horizontal fractures and porous matrix blocks explicitly taken into account, it is observed that the highly transient changes from fully saturated conditions to partially saturated conditions are extremely sensitive to the fracture properties. However, the quasi-steady changes of the fluid flow of a partially saturated, fractured, porous system could be approximately simulated without taking the fractures into account. 22 references, 16 figures.

  9. History of respiratory mechanics prior to World War II.

    PubMed

    West, John B

    2012-01-01

    The history of respiratory mechanics is reviewed over a period of some 2,500 years from the ancient Greeks to World War II. A cardinal early figure was Galen (130-199 AD) who made remarkably perceptive statements on the diaphragm and the anatomy of the phrenic nerves. The polymath Leonardo da Vinci (1452-1519) contributed observations on pulmonary mechanics including the pleural space and bronchial airflow that still make good reading. Vesalius (1514-1564) produced magnificent illustrations of the lung, ribcage, and diaphragm. In the 17th century, the Oxford School including Boyle, Hooke, Lower, and Mayow were responsible for many contributions on mechanical functions including the intercostal muscles and the pleura. Hales (1677-1761) calculated the size and surface area of the alveoli, the time spent by the blood in the pulmonary capillaries, and intrathoracic pressures. Poiseuille (1799-1869) carried out classical studies of fluid mechanics including one of the first demonstrations of flow limitation in collapsible vessels. The culmination of the pre-World War II period was the outstanding contributions of Rohrer (1888-1926) and his two Swiss countrymen, Wirz (1896-1978) and von Neergaard (1887-1947). Rohrer developed the first comprehensive, quantitative treatment of respiratory mechanics in the space of 10 years including an analysis of flow in airways, and the pressure-volume behavior of the respiratory system. von Neergaard performed landmark studies on the effects of surface tension on pressure-volume behavior. Progress over the 2,500 years was slow and erratic at times, but by 1940 the stage was set for the spectacular developments of the next 70 years.

  10. Stability-based classification for ankle fracture management and the syndesmosis injury in ankle fractures due to a supination external rotation mechanism of injury.

    PubMed

    Pakarinen, Harri

    2012-12-01

    sensitivity and specificity of both clinical tests were calculated using the standard 7.5-Nm external rotation stress test as reference. Outcome was assessed after a minimum of one year of follow-up. Olerud-Molander (OM) scoring system, RAND 36-Item Health Survey, and VAS to measure pain and function were used as outcome measures in all studies. In study 1, 85 (53%) fractures were treated operatively using the stability based fracture classification. Non-operatively treated patients reported less pain and better OM (good or excellent 89% vs. 71%) and VAS functional scores compared to operatively treated patients although they experienced more displacement of the distal fibula (0 mm 30% vs. 69%; 0-2 mm 65% vs. 25%) after treatment. No non-operatively treated patients required operative fracture fixation during follow-up. In study 2, AITFL exploration and suture lead to equal functional outcome (OM mean, 77 vs. 73) to no exploration or fixation. In study 3, the hook test had a sensitivity of 0.25 and a specificity of 0.98. The external rotation stress test had a sensitivity of 0.58 and a specificity of 0.9. Both tests had excellent interobserver reliability; the agreement was 99% for the hook test and 98% for the stress test. There was no statistically significant difference in functional scores (OM mean, 79.6 vs. 83.6) or pain between syndesmosis transfixation and no fixation groups (Study 4). Our results suggest that a simple stability-based fracture classification is useful in choosing between non-operative and operative treatment of ankle fractures; approximately half of the ankle fractures can be treated non-operatively with success. Our observations also suggest that relevant syndesmosis injuries are rare in ankle fractures due to an SER mechanism of injury. According to our research, syndesmotic repair or fixation in SER ankle fracture has no influence on functional outcome or pain after minimum one year compared with no fixation.

  11. Tests and Interpretation of Mixed Mode I and II Fully Plastic Fracture from Simulated Weld Defects.

    DTIC Science & Technology

    1986-07-31

    0.1). Tis means that with loi %-hardcning (t\\-nicallv highi strength) alloys, the surroiziding structure must be 3 tines stiffe’r :or fracture-stable...9 tauc / a dFxPfax.,)min t ’o a )/i) min (Eq. 7) Svm O.20050. 166 0.258 0.192 Asvm 0.072 .0 v. I 𔃿 0.18 0.215 0.181 Modified Tearing Modulus. T R E

  12. Mechanism of reductive dissolution of lepidocrocite by S(-II)

    NASA Astrophysics Data System (ADS)

    Behrends, Thilo; Hellige, Katrin; Peiffer, Stefan

    2010-05-01

    Reduction of ferric oxides by dissolved sufide species plays an important role in the redox dynamics of anaerobic subsurface environments. For example, S(-II) may be the dominant reductant for ferric oxides in sulfidic sediments and the reaction significantly contributes to the retention of reduced sulfur in these environments. The mechanism and rates of the reductive dissolution of ferric oxides by S(-II) have been frequently investigated and the reaction is generally considered to be a surface controlled process. The proposed mechanism includes the reduction of Fe(III) at the mineral surface upon S(-II) adsorption followed by the release of Fe(II) into solution, which is eventually followed by the precipitation of FeS at suitable conditions. However, several reported experimental observations, such as the remarkable high rate of lepidocrocite (g-FeOOH) reduction and the accumulation of surface bound Fe(II) (Poulton et al., 2004) are difficult to align with the proposed reaction mechanism. Here, we report experimental results which indicate that the prevailing idea about a surface controlled reaction between lepidocrocite and S(-II) has to be revised. We have studied the reaction of lepidocrocite and S(-II) in batch reactors at constant pH 8.0 by adding Na2S solution to the ferric oxide suspension. During the reaction, wide angle X-ray scattering (WAXS) and spectra from X-ray absorption (XANES and EXAFS) at the Fe K-edge (about 7.1 keV) were collected in situ by pumping suspension through a capillary, which was positioned inside the X-ray beam. These experiments were performed at the beamline BM26a (DUBBLE) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France (Nikitenko et al., 2008). Combining WAXS, XANES, and EXAFS allowed us to follow the change in the long-range periodic structure of the minerals simultaneously with changes in Fe redox state and local coordination environment. At pH 8.0 the reaction between lepidocrocite and S(-II) was

  13. A coupled thermo-poro-mechanical finite element analysis of fractured porous rocks using a cohesive interface element

    NASA Astrophysics Data System (ADS)

    Wang, W.; Regueiro, R. A.

    2014-12-01

    The coupling between multiphase flow, heat transfer, and poromechanics in fractured geomaterials has aroused great interest in the areas of geomechanics, geoenvironmental engineering, and petroleum engineering. Relevant applications include nuclear waste repositories, geological sequestration of CO2, geothermal systems, and exploitation of shale gas reservoirs. The paper presents a fully coupled thermo-poro-mechanical (TPM) cohesive interface element (CIE) model, which can represent fluid and heat flow along and across the fracture, and shear/normal deformation of the fracture surfaces. The proposed model is then applied to analyze two popular geological engineering problems using the finite element method (FEM) with a small strain formulation. The first application is the fracturing process in organic-rich shale due to heating. In the finite element analysis, multiple horizontal microcracks parallel to the bedding plane are assumed to preexist in the porous source rock, and are represented by coupled TPM cohesive interface elements. The porous bulk rock is assumed to be homogeneous, isotropic (for the time being, with transverse isotropy a natural extension), and linearly elastic. The excess pore fluid pressure, which mainly causes the development of the fractures, is actually induced by the rapid decomposition of organic matter during heating according to the literature. However, the involved complex chemical reaction process is beyond the scope of the paper, and is therefore substituted by a fluid injection process within the cracks under room temperature (25C) and high temperature (400C) in the paper. We investigate the fracture propagation due to pore fluid pressure increase and the development of fracture-induced permeability. The second application is a nuclear waste repository in a partially saturated fractured rock. Multiphase transport of moisture and heat, thermally-induced stress, as well as the change of fracture apertures are investigated due to short

  14. How vein sealing boosts fracture widening rates - The buckling-enhanced aperture growth mechanism for syn-tectonic veins

    NASA Astrophysics Data System (ADS)

    Nüchter, Jens-Alexander

    2017-01-01

    The paper introduces the mechanism of buckling-enhanced aperture growth for syn-tectonic veins that formed in simple-shear dominated kinematic frameworks in the middle or lower crust. Apart from the well understood concepts of fracture widening driven by effective tensile stresses, buckling-enhanced fracture aperture growth relates widening to active outward buckling of more viscous incipient cement layers precipitated as hydrothermal minerals for the pore fluid on the walls of juvenile syn-tectonic veins, driven by fracture-parallel compressive creep strain in the host rocks. Thus, the mechanism proposed here follows similar principles as tectonic folding, although important differences exist. Inspired by the structural record of low-aspect ratio veins exposed in HP/LT metamorphic rocks cropping out on south Evia island, Greece, generic numerical models are calculated to study development of buckling instabilities in such incompletely cemented veins and their impact on aperture growth rates. The models indicate (1) that aperture growth rates increase with increasing viscosity contrast between the host rocks and the cement layers, (2) an increase in the thickness of the cement layers cause acceleration of aperture growth, (3) that support of restraining forces at the vein tips offered by the host rocks against buckling of the cement layers cause fully compressive states of stress ahead the fracture tips, and (4) that fracture aperture growth is possible against fully compressive fracture-normal stresses. The buckling-enhanced vein aperture growth mechanism yields important implications for the maintenance and decay of fracture-bound permeability and for the mechanical state of the middle and lower crust in seismically active regions.

  15. Length-scale and strain rate-dependent mechanism of defect formation and fracture in carbon nanotubes under tensile loading

    NASA Astrophysics Data System (ADS)

    Javvaji, Brahmanandam; Raha, S.; Mahapatra, D. Roy

    2017-02-01

    Electromagnetic and thermo-mechanical forces play a major role in nanotube-based materials and devices. Under high-energy electron transport or high current densities, carbon nanotubes fail via sequential fracture. The failure sequence is governed by certain length scale and flow of current. We report a unified phenomenological model derived from molecular dynamic simulation data, which successfully captures the important physics of the complex failure process. Length-scale and strain rate-dependent defect nucleation, growth, and fracture in single-walled carbon nanotubes with diameters in the range of 0.47 to 2.03 nm and length which is about 6.17 to 26.45 nm are simulated. Nanotubes with long length and small diameter show brittle fracture, while those with short length and large diameter show transition from ductile to brittle fracture. In short nanotubes with small diameters, we observe several structural transitions like Stone-Wales defect initiation, its propagation to larger void nucleation, formation of multiple chains of atoms, conversion to monatomic chain of atoms, and finally complete fracture of the carbon nanotube. Hybridization state of carbon-carbon bonds near the end cap evolves, leading to the formation of monatomic chain in short nanotubes with small diameter. Transition from ductile to brittle fracture is also observed when strain rate exceeds a critical value. A generalized analytical model of failure is established, which correlates the defect energy during the formation of atomic chain with aspect ratio of the nanotube and strain rate. Variation in the mechanical properties such as elastic modulus, tensile strength, and fracture strain with the size and strain rate shows important implications in mitigating force fields and ways to enhance the life of electronic devices and nanomaterial conversion via fracture in manufacturing.

  16. Pressurized thermal shock probabilistic fracture mechanics sensitivity analysis for Yankee Rowe reactor pressure vessel

    SciTech Connect

    Dickson, T.L.; Cheverton, R.D.; Bryson, J.W.; Bass, B.R.; Shum, D.K.M.; Keeney, J.A.

    1993-08-01

    The Nuclear Regulatory Commission (NRC) requested Oak Ridge National Laboratory (ORNL) to perform a pressurized-thermal-shock (PTS) probabilistic fracture mechanics (PFM) sensitivity analysis for the Yankee Rowe reactor pressure vessel, for the fluences corresponding to the end of operating cycle 22, using a specific small-break-loss- of-coolant transient as the loading condition. Regions of the vessel with distinguishing features were to be treated individually -- upper axial weld, lower axial weld, circumferential weld, upper plate spot welds, upper plate regions between the spot welds, lower plate spot welds, and the lower plate regions between the spot welds. The fracture analysis methods used in the analysis of through-clad surface flaws were those contained in the established OCA-P computer code, which was developed during the Integrated Pressurized Thermal Shock (IPTS) Program. The NRC request specified that the OCA-P code be enhanced for this study to also calculate the conditional probabilities of failure for subclad flaws and embedded flaws. The results of this sensitivity analysis provide the NRC with (1) data that could be used to assess the relative influence of a number of key input parameters in the Yankee Rowe PTS analysis and (2) data that can be used for readily determining the probability of vessel failure once a more accurate indication of vessel embrittlement becomes available. This report is designated as HSST report No. 117.

  17. An investigation on quench cracking behavior of superalloy Udimet 720LI using a fracture mechanics approach

    SciTech Connect

    Mao, J.; Keefer, V.L.; Chang, K.M.; Furrer, D.

    2000-04-01

    Quench cracking can be a serious problem in the heat treatment of high strength superalloys. A new fracture mechanics approach, quench cracking toughness (K{sub Q}), was introduced to evaluate the on-cooling quench cracking resistance of superalloy Udimet 720LI. A fully automatic computer controlled data acquisition and processing system was set up to track the on-cooling quenching process and to simulate the quench cracking. The influences of grain size, cooling rate, solution temperature, and alloy processing routes on quench cracking resistance were investigated. Research results indicate that quench cracking revealed a typical brittle and intergranular failure at high temperatures, which causes a lower quench cracking toughness in comparison to fracture toughness at room temperature. Fine grain structures show the higher quench cracking resistance and lower failure temperatures than intermediate grain structures at the same cooling rates. Moreover, higher cooling rate results in lower cracking toughness under the same grain size structures. In comparison of processing routes, powder metallurgy (PM) alloys show higher cracking resistance than cast and wrought (CW) alloys for fine grain structures at the same cooling rates. However, for immediate grain structure, there is no obvious difference of K{sub Q} between the two processing route in this study.

  18. Modeling the Progressive Failure of Jointed Rock Slope Using Fracture Mechanics and the Strength Reduction Method

    NASA Astrophysics Data System (ADS)

    Zhang, Ke; Cao, Ping; Meng, Jingjing; Li, Kaihui; Fan, Wenchen

    2015-03-01

    The fracturing process during the progressive failure of a jointed rock slope is numerically investigated by using fracture mechanics and the strength reduction method (SRM). A displacement discontinuity method containing frictional elements is developed for the calculation of the stress intensity factor (SIF). The failure initiation of the jointed rock slope is analyzed by evaluating the SIF. A new joint model is proposed by combining solid elements with interface elements in the commercial software FLAC3D. These represent the discontinuous planes in a rock mass on which sliding or separation can occur. The progressive failure process is simulated by reducing the shear strength of the rock mass, which includes the process of stress concentration, crack initiation, crack propagation, slip weakening, and coalescence of failure surfaces. The factor of safety (FS) and location of the critical failure surface are determined by the SRM. The influence of the joint inclination is investigated using the FS and the SIF. Laboratory experiments on specimens containing an inclined flaw under compression-shear stress are also conducted to investigate the effect of the angle between the shear direction and the flaw inclination, which provides an experimental explanation for the shear behavior of jointed rock. The results show that the joint inclination dominates the failure behavior of jointed rock slope, and two failure patterns have been classified.

  19. Microstructure in linear elasticity and scale effects: a reconsideration of basic rock mechanics and rock fracture mechanics

    NASA Astrophysics Data System (ADS)

    Exadaktylos, George E.; Vardoulakis, Ioannis

    2001-06-01

    An account on the role of higher order strain gradients in the mechanical behavior of elastic-perfectly brittle materials, such as rocks, is given that is based on a special grade-2 elasticity theory with surface energy as this was originated by Casal and Mindlin and further elaborated by the authors. The fundamental idea behind the theory is that the effect of the granular and polycrystalline nature of geomaterials (i.e. their microstructural features) on their macroscopic response may be modeled through the concept of volume cohesion forces, as well as surface forces rather than through intractable statistical mechanics concepts of the Boltzmann type. It is shown that the important phenomena of the localization of deformation in macroscopically homogeneous rocks under uniform tractions and of dependence of rock behavior on the specimen's dimensions, commonly known as size or scale effect, can be interpreted by using this 'non-local', higher order theory. These effects are demonstrated for the cases of the unidirectional tension test, and for the small circular hole under uniform internal pressure commonly known as the inflation test. The latter configuration can be taken as a first order approximation of the indentation test that is frequently used for the laboratory or in situ characterization of geomaterials. In addition, it is shown that the solution of the three basic crack deformation modes leads to cusping of the crack tips that is caused by the action of 'cohesive' double forces behind and very close to the tips, that tend to bring the two opposite crack lips in close contact, and further, it is demonstrated that the fracture toughness depends on the size of the crack, and thus it is not a fundamental property of the material. This latter outcome agrees with experimental results which indicate that materials with smaller cracks are more resistant to fracture than those with larger cracks.

  20. Fundamental Mechanisms of Tensile Fracture in Aluminum Sheet Unidirectionally Reinforced with Boron Filament. Ph.D. Thesis - Virginia Polytechnic Inst.

    NASA Technical Reports Server (NTRS)

    Herring, H. W.

    1971-01-01

    Results are presented from an experimental research effort to gain a more complete understanding of the physics of tensile fracture in unidirectionally reinforced B-Al composite sheet. By varying the degree of filament degradation resulting from fabrication, composite specimens were produced which failed in tension by the cumulative mode, the noncumulative mode, or by any desired combination of the two modes. Radiographic and acoustic emission techniques were combined to identify and physically describe a previously unrecognized fundamental fracture mechanism which was responsible for the noncumulative mode. The tensile strength of the composite was found to be severely limited by the noncumulative mechanism which involved the initiation and sustenance of a chain reaction of filament fractures at a relatively low stress level followed by ductile fracture of the matrix. The minimum average filament stress required for initiation of the fracture mechanism was shown to be approximately 170 ksi, and appeared to be independent of filament diameter, number of filament layers, and the identity of the matrix alloy.

  1. Mechanism of the Two-Phase Flow Model for Water and Gas Based on Adsorption and Desorption in Fractured Coal and Rock

    NASA Astrophysics Data System (ADS)

    Chen, Shikuo; Yang, Tianhong; Ranjith, P. G.; Wei, Chenhui

    2017-03-01

    Coalbed methane (CBM) is an important high-efficiency, clean-energy raw material with immense potential for application; however, its occurrence in low-permeability reservoirs limits its application. Hydraulic fracturing has been used in low-permeability CBM exploration and as a new technique for preventing gas hazards in coal mines. Fractures are the main pathways of fluid accumulation and migration, and they exert some control over the stability of rock mass. However, the differences in progression between the original fractures of the coal mass and the new discrete fractures caused by hydraulic fracturing remain unclear, and the unsaturated seepage flows require further study. Therefore, a cross-scale hydraulic fractured rock mass numerical model was developed by using the 3D fractured extrusion coupling variables reconstruction technique. This paper uses fracture surface parameters combined with the fractal dimension and multi-medium theory to provide a high-precision characterization and interpretation of the fracture mechanics. The mechanism of the permeability evolution of fractured coal and rock under stress-releasing mining combined with water injection was studied by considering gas adsorption and desorption as well as the coupling characteristic of seepage-stress in fractured rock masses. Aperture, contact area ratio, and stress in permeability and fracture development have a strong influence on the permeability and seepage path, which in turn control the effective radius by absolute water injection. All of these factors should be considered when studying the structural characteristics of rock masses.

  2. Complementary hydro-mechanical coupled finite/discrete element and microseismic modelling to predict hydraulic fracture propagation in tight shale reservoirs

    NASA Astrophysics Data System (ADS)

    Profit, Matthew; Dutko, Martin; Yu, Jianguo; Cole, Sarah; Angus, Doug; Baird, Alan

    2016-04-01

    This paper presents a novel approach to predict the propagation of hydraulic fractures in tight shale reservoirs. Many hydraulic fracture modelling schemes assume that the fracture direction is pre-seeded in the problem domain discretisation. This is a severe limitation as the reservoir often contains large numbers of pre-existing fractures that strongly influence the direction of the propagating fracture. To circumvent these shortcomings, a new fracture modelling treatment is proposed where the introduction of discrete fracture surfaces is based on new and dynamically updated geometrical entities rather than the topology of the underlying spatial discretisation. Hydraulic fracturing is an inherently coupled engineering problem with interactions between fluid flow and fracturing when the stress state of the reservoir rock attains a failure criterion. This work follows a staggered hydro-mechanical coupled finite/discrete element approach to capture the key interplay between fluid pressure and fracture growth. In field practice, the fracture growth is hidden from the design engineer and microseismicity is often used to infer hydraulic fracture lengths and directions. Microseismic output can also be computed from changes of the effective stress in the geomechanical model and compared against field microseismicity. A number of hydraulic fracture numerical examples are presented to illustrate the new technology.

  3. Demographics, Mechanisms of Injury, and Concurrent Injuries Associated With Calcaneus Fractures: A Study of 14 516 Patients in the American College of Surgeons National Trauma Data Bank.

    PubMed

    Bohl, Daniel D; Ondeck, Nathaniel T; Samuel, Andre M; Diaz-Collado, Pablo J; Nelson, Stephen J; Basques, Bryce A; Leslie, Michael P; Grauer, Jonathan N

    2016-11-28

    Background This study uses the American College of Surgeons National Trauma Data Bank (NTDB) to update the field on the demographics, injury mechanisms, and concurrent injuries among a national sample of patients admitted to the hospital department with calcaneus fractures. Methods Patients with calcaneus fractures in the NTDB during 2011-2012 were identified and assessed. Results A total of 14 516 patients with calcaneus fractures were included. The most common comorbidity was hypertension (18%), and more than 90% of fractures occurred via traffic accident (49%) or fall (43%). A total of 11 137 patients had concurrent injuries. Associated lower extremity fractures had the highest incidence and occurred in 61% of patients (of which the most common were other foot and ankle fractures). Concurrent spine fractures occurred in 23% of patients (of which the most common were lumbar spine fractures). Concurrent nonorthopaedic injuries included head injuries in 18% of patients and thoracic organ injuries in 15% of patients. Conclusion This national sample indicates that associated injuries occur in more than three quarters calcaneus fracture patients. The most common associated fractures are in close proximity to the calcaneus. Although the well-defined association of calcaneus fractures with lumbar spine fractures was identified, the data presented highlight additional strong associations of calcaneus fractures with other orthopaedic and nonorthopaedic injuries.

  4. A fatal iatrogenic right vertebral injury after transoral odontoidectomy and posterior cervical stabilization for a type II odontoid fracture.

    PubMed

    Scalici, Edoardo; Indorato, Francesca; Portelli, Francesca; Savì, Tommaso; Maresi, Emiliano; Busardò, Francesco P

    2014-02-01

    The authors present a singular case of an iatrogenic right vertebral artery injury, involving a 67 year-old man, who reported a type II odontoid fracture (Anderson and D'Alonzo Classification) and posterior atlantoaxial dislocation following a road traffic accident. A small injury involving the right vertebral artery occurred as a consequence of transoral odontoidectomy and posterior cervical stabilization. It was caused by bone spicules of spinal origin and their presence was confirmed by the histological section of the right vertebral artery at the level of C1-C2. The case confirms how iatrogenic vertebral artery injuries during cervical spine surgery may be potentially lethal, especially where complications arise some days after surgery.

  5. An analytical and experimental stress analysis of a practical mode II fracture-test specimen

    NASA Technical Reports Server (NTRS)

    Chisholm, D. B.; Jones, D. L.

    1975-01-01

    A boundary collocation method has been employed to determine the Mode II stress intensity factors for a pair of through-the-thickness edge cracks in a finite isotropic plate. An elastostatic analysis has been carried out in terms of the complete Williams stress function employing both even and odd components. The results of the numerical analysis were verified by a two-step procedure whereby the symmetric and antisymmetric portions of the solution were independently compared with existing solutions. The complete solution was verified by comparison with a photoelastic analysis. A compact shear specimen (CSS) of Hysol epoxy resin was loaded in a photoelastic experiment designed to study the isochromatic fringe patterns resulting from the Mode II crack tip stress distribution. The experiment verified that a pure Mode II stress distribution existed in the neighborhood of the crack tips and confirmed the accuracy of the boundary collocation solution for the Mode II stress intensity factors.

  6. A compendium of sources of fracture toughness and fatigue crack growth data for metallic alloys. II

    NASA Technical Reports Server (NTRS)

    Hudson, C. M.; Seward, S. K.

    1982-01-01

    A compendium is presented of sources for metallic alloy fracture toughness and fatigue crack growth data, which concentrates on technical reports as the primary source of references and updates the previous Hudson and Seward (1978) compendium references on technical journals. Where available, the accession numbers which are used as code numbers for the ordering of the reports from their publishers are given. The sources of these reports include the AIAA Technical Information Service, the Defense Technical Information Center, the National Technical Information Service, and NASA.

  7. Percutaneous fixation of hand fractures using locked K-wires: mechanical analysis and clinical application.

    PubMed

    De Spirito, Daniele

    2013-09-01

    Closed percutaneous wire fixation of hand fractures frequently requires protection with external splintage. This splintage increases the risk of joint stiffness, prolongs recovery time, and increases therapy input. We have developed a method of linking external Kirschner wires (K-wires), using a metal clamp, after their insertion, so as to increase the security of fixation and facilitate postoperative mobilization. The mechanical properties of this method have been assessed in vitro and compared with conventionally fixed, unlinked, K-wires. We have been able to establish that the linked K-wire system is better able to resist loosening. This work proposes that linkage of K-wires permits omission of all additional external splintage, with no detriment to management. The technique has been applied in clinical cases over the past 8 years and results of treatments were evaluated mainly to detect unexpected complications. We report a low rate of complications and good results in terms of bone healing and recovery of function.

  8. A probabilistic fracture mechanics approach for structural reliability assessment of space flight systems

    NASA Technical Reports Server (NTRS)

    Sutharshana, S.; Creager, M.; Ebbeler, D.; Moore, N.

    1992-01-01

    A probabilistic fracture mechanics approach for predicting the failure life distribution due to subcritical crack growth is presented. A state-of-the-art crack propagation method is used in a Monte Carlo simulation to generate a distribution of failure lives. The crack growth failure model expresses failure life as a function of stochastic parameters including environment, loads, material properties, geometry, and model specification errors. A stochastic crack growth rate model that considers the uncertainties due to scatter in the data and mode misspecification is proposed. The rationale for choosing a particular type of probability distribution for each stochastic input parameter and for specifying the distribution parameters is presented. The approach is demonstrated through a probabilistic crack growth failure analysis of a welded tube in the Space Shuttle Main Engine. A discussion of the results from this application of the methodology is given.

  9. Validation of the Boundary Element Method Applied to Complex Fracture Mechanics Conditions

    DTIC Science & Technology

    1989-12-01

    Goodier (21:91) as a -S t- S I + 3 - cos 2e (3.25) t 2 K r 2) 2( + r4) I * S I I 2a,I ox 3 r I_ SI Figure 3.2. Circular Hole in an Infinite Plate %awdor3...Engineering. Heidelberg, W. Germany: Springer-Verlag Berlin, 1984. 3. Brook, David . Elementary Engineering Fracture Mechanics (Third Edition). The Hague...BIB-Z I I 24. Timoshenko, S.P. and J.N. Goodier . Theory of ElasVicity (Third Edit4on). New York: McGraw-Hill Book3 Company, 1970. I I I I I I I I I I

  10. Characterization methods of bone-implant-interfaces of bioresorbable and titanium implants by fracture mechanical means.

    PubMed

    Tschegg, E K; Lindtner, R A; Doblhoff-Dier, V; Stanzl-Tschegg, S E; Holzlechner, G; Castellani, C; Imwinkelried, T; Weinberg, A

    2011-07-01

    Bioresorbable materials for implants have become increasingly researched over the last years. The bone-implant-interfaces of three different implant materials, namely a new bioresorbable magnesium alloy, a new self-reinforced polymer implant and a conventional titanium alloy, were tested using various methods: push-out tests, SEM and EDX analyses as well as surface analyses based on stereoscopic 3D pictures were conducted. The fracture energy is proposed as a very significant reference value for characterizing the mechanical performance of a bone-implant system. By using a video-extensometer system instead of, as is commonly done, tracking the movement of the crosshead in the push-out tests, the accuracy of measurement could be increased.

  11. Determination of Some Parameters for Fatigue Life in Welded Joints Using Fracture Mechanics Method

    NASA Astrophysics Data System (ADS)

    Al-Mukhtar, A. M.; Biermann, H.; Hübner, P.; Henkel, S.

    2010-12-01

    In this work, the parameters stress intensity factor (SIF), initial and final crack lengths ( a i and a f), crack growth parameters ( C and m), and fatigue strength (FAT) are investigated. The determination of initial crack length seems to be the most serious factor in fatigue life and strength calculations for welded joints. A fracture mechanics approach was used in these calculations based on SIF which was calculated with the finite element method (FEM). The weld toe crack was determined to be equal to 0.1 mm, whereas the weld root crack's length was varied depending on the degree of the weld penetration. These initial crack length values are applicable for all types of joints which have the same crack phenomenon. As based on the above calculated parameters, the new limits of FAT for new geometries which are not listed yet in recommendations can be calculated according to the current approach.

  12. DEFORMATION AND FRACTURE OF POORLY CONSOLIDATED MEDIA - Borehole Failure Mechanisms in High-Porosity Sandstone

    SciTech Connect

    Bezalel c. Haimson

    2005-06-10

    We investigated failure mechanisms around boreholes and the formation of borehole breakouts in high-porosity sandstone, with particular interest to grain-scale micromechanics of failure leading to the hitherto unrecognized fracture-like borehole breakouts and apparent compaction band formation in poorly consolidated granular materials. We also looked at a variety of drilling-related factors that contribute to the type, size and shape of borehole breakouts. The objective was to assess their effect on the ability to establish correlations between breakout geometry and in situ stress magnitudes, as well as on borehole stability prediction, and hydrocarbon/water extraction in general. We identified two classes of medium to high porosity (12-30%) sandstones, arkosic, consisting of 50-70% quartz and 15 to 50% feldspar, and quartz-rich sandstones, in which quartz grain contents varied from 90 to 100%. In arkose sandstones critical far-field stress magnitudes induced compressive failure around boreholes in the form of V-shaped (dog-eared) breakouts, the result of dilatant intra-and trans-granular microcracking subparallel to both the maximum horizontal far-field stress and to the borehole wall. On the other hand, boreholes in quartz-rich sandstones failed by developing fracture-like breakouts. These are long and very narrow (several grain diameters) tabular failure zones perpendicular to the maximum stress. Evidence provided mainly by SEM observations suggests a failure process initiated by localized grain-bond loosening along the least horizontal far-field stress springline, the packing of these grains into a lower porosity compaction band resembling those discovered in Navajo and Aztec sandstones, and the emptying of the loosened grains by the circulating drilling fluid starting from the borehole wall. Although the immediate several grain layers at the breakout tip often contain some cracked or even crushed grains, the failure mechanism enabled by the formation of the

  13. Fracture mechanics of matrix cracking and delamination in glass/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Caslini, M.; Zanotti, C.; Obrien, T. K.

    1986-01-01

    This study focused on characterizing matrix cracking and delamination behavior in multidirectional laminates. Static tension and tension-tension fatigue tests were conducted on two different layups. Damage onset, accumulation, and residual properties were measured. Matrix cracking was shown to have a considerable influence on residual stiffness of glass epoxy laminates, and could be predicted reasonably well for cracks in 90 deg piles using a simple shear lag analysis. A fracture mechanics analysis for the strain energy release rate associated with 90 deg ply-matrix crack formation was developed and was shown to correlate the onset of 90 deg ply cracks in different laminates. The linear degradation of laminate modulus with delamination area, previously observed for graphite epoxy laminates, was predicted for glass epoxy laminates using a simple rule of mixtures analysis. The strain energy release rate associated with edge delamination formation under static and cyclic loading was difficult to analyze because of the presence of several contemporary damage phenomena.

  14. Addendum to the User Manual for NASGRO Elastic-Plastic Fracture Mechanics Software Module

    NASA Technical Reports Server (NTRS)

    Gregg, M. Wayne (Technical Monitor); Chell, Graham; Gardner, Brian

    2003-01-01

    The elastic-plastic fracture mechanics modules in NASGRO have been enhanced by the addition of of the following: new J-integral solutions based on the reference stress method and finite element solutions; the extension of the critical crack and critical load modules for cracks with two degrees of freedom that tear and failure by ductile instability; the addition of a proof test analysis module that includes safe life analysis, calculates proof loads, and determines the flaw screening 1 capability for a given proof load; the addition of a tear-fatigue module for ductile materials that simultaneously tear and extend by fatigue; and a multiple cycle proof test module for estimating service reliability following a proof test.

  15. A fracture mechanics analysis of impact damage in a thick composite laminate

    NASA Technical Reports Server (NTRS)

    Poe, C. C., Jr.

    1985-01-01

    Graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the space shuttle are being made by NASA. The FWC cases are wound with AS4W graphite fiber impregnated with an epoxy resin and are about 1.4 inches or more thick. Graphite-epoxy composite laminates, unlike metals, can be damaged easily by low velocity impacts of objects like dropped tools. The residual tension strength of the FWC laminate, after impact, is being studied at Langley Research Center. The conditions that give minimum visual evidence of damage are being emphasized. A fracture mechanics analysis was developed to predict the residual strength, after impact, using radiographs to measure the size of the damage and an equivalent surface crack to represent the damage.

  16. The role of fracture mechanics in the design of fuel tanks in space vehicles

    NASA Technical Reports Server (NTRS)

    Denton, S. J.; Liu, C. K.

    1976-01-01

    With special reference to design of fuel tanks in space vehicles, the principles of fracture mechanics are reviewed. An approximate but extremely simple relationship is derived among the operating stress level, the length of crack, and the number of cycles of failure. Any one of the variables can be computed approximately from the knowledge of the other two, if the loading schedule (mission of the tank) is not greatly altered. Two sample examples illustrating the procedures of determining the allowable safe operating stress corresponding to a set of assumed loading schedule are included. The selection of sample examples is limited by the relatively meager available data on the candidate material for various stress ratios in the cycling.

  17. Stress and Fracture Mechanics Analyses of Boiling Water Reactor and Pressurized Water Reactor Pressure Vessel Nozzles

    SciTech Connect

    Yin, Shengjun; Bass, Bennett Richard; Stevens, Gary; Kirk, Mark

    2011-01-01

    This paper describes stress analysis and fracture mechanics work performed to assess boiling water reactor (BWR) and pressurized water reactor (PWR) nozzles located in the reactor pressure vessel (RPV) adjacent to the core beltline region. Various RPV nozzle geometries were investigated: 1. BWR recirculation outlet nozzle; 2. BWR core spray nozzle3 3. PWR inlet nozzle; ; 4. PWR outlet nozzle; and 5. BWR partial penetration instrument nozzle. The above nozzle designs were selected based on their proximity to the core beltline region, i.e., those nozzle configurations that are located close enough to the core region such that they may receive sufficient fluence prior to end-of-license (EOL) to require evaluation as part of establishing the allowed limits on heatup, cooldown, and hydrotest (leak test) conditions. These nozzles analyzed represent one each of the nozzle types potentially requiring evaluation. The purpose of the analyses performed on these nozzle designs was as follows: To model and understand differences in pressure and thermal stress results using a two-dimensional (2-D) axi-symmetric finite element model (FEM) versus a three-dimensional (3-D) FEM for all nozzle types. In particular, the ovalization (stress concentration) effect of two intersecting cylinders, which is typical of RPV nozzle configurations, was investigated; To verify the accuracy of a selected linear elastic fracture mechanics (LEFM) hand solution for stress intensity factor for a postulated nozzle corner crack for both thermal and pressure loading for all nozzle types; To assess the significance of attached piping loads on the stresses in the nozzle corner region; and To assess the significance of applying pressure on the crack face with respect to the stress intensity factor for a postulated nozzle corner crack.

  18. Mode and mechanism of fatigue fracture of a pearlitic steel in hydrogen

    NASA Technical Reports Server (NTRS)

    Lo, S. H.; Johnson, H. H.

    1986-01-01

    It is presently suggested that there are two mechanisms that cause fatigue crack initiation in a specimen subjected to a hydrogen environment: either a critical concentration of hydrogen is attained within the specimen, causing Mode I crack initiation, or the presence of some hydrogen (below critical concentration) promotes the early onset of plastic instability at the sites of maximum strain. It is further suggested that in the static loading condition, a high hydrogen concentration may be attained by way of mechanical factors, causing Mode I crack initiation. While cyclic fatigue specimens exhibited Mode II crack initiation in air, only Mode I crack initiation emerged in a hydrogen environment.

  19. Type II topoisomerases--inhibitors, repair mechanisms and mutations.

    PubMed

    Heisig, Peter

    2009-11-01

    Type II topoisomerases are ubiquitous enzymes that play an essential role in the control of replicative DNA synthesis and share structural and functional homology among different prokaryotic and eukaryotic organisms. Antibacterial fluoroquinolones target prokaryotic topoisomerases at concentrations 100- to 1000-fold lower than mammalian enzymes, the preferred targets of anticancer drugs such as etoposide. The mechanisms of action of both of these types of inhibitors involve the fixation of an intermediate reaction step, where the enzyme is covalently bound to an enzyme-mediated DNA double-strand break (DSB). The resulting ternary drug-enzyme-DNA complexes can then be converted to cleavage complexes that block further movement of the DNA replication fork, subsequently inducing stress responses. In haploid prokaryotic cells, stress responses include error-free and error-prone DNA damage repair pathways, such as homologous recombination and translesion synthesis, respectively. The latter can result in the acquisition of point mutations. Diploid mammalian cells are assumed to preferentially use recombination mechanisms for the repair of DSBs, an example of which, non-homologous end joining, is a major error-prone repair mechanism associated with an increased frequency of detectable small deletions, insertions and translocations. However, results obtained from safety testing of novel fluoroquinolones at high concentrations indicate that point mutations may also occur in mammalian cells. Recent data provide evidence for translesion synthesis catalysed by error-prone repair polymerases as a damage-tolerance repair mechanism of DSBs in eukaryotic cells. This paper discusses possible roles of different mechanisms for the repair of DSBs operating in both eukaryotic and prokaryotic cells that result in recombinational rearrangements, deletions/insertions as well as point mutations.

  20. Mechanism of nucleotide sensing in group II chaperonins

    PubMed Central

    Pereira, Jose H; Ralston, Corie Y; Douglas, Nicholai R; Kumar, Ramya; Lopez, Tom; McAndrew, Ryan P; Knee, Kelly M; King, Jonathan A; Frydman, Judith; Adams, Paul D

    2012-01-01

    Group II chaperonins mediate protein folding in an ATP-dependent manner in eukaryotes and archaea. The binding of ATP and subsequent hydrolysis promotes the closure of the multi-subunit rings where protein folding occurs. The mechanism by which local changes in the nucleotide-binding site are communicated between individual subunits is unknown. The crystal structure of the archaeal chaperonin from Methanococcus maripaludis in several nucleotides bound states reveals the local conformational changes associated with ATP hydrolysis. Residue Lys-161, which is extremely conserved among group II chaperonins, forms interactions with the γ-phosphate of ATP but shows a different orientation in the presence of ADP. The loss of the ATP γ-phosphate interaction with Lys-161 in the ADP state promotes a significant rearrangement of a loop consisting of residues 160–169. We propose that Lys-161 functions as an ATP sensor and that 160–169 constitutes a nucleotide-sensing loop (NSL) that monitors the presence of the γ-phosphate. Functional analysis using NSL mutants shows a significant decrease in ATPase activity, suggesting that the NSL is involved in timing of the protein folding cycle. PMID:22193720

  1. Microstructural effects on fracture behavior of particulate composites: Investigation of toughening mechanisms using optical and boundary element methods

    NASA Astrophysics Data System (ADS)

    Kitey, Rajesh

    Particulate polymer composites are used in a variety of engineering applications. These are generally two phase materials with polymeric phase reinforced by a filler phase to improve overall mechanical, thermal and/or dielectric functionalities. From a mechanical perspective, polymers when filled with stiffer particulates generally show enhanced elastic properties and creep resistance. Achieving similar improvement in failure characteristics has not been consistent due to a lack of thorough understanding of microstructural and loading rate effects. This dissertation addresses a few of these issues by studying effects of filler particle size, filler size distribution and filler-matrix adhesion strength on fracture behavior under quasi-static and dynamic loading conditions. Glass-filled epoxy composites consisting of solid spherical particles are studied in this research. Spherical particles of mean dia. (D) 7 mum to 200 mum are used to reinforce epoxy matrix at a constant volume fraction (Vf = 10%) and two different filler-matrix strengths, weak and strong. Optical interferometry in conjunction with high-speed photography is used to quantify crack growth and deformation histories during impact loading. Although elastic characteristics remain unaffected by microstructural variations, significant differences in fracture behaviors are seen. Both weakly and strongly bonded particles in the matrix show higher values of steady-state dynamic fracture toughness, KIss, relative to unfilled material. Filler particle size affects KIss significantly when particles are weakly bonded to the matrix but not when bonded strongly. Weakly bonded fillers result in consistently higher KIss values compared to strongly bonded counterparts. A particle size of 35 mum appears to be the optimum at the chosen Vf. The KIss of two inter-mixed particle sizes (each of 5% Vf) is bounded by the KIss values of the composite with corresponding single particle size. Fracture surface micromeasurements

  2. Early treatment mechanics of the Class II division 2 malocclusion.

    PubMed

    Carapezza, L J

    2000-01-01

    A most common type of early malocclusion that the pediatric dentist comes in contact with daily is the developing Class II Division 2 malocclusion (Fig 1-a,b). It is the malocclusion that the parents of the children we serve bring to our attention. Parental concern is the early crowding that develops in the anterior of the lower arch with risk of periodontal involvement. This malocclusion is readily amenable to interception at age 7 or 8 and can proceed with a protocol of defined objectives and predictable outcomes (Fig 2). With efficient and effective utility arch wire (UAW) mechanics a state of normalcy can be achieved within six to eight months of treatment.

  3. Magnesium alloys as body implants: fracture mechanism under dynamic and static loadings in a physiological environment.

    PubMed

    Choudhary, Lokesh; Raman, R K Singh

    2012-02-01

    It is essential that a metallic implant material possesses adequate resistance to cracking/fracture under the synergistic action of a corrosive physiological environment and mechanical loading (i.e. stress corrosion cracking (SCC)), before the implant can be put to actual use. This paper presents a critique of the fundamental issues with an assessment of SCC of a rapidly corroding material such as magnesium alloys, and describes an investigation into the mechanism of SCC of a magnesium alloy in a physiological environment. The SCC susceptibility of the alloy in a simulated human body fluid was established by slow strain rate tensile (SSRT) testing using smooth specimens under different electrochemical conditions for understanding the mechanism of SCC. However, to assess the life of the implant devices that often possess fine micro-cracks, SCC susceptibility of notched specimens was investigated by circumferential notch tensile (CNT) testing. CNT tests also produced important design data, i.e. threshold stress intensity for SCC (KISCC) and SCC crack growth rate. Fractographic features of SCC were examined using scanning electron microscopy. The SSRT and CNT results, together with fractographic evidence, confirmed the SCC susceptibility of both smooth and notched specimens of a magnesium alloy in the physiological environment.

  4. Dense surface seismic data confirm non-double-couple source mechanisms induced by hydraulic fracturing

    USGS Publications Warehouse

    Pesicek, Jeremy; Cieślik, Konrad; Lambert, Marc-André; Carrillo, Pedro; Birkelo, Brad

    2016-01-01

    We have determined source mechanisms for nine high-quality microseismic events induced during hydraulic fracturing of the Montney Shale in Canada. Seismic data were recorded using a dense regularly spaced grid of sensors at the surface. The design and geometry of the survey are such that the recorded P-wave amplitudes essentially map the upper focal hemisphere, allowing the source mechanism to be interpreted directly from the data. Given the inherent difficulties of computing reliable moment tensors (MTs) from high-frequency microseismic data, the surface amplitude and polarity maps provide important additional confirmation of the source mechanisms. This is especially critical when interpreting non-shear source processes, which are notoriously susceptible to artifacts due to incomplete or inaccurate source modeling. We have found that most of the nine events contain significant non-double-couple (DC) components, as evident in the surface amplitude data and the resulting MT models. Furthermore, we found that source models that are constrained to be purely shear do not explain the data for most events. Thus, even though non-DC components of MTs can often be attributed to modeling artifacts, we argue that they are required by the data in some cases, and can be reliably computed and confidently interpreted under favorable conditions.

  5. The impact of hygrothermal preconditioning on mode II interlaminar fracture toughness in unidirectional carbon fiber reinforced epoxy composites: An experimental investigation

    NASA Astrophysics Data System (ADS)

    Hempowicz, Michael L.

    The correlation between the interlaminar Mode II fracture toughness (GIIC) of a carbon fiber reinforced epoxy and other material properties across different conditioning regimes was investigated. Specimens were preconditioned using select hygrothermal criteria to evaluate how changes in the material and mechanical properties in a carbon fiber/epoxy composite correlations with changes in GIIC for each regime. An increase in GIIC from baseline values was demonstrated across all conditions from end-notched flexure (ENF) testing. Dynamic mechanical analysis (DMA) and tensile tests had varying responses based on preconditioning environment. Since tensile and some DMA properties rely on fiber strength and show property loss with increased plasticization, fiber strength may not have a large impact on GIIC properties. Test data also implied that the GIIC increased when consolidation of the polymer chains occurred in the arid condition as well as when crosslink density increased in the moisture exposed conditions. From these results it is believed that the chemical and physical changes in matrix cohesion are more important to GIIC behavior prediction than fiber behavior.

  6. Macro- and Micro-Mechanics of Mixed-Mode Dynamic Fracture of Concrete. Part 1. Micro-Mechanic Analysis

    DTIC Science & Technology

    1993-02-14

    fracture energy density of concrete were discussed by Hillerborg and Mindess [55-57]. The total external energy needed to quasi-statically fracture a...Composites.: Strzin Rate Effects on Fracture, eds. S. Mindess and S.P Shah, Materials Research Society Symposia Proceeding Vol. 64, 1986 18 S. Mindess ...Nijhoff Publishers, 1985, pp. 617-636. I 1 9 A. Benton, S. Mindess , and N. Benthur, "The Behavior of Concrete Under Impact Loading: Experimental

  7. Geothermal fracture stimulation technology. Volume II. High-temperature proppant testing

    SciTech Connect

    Not Available

    1980-07-01

    Data were obtained from a newly built proppant tester, operated at actual geothermal temperatures. The short term test results show that most proppants are temperature sensitive, particularly at the higher closure stresses. Many materials have been tested using a standard short-term test, i.e., fracture-free sand, bauxite, and a resin-coated sand retained good permeability at the high fluid temperatures in brine over a range of closure stresses. The tests were designed to simulate normal closure stress ranges for geothermal wells which are estimated to be from 2000 to 6000 psi. Although the ultra high closure stresses in oil and gas wells need not be considered with present geothermal resources, there is a definite need for chemically inert proppants that will retain high permeability for long time periods in the high temperature formations.

  8. Influence of ion nitriding regime on mechanical properties and fracture mechanism of austenitic steel subjected to different thermomechanical treatments

    NASA Astrophysics Data System (ADS)

    Moskvina, Valentina; Astafurova, Elena; Ramazanov, Kamil; Melnikov, Eugene; Maier, Galina; Budilov, Vladimir

    2016-11-01

    The effect of thermomechanical treatments and low-temperature ion nitriding on mechanical properties and a fracture mechanism of stable austenitic stainless steel Fe-17Cr-13Ni-1.7Mn-2.7Mo-0.5Si-0.01C (in wt %, 316L-type) was investigated. Irrespective of initial heat treatments of steel and the regime of nitrogen saturation, traditional ion nitriding and nitriding with hollow cathode effect do not influence the stages of plastic flow and strain hardening; instead, they contribute to surface hardening of steel samples and reduce their plastic properties due to formation of a brittle surface layer. Ion nitriding leads to formation of a hardened surface layer with the microhardness of 12 GPa. Formation of a high-defective grain/subgrain structure with high dislocation density contributes to strengthening of steel samples under ion nitriding and formation of a thicker strengthened layer in comparison with fine-crystalline and coarse-crystalline samples.

  9. Mechanisms of hyoid bone fracture after modelling: evaluation of anthropological criteria defining two relevant models.

    PubMed

    Pollard, J; Piercecchi-Marti, M D; Thollon, L; Bartoli, C; Adalian, Pascal; Bécart-Robert, A; Tournel, G; Hédouin, V; Panuel, M; Gosset, D; Leonetti, G

    2011-10-10

    according to the gender and corpulence of an individual because these parameters are correlated. These findings are crucial in establishing a protocol for modelling the mechanism of fracture of the hyoid bone in strangulation. Two models of the hyoid bone appear to be needed to meet the practical requirements that are the purpose of these biomechanical studies.

  10. Dynamic tensile response of Zr-based bulk amorphous alloys: Fracture morphologies and mechanisms

    NASA Astrophysics Data System (ADS)

    Escobedo, J. P.; Gupta, Y. M.

    2010-06-01

    I cracks. A subsequent dilatation, due to the effect of the tensile mean stress, caused the corrugations to evolve to bump-type features with sizes in the range of 10-100 nm. Our proposed mechanisms, although qualitative, constitute a systematic attempt to provide an explanation for the fracture morphologies observed in spalled BAA samples.

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

    SciTech Connect

    Robert Podgorney; Chuan Lu; Hai Huang

    2012-01-01

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

  12. On material fracture criteria

    NASA Astrophysics Data System (ADS)

    Kremnev, L. S.

    2017-01-01

    Based on the nonlinear mechanics of material fracture, a model of the fracture of materials with actual (discrete) structures has been constructed. The model is supported by proofs that crack resistance K 1 c and fracture toughness G 1 c obtained from the energy conservation law without using the assumptions adopted in the linear material fracture mechanics serve as the force and energy criteria in the nonlinear fracture mechanics. It has been shown that energy criterion G 1 c in the nonlinear mechanics is much greater than G 1 c in the linear fracture mechanics.

  13. Fracture of ECAP-deformed iron and the role of extrinsic toughening mechanisms.

    PubMed

    Hohenwarter, A; Pippan, R

    2013-05-01

    The fracture behaviour of pure iron deformed by equal-channel angular pressing via route A was examined. The fracture toughness was determined for different specimen orientations and measured in terms of the critical plane strain fracture toughness, KIC , the critical J integral, JIC , and the crack opening displacement for crack initiation, CODi . The results demonstrate that the crack plane orientation has a pronounced effect on the fracture toughness. Different crack plane orientations lead to either crack deflection or delamination, resulting in increased fracture resistance in comparison to one remarkably weak specimen orientation. The relation between the microstructure typical for the applied deformation route and the enormous differences in the fracture toughness depending on the crack plane orientation will be analyzed in this paper.

  14. Fracture of ECAP-deformed iron and the role of extrinsic toughening mechanisms

    PubMed Central

    Hohenwarter, A.; Pippan, R.

    2013-01-01

    The fracture behaviour of pure iron deformed by equal-channel angular pressing via route A was examined. The fracture toughness was determined for different specimen orientations and measured in terms of the critical plane strain fracture toughness, KIC, the critical J integral, JIC, and the crack opening displacement for crack initiation, CODi. The results demonstrate that the crack plane orientation has a pronounced effect on the fracture toughness. Different crack plane orientations lead to either crack deflection or delamination, resulting in increased fracture resistance in comparison to one remarkably weak specimen orientation. The relation between the microstructure typical for the applied deformation route and the enormous differences in the fracture toughness depending on the crack plane orientation will be analyzed in this paper. PMID:23645995

  15. The Uptake Mechanism of Cd(II), Cr(VI), Cu(II), Pb(II), and Zn(II) by Mycelia and Fruiting Bodies of Galerina vittiformis

    PubMed Central

    Damodaran, Dilna; Balakrishnan, Raj Mohan; Shetty, Vidya K.

    2013-01-01

    Optimum concentrations of heavy metals like copper, cadmium, lead, chromium, and zinc in soil are essential in carrying out various cellular activities in minimum concentrations and hence help in sustaining all life forms, although higher concentration of these metals is lethal to most of the life forms. Galerina vittiformis, a macrofungus, was found to accumulate these heavy metals into its fleshy fruiting body in the order Pb(II) > Cd(II) > Cu(II) > Zn(II) > Cr(VI) from 50 mg/kg soil. It possesses various ranges of potential cellular mechanisms that may be involved in detoxification of heavy metals and thus increases its tolerance to heavy metal stress, mainly by producing organic acids and phytochelatins (PCs). These components help in repairing stress damaged proteins and compartmentalisation of metals to vacuoles. The stress tolerance mechanism can be deduced by various analytical tools like SEM-EDX, FTIR, and LC-MS. Production of two kinds of phytochelatins was observed in the organism in response to metal stress. PMID:24455671

  16. The uptake mechanism of Cd(II), Cr(VI), Cu(II), Pb(II), and Zn(II) by mycelia and fruiting bodies of Galerina vittiformis.

    PubMed

    Damodaran, Dilna; Balakrishnan, Raj Mohan; Shetty, Vidya K

    2013-01-01

    Optimum concentrations of heavy metals like copper, cadmium, lead, chromium, and zinc in soil are essential in carrying out various cellular activities in minimum concentrations and hence help in sustaining all life forms, although higher concentration of these metals is lethal to most of the life forms. Galerina vittiformis, a macrofungus, was found to accumulate these heavy metals into its fleshy fruiting body in the order Pb(II) > Cd(II) > Cu(II) > Zn(II) > Cr(VI) from 50 mg/kg soil. It possesses various ranges of potential cellular mechanisms that may be involved in detoxification of heavy metals and thus increases its tolerance to heavy metal stress, mainly by producing organic acids and phytochelatins (PCs). These components help in repairing stress damaged proteins and compartmentalisation of metals to vacuoles. The stress tolerance mechanism can be deduced by various analytical tools like SEM-EDX, FTIR, and LC-MS. Production of two kinds of phytochelatins was observed in the organism in response to metal stress.

  17. Topical report on subsurface fracture mapping from geothermal wellbores. Phase I. Pulsed radar techniques. Phase II. Conventional logging methods. Phase III. Magnetic borehole ranging

    SciTech Connect

    Hartenbaum, B.A.; Rawson, G.

    1980-09-01

    To advance the state-of-the-art in Hot Dry Rock technology, an evaluation is made of (i) the use of radar to map far-field fractures, (ii) the use of more than twenty different conventional well logging tools to map borehole-fracture intercepts, and (iii) the use of magnetic dipole ranging to determine the relative positions of the injection well and the production well within the fractured zone. It is found that according to calculations, VHF backscatter radar has the potential for mapping fractures within a distance of 50 +- 20 meters from the wellbore. A new technique for improving fracture identification is presented. Analyses of extant data indicate that when used synergistically the (1) caliper, (2) resistivity dipmeter, (3) televiewer, (4) television, (5) impression packer, and (6) acoustic transmission are useful for mapping borehole-fracture intercepts. Improvements in both data interpretation techniques and high temperature operation are required. The surveying of one borehole from another appears feasible at ranges of up to 200 to 500 meters by using a low frequency magnetic field generated by a moderately strong dipole source (a solenoid) located in one borehole, a sensitive B field detector that traverses part of the second borehole, narrow band filtering, and special data inversion techniques.

  18. Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy.

    PubMed

    Withers, P J

    2015-03-06

    To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored.

  19. Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy

    PubMed Central

    Withers, P. J.

    2015-01-01

    To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored. PMID:25624521

  20. Environment enhanced fatigue crack propagation in metals: Inputs to fracture mechanics life prediction models

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.; Kim, Sang-Shik

    1993-01-01

    This report is a critical review of both environment-enhanced fatigue crack propagation data and the predictive capabilities of crack growth rate models. This information provides the necessary foundation for incorporating environmental effects in NASA FLAGRO and will better enable predictions of aerospace component fatigue lives. The review presents extensive literature data on 'stress corrosion cracking and corrosion fatigue.' The linear elastic fracture mechanics approach, based on stress intensity range (Delta(K)) similitude with microscopic crack propagation threshold and growth rates, provides a basis for these data. Results are presented showing enhanced growth rates for gases (viz., H2 and H2O) and electrolytes (e.g. NaCl and H2O) in aerospace alloys including: C-Mn and heat treated alloy steels, aluminum alloys, nickel-based superalloys, and titanium alloys. Environment causes purely time-dependent accelerated fatigue crack growth above the monotonic load cracking threshold (KIEAC) and promotes cycle-time dependent cracking below (KIEAC). These phenomenon are discussed in terms of hydrogen embrittlement, dissolution, and film rupture crack tip damage mechanisms.

  1. Fracture Mechanics Method for Word Embedding Generation of Neural Probabilistic Linguistic Model

    PubMed Central

    Bi, Size; Liang, Xiao

    2016-01-01

    Word embedding, a lexical vector representation generated via the neural linguistic model (NLM), is empirically demonstrated to be appropriate for improvement of the performance of traditional language model. However, the supreme dimensionality that is inherent in NLM contributes to the problems of hyperparameters and long-time training in modeling. Here, we propose a force-directed method to improve such problems for simplifying the generation of word embedding. In this framework, each word is assumed as a point in the real world; thus it can approximately simulate the physical movement following certain mechanics. To simulate the variation of meaning in phrases, we use the fracture mechanics to do the formation and breakdown of meaning combined by a 2-gram word group. With the experiments on the natural linguistic tasks of part-of-speech tagging, named entity recognition and semantic role labeling, the result demonstrated that the 2-dimensional word embedding can rival the word embeddings generated by classic NLMs, in terms of accuracy, recall, and text visualization. PMID:27698659

  2. Fracture Mechanics Method for Word Embedding Generation of Neural Probabilistic Linguistic Model.

    PubMed

    Bi, Size; Liang, Xiao; Huang, Ting-Lei

    2016-01-01

    Word embedding, a lexical vector representation generated via the neural linguistic model (NLM), is empirically demonstrated to be appropriate for improvement of the performance of traditional language model. However, the supreme dimensionality that is inherent in NLM contributes to the problems of hyperparameters and long-time training in modeling. Here, we propose a force-directed method to improve such problems for simplifying the generation of word embedding. In this framework, each word is assumed as a point in the real world; thus it can approximately simulate the physical movement following certain mechanics. To simulate the variation of meaning in phrases, we use the fracture mechanics to do the formation and breakdown of meaning combined by a 2-gram word group. With the experiments on the natural linguistic tasks of part-of-speech tagging, named entity recognition and semantic role labeling, the result demonstrated that the 2-dimensional word embedding can rival the word embeddings generated by classic NLMs, in terms of accuracy, recall, and text visualization.

  3. Mechanics of two interacting magma-driven fractures: A numerical study

    NASA Astrophysics Data System (ADS)

    Zhang, Xi; Bunger, Andrew P.; Jeffrey, Robert G.

    2014-11-01

    To understand magma focusing from broad melting zones in the crust, propagation in brittle rocks of two interacting dikes ascending from a single deep source has been modeled using a time-dependent plane strain hydraulic fracturing model. The source is assumed to generate a constant influx rate to feed the dike growth, which is also aided by buoyancy effects. In contrast to uncoupled model results, the simultaneous parallel growth of two dikes to a certain distance is found to occur provided that the two dikes are initially of different heights, which might be produced either by previous magma intrusion or during nucleation. The shorter dike will chase the longer one and they can either progressively merge or continue subparallel growth at a reduced spacing, depending on the deviator stress between the vertical and horizontal stresses and the initial lateral separation, with parameters given in dimensionless forms. Numerical results reveal the mechanics for simultaneous ascents of two subparallel dikes, in that dike interaction can produce a low-stress field, which is just above the tip of the shorter dike, favorable to growth of the shorter dike. The energy analysis indicates that the energy required for two subparallel dikes is less than that for a single dike during the late-time buoyancy-viscosity propagation stage where considerable ascent occurs. This growth behavior might provide the mechanism for simultaneous, instead of sequential, growth of various dikes in a single set.

  4. A witnessed case of a classic metaphyseal fracture caused during IV line placement in a child: Insight into mechanism of injury.

    PubMed

    Burrell, Tanya; Opfer, Erin; Berglund, Lisa; Lowe, Lisa H; Anderst, James

    2015-10-01

    Recent publications argue that classic metaphyseal fractures are caused by rickets as opposed to trauma. Previous case reports of accidental traumatic classic metaphyseal fractures have been discounted due to lack of identification of the fracture at the time of the traumatic event, and lack of an evaluation for boney metabolic disorders. We report a case of a 20 day old male with a diagnosis of congenital vertical talus who sustained a classic metaphyseal fracture of the distal tibia during manipulation in preparation for intravenous line placement. The mechanics of the event causing the classic metaphyseal fracture were witnessed and accompanied by an audible "pop". Prior x-rays of the tibia demonstrate normal osseous morphology, and an evaluation for boney metabolic disorders was normal. This case identifies a traumatic classic metaphyseal fracture and provides insight into the types of forces necessary to cause such a fracture.

  5. Investigation of the mechanical properties and failure modes of hybrid natural fiber composites for potential bone fracture fixation plates.

    PubMed

    Manteghi, Saeed; Mahboob, Zia; Fawaz, Zouheir; Bougherara, Habiba

    2017-01-01

    The purpose of this study is to investigate the mechanical feasibility of a hybrid Glass/Flax/Epoxy composite material for bone fracture fixation such as fracture plates. These hybrid composite plates have a sandwich structure in which the outer layers are made of Glass/Epoxy and the core from Flax/Epoxy. This configuration resulted in a unique structure compared to prior composites proposed for similar clinical applications. In order to evaluate the mechanical properties of this hybrid composite, uniaxial tension, compression, three-point bending and Rockwell Hardness tests were conducted. In addition, water absorption tests were performed to investigate the rate of water absorption for the specimens. This study confirms that the proposed hybrid composite plates are significantly more flexible axially compared to conventional metallic plates. Furthermore, they have considerably higher ultimate strength in tension, compression and flexion. Such high strength will ensure good stability of bone-implant construct at the fracture site, immobilize adjacent bone fragments and carry clinical-type forces experienced during daily normal activities. Moreover, this sandwich structure with stronger and stiffer face sheets and more flexible core can result in a higher stiffness and strength in bending compared to tension and compression. These qualities make the proposed hybrid composite an ideal candidate for the design of an optimized fracture fixation system with much closer mechanical properties to human cortical bone.

  6. Rib stress fractures among rowers: definition, epidemiology, mechanisms, risk factors and effectiveness of injury prevention strategies.

    PubMed

    McDonnell, Lisa K; Hume, Patria A; Nolte, Volker

    2011-11-01

    Rib stress fractures (RSFs) can have serious effects on rowing training and performance and accordingly represent an important topic for sports medicine practitioners. Therefore, the aim of this review is to outline the definition, epidemiology, mechanisms, intrinsic and extrinsic risk factors, injury management and injury prevention strategies for RSF in rowers. To this end, nine relevant books, 140 journal articles, the proceedings of five conferences and two unpublished presentations were reviewed after searches of electronic databases using the keywords 'rowing', 'rib', 'stress fracture', 'injury', 'mechanics' and 'kinetics'. The review showed that RSF is an incomplete fracture occurring from an imbalance between the rate of bone resorption and the rate of bone formation. RSF occurs in 8.1-16.4% of elite rowers, 2% of university rowers and 1% of junior elite rowers. Approximately 86% of rowing RSF cases with known locations occur in ribs four to eight, mostly along the anterolateral/lateral rib cage. Elite rowers are more likely to experience RSF than nonelite rowers. Injury occurrence is equal among sweep rowers and scullers, but the regional location of the injury differs. The mechanism of injury is multifactorial with numerous intrinsic and extrinsic risk factors contributing. Posterior-directed resultant forces arising from the forward directed force vector through the arms to the oar handle in combination with the force vector induced by the scapula retractors during mid-drive, or repetitive stress from the external obliques and rectus abdominis in the 'finish' position, may be responsible for RSF. Joint hypomobility, vertebral malalignment or low bone mineral density may be associated with RSF. Case studies have shown increased risk associated with amenorrhoea, low bone density or poor technique, in combination with increases in training volume. Training volume alone may have less effect on injury than other factors. Large differences in seat and handle

  7. Fracture Profile and Crack Propagation of Ultra-High Strength Hot-Stamped Boron Steel During Mechanical Trimming Process

    NASA Astrophysics Data System (ADS)

    Han, Xianhong; Yang, Kun; Chen, Sisi; Chen, Jun

    2015-10-01

    Mechanical trimming process for ultra-high strength boron steel after hot stamping was carried out in this study. Shear and tensile tests were designed to analyze the influences of stress state on the fracture mode; trimmed fracture surface and profile were observed and compared to other commonly used steels such as DP980 and Q235 etc.; the crack propagation during trimming process was studied through step-by-step tests. The observation and analysis reveal that the fracture mode of hot-stamped boron steel is highly related to the stress state, it belongs to cleavage fracture on low stress triaxiality but dimple fracture on high stress triaxiality. Such phenomenon is reflected in the trimming process, during which the stress state changes from shear-dominated state to tensile-dominated state. In addition, the burnish zone of trimmed boron steel is much smaller than other high strength steels, and the profile of cutting surface shows an `S'-like shape which is destructive to the trimming tool. Moreover, during the trimming process, most martensite laths near the cutting edge are stretched and rotated markedly to the direction of the shear band, and the main crack expands along those grain boundaries, which may penetrate through a few martensite laths and form small crack branches.

  8. A Protocol for Percutaneous Transarticular Fixation of Sanders Type II and III Calcaneal Fractures With or Without an Added Mini-Open Approach.

    PubMed

    Gamal, Osama; Shams, Ahmed; El-Sayed Semaya, Ahmad

    Intra-articular fracture of the calcaneus is one of the most displeasing fractures if not properly managed. Open reduction and internal fixation have been associated with a high incidence of postoperative soft tissue complications. Closed reduction and percutaneous fixation have resulted in a greater incidence of postoperative subtalar osteoarthritis with improper reduction of the articular surface. In the present study, a mini-open approach was used in cases of failure of articular surface restoration with closed reduction. A total of 64 feet in 57 consecutive patients with an intra-articular calcaneal fracture underwent the proposed minimally invasive surgical protocol. Of the 57 patients, 7 (12.3%) had bilateral fractures. According to Sanders classification, 33 (51.6%) fractures were type II and 31 (48.4%) were type III. Seven (12.3%) patients had wedge fractures of the dorsolumbar spine without neurologic manifestations. The postoperative evaluation included radiographs and completion of the Maryland Foot Score and visual analog scale for pain. The mean follow-up period was 16 (range 12 to 36) months. The mean operative time was 42 (range 35 to 60) minutes. The mean period until union of the fracture was 12 (range 10 to 16) weeks. The clinical results according to the Maryland Foot Score revealed 52 (81%) with satisfactory (27 excellent and 25 good) and 12 (19%) with unsatisfactory (10 fair and 2 poor) results. The mean visual analog scale score was 1.5 ± 0.3 when radiographic fracture healing was observed. Six patients (9.4%) developed superficial pin tract infections that responded to local care and parenteral antibiotic therapy and resolved completely after removal of the Kirschner wires. In conclusion, the presented surgical protocol combining closed reduction with or without an added mini-open approach and percutaneous fixation improves the functional outcome and minimizes the incidence of complications.

  9. Architecture, fracture system, mechanical properties and permeability structure of a fault zone in Lower Triassic sandstone, Upper Rhine Graben

    NASA Astrophysics Data System (ADS)

    Bauer, Johanna F.; Meier, Silke; Philipp, Sonja L.

    2015-04-01

    Close to the western Upper Rhine Graben Main Fault, Alsace, a NNE-SSW-striking fault zone, crosscutting porous, thick bedded Lower Triassic Bunter sandstone was investigated in detail, including its architecture, discontinuity system, mechanical rock properties and implications on its permeability structure and fault zone type. Field observations indicate a three-part fault zone structure including core-, transition- and damage zone. The at least 14 m thick fault core is composed of various slip surfaces and deformation bands, which encompass fractured host rock lenses. When connected, host rock lenses may transport fluids through the core zone. Adjacent transition zones are highly fractured in R1-orientation, show folded beds and contain P1-oriented deformation bands. R1 and P1-fractures are synthetic shear fractures and project with an acute angle (10-20°) toward the fault plane. Only in the damage zone, fault-parallel striking fractures occur. Here, increasing fracture apertures and connectivity may increase the permeability toward the fault core. Mechanical rock properties from 12 rock samples (Young's modulus, uniaxial compressive strength, tensile strength) measured in all the parts of the fault zone, show highest values within the transition zone. In-situ measurements of rebound-hardnesses with a Schmidt-Hammer and analytical approaches, however, indicate that effective Young's moduli are two to sixteen times lower than the Young's moduli of intact rock. Values clearly decrease toward the fault core, even in the transition zone and are in average lower than effective Young's moduli in the damage zone. Although many fault zones in sandstone are sealing structures these field study show, that fault zones in porous sandstone may allow fluid flow.

  10. A mechanism for regulation of chloroplast LHC II kinase by plastoquinol and thioredoxin.

    PubMed

    Puthiyaveetil, Sujith

    2011-06-23

    State transitions are acclimatory responses to changes in light quality in photosynthesis. They involve the redistribution of absorbed excitation energy between photosystems I and II. In plants and green algae, this redistribution is produced by reversible phosphorylation of the chloroplast light harvesting complex II (LHC II). The LHC II kinase is activated by reduced plastoquinone (PQ) in photosystem II-specific low light. In high light, when PQ is also reduced, LHC II kinase becomes inactivated by thioredoxin. Based on newly identified amino acid sequence features of LHC II kinase and other considerations, a mechanism is suggested for its redox regulation.

  11. Ductile fracture in HY100 steel under mixed mode I/mode II loading

    SciTech Connect

    Bhattacharjee, D. . Dept. of Materials Science and Metallurgy); Knott, J.F. . School of Metallurgy and Materials)

    1994-05-01

    A number of criteria have been proposed which predict the direction of cracking under mixed Mode 1/Mode 2 loading. All have been evaluated for brittle materials, in which a crack subjected to tension and shear propagates normal to the maximum tensile stress (i.e. fracture is of the Mode 1 type). In a ductile material, however, a notch subjected to mixed Mode 1/Mode 2 loading may initiate a crack in the direction of maximum shear. This paper shows that the profile of the notch tip changes with increasing mixed mode load in such a way that one side of the tip blunts while the other sharpens. Various specimens, subjected to the same mixed mode ratio, were unloaded from different points on the load-displacement curves to study the change in notch-tip profile. Studies under the Scanning Electron Microscope (SEM) have shown that cracks initiate at the sharpened end, along a microscopic shear band. Using a dislocation pile-up model for decohesion of the carbide-matrix interface, a micromechanical model has been proposed for crack initiation in the shear band. It is shown that a theoretical prediction of the shear strain required for decohesion gives a result that is, of magnitude, similar to that of the shear strain at crack initiation measured in the experiments.

  12. Nose fracture

    MedlinePlus

    Fracture of the nose; Broken nose; Nasal fracture; Nasal bone fracture; Nasal septal fracture ... A fractured nose is the most common fracture of the face. It ... with other fractures of the face. Sometimes a blunt injury can ...

  13. Probability of pipe fracture in the primary coolant loop of a PWR plant. Volume 5. Probabilistic fracture mechanics analysis. Load Combination Program Project I final report

    SciTech Connect

    Harris, D.O.; Lim, E.Y.; Dedhia, D.D.

    1981-06-01

    The primary purpose of the Load Combination Program covered in this report is to estimate the probability of a seismic induced LOCA in the primary piping of a commercial pressurized water reactor (PWR). Best estimates, rather than upper bound results are desired. This was accomplished by use of a fracture mechanics model that employs a random distribution of initial cracks in the piping welds. Estimates of the probability of cracks of various sizes initially existing in the welds are combined with fracture mechanics calculations of how these cracks would grow during service. This then leads to direct estimates of the probability of failure as a function of time and location within the piping system. The influence of varying the stress history to which the piping is subjected is easily determined. Seismic events enter into the analysis through the stresses they impose on the pipes. Hence, the influence of various seismic events on the piping failure probability can be determined, thereby providing the desired information.

  14. Structural mechanisms of the Ih–II and II → Ic transitions between the crystalline phases of aqueous ice

    SciTech Connect

    Zheligovskaya, E. A.

    2015-09-15

    Structural mechanisms are proposed for experimentally observed phase transitions between crystalline modifications of aqueous ice, Ih and II, as well as II and Ic. It is known that the Ih–II transition occurs with the conservation of large structural units (hexagonal channels) common for these ices. It is shown that the Ih → II transition may occur with the conservation of 5/6 of all hydrogen bonds in crystal, including all hydrogen bonds in the retained channels (3/4 of the total number of bonds in crystal) and 1/3 of the bonds between these channels (1/12 of the total number). The transformation of other hydrogen bonds between the retained channels leads to the occurrence of proton order in ice II. A structural mechanism is proposed to explain the transformation of single crystals of ice Ih either into single crystals of ice II or into crystalline twins of ice II with c axes rotated by 180° with respect to each other, which is often observed at the Ih → II transition. It is established that up to 7/12 of all hydrogen bonds are retained at the irreversible cooperative II → Ic transition.

  15. The fracture energy and some mechanical properties of a polyurethane elastomer.

    NASA Technical Reports Server (NTRS)

    Mueller, H. K.; Knauss, W. G.

    1971-01-01

    The energy required to form a unit of new surface in the fracture of a polyurethane elastomer is determined. The rate sensitivity of the material has been reduced by swelling it in toluene. This paper primarily describes the experimental work of measuring the lower limit of the fracture energy. With this value and the creep compliance as a basis, the rate dependence of fracture energy for the unswollen material has been determined. It is thus shown that the dependence of the fracture energy on the rate of crack propagation can be explained by energy dissipation around the tip of the crack. Good agreement between the theoretically and experimentally determined relationships for the rate-sensitive fracture energy is demonstrated.

  16. Are Carotid Stent Fractures Clinically Significant?

    SciTech Connect

    Garcia-Toca, Manuel; Rodriguez, Heron E.; Naughton, Peter A.; Keeling, Aiofee; Phade, Sachin V.; Morasch, Mark D.; Kibbe, Melina R.; Eskandari, Mark K.

    2012-04-15

    Purpose: Late stent fatigue is a known complication after carotid artery stenting (CAS) for cervical carotid occlusive disease. The purpose of this study was to determine the prevalence and clinical significance of carotid stent fractures. Materials and Methods: A single-center retrospective review of 253 carotid bifurcation lesions treated with CAS and mechanical embolic protection from April 2001 to December 2009 was performed. Stent integrity was analyzed by two independent observers using multiplanar cervical plain radiographs with fractures classified into the following types: type I = single strut fracture; type II = multiple strut fractures; type III = transverse fracture; and type IV = transverse fracture with dislocation. Mean follow-up was 32 months. Results: Follow-up imaging was completed on 106 self-expanding nitinol stents (26 closed-cell and 80 open-cell stents). Eight fractures (7.5%) were detected (type I n = 1, type II n = 6, and type III n = 1). Seven fractures were found in open-cell stents (Precise n = 3, ViVEXX n = 2, and Acculink n = 2), and 1 fracture was found in a closed-cell stent (Xact n = 1) (p = 0.67). Only a previous history of external beam neck irradiation was associated with fractures (p = 0.048). No associated clinical sequelae were observed among the patients with fractures, and only 1 patient had an associated significant restenosis ({>=}80%) requiring reintervention. Conclusions: Late stent fatigue after CAS is an uncommon event and rarely clinically relevant. Although cell design does not appear to influence the occurrence of fractures, lesion characteristics may be associated risk factors.

  17. Micro-mechanical investigation for effects of helium on grain boundary fracture of austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Miura, Terumitsu; Fujii, Katsuhiko; Fukuya, Koji

    2015-02-01

    Effects of helium (He) on grain boundary (GB) fracture of austenitic stainless steel were investigated by micro-tensile tests. Micro-bicrystal tensile specimens were fabricated for non-coincidence site lattice boundaries of He ion-irradiated 316 stainless steel by focused ion beam (FIB) micro-processing. Micro-tensile tests were conducted in a vacuum at room temperature in the FIB system. Specimens containing more than 2 at.% He fractured at GBs. The criteria for brittle fracture occurrence on GBs were: (1) He concentrations higher than 2 at.%; (2) formation of He bubbles on the GBs with less than a 5 nm spacing; and (3) matrix hardening to more than 4.6 GPa (nano-indentation hardness). The fracture stress of GB brittle fracture was lower for a specimen with higher He concentration while the size and areal density of the GB He bubbles were the same. The specimens that contained 10 at.% He and had been annealed at 923 K after irradiation fractured at the GB nominally in a brittle manner; however the inter-bubble matrix at the GB experienced ductile fracture. The annealing caused He bubbles to grow but decreased the areal density so that the spacing of the GB He bubbles widened and the hardness decreased, therefore the fracture mode changed from brittle to ductile. The findings revealed that He promotes GB fracture by weakening the GB strength and hardening the matrix due to the formation of He bubbles both on GBs and in the matrix. In addition, the findings suggested that GB segregated He atoms may have a role in GB fracture.

  18. Influence of mechanical rock properties and fracture healing rate on crustal fluid flow dynamics

    NASA Astrophysics Data System (ADS)

    Sachau, Till; Bons, Paul; Gomez-Rivas, Enrique; Koehn, Daniel; de Riese, Tamara

    2016-04-01

    Fluid flow in the Earth's crust is very slow over extended periods of time, during which it occurs within the connected pore space of rocks. If the fluid production rate exceeds a certain threshold, matrix permeability alone is insufficient to drain the fluid volume and fluid pressure builds up, thereby reducing the effective stress supported by the rock matrix. Hydraulic fractures form once the effective pressure exceeds the tensile strength of the rock matrix and act subsequently as highly effective fluid conduits. Once local fluid pressure is sufficiently low again, flow ceases and fractures begin to heal. Since fluid flow is controlled by the alternation of fracture permeability and matrix permeability, the flow rate in the system is strongly discontinuous and occurs in intermittent pulses. Resulting hydraulic fracture networks are largely self-organized: opening and subsequent healing of hydraulic fractures depends on the local fluid pressure and on the time-span between fluid pulses. We simulate this process with a computer model and describe the resulting dynamics statistically. Special interest is given to a) the spatially and temporally discontinuous formation and closure of fractures and fracture networks and b) the total flow rate over time. The computer model consists of a crustal-scale dual-porosity setup. Control parameters are the pressure- and time-dependent fracture healing rate, and the strength and the permeability of the intact rock. Statistical analysis involves determination of the multifractal properties and of the power spectral density of the temporal development of the total drainage rate and hydraulic fractures. References Bons, P. D. (2001). The formation of large quartz veins by rapid ascent of fluids in mobile hydrofractures. Tectonophysics, 336, 1-17. Miller, S. a., & Nur, A. (2000). Permeability as a toggle switch in fluid-controlled crustal processes. Earth and Planetary Science Letters, 183(1-2), 133-146. Sachau, T., Bons, P. D

  19. Application of the Pegasus II Pulsed-Power Facility to the Study of Inertial Instability and Fracture of Cylindrical Tubes of Solid Aluminum

    SciTech Connect

    Chandler, E.A.; Stokes, J.; Fulton, R.D.; Morgan, D.V.; Obst, A.W.; Oro, D.M.; Oona, H.; Anderson, W.E.

    1999-06-23

    Understanding the surface stability of metals undergoing dynamic fracture at shock breakout is important to several applications in metals processing. The advantages of using the Pegasus II facility to investigate the phenomena occurring at shock break out are described. As an example of the data collected, we concentrate on brief descriptions of two experiments that compared the tensile failure, i.e. ''spall'', patterns in the presence of sinusoidal perturbations seeded on the free inner surface of cylindrical samples of 3 types of Al. These samples were composed variously of soft Al 1100-O, structural grade Al 6061-T6, and ultra-pure 99.99% Al and were subjected to Taylor waves with shock pressures of 14 GPa. We show that the material behind the exiting surface undergoes a type of failure termed here ''microspall'', resulting in the production of a significant volume of low-density, probably granular, material. The failure mechanism, combined with the forces that cause inertial instability, leads to rapid pattern growth in the failed material and subsequent pattern growth on the surface. Pattern growth was studied as a function of perturbation wavelength and amplitude. The different Al samples vary by an order of magnitude in yield strength, and some increase in pattern instability was observed at lower yield strength. The ultra-pure Al has exceptionally large grain size, in the mm range. No appreciable variation of spall pattern was observed due to grain size.

  20. Tissue level microstructure and mechanical properties of the femoral head in the proximal femur of fracture patients

    NASA Astrophysics Data System (ADS)

    Lü, Linwei; Meng, Guangwei; Gong, He; Zhu, Dong; Gao, Jiazi; Fan, Yubo

    2015-04-01

    This study aims to investigate the regional variations of trabecular morphological parameters and mechanical parameters of the femoral head, as well as to determine the relationship between trabecular morphological and mechanical parameters. Seven femoral heads from patients with fractured proximal femur were scanned using a micro-CT system. Each femoral head was divided into 12 sub-regions according to the trabecular orientation. One trabecular cubic model was reconstructed from each sub-region. A total of 81 trabecular models were reconstructed, except three destroyed sub-regions from two femoral heads during the surgery. Trabecular morphological parameters, i.e. trabecular separation (Tb.Sp), trabecular thickness (Tb.Th), specific bone surface (BS/BV), bone volume fraction (BV/TV), structural model index (SMI), and degree of anisotropy (DA) were measured. Micro-finite element analyses were performed for each cube to obtain the apparent Young's modulus and tissue level von Mises stress distribution under 1 % compressive strain along three orthogonal directions, respectively. Results revealed significant regional variations in the morphological parameters (). Young's moduli along the trabecular orientation were significantly higher than those along the other two directions. In general, trabecular mechanical properties in the medial region were lower than those in the lateral region. Trabecular mechanical parameters along the trabecular orientation were significantly correlated with BS/BV, BV/TV, Tb.Th, and DA. In this study, regional variations of microstructural features and mechanical properties in the femoral head of patients with proximal femur fracture were thoroughly investigated at the tissue level. The results of this study will help to elucidate the mechanism of femoral head fracture for reducing fracture risk and developing treatment strategies for the elderly.

  1. Structural Mechanics Predictions Relating to Clinical Coronary Stent Fracture in a 5 Year Period in FDA MAUDE Database

    PubMed Central

    Everett, Kay D.; Conway, Claire; Desany, Gerard J.; Baker, Brian L.; Choi, Gilwoo; Taylor, Charles A.; Edelman, Elazer R.

    2016-01-01

    Endovascular stents are the mainstay of interventional cardiovascular medicine. Technological advances have reduced biological and clinical complications but not mechanical failure. Stent strut fracture is increasingly recognized as of paramount clinical importance. Though consensus reigns that fractures can result from material fatigue, how fracture is induced and the mechanisms underlying its clinical sequelae remain ill-defined. In this study, strut fractures were identified in the prospectively maintained Food and Drug Administration's (FDA) Manufacturer and User Facility Device Experience Database (MAUDE), covering years 2006–2011, and differentiated based on specific coronary artery implantation site and device configuration. These data, and knowledge of the extent of dynamic arterial deformations obtained from patient CT images and published data, were used to define boundary conditions for 3D finite element models incorporating multimodal, multi-cycle deformation. The structural response for a range of stent designs and configurations was predicted by computational models and included estimation of maximum principal, minimum principal and equivalent plastic strains. Fatigue assessment was performed with Goodman diagrams and safe/unsafe regions defined for different stent designs. Von Mises stress and maximum principal strain increased with multimodal, fully reversed deformation. Spatial maps of unsafe locations corresponded to the identified locations of fracture in different coronary arteries in the clinical database. These findings, for the first time, provide insight into a potential link between patient adverse events and computational modeling of stent deformation. Understanding of the mechanical forces imposed under different implantation conditions may assist in rational design and optimal placement of these devices. PMID:26467552

  2. Evaluation of Damage and Fracture Mechanisms of Different Characteristic Honeycomb Structures Under Thermomechanical Loading

    NASA Astrophysics Data System (ADS)

    Settet, A. T.; Nour, A.; Zahloul, H.; Naceur, H.

    2014-11-01

    A model able to predict the delamination mechanisms of composite honeycomb structures under thermal loading is presented. The use of a simulation software for some applications may not be sufficient to obtain the results expected; hence, the interest in developing modular calculation codes which would allow one to determine the rigidity matrix of a honeycomb panel, the deformation of its members, the field of shear strains, strains, and stresses in the panel plane on varying the physical parameters and checking the strength of each layer and of the entire panel. In order to test the reliability of the program developed, the results obtained are compared with those given in the literature. A specific model of Young's modulus under thermal loads is proposed, which takes into consideration the heat flux function, the thermal conductivity, the convection heat-transfer coefficients of the surrounding area inside and outside the panel, the exchange area in contact with air, the thickness of the honeycomb core, the upper and lower skins, and the adhesive layer. To verify the fracture strength of each panel, the Tsai-Wu criterion is used.

  3. A review of path-independent integrals in elastic-plastic fracture mechanics

    NASA Technical Reports Server (NTRS)

    Kim, Kwang S.; Orange, Thomas W.

    1988-01-01

    The objective of this paper is to review the path-independent (P-I) integrals in elastic plastic fracture mechanics which have been proposed in recent years to overcome the limitations imposed on the J-integral. The P-I integrals considered are the J-integral by Rice (1968), the thermoelastic P-I integrals by Wilson and Yu (1979) and Gurtin (1979), the J-integral by Blackburn (1972), the J(theta)-integral by Ainsworth et al. (1978), the J-integral by Kishimoto et al. (1980), and the Delta-T(p) and Delta T(p)-asterisk integrals by Alturi et al. (1982). The theoretical foundation of the P-I integrals is examined with an emphasis on whether or not the path independence is maintained in the presence of nonproportional loading and unloading in the plastic regime, thermal gradient, and material inhomogeneities. The simularities, difference, salient features, and limitations of the P-I integrals are discussed. Comments are also made with regard to the physical meaning, the possibility of experimental measurement, and computational aspects.

  4. NASCRAC - A computer code for fracture mechanics analysis of crack growth

    NASA Technical Reports Server (NTRS)

    Harris, D. O.; Eason, E. D.; Thomas, J. M.; Bianca, C. J.; Salter, L. D.

    1987-01-01

    NASCRAC - a computer code for fracture mechanics analysis of crack growth - is described in this paper. The need for such a code is increasing as requirements grow for high reliability and low weight in aerospace components. The code is comprehensive and versatile, as well as user friendly. The major purpose of the code is calculation of fatigue, corrosion fatigue, or stress corrosion crack growth, and a variety of crack growth relations can be selected by the user. Additionally, crack retardation models are included. A very wide variety of stress intensity factor solutions are contained in the code, and extensive use is made of influence functions. This allows complex stress gradients in three-dimensional crack problems to be treated easily and economically. In cases where previous stress intensity factor solutions are not adequate, new influence functions can be calculated by the code. Additional features include incorporation of J-integral solutions from the literature and a capability for estimating elastic-plastic stress redistribution from the results of a corresponding elastic analysis. An example problem is presented which shows typical outputs from the code.

  5. Computational and numerical aspects of using the integral equation method for adhesive layer fracture mechanics analysis

    SciTech Connect

    Giurgiutiu, V.; Ionita, A.; Dillard, D.A.; Graffeo, J.K.

    1996-12-31

    Fracture mechanics analysis of adhesively bonded joints has attracted considerable attention in recent years. A possible approach to the analysis of adhesive layer cracks is to study a brittle adhesive between 2 elastic half-planes representing the substrates. A 2-material 3-region elasticity problem is set up and has to be solved. A modeling technique based on the work of Fleck, Hutchinson, and Suo is used. Two complex potential problems using Muskelishvili`s formulation are set up for the 3-region, 2-material model: (a) a distribution of edge dislocations is employed to simulate the crack and its near field; and (b) a crack-free problem is used to simulate the effect of the external loading applied in the far field. Superposition of the two problems is followed by matching tractions and displacements at the bimaterial boundaries. The Cauchy principal value integral is used to treat the singularities. Imposing the traction-free boundary conditions over the entire crack length yielded a linear system of two integral equations. The parameters of the problem are Dundurs` elastic mismatch coefficients, {alpha} and {beta}, and the ratio c/H representing the geometric position of the crack in the adhesive layer.

  6. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering

    NASA Astrophysics Data System (ADS)

    Çınar, Simge; Tevis, Ian D.; Chen, Jiahao; Thuo, Martin

    2016-02-01

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate (‘/’ = physisorbed, ‘-’ = chemisorbed), from molten Field’s metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity.

  7. Low Magnitude Mechanical Signals Reduce Risk-Factors for Fracture during 90-Day Bed Rest

    NASA Technical Reports Server (NTRS)

    Muir, J. W.; Xia, Y.; Holquin, N.; Judex, S.; Qin, Y.; Evans, H.; Lang, T.; Rubin, C.

    2007-01-01

    Long duration spaceflight leads to multiple deleterious changes to the musculoskeletal system, where loss of bone density, an order of magnitude more severe than that which follows the menopause, combined with increased instability, conspire to elevate the risk of bone fracture due to falls on return to gravitational fields. Here, a ground-based analog for spaceflight is used to evaluate the efficacy of a low-magnitude mechanical intervention, VIBE (Vibrational Inhibition of Bone Erosion), as a potential countermeasure to preserve musculoskeletal integrity in the face of disuse. Twenty-six subjects consented to ninety days of six-degree head-down tilt bed-rest. 18 completed the 90d protocol, 8 of which received daily 10-minute exposure to 30 Hz, 0.3g VIBE, applied in the supine position using a vest elastically coupled to the vibrating platform. The shoulder harness induced a load of 60% of the subjects body weight. At baseline and 90d, Qualitative Ultrasound Scans (QUS) of the calcaneus and CT-scans of the hip and spine were performed to measure changes in bone density. Postural control (PC) was assessed through center of pressure (COP) recordings while subjects stood on a force platform for 4 minutes of quiet stance with eyes closed, and again with eyes opened. As compared to control bedrest subjects,

  8. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering.

    PubMed

    Çınar, Simge; Tevis, Ian D; Chen, Jiahao; Thuo, Martin

    2016-02-23

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate ('/' = physisorbed, '-' = chemisorbed), from molten Field's metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity.

  9. Fracture Mechanics Analyses of the Slip-Side Joggle Regions of Wing-Leading Edge Panels

    NASA Technical Reports Server (NTRS)

    Raju, Ivatury S.; Knight, Norman F., Jr.; Song, Kyongchan; Phillips, Dawn R.

    2010-01-01

    The Space Shuttle Orbiter wing comprises of 22 leading edge panels on each side of the wing. These panels are part of the thermal protection system that protects the Orbiter wings from extreme heating that take place on the reentry in to the earth atmosphere. On some panels that experience extreme heating, liberation of silicon carbon (SiC) coating was observed on the slip side regions of the panels. Global structural and local fracture mechanics analyses were performed on these panels as a part of the root cause investigation of this coating liberation anomaly. The wing-leading-edge reinforced carbon-carbon (RCC) panels, Panel 9, T-seal 10, and Panel 10, are shown in Figure 1 and the progression of the stress analysis models is presented in Figure 2. The global structural analyses showed minimal interaction between adjacent panels and the T-seal that bridges the gap between the panels. A bounding uniform temperature is applied to a representative panel and the resulting stress distribution is examined. For this loading condition, the interlaminar normal stresses showed negligible variation in the chord direction and increased values in the vicinity of the slip-side joggle shoulder. As such, a representative span wise slice on the panel can be taken and the cross section can be analyzed using plane strain analysis.

  10. Development of fracture mechanics data for two hydrazine APU turbine wheel materials

    NASA Technical Reports Server (NTRS)

    Curbishley, G.

    1975-01-01

    The effects of high temperature, high pressure ammonia were measured on the fracture mechanics and fatigue properties of Astroloy and Rene' 41 turbine wheel materials. Also, the influence of protective coatings on these properties was investigated. Specimens of forged bar stock were subjected to LCF and HCF tests at 950 K (1250 F) and 3.4 MN/sq m (500 psig) pressure, in ammonia containing about 1.5 percent H2O. Aluminized samples (Chromizing Company's Al-870) and gold plated test bars were compared with uncoated specimens. Comparison tests were also run in air at 950 K (1250 F), but at ambient pressures. K sub IE and K sub TH were determined on surface flawed specimens in both the air and ammonia in both uncoated and gold plated conditions. Gold plated specimens exhibited better properties than uncoated samples, and aluminized test bars generally had lower properties. The fatigue properties of specimens tested in ammonia were higher than those tested in air, yet the K sub TH values of ammonia tested samples were lower than those tested in air. However, insufficient specimens were tested to develop significant design data.

  11. A review of path-independent integrals in elastic-plastic fracture mechanics, task 4

    NASA Technical Reports Server (NTRS)

    Kim, K. S.

    1985-01-01

    The path independent (P-I) integrals in elastic plastic fracture mechanics which have been proposed in recent years to overcome the limitations imposed on the J integral are reviewed. The P-I integrals considered herein are the J integral by Rice, the thermoelastic P-I integrals by Wilson and Yu and by Gurtin, the J* integral by Blackburn, the J sub theta integral by Ainsworth et al., the J integral by Kishimoto et al., and the delta T sub p and delta T* sub p integrals by Atluri et al. The theoretical foundation of these P-I integrals is examined with emphasis on whether or not path independence is maintained in the presence of nonproportional loading and unloading in the plastic regime, thermal gradients, and material inhomogeneities. The similarities, differences, salient features, and limitations of these P-I integrals are discussed. Comments are also made with regard to the physical meaning, the possibility of experimental measurement, and computational aspects.

  12. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering

    PubMed Central

    Çınar, Simge; Tevis, Ian D.; Chen, Jiahao; Thuo, Martin

    2016-01-01

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate (‘/’ = physisorbed, ‘-’ = chemisorbed), from molten Field’s metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity. PMID:26902483

  13. Engineering geological characteristics and the hydraulic fracture propagation mechanism of the sand-shale interbedded formation in the Xu5 reservoir

    NASA Astrophysics Data System (ADS)

    Lu, Cong; Li, Mei; Guo, Jian-Chun; Tang, Xu-Hai; Zhu, Hai-Yan; Yong-Hui, Wang; Liang, Hao

    2015-06-01

    In the Xu5 formation the sandstone reservoir and the shale reservoir are interbedded with each other. The average thickness of each formation is about 8 m, which increases the difficulty of the hydraulic fracturing treatment. The shale thickness ratio (the ratio of shale thickness to formation thickness) is 55-62.5%. The reservoir is characterized by ultra-low porosity and permeability. The brittleness index of sandstone is 0.5-0.8, and the brittleness index of shale is 0.3-0.8. Natural fractures are poorly developed and are mainly horizontal and at a low angle. The formation strength is medium and the reservoir is of the hybrid strike-slip fault and reverse fault stress regime. The difference between the minimum principal stress and the vertical stress is small, and the maximum horizontal principal stress is 20 MPa higher than the minimum horizontal principal stress and vertical stress. A mechanical model of a hydraulic fracture encountering natural fractures is built according to geological characteristics. Fracture mechanics theory is then used to establish a hydraulic fracturing model coupling the seepage-stress-damage model to simulate the initiation and propagation of a fracture. The hydraulic fracture geometry is mainly I-shaped and T-shaped, horizontal propagation dominates the extension, and vertical propagation is limited. There is a two to three meter stress diversion area around a single hydraulic fracture. The stress diversion between a hydraulic fracture and a natural fracture is advantageous in forming a complex fracture. The research results can provide theoretical guidance for tight reservoir fracturing design.

  14. Variable amplitude corrosion fatigue and fracture mechanics of weldable high strength jack-up steels

    NASA Astrophysics Data System (ADS)

    Etube, Linus Sone

    The tubular welded joints used in the construction of Offshore structures can experience millions of variable amplitude wave induced stress cycles during their operational life. Fatigue has been identified as the main cause of degradation of structural integrity in these structures. As a result, fatigue is an important consideration in their design. Jack-up legs are made from a range of high strength steels with yield strengths up to TOOMPa. These steels are thought to exhibit fatigue resistance properties which are different when compared with conventional fixed platform steels such as BS 4360 50D and BS 7191 355D. The difference in their behaviour was heightened by the discovery, in the late 80s and early 90s, of extensive cracking around the spud can regions of several Jack-ups operating in the North Sea. It was thought that these steels may be more susceptible to hydrogen cracking and embrittlement. There was the additional requirement to study their behaviour under realistic loading conditions typical of the North Sea environment. This thesis contains results of an investigation undertaken to assess the performance of a typical high strength weldable Jack-up steel under realistic loading and environmental conditions. Details of the methodology employed to develop a typical Jack-up Offshore Standard load History (JOSH) are presented. The factors which influence fatigue resistance of structural steels used in the construction of Jack-up structures are highlighted. The methods used to model the relevant factors for inclusion in JOSH are presented with particular emphasis on loading and structural response interaction. Results and details of experimental variable amplitude corrosion fatigue (VACF) tests conducted using JOSH are reported and discussed with respect to crack growth mechanisms in high strength weldable Jack-up steels. Different fracture mechanics models for VACF crack growth prediction are compared and an improved generalised methodology for fast

  15. Future target for geothermal development -- Fractal Fracture Mechanics and its application to conceptual HDR reservoir design

    SciTech Connect

    Takahashi, Hideaki; Watanable, Kimio; Hashida, Toshiyuki

    1995-01-26

    A simple model is proposed for water/rock interaction in rock fractures through which geothermal water flows. Water/rock interaction experiments were carried out at high temperature and pressure (200-350 C, 18 MPa) in order to obtain basic solubility and reaction rate data. Based on the experimental data, changes of idealized fracture apertures with time are calculated numerically. The results of the calculations show that the precipitation from water can lead to plugging of the fractures under certain conditions. Finally, the results are compared with the experimental data.

  16. Structure, mechanical properties and fracture behavior of organosilicate glass thin films

    NASA Astrophysics Data System (ADS)

    Lin, Youbo

    2007-12-01

    Organosilicate glass (OSG) thin films with low permittivity made by means of plasma enhanced chemical vapor deposition are the inter-metal insulator in advanced integrated circuits. These materials are employed to reduce the interconnect delay and power consumption associated with the inter-line capacitance. However the implementation of OSG is hampered by its poor mechanical properties and susceptibility to stress-corrosion cracking. In this work, we present a study of the structure evolution of OSG under various processing conditions, as well as the impact of structure and environment on the mechanical properties and fracture behavior. We will show that the composition and structure of OSG can be finely tuned by changing the parameters during film deposition or post-treatments. Adding carbon content in the film lowers the density and reduces the dielectric constant, accompanied by a decrease of the network connectivity. Ultraviolet-cure is very effective in crosslinking and stabilizing the network structure without causing significant increase in permittivity. With the assist of a structure model, we determined the infrared absorption inverse cross-sections that may be used to analyze infrared spectra of other OSG films. The mechanical properties of OSG are very sensitive to the network structure. Both the mean connectivity number and networking bond density correlate well with mechanical properties. The comparison of cohesive and adhesion energies reveals that plasma treatments substantially enhance the adhesion. However, the enhancement diminishes when the films are exposed to reactive environments. Our study shows that the adhesion energy at given crack velocity changes linearly with the logarithm of the water partial pressure in ambient, or with pH value in aqueous environment. On the other hand, water degrades the electrical property and adhesion when absorbed. We found that the water diffusion in OSG film stacks is very fast, reversible under mild annealing

  17. Application of fracture mechanics and half-cycle theory to the prediction of fatigue life of aerospace structural components

    NASA Technical Reports Server (NTRS)

    Ko, William L.

    1989-01-01

    The service life of aircraft structural components undergoing random stress cycling was analyzed by the application of fracture mechanics. The initial crack sizes at the critical stress points for the fatigue crack growth analysis were established through proof load tests. The fatigue crack growth rates for random stress cycles were calculated using the half-cycle method. A new equation was developed for calculating the number of remaining flights for the structural components. The number of remaining flights predicted by the new equation is much lower than that predicted by the conventional equation. This report describes the application of fracture mechanics and the half-cycle method to calculate the number of remaining flights for aircraft structural components.

  18. Fracture-mechanical analysis of the residual service life of the welded main girders of the highway bridges of Ruedersdorf

    NASA Astrophysics Data System (ADS)

    Edel, Karl-Otto

    1992-07-01

    A fracture mechanics analysis was carried out on a certain type of weld defect contained in the main girders of the Ruedersdorf highway bridges (River Luehlen, Germany). To assess fatigue cracks which start from welding defects of about 10 mm height at the end of the inner cover plates, specimens were taken from the bridges. The fracture mechanical properties of the 55 years old steel and the stress intensity factors were determined to analyze the unstable and stable crack extension. The essential influence on the residual life is the extending traffic density. The assesssment of the critical crack size and that of the crack growth show a residual service life of some years. Only limited data can be generated from specimens removed from the bridges, and the effect of the service environment of any specific structure must be taken into account.

  19. Fracture mechanics data for 2024-T861 and 2124-T851 aluminum

    NASA Technical Reports Server (NTRS)

    Pionke, L. J.; Linback, R. K.

    1974-01-01

    The fracture toughness and fatigue flaw growth characteristics of 2024-T861 and 2124-T851 aluminum were evaluated under plane stress conditions. Center cracked tension specimens were employed to evaluate these properties under a number of different test conditions which included variations in specimen thickness, specimen orientation, test environment, and initial flaw size. The effect of buckling was also investigated for all tests of thin gage specimens, and the effect of frequency and stress ratio was evaluated for the cyclic tests. Fracture toughness test results were analyzed and presented in terms of fracture resistance curves; fatigue flaw growth data was analyzed using empirical rate models. The results of the study indicate that both fracture toughness and resistance to fatigue crack growth improve with increasing temperature and decreasing thickness. The presence of buckling during testing of thin gage panels was found to degrade the resistance to fatigue flaw growth only at elevated temperatures.

  20. Vitamin D and bone fracture mechanisms: what about the non-bone 'D'efense?

    PubMed

    Annweiler, C; Beauchet, O

    2010-04-01

    Osteoporosis is a public health concern because of its high prevalence and consequences in terms of morbidity, mortality and health care costs (1). This growing epidemic highlights the problem of the 'knowledge paradox': on one hand there is an increase in medical knowledge about osteoporotic fractures but, on the other hand, the amount of bone fractures keeps increasing (1-3). In this context, any strategy preventing the occurrence of bone fractures, such as vitamin D supplementation, is welcome. For instance, a very recent meta analysis from Bischoff-Ferarri et al. underlined the efficacy of oral supplemental vitamin D, regardless of any additional calcium supplementation, in non-vertebral fractures prevention among more than 42,000 adults aged 65 years and older (2).

  1. Mechanical output of myosin II motors is regulated by myosin filament size and actin network mechanics

    NASA Astrophysics Data System (ADS)

    Stam, Samantha; Alberts, Jonathan; Gardel, Margaret; Munro, Edwin

    2013-03-01

    The interactions of bipolar myosin II filaments with actin arrays are a predominate means of generating forces in numerous physiological processes including muscle contraction and cell migration. However, how the spatiotemporal regulation of these forces depends on motor mechanochemistry, bipolar filament size, and local actin mechanics is unknown. Here, we simulate myosin II motors with an agent-based model in which the motors have been benchmarked against experimental measurements. Force generation occurs in two distinct regimes characterized either by stable tension maintenance or by stochastic buildup and release; transitions between these regimes occur by changes to duty ratio and myosin filament size. The time required for building force to stall scales inversely with the stiffness of a network and the actin gliding speed of a motor. Finally, myosin motors are predicted to contract a network toward stiffer regions, which is consistent with experimental observations. Our representation of myosin motors can be used to understand how their mechanical and biochemical properties influence their observed behavior in a variety of in vitro and in vivo contexts.

  2. Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials

    NASA Technical Reports Server (NTRS)

    Ceipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

    1972-01-01

    Research on the fracture behavior of silicon nitride and silicon carbide is reported along with the role of anion impurities in the fabrication and behavior of magnesium oxide. The results of a survey of crack propagation in SiC and Si3N4 are presented. Studies in the following areas are reported: development of a fracture toughness testing technique, constant moment beam, microcrack examination, and etching techniques.

  3. Criterion for mixed mode fracture in composite bonded joints

    NASA Technical Reports Server (NTRS)

    Mall, S.; Kochhar, N. K.

    1986-01-01

    A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite/epoxy (T300/5208) composite adherends bonded with a toughened epoxy (EC 3445) adhesive. The mode I, mode II and mixed-mode I-II fracture energies of the tested adhesive were found to be equal to each other. Furthermore, the criterion for mixed mode fracture in composite bonded joints was determined.

  4. Side impact: influence of impact conditions and bone mechanical properties on pelvic response using a fracturable pelvis model.

    PubMed

    Song, Eric; Trosseille, Xavier; Guillemot, Hevé

    2006-11-01

    This study aimed at determining the influence of impact conditions and occupant mechanical properties on pelvic response in side impact. First, a fracturable pelvis model was developed and validated against dynamic tests on isolated pelvic bones and on whole cadavers. By coupling a fixed cortical bone section thickness within a single subject's pelvis and across the population with a parametric material law for the pelvic bone, this model reproduced the pelvic response and tolerance variation among individuals. Three material laws were also identified to represent fragile, medium and strong pelvic bones for the 50th percentile male. With this model, the influence of impact mass, velocity and surface shape on pelvic response was examined. Results indicated that the shape difference between four main impactors reported in the literature has little effect on the pelvic response. Under iso-energy conditions, the relationship of pelvic loading between different combinations of impact mass and velocity was also determined. Based on this relationship, existing data from different impactor tests were scaled and combined to establish a pelvic response corridor in terms of pelvis loading versus impact energy. The relationship between bone mechanical properties and pelvic response and tolerance was also investigated with this model. Results indicated that changes in the mechanical properties due to ageing affected the pelvic tolerance more than the pelvic mechanical response. Assuming that the ultimate stress of the pelvic bone decreases 0.4% per year from 25 to 80 years old, the pelvic tolerance should be scaled by 0.4% per year while the pelvic loading response should be scaled only by 0.1% per year. Finally, it is to be noted that the model developed in this paper is a "global" model, not a "descriptive" model. Therefore, while it may be a useful tool for the analysis presented in this paper (e.g., overall fracture tolerance, overall effects of age, etc.), it cannot be

  5. Application of fracture mechanics to predict the strength of filament-wound composite specimens with surface damage

    NASA Technical Reports Server (NTRS)

    Morris, D. H.; Harris, C. E.

    1988-01-01

    The strength of a thick surface notched filament wound graphite/epoxy tensile specimen was predicted using fracture mechanics analysis. The prediction model depended upon the depth of the surface notch and upon the type of failure. Specimens failed in two stages: first a sublaminate with thickness equal to the depth of the surface cut, and second, for increasing load, a sublaminate with thickness equal to the initial thickness minus the cut depth. Analytical predictions and experimental data were in good agreement.

  6. Study of rib fracture mechanisms based on the rib strain profiles in side and forward oblique impact.

    PubMed

    Leport, Tiphaine; Baudrit, Pascal; Potier, Pascal; Trosseille, Xavier; Lecuyer, Erwan; Vallancien, Guy

    2011-11-01

    Rib fractures constitute a good indication of severity as there are the most frequent type of AIS3+ chest injuries. In 2008, Trosseille et al. showed a promising methodology to exhibit the rib fracture mechanisms, using strain gauges glued on the ribs of Post-Mortem Human Subjects (PMHS) and developing a specific signal analysis. In 2009, they published the results of static airbag tests performed on 50th percentile male PMHS at different distances and angles (pure lateral and 30 degrees forward oblique direction). To complete these already published data, a set of 8 PMHS lateral and oblique impactor tests were performed with the same methodology. The rib cages were instrumented with more than 100 strain gauges on the ribs, cartilage and sternum. A 23.4 kg impactor was propelled at 4.3 or 6.7 m/s. The forces applied onto the PMHS at 4.3 m/s ranged from 1.6 kN to 1.9 kN and the injuries varied from 4 to 13 rib fractures. At 6.7 m/s, the forces applied onto the PMHS ranged from 2.6 kN to 4 kN and the injuries varied from 9 to 16 rib fractures. The results of 24 tests from Trosseille et al. 2008 and 2009 and from the current study were processed in the same way and analyzed together. The time and location of the fractures were determined for each test and a ribcage fracture scenario was defined for each configuration. Strain profile corridors were built for pure lateral and forward oblique impacts, in the case of a rigid impact (impactor) or for an airbag loading. They can be used to assess the human body model biofidelity and the validation of rib fracture mechanisms in these models. Based on these corridors, the effects of the severity, the impact angle and the loading system on rib strain profiles were analyzed and are presented in this paper.

  7. Application of Fracture Mechanics to Specify the Proof Load Factor for Clamp Band Systems of Launch Vehicles

    NASA Astrophysics Data System (ADS)

    Singaravelu, J.; Sundaresan, S.; Nageswara Rao, B.

    2013-04-01

    This article presents a methodology for evaluation of the proof load factor (PLF) for clamp band system (CBS) made of M250 Maraging steel following fracture mechanics principles.CBS is most widely used as a structural element and as a separation system. Using Taguchi's design of experiments and the response surface method (RSM) the compact tension specimens were tested to establish an empirical relation for the failure load ( P max) in terms of the ultimate strength, width, thickness, and initial crack length. The test results of P max closely matched with the developed RSM empirical relation. Crack growth rates of the maraging steel in different environments were examined. Fracture strength (σf) of center surface cracks and through-crack tension specimens are evaluated utilizing the fracture toughness ( K IC). Stress induced in merman band at flight loading conditions is evaluated to estimate the higher load factor and PLF. Statistical safety factor and reliability assessments were made for the specified flaw sizes useful in the development of fracture control plan for CBS of launch vehicles.

  8. Fracture Mechanical Measurements with Commercial Stainless Steels at 4 K and with Cp-Titanium at 173 K

    NASA Astrophysics Data System (ADS)

    Nyilas, A.; Mitterbacher, H.

    2010-04-01

    Using the JETT (J-Evaluation on Tensile Test) technique, measurements have been performed with commercial stainless steels in forged and cast condition for the reason of an assessment for low temperature service down to 4 K. These steels frequently used for industrial applications are designated by German Werkstoff (WNr) 1.4308 and 1.4408 cast stainless steels and a forged material with the number 1.4307. The fracture toughness tests at 4 K with forged material 1.4307 comprised apart from the base metal also the weld zone and additionally the 5% and 8% pre-strained conditions of the base metal. Fracture toughness reduced slightly for cold worked condition gradually as well as for the weld joint. The Reliability of the JETT measurements has been also checked using the ASTM E 1820—99a standard. In addition, to these measurements, commercial pure ASTM grade 2 titanium (WNr 3.7035) has been also examined using the same JETT method for the reason of industrial application and the requirement of minimum fracture toughness of 100 MPa√m was fulfilled at 173 K. Furthermore, test results performed at 7 K of pure titanium plate material (ASTM grade 1) with respect to fracture mechanical JETT method are presented.

  9. ThreadedComposite: A Mechanism for Building Concurrent and Parallel Ptolemy II Models

    DTIC Science & Technology

    2008-12-07

    ThreadedComposite: A Mechanism for Building Concurrent and Parallel Ptolemy II Models Edward A. Lee Electrical Engineering and Computer Sciences...Concurrent and Parallel Ptolemy II Models 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK...Instruments, and Toyota. ThreadedComposite: A Mechanism for Building Concurrent and Parallel Ptolemy II Models ∗ Edward A. Lee UC Berkeley eal

  10. Effect of chemical environment and rock composition on fracture mechanics properties of reservoir lithologies in context of CO2 sequestration

    NASA Astrophysics Data System (ADS)

    Major, J. R.; Eichhubl, P.; Callahan, O. A.

    2015-12-01

    The coupled chemical and mechanical response of reservoir and seal rocks to injection of CO2 have major implications on the short and long term security of sequestered carbon. Many current numerical models evaluating behavior of reservoirs and seals during and after CO2 injection in the subsurface consider chemistry and mechanics separately and use only simple mechanical stability criteria while ignoring time-dependent failure parameters. CO2 injection irreversibly alters the subsurface chemical environment which can then affect geomechanical properties on a range of time scales by altering rock mineralogy and cements through dissolution, remobilization, and precipitation. It has also been documented that geomechanical parameters such as fracture toughness (KIC) and subcritical index (SCI) are sensitive to chemical environment. Double torsion fracture mechanics testing of reservoir lithologies under controlled environmental conditions relevant to CO2 sequestration show that chemical environment can measurably affect KIC and SCI. This coupled chemical-mechanical behavior is also influenced by rock composition, grains, amount and types of cement, and fabric. Fracture mechanics testing of the Aztec Sandstone, a largely silica-cemented, subarkose sandstone demonstrate it is less sensitive to chemical environment than Entrada Sandstone, a silty, clay-rich sandstone. The presence of de-ionized water lowers KIC by approximately 20% and SCI 30% in the Aztec Sandstone relative to tests performed in air, whereas the Entrada Sandstone shows reductions on the order of 70% and 90%, respectively. These results indicate that rock composition influences the chemical-mechanical response to deformation, and that the relative chemical reactivity of target reservoirs should be recognized in context of CO2 sequestration. In general, inert grains and cements such as quartz will be less sensitive to the changing subsurface environment than carbonates and clays.

  11. Mechanics of tidally driven fractures in Europa's ice shell and implications for seismic and radar profiling

    NASA Astrophysics Data System (ADS)

    Lee, S.; Pappalardo, R. T.; Makris, N. C.

    2005-12-01

    Among Europa's surface features, cycloidal cracks are probably the most important for proving the existence of a subsurface liquid ocean. This is because (1) there is strong evidence that they are caused by tidally induced stress [1], and (2) this stress likely only approaches the ice failure strength if an ocean is present. There are a number of outstanding issues, however, in quantitatively explaining cycloidal cracks. First, current estimates of the pure diurnal tidal stress necessary to cause cycloidal cracks even in the presence of an ocean [1,2] is well below the typical stress known to cause tensile failure in natural terrestrial ice [3]. Second, models of ridge formation suggest that cycloidal cracks penetrate through the entire brittle-ice layer [1,4], but current models limit the depth of tidally induced surface cracks to be less than 100 m even in the presence of an ocean [1,5]. Third, the 3-km/h crack propagation speed determined by [1] is three orders of magnitude lower than the roughly 2-km/s speed at which cracks are known to propagate in ice. Our goal is to quantitatively address these issues in a unified manner. To do this, a fracture mechanics model is developed for the initiation and propagation of a crack through an ice layer of finite thickness in the presence of gravitational overburden and porosity. It is shown that Europa's ice shell may be highly porous and salt-rich. This implies that the strength of Europa's outer ice shell may be sufficiently low to make the crack initiation strengths arrived at by current kinematic models [1,2] highly plausible, even though they are much lower than those typically measured for terrestrial ice. A model is developed for the stress intensity factor at a crack tip in an ice shell with finite thickness, gravitational overburden, and depth-dependent porosity. This leads to the conclusion that cycloids are generated as a sequence of discrete and near instantaneous fracture events, each of which penetrates

  12. Solving the cardiac hypertrophy riddle: The angiotensin II-mechanical stress connection.

    PubMed

    Zablocki, Daniela; Sadoshima, Junichi

    2013-11-08

    A series of studies conducted 20 years ago, documenting the cardiac hypertrophy phenotype and its underlying signaling mechanism induced by angiotensin II (Ang II) and mechanical stress, showed a remarkable similarity between the effect of the Gαq agonist and that of mechanical forces on cardiac hypertrophy. Subsequent studies confirmed the involvement of autocrine/paracrine mechanisms, including stretch-induced release of Ang II in load-induced cardiac hypertrophy. Recent studies showed that the Ang II type 1 (AT1) receptor is also directly activated by mechanical forces, suggesting that AT1 receptors play an important role in mediating load-induced cardiac hypertrophy through both ligand- and mechanical stress-dependent mechanisms.

  13. Fracture healing in osteoporotic bone.

    PubMed

    Cheung, Wing Hoi; Miclau, Theodore; Chow, Simon Kwoon-Ho; Yang, Frank F; Alt, Volker

    2016-06-01

    As the world population rises, osteoporotic fracture is an emerging global threat to the well-being of elderly patients. The process of fracture healing by intramembranous ossification or/and endochondral ossification involve many well-orchestrated events including the signaling, recruitment and differentiation of mesenchymal stem cells (MSCs) during the early phase; formation of a hard callus and extracellular matrix, angiogenesis and revascularization during the mid-phase; and finally callus remodeling at the late phase of fracture healing. Through clinical and animal research, many of these factors are shown to be impaired in osteoporotic bone. Animal studies related to post-menopausal estrogen deficient osteoporosis (type I) have shown healing to be prolonged with decreased levels of MSCs and decreased levels of angiogenesis. Moreover, the expression of estrogen receptor (ER) was shown to be delayed in ovariectomy-induced osteoporotic fracture. This might be related to the observed difference in mechanical sensitivity between normal and osteoporotic bones, which requires further experiments to elucidate. In mice fracture models related to senile osteoporosis (type II), it was observed that chondrocyte and osteoblast differentiation were impaired; and that transplantation of juvenile bone marrow would result in enhanced callus formation. Other factors related to angiogenesis and vasculogenesis have also been noted to be impaired in aged models, affecting the degradation of cartilaginous matrixes and vascular invasion; the result is changes in matrix composition and growth factors concentrations that ultimately impairs healing during age-related osteoporosis. Most osteoporotic related fractures occur at metaphyseal sites clinically, and reports have indicated that differences exist between diaphyseal and metaphyseal fractures. An animal model that satisfies three main criteria (metaphyseal region, plate fixation, osteoporosis) is suggested for future research for

  14. Annexin II Dependent Mechanism of Breast Cancer Progression

    DTIC Science & Technology

    2009-06-01

    dependent plasminogen activation. Biochemistry , 37: 16958-16966, 1998. 10 17. blasi, F. a. S., M.P Proteases and cancer invasion: from belief to certainty...2005. 29. Menaa, C., Devlin , R. D., Reddy, S. V., Gazitt, Y., Choi, S. J., and Roodman, G. D. Annexin II increases osteoclast formation by...Chirgwin, J. M., Devlin , R., Haipek, C., Anderson, J., and Roodman, G. D. Cloning and identification of annexin II as an autocrine/paracrine factor that

  15. Erythropoietin (EPO): EPO-receptor signaling improves early endochondral ossification and mechanical strength in fracture healing.

    PubMed

    Holstein, Joerg H; Menger, Michael D; Scheuer, Claudia; Meier, Christoph; Culemann, Ulf; Wirbel, Rainer J; Garcia, Patric; Pohlemann, Tim

    2007-02-13

    Beyond its role in the regulation of red blood cell proliferation, the glycoprotein erythropoietin (EPO) has been shown to promote cell regeneration and angiogenesis in a variety of different tissues. In addition, EPO has been indicated to share significant functional and structural homologies with the vascular endothelial growth factor (VEGF), a cytokine essential in the process of fracture healing. However, there is complete lack of information on the action of EPO in bone repair and fracture healing. Therefore, we investigated the effect of EPO treatment on bone healing in a murine closed femur fracture model using radiological, histomorphometric, immunohistochemical, biomechanical and protein biochemical analysis. Thirty-six SKH1-hr mice were treated with daily i.p. injections of 5000 U/kg EPO from day 1 before fracture until day 4 after fracture. Controls received equivalent amounts of the vehicle. After 2 weeks of fracture healing, we could demonstrate expression of the EPO-receptor (EPOR) in terminally differentiating chondrocytes within the callus. At this time point EPO-treated animals showed a higher torsional stiffness (biomechanical analysis: 39.6+/-19.4% of the contralateral unfractured femur) and an increased callus density (X-ray analysis (callus density/spongiosa density): 110.5+/-7.1%) when compared to vehicle-treated controls (14.3+/-8.2% and 105.9+/-6.6%; p<0.05). Accordingly, the histomorphometric examination revealed an increased fraction of mineralized bone and osteoid (33.0+/-3.0% versus 28.5+/-3.6%; p<0.05). Of interest, this early effect of the initial 6-day EPO treatment had vanished at 5 weeks after fracture. We conclude that EPO-EPOR signaling is involved in the process of early endochondral ossification, enhancing the transition of soft callus to hard callus.

  16. Angiotensin-II mediates ACE2 Internalization and Degradation through an Angiotensin-II type I receptor-dependent mechanism

    PubMed Central

    Lazartigues, Eric; Filipeanu, Catalin M.

    2014-01-01

    Angiotensin Converting Enzyme type 2 (ACE2) is a pivotal component of the renin-angiotensin system, promoting the conversion of Angiotensin (Ang)-II to Ang-(1-7). We previously reported that decreased ACE2 expression and activity contribute to the development of Ang-II-mediated hypertension in mice. The present study aimed to investigate the mechanisms involved in ACE2 down-regulation during neurogenic hypertension. In ACE2-transfected Neuro-2A cells, Ang-II treatment resulted in a significant attenuation of ACE2 enzymatic activity. Examination of the subcellular localization of ACE2 revealed that Ang-II treatment leads to ACE2 internalization and degradation into lysosomes. These effects were prevented by both the Ang-II type 1 receptor (AT1R) blocker losartan and the lysosomal inhibitor leupeptin. In contrast, in HEK293T cells, which lack endogenous AT1R, Ang-II failed to promote ACE2 internalization. Moreover, this effect could be induced after AT1R transfection. Further, co-immunoprecipitation experiments demonstrated that AT1R and ACE2 form complexes and these interactions were decreased by Ang-II treatment, which also enhanced ACE2 ubiquitination. In contrast, ACE2 activity was not changed by transfection of AT2 or Mas receptors. In vivo, Ang-II-mediated hypertension was blunted by chronic infusion of leupeptin in wildtype C57Bl/6, but not in ACE2 knockout mice. Overall, this is the first demonstration that elevated Ang-II levels reduce ACE2 expression and activity by stimulation of lysosomal degradation through an AT1R-dependent mechanism. PMID:25225202

  17. Elastic stress transmission and transformation (ESTT) by confined liquid: A new mechanics for fracture in elastic lithosphere of the earth

    NASA Astrophysics Data System (ADS)

    Xu, Xing-Wang; Peters, Stephen G.; Liang, Guang-He; Zhang, Bao-Lin

    2016-03-01

    We report on a new mechanical principle, which suggests that a confined liquid in the elastic lithosphere has the potential to transmit a maximum applied compressive stress. This stress can be transmitted to the internal contacts between rock and liquid and would then be transformed into a normal compressive stress with tangential tensile stress components. During this process, both effective compressive normal stress and tensile tangential stresses arise along the liquid-rock contact. The minimum effective tensile tangential stress causes the surrounding rock to rupture. Liquid-driven fracture initiates at the point along the rock-liquid boundary where the maximum compressive stress is applied and propagates along a plane that is perpendicular to the minimum effective tensile tangential stress and also is perpendicular to the minimum principal stress. Liquid-driven fractures and dikes propagate along the axes of cylindrical zones that are perpendicular to the minimum compressive principal stress in rocks in non-tectonic regions. The minimum depth for liquid-driven fracture, which is induced by a spherical confined liquid and an isolated magma chamber in the elastic lithosphere, ranges from 2 to 6 km, whereas dikes with hemi-cylinder-shaped ends propagate upwards closer to the surface under gravity. Transmission of pumping pressure, i.e. the pressure differences on the underside of a dike that is connected with a chamber, from the source magma chamber to intermediate and shallow chambers increases liquid pressure and also the effective tensile tangential stress and therefore leads to new fractures and dike formation and to upwards transport of magmas that have stagnated in the intermediate chamber. Tectonic stress alters local stress fields in the surrounding country rocks and therefore synchronously varies the local effective tensile tangential stress and the nature and geometry of the liquid-driven fractures.

  18. Mechanism of Cu(II), Cd(II) and Pb(II) ions sorption from aqueous solutions by macroporous poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate)

    NASA Astrophysics Data System (ADS)

    Nastasović, Aleksandra B.; Ekmeščić, Bojana M.; Sandić, Zvjezdana P.; Ranđelović, Danijela V.; Mozetič, Miran; Vesel, Alenka; Onjia, Antonije E.

    2016-11-01

    The mechanism of Cu(II), Cd(II) and Pb(II) ions sorption from aqueous solutions by macroporous poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (PGME) functionalized by reaction of the pendant epoxy groups with diethylene triamine (PGME-deta) was studied using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis. Atomic force microscopy (AFM) and scanning energy-dispersive X-ray spectroscopy (SEM-EDX) were used for the determination of surface morphology of the copolymer particles. The sorption behavior of heavy metals Cu(II), Cd(II) and Pb(II) ions sorption was investigated in batch static experiments under non-competitive conditions at room temperature (298 K). The obtained results were fitted to pseudo-first order, pseudo-second order and intraparticle diffusion kinetic model. The kinetics studies showed that Cu(II), Cd(II) and Pb(II) sorption obeys the pseudo-second-order model under all investigated operating conditions with evident influence of pore diffusion.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  20. The Mechanisms of Dispersion Strengthening and Fracture in Al-based XD (TM) Alloys

    NASA Technical Reports Server (NTRS)

    Aiken, R. M., Jr.

    1990-01-01

    The influence of reinforcement size, volume fraction, and matrix deformation behavior on room and elevated temperature strength, and the fracture toughness of metal matrix composites of both pure aluminum and Al(4 percent)Cu(1.5 percent)Mg with 0 to 15 vol percent TiB2 were examined. Higher TiB2 volume fractions increased the tensile yield strength both at room and elevated temperatures, and reduced the elongation to fracture. Tensile tests also indicate that small particles provided a greater increase in strength for a given volume fraction than larger particles, whereas elongation to fracture appeared to be insensitive to reinforcement size. The fracture toughness of the Al(4 percent)Cu(1.5 percent)Mg alloys decreased rapidly with TiB2 additions of 0 to 5 vol percent and more slowly with TiB2 additions of 5 to 15 vol percent. Fracture toughness appears to be independent of TiB2 particle size. The isothermal-aging response of the precipitation strengthened Al(4 percent)Cu(1.5 percent)Mg alloys was not altered by the presence of TiB2.

  1. Mechanisms of Plastic and Fracture Instabilities for Alloy Development of Fusion Materials. Final Project Report for period July 15, 1998 - July 14, 2003

    SciTech Connect

    Ghoniem, N. M.

    2003-07-14

    The main objective of this research was to develop new computational tools for the simulation and analysis of plasticity and fracture mechanisms of fusion materials, and to assist in planning and assessment of corresponding radiation experiments.

  2. Fracture mechanics characterization of welds: Fatigue life analysis of notches at welds: J(sub Ic) fracture toughness tests for weld metal

    NASA Astrophysics Data System (ADS)

    Underwood, John H.

    1995-03-01

    In this report two methods of fracture analysis of welds will be emphasized, one addressing fatigue life testing and analysis of notches at welds, and the other addressing the final fracture of the welded component and the fracture toughness tests used to characterize final fracture. These fatigue and fracture methods will be described by referring to recent work from the technical literature and from the U.S. Army Armament Research, Development, and Engineering Center, primarily fracture case study and fracture test method development investigations. A brief general summary will be given of fatigue and fracture methods and concepts that have application to welded structures. Specific fatigue crack initiation tests and analysis methods will be presented, using example results from a welded stainless steel box beam of a cannon carriage. Recent improvements and simplifications in J.integral fracture toughness tests will be described, particularly those related to welds. Fracture toughness measurements for various stainless steel weld metals and heat treatments will also be described.

  3. Mechanism and kinetics of Pb(II) adsorption on ultrathin nanocrystalline titania coatings.

    PubMed

    Yang, Zheng-peng; Zhang, Chun-jing

    2009-12-30

    Pb(II) is a highly toxic substance, exposure to which can cause various diseases. To better understand the application of titania as an adsorbent for removing Pb(II) from wastewater, quartz crystal microbalance (QCM) technique was employed to investigate the adsorption behavior of Pb(II) on ultrathin nanocrystalline titania coatings. The present study focused on the mechanism and kinetics of Pb(II) adsorption. The obtained results show that the driving force of Pb(II) adsorption on titania coatings is electrostatic interaction, and that Pb(II) is adsorbed onto titania coatings by Pb(II) ions coordinating with hydroxyl groups of titania surface. In terms of the in situ frequency measurements of QCM, the adsorption kinetic parameter is estimated to be 4.12x10(5)L/mol. QCM measurement provides a useful method for monitoring the adsorption process of Pb(II) on titania coatings.

  4. Competition of Fracture Mechanisms in Monolithic Dental Ceramics: Flat Model Systems

    PubMed Central

    Zhang, Yu; Kim, Jae-Won; Bhowmick, Sanjit; Thompson, Van P.; Rekow, E. Dianne

    2015-01-01

    Monolithic (single layer) glass-ceramic restorations often fail from chipping and fracture. Using blunt indentation of a model flat porcelain-like brittle layer bonded onto a dentin-like polymer support system, a variety of fatigue fracture modes has been identified and analyzed: outer cone, inner cone, and median cracks developing in the near-contact region at the occlusal surface; radial cracks developing at the internal cementation surface along the loading axis. Our findings indicate that monolithic glass-ceramic layers are vulnerable to both occlusal surface damage and cementation internal surface fracture. Clinical issues in the longevity of ceramic restorations are discussed in relation to biting force, physical properties of ceramic crowns and luting cement, and thicknesses of ceramic and cement layers. PMID:18478533

  5. Mechanisms affecting the transport and retention of bacteria, bacteriophage and microspheres in laboratory-scale saturated fractures

    NASA Astrophysics Data System (ADS)

    Seggewiss, G.; Dickson, S. E.

    2013-12-01

    Groundwater is becoming an increasingly important water source due to the ever-increasing demands from agricultural, residential and industrial consumers. In search of more secure sources, wells are routinely finished over large vertical depths in bedrock aquifers, creating new hydraulic pathways and thus increasing the risk of cross contamination. Moreover, hydraulic pathways are also being altered and created by increasing water withdrawal rates from these wells. Currently, it is not well understood how biological contaminants are transported through, and retained in, fractured media thereby making risk assessment and land use decisions difficult. Colloid transport within fractured rock is a complex process with several mechanisms affecting transport and retention, including: advection, hydrodynamic dispersion, diffusion, size exclusion, adsorption, and decay. Several researchers have investigated the transport of bacteria, bacteriophage, and microspheres (both carboxylated and plain) to evaluate the effects of surface properties and size on transport and retention. These studies have suggested that transport is highly dependent on the physico-chemical properties of the particle, the fracture, and the carrying fluid. However, these studies contain little detail regarding the specific mechanisms responsible for transport beyond speculating about their existence. Further, little work has been done to compare the transport of these particulate materials through the same fracture, allowing for direct observations based on particulate size and surface properties. This research examines the similarities and differences in transport and retention between four different particles through two different laboratory-scale, saturated fractures. This work is designed to explore the effects of particle size, surface properties, ionic strength of the carrying solution, and aperture field characteristics on transport and retention in single, saturated fractures. The particulates

  6. Effects of the precipitation of stabilizers on the mechanism of grain fracturing in a zirconia metering nozzle

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Xue, Qun-hu; Ding, Dong-hai

    2016-09-01

    The mechanism of grain fracturing in a zirconia metering nozzle used in the continuous casting process was studied. The phase composition, microstructure, and chemical composition of the residual samples were studied using an X-ray fluorescence analyzer, scanning electron microscope, and electron probe. Results revealed that the composition, structure, and mineral phase of the original layer, transition layer, and affected layer of the metering nozzle differed because of stabilizer precipitation and steel slag permeation. The stabilizer MgO formed low-melting phases with steel slag and impure SiO2 on the boundaries (pores) of zirconia grains; consequently, grain fracturing occurred and accelerated damage to the metering nozzle was observed.

  7. Fracture mechanisms of Hg 0.8Cd 0.2Te induced by pulsed TEA-CO 2 laser

    NASA Astrophysics Data System (ADS)

    Cai, H.; Cheng, Z. H.; Zhu, H. H.; Zuo, D. L.

    2005-12-01

    The fracture mechanisms of Hg 0.8Cd 0.2Te induced by pulsed TEA-CO 2 laser have been investigated theoretically and experimentally in this paper. The Hg 0.8Cd 0.2Te target was irradiated by a TEA-CO 2 laser with wavelength of 10.6 μm and spike width of 240 ns in an ambient atmosphere. The evident cracks can be found on the surface of the target from the scanning electron microscopy (SEM) photos, indicating that the severe breaks happened during the experiment. Theoretical analysis has also been carried out and the results show that the fracture of Hg 0.8Cd 0.2Te is mainly induced by thermal stresses, although there are three forces (thermal stress, evaporation wave and laser-supported detonation (LSD) wave) exerted on the target surface during the process.

  8. On the Relationship Between J-Integral and Crack Tip Opening Displacement in Elastic-Plastic Fracture Mechanics

    NASA Astrophysics Data System (ADS)

    Pereira, Marcos Venicius; Darwish, Fathi Aref; Campelo, Eduardo

    2013-08-01

    The relationship between J-integral ( J) and crack tip opening displacement (δ), considered fundamental for elastic-plastic fracture mechanics, can be established based on prior knowledge of the constraint factor m, which depends on the work hardening exponent and the material's yield strain. Both J and δ were simultaneously determined at fracture initiation and at different points along the resistance curves for a number of structural steels. The corresponding m values were calculated and then compared with the predictions made by different models. The results indicate that the experimentally determined m values are in fair agreement with the predictions made by ASTM over the whole range of flow parameters considered in this study. The Hutchinson-Rice-Rosengren singularity-based predictions result in overestimating m for steels considered to be of low strength and high strain hardening exponent. Predictions made by other models are predominantly higher in comparison with their experimental counterparts.

  9. Hierarchies, multiple energy barriers, and robustness govern the fracture mechanics of alpha-helical and beta-sheet protein domains.

    PubMed

    Ackbarow, Theodor; Chen, Xuefeng; Keten, Sinan; Buehler, Markus J

    2007-10-16

    The fundamental fracture mechanisms of biological protein materials remain largely unknown, in part, because of a lack of understanding of how individual protein building blocks respond to mechanical load. For instance, it remains controversial whether the free energy landscape of the unfolding behavior of proteins consists of multiple, discrete transition states or the location of the transition state changes continuously with the pulling velocity. This lack in understanding has thus far prevented us from developing predictive strength models of protein materials. Here, we report direct atomistic simulation that over four orders of magnitude in time scales of the unfolding behavior of alpha-helical (AH) and beta-sheet (BS) domains, the key building blocks of hair, hoof, and wool as well as spider silk, amyloids, and titin. We find that two discrete transition states corresponding to two fracture mechanisms exist. Whereas the unfolding mechanism at fast pulling rates is sequential rupture of individual hydrogen bonds (HBs), unfolding at slow pulling rates proceeds by simultaneous rupture of several HBs. We derive the hierarchical Bell model, a theory that explicitly considers the hierarchical architecture of proteins, providing a rigorous structure-property relationship. We exemplify our model in a study of AHs, and show that 3-4 parallel HBs per turn are favorable in light of the protein's mechanical and thermodynamical stability, in agreement with experimental findings that AHs feature 3.6 HBs per turn. Our results provide evidence that the molecular structure of AHs maximizes its robustness at minimal use of building materials.

  10. Double torsion fracture mechanics testing of shales under chemically reactive conditions

    NASA Astrophysics Data System (ADS)

    Chen, X.; Callahan, O. A.; Holder, J. T.; Olson, J. E.; Eichhubl, P.

    2015-12-01

    Fracture properties of shales is vital for applications such as shale and tight gas development, and seal performance of carbon storage reservoirs. We analyze the fracture behavior from samples of Marcellus, Woodford, and Mancos shales using double-torsion (DT) load relaxation fracture tests. The DT test allows the determination of mode-I fracture toughness (KIC), subcritical crack growth index (SCI), and the stress-intensity factor vs crack velocity (K-V) curves. Samples are tested at ambient air and aqueous conditions with variable ionic concentrations of NaCl and CaCl2, and temperatures up to 70 to determine the effects of chemical/environmental conditions on fracture. Under ambient air condition, KIC determined from DT tests is 1.51±0.32, 0.85±0.25, 1.08±0.17 MPam1/2 for Marcellus, Woodford, and Mancos shales, respectively. Tests under water showed considerable change of KIC compared to ambient condition, with 10.6% increase for Marcellus, 36.5% decrease for Woodford, and 6.7% decrease for Mancos shales. SCI under ambient air condition is between 56 and 80 for the shales tested. The presence of water results in a significant reduction of the SCI from 70% to 85% compared to air condition. Tests under chemically reactive solutions are currently being performed with temperature control. K-V curves under ambient air conditions are linear with stable SCI throughout the load-relaxation period. However, tests conducted under water result in an initial cracking period with SCI values comparable to ambient air tests, which then gradually transition into stable but significantly lower SCI values of 10-20. The non-linear K-V curves reveal that crack propagation in shales is initially limited by the transport of chemical agents due to their low permeability. Only after the initial cracking do interactions at the crack tip lead to cracking controlled by faster stress corrosion reactions. The decrease of SCI in water indicates higher crack propagation velocity due to

  11. A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics

    PubMed Central

    Kerfriden, P.; Goury, O.; Rabczuk, T.; Bordas, S.P.A.

    2013-01-01

    We propose in this paper a reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order reduction permits to focus the numerical effort where it is most needed: around the zones where damage propagates. No a priori knowledge of the damage pattern is required, the extraction of the corresponding spatial regions being based solely on algebra. The efficiency of the proposed approach is demonstrated numerically with an example relevant to engineering fracture. PMID:23750055

  12. Fracture mechanics and statistical modeling of ternary blends of polylactide/ethylene-acrylate copolymer /wood-flour composites

    NASA Astrophysics Data System (ADS)

    Afrifah, Kojo Agyapong

    This study examined the mechanisms of toughening the brittle bio-based poly(lactic acid) (PLA) with a biodegradable rubbery impact modifier to develop biodegradable and cost effective PLA/wood-flour composites with improved impact strength, toughness, high ductility, and flexibility. Semicrystalline and amorphous PLA grades were impact modified by melt blending with an ethylene-acrylate copolymer (EAC) impact modifier. EAC content was varied to study the effectiveness and efficiency of the impact modifier in toughening the semicrystalline and amorphous grades of the PLA. Impact strength was used to assess the effectiveness and efficiency of the EAC in toughening the blends, whereas the toughening mechanisms were determined with the phase morphologies and the miscibilities of the blends. Subsequent tensile property analyses were performed on the most efficiently toughened PLA grade. Composites were made from PLA, wood flour of various particle sizes, and EAC. Using two-level factorial design the interaction between wood flour content, wood flour particle size, and EAC content and its effect on the mechanical properties of the PLA/wood-flour composites was statistically studied. Numerical optimization was also performed to statistically model and optimize material compositions to attain mechanical properties for the PLA/wood-flour composites equivalent to at least those of unfilled PLA. The J-integral method of fracture mechanics was applied to assess the crack initiation (Jin) and complete fracture (J f) energies of the composites to account for imperfections in the composites and generate data useful for engineering designs. Morphologies of the fractured surfaces of the composites were analyzed to elucidate the failure and toughening mechanisms of the composites. The EAC impact modifier effectively improved the impact strength of the PLA/EAC blends, regardless of the PLA type. However, the EAC was more efficient in the semicrystalline grades of PLA compared to the

  13. Development of a new code to solve hydro-mechanical coupling, shear failure and tensile failure due to hydraulic fracturing operations.

    NASA Astrophysics Data System (ADS)

    María Gómez Castro, Berta; De Simone, Silvia; Carrera, Jesús

    2016-04-01

    Nowadays, there are still some unsolved relevant questions which must be faced if we want to proceed to the hydraulic fracturing in a safe way. How much will the fracture propagate? This is one of the most important questions that have to be solved in order to avoid the formation of pathways leading to aquifer targets and atmospheric release. Will the fracture failure provoke a microseismic event? Probably this is the biggest fear that people have in fracking. The aim of this work (developed as a part of the EU - FracRisk project) is to understand the hydro-mechanical coupling that controls the shear of existing fractures and their propagation during a hydraulic fracturing operation, in order to identify the key parameters that dominate these processes and answer the mentioned questions. This investigation focuses on the development of a new C++ code which simulates hydro-mechanical coupling, shear movement and propagation of a fracture. The framework employed, called Kratos, uses the Finite Element Method and the fractures are represented with an interface element which is zero thickness. This means that both sides of the element lie together in the initial configuration (it seems a 1D element in a 2D domain, and a 2D element in a 3D domain) and separate as the adjacent matrix elements deform. Since we are working in hard, fragile rocks, we can assume an elastic matrix and impose irreversible displacements in fractures when rock failure occurs. The formulation used to simulate shear and tensile failures is based on the analytical solution proposed by Okada, 1992 and it is part of an iterative process. In conclusion, the objective of this work is to employ the new code developed to analyze the main uncertainties related with the hydro-mechanical behavior of fractures derived from the hydraulic fracturing operations.

  14. Reciprocal roles of angiotensin II and Angiotensin II Receptors Blockade (ARB) in regulating Cbfa1/RANKL via cAMP signaling pathway: possible mechanism for hypertension-related osteoporosis and antagonistic effect of ARB on hypertension-related osteoporosis.

    PubMed

    Guan, Xiao-Xu; Zhou, Yi; Li, Ji-Yao

    2011-01-01

    Hypertension is a risk factor for osteoporosis. Animal and epidemiological studies demonstrate that high blood pressure is associated with increased calcium loss, elevated parathyroid hormone, and increased calcium movement from bone. However, the mechanism responsible for hypertension-related osteoporosis remains elusive. Recent epidemiological studies indicate the benefits of Angiotensin II Receptors Blockade (ARB) on decreasing fracture risks. Since receptors for angiotensin II, the targets of ARB, are expressed in both osteoblasts and osteoclasts, we postulated that angiotensin II plays an important role in hypertension-related osteoporosis. Cbfa1 and RANKL, the important factors for maintaining bone homeostasis and key mediators in controlling osteoblast and osteoclast differentiation, are both regulated by cAMP-dependent signaling. Angiotensin II along with factors such as LDL, HDL, NO and homocysteine that are commonly altered both in hypertension and osteoporosis, can down-regulate the expression of Cbfa1 but up-regulate RANKL expression via the cAMP signaling pathway. We thus hypothesized that, by altering the ratio of Cbfa1/RANKL expression via the cAMP-dependent pathway, angiotensin II differently regulates osteoblast and osteoclast differentiation leading to enhanced bone resorption and reduced bone formation. Since ARB can antagonize the adverse effect of angiotensin II on bone by lowering cAMP levels and modifying other downstream targets, including LDL, HDL, NO and Cbfa1/RANKL, we propose the hypothesis that the antagonistic effects of ARB may also be exerted via cAMP signaling pathway.

  15. Mechanical Engineering Upgrades to the DARHT-II Induction Cells

    DTIC Science & Technology

    2005-06-01

    Lean Manufacturing principles found in industry today [2]. This topic, as it applies to refurbishing the DARHT-II cells, is discussed by Barraza...2005. [2] J.T. Liker, The Toyota Way. New York: McGraw- Hill, 2004. [3] J. Barraza, et al, “Application of Lean Manufacturing Principles to

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

    PubMed

    Cherepanov, Genady P

    2015-03-28

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

  17. Mechanical Comparison of Headless Screw Fixation and Locking Plate Fixation for Talar Neck Fractures.

    PubMed

    Karakasli, Ahmet; Hapa, Onur; Erduran, Mehmet; Dincer, Cemal; Cecen, Berivan; Havitcioglu, Hasan

    2015-01-01

    For talar neck fractures, open reduction and internal fixation have been thought to facilitate revascularization and prevent osteonecrosis. Newer screw systems allow for placement of cannulated headless screws, which provide compression by virtue of a variable pitch thread. The present study compared the biomechanical fixation strength of cannulated headless variable-pitch screw fixation and locking plate fixation. A reproducible talar neck fracture was created in 14 fresh cadaver talar necks. Talar head fixation was then performed using 2 cannulated headless variable-pitch 4-mm/5-mm diameter (4/5) screws (Acutrak; Acumed, Hillsboro, OR) and locking plate fixation. Headless variable-pitch screw fixation had lower failure displacement than did locking plate fixation. No statistically significant differences were found in failure stiffness, yield stiffness (p = .655), yield load (p = .142), or ultimate load between the 2 fixation techniques. Cannulated headless variable-pitch screw fixation resulted in better failure displacement than locking plate fixation in a cadaveric talus model and could be considered a viable option for talus fracture fixation. Headless, fully threaded, variable-pitch screw fixation has inherent advantages compared with locking plate fixation, because it might cause less damage to the articular surface and can compress the fracture for improved reduction. Additionally, plate fixation can increase the risk of avascular necrosis owing to the wider incision and dissection of soft tissues.

  18. Effect of orientation on the in vitro fracture toughness ofdentin: The role of toughening mechanisms

    SciTech Connect

    Nalla, R.K.; Kinney, J.H.; Ritchie, R.O.

    2003-01-28

    A micro-mechanistic understanding of bone fracture thatencompasses how cracks interact with the underlying microstructure anddefines their local failure mode is lacking, despite extensive research nthe response of bone to a variety of factors like aging, loading, and/ordisease.

  19. Fracture Flow Research, Volume 2: Modeling Joint Patterns Using Combinations of Mechanical and Probabilistic Concepts

    DTIC Science & Technology

    2005-08-01

    evidenced by tectonic breccia ) then it is classified as a fault zone (solid vertical lines in Figure 243, relative vertical displacement is also sketched...observed breccia in the chert layers. This means that the chert may be heavily fractured. The material properties that were assumed for the chert in the

  20. Interaction of age and mechanical stability on bone defect healing: an early transcriptional analysis of fracture hematoma in rat.

    PubMed

    Ode, Andrea; Duda, Georg N; Geissler, Sven; Pauly, Stephan; Ode, Jan-Erik; Perka, Carsten; Strube, Patrick

    2014-01-01

    Among other stressors, age and mechanical constraints significantly influence regeneration cascades in bone healing. Here, our aim was to identify genes and, through their functional annotation, related biological processes that are influenced by an interaction between the effects of mechanical fixation stability and age. Therefore, at day three post-osteotomy, chip-based whole-genome gene expression analyses of fracture hematoma tissue were performed for four groups of Sprague-Dawley rats with a 1.5-mm osteotomy gap in the femora with varying age (12 vs. 52 weeks - biologically challenging) and external fixator stiffness (mechanically challenging). From 31099 analysed genes, 1103 genes were differentially expressed between the six possible combinations of the four groups and from those 144 genes were identified as statistically significantly influenced by the interaction between age and fixation stability. Functional annotation of these differentially expressed genes revealed an association with extracellular space, cell migration or vasculature development. The chip-based whole-genome gene expression data was validated by q-RT-PCR at days three and seven post-osteotomy for MMP-9 and MMP-13, members of the mechanosensitive matrix metalloproteinase family and key players in cell migration and angiogenesis. Furthermore, we observed an interaction of age and mechanical stimuli in vitro on cell migration of mesenchymal stromal cells. These cells are a subpopulation of the fracture hematoma and are known to be key players in bone regeneration. In summary, these data correspond to and might explain our previously described biomechanical healing outcome after six weeks in response to fixation stiffness variation. In conclusion, our data highlight the importance of analysing the influence of risk factors of fracture healing (e.g. advanced age, suboptimal fixator stability) in combination rather than alone.

  1. Micromechanics, fracture mechanics and gas permeability of composite laminates for cryogenic storage systems

    NASA Astrophysics Data System (ADS)

    Choi, Sukjoo

    A micromechanics method is developed to investigate microcrack propagation in a liquid hydrogen composite tank at cryogenic temperature. The unit cell is modeled using square and hexagonal shapes depends on fiber and matrix layout from microscopic images of composite laminates. Periodic boundary conditions are applied to the unit cell. The temperature dependent properties are taken into account in the analysis. The laminate properties estimated by the micromechanics method are compared with empirical solutions using constituent properties. The micro stresses in the fiber and matrix phases based on boundary conditions in laminate level are calculated to predict the formation of microcracks in the matrix. The method is applied to an actual liquid hydrogen storage system. The analysis predicts micro stresses in the matrix phase are large enough to cause microcracks in the composite. Stress singularity of a transverse crack normal to a ply-interface is investigated to predict the fracture behavior at cryogenic conditions using analytical and finite element analysis. When a transverse crack touches a ply-interface of a composite layer with same fiber orientation, the stress singularity is equal to ½. When the transverse crack propagates to a stiffer layer normal to a ply-direction, the singularity becomes less than ½ and vice versa. Finite element analysis is performed to evaluate fracture toughness of a laminated beam subjected to the fracture load measured by the fracture experiment at room and cryogenic temperatures. As results, the fracture load at cryogenic temperature is significantly lower than that at room temperature. However, when thermal stresses are taken into consideration, for both cases of room and cryogenic temperatures, the variation of fracture toughness becomes insignificant. The result indicates fracture toughness is a characteristic property which is independent to temperature changes. The experimental analysis is performed to investigate the

  2. Influence of notch shape on deformation mechanisms and energy parameters of fracture of 12Cr1MoV steel under impact loading

    NASA Astrophysics Data System (ADS)

    Panin, S. V.; Vlasov, I. V.; Maruschak, P. O.; Moiseenko, D. D.; Berto, F.; Vinogradov, A.; Bischak, R. T.

    2016-11-01

    Impact loading curves and fracture energy of the notched 12Cr1MoV ductile steel specimens are analyzed. The qualitative description and quantitative parameters are obtained for major stages of ductile and brittle fracture depending on the shape of the notch and the stress stiffness ahead. It is shown that a zone with enhanced plasticity is formed in the vicinity of V-, U-, and I-shaped notches at 20°C testing temperature, giving rise to ductile fracture. The stress stiffness at the notch tip increased with testing temperature reduced to -40°C. Using the quantitative description of fracture surfaces, a physical-mechanical scheme of the specimen fracture was suggested for the case of enhanced and localized (constrained) plasticity near the stress concentrator tip.

  3. Dynamic Mechanical Properties and Fracture Surface Morphologies of Core-Shell Rubber (CSR) Toughened Epoxy at Liquid Nitrogen (Ln2) Temperatures

    NASA Technical Reports Server (NTRS)

    Wang, J.; Magee, D.; Schneider, J. A.

    2009-01-01

    The dynamic mechanical properties and fracture surface morphologies were evaluated for a commercial epoxy resin toughened with two types of core-shell rubber (CSR) toughening agents (Kane Ace(Registered TradeMark) MX130 and MX960). The impact resistance (R) was evaluated by the resulting breaking energy measured in Charpy impact tests conducted on an instrumented drop tower. The resulting fracture surface morphologies were examined using Scanning Electron Microscopy (SEM). Fractographic observations of the CSR toughened epoxy tested at ambient temperature, showed a fracture as characterized by slender dendrite textures with large voids. The increasing number of dendrites and decreasing size of scale-like texture with more CSR particles corresponded with increased R. As the temperature decreased to Liquid Nitrogen (LN 2), the fracture surfaces showed a fracture characterized by a rough, torn texture containing many river markings and deep furrows.

  4. Erwin Schrödinger and the rise of wave mechanics. II. The creation of wave mechanics

    NASA Astrophysics Data System (ADS)

    Mehra, Jagdish

    1987-12-01

    This article (Part II) deals with the creation of the theory of wave mechanics by Erwin Schrödinger in Zurich during the early months of 1926; he laid the foundations of this theory in his first two communications to Annalen der Physik. The background of Schrödinger's work on, and his actual creation of, wave mechanics are analyzed.

  5. Non-Linear Flow, Fracture, Mechanical Quenching, and Computer Modeling of a Glass Cylinder Pressed Between Parallel Plates.

    NASA Astrophysics Data System (ADS)

    Sakoske, George Emil

    Analytical, experimental, and computer modeling studies are conducted for axial pressing of a glass cylinder between parallel plates. The classic "no-slip" parallel plate equation is derived from fundamental fluid mechanics with no geometric limitations and its validity is proved for transient and steady state low Reynold's number flow. Similarly, a "perfect-slip" solution yields the fiber elongation equation sigma = 3etadotvarepsilon. These limiting boundary conditions are studied experimentally by pressing directly on graphite and mica providing slip mechanisms, and non-deformable metal discs for no-slip. Linear, non-linear flow, and elastic fracture are observed by varying time scale over which strain is applied, theta, in relationship to glass structural relaxation time, tau. Linear flow is measured for tau<fracture. Ability to transmit shearing stresses and breakdown of "slip" boundary material is discussed. Fracture occurs as stresses increase within the sample for increasing time and rates. Cracks are driven by hoop and radial stresses where the origin and mode is a function of pressing rate. A Maxwell fluid finite element model is developed which uses experimental parameters as input. FEM results show general agreement with analytical solutions. A viscous heating analysis brings insight to stress overshoot

  6. SEACAS Theory Manuals: Part II. Nonlinear Continuum Mechanics

    SciTech Connect

    Attaway, S.W.; Laursen, T.A.; Zadoks, R.I.

    1998-09-01

    This report summarizes the key continuum mechanics concepts required for the systematic prescription and numerical solution of finite deformation solid mechanics problems. Topics surveyed include measures of deformation appropriate for media undergoing large deformations, stress measures appropriate for such problems, balance laws and their role in nonlinear continuum mechanics, the role of frame indifference in description of large deformation response, and the extension of these theories to encompass two dimensional idealizations, structural idealizations, and rigid body behavior. There are three companion reports that describe the problem formulation, constitutive modeling, and finite element technology for nonlinear continuum mechanics systems.

  7. Design characteristics, primary stability and risk of fracture of orthodontic mini-implants: Pilot scan electron microscope and mechanical studies

    PubMed Central

    Walter, André; Winsauer, Heinz; Marcé-Nogué, Jordi; Mojal, Sergi

    2013-01-01

    Objectives: Orthodontic mini-implants (OMIs) are increasingly used in orthodontics but can fail for various reasons. This study investigates the effects of OMI design characteristics on the mechanical properties in artificial bone. Material and Methods: Twelve self-drilling OMIs (2 small, 6 medium, 4 large) from 8 manufacturers were tested for their primary stability in simulated medium-high cancellous bone and the risk to fracture in high-density methacrylate blocks. For the assessments of the maximum insertion torque (IT) and torsional fracture (TF) 5 of each OMI were used and for the pull-out strength (POS) 10. The OMIs were inserted with a torque screwdriver (12 sec/360°) until the bottom at 8 mm depth was reached. OMI designs were analyzed with a scan electron microscope (SEM). Results: SEM images revealed a great variation in product refinement. In the whole sample, a cylindrical OMI shape was associated with higher POS (p<0.001) but lower IT (p=0.002) values. The outer and inner OMI diameters were design characteristics well correlated with POS, IT and TF values (ranging from 0.601 to 0.961). Greater thread depth was related to greater POS values (r= 0.628), although OMIs with similar POS values may have different IT values. Thread depth and pitch had some impact on POS. TF depended mainly on the OMI inner (r= 0.961) and outer diameters (r=0.892). A thread depth to outer diameter ratio close to 40% increased TF risk. Conclusions: Although at the same insertion depth the OMI outer and inner diameters are the most important factors for primary stability, other OMI design characteristics (cylindrical vs. conical, thread design) may significantly affect primary stability and torsional fracture. This needs to be considered when selecting the appropriate OMI for the desired orthodontic procedures. Key words:Orthodontic mini-implants, primary stability, insertion torque, pullout strength, torsional fracture. PMID:23722125

  8. Micromechanics, Fracture Mechanics and Gas Permeability of Composite Laminates for Cryogenic Storage Systems

    NASA Technical Reports Server (NTRS)

    Choi, Sukjoo; Sankar, Bhavani; Ebaugh, Newton C.

    2005-01-01

    A micromechanics method is developed to investigate microcrack propagation in a liquid hydrogen composite tank at cryogenic temperature. The unit cell is modeled using square and hexagonal shapes depends on fiber and matrix layout from microscopic images of composite laminates. Periodic boundary conditions are applied to the unit cell. The temperature dependent properties are taken into account in the analysis. The laminate properties estimated by the micromechanics method are compared with empirical solutions using constituent properties. The micro stresses in the fiber and matrix phases based on boundary conditions in laminate level are calculated to predict the formation of microcracks in the matrix. The method is applied to an actual liquid hydrogen storage system. The analysis predicts micro stresses in the matrix phase are large enough to cause microcracks in the composite. Stress singularity of a transverse crack normal to a ply-interface is investigated to predict the fracture behavior at cryogenic conditions using analytical and finite element analysis. When a transverse crack touches a ply-interface of a composite layer with same fiber orientation, the stress singularity is equal to 1/2. When the transverse crack propagates to a stiffer layer normal to the ply-direction, the singularity becomes less than 1/2 and vice versa. Finite element analysis is performed to predict the fracture toughness of a laminated beam subjected to fracture loads measured by four-point bending tests at room and cryogenic temperatures. As results, the fracture load at cryogenic temperature is significantly lower than that at room temperature. However, when thermal stresses are taken into consideration, for both cases of room and cryogenic temperatures, the difference of the fracture toughness becomes insignificant. The result indicates fracture toughness is a characteristic property, which is independent to temperature changes. The experimental analysis is performed to

  9. An animal model for open femur fracture and osteomyelitis--Part II: Immunomodulation with systemic IL-12.

    PubMed

    Lindsey, Brock A; Clovis, Nina B; Smith, E Suzanne; Salihu, Sydha; Hubbard, David F

    2010-01-01

    Infection resulting from open fracture is a common problem in orthopedics. The purpose of this project was to study the effect of Interleukin-12 (IL-12) systemic therapy on a previously established open fracture model. One hundred seven male Sprague-Dawley rats were assigned to five groups: (1) normal (baseline), (2) control (controlled for anesthesia), (3) fracture, (4) staph, and (5) staph and IL-12 (SIL). Each group was divided into four time periods: 6, 10, 14, and 21 days after injury and fixation. The operative groups had a standardized femur fracture and fixation using a Kirschner wire as an intramedullary device. The two infection groups (staph and SIL) were inoculated with Staphylococcus aureus following fracture and fixed with an identical technique. The SIL group was treated with systemic IL-12 for a total of 10 doses over 10 days. Significantly decreased serum IL-12 levels were noted at day 10 in the operative groups compared to the normal and control groups. The SIL group showed significantly higher macrophage activation levels and total platelet counts at day 21 compared to all the other groups. The overall infection rate was not changed by IL-12 supplementation; however, bacterial qualitative growth scores were significantly lower in the SIL group at day 10, which corresponded to the lowest level of systemic IL-12 in the fracture group.

  10. Novel fracture technology proves marginal Viking prospect economic, part II: Well clean-up, flowback and testing

    SciTech Connect

    Haidar, S.; Rylance, M.; Tybero, G.

    1996-12-31

    Having completed both fracture treatments as discussed in a companion paper, this paper continues on to describe the post fracture shut-in, clean-up and well testing operations that took place on the Viking Wx exploration well 49/17-12. These operations involved the removal of Resin Coated Proppant (RCP) from the wellbore, via Coiled Tubing (CT), through the use of a specially designed jetting nozzle. The RCP pack stability at a concentration of 3.0 lb/ft{sup 2} (as per planned design) had already been tested in a flowback cell. The use of a Surface Read-Out (SRO) gauge, combined with gas, water and proppant flow rates as well as the viscosity of fracturing fluids returns, enabled real time calculation of the drag forces, on the proppant pack, during clean-up. The flow rate, in the field, was controlled such that the calculated drag forces remained below those observed in the laboratory. Following the clean-up a flow and build-up test was conducted, to evaluate the fracture half length and fracture conductivity, from which a Pseudo-radial skin was calculated. The Non-Darcy effects in the fracture were also evaluated, and finally the short term and long term well deliverabilities were assessed.

  11. Elastic-Plastic Fracture Mechanics Analysis of Critical Flaw Size in ARES I-X Flange-to-Skin Welds

    NASA Technical Reports Server (NTRS)

    Chell, G. Graham; Hudak, Stephen J., Jr.

    2008-01-01

    NASA's Ares 1 Upper Stage Simulator (USS) is being fabricated from welded A516 steel. In order to insure the structural integrity of these welds it is of interest to calculate the critical initial flaw size (CIFS) to establish rational inspection requirements. The CIFS is in turn dependent on the critical final flaw size (CFS), as well as fatigue flaw growth resulting from transportation, handling and service-induced loading. These calculations were made using linear elastic fracture mechanics (LEFM), which are thought to be conservative because they are based on a lower bound, so called elastic, fracture toughness determined from tests that displayed significant plasticity. Nevertheless, there was still concern that the yield magnitude stress