The Experts below are selected from a list of 322503 Experts worldwide ranked by ideXlab platform
E A Patterson - One of the best experts on this subject based on the ideXlab platform.
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local crack plasticity and its influences on the global elastic Stress Field
International Journal of Fatigue, 2013Co-Authors: M.n. James, E A Patterson, Colin ChristopherAbstract:Abstract This paper presents the background and development of a novel ‘plastic inclusion’ approach for dealing with the local plasticity which occurs at the tip of a growing fatigue crack. Localised plasticity arises from crack growth mechanisms and essentially blunts the crack, creates a reversed cyclic plastic zone, and induces shear along the crack flanks, along with the possible generation of wake contact Stresses which act on the applied elastic Stress Field at the boundary of the elastic–plastic enclave surrounding the crack. The paper outlines the development of a meso-scale model of the elastic Stress Field around a growing crack that explicitly incorporates these interaction effects. The outcome is a modified crack tip Stress intensity factor that includes some aspects of the magnitude of plastic wake-induced crack tip shielding and which the authors propose has the potential to help resolve some long-standing controversies associated with plasticity-induced closure. A full-Field approach is developed for Stress using photoelasticity and also for displacement using digital image correlation.
Jun Chang - One of the best experts on this subject based on the ideXlab platform.
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the singular Stress Field and Stress intensity factors of a crack terminating at a bimaterial interface
International Journal of Mechanical Sciences, 2007Co-Authors: Jun ChangAbstract:For the fracture evaluation of inclined cracks terminating at the dissimilar material interface, not only the singularities, but also the detailed Stress Field and its Stress intensity factors are necessary. However, though there are many researches reported on the singularity analysis, the Stress Field and its Stress intensity factors are still not clear. This paper has deduced theoretically the singular Stress and displacement Fields near the tip of a crack terminating at the interface between bonded dissimilar materials, for both cases of real and oscillatory singularities. From the deduced singular Stress Field, the Stress intensity factors are defined for such a crack, and the corresponding numerical extrapolation methods are also proposed. Through the numerical examinations, it is found that the theoretical Stress distributions agree well with the numerical results obtained by the finite element method. Moreover, the proposed extrapolation method shows a good linearity, thus it can be used as an efficient way to determine the characteristics of the Stress and displacement Fields near the tip of a crack terminating at interface.
Martin Schoenball - One of the best experts on this subject based on the ideXlab platform.
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quantifying the heterogeneity of the tectonic Stress Field using borehole data
Journal of Geophysical Research, 2017Co-Authors: Martin Schoenball, Nicholas C DavatzesAbstract:The heterogeneity of the tectonic Stress Field is a fundamental property which influences earthquake dynamics and subsurface engineering. Self-similar scaling of Stress heterogeneities is frequently assumed to explain characteristics of earthquakes such as the magnitude-frequency relation. However, observational evidence for such scaling of the Stress Field heterogeneity is scarce. We analyze the local Stress orientations using image logs of two closely spaced boreholes in the Coso Geothermal Field with sub-vertical and deviated trajectories, respectively, each spanning about 2 km in depth. Both the mean and the standard deviation of Stress orientation indicators (borehole breakouts, drilling-induced fractures and petal-centerline fractures) determined from each borehole agree to the limit of the resolution of our method although measurements at specific depths may not. We find that the standard deviation in these boreholes strongly depends on the interval length analyzed, generally increasing up to a wellbore log length of about 600 m and constant for longer intervals. We find the same behavior in global data from the World Stress Map. This suggests that the standard deviation of Stress indicators characterizes the heterogeneity of the tectonic Stress Field rather than the quality of the Stress measurement. A large standard deviation of a Stress measurement might be an expression of strong crustal heterogeneity rather than of an unreliable Stress determination. Robust characterization of Stress heterogeneity requires logs that sample Stress indicators along a representative sample volume of at least 1 km.
Jeanne L Hardebeck - One of the best experts on this subject based on the ideXlab platform.
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aftershocks are well aligned with the background Stress Field contradicting the hypothesis of highly heterogeneous crustal Stress
Journal of Geophysical Research, 2010Co-Authors: Jeanne L HardebeckAbstract:[1] It has been proposed that the crustal Stress Field contains small-length-scale heterogeneity of much larger amplitude than the uniform background Stress. This model predicts that earthquake focal mechanisms should reflect the loading Stress rather than the uniform background Stress. So, if the heterogeneous Stress hypothesis is correct, focal mechanisms before and after a large earthquake should align with the tectonic loading and the earthquake-induced static Stress perturbation, respectively. However, I show that the off-fault triggered aftershocks of the 1992 M7.3 Landers, California, earthquake align with the same Stress Field as the pre-Landers mechanisms. The aftershocks occurred on faults that were well oriented for failure in the pre-Landers Stress Field and then loaded by the Landers-induced static Stress change. Aftershocks in regions experiencing a 0.05 to 5 MPa coseismic differential Stress change align with the modeled Landers-induced static Stress change, implying that they were triggered by the Stress perturbation. Contrary to the heterogeneous Stress hypothesis, these triggered aftershocks are also well aligned with the pre-Landers Stress Field obtained from inverting the pre-Landers focal mechanisms. Therefore, the inverted pre-Landers Stress must represent the persistent background Stress Field. Earthquake focal mechanisms provide an unbiased sample of the spatially coherent background Stress Field, which is large relative to any small-scale Stress heterogeneity. The counterexample provided by the Landers earthquake is strong evidence that the heterogeneous Stress model is not widely applicable.
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crustal Stress Field in southern california and its implications for fault mechanics
Journal of Geophysical Research, 2001Co-Authors: Jeanne L Hardebeck, Egill HaukssonAbstract:We present a new, high spatial resolution image of Stress orientation in southern California based on the inversion of earthquake focal mechanisms. We use this image to study the mechanics of faulting in the plate boundary region. The Stress Field contains significant spatial heterogeneity, which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause. Temporal changes in the Stress Field are also observed, primarily related to major earthquakes. The observed 15° (±10°) rotation of the Stress axes due to the 1992 M7.3 Landers mainshock implies that the deviatoric Stress magnitude in the crust is low, of the order of 10 MPa. This suggests that active faults in southern California are weak. The maximum principal Stress axis near the San Andreas Fault is often at ∼50° to the fault strike, indicating that the shear Stress on the fault is comparable to the deviatoric Stress. The San Andreas in southern California may therefore be a weak fault in a low-strength crust.
M.n. James - One of the best experts on this subject based on the ideXlab platform.
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local crack plasticity and its influences on the global elastic Stress Field
International Journal of Fatigue, 2013Co-Authors: M.n. James, E A Patterson, Colin ChristopherAbstract:Abstract This paper presents the background and development of a novel ‘plastic inclusion’ approach for dealing with the local plasticity which occurs at the tip of a growing fatigue crack. Localised plasticity arises from crack growth mechanisms and essentially blunts the crack, creates a reversed cyclic plastic zone, and induces shear along the crack flanks, along with the possible generation of wake contact Stresses which act on the applied elastic Stress Field at the boundary of the elastic–plastic enclave surrounding the crack. The paper outlines the development of a meso-scale model of the elastic Stress Field around a growing crack that explicitly incorporates these interaction effects. The outcome is a modified crack tip Stress intensity factor that includes some aspects of the magnitude of plastic wake-induced crack tip shielding and which the authors propose has the potential to help resolve some long-standing controversies associated with plasticity-induced closure. A full-Field approach is developed for Stress using photoelasticity and also for displacement using digital image correlation.
