Stress field

About: Stress field is a research topic. Over the lifetime, 11926 publications have been published within this topic receiving 226417 citations.

Update: Application of the Finite Element Method to Linear Elastic Fracture Mechanics

Abstract: Use of the finite element method to treat two and three-dimensional linear elastic fracture mechanics problems is becoming common place. In general, the behavior of the displacement field in ordinary elements is at most quadratic or cubic, so that the stress field is at most linear or quadratic. On the other hand, the stresses in the neighborhood of a crack tip in a linear elastic material have been shown to be square root singular. Hence, the problem begins by properly modeling the stresses in the region adjacent to the crack tip with finite elements. To this end, quarter-point, singular, isoparametric elements may be employed; these will be discussed in detail. After that difficulty has been overcome, the stress intensity factor must be extracted from either the stress or displacement field or by an energy based method. Three methods are described here: displacement extrapolation, the stiffness derivative and the area and volume J-integrals. Special attention will be given to the virtual crack extension which is employed by the latter two methods. A methodology for calculating stress intensity factors in two and three-dimensional bodies will be recommended.

Fracture Mechanics of Rocks

Abstract: This paper reviews recent studies on (1) AE (acoustic emission) and cracking models, (2) failure processes and (3) frictional sliding processes, mainly based on work carried out in Japan Techniques for AE data acquisition and hypocenter location have been greatly improved; one system can record twenty-one channels of waveforms and can locate the AE hypocenter automatically Another system can also record the occurrence time and the maximum amplitude of the AE event without dead time On the basis of these data, we are able to discuss the relation between the distribution of the hypocenters, the occurrence intervals, and the experimentally controlled physical parameters For this purpose, many studies have tried to develop quantitative expression for the statistical characters of these distributions Techniques for evaluating AE source parameters are still being developed; and there has been a great deal of improvement in our knowledge about cracking mode of AE The focal mechanisms have been systematically studied based on the space distributions of the initial motion directions The studies showed that shear type cracking becomes dominant with increasing axial stress These mechanism solutions agree well with the local stress field suggested by the fracture plane Increasing of the failure strength of rocks with increasing stress and strain rates under relatively low confining pressure has been studied experimentally The failure process and the rate dependency of the fracture strength in the low pressure regime are discussed on the basis of a stress corrosion cracking model The failure mechanism under higher confining pressures of up to 3GPa is also examined Some behavior including the variation of AE activity with axial stress differs between low and high confining pressures although the stress-strain relations clearly show brittle deformation in both regimes On the basis of these differences, the researchers proposed that 'high-pressure' brittle deformation was different from ordinarily observed brittle behavior at low pressure, and examined the failure micromechanisms through an optical and an electron microscopes Frictional sliding has also been intensively examined in the past decade Experiments using large samples have demonstrated that the slip propagation process is well described by a slip-weakening model The relations between the dynamic parameters of slip propagation process and the physical parameters of slip surfaces is becoming clearer

Spatial variations in stress within the 1987 Whittier Narrows, California, aftershock sequence: New techniques and results

Abstract: The ML = 5.9 Whittier Narrows, California, earthquake of October 1, 1987, triggered a complex aftershock sequence. The aftershocks had many different focal mechanisms including thrusting on E-W striking, north dipping planes (similar to the main shock), right-lateral motion on NW-SE striking planes (similar to the ML = 5.3 aftershock on October 4, 1987), thrusting on N-S striking planes, and left-lateral motion on N-S striking planes. I attempt to interpret these mechanisms in terms of a stress field that may have caused them. Previously, stress inversion methods based on focal mechanisms assumed that the stress field was spatially uniform. In order to test for the spatially varying effect of the main shock's dislocation on the aftershocks' focal mechanisms a new inversion technique was developed that solves for a uniform stress field that is superimposed on a given spatially varying stress field. A series of simulations were performed to test both the new method and an older method that uses only the uniform component of the stress field. These simulations show that both techniques work but will be limited by the amount of noise in the data and the accuracy to which the given spatially varying stress field resembles the actual spatially varying stresses. Most importantly, the simulations show that the older methods do work when the stress field has a uniform component that is at least as large as the spatially varying component. The simulations also show that when applying the older stress inversion techniques, one can determine if the results are valid, and the amount of spatially varying stresses present, by examining the misfit between the data and the model. Application of these techniques to the Whittier Narrows aftershocks suggests that the uniform component of the stress field, and the complex faulting, corresponds to the response of an elastic halfspace to a simple regional N-S compression. The misfit between the data and the uniform model demonstrate the presence of spatially varying stresses at Whittier Narrows; however, their form, as shown by the simulations, can not be determined with this data set and these techniques.

Creep deformation at crack tips in elastic-viscoplastic solids

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