Hydrostatic stress

About: Hydrostatic stress is a research topic. Over the lifetime, 1568 publications have been published within this topic receiving 37773 citations.

An Explanation on Fatigue Limit under Combined Stress

Abstract: Fatigue crack initiates in the slip band and exists also in it near fatigue limit; many slip bands are apt to appear in the direction of the maximum shearing stress; crack propagates by the normal tensile stress; the maximum shearing stress on a plane at fatigue limit is reduced by the effect of the normal stress on the same plane. From these results of the experiment, a new criterion is proposed, which coincides with the Gough's empirical formula for the brittle materials under combined stress. As the plane of the maximum shearing stress is varied by the various combination of torsion and bending, the isotropic material should be used in the combined stress experiment. In this paper, the results of experiments on three isotropic and one anisotropic materials are discussed and compared with the criteria proposed up to the present.

Stress distributions and faulting

Abstract: Tectonic deformations result from a condition of internal stress caused, in turn, by primary and secondary forces. In the geological literature, a great deal of discussion is based on a direct connection between forces and deformation, completely by-passing the concept of stress. This paper is a contribution in the intermediate field of stress relations. It presents the complete solutions of certain stress systems caused by various forms of boundary forces. Furthermore, the location and attitude of the fault surfaces likely to be associated with them is determined. The basic concept of stress is briefly reviewed and some of the fundamental differences between the force-vector and the stress-tensor are pointed out. The fallacy of applying the familiar methods of vector-addition of forces to problems in stress is demonstrated. For certain systems of external boundary forces acting on a portion of the earth9s crust, the internal stress distribution can be calculated by means of the familiar equations of elasticity. Appropriate calculation methods for two-dimensional cases are shown and the basic equations applicable to a series of important boundary conditions are derived. The examples here presented include: (1) superposed horizontal compression with constant lateral and vertical gradients; (2) horizontal compression with exponential attenuation; and (3) sinusoidal vertical and shearing forces acting on the bottom of a block. The latter equations provide solutions for differential vertical uplift and for the important case of drag exerted on the bottom of the crust by convection currents in the substratum. Diagrams show configuration of the stress trajectories and distribution of the maximum shearing stress for the resulting stress systems. A parallel series of diagrams shows the disposition between the relatively stable and unstable segments of the blocks and the probable attitude of the fault surfaces likely to be associated with the individual stress systems. The construction of the fault surfaces is based on the original stress distributions alone, the influence of local stress alterations due to the occurrence of fracture being disregarded; The full effect of this inter-action is not known, due to the extreme complexity of the problem. The fault patterns shown are strictly applicable only to the initial stages of fracture, but may also represent fair approximations during the more advanced stages, since the original stress remains the dominating influence and stress-alterations due to faulting diminish rapidly with distance.

The Influence of Initial Stress on Elastic Waves

Abstract: A rigorous treatment is given of the problem of wave propagation in an elastic continuum when the influence of the initial stress is taken into account. After a short review of the theory various cases of initial stress are considered. It is shown that a uniform hydrostatic pressure does not change the laws of propagation. A hydrostatic pressure gradient produces a buoyancy effect which causes coupling between rotational and dilatational waves. Bromwich's equations for the effect of gravity on Rayleigh waves are derived from the general theory and the physical transition from Rayleigh waves in a very rigid medium to pure gravity waves in a liquid is discussed. The case of the vertical uniform stress is also considered and it is shown that the effect of the initial stress on the waves in this case cannot be accounted for by elastic anisotropy alone. Reflections may be produced by a discontinuity in stress without discontinuity of elastic properties.