Hydrostatic stress

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

Influence of the Intermediate Principal Stress on Sandstone Failure

Abstract: This paper reports the results of fracture testing of sandstone under constant minor principal stress (20 MPa) and various intermediate principal stresses. The results show that when the minor principal stress is constant, as the intermediate principal stress increases, the ratio of the octahedral shear stress (τoct) to the octahedral normal stress (σoct) decreases. The strength criterion of τoct/σoct = f(σ2) is obtained. This criterion reflects not only the hydrostatic stress and intermediate principal stress effects but also the Lode angle effect. This criterion reveals the reason why the rock strength increases and then decreases with increasing intermediate principal stress. The decreasing trend is fitted by linear, logarithmic and Boltzmann equations. The applicability of the three fitting equations for strength prediction and the π plane strength envelopes is analysed, and the results of the Boltzmann fitting equation are the best. The deformation characteristics of rock during the failure process are analysed. The changing process of the tangential deformation modulus of the rock is found to be divided into three stages during the loading process: an increasing stage, an initial decreasing stage and a rapidly decreasing stage. Based on an analysis of computed tomography (CT) images of the internal fractures of rock and photographs of the fracture surfaces, the internal fractures are found to be clear and smooth, and the shear stresses in the fracture surfaces are strengthened with increasing intermediate principal stress. The dominant shear stress in the process of failure is considered to cause these phenomena.

Pressure and Stress Effects on Diffusion in Si

Abstract: The thermodynamics of diffusion under hydrostatic pressure and nonhydrostatic stress is presented for single crystals free of extended defects. The thermodynamic relationships obtained permit the direct comparison of hydrostatic and biaxial stress experiments and of atomistic calculations under hydrostatic stress for any proposed mechanism. Atomistic calculations of the volume changes upon point defect formation and migration, and experiments on the effects of pressure and stress on the diffusivity, are reviewed. For Sb in Si, using as input the results of ab initio calculations of the effect of hydrostatic pressure on diffusion by the vacancy mechanism, the thermodynamic relationships successfully account for the measured effect of biaxial stress on diffusion with no free parameters. For other cases, missing parameters are enumerated and experimental and calculational procedures outlined.

Finite element analysis of void growth in elastic-plastic materials

Abstract: Three-dimensional finite element computations have been carried out for the growth of initially spherical voids in periodic cubic arrays and for initially spherical voids ahead of a blunting mode I plane strain crack tip. The numerical method is based on finite strain theory and the computations are three-dimensional. The void cubic arrays are subjected to macroscopically uniform fields of uniaxial tension, pure shear and high triaxial stress. The macroscopic stress—strain behavior and the change in void volume were obtained for two initial void volume fractions. The calculations show that void shape, void interaction and loss of load carrying capacity depend strongly on the triaxiality of the stress field. The results of the finite element computation were compared with several dilatant plasticity continuum models for porous materials. None of the models agrees completely with the finite element calculations. Agreement of the finite element results with any particular constitutive model depended on the level of macroscopic strain and the triaxiality of the remote uniform stress field. For the problem of the initial spherical voids directly ahead of a blunting mode I plane strain crack tip, conditions of small scale yielding were assumed. The near tip stress and deformation fields were obtained for different void-size-to-spacing ratios for perfectly plastic materials. The calculations show that the holes spread towards the crack tip and towards each other at a faster rate than they elongate in the tensile direction. The computed void growth rates are compared with previous models for void growth.