Hydrostatic stress

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

A shear modified enhanced Gurson constitutive relation and implications for localization

Abstract: The most widely used phenomenological constitutive relation to model ductile failure of structural metals at room temperature is based on the work of Gurson (1977) and has the advantage of having both a micromechanics basis and sufficient simplicity to enable complex engineering calculations to be carried out. The predictions of this framework have been most successful in circumstances where the stress triaxiality, the ratio of mean normal stress to Mises effective stress, is relatively large. For stress states with smaller values of stress triaxiality, the predictive capability has typically been much reduced. We present a shear modified enhanced Gurson constitutive relation that combines the shear modification of Nahshon and Hutchinson (2008) with the second porosity concept of Gologanu et al. (1994). This maintains both the connection with micromechanics and the computational simplicity. The predictive capability of the framework is illustrated by the good agreement with cell model calculations for localization of deformation over a wide range of stress states. Strain localization analyses with an initial porosity imperfection predict that for axisymmetric stress states with a superposed hydrostatic tension, the minimum critical strain for the onset of localization follows the onset of coalescence, as defined within the context of the constitutive model here, if the value of the stress triaxiality is sufficiently small. For an imposed shear stress state with a superposed hydrostatic tension, the minimum critical strain for the onset of localization is predicted to precede the onset of coalescence. A strong sensitivity of the critical strain for localization of deformation to the strain or stress range over which void nucleation occurs is also predicted, with void nucleation and localization of deformation essentially coinciding for sufficiently abrupt nucleation.

Simultaneous determination of mean pressure and deviatoric stress based on numerical tensor analysis: a case study for polycrystalline x-ray diffraction of gold enclosed in a methanol ethanol mixture

Abstract: It is known that the {100} and {111} planes of cubic crystals subjected to uniaxial deviatoric stress conditions have strain responses that are free from the effect of lattice preferred orientation. By utilizing this special character, one can unambiguously and simultaneously determine the mean pressure and deviatoric stress from polycrystalline diffraction data of the cubic sample. Here we introduce a numerical tensor calculation method based on the generalized Hooke's law to simultaneously determine the hydrostatic component of the stress (mean pressure) and deviatoric stress in the sample. The feasibility of this method has been tested by examining the experimental data of the Au pressure marker enclosed in a diamond anvil cell using a pressure medium of methanol?ethanol mixture. The results demonstrated that the magnitude of the deviatoric stress is ~0.07?GPa at the mean pressure of 10.5?GPa, which is consistent with previous results of Au strength under high pressure. Our results also showed that even a small deviatoric stress (~0.07?GPa) could yield a ~0.3?GPa mean pressure error at ~10?GPa.

Evaluation of diffusion creep in low melting point materials by nanoindentation creep test

Abstract: In this paper, the behavior of diffusion creep in Sn-37 Pb as a low temperature melting point alloy during nanoindentation creep test was examined. Creep exponent, n, estimated from the relationship between hardness and indenter dwell time decreases as a function of time and is saturated with n=1. From the observation of the indented surface, the surface was pushed by the indenter in the early stage. However, several grains of tin near indenter were transformed in the last stage. A finite element analysis reveals that the rate of the relaxation of the Mises stress is more rapidly than that of the hydrostatic stress because the multi-axial stresses appear near the indenter. The core hydrostatic stress causes the gradient of chemical potential on the grain boundaries. It implies that diffusion creep is activated during the nanoindentation creep test. The transition of mechanism of creep deformation under the indenter from the dislocation creep to the diffusion creep takes place.

Use of Weight Functions to Determine the Stress Intensity for a Cracked Thick-Walled Cylinder,

Abstract: : The use of weight functions to determine stress intensities for cracked specimens is relatively simple, and, while the initial derivation of a suitable weight function for some specimen geometries may be complex, the technique offers substantial benefits. In particular, stress intensities may be estimated for any initial stress distribution, and variations in stress intensity which result from the introduction of residual stress fields may be handled without the need to perform a full re-analysis for each case. The stress intensity at the tip of a crack which grows through a known stress field has been estimated using a weight function technique. The geometry considered is a thick-walled cylinder (Ro/Ri = 1.8) containing a longitudinal crack along the bore surface, and stress distributions corresponding to a variety of loading arrangements are used as examples. (Author)