Hydrostatic stress

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

Limits to ductility set by plastic flow localization

Abstract: The theory of strain localization is reviewed with reference both to local necking in sheet metal forming processes and to more general three dimensional shear band localizations that sometimes mark the onset of ductile rupture. Both bifurcation behavior and the growth of initial imperfections are considered. In addition to analyses based on classical Mises-like constitutive laws, we discuss approaches to localization based on constitutive models that may more accurately model processes of slip and progressive rupturing on the microscale in structural alloys. Among these non-classical constitutive features are the destabilizing roles of yield surface vertices and of non-normality effects, arising, for example, from slight pressure sensitivity of yield. We also discuss analyses based on a constitutive model of a progressively cavitating dila- tional plastic material which is intended to model the process of ductile void growth in metals. A variety of numerical results are presented. In the context of the three dimensional theory of localization, we show that a simple vertex model predicts ratios of ductility in plane strain tension to ductility in axisymmetric tension qualitatively consistent with experiment.. We also illustrate the destabilizing influence of a hydrostatic stress dependent void nucleation criterion. In the sheet necking context, and focussing on positive biaxial stretching, it is shown that forming limit curves based on a simple vertex model and those based on a simple void growth model are qualitatively in accord, although attributing instability to very different physical mechanisms. These forming limit curves are compared with those obtained from the Mises material model and employing various material and geometric imperfections.

Equilibrium fluid distribution in an ultramafic partial melt under hydrostatic stress conditions

Abstract: The geometrical distribution of the fluid phase in partially molten mafic material has been studied under conditions providing close approach to textural equilibrium. Mechanical mixtures of natural dunite and basalt were held at temperatures slightly above solidus and at 10-kbar confining pressure for time durations exceeding 160 hours. For melt fractions of 1–2% fluid phase observed as glass in quenched specimens occurs as a completely interconnected network of channels along intergranular edge intersections. The intergranular facial contacts appear dry, and the grains appear to be in mechanical contact across these faces within the 200-A resolution of a scanning electron microscope. Grain-grain intersection angles near 120° occur between the solid phases, suggesting that crystalline anisotropy plays a minor role in defining surface energies. These results confirm that surface energy plays a dominant role in determining fluid distribution in equilibrium partial melts of silicate composition.

The effect of non-singular stresses on crack-tip constraint

Abstract: The effect of the T-stress on the small-scale yielding field of a crack in plane strain conditions has been examined using modified boundary layer formulations. The numerically calculated stresses at the crack tip are represented by slip line fields for small-strain theory. Positive T-stresses cause plasticity to envelop the crack tip and exhibit a Prandtl field, corresponding to the limiting solution of the HRR field for a nonhardening material. Moderate compressive T-stresses reduce the direct stresses within the plastic zone by decreasing the hydrostatic stress by T. This causes a loss of J-dominance, and a stress distribution represented by an incomplete Prandtl field.