A Critical Reexamination of Classical Metal Plasticity

P. W. Bridgman’s early work on flow and fracture in the presence of hydrostatic pressure showed no systematic effect on strain hardening. This experimental observation led to the conclusions that yielding does not depend on hydrostatic stress and that the yielded material is incompressible. Classical plasticity theory was largely built on these observations. New experiments and nonlinear finite element analyses of 2024-T351 aluminum notched round bars has quantified the effect of hydrostatic tensile stresses on yielding. Nonlinear finite element analyses using the von Mises (yielding is independent of hydrostatic stress) and the Drucker-Prager (yielding is linearly dependent on hydrostatic stress) yield functions was performed. The von Mises results overestimated experimental load-displacement curves by 10–65 percent. The Drucker-Prager results essentially matched the experimental results. The only additional data requirement for the Drucker-Prager yield function is the compressive yield strength.