Effects of work-hardening and rate sensitivity on the sheet tensile test

Abstract

The importance of strain hardening and strain-rate hardening in sheet tensile tests has been investigated using finite-element modeling (FEM). A Hollomon-type material law was examined with n-values (logarithmic work hardening rate) between 0.0 and 0.5 andm- values (logarithmic strainrate sensitivity) between -0.002 and 0.3. A von Mises yield condition with isotropic hardening rule completed the material model. The results of these simulations showed that, as expected, the uniform elongation(e _u ) depends mainly onn, with a small dependence onm. The post-uniform elongation (e _f —e _u ;e _f = total elongation) depends on bothn andm, and is highly nonlinear in either variable for large parametric values. That is, combined increases ofn andm extend ductility more than the additive increase expected from separate effects. Earlier presumptions thatn is unimportant in the post-uniform region appear incorrect. Approximate relations between (e _f ,e _u ) and (n,m) were developed quantitatively. These relations have been compared with superplastic data in the literature and appear to agree well, given uncertainties in specimen geometry and test procedure.