Characterization of strain hardening for a simple pressure-sensitive plasticity model

Summary

Paralleling the development of strain hardening for the pressure-independent von Mises criterion, a simple plasticity model in strain space was presented to characterize strain hardening for pressure-sensitive compressible materials. Two hardening moduli,H _T andH _C , which emerged from the constitutive equations and can becalculated from uniaxial stress-strain curves in tension and compression, were used to characterize the strainhardening responses forgeneral and special stress systems. The results indicated the implications and restrictions of the yield function on the hardening responses. It was also shown that strain softening, under general stress systems, can be a natural consequence of pressure-sensitive yielding. Consequently, a strain-space formulation is recommended for most (if not all) pressure-sensitive plasticity models. Preliminary application to the yielding of polymers under hydrostatic pressure gave reasonable results for polyethylene at moderate pressure and small strains; the results for polycarbonate were generally poor. Finally, the advantages and limitations of the present approach were discussed.