Abstract
This paper presents a variational formulation of viscoplastic constitutive
updates for porous elastoplastic materials. The material model combines
von Mises plasticity with volumetric plastic expansion as induced,
e.g., by the growth of voids and defects in metals. The finite deformation
theory is based on the multiplicative decomposition of the deformation
gradient and an internal variable formulation of continuum thermodynamics.
By the use of logarithmic and exponential mappings the stress update
algorithms are extended from small strains to finite deformations.
Thus the time-discretized version of the porous-viscoplastic constitutive
updates is described in a fully variational manner. The range of
behavior predicted by the model and the performance of the variational
update are demonstrated by its application to the forced expansion
and fragmentation of U-6%Nb rings.
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