The rate-dependent deformations of porous pure iron

A combined experimental and analytical investigation of the finite viscoplastic deformations of porous pure iron is presented. The intent is to provide information useful to the simulation of near-net-shape forming and dynamic powder consolidation processes. Samples of porous pure iron were prepared by cold-isostatic-pressing and subsequent heat-treatment. The final pore volume fractions obtained ranged from zero to 31%. The porous metal was then subjected to compressive deformations to large strains (as high as 35%) at both quasistatic (10(-4)s(-1)) and high (> 10(+3)s(-1)) rates of deformation. Stress-strain curves were obtained over the range of strain rates for each porosity. Special techniques were developed to recover the samples after loading by a single compressive pulse, so that the recovered specimens could be examined to determine the evolution of the microstructure as a result of deformation. Next, a finite deformation viscoplastic model based on the theory of composites is formulated. The model requires information on the 'matrix' material (obtained from the fully dense iron) and on the porosity (considered to be an internal variable). Because of the finite deformations that are developed, the evolution of the porosity has been incorporated into the model. Numerical simulations of the experiments based on this model are able to provide reasonable predictions of the observed behavior. (C) 1997 Elsevier Science Ltd.