THERMO-ELASTO-VISCOPLASTICITY OF ISOTROPIC POROUS METALS

A RATE AND temperature dependent elastic-plastic model for isotropic, moderately porous metallic materials is formulated. This model is intended for material rate-sensitivities in the entire range spanning from highly rate-dependent behavior at high homologous temperatures to nearly rate-insensitive behavior at low homologous temperatures. The predictive capabilities of the constitutive model are verified by comparing results from finite element calculations against results from physical experiments. Specifically, example calculations are presented for: (a) isothermal hot compression of a tapered disk made from an initially porous material. This calculation illustrates the effect of secondary tensile stresses on hot workability of metals. (b) Tension tests, under isothermal conditions at low homologous temperatures, on axisymmetric notched bars made from initially porous materials. This calculation illustrates the effects of nonuniform multiaxial tensile stress states on void growth. Predictions from the computational procedures for both examples agree well with experimental results. The new state variable rate and temperature dependent constitutive model for microporous materials and the associated computational procedures form a basis for the simulation and design of deformation processing operations. This new capability should be useful for the prediction of formation of defects during both cold-working when the material rate sensitivity is low, as well as hot-working when the material is highly rate sensitive. The computational capability should also be useful in simulating the late stages of densification of powder metallurgical products in complex forming operations.