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Analysis of the growth and collapse of isolated voids in power-low viscous solids shows that material nonlinearity initial void aspect ratio and remote stress state influence the history of void volume and shape. Evolution of voids in linearly viscous matrix materials involves spheroidal shapes while evolution in nonlinear material involves a sequence of spheroidal shapes. A Ritz procedure determines the rate of deformation of these voids.

Gurson's theory of dilatational plasticity is examined for its accuracy in predicting deformation of power-law solids that contain spherical voids. The theory does not correctly describe the strains' dependence on the hardening exponent and triaxiality. Gurson theory predictions and additional incorporated factors are compared with precise, numerical data.

An extension of a technique, originally proposed by Ponte Castaneda, for calculating the limits of the deformation response of a two-phase solid is presented. The extended technique uses a comparison solid, as does the Ponte Castaneda method. However, the extended technique utilizes a special class of anisotropic comparison solids, whose generated bounding values behave isotropically.