Scale-dependent deformation of porous single crystals

An elasto-viscoplastic strain gradient crystal plasticity formulation is applied to study the deformation of a porous single crystal and its macroscopic stress carrying capacity under plane strain condition. Both uniaxial and biaxial loadings are considered. Computational model is a unit cell containing one single void. Attention is focused on investigating the effects of varying void size with respect to a representative constitutive length scale l, at arbitrarily fixed void volume fractions, on its growth rate, the local strain distribution around the void and the macroscopic stress sustained by the material. It is found that both void growth rate and the local strain gradient is decreased by several times when its radius is reduced to l. This indicates that "small" voids are less susceptible to growth than 'large' voids. Computations also show that strain gradient effects significantly elevates the macroscopic stress, especially under large biaxiality of loading. Overall, as the void size increases, the gradient theory predictions gradually approach the classical theory predictions which are size-independent. (C) 1998 Elsevier Science Ltd. All rights reserved.