Size-effects in porous metals

The intrinsic size-effect for porous metals is investigated. The analyses are carried out numerically using a finite strain generalization of a higher order strain gradient plasticity model. Results for plane strain growth of cylindrical voids are presented in terms of response curves and curves of relative void growth. The influence of void size compared with a constitutive length parameter is analysed and it is shown that strain gradient hardening suppresses void growth on the micron scale. This increased resistance to void growth is accompanied by an increase in the overall strength of the material. For porous materials with small void volume fractions under highly triaxial tension, void growth is analysed through cavitation instabilities using a finite element Rayleigh–Ritz procedure. Cavitation instabilities are found to be delayed for small voids, so that higher stress levels are needed in order to obtain unstable growth. Cavitation diagrams for cylindrical voids are compared with cavitation diagrams for axi-symmetric void growth of initially spherical voids.