The void-size effect upon void growth in a perfectly plastic solid was studied, based upon the Taylor dislocation model. It was found that the void growth-rate decreased with void size. The study also showed that the shape-changing part of the velocity field, which was neglected in most void-growth models, contributed as much as 40% to the void growth-rate at low and intermediate mean stress levels. The void-size effect acted via the ratio, εl/Ro, where ε was the effective strain imposed on the solid, l was an intrinsic material length of the order of microns, and Ro was the void radius. The shape-changing part of the velocity field exhibited 2 opposite effects. On one hand, it tended to increase the void growth-rate as already shown in classical plasticity. On the other hand, it tended to increase the flow stress and therefore decreased the void growth-rate. For a large ratio, εl/Ro = 1, which corresponded to a sub-micron void (l/R0 = 10) at a large strain, ε = 0.1, the latter became predominant and the void growth-rate was even lower than that found without accounting for the shape-changing part of the velocity field. It was also found that the void growth-rate scaled with the square of the mean stress at large εl/Ro, rather than with the exponential dependence in most void-growth models.

A Study of the Void Size Effect Based on the Taylor Dislocation Model. B.Liu, Y.Huang, M.Li, K.C.Hwang, C.Liu: International Journal of Plasticity, 2005, 21[11], 2107-22