DYNAMIC CRACK-GROWTH IN A POWER HARDENING VISCOPLASTIC MATERIAL

In this paper a finite element analysis of steady-state dynamic crack growth under mode I plane strain small scale yielding conditions has b een performed in a power law hardening rate dependent plastic material , characterized by the Perzyna over stress model. A modified version o f the rats tangent modulus method has been used to update the stress. The main objective of the work is to obtain a quantitative relationshi p between dynamic fracture toughness ratio (K/K-ss) and crack speed. A plastic strain criteria proposed by McClintock (1968) has been applie d to obtain this relationship. It is found that dynamic stress intensi fy factor increases with velocity for all values of beta (a normalized viscosity parameter). At a low value of beta, which corresponds to hi gh rate sensitivity, the fracture toughness ratio (K/K-ss) increases w ith hardening. On the other hand, at a higher beta, the ratio increase s initially and falls subsequently, with increasing hardening.