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

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