Effects of material rate sensitivity and void nucleation on fracture initiation in a circumferentially cracked bar

The influence of material strain rate sensitivity and void nucleation on crack tip stress and deformation fields has been evaluated for the case of a circumferentially cracked bar. Loading is assumed to occur at two very different rates which correspond to the quasi-static and high rate tests of Couque et al.¹ A strain rate-dependent version of Gurson’s² porous-plastic constitutive theory is used which accounts for microvoid nucleation and for void growth by plastic deformation. A phenomenological fracture initiation criterion is used to model the onset of crack growth for the purpose of simulating the fracture toughness tests performed by Couque et al. on a 1020 plain carbon steel. The computed results support the conclusions reached by Couque et al. on relating fracture toughness values obtained at loading rates on the order of K_I = 1 MPa s⁻¹ and K_I = 10⁶ MPa s⁻¹.