Dynamic elastic-viscoplastic crack growth

The scattering of K{dollar}sb{lcub}rm ID{rcub}{dollar} (plane strain dynamic fracture toughness) values indicates that K{dollar}sb{lcub}rm ID{rcub}{dollar} is not a material property. Kanninen and Popelar (1) concluded that the neglect of local crack tip inelastic effects could be responsible for the nonuniqueness of K{dollar}sb{lcub}rm ID{rcub}{dollar} values. The strain-rates for rapid crack growth in metals could reach values on the order of 10{dollar}sp3{dollar} 1/sec to 10{dollar}sp5{dollar} 1/sec at the crack tip. The flow stress exhibits strong rate-dependent in this range. An elastic-viscoplastic analysis is essential to study the fast crack growth.; A small scale yielding finite element analysis is performed for the mode I plane strain, dynamic steady-state crack growth in an elastic-viscoplastic material responding according to the Bodner-Partom model. The implicit/explicit method is developed to integrate the rate-dependent equation. The numerical scheme is proven to be a stable and efficient one.; A critical near-tip stress intensity factor fracture criterion is used to study the cleavage crack growth. The finite element results are compared with the approximate analytical results. Later, the approximate analytical solution is modified, and the modified results agree well with the finite element results. The finite element analysis is also performed to study the ductile crack growth by using a critical plastic strain fracture criterion. It is found that the dynamic steady-state crack growth at low and medium crack-tip speeds is more likely to occur in a ductile manner than in a cleavage manner. A parametric study on the value of limiting plastic-strain rate in the Bodner-Partom model indicates that the dynamic fracture toughness for rapid cleavage fracture is very sensitive to the value of this limiting strain rate.