A continuum damage mechanics model for ductile fracture.pdf

A continuum damage mechanics model for ductile fracture S. Dhara, P.M. Dixita, R. Sethuramanb,* aDepartment of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India bDepartment of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India Received 17 June 1999; accepted 1 February 2000 Abstract Continuum damage mechanics theory together with large deformation elastic±plastic ?nite element analysis has been used to predict crack growth initiation in ductile materials. The damage growth law is based on experimental observations reported in the literature. A local crack growth initiation criterion is proposed. The criterion makes use of the critical damage as the continuum parameter and the average austenite grain size as the characteristic length. To test the validity of this criterion, experiments have been conducted on standard specimens and have also been simulated numerically. The proposed criterion has been used to predict the values of the critical load at crack growth initiation and the fracture toughness. The numerically predicted values compare favourably with the experimental values. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Ductile fracture; Continuum damage mechanics model; Crack growth initiation; Elasto plastic analysis 1. Introduction It has been observed from metallurgical test results that ductile fracture occurs due to void nucleation, growth and ?nally coalescence into a micro-crack. Earlier models of McClintock [1] and Rice and Tracey [2] predict the critical strain at fracture from the study of an isolated void growth in a remote uniform plastic ?eld. The major limitation of this approach is that it ignores effects of void nucleation (as it assumes a pre-existing ?nite size void) and coalescence on the fracture process. The porous plasticity model of Berg [3] and Gurson [4], in which the plastic potential is represented in terms of void volume fraction, incorporates both voi