Damage work as ductile fracture criterion

Abstract

This paper treats the ductile failure initiation in circumferentially-notched tension specimens and explores the local damage model that is able to represent the continuous degradation of the deforming material. With the aid of finite element calculations, the notched specimens have been simulated numerically and the whole strain-stress history for each geometry derived. This allows determination of the evolution of strain-stress fields until fracture occurs. Two damage models were evaluated: the Rice and Tracey cavity growth model and a model which combines the latter with the plastic strain work, to derive an intrinsic parameter called 'damage work'. These models could predict the location where the crack will initiate as well as the crack initiation step which is reached for a relatively constant value of the critical damage.

Ductile Fracture by Central Bursts in Drawn 2011 Aluminium Wire

“…The damage work model of Chaouadi et al (1994) exhibits relatively lower dependence of stress state on damage development (Schiffmann et al, 2003), indicating its pertinence in predicting damage in metal forming processes. In the model, incremental damage may characterised through the following expression:…”

“…In addition, due to the complexity of the equations involved, the applications of such criteria are only suitable for simple geometries and boundary conditions. The availability of finite element computer programs has resulted in the implementation of fracture criteria to metal forming analysis by numerous researchers (Clift et al, 1989;Chevalier, 1992;Chaouadi et al, 1994;Gouveia et al, 1996;Campos and Cetlin, 1998;Choi et al, 1998;Phelan et al, 1999;Ko and Kim, 2000;McAllen and Phelan, 2005). This approach has resulted in some success.…”

“…The damage developed in the wire prior to failure is analysed using a modified damage model. The Chaouadi et al (1994) damage work model has been shown by Schiffmann et al (2003) to exhibit relatively lower dependence on stress state, with maximum deviations occurring at high triaxialities. To improve the failure prediction capability for the complete range of triaxialities, void dilation rates as proposed by Huang (1991) are introduced into the damage work model.…”

“…Fracture criteria capable of predicting fracture in one process may be inadequate in other processes (Clift et al, 1989;Wifi et al, 1995;Landre et al, 2003). In an investigation into the suitability of the Chaouadi et al (1994) work model for predicting ductile fracture, Schiffmann et al (2003) found that the model exhibits relatively lower dependence of stress state on damage development, with maximum deviations occurring at high triaxialities.…”

Critical assessment of the application of the J-integral and CTOD concepts to circumferentially cracked copper bars

“…For very ductile materials, the criterion wv = wvc appears to be the only criterion enabling us to characterize unequivocally the resistance to the crack initiation from macroscopic tests on a circumferentially cracked round bar of limited size. It may be noted that similar damage work criteria [23,24,25] have been proposed in the framework of the so called 'local approach' analysis of fracture.…”