A NEW FAILURE CRITERION FOR THE GURSON-TVERGAARD DILATIONAL CONSTITUTIVE MODEL

In the Gurson-Tvergaard model a failure criterion has to be used to si gnify the void coalescence. In the literature, a constant critical voi d volume fraction criterion has been widely used. However, it is quest ionable whether the critical void volume fraction is a material consta nt and, furthermore, it is also difficult in practice to determine the 'constant'. By modifying Thomason's plastic limit-load model, a new f ailure criterion which is fully compatible with the Gurson-Tvergaard m odel, is presented in this study. In the present criterion, the void c oalescence failure mechanism by internal necking has been considered a nd the material failure is a natural result of the development of dual constitutive, stable and unstable, responses. In practical applicatio n of the present criterion, no critical void volume fraction needs to be pre-determined either numerically or experimentally. Furthermore, a ccording to the new criterion; the void volume fraction corresponding to void coalescence is not a material constant, rather a function of s tress triaxiality. The predictions using the present criterion have be en compared with the finite element results by Koplik and Needleman, a nd very good agreement is observed. The potential advantage of this cr iterion and other related issues are discussed.