A NEW THEORY FOR FREE-SURFACE FORMATION IN SOLID CONTINUA

In essence, fracture mechanics consist of the conventional boundary-va lue problem formulation of continuum mechanics, along with a variety o f fracture criteria that govern the advance of crack fronts. The assum ption that the material response is governed by a local constitutive m odel everywhere in the body, even at points that are arbitrarily close to the crack front, generally leads to an unbounded stress field as t he crack front is approached. Also, processes such as metal-cutting an d penetration share with fracture the essential feature of new-free-su rface formation, but do not fit easily within the conventional fractur e theory. For these and other reasons, it seems worthwhile to seek a b roader theoretical construct which encompasses surface separation in m ore general setting. With this motivation, a new theory is proposed wh ich applies generally to surface separation in solid continua, but whi ch nonetheless yields fracture-mechanics-type predictions in appropria te special cases. The proposed exclusion region theory involves identi fication of a small material neighborhood that contains the separation front. A generalized constitutive description that derives directly f rom the local constitutive model is constructed for the exclusion regi on. A separation criterion is formulated with reference to tractions o n, and/or distortion of, the exclusion region. The direction-of-advanc e of the separation front is determined as a natural consequence of th e separation criterion. The material parameters appearing in the separ ation criterion can generally be determined from conventional fracture tests. The theory has been implemented in a finite element code. Two example problems illustrating certain important aspects of the theory are presented. (C) 1997 Elsevier Science Ltd.