Fracture failure prediction using a moving finite element mesh refinement scheme

Abstract

A two-dimensional fracture mechanics finite element computer program using an automated mesh refinement scheme in regions of high stress concentration is presented. Constant stress-strain triangular elements are used to discretize the structural system so as to predict the initiation and propagation of fracture, yield patterns, load-displacement history and failure load under monotonically increasing loads. The material stress-strain curve is idealized by selecting yield points on the nonlinear portion of the curve and joining them by linear segments. For each yield point taken, a minimum element area is specified which is gradually decreased as one moves from a lower yield point stress (or strain) to a higher yield point stress (or strain). As loads are incremented, regions of high stress/strain concentration in an input coarse finite element mesh are detected by using either the von Mises or the St. Venant yield criterion. Then the elements in these regions are repeatedly refined until their areas reach the prescribed minimum area requirements. A five-noded triangular element is used to confine the mesh refinement locally. To redistribute the energy of the fractured element into the unfractured media the zero modulus unload-reload method is used. The method is demonstrated for a center-cracked rectangular panel under tensile load.