Numerical investigation of crack growth behaviour using a cohesive zone model

This thesis concerns modeling ductile fracture using a cohesive zone model (CZM) and finite element (FE) methods. A FE program system (FECGS), which includes a pre-processor and a post-processor, has been developed for that purpose. A simple CZM has been proposed. A FE CZM technique has been developed for implementation of the continuum cohesive zone model into FE code FECGS. The model has been applied to study fracture behaviour of homogeneous materials under mode I small scale yielding (SSY) condition with emphasis on the effect of material properties, cohesive zone parameters and T-stress on prediction, and large scale yielding (LSY) crack growth with focus on prediction of the geometry and size effects. The model has been extended to simulate three-dimensional crack growth. Approaches for determination of the CZM parameters have been suggested. Comparisons of experiments and numerical predictions have been made for a round notched tension bar, a three-dimensional side-grooved compact tension and a three-dimensional surface cracked tension specimen of an aluminum alloy 2024FC with aim of verification of the model. Systematic parameter studies have been performed for a heterogeneous material system (a thin ductile layer bonded by two elastic substrates) under both SSY and LSY conditions, emphasizing the effect of geometry and mismatch in material properties on fracture behaviour and mechanisms such as plastic cavitation and fracture instability. The aim of this investigation is to develop a predictive tool for the engineering application such as prediction of mechanical performance of structure and for understanding the material failure, based on a simple material model. (orig.)