3-DIMENSIONAL FRACTURE-ANALYSIS OF CT SPECIMENS WITH A DUCTILE DAMAGEMODEL-BASED ON ENDOCHRONIC PLASTICITY THEORY

For many fracture problems of practical engineering importance, the th ree-dimensional effects are significant and a three-dimensional analys is for the problems is thus required. In this paper, an endochronic th eory coupled with anisotropic damage is first established, which is ac tually an elasto-plastic damage theory coupled with isotropic-nonlinea r kinematic hardening. The ductile damage evolution equation is derive d from the orthogonality rule with a new intrinsic time scale introduc ed especially for damage evolution. Then, a three-dimensional finite e lement program incorporating the endochronic damage model is formulate d and employed to analyze the widely used CT fracture specimen. Two fa ilure criteria are proposed for the prediction of crack initiation dir ection and crack initiation load. From the analysis, significant three -dimensional effects are observed and the crack is estimated to initia te first at the middle of the crack front line. Experiments have been conducted to verify the proposed theory and the results are found to c ompare well with the theoretical values.