Numerical simulation of stable fatigue crack growth rate using a cohesive zone model

Predicting the remaining fatigue life of a structure with crack(s) is generally conducted by the fracture mechanics method. This method is aimed at predicting the crack growth and final fracture due to fluctuating loads. The crack growth curve required for these calculations is constructed on the basis of experiments. However, obtaining these experimental data is a time consuming and costly process. In this work, a numerical method is pursued to simulate the steady crack growth using a cohesive zone model. The cohesive zone model is used to simulate crack propagation under cyclic loading by introducing a damage mechanism into the cohesive zone. Crack propagation is represented by fully damaged cohesive element(s). The damaged elements are identified by diminished cohesive strength. Based on this cohesive zone model, finite element models of a single edge notched specimen subjected to cyclic loading are developed. The cohesive surfaces are placed in front of the cracktip along a predefined crack path. The simulation is performed in the finite element code Abaqus and the cohesive elements' behavior is implemented through the user element subroutine UEL. The model is able to reproduce the steady crack growth (Paris law) region with a few parameters obtained from fairly simple tensile and fracture tests.