Simulation of fatigue crack growth under large scale yielding conditions

A simple mechanism based model for fatigue crack growth assumes a linear correlation between the cyclic crack-tip opening displacement (Delta CTOD) and the crack growth increment (da/dN). The objective of this work is to compare analytical estimates of Delta CTOD with results of numerical calculations under large scale yielding conditions and to verify the physical basis of the model by comparing the predicted and the measured evolution of the crack length in a 10%-chromium-steel. The material is described by a rate independent cyclic plasticity model with power-law hardening and Masing behavior. During the tension-going part of the cycle, nodes at the crack-tip are released such that the crack growth increment corresponds approximately to the crack-tip opening. The finite element analysis performed in ABAQUS is continued for so many cycles until a stabilized value of Delta CTOD is reached. The analytical model contains an interpolation formula for the J-integral, which is generalized to account for cyclic loading and crack closure. Both simulated and estimated Delta CTOD are reasonably consistent. The predicted crack length evolution is found to be in good aggrement with the behavior of microcracks observed in a 10%-chromium steel.