On the energy release rate extraction and mixed mode behavior of fatigue cohesive model

This paper presents a comprehensive study on the energy release rate (ERR) extractions and mixed mode behavior of fatigue cohesive model. The development of the non-linear cohesive zone ahead of a crack tip is influenced by multiple factors, where the extractions of ERRs and mode ratios are crucial for accurate fatigue analysis in Paris law-based models. Investigations into the effects of different parameters e.g. interfacial strengths, shapes of the cohesive laws and element sizes on the extracted ERRs are conducted. In addition, two novel mixed mode bending models i.e. multi-stage mode ratio (MSMR) and continuously various mode ratio (CVMR) models are proposed for mixed-mode behavior study. All results are compared to the theoretical fracture mechanics analysis and to each other. It is found that if the interfacial strength becomes too low, an excessively long cohesive zone can form, where the mode ratio could significantly deviate from the true value and negatively impact the accuracy. The shape of cohesive laws is also found to influence the ERRs and mode ratios to some extent but are not the dominating factor.