An improved delamination fatigue cohesive interface model for complex three-dimensional multi-interface cases

This work presents a cohesive interface model for predicting interlaminar failure of composite laminates under tension-tension fatigue loading. The model features improvements on previous formulations and utilizes four-integration-point elements, which offer several new advantages, while maintaining the merits of the previous single-integration-point elements. An element-based crack tip tracking algorithm is incorporated to confine fatigue damage to crack-tip elements only. A new local rate approach is proposed to ensure accurate integration of strain energy release rate from local elements. Furthermore, a dynamic fatigue characteristic length is proposed to offer a more accurate estimation of fatigue characteristic length in complex threedimensional cases. Fatigue initiation is incorporated by using a strength reduction method, without changing the propagation characteristics. The numerical approach has been verified and validated using multiple cases and was then applied to fatigue damage development in open-hole laminates, where a good agreement between numerical analysis and experimental results was obtained.