Plasticity-induced crack closure identification during fatigue crack growth in AA2024-T3 by using high-resolution digital image correlation

Fatigue crack growth in ductile materials is primarily driven by the interaction between damaging and shielding mechanisms. In the Paris regime, the predominant mechanism for retardation is plasticity-induced crack closure (PICC). However, some of the mechanisms behind this phenomenon are still unclear. Identifying and separating the three-dimensional aspect from other shielding aspects during experiments is extremely complex. In this paper, we analyze the crack opening kinematics based on local crack opening displacement measurements in both 2D high-resolution digital image correlation data and 3D finite element simulations. The results confirm that the crack opening stress intensity factor K op differs along the crack path. we present a new method to determine K op at the crack front allowing to identify PICC as the predominant shielding mechanism in fatigue crack growth experiments. Furthermore, this work contributes to the discussion on the damage-reducing effect of PICC, since we find that the influence on fatigue damage in the plastic zone remains negligible when the crack is closed and crack surface contact is directed towards the surface. • 3d finite element analysis of fatigue crack propagation including crack closure. • Robot-supported high-resolution DIC to analyze the local crack opening. • K op is strongly dependent on the measurement position within the HR-DIC displacement field data. • It identifies plasticity-induced crack closure as the acting crack closure mechanism • The fracture roughness seems not to affect the plasticity-induced crack closure mechanism.