Fatigue crack growth and closure behavior of embedded cracks

A three-dimensional elastic-plastic finite-element analysis capable of extending the crack was used to investigate crack closure and opening behavior of nodes on the crack-surface plane. Three-cracked geometries, rectangular, elliptical and circular embedded shapes were investigated under constant amplitude crack extensions under different R-ratios and stress levels The material was an elastic-perfectly plastic AL 2024 alloy. The linear strain isoperimetric cubic elements were utilized in the analysis. The plasticity part of the program uses initial stress approach. The crack was extended one element size at the maximum applied stress of each load cycles. Crack closure and opening behavior of nodes on the crack surface plane after some cyclic crack extensions were investigated by using unloading and reloading portions of loading cycles. Crack surface displacements were investigated for different regions of crack surface plane for the specified load histories.