The effects of the delamination on the fatigue behavior of composite structures

The aim of the present study is to investigate the role played by delamination on the fatigue behavior of centrally holed CFRP laminates. To reach this objective, both theoretical and experimental studies were performed. As to the theoretical analysis and the relevant numerical predictions of the 3D state of stress, the study proposes the use of a finite element procedure based on a multi-layer higher-order laminate theory developed by the authors in conjunction with the application of an interlaminar failure criterion. The approach assumes that significant information on the fatigue life of holed laminate can be obtained by performing a static prediction only. Two types of rectangular laminates with stacking sequences [+45)4/(-45)4]s, and [0/90]3s manufactured with T300/934 are examined. The static and the fatigue failure of the above mentioned laminates were then investigated in a series of experiments in order to verify the initiation of delamination both in the static case and during the fatigue loading process, ultrasonic nondestructive inspections were also made. The obtained results show a significant correspondence between the experimental static and fatigue behavior of the laminates and the theoretical predictions. They show also that an efficient numerical tool of the 3D state of stress prediction is used.