Fatigue damage mechanisms and evolution of residual tensile strength in CFRP Composites: Stacking sequence effect

This study explores the effect of fiber orientation on the fatigue resistance of carbon fiber reinforced polymer composite laminates. First, fatigue damage mechanisms of composite laminates with different stacking sequences at various stress levels are analyzed by utilizing digital image correlation (DIC) and scanning electron microscope (SEM) techniques. The findings highlight that the fiber orientation of the laminate has a significant effect on the fatigue life of the specimens. Prior to final fatigue failure, laminates with 0° fiber orientation experience only a 30 % reduction, while laminates with ± 45° fiber orientation show up to 93 % stiffness reduction. The fracture modes of laminates with a 0° fiber orientation vary depending on stress levels. Microscopic observations confirm that in the case of laminates with ± 45° fiber orientations under compressive loading, fiber flexion, and delamination are the predominant failure mechanisms. Further, the post-fatigue tensile tests reveal that the residual tensile strength of the laminates with ± 45° fiber orientations increases by 6.3 % after 15 % of the total cycles (7.2 × 10⁴) at a 30 % stress level. The contribution of this study provides vital insights into the structural design of laminates and offers a pathway for improving their fatigue performance.