Static and fatigue cracking of thick carbon/glass hybrid composite laminates with complex wrinkle defects

This study presents an experimental investigation of cracking behavior of thick carbon/glass fiber hybrid composite laminates with manufacturing-induced ply wrinkles. Both pure glass fiber and glass/carbon fiber hybrid epoxy composite laminates are tested under static and cyclic tension. Stress–strain responses of the specimens under static tension are recorded and the failure sequences are identified. The cyclic loading is applied to the specimens under tension-tension fatigue. The stiffness degradation of the specimens is measured and the cracking events during the fatigue test are identified. The study shows that the glass/carbon fiber epoxy composite laminates first crack at a lower stress level than the pure glass ones despite their higher extension stiffness. The first cracking in the hybrid laminates occurs at the interface between different glass fiber layers while the first cracking in the pure glass laminates occurs between the rich region and the adjacent glass fiber layer in the wrinkled region. Under fatigue loading, the first cracking in hybrid laminates occurs within the carbon fiber layer while the one in the pure glass laminates occurs within the unidirectional glass fiber layer. This study also proposes a novel yet simple image difference analysis method, that by only using optical images of the specimens under fatigue loading, can accurately and efficiently pinpoint the stiffness drops at different fatigue cycles. This study provides new experimental insights into the failure of glass/carbon hybrid laminates toward a more damage-tolerant design.