Compressive mechanical behavior of hybrid laminates made of thick- and thin- plies with impact damages

The ply level hybridization of thin plies and thick plies can significantly improve the impact damage resistance of composite structures because of thin-ply composites with the obvious damage suppression capability. To study the mechanical behavior of compression after impact (CAI) of hybrid laminates, two hybrid laminates were designed based on the quasi-isotropic thick-ply laminate. The low-velocity impact (LVI) method was used to introduce damages inside the laminates. No-standard compression specimens were prepared based on the ultrasonic C-scan test results. Subsequently, non-standard compression tests of laminated composites with impact damages were carried out. The digital image correlation (DIC) technology was selected to real-time monitor the outside surface deformation behavior of laminated plates. The compression failure characteristics on the side of the specimens were recorded by camera. Experimental results show that the hybrid design of thick- and thin- plies improves the effective residual compressive stiffness and residual compressive strength of composite laminates. The damage characteristics of thick-ply laminates and hybrid laminates subjected to compressive loading are different. Among them, thick-ply laminates exhibit a large number of aggregate matrix cracks near the neutral layer, while hybrid laminates exhibit shear failure of sub-ply plates near the neutral layer and show a distinct shear failure plane. The outputs of this experimental research can provide reference for lightweight design and safety evaluation of hybrid structures made of thin plies and thick plies.