Damage characteristics of low-velocity impact of hybrid laminates made of thick- and thin- plies

The ply level hybridization design employs multiple thin layers instead of a single thick layer, resulting in an increased complexity of the interface. To investigate the hybrid effect between thick and thin plies of laminated composites subjected to low-velocity impact loading, two hybrid laminates were designed based on the quasi-isotropic stacking sequence. The LVI tests including the baseline laminate and hybrid laminates were carried out. The ultrasonic C-scan and de-ply technology were respectively used to make a non-destructive and destructive detection on laminates with impact damages. Impact damages were qualitatively and quantitatively evaluated based on the detection results. Subsequently, the performances and failure modes of compression after impact (CAI) were analyzed. Experimental results show that hybrid design of thick- and thin- plies makes full use of the damage suppression characteristics of thin-ply composite, improves the impact damage resistance of composite structures, reduces the projected delamination area and total interface delamination area, shortens the distance between the largest single delamination and the neutral layer, and significantly improves the CAI strength of composite structures. The outputs of this experimental research serves as an indication for the optimal design and safety evaluation of hybrid structures.