Experimental study on the behavior and characterization methods of composite laminates to withstand impact

An experimental study on the impact resistance and compressive strength of damaged laminates was carried out by using about 800 specimens of 14 composite systems. It has been found that there is a common knee point for the impact energy-dent depth curve and the dent depth-compressive strength curve for the same type of composite laminates. The overlapped area of the inner delaminations does not increase and its compressive strength does not reduce generally after the knee point occurs. Some fiber breakage at the impact location on the surface could be visible after the knee point occurs. The damage tolerance behavior characterized by the traditional CAI method may get the opposite conclusion obtained from the structural verification test results. Therefore，a characterization system for damage tolerance and damage resistance behaviors of composite systems is proposed by using the knee point features of the capability of composite laminates to withstand impact (including damage resistance and damage tolerance)，i.e. the damage resistance and damage tolerance behavior is characterized by means of the maximum contact force，F_maxand the compressive failure threshold value (strength or failure strain) (CAIT) of the specimens with quasi-isotropic stacking sequence respectively.