A parametric study of residual strength and stiffness for impact damaged composites

A parametric study of residual strength and stiffness for low-velocity impact damaged composites was performed. Possible compression after impact failure mechanisms, which may be caused by stiffness and strength degradation inside the damage region, were discussed. In order to understand the scaling effects on impact damage residual strength, finite element analysis was performed. With stiffness degradation inside the damaged area, the stress fields of small coupon and larger stiffened panels with the same damage were calculated numerically. The stress redistributions were found to be almost identical between the coupon and panels. This indicates that the stress redistribution is a local phenomenon, and will not be affected much by the existence of the stiffeners. It is believed that the residual strength of impact damaged composite structures is related more to the damage severity than to the load redistribution. The dependency of the stress concentration factor on the anisotropic engineering elastic constants of a laminate was extended from an analytical study by Lekhnitskii (Anisotropic Plates, Gordon and Breach Science Publishers, New York, USA, 1968).