Impact-Induced Delamination—A View of Bending Stiffness Mismatching

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Abstract
Fiber-reinforced composite materials are very susceptible to impact loading. The damage characteristics of a composite material subjected to subperforation impact can be classified as indentation, fiber breakage, matrix cracking, fiber-matrix debonding and delamination. Among these damage modes, delamination has been found to be important for all cases of loading. In this study, the damage characteristics of many composite plates made of glass/epoxy, Kevlar/epoxy, and graphite/epoxy were investigated. Delaminations in the impacted composite plates were inspected by high-intensity light, X-ray radiog raphy, ultrasonic imaging system and edge replication. It was found that delamination in every interface of impacted composite plates had a peanut-like shape. Since membrane ef fect could be ignored in this study, stresses caused by bending were the major stresses which should be responsible for the delamination. Although the interlaminar stresses had been analyzed by many investigators for the determination of delamination, in this study, however, the mismatching of bending stiffness between two adjacent laminae was pro posed as an indicator of delamination in the composite laminates subjected to subperfora tion impact. The effects of material properties, stacking sequence and thickness on the delamination were discussed. The justification of the hypothesis of bending stiffness mis matching was also presented.