The Controlled-Damage Concept in Design of Laminated Composites

Laminated composites are highly susceptible to foreign object impact damage. One common form of impact damage is delamination. In this study an attempt to control delamination, referred to as the Controlled-Damage Concept (CDC), uses adhesive strips at the 0/90 graphite/epoxy composite interface. The concept is demonstrated through high velocity impact tests, which show that delamination is substantially reduced when adhesive is used. The effect of the CDC on stiffness and notched and unnotched strength is investigated. A micromechanical model developed for stiffness predictions of CDC composites is found in good agreement with experimentally obtained mechanical properties. Interlaminar fracture toughness of composites with adhesive is investigated through the use of a nonlinear quasi-static analytical beam model developed in this study. The critical strain energy release rate (G$\sb{\rm c}$) determined from the beam model using static crack growth data, indicates substantial increases in G$\sb{\rm c}$ for CDC composites. Critical load and crack growth data obtained from instrumented drop impact tests verify the use of the model for low velocity impact problems where contact times are large