Fatigue Damage in Laminated Composites

The present work investigates the damage development under fatigue and static loading in graphite/epoxy laminates. The tensile strength, modulus and tension- tension fatigue data for [0/0/90] _3s laminate were generated at three stress levels (70%, 80% and 90% of ultimate strength). The residual strength and modulus of the specimens were determined at 70% and 90% of the ultimate strength. The characteristic lives of cycles to failure ( N _f ) as a function of applied stress were determined using Weibull analy sis. The specimens were subjected to cyclic loading a determined percentage of the charac teristic life at a given stress level, and the progressive damage determined as a function of applied number of cycles was analyzed using ultrasonic non-destructive technique.