Fatigue behavior of graphite-epoxy laminates at elevated temperatures

An examination and analysis is presented of the elevated temperature fatigue behavior of multidirectional graphite-epoxy laminates in terms of single lamina behavior. The laminate strength is predicted by considering the cyclic stress field in each lamina, the interlaminar stresses, and the experimentally determined temperature-effect 'shifting factors'. The initial failure of a lamina in a laminate is examined first in terms of stress redistribution, and then in terms of total failure and final laminate fracture; these analytical results are then compared with the actual fatigue behavior of T300/5208 graphite-epoxy composite laminates. In view of the agreement obtained, it is concluded that the temperature 'shifting factors' introduced here enable one to predict long-term behavior at a given temperature from short-time testing at elevated temperatures.