Some fundamental aspects of the fatigue and fracture response of composite materials

A simple analytical model, based on the concept that the constraining plies surrounding cracks through the thickness of a given ply or plies control the spacing of those cracks by controlling the surrounding stress state, appears to agree well with experimental data. Such a model can be used to evaluate critically various constraint situations including the prediction of the ability of a given constraint layer to arrest flaw development. The analytical model, which uses an equilibrium element approach in the present case, is sensitive to lamina and laminate elastic properties, flaw size, stacking sequence, and an interlaminar stress transfer distance which is estimated from experimental observations. The analysis is easily extended to study flaw growth and plastic region formation.