A CUMULATIVE DAMAGE MODEL FOR FATIGUE LIFE OF COMPOSITE LAMINATES

The objective of the research is to make an attempt at relating the fatigue failure of a composite laminate to the fundamental damage and fatigue behavior of its laminae. Damage accumulation and property degradation of each lamina in the laminate are studied. Internal load redistribution among all the laminae is evaluated from the model of stiffness reduction. A nonlinear cumulative damage model is developed to determine the failure of the critical lamina which controls the final fracture of the laminate. The predictions of fatigue life agree with experimental data of cross-ply laminates made of graphite/epoxy. The research provides a unique opportunity to study the fundamental issues of fatigue damage and life. and to address the question of how fatigue life is controlled and optimized by the manner in which such composites are made. The data needed to predict the life of a laminate under variable amplitude fatigue are those of its laminae. Therefore, it is possible to establish a data base for different unidirectional laminae and predict the fatigue life of a laminate based on the data of its laminae and the laminate stacking sequence.