Reduction of Elastic Moduli of Fiber Composites by Fatigue Crack Accumulation

摘要

The problem of reduction of elastic moduli of unidirectional fiber composites due to parallel cracks, either parallel or normal to fibers, is considered on the basis of variational techniques. Expressions for effective elastic moduli are given for the case of a small number of non-interacting cracks. It is shown that these are upper bounds on effective elastic moduli for the case of arbitrary distributions of parallel cracks. Lower bounds for Young's moduli for special parallel crack distributions are also constructed. In addition, the 'self consistent scheme' approximation is also applied to the present problem. The problem treated is of significance for fatigue damage of fiber composites since such damage consists primarily of formation of such cracks. Experimental determination of moduli reduction due to cyclic stress (wearout) can thus provide a measure of the number of cracks formed. (Author)