Strength Prediction and Optimization of Composites with Statistical Fiber Flaw Distributions

For continuous fiber reinforced polymeric composites the process domi nating tensile strength is fiber fracture. This phenomena results in stress concentrations in adjacent fibers over some distance which is directly associated with the ineffective length. This length is the controlling factor in the theory of bundle strength for polymer-based composites. The associated stress concentration factor, C, is normally associated with fracture propagation in both the matrix and surrounding fibers, and should also be in cluded as an important part of any representation of the mechanism controlling tensile fail ure in fibrous composites. In this paper, we combine bundle theory with the mechanics of local stress concentration in the development of a mechanistic representation of tensile strength. The resulting analysis is applied to numerical studies of the influence of micromechanical properties and irregular fiber spacing on the tensile strength, and a dis cussion of optimal design parameters for composites.