Strength Prediction and Measurement in Model Multilayered Discontinuous Tow Reinforced Composites

Abstract

The purpose of this work is to perform analytical modeling and experimentally produce idealized composite laminates reinforced with high-modulus discontinuous-fiber tows to evaluate the theoretical upper limits of tensile strength as compared to continuous-fiber composites. The idealized composite represents a staggered mosaic of prepreg tape strips of equal width and length. Three-dimensional analysis was performed to evaluate the energy release rate of the possible damage accumulation modes, such as tow delamination and splitting emanating from tape strip ends in plies with different orientations. The effect of residual stress was also evaluated on the delamination propagation energy release rates as well as tow end crack formation loads. Failure mechanisms for unidirectional and quasi-isotropic laminates were established by comparing the calculated energy release rates for tows in different locations to the critical Mode II energy release for axial cracking in the material system. Specially designed experiments were conducted to verify the failure mechanism predictions and evaluate proposed design changes for strength increase in the discontinuous-fiber tow reinforced composites.