Strength Analysis of Unidirectional Composites to Explain Fiber Bundle Splitting

Abstract

This paper proposes a 0º tensile strength prediction model for unidirectional composites with a low interfacial strength or low matrix yield stress by investigating carbon fiber reinforced polypropylene. First, a critical cluster dimension in the presence of splitting is formulated using the principles of fracture mechanics. Based on the geometry of fiber packing, a relation between the rate of fiber breakage and the probability distribution of the cluster dimension is then derived. Lastly, the assumption that the cross-sectional area separated by splitting sustains no load is used as a discounting factor to reduce the tensile stress in the unidirectional composites; a stress–strain curve of the composites can then be predicted. The discounting factor is calculated by comparing the probability distribution for the cluster dimensions estimated from the rate of fiber breakage with that of the critical cluster dimension, both of which are functions of fiber stress. When the interfacial toughness related to the critical cluster dimension is estimated from the single-fiber pull-out test and substituted into this model, the predicted tensile strengths are in good agreement with the experimental results.