The effect of fiber‐matrix stress transfer on the strength of fiber‐reinforced composite materials

A model for the mechanism of tensile failure in oriented fiber composites based on random fragmentation of the reinforcing fibers biased by stress concentrations at fracture sites has been developed. Single‐fiber composites and composite strands of 34 to 36 volume percent fiber were prepared from an epoxy resin reinforced with Hercules AS4, HMS4, and IM6G carbon fibers. Fiber strength distributions and single‐fiber composite fragmentation data were used to calculate theoretical composite tensile strengths, which were then compared with experimental values. The fractures in single‐fiber composites were observed in situ under cross‐polarized light, and the mechanisms of interfacial failure were discussed.