ALIGNED SHORT-FIBER-REINFORCED THERMOSETS - EXPERIMENTS AND ANALYSIS LEND LITTLE SUPPORT FOR ESTABLISHED THEORY

Experiments with epoxy resins reinforced with aligned short carbon fib res give results which disagree sharply with traditional fibre reinfor cement theory based on interface yielding and slip and the concept of the critical fibre aspect ratio. Earlier results and evidence from int erface studies are therefore reviewed, and it is shown that, as the ca rbon/polymer interface is brittle, the progressive interface failure p rocess previously envisaged almost certainly does not take place. Furt hermore, a careful reading of the sources of data relating to the yiel ding and slip theory indicates that the evidence in support of it is v ery weak. Thus, the idea of the critical fibre aspect ratio, borrowed from the metallurgists, may not be appropriate for short-fibre reinfor ced plastics. Instead, a process involving brittle fibre debonds shoul d be considered. These debonds could trigger matrix cracking and hence explain the anomalously low composite breaking strains observed when the breaking strain of the fibre is greater than that of the polymer, and other properties of aligned short-fibre composites.