Weaving aramid with carbon makes for better composites

“Kevlar has lower strength and stiffness, but is less brittle and has good elasticity relative to carbon”, says Dr Hossein Saidpour at the University of East London. “By combining the two, we have a hybrid composite with optimum properties.” The two fibres are best combined by either weaving or knitting, and the conclusions are the result of a long running research programme at the university undertaken with a research student. Dr Saidpour explains: “We wanted to identify what causes failure when you load the fabric in different directions. Fabrics show a very complicated behaviour because the warp and weft interact, which leads to a complex failure mechanism. Rather than doing an enormous number of tests, we started using iDEAS finite element analysis on small, repeating cells in order to reduce stress concentrations.” Studying the results, maximum load bearing would appear to be obtained with 17% Kevlar and 83% carbon, producing a maximum ultimate tensile strength of 614MPa. Applications are seen in automotive and aerospace, although as Dr Saidpour says: “We followed aerospace standards because they are more stringent.”