The effect of fibre alignment on composite strength: I. Single-fibre studies

Abstract

Tests have been carried out in which a fibre was embedded normally in a polymer, and pulled at an angle to the normal to the polymer surface. It was found that some fibres, especially Kevlar, had to be pulled at quite large angles in order for the strengths to be much reduced. A criterion, the 50% angle, was developed. This is the angle of pull at which the fibre breaks at half its normal strength. 50% angles were: 20 ° for glass, 30–40 ° for carbon and 45 ° for Kevlar. Thus, although Kevlar fibres are weaker than glass, they should make stronger random-fibre composites as long as the fibres are long enough so that they are broken in the fracture process. Testing at 30 ° gives information about the strength of extremely small volumes of fibre material and indicates that AS4 carbon may have an intrinsic strength as high as 30 GPa.