SHEAR-STRENGTH OF POLYMERS AND FIBER COMPOSITES .2. CARBON/EPOXY PULTRUSIONS

Pultrusions were made with carbon fibres and an epoxy resin. Three different curing agents were used, so that the matrices were resins with different glass transition temperatures. The composites were tested for shear strength at different temperatures, so that the effect of the resin shear strength on composite shear strength could be observed, with a fixed fibre architecture. It was found that the composite was always much stronger than the resin both for the 0 and 90 degrees fracture modes. The 90 degrees fracture surfaces contained many broken fibres, and shear hackles were observed in the resin-rich regions. These suggested that shear failure (rather than tensile failure) took place in the Iosipescu test for the 90 degrees specimens. It was concluded that the fibre architecture played a dominant role in the composite shear strength, with interphase effects being involved also.