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

Pultrusions were made with carbon fibres and an epoxy resin. Three dif ferent curing agents were used, so that the matrices were resins with different glass transition temperatures. The composites were tested fo r shear strength at different temperatures, so that the effect of the resin shear strength on composite shear strength could be observed, wi th a fixed fibre architecture. It was found that the composite was alw ays much stronger than the resin both for the 0 and 90 degrees fractur e modes. The 90 degrees fracture surfaces contained many broken fibres , and shear hackles were observed in the resin-rich regions. These sug gested 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.