Impact fatigue of glass fibre–vinylester resin composites

Abstract

Abstract An impact fatigue study has been made for the first time on 63.5% glass fibre reinforced vinylester resin, notched composites. The study was conducted using a pendulum type repeated impact apparatus specially designed and fabricated for determining single and repeated impact strengths. Well-defined impact fatigue ( S – N ) behaviour, having a progressive endurance below the threshold single cycle impact fracture strength, with a limit, has been demonstrated. Fractographic analysis revealed fracture by primary debonding, with fibre breakage and pull-out in the tensile zone, but a shear fracture of fibre bundles in the compressive zone of the specimen. Residual strength measured after impact fatigued showed retention of the property at high impact energy levels, up to about 10 2 impact cycles, thereafter a gradual drop to about 10 3 impact cycles followed by a rapid drop. The residual modulus and toughness showed a gradual drop with the increasing number of impacts endured. It is suggested that a few large cracks and an increased volume of microcracks in the matrix, with damaged fibres at high and low impact endurances, respectively, account for the failures of the composites under impact fatigue.