Abstract
A technique is developed whereby Silicon Carbide whiskers may be incorporated uniformly into epoxy resin using an ethanol transport medium. Volume fractions up to 10% are achieved. The mechanical properties of the whisker loaded resin are studied using uniaxial tensile coupons and compact tension test methods. With increasing fraction of whisker, the tensile modulus, tensile strength and fracture toughness are all found to increase significantly. A method for producing hybrid E-glass fibre/epoxy resin/SiC whisker crossply laminates is developed from an existing frame winding technique. Scanning electron microscopy of polished sections of the resultant laminates confirm that an reasonable distribution of the whisker in the matrix is achieved. Laminates containing 0%, 2% 5% and 10% matrix volume fraction of SiC whisker are fabricated. Tensile coupons taken from the laminates were tested under quasi-static and tension-tension fatigue loading conditions. Under both static and fatigue loading, the residual stiffness and accumulation of cracks in the transverse ply are monitored. It is shown that the presence of whisker delays the onset of matrix cracking and the subsequent multiplication of transverse ply cracks under both static loading and fatigue loading conditions. A model to describe the transverse ply crack spacing-applied stress relationship for each laminate type under static loading conditions is developed. The model is based on a combination of a shear-lag stress analysis with a two parameter Weibull statistical description of the transverse ply strength variation. A computer simulation is developed which simulates the propagation of transverse ply cracks across the width of a laminate based on a fracture mechanics analysis. Using a Paris law expression to describe the growth of individual cracks modified to allow for crack interaction the model predicts the variation in residual stiffness with increasing fatigue cycling.