Yield stress of epoxy composites filled with quartz powder

The effect of the amount of quartz powder in an epoxy resin matrix was studied by compression testing. Compressive tests near room temperature and at several strain rates were performed on samples with different filler volume fractions. The data show that both the composite Young's modulus and yield stress increase with increasing volume fraction of filler. The behaviour of the composite Young's modulus follows the Lewis and Nielsen model with a value for maximum packing fraction of the filler close to that for a random packaging of quartz particles inside the epoxy matrix. In order to understand the behaviour of the yield stress, a model with physical meaning was developed. The observed strengthening effects are explained by an alternative model related to thermal internal stress. (C) 2002 Society of Chemical Industry.