Aspects of the Tensile Response of Random Continuous Glass/Epoxy Composites

Abstract

The impact properties of a material represent its capacity to absorb and dissipate energies under impact shock loading. If a material is strain rate sensitive, its static mechanical properties cannot be used in designing against impact failure. In addition, the failure modes in dynamic conditions can be quite different from those observed in static tests. The effect of strain rate on failure mechanisms was investigated by viewing fractured surfaces of tensile specimens using a scanning electron microscope (S.E.M.). The relationship between the energy dissipated and fibre content was also evaluated. Tensile tests were conducted on a random continuous glass/epoxy laminate at increasing rates of strain. A second laminate (with random continuous glass reinforcement) was tested in tension at various fibre volume fractions in order to ascertain the relationship between fibre content and energy dissipated. The results suggest that although the fibres fail in a brittle mode, the matrix failure mode is dominant as strain rate is increased. In addition, increasing the test speed results in catastrophic failure due to enhanced crack propagation rate. The results also indicated that increasing the fibre volume fraction saw an initial increase in energy to a peak value, followed by a decrease as the fibre content was increased. This implies that there is a point where increasing the fibre volume fraction becomes detrimental to energy absorption. This has been identified as the point where there is poor wetting of the glass fibres, possibly due to the resin penetration of the glass being restricted by the packing density.