Aspects of the tensile response of random continuous glass epoxy composites

The impact properties of a material represent its capacity to absorb and di ssipate energies under impact shock loading, Ifa material is strain rate se nsitive, its static mechanical properties cannot be used in designing again st 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 microsco pe (S.E.M.). The relationship between the energy dissipated and fibre conte nt 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 glas s reinforcement) was tested in tension at various fibre volume fractions in order to ascertain the relationship between fibre content and energy dissi pated. The results suggest that although the fibres fail in a brittle mode, the ma trix failure mode is dominant as strain rate is increased. In addition, inc reasing the test speed results in catastrophic failure due to enhanced crac k 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 when increa sing the fibre volume fraction becomes detrimental to energy absorption. Th is has been identified as the point where there is poor wetting of the glas s fibres, possibly due to the resin penetration of the glass being restrict ed by the packing density.