The effects of strain rate and failure modes on the failure energy of fibre reinforced composites

The utilisation of polymer composite materials in safety critical structures necessitates their full characterisation. This will bring about the much needed boost in confidence for their application to industrial situations, especially where high speed impact is a concern. Impact performance can in some way be measured by the energy absorbed or expended to failure of a material. Hence, establishing the rate effect on energy absorption is of paramount importance when designing for impact. Tensile, shear and 3point bend tests were conducted on a woven glass/epoxy laminate at increasing rates of strain. The results suggest a linear relationship between expended energy and the log of strain rate in the laminate tested. Furthermore, it was found that a relationship exists between the flexural energy obtained at low strain rate and the high speed (2¯4 ms-1) test values. Magnified views of the failed specimen surfaces, viewed under a scanning electron microscope, indicate a change in failure modes as strain rate is increased, which brought about the increase in energy observed.