Abstract
A thorough review of the literature has been undertaken on the prediction of the properties of composite materials from the properties of the components. This suggests that least progress has been made in the property area of toughness, and it is evident that the major techniques for the assessment of toughness are impact tests. A study of the influence of material parameters on the impact performance of fibre reinforced plastics is reported in this work. The material parameters studied were fibre type, diameter, geometry and volume fraction, and matrix properties. In order to study the failure process and energy absorption mechanisms in notched and unnotched specimens, both Charpy impact and slow rate tests were conducted using identical test geometries. Failure analysis depended to a large extent on optical and scanning electron microscope fracturegraphic observations of tested specimens. It was found that similar complex failures occurred at both test rates that could be analysed in terms of the standard strength and stiffness properties of the materials under test, provided that full consideration was given to the test geometry. Models have been developed to predict the critical conditions controlling the mode of failure, and it was possible to evaluate the influence of both test and material parameters. The energy absorbed was found to be dependent on the fibre failure conditons including modifications due to the specimen failure mode. These results suggested that the micro-mechanisms of energy absorption (eg debonding) were a secondary effect of straining the fibres to failure. The overall conclusion is that the Charpy test cannot be recommended for the comparison or characterisation of composite materials. Alternative techniques, based on the determination of the strain rate dependence of standard properties have been recommended together with preliminary supporting results.