Post-impact compressive behaviour of low temperature curing woven CFRP laminates

The polymeric matrix in a fibre-reinforced composite serves to bind the fibres together, transfer load to the fibres and protect them against environmental attack and damage due to handling. The matrix has a strong influence on several mechanical properties of the composite such as transverse modulus and strength, impact resistance, shear properties and properties in compression. This paper describes the results of an experimental study to determine the effect of resin (matrix) on the post-impact compressive behaviour of carbon fibre woven laminates. Three new low temperature cure (50–125°C) epoxy resins are examined: an unmodified (LTM12), a rubber-modified (LTM25) and a thermoplastic toughened epoxy resin (MT8E). Note, however, that the first two are post-cured at 190°C. Velocities and impact energies were used to simulate momenta typical of low velocity impact hazards associated with aircraft in-service. Measurements of impact damage and damage growth during compression are made using ultrasonic C-scanning and penetrant-enhanced X-ray radiography techniques. For low impact energies the superior performance of the thermoplastic toughened epoxy is confirmed. Its residual compressive strength compares favourably with that obtained for high strength carbon fibre/epoxy laminates manufactured from unidirectional sheets cured at 190°C.