The effects of fibre surface coatings on the mechanical properties of CFRP

Abstract

Some of the methods of absorbing energy in a unidirectional carbon fibre epoxy resin composite are reviewed and an attempt is made to quantify and compare the increases in fracture energy that can be obtained by varying the matrix properties, type of fibre and interlaminar shear strength. It is found that changes in the latter are the most likely to cause a significant increase in fracture energy. One means of decreasing the shear strength in a controlled manner is by coating carbon fibres with small amounts of silicone rubber and curing this prior to making the composite. The effects of the percentage of rubber on the work of fracture and flexural and interlaminar shear strengths are studied and it is found that 1 per cent of silicone rubber leads to an increase of 107 per cent in the work of fracture without a decrease in the flexural strength. It is believed that, for the starting materials used here, this increase in work of fracture is approximately the maximum that can be obtained without a fall off in flexural strength. A simple criterion is proposed to estimate the amount of rubber which can be added before a decrease in flexural strength occurs and a series, Reuss, model is assumed in order to account for the effect of the silicone rubber in decreasing the shear strength. The work of fracture is reasonably successfully accounted for, as a function of the silicone rubber content, in terms of fibre pull out, stress relaxation and debonding mechanisms.