Development and healing of matrix microcracks in fibre reinforced glass matrix composites: assessment by internal friction

A non-destructive forced resonance technique was used as an indirect method to assess the development and healing of microcracking damage in SiC fibre reinforced glass matrix composite materials. Matrix microcracks were induced by both mechanical stressing and thermal-shock cyclic loading. Mechanical stressing involved applying a series of successive incremental loadings in the range 43–90% of the flexural strength via three-point flexure. The thermal-shock loading involved cyclic quenching of the sample from a high temperature (620°C) to room temperature in a water bath. A semi-empirical equation for the variation of the internal friction with microcrack evolution was derived using the experimental results and a model available in the literature for the effective Youngʹs modulus of a microcracked composite. The possibility of thermal healing of matrix microcracks was investigated by subjecting microcracked samples to a heat-treatment (annealing) for 12 h at 550°C. Internal friction was shown to be an excellent indicator of microcracking evolution by comparison of the measured data for as-received, microcracked and heat-treated materials.