EFFECT OF MATRIX CRACKING AND INTERFACE SLIDING ON THE THERMAL-EXPANSION OF FIBER-REINFORCED COMPOSITES

The effect of matrix cracking on the thermal expansion behaviour of br ittle, unidirectional fibre-reinforced composites is studied. Sliding along the fibre-matrix interface accompanying matrix cracking has a ma jor effect on the change in thermal expansion. This problem is also ad dressed, both with and without friction. For the most common composite systems, whose fibres have a smaller coefficient of thermal expansion than that of the matrix, matrix cracking and interface sliding result in a reduction of the thermal expansion of the composite. A cylindric al cell model of a composite with uniformly spaced matrix cracks is in voked for analysis. Shear-lag approximations, enhanced by selected fin ite element solutions to the cell model, provide estimates of the func tional dependence of thermal expansion on constituent properties, matr ix crack density and extent of sliding. Hysteresis behaviour during th ermal cycling is analysed accounting for reverse frictional sliding al ong debonded portions of the fibre-matrix interface. A nondimensional parameter, E(m) Delta alpha Delta T/tau (where E(m) is the matrix modu lus, Delta alpha the thermal expansion mismatch between fibre and matr ix, Delta T the amplitude of the temperature cycle and tau the frictio nal resistance to sliding), is identified which governs the extent to which sliding reduces the effective expansion coefficient of the compo site.