UNIAXIAL TENSILE AND CREEP-BEHAVIOR OF AN ALUMINA FIBER-REINFORCED CERAMIC-MATRIX COMPOSITE .2. MODELING OF TERTIARY CREEP

The tertiary creep of an alumina fibre-reinforced silicon carbide comp osite is modelled on the basis of the damage mechanisms activated duri ng tensile creep tests carried out under vacuum at 1100-degrees-C. Pro gressive fibre-matrix debonding induced by the difference between the radial creep strain of the fibres and that of the matrix mantle is use d to explain the axial creep behaviour. Fibre failure and the subseque nt stress redistribution are also taken into account. The modelling ap proach successfully describes: (i) the time evolution of the creep rat e, (ii) the decrease of the elastic modulus, (iii) the failure mode af ter tertiary creep and (iv) the stress dependence of the creep rate in the secondary stage and of the time to rupture of the composite. It i s shown that a conventional creep stress exponent cannot be determined in this and similar composite materials because of the stress depende nce of the damage accumulated in the composite before the secondary st age is reached.