Modelling of temperature dependent failure process in fibre reinforced titanium alloy

Titanium matrix composite (TMC) is a candidate material for application in gas turbines. For this reason it is necessary to know which parameters influence its high temperature strength. In the present investigation modelling of the high temperature strength (from room temperature up to 1000°C) of SCS-6-fibre reinforced IMI834 is performed and compared with experimental results. Modelling is done in two steps. Firstly, three dimensional finite element (FE) calculations are performed to determine the stress distribution around a broken fibre. TMC is a composite with a low fibre/matrix bond strength, so that stress transfer at the fibre/matrix interface mainly takes place as a result of frictional shear stresses. For this reason in the FE calculation two non-linear effects reducing the stress concentration in fibres neighbouring a broken fibre are considered: interfacial sliding and matrix ductility. The stress distribution determined this way is used in a Monte Carlo simulation of the global composite behaviour based on a Weibull strength distribution determined on single fibres. In this simulation influence functions are incorporated to describe the interfering stress fields of fibre breaks. The main reason for a reduction of the tensile strength at increasing test temperature is found to be the strength loss of the matrix. A smaller contribution to the strength reduction results from the reduced stress transfer (leading to a larger ineffective fibre length) at increased test temperature.