Measurement of interfacial fracture energy by single fibre push-out testing and its application to the titanium–silicon carbide system

Abstract

A fracture mechanics model is presented for the advance of an interfacial crack during push-out testing. The effects of thermal residual stresses and interfacial frictional sliding are included. The model is based on the approach of Majumdar and Miracle ( Key Eng. Mater., 1996, 116/117, 153) and leads to mathematical results which are very similar to those of Liang and Hutchinson ( Mech. Mater., 1993, 14, 207). The equations presented can be used to obtain a value for the interfacial fracture energy from the applied load at which a crack of known length is observed to propagate. Such information can in many cases be deduced from load–displacement data obtained during push-out testing. It is assumed that the interfacial crack propagates from the top (loaded) face of the specimen. However, for cases where propagation occurs from the bottom face, the model can still be applied to give a lower bound on the interfacial fracture energy. Experimental data are presented from push-out testing of titanium reinforced with SiC monofilaments. These data have been obtained over a range of test temperatures. This has allowed exploration of the effect of varying the residual stress state within the specimen. The experimental data have been interpreted using the analytical model. Some finite element modelling has also been carried out. It is concluded that the interfacial fracture energy in these composites can be lower bounded at about 10 J m −2, or at a somewhat lower value at elevated temperature. Information is also presented about the average shear stress at which interfacial sliding occurs. This is strongly dependent on the (thermal) radial clamping stress and falls from about 150 MPa at room temperature to about 10 MPa at 800°C.