The interfacial strength of beta-Ti composites was increased via ageing, to investigate the effects of interfacial strength on the crack opening. Prior to crack opening displacement (COD) measurements, the number and location of fractured fibres were identified by acoustic emission and fibre probing techniques. This was later used to model the crack opening for number of tests conditions, such as different values of applied stress intensity factor, interfacial strengths and test temperatures. COD measurements were performed on bridged cracks, which were obtained by cycling the specimens under tension-tension loading. Test results have shown that crack opening is affected by both intrinsic factors such as interfacial debonding and frictional sliding stresses and extrinsic factors such as the maximum applied stress intensity factor and test temperature.