Effect of increased interfacial strength on the fatigue crack growth resistance and crack opening displacement of β Ti21S/SCS 6 composites

Fatigue crack growth resistance of metastable β titanium composite was investigated in different heat treatment conditions. The effects of increased interfacial strength due to peak ageing on the fatigue crack growth, crack opening displacement and fibre bridging were examined and results of fibre fractures monitored by acoustic emission and fibre push back tests were correlated with fatigue crack growth and crack opening behaviour of the composites. It is shown that at maximum applied intensity factor values higher than crack arrest/catastrophic failure transition, peak ageing reduces the fatigue crack growth resistance of composite due to higher number of fibre fractures which occurs as fibre stress is increased due to increased interfacial shear stress. However, below transition heat treated composite shows better crack growth resistance compared to as-received condition under fixed Kmax,ini values. This favourable effect of increased interfacial strength on the crack growth behaviour is prominent in the composites with smaller initial unbridged defect size.