Fatigue crack growth in laser-shock-peened Ti-6Al-4V aerofoil specimens due to foreign object damage

Foreign object damage (FOD) has been identified as one of the primary life limiting factors for fan and compressor blades. A comprehensive study is reported here on the fatigue crack growth behaviour in a generic aerofoil specimen of Ti-6Al-4V alloy treated by laser shock peening (LSP) prior to FOD, using both experimental and numerical approaches. 3D finite element analyses have been carried out to simulate the FOD impact on the LSPed aerofoil specimen and to derive an effective stress intensity factor range, considering both the 3D residual stress fields due to LSP and FOD and crack closure due to the compressive residual stresses. The effective stress intensity factor was then used to provide a rational analysis of fatigue crack growth in a complex residual stress field under low cycle, high cycle and combined low and high cycle fatigue condition.