Damage Tolerance Improvement of Ti-6-4 Fan Blades with Low Plasticity Burnishing

Low plasticity burnishing (LPB) has been demonstrated to increase the damage tolerance of Ti-6Al-4V fan blades by an order of magnitude. First stage Ti-6Al-4V fan blades were LPB processed using a conventional 4-axis CNC machine tool. LPB dramatically improved surface finish with negligible blade distortion and produced compressive residual stresses of-690 MPa (-100 ksi) through the entire thickness of the blade leading edge. Fatigue testing demonstrated that the deep compression of LPB provided a 3X improvement in HCF endurance limit, complete tolerance of FOD up to 1.3 mm (0.050 in.) deep, and an order of magnitude improvement in fatigue life. Damage tolerance for the TI-6AL-4V fan blade was improved by an order of magnitude. The benefit of the LPB generated compressive layer in improving damage tolerance was confirmed using the fatigue crack growth code AFGROW. Crack growth modeling indicates tolerance of deeper FOD is achievable with optimization of the depth and magnitude of the residual stress field. LPB has been demonstrated to be an effective and affordable means of improving the damage tolerance of Titanium alloy fan and compressor blades. Application of LPB during manufacturing and overhaul operations could significantly reduce the cost of engine inspection and maintenance while improving fleet readiness