Vibration Fatigue Fracture Characteristics of K417G Low Pressure Turbine Rotor Blades

The morphology and distribution of cracks and characteristics of fracture surface of 101 low-pressure turbine blades cracking during vibration test were studied. The results show that the cracks of all the blades are transverse cracks, most of which have no defects at the source areas. The cracks are mainly located at the leading edge of the intake side or the trailing edge of the exhaust side near the blade root. A small fraction of the cracks originated from loose defects, and were randomly distributed. The facture surfaces of the blades all have three regions: the source region, the first-stage extending region along the 111 slip plane and the second-stage extending region perpendicular to the blade radial direction. The source areas are mainly single fatigue source. In the first stage, the expansion area is fully developed. On the macro level, there are reflective small planes roughly 45° from the radial direction of the blade. On the micro level, the fracture surface can be seen to have river pattern, sliding steps and zigzag section. In the second stage, the section of the expansion area is flat. On the micro level, there are fine fatigue stripes with the spacing of less than 1 μm.