Failure analysis of fatigue tested LPT rotor blades failed from root region

During fatigue test of an aeroengine, a few LPTR blades were found to have developed cracks at the root region. Two of these blades bearing serial numbers AAT17 and ABB23 were forwarded to the laboratory for analyzing the cause of this unusual failure. Investigation revealed that in both the blades, the crack had developed in between the lobes and at the leading edge of the concave side and propagated along the face of the root. Fractographic study showed that the crack was generated by fatigue mechanism. Evidences suggest that the generation of crack was due to non-uniform loading on the fir tree of the blades resulting from inappropriate holding of the blade in the fixture. It may be noted that failure at the root of the blades was also noticed during earlier tests (refer NAL Report No. MT-FA-1040-03-07). A detailed analysis of the failure is presented in this report