Premature Fatigue Failures in the Hot Zone of Low Pressure Turbine Rotor (LPTR) Blades of Aero-Engine
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Generally, the fatigue failures in gas turbine blades occur at 1/3rd height of the airfoil, where the bending stresses on the blades are maximum. In contrast, the creep and the stress-rupture damages are observed at around 2/3rd height of the blade, which is the maximum temperature zone on the leading edge. However, irrespective of the mechanism of crack generation, the major part of the crack propagation in the turbine blades takes place by fatigue mechanism because of the cyclic nature of the loads. Therefore, identification of the primary mechanism of crack initiation while analyzing these failures is of prime importance. Unless this is established unambiguously, identification of the primary cause of failure is not possible. In this paper, analysis of a prematurely failed low pressure turbine rotor (LPTR) blade is presented. Although the fracture in the blade occurred by fatigue mechanism, the initial crack initiation in the blade was found to be by stress-rupture mechanism. Detailed metallurgical investigation showed that the stress-rupture in the blade was promoted due to overheating of the blades for short durations. The reason for overheating of the blades was due to failure elsewhere in the system which resulted in faulty feedback on the actual engine temperature during operation.
KeywordsSuperalloy Gas turbine blades Overheating Stress-rupture Fatigue
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