Mechanism analysis of sequential failure in aeroengine turbine assembly under non-uniform preload

Turbine assembly (TA) failure poses severe threats to aeroengine safety. This paper reconstructs the sequential failure process involving multiple TA components, thereby revealing a new assembly-induced failure mode. Fractographic and microscopic examinations of the fracture surfaces, and vibration analysis, were used to estimate the timing and location of failure events. Combining the above information, the mechanical process was resolved to identify the primary fracture site and the sequence of component failures. Finite-element simulations, which combined typical operating loads with non-uniform preload (arising from improper nut assembly), were conducted to evaluate structural stresses, dynamic response, and fatigue life. The non-uniform preload was applied via a proposed nut-tilt loading method, and the dynamic progression was mapped into quasi-static steps to improve computational efficiency. The simulations match the observed fracture locations, engine history, and morphologies, validating the mechanism. Results indicate that assembly-induced non-uniform preload initiates primary fracture at turbine-disc cooling holes and alters the load path. During continued operation, impact and rubbing at the fractured hole excite cover-plate modes, imposing alternating stresses on the cover plate and preload nut that drive fatigue crack initiation and growth to final failure. Mitigation requires ensuring a uniform preload during assembly by improving tightening concentricity, adding in-process strain-gauge checks, and designing the TA's axial stiffness.