Prediction of Fatigue and Fracture Life of an Autofrettaged Turbine Compressor Disc Using Finite Element Analysis

Abstract

Gas turbine compressor discs are highly stressed components as they rotate at high speed. Bore region of the disc is the most critical region because any failure at the bore would lead to catastrophic failure of entire gas turbine. Engine start-up and shutdown, as well as major throttle excursions during operation, induce cyclic tensile stresses in this region. These cyclic tensile stresses can exceed yield strength of the material and can thus lead to low cycle fatigue failure. Hence, there is a strong need to enhance fatigue and fracture life of the bore region in order to meet the growing design life requirements. In the present work, method of autofrettage to reduce tensile stresses at bore region has been evaluated. In this case, pre-spin has been used to induce compressive pre-stresses in the bore region. A typical gas turbine compressor rotor forward stage disc was modeled based on design parameters available in literature. Analysis was carried out in 2 stages — non-linear structural analysis of pre-spin to induce compressive stresses and then with operation load to evaluate the effect of pre-stress on stresses and fatigue life in operational conditions in the bore region. Stress intensity factor, KI at the bore region was used to calculate fracture life using LEFM methodology. Comparison of the results for post-spin life with that of the baseline showed 3 times increases in fatigue and 75% increase in fracture life.