Fatigue life prediction and failure analysis of a gas turbine disc using the finite-element method

A numerical prediction of the life of a gas turbine model disc by means of the finite-element technique is presented and the solution is compared with an experimental rim-spinning test. The finite-element method was used to obtain the K solution for a disc with two types of cracks, both at the notch root of the blade insert and located in the corner and in the centre. A crack aspect ratio of (a/c) = 1 was assumed. The fracture mechanics parameters J-integral and K were used in the assessment, which were computed with linear elastic and elastic-plastic material behaviour. Using a crack propagation program with appropriate fatigue-creep crack growth-rate data, previously obtained in specimens for the nickel-based superalloy IN718 at 600 °C, fatigue life predictions were made. The predicted life results were checked against experimental data obtained in real model discs. The numerical method, based on experimental fatigue data obtained in small laboratory specimens, shows great potential for development, and may be able to reduce the enormous costs involved in the testing of model and full-size components.