Influence of the level of damage on the high temperature fatigue life of an aircraft turbine disc

This paper analyses the effect induced by those scratches produced during the handling and mounting of an aircraft turbine disc on their fatigue life. Fatigue tests were performed at 300 and 600 °C on specimens without and with various levels of damage. At 600 °C, an inverse relationship between the depth of the scratches and the fatigue life was found. However, at 300 °C no effect of these scratches on fatigue life was detected, obtaining very similar results in all of them. Examination of the failed specimens revealed that failure originated away from the scratch. Measurement of residual stresses helps to find an explanation to this apparently anomalous behaviour. It was observed that machining of the specimens induced high tensile residual stresses. At 600 °C, these stresses are relieved and failure at the scratched zone is promoted.