Conception of cycle life additivity and its application for determining the resource of aero engine disks

Abstract

Taking into account the universal character and high energy intensity of the mechanism of low cycle fatigue(LCF) crack stable growth which ensures a long safety period for the growth of such cracks a conception of cyclelife additivity is proposed. According to the conception the cycle life of an aero engine disk is determined up to thelimiting state connected with the transition of a LCF crack to unstable growth in the critical area of a disk. The cyclelife prior to the first overhaul is calculated by adding the life cycle before the crack origination and that of stablecrack growth (survivability resource); the overhaul period is determined by the survivability resource. The latter isalso the lower bound of the disk life at the design stage. To estimate the overhaul period we suggest using survivabilitydiagrams representing the dependence of LCF crack stable growth in the critical area of the disk on the size ofthe crack. Methods of constructing survivability diagrams have been developed for simple and complex loadingcycles. Examples of applying the conception for the estimation of cycle life of aero engine disks made of wroughtand powder alloys are presented.