Application of the cyclic life additivity concept for the determination of service life of aero engine disks made from powder alloys

Abstract

An approach to the estimation of cyclic life of aero engine disks made from powder alloys on the basis of the concept of cyclic durability additivity is proposed. Within the framework of this approach the durability of aero engine disks includes both the service life prior to low-cycle fatigue crack initiation and safe crack propagation life which is calculated as the crack stable growth period. Complex studies including the analysis of metallurgical defects in the areas of low-cycle fatigue crack initiation in disks of aircraft gas turbine engines, microfractographic reconstitution of crack kinetics and mathematical modeling of the disk stress-strain condition have been conducted. On the basis of these studies the connection between 1) the size, location and type of the defects, 2) the crack free life prior to low-cycle crack initiation caused by these defects, 3) the period of the crack growth and 4) the characteristics of stress-strain condition and the temperature of the disk in the area of crack initiation has been established. Comparative analysis of defects in granular nickel alloys produced by various technologies (for various maximum size of the grains) has been carried out. The maximum size of the defects and their number in a unit volume are shown to decrease considerably as the grain size decreases. The number of defects in critical areas of engine disks, however, remains quite large, even for the minimal size of the grains. The expedience of applying the deterministic approach for the calculation of disk survivability is shown.