Effect of double crack on fatigue crack growth life of 3D printing compressor impeller

Abstract

A compressor impeller with pressure ratio less than 3 is taken as the research object. The 3D printing residual stress was introduced into damage tolerance assessment of blades, and the effect of double crack on Fatigue Crack Growth Life (FCGL) was investigated. The impeller was printed by selective laser melting technology and then heat treated. Finite element method was applied to numerically simulate 3D printing process, heat treatment process and actual working process of impeller, and mechanical quantities such as stress and deformation were completely analyzed. Numerical simulation results agreed well with the experimentally observed crack location in the middle of the blade. Forman–Newman–de Koning model and linear elastic fracture mechanics theory were applied to give the growth law of impeller under single and double crack conditions. The result shows that crack initiation locations of impeller during printing and operating are respectively middle part and root part of blade. The stress intensity factor at the initial crack tips of single and double cracks exhibits a quadratic relationship with rotational speed when only external load is considered. The crack growth paths of single crack in middle and root are radial and axial respectively, and the FCGL of single crack in root is lower than that of single crack in middle. With the increase of rotational speed, the critical crack length decreases linearly and the cycles decreases nonlinearly in both single and double crack conditions. The FCGL of double crack is between two single cracks at low speed and lower than two single cracks at high speed. The critical crack length of double crack is lower than that of corresponding single crack. At 60000rpm, the dominant crack changes from middle crack to root crack.