Probabilistic Analysis of Gas Turbine Disk Multi-Crack Propagation

Abstract

An approach of predicting probabilistic life of multi-source surface crack growth problem is described in the paper. Multi-source circumferential surface cracks occur occasionally on aircraft engine turbine disk. A serious of semi-elliptical cracks which located in a certain radius but different circumferential position on turbine disk was caused by low-cycle fatigue. The residual life should be predicted according to the damage tolerance design theory. A typical turbine disk was studied as a numerical example by using finite element method. The existing experimental result in literature shows that the surface crack propagates faster on circumferential direction than on axial direction, and the surface cracks are going to merge on circumferential direction, which made the multi-crack a closed ring crack. The experiment shows that the multi-cracks would merge into a 2/3 circle crack after certain number cycles which agrees the numerical simulation. Then the crack model was reasonable simplified to axial direction 2-D crack problem in meridian plane of turbine disk. This 2-D axisymmetric simplification significantly reduces the probabilistic analysis computational time. The randomness of materials, load and geometric imperfection is considered in sensitivity analysis by using response surface method. Then the probabilistic life is predicted by considering the major random variables of initial crack length and engine speed. The probabilistic life analysis result is also compared with the existing experimental results.