Research On Fatigue Crack Initiation And Propagation Characteristics Of A High-pressure Turbine Disk

This paper takes a high-pressure turbine disk of a turbofan engine as the research object.The fatigue crack initiation and propagation characteristics of this high-pressure turbine disk are studied by the combination of crack initiation life simulation,crack propagation simulation and the fatigue test.The main research work is as follows:(1)The fatigue initial life of the turbine disk is calculated by the finite element software on the fatigue analysis.The stress state of the turbine disk is analyzed by the finite element simulation.The equivalent stress nephogram shows that the stress in the eccentric hole is the largest,so the eccentric hole is chosen as the dangerous part to be assessed.Then,the standard samples made of the material that is cut out from the real turbine disk is introduced.The fatigue test is carried out on these samples.There are five kinds of stress states about these standard samples,so the fatigue test of 43 samples are completed altogether.At the end of the test,each fracture part of these samples is analyzed,and the initiation life of the sample is calculated,so the stress-initiation life data of the standard sample is obtained.Finally,the finite element simulation of the turbine disk and the stress-initiation life data of the standard samples are imported into the fatigue analysis software,and the minimum crack initiation life at the eccentric hole of the turbine disk can be obtained.(2)The crack propagation life of the turbine disk is calculated by the crack propagation finite element software.The sub-model technique is used in a fracture mechanics software called FRANC3 D.An initial crack with the length of 0.76 mm which is defined as an engineering crack is inserted into the eccentric hole at the point of the maximum stress.Then,the stress intensity factor is calculated,and the crack propagation model,the propagation direction and the failure criterion are determined.Finally,the historical developments of the crack length,cycle number and stress intensity factor are obtained.Additionally,the calculated value of the crack propagation life at the eccentric hole of the turbine disk is also shown.(3)The fatigue crack initiation and propagation test of the turbine disk is performed using a spin rig facility.During the test,the test sample is periodically disassembled to carry out the fluorescence and penetration detection in order to detect the crack length before the disk is burst.After the rupture,the crack propagation characteristics on the fatigue fracture are obtained by the scanning electron microscope,and the fracture is calculated according to the Pairs formula.These experimental values of the fatigue life of crack initiation and propagation are obtained.These results show that these fatigue initiation life prediction are all within reasonable limits.The simulation can realize the analysis and prediction of fatigue crack initiation life.The results of the crack propagation simulation are consistent with the test in the initial position,the propagation direction and the front of cracks.The changes of the length of crack propagation are basically consistent at the beginning,and the results of the test are slightly smaller than the simulation during the latter period,but the overall changing trend is consistent.This paper combines fatigue testing technology and simulation analysis to carry out the related research.It hopes that this paper can provide reference for the follow-up research.