Notice of RetractionDamage tolerance analysis of jet engine compressor disk using FEM

Abstract

Traditional, jet engine manufacturers have used a life estimation procedure known as the “initiation criterion” to determine the safe lives of engine rotary components such as disks, shafts, etc. This criterion is used to determine the safe life of low cycle fatigue life limited components. The inadequacy of this approach led to the development of the damage tolerance based maintenance methodologies. Once the design life has been exhausted, the components are inspected for service induced damage. If a component is found to contain a flaw or crack then it is retired from service.Main goals of this study is to determine the retired jet engine compressor disks conditions, the stress concentration sites, stress intensity factors and detect probable cracks in the disks. To cover all the objectives, ten retired disks were selected. Firstly, mechanical tests and material tests applied on standard samples from two destructed disks. Secondly, the disk model designed and imported to ANSYS, then the disk properties added to the model. Moreover, boundary conditions and loads concluding 4672 rpm rotational speed, fixing supports at two sets of bolt holes, etc. added to the model. To decrease calculation time, only 30 π of the disk were analyzed. Thirdly, 3D standard imaginary cracks were modeled at the stress concentrations areas. Calculating the stress intensity factors and determining the vulnerable to crack sites was the end of the third part. At last, NDI tests containing human visual inspection and eddy current test were performed on eight remaining disks. Mechanical and chemical tests showed 5% reduction in the disk UTS and yield stress but the composition remained nearly unchanged comparing with original disk (AMS6305). Disks average hardness was 36.7 HRC which is in the standard range. 3D finite element analysis indicated that maximum stress (VonMises) occurred at the first row of bolt holes and maximum displacement was at the same point. Stress concentrations at the two sets of holes were 2.08 and 2.25 respectively. 3D Crack analysis results indicated that stress intensity factor approximately increases linearly with crack growth. As the results of visual inspection, two disks were rejected having surface scratches nears the maximum stress area and one disk rejected due to detected crack in eddy-current test. Generally, fifty percents of retired compressor disk returned back to engines for 600 hours of working before next RTS (return to service) time.