A Study On Fatigue Properties Of Centrifugal Compressor Impeller In Very High Cycle Fatigue Regime

Large-scale centrifugal compressor,an important energy conversion device,is widely used in a great many industrial departments.Because of the complicated working conditions and high speed of compressor impeller,the uniformity of dynamic load distributions on blades gets worse,which can result in fatigue failure of blades easily.Considering the complicated structure,high cost and poor substitutability of impeller,remanufacturing has become an imperative way to save energy and reduce costs.In order to provide a theoretical basis for remanufacturing,it is needed to know the mechanical and fatigue properties of blades.However,centrifugal compressor is often designed to operate at least ten years,which is in very high cycle fatigue(VHCF)regime.At present,research about fatigue properties of impeller in our country is few,especially in life prediction of FV520B-I high strength steel,a common material for blades,in VHCF regime.Consequently,the mechanical properties of blades and the fatigue properties of FV520B-I high strength steel in VHCF regime were studied in this paper to provide theoretical basis for remanufacturing.Firstly,dynamic load and stress distribution on blades in three different working conditions were analyzed by Fluent software,which identified the significant influence of air flow turbulence on mean stress and stress amplitude of blades and gave an explanation for fatigue failure of blades.According to the analyzed results and fracture damage mechanics,the stress and displacement fields as well as the stress intensity factors at the crack tip were calculated,which confirmed the most dangerous site of blade and the predominant type of crack.Then,ultrasonic fatigue tests were performed on FV520B-I high strength steel.According to fracture morphology analysis,the mechanism of fatigue failure in VHCF regime was discussed and the influence of characteristic sizes like size of nonmetallic inclusions,on fatigue properties was analyzed.Besides,the fatigue limit of FV520B-I high strength steel at 109 cycles was predicted based on those characteristic sizes.What’s more,a life prediction model of FV520B-I high strength steel in VHCF regime was obtained based on classic life prediction models and related theories.The predicted results agreed well with experimental results.At last,considering the existed evaluation models of remanufacturing comprehensively,the remanufacturability evaluation of impeller was performed.Through the study of this paper,the fatigue properties of compressor impeller in VHCF regime is known better,which provides a good theoretical basis for impeller remanufacturing.