Research On Accelerated Lifetime Test Method For Aeroengine Mainshaft Bearing

High thrust-to-weight ratio,high reliability and long life have become the main development direction of aeroengines.The high performance requirements of aeroengines require the improvement of DN value of aeroengine mainshaft bearings.The high temperature and high speed conditions caused by the improvement of aeroengine performance make the abnormal failure rate of aeroengine mainshaft bearings larger.At the same time,with the progress of bearing materials and technology,The failure mode of aeroengine mainshaft bearings under severe conditions has changed from fatigue failure to coexistence of fatigue and early failure.However,our country still has a shortage of technical data reserve for aeroengine mainshaft bearing.The equal life assessment method and domestic life test ability can not meet the requirements of aeroengine mainshaft bearing which has developed from several hundred hours of limited life to tens of thousands of hours of long life assessment.Therefore,based on the analysis of failure modes of aeroengine mainshaft bearings,this paper proposes a method to establish the boundary of fatigue failure safety conditions.The accelerated life test theory and life equivalence method of aeroengine mainshaft bearings are tested on the developed aero-bearing test rig.These works have important theoretical significance and engineering application value for improving the reliability of aeroengine mainshaft bearings.Based on the theory of contact fatigue life calculation,the relationship between load and fatigue life was established on the premise of covering the requirements of aeroengine under harsh working conditions.The above contents are used as the theoretical basis for accelerated life test of aeroengine bearings.The fatigue life of aeroengine mainshaft bearings affected by high rotating speed and working environment temperature is analyzed.Because most of the aeroengine mainshaft bearings are early failure such as gluing,skidding and overheating,and the abrupt change of working conditions easily leads to the change of failure mode,in order to ensure that the failure mode of bearings is progressive and benign fatigue failure,The influence of working condition parameters of friction interface(such as load,rotation speed,etc.)on failure mode transformation is analyzed by pseudo dynamic method.Major dynamic parameters related to failure modes,such as contact stress,PVvalue and film thickness ratio,are selected as failure criteria.The failure modes caused by off-design conditions are predicted and the safety allowable boundary of accelerated life equivalent test is established,which provides theoretical basis and boundary constraints for accelerated life test and ensures the consistency of accelerated life test results.In order to meet the special requirements of aeroengine mainshaft bearing structure and critical condition assessment and avoid the huge time and capital cost of equal life test,a new type of aeroengine mainshaft bearing tester is developed in this paper.It can simulate high temperature,high speed and other harsh conditions,and can realize multi-load spectrum combined operation.It can complete high-speed performance test,durability life test and oil-break test of aeroengine mainshaft bearings,and provide an examination and verification platform for accelerated life test,reliability growth and condition adaptability evaluation of aeroengine mainshaft bearings.The dynamic performance of the test rig and the shafting stability are analyzed by the virtual prototype.The high-speed performance test and functional verification test show that it meets the simulation test requirements of aeroengine mainshaft bearings.The spectrum detection method of bearing fault vibration signal based on spectral kurtosis is proposed which can effectively identify the bearing fault vibration signal,In this paper,a certain type of aeroengine bearing is selected as the test sample to carry out equivalent accelerated life test under Type I censoring sample with constant stress in which the final failure mode is fatigue failure,and the more advantageous axial load is selected as the accelerated stress.The fatigue life under two stress levels was obtained,and the acceleration factor and the inverse power law Acceleration Formula of life were obtained by fitting the Weibull distribution function.Considering the cyclic and time-varying working conditions of aeroengine bearings in conventional test,the theory of bearing load equivalence and the theory of fatigue cumulative damage considering the loading sequence are introduced to link the accelerated bearing life test results with the conventional fatigue life.This paper provides a rapid evaluation method for the application of new materials,structural optimization verification,durability test of long-life bearings and accumulated basic failure data of aeroengine mainshaft bearings.It also provides a fast and scientific method support for the life extension,reliability growth and condition adaptability evaluation of aeroengine mainshaft bearings.