Life Prediction Of Vibration Fatigue Based On Multiaxial Stress Equivalent

Under the dynamic load,the local part of the aircraft will produce a large response,and the resulting fatigue damage is one of the main forms of structural damage.Therefore,it is very significant to analyze the vibration fatigue life of the typical structure of the aircraft under random dynamic load excitation.In this paper,the life prediction of aircraft structures under complex stress is estimated from the perspective of multiaxial stress equivalent,in order to achieve more accurate prediction of multiaxial vibration fatigue life.In the multiaxial stress equivalent method,the multiaxial stress is equivalent to uniaxial stress according to the Von Mises equivalent method,and the structural damage caused by multiaxial stress is converted into equivalent by the bias stress projection method(PBP method).The uniaxial stress structure damage,and the existing uniaxial vibration fatigue calculation method in the frequency domain is used to estimate the life of typical aerospace structural parts,and the multi-axis fatigue life prediction problem under random loading is solved.In order to verify the accuracy of the multi-axis life prediction method,a random multi-axis vibration fatigue experiment was carried out in this paper.Different working conditions were set to investigate the variation of the life of the test piece under different loading conditions.The test piece was LY12-CZ aluminum alloy,and then in the same case of boundary conditions,the finite element analysis is carried out to obtain the stress danger parts and estimate the vibration fatigue life.In this process,PBP method and Von Mises method are used to study the variation of vibration fatigue life under different multiaxial stress ratios and different correlation coefficients,and the following conclusions are drawn: on the one hand,the closer the ratio of normal stress and shear stress to the structure is,the closer it is to life.The shorter the load correlation coefficient is,the shorter the life is.On the other hand,although the life predicted by the Von Mises method and the PBP method are within 5 times of the error range,the normal stress and the shear stress of the material are close.Or the life expectancy of the Von Mises method is greatly deviated from the experimental results when the correlation coefficient is low,and the life prediction error of the PBP method is within 1 time.It can be considered that the PBP method is a more accurate and efficient multiaxial stress equivalent.method.