Research On Accelerated Fatigue Spectrum Editing Methods Of Multi Axial Random Vibration

Due to the effects of track irregularity or other factors, Vehicle is subjected to random vibration loads during working. Facilities and structures on the vehicle become failure easily under such complex loads,thus posing a grave threat to passengers' life and property safety. To guarantee the high reliability of structure, fatigue tests shall be conducted in the initial physical design stage to predict fatigue life. Rig tests with the actual load spectrum always cost plenty of time and human resources. So, how to edit the actual load spectrum to get an accelerated compressed one, which can cause the same damage as the former and could be applied in practical rig tests, is of great significance for time saving and shortening development period.In this paper,methods about preprocessing of spectrum and theories correlated with random vibration as well as some parameter definitions were introduced. When subjected to combined loadings, structure stress state behaves as a multi-axial form. At present, to predict the fatigue life of a structure under multi-axial stress state, convert methods transforming multi-axial stress state to uniaxial were adopted. So, equivalent methods for stress and stress power spectral density were introduced. Technology roadmap was created for calculating fatigue life in time domain and frequency domain respectively.In this paper, the principles of accelerated methods in time domain and frequency domain were introduced. Time correlating damage editing method and equivalent damage method were adopted. Stress time series were classified to three different levels,to which optimal parameter values for accelerate editing were obtained respectively. Results were used to acquire accelerated test load spectrum from actual measured load spectrum in time domain and frequency domain respectively. Frequency content, extreme response spectrum and shock response spectrum were compared. Results showed that accelerated spectrum can keep the same failure mechanism and similar frequency content.In this paper, the finite element model of vehicle auxiliary installation support subjected to multi-axial load was established by considering the real load condition. Weld fatigue damage was calculated in time domain and frequency domain respectively when structure was driven by actual measured load and accelerated load. 20 most damaged elements were listed before and after accelerating with maximum error 1.04% in time domain and 8.55% in frequency domain. The results indicated that accelerated spectrum did not change the failure mechanism, caused almost same damage and got a same damage distribution as the original spectrum.