Research On Loading Spectra Compilation Methodology For Vehicle Four-channel Accelerated Simulation Test

Fatigue durability is always one of the most important performances of vehicle product.In order to shorten product development cycles and reduce development costs,the accelerate durability evaluation has become a primary method for vehicle companys to verify their products.The vehicle companys need to conduct accelerated durability tests during the validation phase to achieve fatigue life assessment as soon as possible.In order to truely simulate the actual condition and accelerate test process,this research will focus on vehicle four-channel accelerated simulation test and investigate the compilation methodology of loading spectra.Taking the spectrum measured in proving ground as an object,in this paper,a spectrum compilation methodology for vehicle four-channel accelerated simulation test is proposed based on traditional linear damage accumulation rule by considering the strengthening effect of loads below the fatigue limit.The main contents are as follows:(1)Measuring the spectra of multiple channels under proving ground,which supplied original data for the establishment of the accelerated test loading spectra.Synthesizes the finite element analysis results and test experience,One hundred and fifty-seven channels of signal were measured from standard driving cycles.In order to elemate the discreteness of the spectra,the spectra were measured by nine times.(2)Analyzing and comparing the signal characteristics of the nine groups of spectra within time-domain,amplitude-domain,frequency-domain and fatigue damage,so as to assessment the stability of total spectra.In traditional,the median fatigue damage spectrum is selected as the original target spectrum,yet this method is not reasonable in physics.Taking the minimum standard deviation spectrum as the original target spectrum is proposed in this paper.Upon 12 channels of spectra,the minimum standard deviation spectra of twelve conditions were located among nine groups of spectra.The original target spectra was established by connecting the minimum standard deviation spectra of twelve conditions.(3)Determining the omitting rule of non-effect loads for all channels.When developing the loading spectra for accelerated durability test,the non-effect loads should be omitted.Based on the feature of low-amplitude load strengthening,the non-effect loads at same phase in all significient channels was deleted;damage loads and strengthening loads are reserved,which ensure the time-domain,amplitude-domain,frequency-domain and fatigue damage of the accelerated spectra are accordant with the original target spectra.(4)Iterating accelerated spectra to generate loading spectra.First,using whitenoise signal to conduct feature test for system,which would obtain transfer function from the system.Then loading spectra could be reversed through accelerated spectra.So as to ensure the convergence process of the road system had enough buffer and response time,adding half-sine transition signals between every two working conditions to achieve smooth transition signals.(5)Conducting vehicle four-channel simulation test to verify the effectiveness and feasibility of loading spectra.Arranging vehicle in four-channel road simulator and carrying out accelerated test to vehicle with loading spectra in wheel coupling mode.The results showed that the vehicle four-channel simulation test had the same failure sites and failure modes with the proving ground test,and the test time was saved by 32% comparing to proving groung test.On the basis of the above summarizes,the paper proposed a loading spectra compilation methodology for vehicle four-channel simulation test,which would well reflect users' fatigue characteristics.The innovation of the works were mainly manifested as follows:(1)Considering low-amplitude load strengthening characteristics in the compiling process of loading spectra for vehicle four-channel simulation test,a rule for determining the non-effect loads was brought out.The non-effect load should be deleted and the strengthening load would be preserved;(2)The method of determining target spectrum,which comes from minimum standard deviation spectrum,was released in this paper.The target spectrum could simulate the actual road condition of proving ground;(3)The non-effect loads of each channel were deleted at same phase,so that the load sequences were reserved,thus the spectra could reflect the actual fatigue process of the vehicle tested under proving ground;(4)Proposing a loading spectra complation methodology for vehicle four-channel accelerated simulation test,this could be a reference for other areas in complation loading spectra.The results of this research were of great significance for enterprises to lift the vehicle evaluation ability and the product development level.