Research Of Load Spectra Editing Method Based On The Wavelet Transform To The Durability Tests Of Automotive Steering Knuckles

Fatigue durability is one of the important performance of vehicles,and it is directly related to the safety for driving.According to statistics,more than 90% parts of a vehicle are damaged by fatigue.Once fatigue damage occurs in vehicles,it will be very dangerous.Therefore,in order to improve the safety performance of automobiles,higher requirements should be placed on the fatigue durability for vehicles,and the study of fatigue durability testing and simulation technology is particularly important.It is urgent to explore a set of engineering methods with high accuracy and low cost for fatigue life prediction.The accuracy of durability analyses is determined by the quality of load spectra.Accelerated editing for load spectra is an important part of durability analyses,and it affects the efficiency and accuracy of durability analyses.There are many methods for accelerated editing and they have different characteristics for obtaining accelerated spectra.In addition,the quality of accelerated editing is closely related to the editing method and its parameters.The key technology in accelerated editing is still an important issue that needs to be investigated in further detail.Accurate and efficient editing methods are of great significance to improve the efficiency and quality of durability analyses.To improve the accuracy of durability analyses effectively and shorten the vehicle development cycle,the road durability tests of vehicles are combined with simulation analyses.The results are compared with fatigue endurance bench tests.In this paper,the research object is an automotive steering knuckle.The aim is to edit road load spectra collected at an automotive test site.The research method combines techniques such as load decomposition and reconstruction,finite element analysis and fatigue damage calculation.The main works in the dissertation are listed as follows:(1)The basic theories of wavelet transform are introduced,and the cause of energy leakage in discrete wavelet transform are discussed.The band range of wavelet coefficients is clarified using the Nyquist frequency interval,and more detailed calculation methods are proposed for the energy leakage intensity of wavelet detail coefficients and approximation coefficients respectively.The wavelet parameters affecting the results of discrete wavelet transform are discussed,and a method for selecting the optimal wavelet parameters based on energy leakage is proposed.The choice of optimal wavelet parameters for the durability load spectra of vehicles components is clearly defined mainly in the choice of vanishing moments.(2)The characteristic parameters(damage retention,statistical parameters,power spectral density)of vehicles durability load spectra are discussed and acceptable error ranges for those characteristic parameters before and after accelerated editing are specified.The principle of the rainflow counting method is discussed and an improved threshold processing method based on rainflow counting method is proposed for accelerated editing of vehicle components load spectra.Based on the above selection of optimal wavelet parameters and improved threshold processing method,an accelerated editing method for vehicle components load spectra is developed and programmed to form a complete editing process in Matlab.(3)A complete vehicle durability road test is conducted at an automotive test field.To ensure the accuracy of load spectra,the collected load spectra are filtered,resampled and validated.The optimal wavelet parameters are selected for the durability load spectra of vehicle components by using the proposed method based on the energy leakage.The chosen wavelet parameters are used to perform the proposed accelerated editing method based on the wavelet transform for the load spectra.In order to verify the theoretical effectiveness of the proposed method for editing the durability load spectrum of vehicle components based on wavelet transform,the obtained accelerated load spectrum is compared with the original load spectrum in terms of signal time compression ratio,statistical parameters(mean,root mean square and cliff coefficient),power spectral density and rainflow counting results respectively.(4)A finite element model of steering knuckle is established.Inertia release analysis is carried out to obtain the stress distribution of steering knuckle under unit load.Based on the fatigue load spectra of the steering knuckle,the finite element analysis results and the S-N curves of material,fatigue life simulation analysis is carried out in n Code software to obtain the fatigue damage areas and points of the steering knuckle.In order to verify the practical effectiveness of the durability load spectra editing method based on wavelet transform for vehicle components proposed in this paper,the original and accelerated load spectra are used as excitation loads to calculate fatigue damage of the steering knuckle,and the accuracy of accelerated spectra is evaluated by the damage error and damage retention.