Study On Accelerated Load Spectrum Of Helical Spring Fatigue Test Based On Damage Equivalent

With the development of my country’s auto industry,encouragement of cars into the family and the implementation of a series of related policies,the penetration rate of family cars has been continuously improved,and people’s requirements for cars have also increased.Among them,people’s comfort,safety of cars and cost-effective requirements are also constantly prompting car companies to seek breakthroughs by improving the performance of auto parts.Coil spring is a more important part of vehicle parts.It connects the axle and the frame in the form of elastic connection,and bears the impact force of the axle or the frame on it when the road surface is uneven.The performance of the coil spring greatly affects the comfort and safety of the car,so the fatigue durability test of the coil spring is particularly important in the test of auto parts,and its durability is naturally widely concerned by consumers.In order to reproduce the durability problem of the coil spring in the road test field and the problem of the long fatigue endurance test cycle of the current coil spring,a method for compiling the accelerated load spectrum of the coil spring fatigue test based on damage equivalent is proposed.The test results show that,the load spectrum compilation method reproduces the problem of spring fracture in the road test field,and effectively compresses the time of the fatigue durability test of the coil spring,which improves the research and development efficiency of the coil spring.The innovations and specific contents of this paper are as follows:1.Paste the strain gauge on the coil spring,and calibrate it on the universal material testing machine to obtain the relationship between spring force and strain,spring displacement and strain,and the true stiffness of the spring.Then,based on the damage-equivalent load spectrum acquisition technology,the load spectrum data of the structural durability-enhanced road is collected at the Tongzhou Vehicle Test Site in Beijing,the collected data is preprocessed,and the spring load spectrum data that we need to study is extracted.2.Convert the spring strain signal into a stress signal according to the relevant theory,use the rainflow statistical method to count the load spectrum of the coil spring,analyze the load distribution law based on the rainflow statistical results,and estimate the probability density of its load amplitude and load mean value.function,and proved their independence by the chi-square contingency method,and then extrapolated the load spectrum based on the damage equivalence principle according to the load statistics.3.The S-N curve of the coil spring is fitted by the piecewise fitting method,and then based on the damage equivalent theory,the damage calculation method based on the equivalent load extrapolation method is adopted.On the basis of the extrapolated load spectrum,combined with the eight-point Gauss-Legendre integral The damage calculation of the coil spring is carried out by the method.4.According to the calculation results of the fatigue damage of the coil spring,the small load spectrum is truncated,a large number of cycles are reduced,and most of the load damage of the coil spring is retained to achieve the effect of acceleration.Then,on the basis of the truncated load spectrum,according to the Conover study,the load amplitude and the load mean can be divided into eight levels,but due to the truncated data,it is only divided into an 8×7 load matrix,that is,a two-dimensional load spectrum.Then,according to the damage equivalence principle,the damage equivalent of each graded area is converted into the cycle times of the maximum damage point,so that the load spectrum of the coil spring is accelerated again.5.Finally,according to the results of the coil spring in the universal material testing machine,the stress load spectrum of the coil spring is converted into the displacement load spectrum required for the test.The final test results show that the accelerated load spectrum test studied in this paper can reproduce the helical The spring cracked in the road test field,and the test cycle of the bench was greatly reduced compared to the original bench test.