Study On Structure And Fatigue Strength Evaluation Method Of Commercial Vehicle Battery Box Bracket

In the field of vehicle,aerospace,engineering machinery,the fatigue life evaluation of metal parts has been a hot topic.The existing fatigue life evaluation of metal products is mainly obtained by collecting the surface stress of components,combining the fatigue life curve of materials and rain flow counting,the internal damage in the process of parts processing and manufacturing can’t be fully considered,which leads to a large deviation between the predicted life and the actual failure data.In order to solve these problems,a new method based on component’s strain-life curve is proposed to improve the precision of fatigue strength evaluation.The findings are as follows:(1)According to the failure position of π bracket of battery case in vehicle test,the load data of bracket are collected and analyzed on different road surface of test field.Taking the strain signal of failure position as the iterative target,the single-axis bench road simulation test is carried out to reproduce the failure phenomenon of the π-shaped bracket,the failure mileage of the bench is consistent with the cracking mileage of the real vehicle test.(2)A fatigue life evaluation method based on component strain-life curve is proposed to solve the problem of over-reliance on material strain-life curve and low evaluation accuracy.First,the load of the battery box bracket is classified by rain flow counting.The results show that the damage of the third load,which only accounts for 0.27% of the total load,is 99.5% of the total damage,the constant amplitude bench test was carried out,and the strain-life curve of π support was calculated by using double logarithm fatigue life equation,the strain-life curves of materials and components are used to evaluate the fatigue life of the π-shaped bracket.The results show that the prediction error of fatigue life based on the strainlife curves of materials is 31.3 times,the prediction error of fatigue life based on the strainlife curve of components is 2.8 times.The accuracy of the fatigue life evaluation method presented in this paper is greatly improved.(3)Aiming at the position of fatigue failure of π shape support,the optimal design of π shape support structure is made into II shape support.Firstly,the finite element analysis of the π and II shaped scaffolds is carried out by using Hyper Work software.The life of the II shaped scaffolds is estimated according to the maximum stress.The results show that the life of the II shaped scaffolds is increased by 9.9 times.Then,the fatigue life is increased from 3.6 hours to 23 hours in the electromagnetic shaking table test.The fatigue life evaluation method proposed in this paper provides a reference for the fatigue life evaluation of metal structures,and has certain engineering application value in the fields of vehicles,engineering machinery,aerospace and aeronautics.