Transient Fatigue Analysis Of Subframe Based On Finite Element System Model

Due to the tough competition of current automobile market,product quality has become the core distinguisher among major OEMs.In modern automobile design process,the development of automobile chassis is critically important.For most of the time,the quality of chassis can determine the positioning of OEM in the market.Considering the chassis performance,component fatigue life is an important index in chassis development.In the product development stage,focus on the accuracy and effectiveness of solution of chassis parts fatigue and durability issues can shorten the development cycle,reduce the cost of product development,and improve the competitiveness of vehicle models.In the traditional fatigue analysis,the random loads of the corresponding parts are mainly extracted from the dynamic software such as Adams.The analysis and calculation are done by the quasi-static fatigue analysis method.This method can be applied to the structure whose first natural frequency is more than three times of the load frequency,but it is not suitable for solving the nonlinear fatigue problems involving large deformation and part contact.This difficulty rises from the fact that Adams and other dynamic software are written based on the multi-body dynamic algorithm,which has inherent defects in the accurate simulation of flexible body structure.At the same time,Adams multi-body analysis can only provide random load for fatigue analysis,but not the stress results of components.Therefore,it is necessary to use unit load for static calculation to obtain the stress results of components,and then combine with the fatigue theory to calculate the fatigue life of the components.Because the analysis accuracy of components depends on the factors of load,material curve(S-N curve)and stress analysis results,the tradition method of load and stress analysis results have to transform,and certain errors will be introduced into the process.Therefore,it is necessary to develop a new method to solve the problem of load and stress analysis simultaneously.Based on the prior statement,we can take the traditional Mc Pherson suspension as the research object,simulate the connecting parts of suspension such as bushing,shock absorber,spring,buffer block and ball joint by the connection unit of ABAQUS software,which also provides the material properties for the connecting parts by the component test done in the laboratory,and establishes the finite element suspension assembly model including the nonlinear effect and part contact.Through the actual road test of the test vehicle in the test site,the road spectrum data are collected and processed.Taking the processed six component load data of wheel center as input,the direct transient response analysis of chassis system is carried out by using finite element software ABAQUS.Based on the results of transient response analysis,the transient fatigue analysis of sheet metal and weld joint of subframe is carried out in the software n Code.At the same time,in the unqualified transient fatigue analysis,a complete set of optimization process of the subframe system performance is established.Using the optimization software mode FRONTIER,the optimization method and the opportunities of optimization can be quickly identified.It provides accurate and effective optimization design for unqualified subframe,greatly reducing the difficulty of optimization work,and accelerating the development process.In the following chapters,a direct transient response analysis model of suspension system based on ABAQUS is established.Comparing to the dynamic model of Adams,the ABAQUS suspension model has higher accuracy,and the numerical efficiency also improves to meet the engineering requirements.In the transient response analysis of suspension,the motion of the system and the stress and strain of the high-risk locations can be monitored in real time.Then,the occurring time and the possible position of the troubled area in the system can be visualized,and the material exceeding its yield point can be effectively identified.To conduct the fatigue analysis of the subframe,it requires the local strain method.The results of ABAQUS transient response analysis also accurately capture the stress and strain on the subframe,which help improves the accuracy of fatigue analysis.In the process of optimization,to assure the accuracy and efficiency of optimization process,and provides sufficient support and guarantee for the effective improvement of the subframe design,we can selectively intercept the time period of great influence on the stress results of transient analysis in the load spectrum.Later,a set of effective and high precision fatigue analysis method is established for suspension system to solve critical issues for traditional chassis component analyses.