Research On The Impact Of The Stamping Process On The Fatigue Performance Of Auto Body Structures

The auto-body is mostly made by cold stamping. This paper discusses the influence of stamping on fatigue performance of auto-body mainly from the two aspects of thickness thinning of sheet metal and residuary deformation by stamping.This article reads as follows:The article describes the history of fatigue, the status of the influence of stamping on fatigue performance of auto-body structure and the main contents of this article. This paper makes a finite element analysis and fatigue analysis of auto-body structure mainly from the two aspects of the thickness thinning of sheet metal and residuary deformation by stamping and makes a proper evaluation of fatigue performance of auto-body structure.The article makes a systematic research on the process and method of fatigue analysis and describes in detail the two most commonly used fatigue lifetime prediction models---the nominal stress method and the local stress-strain method. Researches are made on the two different analyses based on quasi-static and transient response. Detailed study of the basic principles, the choice of methods, modal truncation, data sampling and procedure analysis of the transient response analysis is made to make a preparation for the subsequent fatigue analysis. Researches are made on the vibration fatigue analysis based on the frequency response and lay the foundation for the research of fatigue lifetime of the cab structure by the use of vibration fatigue analysis.The article mainly studies the influence of stamping process on the fatigue performance of material. Through the tension test of pre-stretch specimen, yield limits and persistent fatigue limits are measured under different pre-deformation. And through the Gerber amendment, persistent fatigue limits are measured under symmetric loop. In order to get the pre-deformation by stamping simulation and pre-stretch deformation unified, the engineering strain by pre-stretch deformation will be changed into a true strain. By curve fitting of the relation between true strain and the yield limit and the relation between true strain and endurance limit, curving fairing is obtained. Finally, by simplifying the material S-N curve and curve fitting, S-N curve is obtained through different pre-deformations, which makes a preparation for the simulation of fatigue analysis.The article firstly analyzes the components of auto-body for formability analysis, and then thinning volume and residuary deformation volume are obtained. Through programming by FORTRAN language, thinning volume and residuary deformation volume are introduced into structural analysis and fatigue analysis. Then based on quasi-static, transient response and frequency response analysis, this paper makes a research about the influence of stamping on fatigue performance of auto-body structure. The results shows that by the use of the above three methods, the distribution of high stress is nearly the same, the maximum stress is increased slightly, and the minimum fatigue lifetime has an increase of 130%. The result indicates that the reinforcing of fatigue performance of material by stamping residuary deformation is greater than the weakening of that by thinning of sheet metal. Because the natural frequency of random load spectrum is close to the first natural frequency of outer beam pillar, the fatigue lifetime calculated by quasi-static method is longer than that calculated by transient response method. Then the quasi-static method is no longer applicable. The results of fatigue analysis based on transient response and frequency response are very close, which indicates that vibration fatigue analysis based on frequency response analysis is available under random load. The calculating speed is high, and little memory is needed, which are not possessed by fatigue analysis based on transient response.Taking the above outer plate beam as a typical component, this paper analyzes the fatigue lifetime of the cab under random loading, and makes a research about the influence of stamping on fatigue performance of auto-body structure by the method of vibration fatigue analysis. The result shows that, considering the effect of stamping, the fatigue lifetime was increased by 29.7%. Although the lifetime increase is less than the rate of increase of a single piece, it also indicates that stamping is ignorable in strengthening the auto-body structure.The article summarizes the whole passage, including the main research methods and contents, and draws a consistent conclusion that stamping can help to improve the fatigue performance of auto-body structure. At last, inadequacies of this article are prospected in order to get more accurate fatigue lifetime.