Test Study On Fatigue Property Of Thin Steel Sheet For Automobile

Automobile steel sheets mainly resist impact and pressure. However, the fatigue property which can not be neglected is also one of the significant factors. Continuous vibration happens all over the steel sheets while the vehicle is in motion. Especially, the classis of the vehicle could generate fatigue damage step by step under the condition of cyclic loading. Hence, in the condition above, the fatigue property becomes particularly important.The main research mission in this paper is to launch tests on fatigue property of four kinds of steel sheets. The detail content is shown as below:The first part:the tensile test is conducted on the thin steel sheets named SAPH440, B340LA, DP590and DC04in order to acquire the yield strength, the tensile strength, the modulus of elasticity and the elongation after fracture.The second part:the up and down method is conducted under the stress ratio0.15and the cycle-index107. The confidence level of test is90%and the failure probability is10%. The fatigue strength limits for the steel sheets are calculated from the test results. The grouping test is conducted in higher stress region in order to gain the fatigue life, S-N curve and the inferior limit of fatigue life. The confidence level of grouping test is90%. The whole fatigue data for each kind of steel sheet is collected and fitted to achieve the total S-N curve. The fatigue strength limit and the total S-N curve for B340LA and DP590are determined through the improved stress step under the stress ratio0.15and the cycle-index107, according to the mean value and standard deviation of fatigue strength which are obtained from the front tests. The confidence level of the improved up and down method is50%. The inferior limit of fatigue life and S-N curve in the higher stress region for SAPH440and DC04are acquired through the grouping test under the stress ratio0.2. The confidence level of grouping test is90%and the failure probability is10%.The third part:the software Patran2010and MSC.Fatigue are adopted to simulate and analyze the static mechanical property and fatigue property of fatigue sample for thin steel sheet named DP590under the stress ratio0.15and the failure probability50%. The distribution of static stress and the fatigue life is got from the fatigue analysis under two kinds of stresses at the ends of geometrical modal.