Fatigue Life Prediction Of ST12 Steel Tensioning And Weldment

Resistance spot welding is one of the important methods for jointing of sheet metals, because of its simple operation, low cost, high efficiency and easiness to be automatic controlled, which make it very suitable for mass production, it is widely applied in various fields in today’s manufacturing industries. However, spot welded structures always work under multiaxial stress and complicated load cases, the mechanical analysis and fatigue life prediction of which are very difficult, making the study of fatigue and cumulative damage properties of the welded structures of great significance. This article concerns the tension-shear lap joints made of ST12 low carbon steel, which were tested under the constant amplitude loading and multi-stage loading cases with MTS fatigue test frame .The paper mainly studied the following aspects:1.On the basis of spot welding specimen fatigue strength experiments, the elastic-plastic finite element analysis was carried out for the specimen, based on fracture mechanics analyzed the stress intensity factor distribution around the joint nugget of the specimens. Compared the finite element analysis results with experiment data for crack initiation location, analysis results showed that fatigue crack of spot welded specimens initiateat a certain distance from the notch root. for the band gap of spot welding structure, and compared2.Based on fatigue durability analysis software nCode, life prediction for spot welds under constant amplitude loading component were carried out. Analysis using finite element analysis method based on the structural stress, the other analysis using the s-n curve based on BS7608 standard selection method, the last using the based on the experimental data fitting s-n curve of life prediction methods were compared to the methods..3.this part is analyzed with the experimental data under the two level loading by linear cumulative damage criterion of fatigue,based on the stress ratio and load level of two-stage fixed Miner rule under load, and carries on life prediction.Through a nonlinear fatigue cumulative damage rule and double linear fatigue cumulative damage rule of two-stage loading experiment to predict the fatigue life under loading, and the linear cumulative damage under the secondary load of the fatigue life prediction of contrast and analysis of nonlinear and bilinear criterion on the prediction accuracy and the applicability of spot welding structure.Analysis of nonlinear cumulative damage formula of the selected parameters and cut-off double linear cumulative damage parameter for life prediction.