The Study Of Fatigue Life Simulation Prediction Method For High Strength Weld Joints Based On Average Equivalent Stress Intensity Factor

Generally speaking, the welding structure have the advantages of high strength,high design flexibility, good sealing, easy processing connection and easy to realize automation. Welding is the main connection way of the vehicle body, the frame and the chassis. At present, the weight of welding structure has account for more than half of the total output of iron industry, even the proportion is close to 70% in developed countries. As the main component of the welding structure, the fatigue life of the welded structure is determined by the welded joints. According to the statistics, about90% of the vehicle structure damage caused by fatigue. Therefore, the weld joints fatigue life prediction by means of computer aided analysis in the early stages of the design has important practical significance in effectively reducing the production cost,shortening the auto design development cycle and improving the quality of products.With the rapidly development of the automobile industry, the resulting energy shortages, environment pollution and series of problems are becoming more and more serious. Therefore, reducing the weight of vehicle, fuel consumption and emission becoming the key to the automobile industry. High strength steel has become promising application of lightweight materials. Therefore, the study of the fatigue simulation prediction method for high strength steel weld joint is done in this background.At present, the fatigue simulation analysis method of the weld joints are mainly the nominal stress method and the normal structure stress method. As the limitations in application and the prediction accuracy is not high, this article proposes a new fatigue life prediction method, this method is based on the theory of fracture mechanics, figures out the structural stress of the weld crack, then calculates out a average equivalent stress intensity factor (?) through the weld crack propagation path as the evaluation parameters of fatigue life. Through conducting shear fatigue test for two high-strength steel—DP800GI and HSLA350 GI resistance welding joints,conducting comparative analysis of prediction accuracy with the nominal stress method and the normal structure stress method, the results show that the prediction accuracy of fatigue life forecasting method of welds joints in this paper is higher. The main contents of this paper are as follows:(1) The research status of high strength steel welding is introduced, and thefatigue life prediction method of the weld joints are briefly described. The theoretical basis of the fracture mechanics and the fatigue theory are summarized.(2) Introducing the traditional method of the weld seam, pointing out that the simulation is not accurate, modeling and calculation of low efficiency, and introducing the method of weld seam modeling in this paper.(3) Extracting the node force and moment around the welding lines through the finite element, figuring out the structural stress of the weld crack, and calculating out an average stress intensity factor (?) through the weld crack propagation path as the evaluation parameters of fatigue life.(4) Conducting shear fatigue test for two high-strength steel DP800 GI and HSLA350 GI resistance welding joints, obtaining a master (?) curve as the fatigue life prediction curve for welds joints, conducting comparative analysis of prediction accuracy with the nominal stress method and the normal structure stress method.This paper studies show that: the fatigue life prediction method for weld joints based on average equivalent stress intensity factor can predict the fatigue life of the weld joints effectively and the prediction precision is higher, has high engineering application value.