| In general, the typical structure of the white body usually contains up to 3000 ~ 5000 spot weld joints.There are serious stress concentration around the spot weld joints, fatigue crack is easy to form and expand. According to statistics, about 50% fatigue problems of the vehicle structure related to spot weld, about 80% fatigue problems of the body related to spot weld.Therefore, the spot weld joint 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.Today because of energy shortage, environment pollution and a series of important problems of human development in the 21 st century, reduce automobile weight, reducing fuel consumption has become the key to improve the competitive ability of different car manufacturers.As a result, the traditional low carbon steel is increasingly replaced by high strength steel, which can reduce the vehicle weight under the premise of not reduce the body strength and stiffness and various performance targets. Hence related research work of the fatigue simulation prediction method for high strength steel spot weld joint is done in this background.As there exist that prediction accuracy is not high, modeling and computation efficiency is low and some other issues for the traditional simulation methods of spot weld joint fatigue life—LBF method based on force and LMS method based on the stress, a new fatigue life prediction method for spot welds is proposed in this paper, which considers the fatigue failure of spot welds from the point of fracture mechanics. A modular spot weld model is adopted, an average stress intensity factor through the thickness crack propagation path is proposed as the evaluation parameters of fatigue life in this paper.And shear fatigue test is implemented for two high strength steel—high strength low alloy steel(HSLA340GI) and dual phase high strength steel(DP600GI), four different thickness resistance spot weld joints, and comparative analysis of prediction accuracy is implemented among these three method.The main research content is as follows:(1) the research status of high strength steel resistance spot welding is introduced, and the research status of spot weld fatigue life prediction is briefly described, the development process of fatigue theory is introduced, and it is pointed out that the traditional forecasting method cannot be directly applied to the spot weld joint fatigue life of high strength steel.(2) a modular spot weld joint modeling method is adopted. Compared with the traditional LBF and LMS spot weld joint modeling method, the model can accurately simulate the actual spot weld location, more in line with the physical and geometric features of spot weld joints, and will not reduce the modeling and computational efficiency. More accurate results can be obtained using this model to predicte the fatigue life of spot weld joints.(3) An average stress intensity factor through the thickness crack propagation path is adopted as the evaluation parameter of spot weld fatigue life, shear fatigue test is implemented for two high-strength steel—HSLA340GI and DP600 GI, four different thickness resistance spot weld joints, the fatigue life data of different spot weld samples is obtained. Through the regression analysis between DK and fatigue life data, a master DK- N curve can be obtained, then comparative analysis of prediction accuracy is implemented among these three method, the results show that the proposed spot weld fatigue life prediction model can effectively predict the fatigue life of high strengh steel spot weld joints, and the prediction precision is higher than the traditional LBF and LMS method.This paper's studies show that: the spot weld joint fatigue life simulation prediction model proposed in this paper can can effectively predict the fatigue life of high strengh steel spot weld joints, and the prediction precision is higher than the traditional LBF and LMS method, has high engineering application value. |
PDF Full Text Request