基于平均应力强度因子的高强钢焊点疲劳寿命仿真预测方法研究

发布时间：2018-07-25 15:05

【摘要】：一般情况下,典型的白车身结构通常含有多达3000~5000个焊点。焊点周围存在较严重的应力集中,疲劳裂纹易于形成和扩展,据统计大约50%的汽车结构的疲劳问题和焊点有关,大约80%的车身疲劳问题和焊点有关。因此,在设计的早期运用计算机辅助分析的手段,对焊点进行疲劳寿命预测,对于有效降低生产成本,缩短汽车设计开发周期,提高产品的质量有着重要的现实意义。现今面对能源短缺、环境污染等一系列21世纪人类发展的重要问题,减轻汽车自重、降低燃油消耗已成为各大汽车生产商提高竞争能力的关键。因此,传统的低碳钢正越来越多地被高强度钢所取代,它能够在不降低车身强度、刚度等各项性能指标的前提下,减少车身重量。本文正是在此背景下对高强钢点焊接头的疲劳仿真预测方法展开相关研究工作。针对传统的基于力的LBF方法和基于应力的LMS方法这两种焊点疲劳寿命仿真预测方法所存在的预测精度不高、建模和计算效率偏低等问题,本文提出了一种新的焊点疲劳寿命仿真预测模型,从断裂力学的角度考虑焊点的疲劳失效,采用一种模块化焊点模型,提出了一种焊点裂纹在板厚扩展路径上的平均应力强度因子DK作为疲劳寿命的评价参量。选择目前常用的高强度低合金钢(HSLA340GI)和双相高强钢(DP600GI)这两种高强钢材料、4种板厚组合的电阻点焊接头进行了剪切疲劳试验,并与传统的LBF和LMS方法进行预测精度的对比分析。主要的研究内容如下:(1)介绍了高强钢电阻点焊的的研究现状,简要叙述了点焊接头疲劳寿命预测的研究现状,介绍了疲劳理论的发展过程,指出传统的焊点疲劳寿命预测方法无法直接应用到高强钢焊点疲劳寿命预测中。(2)采用了一种模块化焊点建模方法,相对于传统LBF和LMS方法所采用的焊点模型,该模型可以准确模拟焊点实际位置,更加符合焊点的物理几何特征,并且不会降低建模和计算效率,运用该模型进行焊点疲劳仿真分析能够获得更准确的疲劳寿命预测结果。(3)采用焊点疲劳裂纹在板厚扩展路径上的平均应力强度因子DK作为焊点疲劳寿命的评价参量,对HSLA340GI和DP600GI两种高强钢材料、4种板厚组合的电阻点焊接头进行了剪切疲劳试验,得到了不同点焊接头样件的疲劳寿命数据,通过DK与焊点疲劳数据的回归分析,得到一条主DK-N曲线,并与传统的LBF和LMS方法进行了预测精度的对比分析。结果表明本文提出的焊点疲劳寿命仿真预测模型能够有效预测高强钢点焊接头的疲劳寿命,且预测精度高于传统的LBF和LMS方法。本文研究表明:本文提出的基于平均应力强度因子的焊点疲劳寿命仿真预测模型能够有效预测高强钢点焊接头的疲劳寿命,并且预测精度高于传统的LBF和LMS方法,具有较高的工程应用价值。
[Abstract]:Typically, a typical white-body structure contains as many as 3, 000-5, 000 solder joints. There is a serious stress concentration around the solder joint, and fatigue cracks are easy to form and expand. According to statistics, about 50% of the fatigue problems of automobile structures are related to solder joints, and about 80% of the body fatigue problems are related to solder joints. Therefore, in the early stage of design, using the means of computer aided analysis to predict the fatigue life of butt welding spot is of great practical significance to effectively reduce production cost, shorten the period of automobile design and development, and improve the quality of products. In the face of energy shortage, environmental pollution and a series of important problems of human development in the 21st century, reducing auto weight and fuel consumption has become the key to improve the competitiveness of automobile manufacturers. Therefore, traditional low carbon steel is more and more replaced by high strength steel, which can reduce the weight of body without reducing the body strength, stiffness and other performance indexes. In this paper, the fatigue simulation prediction method of spot welding joint of high strength steel is studied in this paper. The traditional force-based LBF method and the stress-based LMS method are used to predict the fatigue life of solder joint. The prediction accuracy is not high and the efficiency of modeling and calculation is low. In this paper, a new simulation model for predicting the fatigue life of solder joint is proposed. The fatigue failure of solder joint is considered from the point of view of fracture mechanics, and a modular solder joint model is adopted. The average stress intensity factor (DK) of solder joint crack on the plate thickness propagation path is proposed as the evaluation parameter of fatigue life. The shear fatigue tests of resistance spot welding joints with four kinds of plate thickness combination of high strength low alloy steel (HSLA340GI) and dual phase high strength steel (DP600GI) were carried out, and the prediction accuracy was compared with that of traditional LBF and LMS methods. The main research contents are as follows: (1) the research status of resistance spot welding of high strength steel is introduced, the research status of fatigue life prediction of spot welding joint is briefly described, and the development process of fatigue theory is introduced. It is pointed out that the traditional prediction method of solder joint fatigue life can not be directly applied to the prediction of fatigue life of high strength steel solder joint. (2) A modular solder joint modeling method is adopted, compared with the solder joint model used by traditional LBF and LMS methods. The model can accurately simulate the actual position of solder joint, which is more consistent with the physical geometric characteristics of solder joint, and does not reduce the efficiency of modeling and calculation. Using the model to simulate solder joint fatigue can obtain more accurate prediction results of fatigue life. (3) the average stress intensity factor (DK) of solder joint fatigue crack on the plate thickness propagation path is used as the evaluation parameter of solder joint fatigue life. The shear fatigue test of resistance spot welding joint with two kinds of high strength steel materials (HSLA340GI and DP600GI) was carried out. The fatigue life data of different spot welded joints were obtained, and the regression analysis between DK and joint fatigue data was carried out. A main DK-N curve is obtained and compared with the traditional LBF and LMS methods. The results show that the model proposed in this paper can effectively predict the fatigue life of high-strength steel spot welded joints, and the prediction accuracy is higher than that of the traditional LBF and LMS methods. The results show that the proposed simulation model based on average stress intensity factor can effectively predict the fatigue life of high-strength steel spot welded joints, and the prediction accuracy is higher than that of traditional LBF and LMS methods. It has high engineering application value.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U466;TG405

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