基于等效结构应力法的起重机箱形主梁疲劳寿命分析

发布时间：2018-02-27 16:19

本文关键词： 起重机箱形主梁焊缝等效结构应力法子模型技术疲劳寿命　出处：《郑州大学》2014年硕士论文　论文类型：学位论文

【摘要】：起重机是最为常用和重要的特种设备，主要是由大型板材通过焊接而成的箱形结构，因此焊接结构的疲劳失效形式在很大程度上就决定了起重机结构的失效。受到焊接过程中的各种不确定性因素的影响，在焊接结构的焊缝位置难免会存在一定的焊接缺陷（气孔、夹渣、未熔透等）和应力集中现象，所以疲劳失效也往往主要发生在焊缝位置。焊缝处的节点应力奇异，使用传统有限元法分析得到的焊缝位置的应力，其结果对有限单元网格尺寸和类型相当敏感，故而难以计算出符合工程实际的应力结果，对结构的疲劳寿命预测造成困难。为了能够合理有效地评估起重机结构的疲劳失效性能，本文首先对结构疲劳寿命分析的研究背景及国内外发展现状进行了概述和总结，并且通过对比分析现有评估方法中存在的一些问题，确定本课题研究的方法：基于网格不敏感结构应力和主S-N曲线法（等效结构应力法）来预测起重机金属结构的疲劳寿命。其次，为了有效应用等效结构应力法，文中重点对其理论进行了整理，并结合现有知识对该方法中的重要公式进行了理论推导。接着根据起重机的疲劳失效形式，确定以某厂生产的最大额定起升重量为50吨，，跨度为31.5米的桥式起重机箱形主梁为分析对象，采用有限元方法对其进行静态分析，结果表明该起重机主梁结构的静强度和刚度都符合设计要求。接着，对比静态分析结果与试验测试结果，验证了力学模型简化、建模方式的正确性以及分析结果的可靠性。以结构静态分析为基础确定危险焊缝位置，采用“壳到实体”有限元子模型分析技术建立了关键位置处包含焊缝细节的子模型，并对其进行静力分析。随后，对疲劳主S-N曲线的数学模型进行了概述，并结合实例验证了等效结构应力法的网格不敏感性及寿命预测结果的准确性。最后，将子模型分析的应力通过结构应力转化计算主要焊缝的等效结构应力，进而对该金属结构的疲劳寿命进行了预估，结果表明，主要焊缝具有很好的抗疲劳性能，满足设计要求。最后，本文还对课题研究过程中存在的不完善之处进行了分析和总结，并提出了有待进一步解决的问题，希望在后期研究中得以完善和解决。
[Abstract]:Crane is the most commonly used and important special equipment, mainly made of large plate through welding box structure, Therefore, the fatigue failure form of welded structure determines the failure of crane structure to a great extent. It is inevitable that there are some welding defects (porosity, slag inclusion, not penetration) and stress concentration in the weld position of the welded structure, so fatigue failure often occurs in the weld position. The stress singularity of the joints at the weld seam is very sensitive to the size and type of finite element mesh, so it is difficult to calculate the stress results which accord with the engineering practice. It is difficult to predict the fatigue life of the structure. In order to evaluate the fatigue failure performance of the crane structure reasonably and effectively, this paper firstly summarizes the research background of the fatigue life analysis of the structure and its development status at home and abroad. And through the comparative analysis of some problems in the existing evaluation methods, In order to effectively apply the equivalent structural stress method, the fatigue life of crane metal structure is predicted based on the grid insensitive structural stress and the principal S-N curve (equivalent structural stress method). In this paper, the theory of the crane is mainly sorted out, and the important formulas in this method are deduced in combination with the existing knowledge. Then, according to the fatigue failure form of crane, it is determined that the maximum rated lifting weight of a certain factory is 50 tons. The box girder of the bridge crane with a span of 31.5 meters is analyzed by using the finite element method. The results show that the static strength and stiffness of the main girder structure of the crane meet the design requirements. By comparing the static analysis results with the test results, the simplified mechanical model, the correctness of the modeling method and the reliability of the analysis results are verified. The location of the dangerous welds is determined on the basis of the structural static analysis. In this paper, the finite element submodel analysis technique of "shell to solid" is used to establish the submodel containing weld details at the key position, and the static analysis is carried out. Then, the mathematical model of the fatigue principal S-N curve is summarized. The grid insensitivity of the equivalent structural stress method and the accuracy of the life prediction results are verified by an example. Finally, the equivalent structural stress of the main weld is calculated by transforming the stress of the sub-model into the structural stress. Furthermore, the fatigue life of the metal structure is predicted. The results show that the main weld has good fatigue resistance and meets the design requirements. Finally, this paper analyzes and summarizes the imperfections existing in the course of the research, and puts forward the problems to be solved further, hoping to be perfected and solved in the later research.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TH21

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