钢桥典型构造焊接残余应力有限元分析

发布时间：2018-07-16 09:42

【摘要】：焊接是一个涉及到传热学、固体和流体力学、电磁学和材料冶金学等多个学科交融的复杂现象。焊接现象包括焊接时的传热过程、金属的熔化和凝固、冷却时的相变以及焊接残余应力以及变形等。全焊钢桥中存在着大量的焊接,目前还不能完全控制和消除残余应力,在焊接部位还存在着大量残余应力。残余应力的存在会使结构稳定性下降,会严重影响到结构的强度和承载能力。因此有必要了解焊接后残余应力的分布情况。本文利用有限元分析软件ANSYS建立T形接头和钢桁架焊接整体节点的有限元模型,查看温度场和应力场的分布情况。主要工作有以下几方面:(1)简要介绍了焊接残余应力的基本理论和数值模拟的常用方法,以及残余应力的存在对结构的影响。(2)确定了不同温度下材料的热物理参数和力学参数,以及焊接热源模型等。利用APDL命令编写循环命令流实现焊接热源的加载和移动,并且通过生死单元技术实现焊缝单元的生成。(3)建立有限元模型,求解并得出温度场计算结果。随着热源的移动,热源在焊缝单元上形成准稳态温度场。热源前方等温线密集,温度梯度大;热源后方等温线稀疏,温度梯度小,从而论证了焊接温度场模拟的正确性。通过温度场和应力场的间接耦合,读入温度场的温度荷载,求解得出应力场结果。随着焊接的进行,应力影响面逐渐增大,等效应力接近于屈服应力,焊件冷却后达到了屈服应力。整体节点模型的最大纵向应力达到了 388MPa,超过了屈服应力。(4)在含有残余应力的整体节点模型基础上施加外荷载,分析计算结果。在外荷载和焊接应力的共同作用下,近焊缝区应力变化比较明显,也存在着应力突变,而远离焊缝区时,应力变化不是很显著。外力作用使应力出现重分布,屈服面增大,而部分区域应力得到释放。
[Abstract]:Welding is a complex phenomenon involving heat transfer, solid and hydrodynamics, electromagnetism and material metallurgy. Welding phenomena include heat transfer during welding, melting and solidification of metals, phase transformation during cooling, welding residual stress and deformation, etc. There is a large number of welding in the whole welded steel bridge, so it is not possible to completely control and eliminate the residual stress at present, and there is still a large amount of residual stress in the welding position. The existence of residual stress will decrease the stability of the structure and will seriously affect the strength and bearing capacity of the structure. So it is necessary to know the distribution of residual stress after welding. In this paper, the finite element model of T-joints and welded integral joints of steel truss is established by using the finite element analysis software ANSYS, and the distribution of temperature field and stress field is observed. The main works are as follows: (1) the basic theory of welding residual stress and the common methods of numerical simulation are briefly introduced, and the influence of residual stress on the structure is introduced. (2) the thermophysical and mechanical parameters of materials at different temperatures are determined. And welding heat source model and so on. The APDL command is used to write the cyclic command flow to realize the loading and moving of the welding heat source, and the generation of the welding seam element is realized by the birth and death element technique. (3) the finite element model is established, and the temperature field is solved and calculated. As the heat source moves, the heat source forms a quasi-steady temperature field on the weld line. The isotherm in front of the heat source is dense and the temperature gradient is large, and the isotherm behind the heat source is sparse and the temperature gradient is small, thus proving the correctness of welding temperature field simulation. Through the indirect coupling of the temperature field and the stress field, the temperature load of the temperature field is read, and the results of the stress field are obtained. With the welding, the stress influence surface increases gradually, the equivalent stress is close to the yield stress, and the yield stress is reached after cooling. The maximum longitudinal stress of the whole node model reaches 388MPa, which exceeds the yield stress. (4) the external load is applied on the basis of the integral node model with residual stress, and the calculated results are analyzed. Under the combined action of external load and welding stress, the stress change in the near weld zone is obvious and there is a stress mutation, but the stress change is not very significant when the weld is far away from the weld zone. The external force redistributes the stress, increases the yield surface, and releases some regional stresses.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG404

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