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LNG(液化天然气)运输船舶建造过程中,焊接残余应力不仅可能使LNG运输船独立液罐产生裂纹,还可能与外加载荷叠加后改变独立液罐的承载能力。因此要了解独立液罐焊接后的应力分布,就有必要对其焊接残余应力进行有限元分析。应用轴对称模型及单元生死技术研究了某LNG运输船舶独立液罐焊接残余应力的分布规律,参照现有国标对独立液罐坡口尺寸进行了对比研究,探讨了坡口尺寸与焊接残余应力之间的关系,以及热处理对焊接残余应力的影响。研究结果表明:在独立液罐坡口角度为最小建议值的情况下,焊接残余应力(等效应力)随坡口深度的增大呈先减小后增大的趋势,当坡口深度为6 mm时,其残余应力达到最小值;与V型坡口角度和U型坡口角度相比,坡口深度对焊接残余应力的影响更加显著;结合实际结构及工艺,为减少焊接残余应力,尽量选择较小的坡口深度和坡口角度;独立液罐焊后热处理可以降低其焊接残余Mises应力,降低幅度达到了21%。研究结果为独立液罐焊接结构的设计、生产工艺的优化及降低焊接残余应力提供了理论依据。
During the construction of LNG (liquefied natural gas) ships, the welding residual stress may not only cause cracks in the LNG carrier’s independent liquid tank, but also may change the carrying capacity of the independent liquid tank after being superposed with the applied load. Therefore, to understand the stress distribution of the independent tank after welding, it is necessary to analyze the residual stress of the welding. Axial symmetry model and unit life and death technology were used to study the distribution of welding residual stresses in an independent LNG tanker ship. Comparing with the existing national standard, the groove dimensions of independent tanks were compared. The relationship between groove size and welding residual stress The relationship between heat treatment and welding residual stress. The results show that the welding residual stress (equivalent stress) tends to decrease first and then increase with the increase of groove depth, when the groove angle of independent tank is the minimum recommended value. When the groove depth is 6 mm, the residual stress reaches the minimum value. Compared with the V-groove angle and the U-groove angle, the influence of groove depth on the welding residual stress is more significant. In order to reduce the welding residual stress, as far as possible, considering the actual structure and process, Choose a smaller groove depth and groove angle; independent tank after-heat treatment can reduce the welding residual Mises stress, a decrease of 21%. The results provide a theoretical basis for the design of soldering tank structure, the optimization of production technology and the reduction of welding residual stress.