【摘要】：焊接是一個(gè)涉及到傳熱學(xué)、固體和流體力學(xué)、電磁學(xué)和材料冶金學(xué)等多個(gè)學(xué)科交融的復(fù)雜現(xiàn)象。焊接現(xiàn)象包括焊接時(shí)的傳熱過(guò)程、金屬的熔化和凝固、冷卻時(shí)的相變以及焊接殘余應(yīng)力以及變形等。全焊鋼橋中存在著大量的焊接,目前還不能完全控制和消除殘余應(yīng)力,在焊接部位還存在著大量殘余應(yīng)力。殘余應(yīng)力的存在會(huì)使結(jié)構(gòu)穩(wěn)定性下降,會(huì)嚴(yán)重影響到結(jié)構(gòu)的強(qiáng)度和承載能力。因此有必要了解焊接后殘余應(yīng)力的分布情況。本文利用有限元分析軟件ANSYS建立T形接頭和鋼桁架焊接整體節(jié)點(diǎn)的有限元模型,查看溫度場(chǎng)和應(yīng)力場(chǎng)的分布情況。主要工作有以下幾方面:(1)簡(jiǎn)要介紹了焊接殘余應(yīng)力的基本理論和數(shù)值模擬的常用方法,以及殘余應(yīng)力的存在對(duì)結(jié)構(gòu)的影響。(2)確定了不同溫度下材料的熱物理參數(shù)和力學(xué)參數(shù),以及焊接熱源模型等。利用APDL命令編寫(xiě)循環(huán)命令流實(shí)現(xiàn)焊接熱源的加載和移動(dòng),并且通過(guò)生死單元技術(shù)實(shí)現(xiàn)焊縫單元的生成。(3)建立有限元模型,求解并得出溫度場(chǎng)計(jì)算結(jié)果。隨著熱源的移動(dòng),熱源在焊縫單元上形成準(zhǔn)穩(wěn)態(tài)溫度場(chǎng)。熱源前方等溫線(xiàn)密集,溫度梯度大;熱源后方等溫線(xiàn)稀疏,溫度梯度小,從而論證了焊接溫度場(chǎng)模擬的正確性。通過(guò)溫度場(chǎng)和應(yīng)力場(chǎng)的間接耦合,讀入溫度場(chǎng)的溫度荷載,求解得出應(yīng)力場(chǎng)結(jié)果。隨著焊接的進(jìn)行,應(yīng)力影響面逐漸增大,等效應(yīng)力接近于屈服應(yīng)力,焊件冷卻后達(dá)到了屈服應(yīng)力。整體節(jié)點(diǎn)模型的最大縱向應(yīng)力達(dá)到了 388MPa,超過(guò)了屈服應(yīng)力。(4)在含有殘余應(yīng)力的整體節(jié)點(diǎn)模型基礎(chǔ)上施加外荷載,分析計(jì)算結(jié)果。在外荷載和焊接應(yīng)力的共同作用下,近焊縫區(qū)應(yīng)力變化比較明顯,也存在著應(yīng)力突變,而遠(yuǎn)離焊縫區(qū)時(shí),應(yīng)力變化不是很顯著。外力作用使應(yīng)力出現(xiàn)重分布,屈服面增大,而部分區(qū)域應(yīng)力得到釋放。
[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.
【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TG404

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