焊接應(yīng)力和變形的數(shù)值模擬研究

1、焊接應(yīng)力和變形的數(shù)值模擬研究武漢理工大學(xué)摘 要焊接是一個牽涉到電弧物理、傳熱、冶金和力學(xué)的復(fù)雜過程。焊接現(xiàn)象包括焊接時的電磁、傳熱過程、金屬的熔化和凝固、冷卻時的相變、焊接應(yīng)力與變形等等。要得到一個高質(zhì)量的焊接結(jié)構(gòu)必須控制這些因素。一旦各種焊接現(xiàn)象能夠?qū)崿F(xiàn)計算機模擬,我們就可以通過計算機系統(tǒng)來確定焊接各種結(jié)構(gòu)和材料時的最佳設(shè)計、最佳工藝方法和焊接參數(shù)。本文從這一點出發(fā),在總結(jié)前人的工作基礎(chǔ)上結(jié)合數(shù)值計算的方法,對焊接過程產(chǎn)生的溫度場、應(yīng)力場、變形以及焊后的殘余應(yīng)力和變形進行了三維實時動態(tài)模擬的研究,提出了基于ANSYS軟件的焊接溫度場、應(yīng)力和變形的模擬分析方法,并針對平板堆焊問題進行了實例計算

2、,而且計算結(jié)果與傳統(tǒng)的分析結(jié)果和理論值相吻合。由于焊接是一個局部快速加熱到高溫,并隨后快速冷卻的過程。隨著熱源移動,整個焊件的溫度隨時間和空間急劇變化,材料的物理性能參數(shù)也隨溫度劇烈變化,同時還存在熔化和相變時的潛熱現(xiàn)象。因此,焊接溫度場的分析屬于典型的非線性瞬態(tài)熱傳導(dǎo)問題.因為焊接溫度場分布十分不均勻,在焊接過程中和焊后將產(chǎn)生相當(dāng)大的焊接應(yīng)力和變形。焊接應(yīng)力和變形的計算中既有大應(yīng)變、大變形等幾何非線性問題又有彈塑性變形等材料非線性問題。雖然 焊 接 溫度場與應(yīng)力應(yīng)變場是雙向禍合的,由于應(yīng)力應(yīng)變場對溫度場的影響非常小,加上計算條件的限制,所以本文只考慮溫度場對應(yīng)力應(yīng)變場的影響這一單向藕合。在模

3、擬計算時,采用ANSYS軟件的熱一結(jié)構(gòu)藕合功能,利用間接法,先計算焊接溫度場,溫度場模擬準(zhǔn)確之后保存其結(jié)果,再進行焊接應(yīng)力和變形的計算。模擬計算中一個最大的問題就是計算時間過長,分析其原因主要有三點:(1 嚴(yán)重的材料和幾何非線性導(dǎo)致求解過程收斂困難;(2 三維模型中自由度數(shù)目龐大;(3 因熱源移動需采用多步載荷進行計算。為了解決這一問題并提高計算精度,本文對高溫時材料的物理性能參數(shù)進行了適當(dāng)?shù)倪x取和處理;采用過渡網(wǎng)格劃分形式劃分網(wǎng)格以保證焊縫處網(wǎng)格足夠細(xì)小;選取高斯函數(shù)分布的熱源模型,利用ANSYS軟件的APDL(ANSYS Parametric Design Language語言編寫程序?qū)崿F(xiàn)

4、移動熱源的加載,選取適當(dāng)?shù)牡挠嬎銜r間步長;采用“生死單元”法模擬熔池金屬的熔化和凝固。通過研究和算例驗證,本文建立了可行的三維焊接溫度場、應(yīng)力和變形的動態(tài)模擬分析方法,為復(fù)雜焊接結(jié)構(gòu)進行三維焊接溫度場、應(yīng)力和變形的分析提供了理論依據(jù)和指導(dǎo),促進了有限元分析技術(shù)在焊接力學(xué)分析以及工程中的應(yīng)用。關(guān)鍵詞:焊接 有限元 數(shù)值模擬 溫度場 應(yīng)力變形。AbstractWelding is a complicated physicochemical process which involves in electromagnetism, heat transferring, metal melting and

5、 freezing, phase-change, welding stress and deformation and so on. In order to get high quality welding structure, we have to control these factors. If welding process can be simulated with computer, we will easily determine the best design, procedure method and optimum welding parameter. Based on s

6、umming up others' experience, employing numerical calculation method, this paper researches how to realize the 3D dynamic simulation of welding temperature field, stress field and welding deformation when weldment is been welding and welding residual stress and residual deformation when weldment

7、 is cooled, then uses the research result to simulate the welding process of board surfacing. At the same time, the calculation result accords with traditional analysis results and theory results.Welding process is that parts of an area is quickly heated to high temperature and then rapidly cooled.

8、With the heat source moving, the whole weldment's temperature sharply changes, and the material's physical property parameters also sharply change. At the same time, there is latent heat of melt and phase-change. Therefore, the analysis of welding temperature field is a typical nonlinear tra

9、nsient heat conduction problem. Because of non-uniform temperature distribution, at the course of welding and postweld, weldment takes on serious welding stress and deformation. Calculation of welding stress and deformation includes geometrical nonlinear problem and material nonlinear problem.Althou

10、gh welding temperature field and stress, strain field are bi-directional couple, because stress and strain field have little influence on temperature field, this paper only considers the single couple which temperature field effects on stress and strain field. When calculating, through ANSYS' th

11、ermal-structure couple function, firstly calculate welding temperature field and save the result, then use the temperature result as load to calculate welding stress and deformation.The most important problem, we have to face when calculating, is that the counting time is too long. There are three r

12、easons:1 Serious material and geometrical nonlinear result in difficult solving convergence.2 3D model has enormous degree of freedom.3 Have to employ multi-step load for moving heat source.In order to solve the problem and improve solution accuracy, this paper chooses suitable material property par

13、ameter, uses transition mesh, chooses Gauss function heat source model, uses ANSYS' APDL (ANSYS Parametric Design Language to compile program to apply load of moving heat source, chooses suitable time step, uses the method of "birth and death" method to simulate the weld pool's melting and freezing Through research and practical verify, this paper establishes a feasible dynamic simulation method on 3D welding temperature field, stress and deformation, which provides theory foundation a