铝合金平板搅拌摩擦焊接应力变形分析.pdf

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1、收稿日期:2007-05-093 参加此项研究工作的还有刘 园铝合金平板搅拌摩擦焊接应力变形分析李红克,史清宇,王 鑫,李 亭3(清华大学机械工程系 先进成形制造教育部重点实验室,北京 100084)摘 要:针对6056-T6铝合金平板进行搅拌摩擦焊接和试板变形检测试验。并用数值方法对试板变形进行模拟,考察了模拟温度、应力场分布和试板变形情况,对试验和模拟温度、变形进行比较。结果表明,在文中条件下,沿焊缝长度方向试板产生下挠,最大变形量6.3 mm;沿试板宽度方向试板相对发生上拱,最大变形量4.5 mm,模拟与实测变形趋势非常吻合。纵向残余应力在焊缝中心线两侧非对称性分布,前进侧大于回转侧。关

2、键词:搅拌摩擦焊;焊接变形;数值模拟中图分类号:TG435 文献标识码:A 文章编号:0253-360X(2008)02-0081-04李红克0 序 言搅拌摩擦焊1(friction stir welding,简称FSW)是一种新型固相连接技术。由于材料在熔点以下温度实现成形与连接,因而能够避免母材成分损失,减少焊接缺陷,保持力学性能2。通常认为FSW可以获得较小残余应力和结构变形3。但对较大尺寸薄板,实际发现还是存在变形现象。因而,开展FSW变形研究十分必要。而且,FSW已进入工程结构应用阶段,对结构可能产生的变形进行研究,也是该技术的一个发展方向。尽管对于熔化焊接变形数值模拟已具有坚实的理

3、论、实践基础4,但对FSW,除存在与熔焊相似温度场作用外,同时还存在较大外部压力、转矩作用。因而,研究该技术特点下数值方法在焊接试板变形中的应用,也是复杂工程结构变形模拟的必要前提和基础。针对航空结构用6056-T6铝合金平板进行FSW试验,检测并记录相关参数,采用三坐标仪测量试板变形情况。同时利用数值方法模拟焊板温度、应力场及变形行为,比较实测变形与模拟结果的差异,为复杂结构FSW变形研究提供基础。1FSW试验及变形测量焊接材料6056-T6,单个焊板规格400 mm150 mm3 mm。焊接起始及终了端各留20 mm未焊,焊缝总长360 mm。搅拌工具轴肩直径13 mm,搅拌针直径5 mm

4、,长2.6 mm,倾角2。被焊板材置于钢质垫板之上,上部焊缝中心两侧施加4对固定约束,装配如图1所示。工艺参数为:转速1 850转/min,焊速700 mm/min,焊接过程测量搅拌工具下压力和转矩,同时在距焊缝一定位置处测量焊接过程温度。相关FSW试验在德国科隆DLR和EADS德国研究中心合作完成。图1 焊接装配示意Fig11Assembly of panel and constraint plates焊后试板在三坐标测量仪上进行变形检测。检测数据点呈网格分布,网格间距20 mm20 mm。2 焊接变形数值模拟2.1 数值模型FSW数值模拟采用ABAQUS商业软件建模。焊接温度场和应力变形以

5、解耦方式计算。模型尺寸及组配与试验过程一致。对被焊铝板,采用三维实体单元,厚度方向划分两层。沿宽度方向划分单元时,焊缝区采用较细的单元网格,其他部位则采用粗第29卷第2期2 0 0 8年2月焊 接 学 报TRANSACTIONS OF THE CHINA WELDING INSTITUTIONVol.29No.2February2008化及过渡网格。钢质垫板与上部压板则采用壳单元建立,网格划分与被焊板材类似,单元详细信息可参阅相关文献5。模型及单元划分如图2所示。图2 几何模型及网格划分Fig12Geometric model and mesh for welding panel andbac

6、king plate2.2 焊接温度场计算在稳定焊接阶段,假设热输入为常数,输入总热量可由搅拌工具转矩计算得到Q=M=2 nM/60(1)式中:Q为总热量,单位W;为功率系数,这里设为0.92;n为搅拌工具转速,单位r/min;M为转矩,单位N/m。总热量被划分为轴肩面热源和搅拌针体热源两种形式分别施加于搅拌工具作用区域。搅拌针热量采用简化方法,以总热量的25%计算6。温度场计算过程中主要边界条件为焊板底面与钢质垫板、上压板之间的接触热传导,以及焊板、垫板、压板自由表面的对流散热。接触热传导系数与温度相关,高温数据由低温数据点外推得到。对所有暴露在空气中的自由表面,对流散热系数设定为15 W/

7、(m2)。2.3 焊接应力场及变形计算应力分析中外载荷主要包括搅拌工具下压力、转矩等。对下压力,假设沿轴肩面均匀分布,以平面压力表示。对转矩,将其分解为工具区域下作用在单元x,y向的剪切分量,由一定厚度下体力实现。面压力及体力通过子程序DLOAD加载。应力变形分析中边界条件主要包括垫板支撑作用、上压板固定约束、侧边位移约束和在上述约束去除后为防止焊板刚性位移而施加的固定约束。2.4 材料性能模型所采用的材料性能由EADS德国研究中心提供,如图3,图4所示。图3 热导率和比热容与温度关系Fig13Thermo properties图4 材料屈服强度和断后伸长率与温度关系Fig14Y ield,t

8、ensile stress and elongation3 结果与讨论3.1 温度场模拟结果焊接稳定阶段,测量所得工具下压力和转矩平均值分别为8.06 kN和8.76 N/m,由此得到面热流及体热流密度为:1 171 W/m2和390 W/m2。在焊缝长度200 mm处焊缝中心位置,模拟所得温度历程如图5a所示,与峰值温度对应时刻沿焊缝横向的温度分布则如图5b所示。图5a中,温度时间曲线呈突兀峰状分布,最高温度462.5。沿焊缝横向,如图5b,随着距焊缝中心线距离的增加,温度降低。但在l3.75 mm区域内形成一个高温台阶;此后温度迅速降低,最终在试板边缘处接近室温。82焊 接 学 报第29卷

9、图5 模拟温度分布Fig15Simulated temperature distributions对相同位置模拟和测量温度结果的分析表明,在近焊缝区,模拟温度稍高于测量温度,在远离焊缝区,测量温度稍高于模拟值,但误差均 10%。3.2 应力场模拟结果在焊板长度200 mm处,垂直于焊缝中心线处模拟所得纵、横向残余应力分布如图6所示。可以看到,在焊缝中心两侧各10 mm区域内,纵向残余应力表现为较大的拉应力,10 mm以外则呈现为压应力。在拉应力区,残余应力呈现不对称性分布,前进侧拉应力高于回转侧。在焊缝两侧各3.75 mm处,应力值分别为269和247 MPa,相差22MPa。这一现象与实测特

10、点一致7。焊缝两侧拉应力差异的出现是由于焊接过程热应力与机械应力叠加产生的结果。在前进侧材料承受机械拉应力,而在回转侧则受到机械压应力作用,二者与热应力复合即形成不对称分布。在压应力区,应力沿焊缝中心对称分布,最大压应力为37.1 MPa,且随着距焊缝中心距离的增加,应力值减小,并在试板边缘达到最小值9.6 MPa。横向残余应力集中于焊缝中心及附近区域,其性质与夹具约束有关,这里主要表现为拉应力,且沿焊缝中心线具有不对称性,但差值很小。最大横向应力为19.3 MPa,位于前进侧搅拌针半径外缘。对焊接试板长度中间位置、焊缝上、下表面纵向图6 纵横向残余应力分布Fig16Longitudinal

11、and transverse stress distributions残余应力的分析表明,在焊缝中心左右各3.75 mm区域内,下表面拉应力大于上表面应力,最大差值27 MPa。但在试板无应力作用区域内,上表面压应力大于下表面,平均高出约20 MPa。且在远离焊缝中心区域下表面纵向应力由压应力转变为拉应力,并在试板边缘达到11.4 MPa。3.3 试板变形及模拟和测量结果比较焊后试板变形及模拟所得变形情况如图7所示。其中图7b中网格为试板原始位置,变形放大倍数为5。实际焊板变形形式为:沿焊缝长度方向,试板整体形成下挠,并在两侧边中心位置达到最大值。在焊缝横向,试板出现上拱,并在焊缝中心线达到高

12、值。在图7b中,模拟变形明显具有与实际焊板相同的变形趋势。对FSW而言,焊接变形的产生除与局部加热和快速冷却在焊缝及近缝区产生的热应变和压缩塑性应变相关外,还与焊接过程外部机械载荷作用密不可分。塑性变形的产生进而导致内应力的出现,最终形成构件的变形。为进一步比较试验和模拟变形之间的差异,将试板四边变形结果示于图8。从中可见,测量变形曲线出现交叉现象,说明试板存在一定程度扭曲。扭曲的出现一方面为试板本身变形所致,另一方面可能来源于变形测量误差。对于模拟结果,四边位移曲线相对规律,变形同样存在不对称性。在长度方向上,前进侧边位移量同样大于回转侧,但小于实第2期李红克,等:铝合金平板搅拌摩擦焊接应力

13、变形分析83图7 焊后试板变形与模拟变形Fig17Panel real and simulated distortions图8 试板四边模拟变形与测量结果比较Fig18Distortion comparisons along panel edges for simulat2ed and measured results测变形量。模拟变形与测量结果最大差异出现在试板四个角点,差值在1.682.51 mm之间变化。在试板长度中间位置,模拟结果接近或等于实际变形,误差仅为0.58和0.03 mm。模拟变形与实测结果的差异主要来源于以下几个方面。(1)模拟温度场与实际存在10%左右的差异;(2)模型材

14、料性能在高温阶段具有一定的不准确性,尤其是高温应变数据为外推得到;(3)焊接过程中工具下压力和转矩随时间变化,而模型中假设为恒定机械载荷;(4)实际焊板两端各存在20 mm的未连接区域,而数值模型未予考虑。但从上述结果和分析可以发现,采用数值方法模拟FSW试板和结构的变形可以获得一致的变形趋势。而且随着数值模型的改进,模拟精度还可进一步提高,因而对于指导FSW实践具有较大应用价值。4 结 论(1)FSW焊后试板发生较大变形,沿焊缝纵向,试板形成下挠,沿焊缝横向,试板相对发生上拱。(2)利用数值方法,可以实现对具有较大外部载荷条件下搅拌摩擦焊接试板变形情况的模拟,并获得与实际焊板相一致的变形趋势

15、。(3)搅拌摩擦焊接纵向残余应力在焊缝中心两侧呈不对称分布,前进侧高于回转侧。致 谢研究项目得到863及EADS德国研究中心支持,相关试验在德国合作完成。在此对参与该项目的德方Jurgen Silvanus先生表示衷心感谢。参考文献:1Thomas W M T,Nicholas E D,Need ham J C,et al.“Friction stirbutt welding”:UK,International patent application no.PCT/G B92/02203 and G B patent application no.9125978.8 P.1991-12-01.2

16、Mishra R S,Ma Z Y.Friction stir welding and processingR.Mate2rials Science and Engineering,2005,50:1-78.3 栾国红,关 桥.高效、固相焊接新技术 搅拌摩擦焊J.电焊机,2005,35(9):8-13.4 蔡志鹏.大型结构焊接变形的数值模拟研究与应用D.北京:清华大学,2001.5 李红克,史清宇,赵海燕,等.热量自适应搅拌摩擦焊热源模型J.焊接学报,2006,27(11):81-85.6Shi Qingyu,Dickerson T,Shercliff H R.Thermo2mechanica

17、l analysison welding process of aluminium 2024 with TIG and FSWCPro2ceedings of the 6th International Conference on Trends in Welding Re2search,2003:247-252.作者简介:李红克,男,1974年出生,博士研究生。主要从事搅拌摩擦焊接机理及数值模拟研究。发表论文12篇。Email:hongkelee 84焊 接 学 报第29卷under low heat inputZHANG Fuju1,WANG Yan2,ZHANGGuodong1,Wang

18、Yutao3(1.College of Power&Mechanical Engi2neering,Wuhan University,Wuhan 430072,China;2.College ofMechanical&Material Engineering,China Three G orges University,Y ichang 443002,Hubei,China;3.Research Institute of WuhanIron&Steel Group Corporation,Wuhan 430080,China).p77-80Abstract:The formation and

19、mechanical propertiesof weldedjoint for 400 MPa ultra2fine grain steel were studied based on surfacetension transfer technology,CO2arc welding,special narrow grooveand different heat input.The results showed that the welded jointwith good fusion,one side welding with back formation and narrowHAZ(hea

20、t2affected zone)(about 1 mm)was obtained with 324 kJ/cm heat input.The hardness and tensile strength of the joint werehigher than those of the base metal.The embrittlement and softeningof HAZwas not found,and the bending plasticitywas qualified.Theimpact toughnessof HAZwas about 60%higher than that

21、of the basemetal,which can be caused by the granular pearlite transition,mul2ti2phase non2equilibrium microstructure and higher yield stress.Key words:ultra2fine grain steel;welded joint;heat input;CO2arc weldingResidual stress and distortion of Al alloy panels welded by FSWLI Hongke,SHI Qingyu,WANG

22、 Xin,LI Ting,LIU Yuan(Department of Mechanical Engineering,Key Laboratory for Ad2vanced Materials Processing Technology Ministry of Education,Ts2inghua University,Beijing 100084,China).p81-84Abstract:FSW 60562T6 Al alloy panel was welded by FSWand its distortion was measured.Also numerical model was

23、 estab2lished to simulate the distortion,temperature field and stress fields.The simulated temperature and distortion were compared with those ofexperiments.The results indicated that the panel bent down alongwelding direction and maximum distortion reaches 6.3 mm.Alongthe transverse direction,the p

24、anel bent up relatively to the longitudi2nal sides and the maximum displacement was 4.5 mm.There werehigh accordance trendsof simulated distortion to the experiment.Thelongitudinal residual stress was asymmetric with the weld center lineand it is higher on advancing side.Key words:friction stir weld

25、ing;welding distortion;numer2ical simulationMicrostructure and mechanical properties of K 418 and 42CrModissimilar metal laser weldingPANGMing,Y U Gang,WANGHenghai,ZHENG Caiyun(Institute of Mechanics,Chinese Acade2my of Sciences,Beijing 100080,China).p85-88Abstract:The influences of welding heat inp

26、ut on weld oflaser welding of K418 and 42CrMo dissimilar metal were experimen2tally investigated using continue wave Nd:Y AGlaser of output power3 kW.Microstructure of the welded joint was studyed by optical mi2croscope,scanning electron microscope,X2ray diffraction,and en2ergy dispersive spectromet

27、er.Mechanical properties of the weld wereevaluated by hardness and tensile strength test.Results show thatweld penetration of keyhole welding mode is larger than of heat con2duction welding mode with constant linear heat input.Particle of richNb,Ti and Mo and deleted Fe and Ni and needle of rich Nb

28、and Tiare observed in the fusion zone.The tensile strength of weld is high2er than that of base metal of 42CrMo by optimizing laser welding pa2rameters.Key words:laser welding;heat2affected zone;K418 nickelalloy;42CrMo steel;microstructureWeld defect classification in ultrasonic testing basing on ti

29、me2frequency discriminant features DU Xiuli1,2,SHEN Y i2,WANG Yan2(1.School of Information Engineering,Dalian Univer2sity,Dalian,116622,China;2.School of Astronautics,Harbin In2stitute of Technology,Harbin 150001,China).p89-92Abstract:According to transient property of ultrasonic sig2nal,the discrim

30、inant pursuit method was proposed to extract localtime2frequency featuresof defect signal and the featureswere fed to aprobabilistic neural networks to classify the defects.During extract2ing features,the correlation between the incoming atom and theatoms selected before was considered to reduce the

31、 redundance a2mong the selected atoms so that the extracted features discriminateddifferent class of signals effectively.Finally,the defects of an elec2tronic welded joint were classified byproposed approach,and the ex2perimental results show that time2frequency discriminant features areappropriate

32、for defects classification in ultrasonic testing,and cansuppress the effect of grain noise.In addition,the higher accuracycan be reached if considering the correlation of the selected atoms.Key words:ultrasonic test;discriminant pursuit;time2fre2quency discriminant feature;probabilistic neural netwo

33、rksPrediction of area of gray2spots flaw in alternate rail flash buttwelded joint based on RBF neural networkLQibing,TANKeli,LUO Deyang,TAN Hongtao(Institute of Welding,SouthwestJiaotong University,Sichuan Chengdu 610031,China).p93-96Abstract:On the basis of imported AMS60 alternate railflash butt w

34、elding machine,the welding current,the welding voltageand the displacement of welding procedure experiment of U71Mn railwere acquired with high frequency.Eight weld quality characteristicvalues such as the percentage of the flashing time of the acceleratedflashing stage,the percentage of the flashin

35、g time of low voltageand stable flash stage,the power input of weld,the flashed length ofrail,the welding time,the short and broken circuit factor of lowvoltageand stable flash stage and the short and broken circuitfactor of the accelerated flashing stage and upsed length,which hadinfluence on the g

36、rey2spot flaw area in the alternate rail flash buttwelded joint,were used as input data of radial basic function neuralnetwork the rail weld grey2spot flaw.The prediction model whosespread rate was 1.5 was built,and according to the TB/T1632-2008,Vol.29,No.2TRANSACTIONS OF THE CHINA WELDING INSTITUTION

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