Experimental and computational analysis of residual buckling distortion of bead-on-plate welded joint

A test specimen with a thickness of 2.28 mm was selected as the examined object, to investigate welding induced buckling. Bead-on-plate welding was conducted on the test specimen and residual buckling distortion was observed. A thermal-elastic-plastic (TEP) FE analysis using solid elements model was carried out to predict welding induced buckling after cooling. The inherent deformation of the examined welded joint was also evaluated from the computed results of TEP FE analysis. A shell elements model of the test specimen was used for eigenvalue and elastic FE analyses based on the inherent deformation theory. Eigenvalue analysis predicted the buckling mode and corresponding tendon force in the examined welded joint. Considering large deformation and initial deflection, an elastic FE analysis was carried out to predict the out-of-plane welding distortion, which showed a good agreement with measured distortion.The generation mechanism of buckling in bead-on-plate welded joint was clarified employing the inherent deformation theory. The tendon force (longitudinal inherent shrinkage) is the dominant reason to produce buckling and the disturbance (initial deflection or inherent bending) triggers buckling but does not influence the buckling mode.     

焊接变形预测技术研究进展

焊接变形是影响焊接结构质量和生产率的主要问题之一，焊接变形的存在不仅影响着焊接结构的制造过程，而且影响着焊接结构的使用性能。一般认为，焊接过程中材料的不均匀受热、板厚方向的热梯度、材料的局部非协调塑性应变以及焊接残余应力的作用是产生各种焊接变形的根本原因。焊接变形预测方法大都基于有限元分析。文中详述了国内外有关焊接变形预测技术的最新研究进展，具体介绍了热弹塑性有限单元法、固有应变法以及基于传统有限元的优化设计法与人工神经网络模型等先进的焊接变形预测方法。     

Prediction of welding distortion during assembly process of thin plate structures

0IntroductionApplication of welding process in fabricating largestructures offers several advantages over mechanical joiningmethods such as improved structural performance,flexibil-ity of design,weight reduction and cost savings etc.Inship and automobile …     

固有应变有限元法预测焊接变形理论及其应用

介绍了固有应变的概念、固有应变有限元法预测焊接变形的理论和方法。固有应变存在于焊缝与近缝区 ,并与焊接热输入和板厚等因素有关 ,通过试验和热弹塑性分析 ,可以确定它们的关系曲线。固有应变法只需一次弹性有限元计算 ,因而是预测大型复杂结构焊接变形的一种十分有效的方法。文中介绍了若干工程中成功的应用实例     

板料焊接屈曲变形测量

板料屈曲变形在焊接工艺中不可避免且难以控制矫正,采用先进的测量手段获得焊接屈曲变形规律进而揭示变形机理是目前研究焊接变形的难点问题.文中拟采用一种基于数字图像相关法的非接触测量方法获取板料焊接屈曲变形的全场全过程变形状态.首先,提出了一种针对弱相关和大变形的对应点匹配算法;其次,建立试验平台并利用DIC测量系统对平板堆焊变形进行测量;最后,在平板堆焊试验的基础上,通过分析变形数据,揭示屈曲变形规律.结果表明,低碳钢在板料焊接与冷却过程中均发生屈曲变形,分别呈碟形与马鞍形;板料焊接产生的应变主要分布在焊缝周围;焊缝纵向收缩是引起板料塑性屈曲变形的主要原因.板料焊接屈曲变形规律试验不仅能验证焊接变形预测有限元理论,而且对焊接矫正方法提供依据和思路,同时对板料焊接工艺的发展具有积极的促进和指导作用.     

Cr2N沉淀相对2101双相不锈钢焊接接头综合性能的影响

对经济型2101双相不锈钢焊接接头1050℃固溶后在700℃进行不同保温时间的时效处理.采用光学显微镜、SEM和TEM观察接头各区域的组织演变,对接头进行低温冲击试验和动电位极化腐蚀试验.结果表明,1050℃固溶处理改善了接头的组织和性能;700℃时效处理后焊缝和HAZ析出Cr₂N沉淀相,随着时效时间延长,沉淀相长大,数量变多并向铁素体内部生长,使接头冲击韧性降低,断口由塑性断裂的韧窝状转变为脆性断裂的解理状;固溶处理试样点蚀发生在铁素体内部,时效处理后点蚀发生在Cr₂N周围的二次奥氏体区,时效时间越长,接头的抗点蚀能力越差.Cr₂N的析出对接头焊缝区的影响最为显著.     

焊接应力变形原理若干问题的探讨(二)

提出焊接残余应力形成和消除原理:焊接残余应力不是压缩塑性应变引起的,而是由于焊缝和近缝区金属在"力学熔点"及以下温度冷却收缩受阻产生的;消除焊接残余应力不是产生拉伸塑性应变以减少、抵消和补偿压缩塑性应变,而是将残余弹性应变转变为塑性应变;消除焊接残余应力并不是必须去除固有应变,部分去除或完全不去除固有应变也能完全消除残余应力.提出随焊后热精确控制应力变形焊接法,既可实现无应力焊接和无应力无变形焊接,也可实现适当压应力无变形焊接和较大压应力微变形焊接;并对传统方法与有限元法进行了分析比较.     

薄板搭接接头固有变形逆解析方法

文中采用变形测试和数值模拟技术相结合的研究手段对低碳钢薄板搭接接头固有变形的求解方法进行了研究,提出了该接头的固有变形分布简化模型,并利用固有变形逆解析方法推定了3 mm低碳钢薄板的固有变形.使用该方法得到的固有变形值来预测焊接变形能较好的再现试验结果.结果表明,采用文中提出的固有变形分布简化模型能获得高精度的固有变形值,搭接接头固有变形的逆解析算法是正确有效的.     

利用振动时效控制吊钩侧板变形的实验研究

吊钩侧板销孔处焊接凸台在提高吊钩承载能力的同时常常引起侧板变形,严重影响了吊钩的装配。本文介绍了利用振动时效的方法来降低焊接残余应力和控制吊钩侧板的焊接变形。首先从应力应变机制和位错移动两个方面进行理论分析,然后进行了振动时效的实验研究。实验结果表明:相对于未处理的吊钩侧板件,振动时效处理后的侧板件变形量降低了66.9%,达到了侧板的装配要求,同时使用超声波探伤仪检测侧板焊缝,且没有引入内部缺陷。     

Efficient Simulation of Welding Distortion in Large Structures and Its Reduction by Jig Constraints

Two large construction machinery structures were welded separately with and without jig constraints. The welding distortion of the entire structure was measured by a 3D coordinate measuring system and simulated by elastic FEM using the inherent deformation method. To obtain an accurate inherent deformation, a thermal elastoplastic FE analysis of simple one-side fillet joints with and without jig constraints was performed. Efficient simulation of welding distortion in large structures was accomplished by applying inherent deformation in a localized region, and the effect of jig constraint on the reduction of welding distortion was clarified. The computation of inherent deformation, the weld zone definition and the conversion of inherent deformation into inherent strain were automated. Measured and computed welding distortions in large structures had a good correspondence with respect to both tendency and magnitude. Further investigation of jig configuration was performed for enhanced reduction of welding distortion. Alternative controlling techniques for common welded structures were also addressed.     

电磁锤随焊锤击控制焊接应力变形新工艺

通过用电磁锤锤头对焊后尚处于高温状态的焊趾和焊缝区金属施加一定频率的锤击力,迫使焊趾处的金属向焊缝中心流动,抵消致裂拉伸应变,达到防止焊接热裂纹的目的;同时使焊缝金属在纵向和横向充分延展,降低了焊接残余应力.试验结果表明:该工艺简单可靠、轻便灵活,不但能控制焊接变形、防止焊接热裂纹的产生,而且能使焊缝组织均匀细化;与未锤击时相比,试件焊缝纵向残余应力平均下降了约90%.     

焊接应力应变与变形的数值研究进展

综述了焊接应力应变与变形的数值模拟的新进展，介绍了焊接应力应变的形成机理和数值分析的理论发展，并讨论了建立模型的一些重要的要求和模拟分析的关键技术。     

Evaluation of 2D, 3D and applied plastic strain methods for predicting buckling welding distortion and residual stress

Abstract

Welding induces residual stresses which in thin section structures may cause buckling distortion. The magnitude of longitudinal residual stress is critical in the prediction of buckling distortion, which affects numerous welding applications in the ship building, railroad and other industries. The objectives of this paper are to overview and evaluate modelling procedures for bucking distortion. Moving source two-dimensional (2D), three-dimensional (3D) small deformation, 3D large deformation, and 2D–3D applied plastic strain analyses are evaluated by comparing computed residual stress and distortion against experimental measurements. Guidelines for modelling welding distortion are developed along with an assessment of the efficiency and limitations of the various analysis methods.     

采用三维光学测量技术对薄板焊接失稳变形的分析

采用一种新的测试方法——三维光学面扫描测量系统对低碳钢板平板堆焊过程中的失稳变形进行了研究,通过对低碳钢薄板焊前和焊后状态进行测量,得到薄板焊前和焊后的全场面外变形形貌;并结合基于固有应变法的有限元数值模拟,分析可知焊接引起的这种凹_凸变形属于失稳变形.进而采用小孔法进行残余应力测量.结果表明,远离焊缝区存在较大的残余压应力,纵向残余压应力是导致失稳变形的主要作用力.采用三维光学全场测试技术结合有限元数值模拟分析的方法,对薄板失稳变形的机理及影响因素的探究更加深入、准确.     

采用固有应变法预测超薄板的焊接变形

文中以汽车制造中常用的1 mm厚的薄板为分析对象,采用热-弹-塑性有限元分析了焊缝长度对固有变形分布特征的影响,通过比较热-弹-塑性有限元法及固有应变法预测的变形结果,定量分析了焊缝长度对固有应变法预测超薄板焊接变形时计算精度的影响.结果表明,当焊缝长度达到一定临界长度时,固有应变法可适用于板厚为1 mm左右超薄板焊接接头的焊接变形预测.     

New technique to control welding buckling distortion and residual stress with non-contact electromagnetic impact

Abstract

A new technique using non-contact electromagnetic forces has been proposed for controlling welding buckling distortion and residual stresses in welded thin plates. The experimental results show that the method can successfully eliminate the buckling distortion and reduce the residual stresses. Three-dimensional finite element modelling has been developed to study the evolution of the stress and strain throughout the welding and electromagnetic impacts. The predicted welding distortion and residual stresses are in good agreement with the experimental results. The numerical analyses show that the reduction in distortion and stress is a result of the change of the plastic strain field in the weld region: electromagnetic impacts reduce longitudinal compressive plastic strain in the local region near the weld, and even produce the tensile plastic strain. Moreover, it is found that the residual stress can promote the changes of the longitudinal plastic strain state under electromagnetic impact.     

货车侧墙薄板结构的焊接变形预测与控制

货车侧墙薄板结构在焊接过程中由于焊缝处收缩产生压应力导致侧墙板失稳,产生波浪变形,一方面使结构强度降低,另一方面影响了表面的平整和美观,有效预测和控制它的焊接变形是个难题.基于固有应变等效载荷的有限元方法,对货车侧墙的焊接变形进行预测,分析其焊接变形的规律.结果表明,仿真数值与实测数值基本一致.同时在此仿真模型的基础上,通过正交设计方法调整设计参数与焊接参数,研究不同因素对焊接变形的影响程度,最后得出最优方案,从而为控制薄板侧墙的焊接变形提供理论根据.     

基于固有应变法筒体对接多道焊焊接变形的预测

对于全焊接阀体球阀,由于最后一道工序是焊接,为了确保焊后阀芯的转动和阀门的密封,焊接变形应该严格的控制,选择一个有效的方法准确地预测焊接变形,为焊前阀体的加工提供参考数据.采用了基于固有应变理论的有限元法预测与阀体结构相似的筒体对接多道焊的焊接变形.对于多道多层焊,轴向变形采用了分层计算的方法,径向变形进行一次计算.与试验测量的结果比较,计算值与测量值比较吻合,验证了固有应变法的准确性及可靠性,为阀体焊接工艺参数的优化和焊接结构的加工提供了重要的参考依据.     

基于电磁力随焊控制残余应力和变形的可行性分析

提出了基于脉冲电磁力随焊控制焊接应力及变形新方法.针对平面螺旋线圈,采用ANSYS软件论证了该方法的可行性.该方法的基本思想是将电磁线圈置于焊件上方,并在焊接过程中使其始终处于靠近焊枪的合适位置.将线圈通入较大的脉冲电流,产生变化磁场,使焊件感生涡流,线圈和焊件之间产生电磁力的作用.依靠电磁力对热态焊缝及近缝区金属的延展作用控制残余应力及变形.结果表明,平面螺旋线圈轴向电磁力的方向垂直板面向下,能够延展高温金属.基于电磁力随焊控制焊接残余应力和变形是可行的.