基于弹性理论的残余应力反演和变形计算

毛坯在制造过程中,材料力学性能的非均匀性导致其内部产生残余应力.残余应力会造成结构破坏,在工件的切削去除过程中,残余应力会逐渐释放并引起变形.采用有限元的“生死单元”技术模拟材料的切削去除过程,并转化为残余应力的释放,基于板壳理论、小变形理论、弹性理论和叠加原理,将径向基函数插值法与几何方程、物理方程相结合,开发出一种新的解析方法,反演残余应力场并计算变形.结果表明解析方法的理论解与有限元解高度吻合,能够用于判断残余应力分布并计算残余应力弹性释放引起的变形.     

考虑焊接残余应力的波形钢腹板PC梁关键细节疲劳可靠度研究

焊接残余应力对波形钢腹板细节疲劳寿命的影响不可忽略,本文以头道河大桥为工程背景,基于ABAQUS有限元软件,建立波形钢腹板焊接构件数值模型,提出不同波折角度的波形钢腹板残余应力模型。采用瞬态分析方法,分析6种典型车辆作用下波折角区域焊缝细节的应力时程。在此基础上,构建考虑焊接残余应力和车辆荷载共同作用下的波形钢腹板细节疲劳极限状态方程,讨论不同波折角度和交通增长率对疲劳可靠度指标的影响规律。研究表明,翼缘板-波形钢腹板焊接构件斜边两侧的纵向残余应力呈对称分布,焊接细节转角区域圆弧外侧的纵向残余应力整体高于圆弧内侧,随着波折角度的增加,两侧焊缝附近的纵向残余应力变大;在桥梁设计基准期取100年时,30°波折角度焊缝细节疲劳可靠度是60°波折角度的1.05倍;交通量的线性增长对头道河大桥焊缝细节的疲劳可靠度影响较大,不考虑交通增长率的焊缝细节疲劳可靠度是α=5%的1.84倍。     

高温MEMS剪应力传感器残余应力分析

采用理论分析与数值模拟相结合的方法,研究了残余应力对静电反馈式MEMS高温剪应力传感器的结构设计的影响.研究表明:在电极宽度和间距不变的情况下,增加电极数和减小电极长度可有效地减小由静电力引起的应力和变形;残余应力对结构应力和变形的影响远大于静电力.     

云纹干涉与钻孔法测量搅动摩擦焊接头的残余应力

搅动摩擦焊是90年代出现的一种新型焊接技术,特别适用于熔化焊接性差的有色金属等材料.搅动摩擦焊接头的残余应力分别具有高应力梯度的特点,传统的应变片钻孔法不能满足测量要求.本文结合云纹干涉法与钻孔法的技术,得到了铝合金薄板搅拌摩擦焊接头残余应力沿深度和沿垂直焊缝方向的分布.     

残余应力对含裂纹缺陷管道疲劳寿命的影响

针对焊缝区含表面轴向裂纹管道的疲劳寿命问题,探究管道在内压波动下裂纹扩展的规律。建立了焊缝区裂纹仿真模型。采用ABAQUS有限元软件的多层生死单元技术计算了长输管道X80钢的残余应力场。将焊接残余应力场作为裂纹扩展分析的初始应力场导入裂纹仿真模型,结合该软件的扩展有限元法(XFEM)和二次开发计算了在焊接残余应力下裂纹扩展的规律。结果表明:由于焊接残余应力的影响,热影响区含裂纹缺陷的X80管道疲劳寿命明显降低,降低幅度约达40%;裂纹长度对管道的疲劳寿命影响不显著,裂纹深度对其有一定影响,而应力比影响最大,且应力比R=0.1最为显著。     

爆炸处理消除大型柱壳结构环焊缝残余应力实验研究

为探讨大型耐压柱壳结构对接环焊缝焊接残余应力消除方法,根据耐压柱壳结构环焊缝焊接工艺,设计并制作了大型耐压柱壳结构对接环焊缝模拟焊接模型,并采用沿焊缝条状布药,分别进行了单、双面布药爆炸处理消除大型耐压柱壳结构对接环焊缝焊接残余应力模型实验。结果表明:大型耐压柱壳结构对接环焊缝存在较大的焊接残余应力;单、双面爆炸处理均能有效调整、消除焊接残余应力,残余应力分布明显均匀化;焊后残余应力越大,爆炸处理效果越明显,当焊接残余应力大于0.5s时,单面爆炸处理后残余应力m下降幅度在40%以上,双面爆炸处理后残余应力m下降幅度在60%以上;采用沿焊缝条状布药,爆炸处理能有效消除沿焊缝的纵向残余应力;双面爆炸处理效果优于单面爆炸处理效果。     

爆炸法消除焊接接头残余应力的数值模拟

利用非线性动力有限元法对爆炸处理消除焊接接头残余应力的全过程进行了数值模拟。首先，采用温度场与位移场的间接耦合方法计算了钢板对接焊的焊后冷却及残余应力的生成过程，求得焊接接头处由高温冷却到室温由于变形受到阻碍而产生的不均匀的残余塑性变形和应力。然后，在焊缝区引入移动的爆炸载荷，计算了爆炸波作用下该钢板焊接接头附近应力的变化。计算结果表明，爆炸处理可引起板内应力的重新分布，从而有效地释放超过塑性极限的残余应力。利用炸药爆炸消除大型焊接结构残余应力是一种经济有效的方法，本文的数值模拟为研究炸药爆炸消除焊接结构残余应力的机理提供了有力的工具。     

焊管的残余应力测试与研究

通过小孔法与分割法对φ272mm螺旋埋弧焊管和φ380mm对接焊管的残余应力测试,分析探讨了螺旋焊缝、环焊缝以及焊缝热影响区的残余应力分布。研究结果表明,不同工艺焊接成型的圆管,其焊缝纵向均匀为拉应力分布,焊缝横向均为压应力分布,焊缝热影响区的残余应力分布各异。     

基于轮廓法测量钛合金激光熔覆中的残余应力

由于激光熔覆过程中有温度变化快、局部温度梯度大和伴随固液相快速转化等特性,在熔池和热影响区会产生很大的残余应力和变形,不利于金属增材制造和局部修复的精确可控。本文对Ti-6Al-4V(TC4)合金开展激光熔覆实验,采用轮廓法测量了激光熔覆所产生的残余应力;通过三维热力耦合有限元模型计算了温度场和残余应力场,仿真计算结果与轮廓法测量的残余应力趋势一致。结果表明,残余应力在熔覆位置有最大拉伸应力,随着远离焊缝急剧变成压缩应力并逐渐减小。上述工作有利于研究熔覆过程中的温度分布规律及残余应力的生成机制,可为熔覆过程的工艺控制提供参考。     

利用焊接残余应力及深冷预制裂纹技术的探索

本文探索了利用焊接残余应力及低温深冷技术预制裂纹的方法，并用带纵向焊缝的试板进行试验，证明了该方法的可行性。     

Calculation of residual stresses in injection molded products

Both flow- and thermally-induced residual stresses which arise during the injection molding of amorphous thermoplastic polymers are calculated in the filling and post-filling stage. To achieve this, a compressible version of the Leonov model is employed. Two techniques to calculate flow-induced residual stresses are investigated. First, a direct approach is developed where the pressure problem is formulated using the viscoelastic material model. Second, generalized Newtonian material behavior is assumed in formulating the pressure problem, and the resulting flow kinematics is used to calculate normal stresses employing the compressible Leonov model. The latter technique gives comparable results, while reducing the computational cost significantly.     

A general form for calculating residual stresses detected by using the holographic blind-hole method

A general form used for analyzing residual stresses measured using the holographic blind-hole method is introduced in this paper. Adopting the general form presented, the residual stresses can be obtained using three relative displacements measured from a single interference fringe pattern. Even for the case in which phase-shifting holographic interferometry is not employed, interpolating calculations for determining the fringe orders are not needed, since the choice of data points becomes more flexible when using this general form. Two experiments, the first one carried out by the authors and the second one published previously, are used to illustrate the applicability and usefulness of this general form. Suggestions for the applications of this general form are also established via the upper bound error estimations.     

Effect of capillary pressure on the approach to residual saturation

The approach to residual oil saturation during the immiscible displacement of oil as predicted by the multiphase Darcy equations is studied. It is well known that when the capillary pressure term is neglected, one arrives at the Buckley-Leverett formulation according to which the inlet face attains residual oil saturation instantaneously. This result may, however, be strongly influenced by the inclusion of the capillary pressure term. In this paper it is shown that when the relative permeability and capillary pressure functions have power law dependencies on the saturation deviation from residual oil condition, the long time solution exhibits a power law decay toward residual saturation. Moreover, the power law decay solution is found to be unique and independent of the initial condition. The relationship of this solution to the classical Buckley-Leverett result is shown. Finally, generalization to the time varying flow rate case is addressed. As a verification of the theoretical conjectures, the power law solution is compared with direct numerical simulation of the two phase flow equations.     

An acoustoelastic method for measuring residual stresses in slightly orthotropic materials

An acoustoelastic method for residual stress measurement in slightly orthotropic materials by using ultrasonic longitudinal and shear waves is presented. A shear transducer with small vibrator 2 × 2mm² is developed and described, and the measurement of 2-D residual stresses in a seam welded plate was carried out by this method with the shear transducer developed.This project was supported by National Natural Science Fundation of China     

复合材料层合板粘弹性固化残余应力分析

基于Ｓｃｈａｐｅｒｙ积分型粘弹性本构关系，推导了考虑横向剪切效应的复合材料层合板线性热粘弹性有限元分析列式，对层合板的粘弹性响应和加工成型过程中的残余应力进行了分析，给出一些有意义的结果     

Geometrical nonlinear analysis of structures using residual variables

The capability of nonlinear analysis methods in tracing the equilibrium path depends on how to return to static status. In this paper, some residual factors existed in the iteration steps are employed. By setting the residual load parameter to zero, minimizing its factor and the residual displacement parameter, three novel constraint equations are obtained. The new formulas are proved by numerical examples. All obtained results illustrate the minimum residual load scheme's robustness in comparison with the cylindrical arc-length algorithm and other previous strategies. Moreover, the capacities of new procedures in tracing the load and displacement limit points are assessed.     

NUMERICAL PREDICTION OF PROCESS-INDUCED RESIDUAL STRESSES IN GLASS BULB PANEL

A numerical simulation model for predicting residual stresses which arise during the solidification process of pressed glass bulb panel was developed. The solidification of a molten layer of glass between cooled parallel plates was used to model the mechanics of the buildup of residual stresses in the forming process. A thermorheologically simple thermoviscoelastic model was assumed for the material. The finite element method employed was based on the theory of shells as an assembly of flat elements. This approach calculates residual stresses layer by layer like a truly three-dimensional calculation, which is well suited for thin pressed products of complex shape. An experimental comparison was employed to verify the proposed models and methods.     

Numerical residual elimination method of finite differential equations

In this paper,a new elimination of finite differential equations has been discussed.It applies the numerical direct iteration to obtain the residual equations,in which the number of unknowns has been reduced greatly.The solution process is simple and efficient,and the solution is exact     

Using laser ultrasonics for nondestructive residual stress evaluation

A non-contact measuring technique of ultrasonic waves velocity is proposed, in which Rayleigh waves are detected by a laser Doppler velocimeter and the velocity is measured precisely by means of a sing-around unit and a digital oscilloscope. With the proposed technique, the acoustoelastic coefficient of Rayleigh waves in mild steel SS41 is obtained, which is in good agreement with that obtained by the contact method. Furthermore the non-contact technique is applied to evaluate the residual stress in a butt-welded steel plate, the result is reasonable.     

Transient temperature fields and residual stress fields of metallic materials under welding

Based on the situation of welding thermal conduction and thermo-elasto-plasticityresearch,Ms paper explores some problems in this field.First,the boundary elementmethod for nonlinear problems is improved by linearization of nonlinear problems and usedin welding thermal conduction analysis.Second,the thermo-elasto-plastic finite elementmethod is used for the welding stress calculation,in which the phase transformation isconsidered by the"equivalent linear expansion coefficient method".The comparison of the calculated results with experimental data shows that themethods provided in this paper are available.