Zr-4合金管电子束焊接瞬态温度场和应力场的数值模拟

Zr-4合金广泛用作大多数压水堆和反应堆的燃料包壳材料,因此针对其焊接的研究有非常重要的现实意义。论文采用数值模拟方式研究Zr-4合金电子束焊接的瞬态过程,采用双椭球热源模型,结合接触及辐射等边界条件,采用变密度六面体网格,耦合温度场和应力场,建立了Zr-4合金管电子束焊接的有限元瞬态数学模型,采用自适应时间步,计算了Zr-4合金管真空电子束焊接的三维瞬态温度场和应力场。数值模拟结果表明:在电子束功率相对较小的条件下,焊缝深宽比较小,采用双椭球热源模型进行数值模拟,所获熔池形状与实验所得焊缝成形吻合良好,证明了该数学模型的合理性,从而可为制定实际焊接工艺提供理论指导。在所设定的计算条件下,筒盖和筒体均变形均匀,主要表现形式为沿径向突出,且筒盖变形大于筒体,和实际焊接现象基本一致;焊后最大整体变形约0.02 mm。     

铝合金激光深熔焊接热过程有限元数值模拟

对铝合金5A06简体纵缝进行激光深熔焊接。建立了该条件下的焊接热源模型,热源模型由沿激光入射方向的旋转高斯体热源构成。使用该热源模型和ANSYS有限元分析软件对前述的试验进行了数值模拟。为制定和优化焊接工艺提供必要的参考。     

含稀土元素的对接接头焊接数值模拟的现状与应用

稀土元素对焊接材料有画龙点睛的作用。通过添加稀土元素,熔敷金属的力学性能得到显著提高。传统确定含稀土元素焊接工艺参数的方法要进行大量试验,极大的增加生产成本。而焊接的数值模拟是低成本且安全可靠的确定工艺参数的方法。通过分析含稀土元素的对接接头试验、焊接热源、焊接工艺参数、焊接构件的残余应力和变形的数值模拟的现状,结果表明,寻找并建立符合实际的添加稀土元素的焊接接头显微组织模型及热源模型是模拟成功的关键。今后焊接数值模拟的重点是研究含稀土元素的多层多道焊接数值模拟,以及进行焊接原材料成分、焊接工艺与熔敷金属性能耦合关系的研究。     

M42高速钢/X32弹簧钢电子束焊接温度场的数值模拟与实验研究

选择双椭球热源模型对M42高速钢/X32弹簧钢双金属带锯的电子束焊接的温度场进行Ansys数值模拟,确定焊接的最佳工艺参数,并进行焊接试验,利用扫描电镜观察M42/X32接头的微观组织。结果表明,最佳焊接工艺为焊接电压U=140 k V,焊接电子束电流Ib=20 m A,焊接速度v=2 m/min。在此工艺条件下进行电子束焊接实验,焊缝宽度实验值和计算值的相对误差为-3%~1.5%,二者吻合较好,验证了双椭球热源模型在电子束焊接温度场模拟中的适用性。M42/X32接头的焊缝中心为等轴晶和柱状晶的典型铸态组织;M42熔合区(FZ)组织为马氏体和M2C型碳化物,M42热影响区(HAZ)组织为马氏体、残余奥氏体及碳化物。X32熔合区(FZ)由类马氏体层和马氏体组织组成,X32热影响区(HAZ)组织为马氏体、残余奥氏体以及M23C6。     

钛基非晶合金电子束焊接热力耦合模拟及非晶化

根据电子束焊接焊缝形貌特征及其深宽比大等特点,选用复合热源作为热源模型.通过线性插值等方式估计材料热力学参数随温度变化,模拟Ti基非晶合金电子束焊接温度场.模拟结果与实际焊缝取得良好的吻合,验证了热源模型的准确性.获得一定变量参数下电子束焊接钛基非晶合金温度场及热循环曲线.在温度场的基础上再进行焊接应力场的模拟,获得残余应力分布曲线.实验验证整个焊件没有晶化相析出,验证了该焊接工艺的可行性.      

矿山废石场散体变形参数计算模型的改进

针对过去采用弹塑性体邓肯应力－应变模型确定矿山废石场散体的弹性模理（Ｅ）及泊松比（μ）的计算过程繁琐、计算公式复杂，提出了改进的计算模型。新模型将原来确定模型参数的５个关系式减少到２个，使计算公式和计算过程简化。     

能源桩三维螺旋线热源的瞬态传热模型

将螺旋埋管等效为三维螺旋线热源,考虑螺旋埋管能源桩的传热过程,运用格林函数和第一型曲线进行积分,推导给出了考虑时间、空间位置、埋管参数和岩土体热物理性质4参数的螺旋埋管能源桩的温度场解析解,建立高精度三维螺旋埋管能源桩的传热模型。并通过在数值模拟软件中建立螺旋埋管能源桩三维模型,依据边界条件,求解得出三维螺旋埋管能源桩温度场数值解。对比结果表明:所建立的能源桩三维螺旋线热源模型具有很高的解析精度。最后,基于解析模型讨论了螺旋埋管能源桩换热温度场的空间分布和时间效应。      

04Cr13Ni5Mo超级马氏体不锈钢焊接性能研究

模拟了04Cr13Ni5Mo超级马氏体不锈钢不同焊接热循环条件下热影响区组织,进行了焊条电弧焊接及焊后热处理试验,分析了焊接热模拟试样及焊条电弧焊接头的微观组织、力学性能.焊接热模拟试验结果表明,模拟热影响区的组织主要为低碳板条马氏体,其硬度较母材有较大提高,冲击韧性有所下降;模拟单道焊或多道焊时,不同的冷却速度及层间热处理对模拟热影响区的硬度及冲击韧性影响不大,600℃焊后回火热处理可以明显软化模拟热影响区组织,并让其冲击韧性恢复到较高水平.焊条电弧焊接结果表明,采用04Cr13Ni5MoRe型焊条及配套的焊后热处理工艺,可以获得良好综合力学性能的焊接接头.     

烘烤炉内彩涂板传热过程的数值模拟

根据集总参数法的基本原理对彩涂板传热过程进行了理论分析,建立了一维有内热源的彩涂板传热数学模型,热源项包括炉气与钢板间的喷射对流换热量,涂料溶剂的挥发吸热量以及涂料固化放热量三部分.用该模型对彩涂板在烘烤炉内的升温过程进行了数值模拟,得到彩涂板的出炉温度.通过对9841个炉次的工况计算,并与现场测试值对比,计算结果与实测值差值绝对值在5℃以内的样本共有9029个,占总样本量的91.75%,证明模型正确,计算结果可靠,可用于快速预测彩涂板的出炉温度.     

AH36薄板激光-电弧复合焊熔滴过渡与熔池分析

采用激光-电弧复合焊,激光前置焊接海工钢AH36薄板。利用高速摄像分析熔滴过渡特征与影响因素。运用计算流体力学体积分数法建立固液气三相流体动力学模型。采用高斯面热源、高斯旋转体热源和双椭球热源表征复合焊热源。数值模型考虑了表面张力、电磁力、浮力、反冲压力、蒸发冷凝、蒸发换热等多种物理场的耦合作用。对熔滴过渡冲击及其对熔池形貌、流动与温度的影响进行研究。结果表明,熔滴冲击熔池可促进熔池流动与传热。熔滴过渡受电磁力与蒸气反冲压力抑制,致使大熔滴出现。适当增加激光功率可降低熔滴表面张力,增加熔滴过渡频率,减小熔滴尺寸。激光功率过大或光丝间距过小时,出现熔滴破裂与飞溅。     

Thermal analysis of the arc welding process: Part I. General solutions

An analytical solution for the temperature-rise distribution in arc welding of short workpieces is developed based on the classical Jaeger’s moving heat-source theory to predict the transient thermal response. It, thus, complements the pioneering work of Rosenthal and his colleagues (and others who extended that work), which addresses quasi-stationary moving heat-source problems. The arc beam is considered as a moving plane (disc) heat source with a pseudo-Gaussian distribution of heat intensity, based on the work of Goldak et al. It is a general solution (both transient and quasi-steady state) in that it can determine the temperature-rise distribution in and around the arc beam heat source, as well as the width and depth of the melt pool (MP) and the heat-affected zone (HAZ) in welding short lengths, where quasi-stationary conditions may not have been established. A comparative study is made of the analytical approach of the transient analysis presented here with the finite-element modeling of arc welding by Tekriwal and Mazumder. The analytical model developed can determine the time required for reaching quasi-steady state and solve the equation for the temperature distribution, be it transient or quasi-steady state. It can also calculate the temperature on the surface as well as with respect to the depth at all points, including those very close to the heat source. While some agreement was found between the results of the analytical work and those of the finite-element method (FEM) model, there were differences identified due to differences in the methods of approach, the selection of the boundary conditions, the need to consider image heat sources, and the effect of variable thermal properties with temperature. The analysis presented here is exact, and the solution can be obtained quickly and in an inexpensive way compared to the FEM. The analysis also facilitates optimization of process parameters for good welding practice.     

连续驱动摩擦焊接技术的研究与工程应用

在对摩擦焊接进行分类并简要说明的基础上,对连续驱动摩擦焊接技术的研究发展和应用现状进行了全面梳理和深入剖析,涉及焊接工艺过程特征和主要工艺参数、工艺探索及工艺参数对接头性能的影响、数值分析和模拟及工艺参数优化、异种金属和非金属材料摩擦焊接与工艺创新、实际工程应用和焊接设备等方面。从摩擦焊接技术的潜在应用、核心科学问题、新型摩擦焊接设备的研发、数值分析和模拟、与新兴技术的结合等方面,对连续驱动摩擦焊接技术进行了评述和探讨。      

A new finite element model for welding heat sources

A mathematical model for weld heat sources based on a Gaussian distribution of power density in space is presented. In particular a double ellipsoidal geometry is proposed so that the size and shape of the heat source can be easily changed to model both the shallow penetration arc welding processes and the deeper penetration laser and electron beam processes. In addition, it has the versatility and flexibility to handle non-axisymmetric cases such as strip electrodes or dissimilar metal joining. Previous models assumed circular or spherical symmetry. The computations are performed with ASGARD, a nonlinear transient finite element (FEM) heat flow program developed for the thermal stress analysis of welds.* Computed temperature distributions for submerged arc welds in thick workpieces are compared to the measured values reported by Christensen¹ and the FEM calculated values (surface heat source model) of Krutz and Segerlind.² In addition the computed thermal history of deep penetration electron beam welds are compared to measured values reported by Chong.³ The agreement between the computed and measured values is shown to be excellent.     

Numerical analysis of metal transfer in gas metal arc welding under modified pulsed current conditions

A method has been proposed to pulsate current in gas metal arc welding (GMAW) to achieve a specific type of desirable and repeatable metal transfer mode, i.e., one drop per pulse (ODPP) mode. This method uses a peak current lower than the transition current to prevent accidental detachment and takes advantage of the downward momentum of the droplet oscillation to enhance the detachment. A numerical model with advanced computational fluid dynamics (CFD) techniques, such as a two-step projection method, volume of fluid (VOF) method, and continuum surface force (CSF) model, was used to carry out the simulation for the metal transfer process. The Gauss-type current density distribution was assumed as the boundary condition for the calculation of the electromagnetic force. The calculations were conducted to demonstrate the effectiveness of the proposed method in achieving the desired metal transfer process in comparison with conventional pulsed current GMAW. Also, the critical conditions for effective use of this proposed method were identified by the numerical simulation. Comparison showed good agreement between calculation and experimental results.     

基于应力与疲劳的锻锤结构分析

锻锤是径向精锻机的一个关键部件,它的强度和使用寿命对整机的安全可靠运行具有十分重要的影响。针对弧面锻锤与平面锻锤锻造圆柱形工件的受力与寿命问题,构建锻锤锻造的有限元计算模型,进行有限元锻造模拟,对其进行应力和寿命分析及结果对比,确定锻锤易损点。结果表明:在锻造圆柱工件时,两种锻锤的等效应力主要出现在过渡圆角处;弧面锻锤受等效应力比平面锻锤小7.75%,其寿命可以增加3.9%。     

Numerical analysis of metal transfer in gas metal arc welding

The present article describes a numerical procedure to simulate metal transfer and the model will be used to analyze the transport processes involved in gas metal arc welding (GMAW). Advanced Computational fluid dynamics (CFD) techniques used in this model include a two-step projection method for solving the incompressible fluid flow; a volume of fluid (VOF) method for capturing free surface; and a continuum surface force (CSF) model for calculating surface tension. The electromagnetic force due to the welding current is estimated by assuming several different types of current density distribution on the free surface of the drop. The simulations based on the assumption of Gaussian current density distribution show that the transition from globular to spray transfer mode occurs over a narrow current range and the size of detached drops is nonuniform in this transition zone. The analysis of the calculation results gives a better understanding of this physical procedure. Comparisons between calculated results and experimental results are presented. It is found that the results computed from the Gaussian assumption agree well with those observed in experiments.     

50MN挤压机张力柱的断裂修复

分析50MN挤压机张力柱的断裂原因,介绍采用埋弧自动焊焊接修复大型工件的工艺过程、焊接采取的措施,以及焊接修复后张力柱的强度校核。     

Thermal analysis of the arc welding process: Part II. effect of variation of thermophysical properties with temperature

This article is Part II of a two-part series on the thermal analysis of the arc welding process. In Part I, general solutions for the temperature rise distribution in arc welding of short workpieces were developed based on Jaeger’s classical moving heat source theory for a plane disc heat source with a pseudo-Gaussian distribution of heat intensity and constant values of thermophysical properties at one temperature (400 °C). This was extended in this investigation (Part II) to consider different thermophysical properties at different temperatures (from room temperature (25 °C) to 1300 °C) for a mild steel work material. The objective is to develop a rationale for the selection of an appropriate temperature for the choice of the thermophysical properties for the thermal analysis of arc welding. Since the quality of the weld for a given work material depends both on the thermodynamic and kinetic considerations, namely, the maximum temperatures and the temperature gradients (cooling rates) in appropriate sections of the welded part including the weld bead and the heat-affected zone (HAZ), they were determined in this investigation. The main output parameters from a thermal point of view are the widths and the depths of the melt pool (MP) and the HAZ at the weld joint. Although the length of the weld pool is also a consideration, if the entire length participates in the welding process, which is generally the case, then this is not such an important consideration. It is found that for welds produced in a conductive mode only (i.e., not considering the case of deep penetrating welds produced with keyhole mode), the values of the widths and the depths of the MP and the HAZs are nearly the same (within 10 to 20 pct), irrespective of the values of thermal properties for temperatures in the range of 400 °C to 1300 °C. Hence, the emphasis on the need to consider variable thermal properties with temperature in welding appears to be somewhat exaggerated. Also, based on the thermal analysis of the welding process, it appears that the room-temperature thermophysical properties may not be appropriate, as rightly pointed out by other researchers. The thermal history and the cooling rates were also determined analytically for arc welding of long workpieces, where quasi-steady-state conditions are established and the boundary effects can be ignored, as well as short workpieces, where transient conditions prevail and boundary effects need to be considered. This information can then be used in the appropriate time-temperature-transformation (TTT) diagram for a given steel work material to investigate the nature of the metallurgical transformation and the resulting microstructure in the welding process both in the weld bead and in the adjacent HAZs on either side.     

数值模拟在汽车板成形中的应用

在汽车和冶金工业中,板成形数值模拟广泛地应用于零件的选材和模具的设计.文章论述了板成形数值模拟的基本方法及其发挥的重要作用,并采用动力显式有限元软件DYNA3D对轿车顶板的冲压成形过程进行仿真计算,分析了成形安全裕度.     

Numerical Investigation of Residual Stress in Thick Titanium Alloy Plate Joined with Electron Beam Welding

A finite-element (FE) simulation process integrating three dimensional (3D) with two-dimensional (2D) models is introduced to investigate the residual stress of a thick plate with 50-mm thickness welded by an electron beam. A combined heat source is developed by superimposing a conical volume heat source and a uniform surface heat source to simulate the temperature field of the 2D model with a fine mesh, and then the optimal heat source parameters are employed by the elongated heat source for the 3D simulation without trial simulations. The welding residual stress also is investigated with emphasis on the through-thickness stress for the thick plate. Results show that the agreement between simulation and experiment is good with a reasonable degree of accuracy in respect to the residual stress on the top surface and the weld profile. The through-thickness residual stress of the thick plate induced by electron beam welding is distinctly different from that of the arc welding presented in the references.