铝合金变极性等离子弧焊应力场数值分析

以传热学及热弹塑性有限元分析法为理论基础,利用ANSYS有限元分析软件,对铝合金变极性等离子弧焊接温度场、应力场进行数值模拟. 建立 "高斯+双椭球"热源模型,通过正反极性不同尺度热源模型的循环加载,实现对焊接温度场及其应力场较准确的计算;焊后在焊缝的纵、横方向选取不同的点进行残余应力实际测量. 结果表明,不同路径上焊接残余应力值其分布规律与理论基本相同;实际测量结果同计算结果进行比较,二者数值相差较小,说明数值分析的计算结果具有一定的理论指导意义.     

马氏体/贝氏体异种耐热钢接头焊接应力数值模拟

采用热弹塑性有限元方法对马氏体耐热钢9Cr1MoVNbN(T91)与低合金贝氏体耐热钢12Cr2MoWVTiB(G102)异种钢接头的温度场、应力场进行了数值模拟;并比较了接头在不同焊接线能量条件下的温度场、应力场。模拟计算结果表明,由于异种钢接头热物理性能的差异,其焊接温度场和应力应变场均不对称。由于T91的导热系数小于G102,加热过程中,G102侧的升温速度较快。而在冷却过程中,T91侧的温度梯度较G102侧小,而热影响区更宽。焊后T91钢一侧的应力梯度小于G102,但高应力区域比G102一侧宽。通过对模拟结果的比较分析,从降低焊接残余应力的角度出发,采用小线能量可减少接头中的拉伸残余应力。     

高温喷丸强化Ti6Al4V合金的热力耦合数值模拟

发展一种连接喷丸强化与高温加载传热的热力耦合有限元方法,模拟高温喷丸强化Ti6Al4V合金的过程。首先建立一圆盘模型模拟待喷材料的高温加载传热过程。然后将圆盘模型的受热部分取出一小块建立对称胞元喷丸模型,并且将高温加载所致的温度场和热应力场通过解析场的方式导入到对称胞元喷丸模型,模拟高温喷丸强化过程。最后通过回弹计算获得稳定的残余应力场和温度场。创建4种模拟工况：常温喷丸、单独导入温度场的喷丸、单独导入热应力场的喷丸和高温喷丸,探究高温喷丸的残余压应力强化机理。结果表明：在常温环境下,对称胞元喷丸模型模拟的Ti6Al4V表层残余应力与试验结果具有很好的一致性。在高温加载作用下,随着热流密度的增加,受喷材料表层残余压应力有所减小,材料亚表层的残余压应力逐渐增大。影响高温喷丸强化的残余压应力的主要因素是高温加载所致的温度场,热应力场对残余压应力强化起次要作用。     

95W-5Ta激光粉末床熔融应力场演变及变形控制

以95W-5Ta混合粉末研究对象,针对95W-5Ta激光粉末床熔融工艺成形过程中存在的热应力较大和变形严重的问题,基于有限元方法对成形中应力场演变过程进行数值模拟. 模拟结果表明,应力变化是一个多重循环过程,增大激光功率和降低扫描速度都会导致热应力增大,分区扫描策略能使热应力均匀分布,避免在零件的敏感区域出现应力集中. 通过开展工艺实验分析影响变形量的因素,发现变形程度对激光功率更加敏感,同时与扫描线长度、层间交错角和扫描策略有关. 试验表明,采用较短的扫描线、67°层间交错角和较小的分区扫描能获得较小的变形量.     

焊后热处理对P92钢管道焊接残余应力场的影响

采用红外热成像仪测量了P92钢管道在焊接过程中的温度场分布,由此获得P92钢焊接过程的温度循环曲线;采用有限元方法模拟了P92钢管道多层多道焊的整个焊接过程,获得焊接温度场分布,与P92钢焊接温度场实测结果吻合良好,验证了模拟计算的准确性;采用间接法,利用温度场结果计算了P92钢管道环焊缝焊接形成的残余应力场,并重点分析了焊后热处理前后的焊接残余应力变化情况.结果表明,焊后热处理对P92钢管道焊接残余应力具有明显的消除作用,但不能完全消除,焊缝中依然存在较大的拉伸残余应力.     

Distortion and Residual Stress in High-Pressure Die Castings: Simulation and Measurements

Two individual high-pressure die casting geometries were developed to study the influence of process parameters and alloy composition on the distortion behavior of aluminum alloy castings. These geometries, a stress lattice and a V-shaped lid, tend to form residual stress due to a difference in wall thickness and a deliberate massive gating system. Castings were produced from two alloys: AlSi12(Fe) and AlSi10MnMg. In the experimental castings, the influence of important process parameters such as die temperature, ejection time, and cooling regime was examined. The time evolution of process temperatures was measured using thermal imaging. Subsequent to casting, distortion was measured by means of a tactile measuring device at ambient temperatures. The measured results were compared against a numerical process and stress simulations of the casting, ejection, and cooling process using the commercial finite element method software ANSYS Workbench. The heat transfer coefficients were adapted to the temperature distributions of the die, and the castings were observed by thermal imaging. A survey of the results of the comparison between simulation and experiment is given for both alloys.     

基于有限单元法的铸件热应力场数值模拟

重点论述了基于有限单元法(FEM)对铸件热应力场进行数值模拟的理论基础和实际方法,开发了基于有限单元法的铸造热应力场模拟程序.采用典型试件进行了算例验证,并与ANSYS的模拟结果及实际铸件浇注结果进行了对比,结果吻合.研究表明,开发的基于有限单元法的铸件热应力场数值模拟程序,模拟结果精确,运行可靠.     

分区扫描对激光沉积修复钛合金热力耦合场的影响

为了控制激光沉积修复过程中残余应力,减少基材的变形,利用ANSYS参数化设计编程语言实现了激光沉积修复面缺陷损伤零件热力耦合场的数值模拟,得到了短光栅连续扫描和分区扫描情况下的节点热循环特性、温度场和残余应力场分布规律.结果表明,不同扫描方式下节点的热循环分布规律相似,但分区扫描时基材热量累积明显减小,且温度分布较为均匀,从而改善了基材中应力集中,使残余应力降低.为了验证结果的正确性,采用红外测温仪和压痕应变仪对不同扫描方式下激光沉积修复温度场和修复件表面残余应力进行了测量,并绘制了基材变形曲线.二者具有较好的一致性.     

基于MATLAB平台有限单元法的铸造热应力数值模拟

采用有限单元法(FEM)对铸件凝固过程热应力场进行了三维数值模拟研究,开发了基于MATLAB平台的FEM铸造热应力场模拟程序,采用典型应力框试件对所开发的算法和程序进行了算例验证,并与采用商品化软件ANSYS进行模拟的结果进行了对比,二者吻合良好.结果表明,所采用的算法及开发的程序能较好地预测铸件变形及热应力的集中位置.     

复杂铝型材挤压过程的模拟与试模(英文)

采用任意拉格朗日-欧拉描述法(ALE) 的自适应网格划分技术,运用 HyperXtrude 软件对铝加工的挤压过程进行仿真模拟,获得挤压时金属流动的应力—应变场、温度场以及速度场,并将模拟仿真结果与试模结果进行对比分析,其结果基本一致,证明运用该仿真模拟方法可以预测实际生产过程中的一些缺陷。     

Finite element simulation for mechanical response of surface mounted solder joints under different temperature cycling

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TI-6Al-4V钛合金电子束焊接有限元分析

采用有限元方法模拟分析了厚6 mm的Ti-6Al-4V钛合金电子束焊接过程,计算研究了瞬态温度场的分布特点、规律及特征点的温度变化历程,在准确计算焊接温度场的基础上通过热-应力顺序耦合,模拟计算了Ti-6Al-4V钛合金电子束焊接头的应力场的分布特征.结果表明:模拟计算的焊缝形貌与实际焊接试验所得基本吻合,焊接温度场整...     

Discussion on modeling of thermal fatigue cracks in numerical simulation based on eddy current signals

This study evaluates modeling of thermal fatigue cracks by the finite element method from the view point of eddy current testing. Five artificial thermal fatigue cracks introduced into type 304 stainless steel plates were prepared for the research. Eddy current signals were gathered by a differential type plus point probe and subsequent destructive tests were performed to confirm the true profiles of the cracks. Numerical simulation based on the results of eddy current testing and destructive tests were carried out to show how the thermal fatigue cracks should be modeled in numerical simulations. The results of the numerical simulations revealed that thermal fatigue cracks tend to be much less conductive than stress corrosion cracks if they are assumed to have uniform conductivity inside. The results also imply that taking consideration of magnetization induced by the thermal fatigue process enables eddy current signals to be analyzed more quantitatively.     

Numerical simulation of welding-induced distortion in thin-walled structures

Abstract

A sequentially coupled thermal stress analysis approach is presented for modelling temperature and distortion profiles resulting from welding thin-walled structures. The material is modelled as thermo-elastic–plastic with isotropic strain hardening. The heat source is modelled as a three-dimensional (3-D) double ellipsoid, and 3-D finite element (FE) models are employed for predicting ensuing distortions. Comparisons between the simulation results and experiments performed for eight weld configurations are presented. The weld configurations include bead-on-plate, butt weld and tee joint welds with varying plate thicknesses. Temperature measurements using thermocouples and an infrared (IR) imaging radiometer are directly compared to the thermal simulations. Likewise, distortions measured directly on the experimental set-ups are compared to the FE distortion predictions. Very good correlation is obtained for temperature as well as distortion predictions between experimental and proposed numerical approaches. Lastly, details of a weld simulation for the rear section of a motorcycle frame are presented.     

BT20钛合金筒形件真空热胀形过程热力耦合有限元分析

建立了BT20钛合金筒形件真空热胀形的二维非线性准静态热弹塑性有限元模型。该模型考虑了辐射传热和材料热物性非线性等因素的影响。使用有限元软件MSC．Marc对BT20钛合金筒形件真空热胀形过程进行数值模拟,计算了BT20钛合金筒形件真空热胀形过程的温度场、变形场和应力场,并进行了相应的实验验证。数值模拟结果与实验结果吻合较好,说明了所建立的热力耦合模型的有效性。     

回流焊冷却过程中PBGA焊点力学行为分析

以热弹塑性理论为基础,建立球栅阵列PBGA焊点在回流焊工艺中焊接应力的有限元模型,利用ANSYS的热结构耦合功能,采用生死单元法对Sn-Ag-Cu焊点回流焊的冷却过程进行数值模拟分析.焊点冷却结晶后的初始阶段,等效应力随温度的降低快速增加,当焊点的温度逐渐降低至室温时,等效应力为最大.结果表明,在回流焊接工艺中,PBGA焊点的裂纹极可能发生在焊料冷却结晶后的初始阶段,在焊点高应力集中区首先开裂,并在应力的作用下沿界面逐渐扩展.对焊料凝固初期冷却速率的控制是减少焊接裂纹产生的有效方法.     

数值模拟和实验研究Ti6Al4V合金激光熔透焊接残余应力

采用热-弹塑性三维有限元法研究激光熔透焊接Ti6Al4V合金的残余应力,并采用小孔法测量焊接残余应力以和计算结果进行比较.有限元计算时,建立了以焊缝形貌尺寸为参数的统一锥形热源模型来模拟不同热输入时的焊接温度场,并讨论了边界条件和有限元网格大小的确定.研究结果表明:采用焊缝轮廓尺寸作为热源参数能准确模拟焊缝横截面轮廓;钛合金激光熔透焊接的纵向残余应力分布梯度陡;在焊件表面和内部残余应力分布趋势不同,采用小孔法测量的残余应力分布和计算的焊接件内部残余应力分布相似.     

A three-dimensional finite element analysis of the temperature field during laser melting of metal powders in additive layer manufacturing

Simulating the transient temperature field in additive layer manufacturing (ALM) processes has presented a challenge to many researchers in the field. The transient temperature history is vital for determining the thermal stress distribution and residual stress states in ALM-processed parts that utilise a moving laser heat source. The modelling of the problem involving multiple layers is equally of great importance because the thermal interactions of successive layers affect the temperature gradients, which govern the heat transfer and thermal stress development mechanisms. This paper uses an innovative simulation technique known as element birth and death, in modelling the three-dimensional temperature field in multiple layers in a powder bed. The results indicate that the heated regions undergo rapid thermal cycles that could be associated with commensurate thermal stress cycles. Deposition of successive layers and subsequent laser scanning produces temperature spikes in previous layers. The resultant effect is a steady temperature build-up in the lower layers as the number of layers increases.     

金属凹模中半埋藏环形裂纹电磁热止裂的数值模拟

采用有限元方法研究了带半埋藏环形裂纹的Cr12MoV圆筒形凹模的电磁热止裂问题 ,建立了超强脉冲电流放电瞬间 ,环形裂纹尖端附近电场、温度场和热应力场的藕合关系。数值模拟分成热—电藕合 (焦耳热问题 )和热—机械藕合两个过程来实现 ,通过数值解析轴对称模型 ,给出了脉冲放电瞬间Cr12MoV凹模中电流—温度—热应力的求解过程 ,得到了脉冲放电瞬间带半埋藏环形裂纹凹模的温度场和热应力场。     

铸件热应力场数值模拟

基于有限差分法(FDM)对铸造过程热应力场进行了三维数值模拟研究，并对标准应力框试件和箱体铸件进行了热应力场模拟，得到比较满意的结果。此方法使得铸件应力应变分析与传热分析使用同一离散模型，避免了FDM／FEM不同模型之间的节点匹配及单元温度载荷传递，能使流动场、温度场、应力场数值模拟统一采用差分格式。