刚塑性无网格方法中精度影响因素的研究

将无网格方法引入金属塑性成形过程分析,基于刚塑性材料假设,采用移动最小二乘法对速度场进行逼近,利用变换法施加本质边界条件,实现了金属塑性成形过程的无网格方法模拟。在此基础上,结合典型锻造过程分析实例,重点研究了应用无网格方法分析金属塑性成形问题时,诸如:基函数、正交化与否、权函数、权函数影响域大小、积分方案、高斯积分阶次、节点分布密度以及针对体积闭锁问题而提出的体积应变率映射方法等对于模拟精度和效率的影响规律,给出了提高无网格模拟精度和效率的影响因素的选择方法。     

Characteristics of the tensile flow behavior of Ti–46Al–9Nb sheet material – Analysis of thermally activated processes of plastic deformation

Flow behavior, strain hardening and activation parameters, i.e. activation volume, stress exponents and normalized free enthalpy of activation, of Ti–46Al–9Nb sheet with near-gamma microstructure have been investigated in tension tests between 700 and 1000 °C. The dependence of yield stress on temperature and strain rate, the course of the strain hardening curves and the values of activation parameters show that thermally activated dislocation mechanisms are mainly involved in the tensile deformation process of the investigated material. At constant temperature the value of the activation volume depends both on plastic strain and strain rate. The activation volume generally decreases with increasing strain. The decrease is particularly well observable for higher strain rates, thus indicating a growing role of thermally activated climb mechanisms governing the process of dynamic recovery. The activation volume calculated for a constant plastic strain (2% in case of this study) is a function of temperature and strain rate. At lower deformation rates, or alternatively at higher temperatures, the activation volume increases. Such behavior indicates a decrease in dislocation density due to the onset of dynamic recrystallization. The analysis of stress exponents and the obtained free enthalpy of activation confirm that different thermally activated processes are acting during deformation under the tensile test conditions studied.     

斜轧穿孔过程的刚塑性无网格法数值模拟

斜轧穿孔工艺由于材料变形剧烈,涉及大量的材料非线性、几何非线性和接触非线性,而且在穿孔过程中金属伴有坯料晶粒翻转,其变形过程极其复杂。金属变形的剧烈和流动的复杂性,给斜轧穿孔过程的求解带来了难度。该文结合刚塑性材料流动法则,采用无网格法对斜轧穿孔过程进行数值模拟,分析了穿孔过程中金属的流动规律、力能参数、应力应变规律。实验结果与模拟结果较为吻合,证明该文方法具有可行性和有效性。     

双孔模型材挤压过程的有限元分析

本文采用大变形弹塑性有限元理论 ,对双孔模型材挤压成形过程进行了有限元分析。模拟了双孔模非对称角铝型材挤压变形过程 ,获得了挤压变形时网格畸变、流速、应力和应变分布 ,展示了型材挤压件变形不均匀细节。并与单孔模型材挤压过程进行了比较 ,发现双孔模[1] 挤压时 ,变形体内存在两个互为相反方向的涡流场 ,它们相互抵消 ,从而可以消除型材挤压过程中产生的扭拧、波浪、弯曲等缺陷。为提高挤压件质量 ,优化设计多孔型材挤压模以及制定合理的工艺 ,提供了理论依据     

基于SPH法的AZ31镁合金BP-ECAP过程三维数值模拟

光滑粒子流体动力学方法(Smooth Particle Hydrodynamics,SPH)在求解大变形问题方面具有优势。基于SPH法编写程序对AZ31镁合金的BP-ECAP过程进行三维数值模拟,并与相关研究文献进行对比,验证了编写的SPH法背压程序的正确性。对不同工艺参数下AZ31镁合金的背压-等通道挤压过程进行模拟,并从等效塑性应变及损伤值分布角度进行分析。模拟结果表明,选择恰当的背压值能有效地阻止镁合金变形过程中裂纹的萌生及扩展。     

面向应变均匀性和成形力的等径道角挤压模具结构参数优化

面向等径道角挤压成形应变均匀性和成形力,以3003铝合金为研究对象,采用有限元法分析不同模具外角、内角、内角半径挤压变形的等效应变均匀性和挤压成形力。研究结果表明:外角ψ对等效应变均匀性影响显著,而内角φ主要对挤压成形力影响较大,内角半径r对二者影响不明显。因此采用合理的模具结构参数,既可以提高应变均匀性,又能降低挤压成形力。基于正交试验分析得到了模具结构参数为:ψ=40°,φ=105°,r=1.5 mm,这为研究试样宏观塑性变形与细化晶粒微观组织演变规律、模具结构设计参数提供理论依据。     

Fracture of Magnesium Alloy in Cold Forging

In order to clarify the forming limit of magnesium alloy in cold forging, the workability of magnesium alloy AZ31B (Mg-3%Al-1%Zn) is examined by upsetting and backward extrusion. In the upsettability test, shear type fracture occurs at a small equivalent strain of about 0.15 at temperatures lower than 170 °C. At a higher temperature, the flow stress curve has a peak at an average equivalent strain of 0.2-0.3, showing a clear tendency to work soften. In cold backward extrusion with a conical punch, the local strain can reach a very large value, 3.0 or greater, without fracture. To explain the experimental results, the mechanism of fracturing is discussed on the basis of strain localization, and a fracture criterion of magnesium alloy in cold forging is suggested. The newly proposed criterion provides much better results than the existing criteria.     

铅黄铜C3771截止阀成形工艺优化研究

模拟铅黄铜C3771锻压和挤压工艺截止阀成形过程,得到锻压和挤压的工艺参数对铅黄铜C3771变形区的应变分布、等效应力分布和冲压载荷的影响规律.结果显示,从载荷分布分析,挤压工艺所用设备较锻压工艺设备的寿命长;.从等效应变来看,挤压模存在应力集中现象;锻压工艺成形时全局流体速率矢量分布较为均为,而挤压工艺成形时的全局流体速率分布不均匀,法兰部位和气门嘴部位的全局流体速率要大于其余部位,气门嘴部位型腔不易充填.     

Investigation and numerical analysis of strain distribution in the twist extrusion of pure aluminum

The effects of performing three twist extrusion passes on high purity aluminum samples were studied in this paper in regard to numerical analysis and experimental studies. The finite element analysis of the von-Mises stress and the equivalent plastic strain in the outer longitudinal and transverse cross-sections, which are parallel and normal to the billet axis respectively, was carried out. The simulation results showed that the end of the workpiece underwent more equivalent plastic strains in contrast to the head of the sample. Moreover, the corner regions experienced more strains than the center zone did. However, the heterogeneity in strain distribution in both longitudinal and transverse cross-sections decreased by performing the sequential twist extrusion passes. The experimental outcomes such as microstructure evolutions, microhardness and tensile tests validated the simulation results.     

1050铝合金扭转挤压加工的3D有限元分析(英文)

研究了扭转挤压做为一种大塑性变形加工技术的可行性,并将其与普通的正挤压进行比较。在室温下对AA1050铝合金成功进行了扭转挤压和正挤压。采用商用有限元软件ABAQUS/Explicit模拟挤压过程。结果表明,在扭转挤压中,所需的载荷要比正挤压所需的小。有限元分析结果表明,在扭转挤压中,试样承受了较高的等效塑性应变,在挤压的最后阶段扭转挤压试样中的应变分布较之正挤压更为平滑,均匀。     

无网格法在金属塑性成形中的研究与应用进展

介绍了无网格方法的基本原理;论述了无网格法在金属塑性成形领域里国内外的研究与应用现状;总结了相关关键处理技术,包括权函数的选取、本质边界的施加、离散积分方案、动态接触边界的自动处理以及金属塑性力学摩擦模型的选取等;最后对无网格法在金属塑性成形领域未来的研究方向进行了展望,并指出无网格法在金属塑性成形领域将有着更为广阔的发展与应用前景。     

链条滚子反挤压刚塑性有限元模拟研究

采用刚塑性有限元模型,应用Marc软件对链条滚子的反挤压成形过程进行了数值模拟分析,得出了应力应变分布规律和压力行程曲线,其中压力-行程曲线与实验测试数据吻合良好.计算得到的变形规律对于链条滚子的反挤压工艺设计具有一定的参考作用.     

On the application of a meshless method to shear band problems

Themultiple-scale Reproducing Kernel Particle Method (RKPM), one of the meshless methods, is applied to the analysis of a strain localization problem. The LagrangianRKPM formulation and explicit time integration are employed for the simulation of shear band formation in a viscoplastic material. The mul-tiresolution study is also performed using the multiple-scaleRKPM and then, an efficient high-scale component from the viewpoint of meshless method is proposed for mesh-free adaptive procedures that will be accomplished in the future.     

TA15钛合金热挤压过程中金属变形行为及组织分析

运用MSC.Marc有限元软件对TA15钛合金热挤压变形过程进行有限元模拟,得到热挤压成形过程中应力场和应变场分布情况。对有限元模拟所得到的应力、应变数据进行后处理,利用应力偏量不变量J2进行变形分区,采用罗德系数对塑性区内材料的应变类型进行划分。结合有限元模拟结果以及变形分区和变形类型的划分,对热挤压实验后的试样进行组织取样,在不同温度条件下对试样进行微观组织观察,分析微观组织的演化规律,这对于分析金属挤压成形问题及其在实际中的应用具有重要意义。     

Simulation of sheet metal extrusion processes with Arbitrary Lagrangian-Eulerian method

An Arbitrary Lagrangian-Eulerian（ALE） method was employed to simulate the sheet metal extrusion process, aiming at avoiding mesh distortion and improving the computational accuracy. The method was implemented based on MSC/MARC by using a fractional step method, i.e. a Lagrangian step followed by an Euler step. The Lagrangian step was a pure updated Lagrangian calculation and the Euler step was performed using mesh smoothing and remapping scheme. Due to the extreme distortion of deformation domain, it was almost impossible to complete the whole simulation with only one mesh topology. Therefore, global remeshing combilaed with the ALE method was used in the simulation work. Based on the numerical model of the process, some deformation features of the sheet metal extrusion process, such as distribution of localized equivalent plastic strain, and shrinkage cavity, were revealed. Furthermore, the differences between conventional extrusion and sheet metal extrusion process were also analyzed.     

挤压过程自适应耦合无网格-有限元法数值模拟

提出面向金属体积成形过程的自适应耦合无网格-有限元法,阐述了实现自适应耦合的具体算法,及有限元区域与无网格区域的双向动态转换。在数值计算过程中,对发生畸变的有限元区域,将其转换为无网格区域;对已经脱离主变形区的无网格区域,将其转换为有限元区域。该方法保证了只在需要的地方实施无网格法,既能避免有限元法带来的网格重划分,又能有效克服纯无网格法计算效率低下的缺陷,充分发挥耦合方法的优势。采用自适应耦合方法对轴对称复合挤压过程进行数值模拟,与有限元法计算结果对比,验证了该方法的正确性和有效性。     

焊接应力场与应变场的计算与讨论

经典的观点认为焊缝存在残余压缩塑性应变,而目前有学者认为焊缝是在冷却的过程中形成的,与加热过程无关,认为焊缝只存在拉伸塑性应变,而不存在压缩塑性应变.针对这一对传统残余塑变理论的质疑,采用有限元方法对薄板熔焊对接接头纵向应力和应变的瞬态变化以及由焊缝中心到母材边缘的纵向应力和应变分布情况进行了计算.结果表明,焊缝及近缝区存在着残余压缩塑性应变,应力状态为拉应力,由焊缝中心到母材边缘其纵向应力由拉应力转变为压应力,纵向压缩塑性变形量逐渐下降,离焊缝较远受温度场影响较小的母材不产生塑性变形.     

往复挤压变形ZK60镁合金应变分布的有限元数值模拟

利用有限元法研究ZK60镁合金在多道次往复挤压过程中的应变分布。为优化往复挤压工艺,研究摩擦条件和模具结构尺寸对ZK60合金总等效塑性应变分布的影响。结果表明：ZK60合金试样经往复挤压后内应变分布不均匀。试样两个端部的应变量低于试样中间部位的应变量。工艺参数对应变分布的影响很大。试样和模具间的摩擦不利于试样内应变量的均匀分布,因而应尽量降低摩擦。为了提高应变量的均匀分布,应该使用较大的过渡圆角半径和较低的挤压角度。     

减速顶滑动油缸体温挤工艺的数值模拟

采用温挤压成形工艺生产减速顶滑动油缸体时,冲头经常会出现磨损和断裂失效。本文采用基于ＡＮＳＹＳ软件的二维弹塑性热力耦合数值模拟系统,对该工艺进行数据模拟,得到了变形过程中的金属流动、工件及模具的应力场、应变场和温度场的变化,并根据这些结果对冲头失效的原因进行了分析。     

稳态挤压过程刚塑性无网格伽辽金方法分析

采用刚塑性材料假设,建立了刚塑性无网格伽辽金方法。利用变换法施加本质边界条件;采用反正切摩擦模型描述摩擦力边界,在局部坐标系下施加摩擦力边界条件;采用Newton-Raphson迭代方法求解刚度方程。对于挤压过程而言,当高径比较大时,可被近似为稳态流动。由于口模内速度变化梯度较大,采用最小二乘近似节点控制方法来控制近似效果。根据建立的刚塑性无网格伽辽金方法对正向、反向和复合挤压过程等进行了稳态分析,并与刚塑性有限元软件Deform模拟结果进行了相应的比较,验证了无网格伽辽金方法分析结果的正确性。