3104铝合金薄板深冲制耳的有限元模拟

采用由板材织构信息进行加权的CMTP屈服函数并考虑了摩擦和压边力的变化对3104铝合金薄板的深冲制耳进行了有限元模拟；并与采用Barlat(1991)屈服函数的预测值及实测值进行了比较；分析了深冲过程中圆片的厚度变化规律；讨论了进一步提高预测精度需考虑的因素。结果表明：采用CMTP屈服函数模拟的制耳轮廓与实测值比较吻合，随摩擦和压边力的增加，制耳轮廓高度也增加；且比采用Barlat(1991)屈服函数模拟的精度要高。模拟深冲过程中圆片厚度的变化规律与实际情况一致。     

油底壳冲压过程的有限元数值模拟

采用有限元软件MARC，基于更新拉格朗日的弹塑性本构方程建立了一个有限元模型来模拟油底壳的成形过程。模拟得出了油底壳变形过程中板材的应力、应变、摩擦和厚度分布，揭示了成形过程中金属的塑性变形规律，并预测了可能发生失效的区域，为成形工艺设计提供了有效的分析工具。     

钢铝异种金属回填式搅拌摩擦点焊的数值模拟研究

本文提出一种模拟异种金属双层板搭接回填式搅拌摩擦点焊下扎过程的方法。以2 mm厚度的AA6061-T6铝合金板和AISI4340普通钢板为研究对象,建立完全热力耦合模型以及库伦摩擦和常应力摩擦混合的热源模型,利用DEFORM软件模拟焊接过程中的温度场、搅拌头受力情况和材料变形情况。结果表明:搅拌针与下板材接触时的下扎距离大于上板材厚度,焊接区域结合面温度分布均匀,板材结合面在搅拌针施加力的方向发生搅拌针底边缘部凹中心凸的变形,凹陷变形方向与温度扩散方向一致,结合面的变形是造成钩状缺陷的主要原因。     

航空铝合金板材搅拌摩擦连接有限元分析

根据搅拌摩擦连接特点,充分考虑搅拌摩擦连接过程中搅拌针各部位与连接板材之间的摩擦生热及在连接过程中连接板材摩擦系数随温度变化规律,建立了适合搅拌摩擦连接自身特点的动态热元模型,并利用此模型进行了航空铝合金板材搅拌摩擦连接过程的有限元分析模拟.通过模拟结果和试验结果对比验证了所建立的动态热源模型和有限元分析过程是合理的.模拟结果显示搅拌摩擦连接残余拉应力主要集中在连接区,且在连接区中间位置出现最大残余拉应力区,连接区两端及其它部位出现残余压应力.     

铝合金搅拌摩擦焊三维模拟流场厚度方向流动状况分析

采用计算流体力学软件FLUENT，建立搅拌摩擦焊的三维流场模型。对所建流场模型分别作横、纵向切片，得到不同位置的厚度方向流动状况，分析结果表明：模拟流场结果与试验所测流场基本吻合。厚度方向的流动较水平方向流动弱，流动状况也较复杂，试验不易观测，所测流场误差较大；焊缝中部和上部，前进侧金属旋转向前流动，返回测金属旋转向后流动；焊缝下部，两侧金属均向后流动以填补摩擦头前进所留下的空隙；厚度方向的流动状况与温度场分布密切相关；摩擦头前方的自底部向顶部的向上流动以及摩擦头后方自顶部向底部的旋涡流动与摩擦头焊接时的倾斜角度也有关系。     

Sn-Bi合金介质压力成形下轻质铝板的成形性

提出了Sn-Bi合金介质压力成形方法，利用Sn-Bi合金介质的热敏感特性，通过温度控制其流变行为，可以改变板材压边区的流动状态，同时可实现板材的无压边成形。采用欧拉-拉格朗日自适应网格建立了有限元模型，分析了Sn-Bi合金介质的厚度对成形板材在成形过程的应力、应变和板材厚度分布的影响。揭示了Sn-Bi合金介质压力成形下抑制起皱、破裂的机理。数值模拟结果与试验结果一致，Sn-Bi合金介质压力成形可改善板材成形应力分布，提升板材成形材料流动均匀性，抑制板材失效，为板材的无余量防皱成形方法提供了理论依据。     

基于有限元方法Ti-50A筒形件拉深成形过程研究

通过对Ti-50A板材拉深过程的数值模拟,研究了参数选择与状态控制的基本途径,建立了对拉深过程进行数值模拟所用的几何模型.选择了壳单元为离散模型,采用映射网格划分技术对几何模型进行了网格划分,并对板料拉深数值模拟过程采用了自适应网格划分.针对Ti-50A钛合金给出了合适的材料本构模型.解决了加载、边界约束及求解过程当中最佳的时间和步长问题.利用接触理论和经典的库仑摩擦定律处理了模拟过程当中板坯与模具的接触与摩擦问题,最终完整地建立了符合实际的Ti-50A拉深成形过程数值模拟的有限元模型.通过有限元模拟与实际情况对比,验证了所提出的技术方案.     

板材成形模拟的研究和应用

介绍了板材成形数值模拟技术的研究和应用在国内外发展的概况，并从基本算法、单元模型和网格划分、材料模型、接触摩擦、起皱问题、破裂问题和回弹计算等方面介绍了弹塑性有限元的基本原理、关键技术和主要难点，结合在工厂实际生产中的使用情况和存在的问题，展望了板材数值模拟技术今后的发展方向。     

数控渐进成形中挤压方向对钣金件厚度均匀化影响

针对数控渐进成形中钣金件厚度不均匀的问题,提出一种新的挤压方向与水平面成一定角度的倾斜挤压成形方式。该方法采用根据成形角优化的倾斜轨迹,并沿着垂直于该倾斜轨迹的方向挤压板材。而传统方法多采用挤压工具沿Z轴方向的竖直挤压成形方式。采用数值模拟和实际成形实验相结合,对比分析了倾斜挤压方式和竖直挤压方式对成形件厚度均匀化的影响。数值模拟结果表明:竖直挤压时板材件厚度差为0.4011 mm,倾斜挤压时板材件厚度差为0.3883 mm,即倾斜挤压时板材件厚度差较竖直挤压时小,说明倾斜挤压时板材件厚度更均匀一些。成形实验结果也表明:竖直挤压时板材件厚度标准差为0.099 mm,倾斜挤压时板材件厚度标准差为0.0933 mm,因此,倾斜挤压成形较竖直挤压成形能够使板材件厚度分布更均匀。     

基于流函数法的铝合金板材异步轧制应变计算数学模型

作为一种剧烈塑性变形技术，异步轧制是提高铝合金板材变形均匀性的重要方式。但由于异步轧制中存在多变量、强耦合、非线性等特点，其厚度方向变形机制难以精准解析。为深入研究异步轧制厚度方向变形情况，建立了一种板材异步轧制沿厚度方向应变计算模型。根据轧制过程的运动学特点，变形区被分为刚性-塑性-刚性区。在此基础上对变形区边界条件进行了修正，并采用流函数法建立近真实的运动学容许速度场。根据最小能原理和线性化积分手段建立了轧制功率消耗模型，解决了计算过程中的多参量非线性耦合问题，实现了变形区边界模型的快速计算。结合速度分量与应变速率分量，最终建立了异步轧制轧后应变计算模型。为了验证理论模型的准确性进行了数值模拟与异步轧制试验。与试验结果进行对比，计算结果最大误差为13.44%，最小误差为1.33%，整体计算耗时缩减到1 s以下。模型的建立可为异步轧制板材质量调控与预测提供重要理论参考。     

Prediction of cutting forces in three and five-axis ball-end milling with tool indentation effect

Simulation of multi-axis ball-end milling of dies, molds and aerospace parts with free-form surfaces is highly desirable in order to optimize the machining processes in virtual environment ahead of costly trials. This paper presents a mechanics model that predicts the cutting forces in feed (x), normal (y) and axial (z) directions by modeling the chip thickness distribution, and cutting and indentation mechanics. The shearing forces are based on commonly known cutting mechanics models. The indentation of the cutting edge into the work material is modeled analytically by considering elasto-plastic deformation of the work material pressed by a rigid cutting tool edge with a positive or negative rake angle. The distribution of chip thickness and geometry of indentation zone are evaluated by considering five-axis motion of the tool along the toolpath. The proposed model has been experimentally validated in plunge indentation, as well as in three and five-axis ball-end milling of free-form surfaces. The prediction of axial (z) cutting forces is shown to be improved significantly when the proposed indentation model is integrated into the mechanics of ball-end milling.     

An Experimental Evaluation of Material Properties and Fracture Simulation of Cryorolled 7075 Al Alloy

This work presents an experimental evaluation of yield strength, tensile strength, and impact toughness of 7075 Al alloy. The extended finite element method (XFEM) has been chosen for quasi-static crack growth simulations using Charpy impact energy as the crack growth criterion for both Bulk and ultrafine-grained (UFG) 7075 Al alloy. The 7075 Al alloy is rolled for different thickness reductions (40 and 70%) at cryogenic (liquid nitrogen) temperature, and its mechanical properties are studied by performing the tensile and Charpy impact testing. The microstructural characterization of the alloy was carried out using field emission scanning electron microscopy (FE-SEM). The rolling of the Al alloy at cryogenic temperature suppresses dynamic recovery, and dislocation cells formed during processing, transformed into fully formed ultrafine-grains (600?nm) at 70% thickness reduction. The impact energy used as the crack growth criterion under quasi-static loading condition based on the Griffith energy concept. The elastic-plastic ductile fracture simulations are performed by XFEM using ABAQUS Software (Version 6.9). For crack modeling, two different types of functions are used to model a crack based on partition of unity concept. A discontinuous function is used to model the portion behind the crack tip, whereas crack tip is modeled by near-tip asymptotic functions. This permits the crack is to be represented explicitly without meshing the crack surfaces, thus crack propagation simulations can be carried out without a need of re-meshing. Strain energy release and stress distribution ahead of the crack tip is found for some practical crack problems. The numerical examples indicate a significant improvement in crack growth properties of UFG 7075 Al alloy as compared to its bulk form due to an effective grain refinement.     

Finite element modeling of segmental chip formation in high-speed orthogonal cutting

An explicit, Lagrangian, elastic-plastic, finite element code has been modified to accommodate chip separation, segmentation, and interaction in modeling of continuous and segmented chip formation in highspeed orthogonal metal cutting process. A fracture algorithm has been implemented that simulates the separation of the chip from the workpiece and the simultaneous breakage of the chip into multiple segments. The path of chip separation and breakage is not assigned in advance but rather is controlled by the state of stress and strain induced by tool penetration. A special contact algorithm has been developed that automatically updates newly created surfaces as a result of chip separation and breakage and flags them as contact surfaces. This allows for simulation of contact between tool and newly created surfaces as well as contact between simulated chip segments. The work material is modeled as elastic/perfectly plastic, and the entire cutting process from initial tool workpiece contact to final separation of chip from workpiece is simulated. In this paper, the results of the numerical simulation of continuous and segmented chip formation in orthogonal metal cutting of material are presented in the form of chip geometry, stress, and strain contours in the critical regions.     

板料成形模拟坯料网格尺寸的控制

建立方盒拉深件有限元模型,用不同的坯料板厚、网格尺寸进行成形模拟计算,讨论了坯料网格尺寸对计算精度的影响;提出了合适的坯料网格尺寸的确定原则及其定量标准.     

Tribological Performance of Coated Surfaces

The fundamentals of coating tribology is presented in a generalised holistic approach to friction and wear mechanisms of coated surfaces in dry sliding contacts. It is based on a classification of the tribological contact process into macromechanical, micromechanical, tribochemical contact mechanisms and material transfer. The tribological contact process is dominated by the macromechanical mechanisms, which have been systematically analysed by using four main parameters: the coating-to-substrate hardness relationship, the film thickness, the surface roughness and the debris in the contact. In this paper special attention is given to the microlevel mechanisms, and in particular new techniques for modelling the elastic, plastic and brittle behaviour of the surface by finite element (FEM) computer simulations. The contact condition with a sphere sliding over a plate coated with a very thin hard coating is analysed. A three dimensional FEM model has been developed for calculating the first principal stress distribution in the scratch tester contact of a diamond spherical tip moving with increased load on a 2μm thick titanium nitride (TIN) coated steel surface. The model is comprehensive in that sense that it considers elastic, plastic and fracture behaviour of the contact surfaces. By identifying from a scratch experiment the location of the first crack and using this as input data can the fracture toughness of the coating be determined.     

Mathematical and numerical modeling of the effect of input-parameters on the flushing efficiency of plasma channel in EDM process

In the present study, the temperature distribution on the surface of workpiece and tool during a single discharge in the electrical discharge machining process has been simulated using ABAQUS code finite element software. The temperature dependency of material properties and the expanding of plasma channel radius with time have been employed in the simulation stage. The profile of temperature distribution has been utilized to calculate the dimensions of discharge crater. Based on the results of FEM and the experimental observations, a numerical analysis has been developed assessing the contribution of input-parameters on the efficiency of plasma channel in removing the molten material from molten puddles on the surfaces of workpiece and tool at the end of each discharge. The results show that the increase in the pulse current and pulse on-time have converse effects on the plasma flushing efficiency, as it increases by the prior one and decreases by the latter one. Later, the introduced formulas for plasma flushing efficiency based on regression model were utilized to predict the cardinal parameter of recast layer thickness on the electrodes which demands expensive empirical tests to be obtained.     

Modeling of Thickness and Profile Uniformity of Thermally Sprayed Coatings Deposited on Cylinders

In thermal spraying processes, kinematic parameters of the robot play a decisive role in the coating thickness and profile. In this regard, some achievements have been made to optimize the spray trajectory on flat surfaces. However, few reports have focused on nonholonomic or variable-curvature cylindrical surfaces. The aim of this study is to investigate the correlation between the coating profile, coating thickness, and scanning step, which is determined by the radius of curvature and scanning angle. A mathematical simulation model was developed to predict the thickness of thermally sprayed coatings. Experiments were performed on cylinders with different radiuses of curvature to evaluate the predictive ability of the model.     

The prediction of cutting force in ball-end milling

Due to the development of CNC machining centers and automatic programming software, the ball-end milling have become the most widely used machining process for sculptured surfaces. In this study, the ball-end milling process has been analysed, and its cutting force model has been developed to predict the instantaneous cutting force on given machining conditions. The development of the model is based on the analysis of cutting geometry of the ball-end mill with plane rake faces. A cutting edge of the ball-end mill was considered as a series of infinitesimal elements, and the geometry of a cutting edge element was analysed to calculate the necessary parameters for its oblique cutting process assuming that each cutting edge was straight. The oblique cutting process in the small cutting edge element has been analysed as an orthogonal cutting process in the plane containing the cutting velocity and chip flow vectors. And with the orthogonal cutting data obtained from end turning tests on thin-walled tubes over wide range of cutting and tooling conditions, the cutting forces of ball-end milling could be predicted using the model. The predicted cutting forces have shown a fairly good agreement with test results in various machining modes.     

管件壁厚对收口影响的研究

建立了管件收口工艺的刚塑性有限元模型,运用DEFORM-2D软件对不同的管件壁厚进行收口成形的模拟研究,分析了不同的壁厚对收口质量、应力应变分布规律和行程载荷变化以及可能产生的缺陷等。结果表明：为了满足管件收口的尺寸要求,必须严格控制在该模具下的收口,应该保证管件的壁厚大于5mm而小于15mm。     

The modeling of coating thickness, heat transfer, and fluid flow and its correlation with the thermal barrier coating microstructure for a plasma sprayed gas turbine application

The plasma sprya deposition of a zirconia thermal barrier coating (TBC) on a gas turbine component was examined using analytical and experimental techniques. The coating thickness was simulated by the use of commercial off-line software. The impinging jet was modeled by means of a finite difference elliptic code using a simplified turbulence model. Powder particle velocity, temperature history, and trajectory were calculated using a stochastic discrete particle model. The heat transfer and fluid flow model were then used to calculate transient coating and substrate temperatures using the finite element method. The predicted thickness, temperature, and velocity of the particles and the coating temperatures were compared with these measurements, and good correlations were obtained. The coating microstructure was evaluated by optical and scanning microscopy techniques. Special attention was paid to the crack structures within the top coating. Finally, the correlation between the modeled parameters and the deposit microstructure was studied. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.