基于MSC.SuperForm的金属体积成形数值模拟摩擦模型的二次开发

针对金属体积成形数值模拟,在反正切摩擦模型基础上,建立了考虑温度、压力和变形程度等的多因素摩擦模型,可以充分地考虑体积成形过程中速度、温度、单位压力和变形程度对变形体与模具之间界面的影响.采用该多因素摩擦模型对体积成形软件MSC.SuperForm进行了二次开发,通过实际算例分析,并与已有的文献结果对比,说明了提出的多因素摩擦模型的合理性.     

基于摩擦修正的TC6钛合金低应变速率变形本构模型建立

采用Thermecmastor-Z100kn热模拟试验机对TC6钛合金进行了低应变速率大变形热压缩试验,获得了变形温度范围为900～945℃、应变速率范围为0.0001～0.1 s^-1、变形程度为70%时的真应力-真应变曲线。分别使用传统摩擦修正模型与改进摩擦修正模型对真应力-真应变曲线进行修正,并建立了基于摩擦修正的应变补偿型Arrhenius模型。结果表明：改进摩擦修正模型能更好地表征材料在大变形状态下的真应力-真应变动态响应。经摩擦模型修正的应变补偿型Arrhenius模型相线性相关度较高,平均绝对误差较小,预测值精度较高。     

塑性成形中摩擦的研究进展和发展趋势(英文)

塑性成形中的摩擦是影响成形力、材料变形、成形质量和模具寿命的关键因素,也是受到多因素影响的高度非线性的物理问题,国内外学者在塑性成形摩擦机理研究和摩擦控制等方面做了大量的研究。从四方面总结和讨论塑性成形中摩擦的研究进展,分别是:摩擦测试方法、摩擦行为表征、摩擦模型以及摩擦优化/控制。并基于航空航天和汽车等高技术领域对高性能轻量化复杂构件的绿色、高效和精确成形制造的迫切需求,提出塑性成形中摩擦研究的发展趋势和挑战。     

基于数值模拟评价刮板锻造工艺的研究

以运输机刮板锻造工艺为研究对象,通过数值模拟研究了变形、热传导、变形生热、摩擦生热和磨损等因素对体积成形的影响,建立了成形过程中多因素动态耦合仿真模型。应用Archard模型分析了模具在复杂多因素耦合情况下的磨损,预测了单次磨损的深度分布,为间接预测模具寿命提供了依据。分析了锻造成形后的模具及锻件温度场分布、成形载荷等,为评价刮板热塑性成形工艺提供了理论依据。     

7022铝合金搅拌摩擦焊变形有限元分析

为了探究搅拌摩擦焊焊接变形规律,利用ANSYS有限元软件,建立了7022铝合金搅拌摩擦焊的数值模型,通过该仿真模型获得了搅拌头转速和进给速度对变形的影响.结果表明,高的搅拌头转速和低的进给速度会产生较大变形,并且搅拌头转速时变形的影响更显著.最后,通过搅拌摩擦焊试验和变形检测试验结果均表明焊件边角呈向上翘曲状态,焊板的...     

刚柔耦合关节SCARA机器人的双柔性动力学模型北大核心

针对电子装配机器人高速高精要求,提出一种能够利用柔性铰链变形补偿轴承摩擦死区,实现高精度定位运动的刚柔耦合关节SCARA机器人的概念设计,并建立考虑柔性铰链变形与机械臂一阶弹性变形的双柔性动力学模型。首先,设计一种刚柔耦合轴承的结构,通过轴承中柔性铰链的变形量主动补偿摩擦死区引起的定位误差;在每个关节处引入两个扭转弹簧,分别模拟柔性铰链和机械臂的弹性变形;其次,建立关节的摩擦模型以模拟关节摩擦环境;然后,使用拉格朗日动力学方法建立包含摩擦信息与振动信息的动力学模型。设计开环和闭环的数值仿真进行验证,结果表明该模型理论分析的有效性。     

板料拉深成形数值模拟摩擦模型及参数化实现研究

对板料拉深成形过程数值模拟新技术进行了研究，提出现有的摩擦模型的不足之处，拟提出一种全面考虑板料及模具的材质、表面粗糙度、接触应力、变形温度、变形程度、所用润滑剂的组分等情况的新摩擦模型，并拟用新摩擦模型来实现板料拉深成形过程数值模拟的的参数化研究。     

铝合金薄板搅拌摩擦焊接残余变形的数值分析

大尺寸6056铝合金薄板经过搅拌摩擦焊接实验后出现了严重的面外变形,虽然变形程度小于熔化焊结果,但已经影响到被焊薄板的装配和使用.为详细研究和预测铝合金薄板在搅拌摩擦焊后的残余变形,以焊接实验条件为基础,建立了搅拌摩擦焊接三维有限元热力耦合分析模型.模型中涉及了利用搅拌头工作转矩计算热输入量、工件和卡具之间的接触热传导、随温度变化的材料模型,以及综合考虑搅拌头机械作用等工作.利用该模型可以得到不对称的纵向残余应力结果,残余变形的趋势在整块板上都与实验结果相同,而且变形量和实验测量值之间的误差在20%以内.     

NUMERICAL ANALYSIS ON THE RESIDUAL DISTORTION OF Al ALLOY SHEET AFTER FRICTION STIR WELDING

大尺寸6056铝合金薄板经过搅拌摩擦焊接实验后出现了严重的面外变形,虽然变形程度小于熔化焊结果, 但已经影响到被焊薄 板的装配和使用.为详细研究和预测铝合金薄板在搅拌摩擦焊后的残余变形, 以焊接实验条件为基础, 建立了搅拌摩擦焊接三维有限元 热力耦合分析模型. 模型中涉及了利用搅拌头工作转矩计算热输入量、工件和卡具之间的接触热传导、随温度变化的材料模型, 以及综合 考虑搅拌头机械作用等工作.利用该模型可以得到不对称的纵向残余应力结果, 残余变形的趋势在整块板上都与实验结果相同, 而且变形量和实验测量值之间的误差在20%以内.     

张力减径过程仿真系统摩擦问题的研究

针对张力减径过程中金属变形的摩擦问题,建立了摩擦模型,比较准确地解决了轧制过程仿真时的接触摩擦问题.     

圆形等通道转角挤压过程三维数值模拟

基于网格重划分技术,采用有限元软件Marc对等通道转角挤压(Equal Channel Angular Pressing,ECAP)进行数值模拟,得到了模具转角φ=90°、ψ=0°以及不同摩擦条件下圆形试样ECAP变形过程的网格、载荷变化以及等效应变分布规律。结果表明:由于剪切变形和外摩擦作用,底部网格产生畸变,出口端部形成半球形;圆形ECAP过程经历开始变形、稳定变形和终了三个阶段,在开始变形阶段载荷急剧增加,进入稳定阶段后变化平稳,但由于摩擦和加工硬化作用载荷继续增加;与无摩擦情况相比,摩擦的存在增加了试样与模具接触的接触面积、载荷值以及变形的不均匀性。此外,试样中心较表面变形更均匀,而中间截面相比头尾变形较为均匀。     

Effect of High Strain-Rate Deformation and Aging Temperature on the Evolution of Structure,Microhardness, and Wear Resistance of Low-Alloyed Cu–Cr–Zr Alloy

The effect of the preliminary high strain-rate deformation, performed via the method of dynamic channel-angular pressing (DCAP), and subsequent annealings on the tribological properties of a dispersionhardened Cu–0.092 wt % Cr–0.086 wt % Zr alloy has been investigated. It has been shown that the surfacelayer material of the alloy with a submicrocrystalline (SMC) structure obtained by the DCAP method can be strengthened using severe plastic deformation by sliding friction at the expense of creating a nanocrystalline structure with crystallites of 15–60 nm in size. It has been shown that the SMC structure obtained by the high strain-rate DCAP deformation decreases the wear rate of the samples upon sliding friction by a factor of 1.4 compared to the initial coarse-grained state. The maximum values of the microhardness and minimum values of the coefficient of friction and shear strength have been obtained in the samples preliminarily subjected to DCAP and aging at 400°С. The attained level of microhardness is 3350 MPa, which exceeds the microhardness of the alloy in the initial coarse-grained state by five times.     

Mechanism investigation of friction-related effects in single point incremental forming using a developed oblique roller-ball tool

Single point incremental forming (SPIF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. In the SPIF process, a ball nose tool moves along a predefined tool path to form the sheet to desired shapes. Due to its unique ability in local deformation of sheet metal, the friction condition between the tool and sheet plays a significant role in material deformation. The effects of friction on surface finish, forming load, material deformation and formability are studied using a newly developed oblique roller ball (ORB) tool. Four grades of aluminum sheet including AA1100, AA2024, AA5052 and AA6111 are employed in the experiments. The material deformation under both the ORB tool and conventional rigid tool are studied by drilling a small hole in the sheet. The experimental results suggest that by reducing the friction resistance using the ORB tool, better surface quality, reduced forming load, smaller through-the-thickness-shear and higher formability can be achieved. To obtain a better understanding of the frictional effect, an analytical model is developed based on the analysis of the stress state in the SPIF deformation zone. Using the developed model, an explicit relationship between the stress state and forming parameters is established. The experimental observations are in good agreement with the developed model. The model can also be used to explain two contrary effects of friction and corresponding through-the-thickness-shear: increase of friction would potentially enhance the forming stability and suppress the necking; however, increase of friction would also increase the stress triaxiality and decrease the formability. The final role of the friction effect depends on the significance of each effect in SPIF process.     

利用圆环镦粗法测定7050铝合金高温变形摩擦系数

采用圆环镦粗法进行了7050铝合金高温变形摩擦系数测试实验,研究了7050铝合金在不同变形速度、不同变形温度、不同变形程度、不同润滑剂条件下的高温变形摩擦。实验结果表明,润滑状态对其高温变形摩擦影响最大,变形温度次之。     

PERFORMANCE OF LUBRICATING OIL FILMIN ALUMINIUM FOIL ROLLING

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基于摩擦补偿的电液作动器高精度控制

电液作动器因其集成度高、占用空间小,容易组成分布式集中控制系统,在航空航天与工程机械领域飞速发展,但是在低速运行工况下,由于摩擦力以及液压系统的非线性等因素,难以完成高精度轨迹跟踪工作甚至产生低速爬行。为此,从摩擦特性对电液作动器轨迹跟踪精度的影响出发,提出一种前馈补偿+ESO的控制策略,引入LuGre动态摩擦力中的鬃毛平均变形量,建立精确伺服系统状态空间方程,在Simulink平台上搭建摩擦力模型和泵控非对称缸模型,采用正弦位置指令对该解决方案的轨迹跟踪精度进行了仿真验证。结果表明:前馈补偿+ESO的控制策略跟踪误差仅为常规PID控制的1/4,跟踪精度达到0.2 mm。     

Effect of hardening friction treatment with hard-alloy indenter on microstructure, mechanical properties, and deformation and fracture features of constructional steel under static and cyclic tension

It has been studied how a hardening friction treatment with a sliding hard-alloy indenter influences the chemical composition and roughness of the surface, the structure, the distribution of the microhardness and the density of dislocations in depth of the surface layer, the mechanical properties upon static tension and the features of deformation and fracture upon cyclic tension of the annealed low-carbon (0.17 wt.% C) steel grade 20. It has been found that friction hardening of the steel (an increase in the microhardness up to 4.25 GPa) is due to a considerable dispersion of the ferritic base (with the formation of alpha-phase fragments no less than 100 nm in size) and pearlite colonies (crushing and partial dissolution of cementite plates) under the action of a severe friction deformation; hardening is not connected with the carryover of separate particles of the hard alloy to the steel surface. A finite-element model describing the process of the friction treatment with a sliding cylindrical indenter has been constructed. This model was used to determine how the number of the indenter strokes, the friction coefficient, and the shear component of the deformation affect the value of the accumulated deformation. It has been shown that the friction treatment improves the strength characteristics of the steel upon static tension. The hardened surface layer is susceptible to further considerable hardening (an increase in the microhardness up to 5.6-5.9 GPa) at the initial stages of the cyclic deformation and, therefore, has some margin of plasticity. The plastic flow in the surface-hardened steel under cyclic loading is due to the formation of numerous bands of localized deformation. It has been found that the friction-hardened surface layer is more prone to cracking under cyclic loading. The methods by which cracking of the hardened layer can be diminished have been discussed.     

铝板冷轧润滑模型及应用

提出一种建立于流体动力学及塑性变形原理基础上的铝板冷轧润滑模型。可用于预测分析轧制变形区内油膜厚度、前滑、轧制压力及摩擦力分布等。该模型首先求解板材入口速度，然后得到油膜厚度，进行了高粘度矿物油铝板轧制试验，实测了不同压下率下入口油膜厚度，结果表明：实测值与计算值相当吻合，该模型为进一步研究板材冷轧及其润滑过程，优化生产工艺提供了依据。     

摩擦焊接过程数值模拟技术研究进展

根据摩擦焊接过程数值模拟存在的主要难点,重点介绍了摩擦焊接热输入、焊合区金属塑性变形、以及焊接过程主要参量场,如温度场、应力应变场有限元热力耦合分析的几种模型及其研究进展。文献研究表明,目前摩擦焊接过程物理参量场的数值模拟主要采用二维、非稳态、变物性模型。一般忽视辐射及对流换热。焊接界面上热流量可以根据扭矩曲线或摩擦系数分布曲线计算,热流分布采用均布或线性假设,近年来有关学者直接根据焊接材料的性能数据和设定的焊接规范参数进行摩擦焊接过程特征参量及相应物理参量场的模拟研究工作,并模拟了摩擦焊接过程的两种产热模型及其转化规律（摩擦初期的摩擦产热与摩擦后期的塑性变形产热）。