基于样条曲面描述的大变形有限元数值模拟关键技术探索

模具型腔描述、锻件有限元网格划分、界面接触约束是制约三维复杂体成形有限元数值模拟技术应用的3个关键性问题。以3次B样条曲面描述为基础,对三维复杂工具表面离散、变形体三维网格自动划分、变形体边界节点与模具接触状态判断的一体化技术进行了研究。利用B样条曲面的直观性、局部性、通用性、造型灵活性等特点,构造复杂模具型腔曲面及变形体边界,提出三维网格样条生成法、改进的分块样条生成法及接触判断的区域层次搜索技术。     

基于ANSYS渐开线花键冷搓成形全过程的数值模拟

依据大变形弹塑性有限元理论和接触理论，综合考虑成形中的几何非线性、状态非线性、材料非线性以及工件与刀具的接触摩擦因素，借助有限元软件ANSYS对渐开线花键冷搓成形的过程进行数值模拟，方法新颖独特，其应用将对刀具的设计有参考作用。     

双粗糙接触模型的表面温度在滑动摩擦过程中变化分析

建立三维双粗糙体分形表面的热力耦合接触模型,在固定滑动速度工况下综合考虑了钛合金材料的磨损失效、界面粘着及接触过程中的热力耦合,动态探讨了粗糙体在滑动过程中接触表面的温度变化情况。运用有限元方法对滑动过程的温度场进行模拟仿真并得出:滑动摩擦初始时刻摩擦表面接触温度急剧上升,随着滑动距离的增加,最高接触温度处于波动状态;界面剪切强度越大,最高温度越高。通过研究接触表面的温度场分布情况,以探索滑动过程钛合金材料摩擦磨损的真正起因。将结果与相关文献实验进行比较,得出了模拟仿真的合理性。     

电子封装中超声波线焊的三维/二维非线性有限元分析

用三维和二维的有限元方法对超声波线焊进行了模拟，其间考虑了材料非线性、几何非线性和接触边界非线性的影响。实验显示，金线和焊接平台的接触界面为长椭圆形状，其中焊接部位发生在接触界面的周边。有限元模拟的结果显示，最大的接触压力以及由此导致的最大摩擦能密度也发生在接触界面的周边，从而解释了实验现象。分析了各工作参数对超声波线焊产生的影响。结果表明，并不是压碳按压力越高，接触压力就越大，这意味着提高压碳按压力不一定能提高焊接的可能性，有限元分析有助于确定合适的压碳按压力。     

基于模具解析描述的两维金属成形模拟中的通用接触处理方法

接触处理方法是影响有限元数值模拟精度和效率的关键因素。针对两维金属成形中模具可以用线段和圆弧分段解析描述的特点 ,提出了一种通用的 ,以节点位置和边界约束修正为核心的接触处理方法 ,它具有较高的计算精度 ,可以真实反映金属和模具之间的接触状态。     

双粗糙面滑动过程摩擦因数的变化分析

采用W-M函数建立具有分形特征的三维双粗糙面接触模型,考虑了接触界面间的黏着效应,在滑动速度、法向载荷及界面剪切强度等参数变化下,运用有限元方法探讨了粗糙体在滑动过程中摩擦因数的变化情况。结果显示,滑动速度、法向载荷及界面剪切强度等参数对摩擦因数的变化有一定的影响,边界润滑工况下平均摩擦因数为0.28,无润滑工况下平均摩擦因数为0.713,最大界面剪切强度时的平均摩擦因数为0.73;随着界面剪切强度的减小、法向载荷的增大、滑动速度的增加,滑动摩擦因数有所减小。与相关文献结论或实验结果进行比较,证明了上述结果的正确性。分析结果可为摩擦学设计和摩擦材料的制备提供理论参考。     

摩擦液柱成形初始阶段的二维轴对称数值模拟 

基于二维轴对称有限元模型,通过外部施加表面热流强度的手段对摩擦液柱单元成形(FHPP)初始阶段的热力耦合接触摩擦问题进行了数值模拟。结果表明：金属棒接触摩擦表面上的温度上升迅速,当其材料的屈服强度降低到一定值后就会在轴向应力的作用下发生塑性流动,进而对预钻孔底部进行填充;所施加的轴向应力、转速以及金属棒与预钻孔之间的径向间隙对成形过程都有不同程度的影响,轴向应力对成形过程的影响较转速对成形过程的影响略大,而径向间隙对成形过程的影响相对较小。     

双粗糙面滑动过程考虑黏着时的摩擦学性能分析

建立了二维双粗糙体分形表面的接触模型,在固定滑动速度工况下考虑材料的磨损失效,针对是否考虑接触过程中的黏着因素,动态探讨了粗糙体在滑动过程中的摩擦磨损变化情况。运用有限元方法对滑动过程的摩擦磨损进行模拟仿真,得出考虑黏着因素的界面剪切强度τ=σy/3(σy为材料的屈服应力)时的摩擦因数平均值为0.48;对滑动过程是否考虑黏着因素的磨损率及振动情况进行分析比较,引入快速傅里叶函数对摩擦振动进行变换得到功率谱,结果发现,考虑黏着因素的情况下,相应的磨损率较大,功率谱低频成分较多,振动相对比较平缓,所需要的能量也相应比较大。将模拟仿真结果与实验进行比较,验证了模拟仿真的合理性,也加深了对摩擦磨损过程物理图像的理解。     

滑动接触中摩擦发热的数值分析

在滑动接触中，存在摩擦起热问题，运动机理对接触行为参数特性的影响不同于纯滚动接触，采用有限元方法，利用ANSYS软件，对2维滚滑模型进行分析，通过研究接触区的温度，接触应力和变形在运动学状态下的变化特性，可以看到接触状态的非稳定性必定会造成实际摩擦状态的不同，这也是形成接触表面不均匀磨损的原因之一。     

变摩擦条件下三维接触问题有限元分析改进

首先对三维弹性接触问题的有限元求解算法进行研究,将接触条件转换到法向与滑动方向组成的局部二维坐标系内进行求解,并利用FORTRAN语言编制接触问题求解的程序包。然后应用该程序包对变摩擦条件下的接触算例进行研究,揭示摩擦因数随滑动速度改变时接触点随接触状态、接触力的变化规律。最后利用有限元软件对计算结果进行验证,证明了算法的有效性。     

Elastic deformation of a fixture and turbine blades system based on finite element analysis

Finite element analysis (FEA) has been used to recapitulate the interactions between fixtures and components over the last decade. Most of the researches were focussed on the 3-2-1 fixture for components with regular geometry using point-to-point contact elements, where the fixture element is represented by a point-contacting component. Due to predicable behaviour of the fixture–component pair, such a point-to-point contact representation may be sufficient. However, when components with complex geometry, e.g. B-spline surfaces, which are widely used in the automotive and aero-engine industries, are of interest, the point-to-point method can no longer be satisfactory. This paper proposes a method of FEA on a system of a fixture and turbine blades by considering the complex contact geometry and complicated contact status of fixture–component pairs using surface-to-surface contact elements. A complete procedure of FEA modelling including geometry simplification, contact modelling, stiffness of locators, mesh generation, boundary condition and loading sequence is explained in detail. Having verified the FEA prediction of the elastic deformation with the displacement of the workpiece measured by coordinate measurement machines (CMMs), the influential factors of deformation, such as friction and machining directions, are analysed.     

基于正应力摩擦模型的金属切削有限元仿真

刀-屑摩擦模型是金属切削仿真的关键问题,采用基于前刀面正应力的摩擦系数模型能够真实反映刀-屑接触长度内的摩擦状况,通过仿真和试验证明,采用该模型可获得较好的仿真精度,而且通过降低工件材料的剪切流动应力能够较好地模拟切削液的润滑效果对切削过程的影响.     

A class of slipline field solutions for metal machining with slipping and sticking contact at the chip-tool interface

In the present investigation slipline field solutions for orthogonal machining are presented when the plastically stressed region in the chip/tool contact length consists of both slipping (τk) and sticking (τ=k) zones. The interface friction in the slipping region is assumed to obey Coulomb's law and the fields are analysed using the linear approximation to the above non-linear boundary value problem as suggested by Dewhurst. The range of validity of the above slipline fields is examined from the consideration of overstressing of rigid vertices in the assumed rigid regions. Results are presented for variation of cutting forces, cutting ratio, chip curl radius and contact length with variation in rake angle and interface friction coefficient. Solutions incorporating elastic effects are obtained by the method suggested by Childs. Results from the theoretical analysis are compared with experimental values reported in literature.     

子午线轮胎静态侧倾性能有限元分析及试验研究

采用三维非线性有限元分析方法,在模型中考虑了轮胎的几何非线性、材料非线性以及轮胎接触非线性,计算了子午线轮胎195/60R14在不同角度侧倾接地时的变形情况,与试验结果进行了比较。分析了轮胎在静态不同角度侧倾接地状况下载荷-下沉量变化、接地区压力分布、接地区摩擦力分布、侧倾侧向力-侧倾角变化关系;采用连续加载-卸载方式,开展了轮胎侧倾接地试验,实时记录了轮胎受力与变形关系,采用压力敏感膜测量了轮胎侧倾接地时的接地区压力分布状况。结果表明,轮胎侧倾接地状况下的变形及接地区压力分布趋势的计算结果与试验测试结果一致。     

钢球展开过程运动学及动力学分析

钢球表面质量检测常用的办法是依靠展开机构中的摩擦力将钢球表面完全展开,摩擦力对钢球表面检测效率和精度有着重要影响。为分析摩擦对钢球展开的影响,根据展开轮与钢球接触的几何约束关系,对钢球与展开轮接触模型进行运动学分析,得到钢球与展开轮接触点位置的变化规律;由于展开装置构件之间全部依靠干摩擦接触约束,在古典Coulomb摩擦模型基础上,结合展开装置特性,建立修正的Coulomb摩擦模型,建立钢球和展开轮的运动微分方程,得到钢球与展开轮接触点处摩擦力的变化规律,并分析接触点处接触力的影响因素;同时根据展开原理构建实体模型进行虚拟仿真并搭建物理样机进行试验,结果表明驱动轮转速直接影响钢球与展开轮接触点法向接触力变化,从而影响接触点处摩擦力变化特性,通过摩擦力变化特性,解释了展开轮能实现钢球表面展开的工作原理。     

Thermal Behaviour of a Slipping Wet Clutch Contact

Wet clutches are used in automatic transmissions to enable gear changes and also to reduce energy loss in the torque converter. These friction devices are susceptible to stick–slip effects, which result in the vehicle giving an unsteady ride. Stick–slip effects can be avoided by ensuring the wet clutch and lubricant combination produces a friction coefficient that increases with sliding speed. Although wet clutches have been studied throughout the industry for many decades, the mechanism of the generated friction is still not fully understood. It is known that, because of the fibrous nature and thus very large roughness of friction material, the overall contact between clutch plates actually consists of many small, independent, contact units, which are the sites of the generated friction. Some authors have suggested that a temperature rise due to friction either at these contact units or of the overall clutch plate may be important in controlling friction behaviour. In this study, the flash temperatures at the contact units formed in the wet clutch contact have been measured using an infrared camera. Three friction materials have been tested. It was found that measured flash temperature in a pure sliding system similar to that present in a slipping clutch remain well below 5 °C, and are therefore unlikely to play a major role in the observed friction-speed dependency of slipping wet clutches at speeds below 2 m/s.     

MODELING COMPLIANT NONPENETRATION CONSTRAINT FOR VP MOTION SIMULATION

A unilateral non-penetration constraint dynamical simulation model with friction is constructed based on compliant model for mechanical system VP (virtual prototyping) simulation. This model combines computer graphics with multi-body system dynamics. It avoids handling multiplicity of solution, such as cases of no solution, multi-solution brought about by friction during traditional construction of non-penetration constraint based on rigid model. At the same time, the realism of VE (virtual environment) is improved in process of simulation. Furthermore, the valid condition of rolling and sliding unilateral contact is constituted based on singular perturbation and linear complementary theory. Finally, the compliant method is verified by an interaction between a multi-legged robot and VE.     

基于ANSYS的轮轨摩擦热效应分析

随着铁路的高速化和重载化,车辆运行环境日益恶化,破坏的程度也越严重。针对机车特定轮重、相对滑动速度、摩擦系数的工况,应用有限元分析软件ANSYS对钢轨瞬态温度场作了计算研究,并利用其中的参数化设计语言(APDL)实现了移动载荷的加载。结果表明钢轨轨表面温度随摩擦系数和相对滑动速度的增加而增大,最高温升与摩擦系数和相对滑动速度呈线性关系。得出的温度场为钢轨结构优化设计提供了依据。     

Friction Reduction in Mixed Lubrication

Minimization of frictional losses in the drivetrain of heavy-duty vehicles is important from both consumer satisfaction and environmental perspectives. Approaches to friction reduction in these components can be evaluated using simulation-based investigations. However, nearly all drivetrain components operate in the mixed lubrication regime which is difficult to model because both hydrodynamic lubrication and surface contact are significant and therefore, the total friction consists of hydrodynamic friction due to lubricant shearing and boundary film friction at asperity contact locations. Recent advances in simulation methods for mixed elastohydrodynamic lubrication (EHL) have enabled improved virtual design tools, such as those developed by Zhu and Hu and further improved by Liu et al. Here, these simulation tools are used to evaluate friction reduction and predict the effects on a mixed EHL interface under severe operating conditions. Three practical means of friction reduction are discussed based on the experimentally validated mixed lubrication friction model and its predictions made for representative, sample cases.     

面向制动噪声的盘式制动器有限元复模态分析

结合复模态分析理论和有限元法,在ANSYS平台上,利用自定义的摩擦单元实现了制动盘和制动块间的摩擦耦合,并用约束方程实现了盘式制动器中其它部件间的连接,建立了盘式制动器的有限元模型.最后以某典型盘式制动器为例计算了18kHz以下的复模态,并分析了其与制动噪声的关系.