扭动微动摩擦力数值分析

为揭示扭动微动接触表面摩擦力分布规律及其对表面磨损的影响,进一步丰富和完善扭动微动损伤机理,基于试验中扭动微动摩擦扭矩的变化,利用ABAQUS用户子程序Fric引入动态变化的摩擦因数,对扭动微动表面摩擦力学行为开展数值模拟分析。摩擦扭矩数值模拟和试验结果的对比分析验证了数值模拟方法的正确性。接触表面摩擦力分布及与试验磨损形貌的对比分析表明:摩擦应力的剪切作用对表面材料损失起着至关重要的作用,不同滑移区摩擦应力分布不同,故呈现的磨痕形貌不同。     

颗粒介质双筒剪切单元摩擦阻力的研究

为了研究颗粒流在摩擦副间隙中的运动和润滑特性,构建了一个双筒剪切装置来模拟无限剪切运动,并观察颗粒受剪切时所表现的特有现象。实验通过改变双筒的表面结构、转速、颗粒尺度和数量等因素来研究颗粒流的运动特性和对摩擦副的影响。结果表明：摩擦副表面越粗糙、颗粒数量越多、颗粒尺度越小,摩擦力越大;在剪切实验中,颗粒流表现出剪切膨胀现象,进而造成振动,其成因与颗粒架拱及强力链有关。     

对数螺线及直线型面单向联轴器摩擦自锁机制的显式动力学数值模拟比较研究

为保证综合式液力变矩器在偶合器及闭锁工况下的可靠、高效传动,以其换相工作的关键部件单向联轴器为研究对象,分析了其型面结构和自锁摩擦机制,构建了对数螺旋线型面和直线型面2种单向联轴器的计算模型,基于显式动力学分别对其楔紧过程的动态行为进行了数值模拟,并进行了摩擦过程的动态应力分布计算.结果表明,与有限元静力接触分析相比,采用显式动力学分析方法可以更为深入地了解摩擦自锁过程机制,以及准确计算动态过程中的应力分布和变化,分析结果表明对数螺旋线型面与直线型面相比,其应力峰值较小,楔紧过程较为合理,承载性能较好.     

分子动力学模拟纳米颗粒添加剂对边界润滑的影响

通过试验和模拟的方法研究了不同压力条件下纳米铜颗粒添加剂在正十六烷基础油中的边界润滑行为。建立具有正弦曲面粗糙峰的边界润滑模型,采用分子动力学分别模拟了在25,50,100,200 MPa 4种压力下,含纳米铜颗粒与不含纳米铜颗粒时润滑油沿膜厚方向的密度分布。在润滑体系的上下固体壁面施加方向相反的剪切速度,计算出壁面原子与铜颗粒原子的应力、固液界面摩擦力、正压力和摩擦因数。采用微纳米划痕仪测量了含铜颗粒润滑剂的摩擦因数。结果表明：不同压力下两种润滑体系中的十六烷基础油均出现分层现象;纳米粗糙峰直接接触时,接触界面仍存在少量的正十六烷分子,且分子主链的排列方向与剪切方向相同;在200 MPa时铜颗粒使固体壁面的最大应力减小35.3%,提高了润滑体系的承载能力;不含铜颗粒润滑体系润滑油膜在50 MPa时破裂,含铜颗粒润滑体系润滑油膜在200 MPa时破裂;模拟计算的边界润滑状态下两种润滑体系的摩擦因数符合试验测量值。     

考虑软三体接触的粗糙界面混合润滑模型研究

软三体颗粒润滑是利用大量松散的固体软颗粒在界面中的承载和剪切行为实现特殊环境下界面的减摩,因此研究软颗粒介质摩擦界面在剪切过程中的受力情况,对软三体颗粒润滑机理的分析以及润滑装置的设计都具有重要意义。研究中将第三体颗粒类比为流体,基于雷诺方程、黏度方程、Greenwood和Williamson接触模型（G-W模型）等建立了含大颗粒粗糙界面的混合润滑模型。该模型中摩擦副的总载荷及总摩擦力由流体、微凸体和大颗粒三部分共同构成。通过采用有限差分法对上述物理模型进行求解分析,探究膜厚比、第三体大颗粒的质量浓度、粒径以及试件的表面形貌、弹性模量对三体接触界面的承载和摩擦力的影响情况,进而分析大颗粒粒径和接触表面粗糙度耦合时软三体接触界面的力学性能。基于对所构建的软三体接触界面混合润滑模型的研究可知：合理选择大颗粒质量浓度、粒径以及试件的表面形貌、弹性模量有助于提高承载、减小摩擦力,使得软三体颗粒流具有更好的减摩润滑性能。     

冲压成形CAE技术中接触摩擦计算的新方法

以显式有限元仿真技术为背景 ,讨论冲压成形中模具与工件接触摩擦界面的计算问题 ,提出了一种新的接触界面计算方法 ,并应用非线性摩擦定律来计算作用在工件上的摩擦力。为避免用于计算接触力的罚函数法中的罚因子影响显式仿真算法的稳定性 ,采用了局部质量密度因子来抵消罚因子的负面影响。仿真计算实例结果验证了本方法的正确性以及在可靠性和计算速度方面的明显提高。     

基于动力显式算法的镍镀层钢带成形模拟

利用LS-DYNA软件采用实体单元及动力显式算法模拟了镍镀层钢带深冲成形过程。板料与模具之间采用主从面对算法,摩擦力服从库仑摩擦定律,界面结合采用固连断开接触模型。结果表明:镀层与基体在深冲成形过程中不会出现界面失效,基体与镀层应力-应变分布以及材料流动规律大致相同,但镀层的应力-应变分布情况更复杂,表现为个别地方分布的不均匀;同时通过改变板料与模具间的摩擦因数,可减小摩擦有利于材料成形性能的改善。     

膨胀管实体膨胀锥受力分析与膨胀试验验证

膨胀管技术主要应用在油气田开发领域,膨胀锥是膨胀管技术主要工具之一,在工作时受到极大的界面应力,因此膨胀锥表面过快磨损是制约膨胀管技术发展的主要问题之一。为探究膨胀过程中膨胀锥体表面受力和应力分布,结合弹塑性理论推导膨胀锥接触应力和摩擦力计算模型,采用有限元方法模拟膨胀管膨胀过程,研究膨胀锥表面应力、接触摩擦应力和膨胀推力变化情况,并通过膨胀试验验证了有限元模拟结果的合理性。结果表明：影响膨胀锥接触应力和摩擦力的主要因素是膨胀管屈服强度和膨胀锥锥角;膨胀锥的最大等效应力集中在大径圆角处,最大摩擦应力集中在膨胀锥小径和大径处;膨胀锥膨胀区只有部分与膨胀管内壁接触,膨胀锥小径处受拉应力,大径处受压应力,最大接触压应力集中在大径处。     

O形圈动密封特性的有限元分析

利用软件ABAQUS建立了O形圈的轴对称有限元模型,分析了其在往复动密封中的密封性能,并对其不同工况下的力学性能进行了研究。结果表明:往复动密封中,O形圈主密封面最大接触应力与Von Mises应力的作用位置随运动方向的变化而改变,且大小随时间呈波动变化;速度小于0.25 m/s时,速度对摩擦力与剪切应力几乎无影响;随着摩擦系数、介质压力的增大,摩擦力与剪切应力对速度的敏感性变高;介质压力与摩擦系数对摩擦力与剪切应力影响较大,剪切应力与摩擦力呈同步变化;密封外行程Von Mises应力与剪切应力均大于内行程,更易引起疲劳与剪切破坏;预压缩率增加到一定值时,O形圈在动密封中所受的摩擦力急剧上升,动密封中预压缩率不宜过大。     

工艺参数对耐磨钢冷轧应力特性的影响

冷轧是耐磨钢材的重要加工方法。为了确定工艺参数对耐磨钢冷轧应力的影响,采用有限元分析软件ABAQUS对轧压过程进行了有限元分析,通过显式动力学和单一变量方法,分别在不同的轧压前、后张力和摩擦因数条件下计算应力变化特性。结果表明:在不同的前、后张力条件下,应力均随着轧压方向先增大后减小,摩擦因数增大到一定数值后可显著增大冷轧应力。     

Analytical model of corner filling with granular media to investigate the friction effect between tube and media

In a tube forming process, granular matter is used as pressure transmission medium instead of liquid to expand a circular tube into one with square section. In this process, the friction at media/tube interface has a significant effect on the final result. In this paper, an analytical model was developed to determine the influence of the friction on the deformation developing process and final thickness distribution along the tube section. Experimental researches were also implemented to evaluate the analytical model in the end. In this model, four friction situations were applied to the numerical analysis process according to the active or negative function of friction on the flow of metal. The analysis result showed that different friction situations could lead to different deformation processes and thickness distributions. The examination on experiments of AA6061 tube indicated that the experimental data of thickness was extremely close to the analysis result with the friction situation in which the metal flow toward the corner of square section die was impeded by the friction force. However, the analytical prediction of thinning trend of thickness had a deviation compared with the experimental data in the corner region. In addition, the breaking and caking of granules in the tube forming process make the friction situation between the tube and media very complex. Therefore, a further research needs to be conducted from the direction of granular matter mechanics and friction mechanism in order to acquire a more explicit result.     

Utilizing the Explicit Finite Element Method for Studying Granular Flows

Granular flows are systems of complex dry particulates whose behavior is difficult to predict during sliding contact. Existing computational tools used to simulate granular flows are particle dynamics, cellular automata (CA), and continuum modeling. In the present investigation, another numerical tool—the explicit finite element method (FEM)—is analyzed as a potential technique for simulating granular flow. For this purpose, explicit dynamic finite element models of parallel shear cells were developed. These models contained 52 particles and consisted of granules that are both round and multi-shaped (diamond, triangle, and rectangle). Each parallel shear cell consisted of a smooth stationary top wall and a rough bottom surface that was given a prescribed velocity of U = 0.7 in/sec (1.78 cm/s). The coefficient of friction (COF) between the particle–particle and particle–wall collisions was varied between 0.0 and 0.75. Utilizing the output of the simulations, results are presented for the shear behavior, particle kinetic energy, and particle stresses within the shear cell as a function of time. As a means of validating the explicit technique for granular flow, a 75 particle, zero roughness, couette shear cell model (solid fraction of 0.50) is subsequently presented for which direct comparisons are made to the results published by Lun. [Lun, C.K. et al.: Phys. Fluids 8, 2868–2883 (1996)] Overall, the results indicate that the explicit FEM is a powerful tool for simulating granular flow phenomena in sliding contacts. In fact, the explicit method demonstrated several advantages over existing numerical techniques while providing equivalent accuracy to the molecular dynamics (MD) approach. These advantages included being able to monitor the collision (sub-surface and surface) stresses and kinetic energies of individual particles over time, the ability to analyze any particle shape, and the ability to capture force chains during granular flow.     

考虑摩擦因数与滑动速度相关时的轮轨滚动接触有限元分析

使用与滑动速度相关的摩擦因数替代库伦摩擦定律中的常系数,结合mixed Lagrangian/Eulerian方法建立轮轨滚动接触有限元模型,分析牵引力主导的蠕滑工况下的干燥状态的轮轨滚动接触特性。通过与摩擦因数取值为常数的轮轨滚动接触分析结果对比发现:与滑动速度相关的摩擦因数对轮轨滚动接触最大接触应力和接触斑面积影响不大,均在1%以内;但是对轮轨接触斑内最大Mises应力、最大纵向切应力、最大横向切应力和最大等效塑性应变影响较大,特别是对最大纵向切应力影响幅度近20%;更需要引起注意的是对轮轨滚动接触摩擦力矢量分布和切向塑性应变分布影响明显,这对轮轨滚动接触疲劳损伤分析非常重要。     

新型围限颗粒介质联轴器持续剪切下的扭矩涨落行为

利用颗粒介质持续剪切下的力学响应特性设计了新型联轴器,探明了联轴器的扭矩涨落行为,进而实现扭矩传递特性的调控。通过设计专用轴向施压持续剪切实验装置,利用扭转实验台开展系列实验,获取低速范围内不同剪切速率、初始法向应力以及颗粒堆积厚度下围限颗粒介质联轴器的扭矩传递特性。实验结果表明颗粒介质持续剪切变形过程与堵塞密度φJ相关,并且该实验装置从原理上提供了堵塞密度的一种可能的测量方法。研究结果进一步表明：对剪切速率、初始法向应力以及颗粒堆积厚度等因素进行选择,可实现围限颗粒介质预期的具有速度敏感性的扭矩传递特性;通过对堵塞密度的控制,可实现围限颗粒介质联轴器扭矩涨落特性的调节。     

Novel instrument to characterize dry granular materials at low consolidations

The performance of traditional instruments for measuring the flow properties of dry granular materials at small consolidation stresses is not fully satisfactory. Generally, commercial quick tests, as, for example, the angle repose method, do not yield intrinsic material properties. This difficulty is solved in currently available ring shear testers, in which the externally applied torque necessary for shearing the sample is measured as a function of the normal stress previously applied through an annular lid. In this article we show a novel device in which the shear stress is caused by the action of a centrifugal force on a vertical layer of unconsolidated material, which is rotated around its vertical axis. At a critical point the shear stress is large enough to drive material avalanches. From a theoretical analysis of these avalanches based on Coulomb's method of wedges, we derive the angle of internal friction and cohesion of the granular material. To illustrate the functioning of the instrument, measurements on steel, ferrite, and magnetite beads of different particle size are presented. The data obtained are used to analyze the gravity-driven avalanches of these materials in a slowly rotated drum.     

Pre-sliding Behaviour of Single Asperity Contact

The pre-sliding and static friction force behaviour at asperity level between a smooth ball and a smooth flat surface at different normal loads, as well as friction behaviour during full slip has been studied. The normal load dependence of the friction force and the preliminary displacement is discussed when the mean contact pressure is kept under 100 MPa. The theoretical model to calculate the shear stress and the preliminary displacement in the contact is discussed and the experimental data were used to verify the model. The results show that for low applied normal loads the adhesion force has an influence on the friction force measurements. Furthermore, the results for the friction force and preliminary displacement show good agreement with the theoretical trends. The experiments along with the model can be used to analyse the tangential traction in the contact and the behaviour of the stick–slip area. The measurement results along with the model were used to calculate the maximum shear stress at the point of sliding for different applied normal loads. It is also shown that at low applied normal loads the shear stress is not constant as compared to relatively high applied normal loads due to the presence of adhesion force.     

Stress analysis of cushion form bearings for total hip replacements.

Cushion form bearings comprise a thin layer of low elastic modulus material on the articulating surface of the bearing, which can deform to help preserve a film of lubricant between the bearing surfaces and therefore reduce friction and wear. The long-term function of this type of bearing is dependent on the strength and durability of this compliant layer. Finite difference and finite element methods have been used to analyse the stress distribution in the compliant layer of cushion form bearing for artificial hip joints under physiological loading conditions. A good agreement between finite difference and finite element methods was found. Under normal loading, the highest value of the maximum shear stress was found to be at the interface between the compliant layer and the more rigid substrate close to the edge of the contact. The values of maximum shear stress in the centre of the contact close to the articulating surface were lower than in the equivalent Hertzian contact. A friction force acting at the surface had little effect on the stress distribution for coefficients of friction less than 0.05. However, for higher values of friction coefficient (larger than 0.2), corresponding to inadequate lubrication, the maximum shear stress increased by a factor of four and was found to be located at the surface. The analysis predicts that the mode of failure will be at the interface with the substrate under fluid film or mixed lubrication conditions and at the articulating surface when the bearing runs dry with higher levels of friction. Both failure modes have been observed experimentally under the conditions specified.     

磨料水射流对金属材料去除力和去除模型的研究

磨料水射流抛光技术作为一种新型技术,广泛应用于表面抛光加工作业中,利用含有细小磨料粒子的抛光液在高压作用下,与工件表面发生冲击、冲蚀而去除材料,以达到抛光目的。采用单颗粒磨料粒子使材料产生塑性变形模型来研究磨料水射流对金属材料的去除力,通过对纯水射流冲击材料的作用力和射流中磨料射流对材料的作用力以及接触应力的理论推导,得出磨料射流中轴线上磨料颗粒去除金属材料最大打击力和最大剪应力以及最大拉应力;通过建立伯努利方程,得到射流压力与金属材料的剪切力和拉应力的直接关系,为工程上磨料水射流抛光喷嘴设计和泵压选择提供了理论参考依据。     

牵引绳用调控式高压往复密封性能研究

采用ABAQUS软件对牵引绳用调控式往复密封装置在高压环境下的密封性能进行有限元分析,获得密封组件与牵引绳的应力分布及变形情况,分析调控压力与介质压力对密封泄漏率及摩擦力的影响规律。设计搭建主密封试验装置并进行试验验证。结果表明:采用合理的调控压力与密封结构设计可以实现较好的接触应力分布,显著地减少密封泄漏;随着调控压力的增加,密封泄漏率先迅速下降,而后缓慢下降并逐渐趋于稳定,当调控压力大于介质压力的1.3倍时,泄漏率接近于0;增加调控压力导致摩擦力呈现先缓后急的增长趋势;介质压力对密封环具有开启作用,能够降低流体膜压力而减小摩擦力;工程应用中,维持调控压力比介质压力高出0.2~0.5 MPa时密封效果最好。