滑动摩擦振动噪声的非线性显式动力学分析

利用有限元软件ABAQUS/Explicit(显式动态求解器)对球-平面接触条件下的滑动摩擦振动噪声进行了数值模拟分析。对比试验结果,探讨了摩擦噪声的发生机制,并分析了摩擦噪声发生时接触界面的运动特性。结果表明,摩擦噪声主要是由摩擦系统的自激振动引起的,法向振动与切向振动的耦合是系统产生自激振动和摩擦噪声的一个重要因素。当摩擦系统发生自激振动时,从面节点与主面的接触并不是连续不变的,两者在相对运动的过程中具有黏着-滑动-分离-黏着的特性。     

Measurements of friction-induced surface strains in a steel/polymer contact

The paper describes an experimental study combined with analyses and numerical simulations of the surface strains developed in a metal–polymer contact under a variety of loading configurations. Specifically, a steel ball is caused to slide over a poly(methylmethacrylate) flat counterface under a fixed normal load where the imposed motions are small and consist of sliding and rotation and the combination of both. The surface strains have been measured directly using conventional strain gauges in two types of configurations specifically designed to monitor the strains for sliding and rotation. Calculations of frictional forces provide friction coefficients which are self-consistent and the computed ‘friction displacement loops’ correspond closely to those measured. In addition, the surface strain measurements provide a convenient and accurate insight into the stick–slip transitions in fretting contacts.     

The contact forces of lip seals for a ball bearing

Simplified equations are derived for the evaluation of the axial contact forces for a special design of lip seal for bearings. The contact forces of the lip seals for a ball bearing are analysed as a function of the ratio of real contact length, the thickness of the seal lip, the inclined angle of the seal lip, and the deflected interference between the edge of the seal lip and the rotating inner ring. An experimental apparatus is developed for testing the seal lip contact forces. Using a non-linear FEM program, the contact force of the seal lip was analysed for various values of the deflected interference. The calculated results show that the deflected interference and the circumferential stress cause considerable change of contact forces for the low sealed lubricant pressure. The results of contact forces obtained from the derived equation for the contact force are in good agreement with experimental and numerical results.     

Investigation of frictional properties of lubricants at transient elastohydrodynamic conditions

In the assessment of lubricant properties and in various contact applications, it is of importance to know the frictional qualities. Under quasi-static conditions, normal and transverse forces are measured using force transducers but the task is more difficult when loads are high and transient, as they often are in elastohydrodynamic conjunctions. The experimental method presented in this paper is based on analysis of propagating waves in a beam, due to an impact on its end surface, using FFT analysis. Since the impact is oblique, both non-dispersive compression waves and dispersive flexural waves are generated. The normal force originating from the axial wave is measured using straingauges, while the transverse force is derived from the FFT's of two lateral acceleration histories using Euler–Bernoulli dynamic beam theory. The relation between normal- and transverse force histories displays the frictional properties at the impact as a function of time, i.e. variations in frictional properties during loading and unloading (typically 200–400 μs in ball bearings and gears) can be observed. A variety of lubricants have been studied up to a Hertzian pressure of 2.5 GPa, and the method and results are presented.     

Dynamics in carom and three cushion billiards

This paper presents the analysis results of dynamics in the billiards game within the framework of rigid-body mechanics and a numerical simulation program. The friction exists between the ball and the table bed as well as between the ball and the rail. There are three parts in the dynamic behavior of the ball on the table bed; motion of the ball on the table bed, collision between balls, and collision between the ball and the cushion. During the development of the simulation program, the dynamics problems such as rolling motion and three-dimensional frictional impact motion have been analyzed in detail. The theoretical issues are implemented into a viable graphic simulation program and its efficacy is demonstrated through the experimental validation of the billiards game. The resulting analysis results are verified quantitatively and qualitatively using high-speed video camera. Through the experimental tests, it was found that the physical parameters such as coefficients of restitution and friction vary according to the motion variables and corresponding empirical formulations were developed. The simulation and experimental results agree well.     

热力耦合下微接触点塑性应变沿深度变化分析

在考虑粗糙实体弹塑性变形、热力耦合、微凸体间相互作用和摩擦热流耦合等影响下,运用有限元法数值模拟具有三维分形特性的粗糙面与刚性平面间滑动摩擦过程,分析了粗糙实体接触凸点塑性变形随深度变化情况。发现：在速度的突变和闪点温度形成时,摩擦接触表层等效塑性应变增大明显;在这一摩擦表层,过不同接触点的纵向剖面塑性应变沿深度分布不同：有的是接触表面塑性变形最大,有的是在接触微凸体表面下某一深度塑性变形最严重,而接触凸点表面的塑性应变稍小些。这与相关文献用SEM研究干摩擦后金属摩擦表层变形照片后发现的结果一致。滑动摩擦过程中,金属粗糙摩擦接触表层塑性变形的不断累积,将会导致材料表层中的夹杂或微观缺陷周围萌生微孔和裂纹源。     

Experimental and numerical investigation of the behaviour of articular cartilage under shear loading—Interstitial fluid pressurisation and lubrication mechanisms

In this paper, the mechanical and frictional responses of articular cartilage when subjected to alternating shearing forces under a constant load were investigated. Shear testing was performed at physiological contact pressures to ascertain the influence of interstitial fluid support on the evolution of frictional forces during cyclic loading.Numerical studies were also performed using the finite element software Abaqus. The tissue was modelled as a biphasic material with strain dependent permeability. The influence of the material characteristics on the lubrication mechanisms occurring when cartilage is subject to compression and shear was studied to corroborate the experimental findings.     

压力测试平台在燃料泵送系统中的应用

针对燃料泵送系统存在的水击压力过大、气液分离不足以及汽蚀等问题，采用压力传感器和数字信号采集系统建立燃料泵送系统压力测试平台。根据测得的压力信号，对燃料枪关闭瞬间流量、管长、溢流阀调定压力以及主阀弹簧刚度对水击效应引起的峰值压力的影响进行研究，并通过频率分析方法和小波分析方法较精确地获得系统的气液分离值和临界汽蚀压力点。该测试平台不仅能实时可靠地对系统压力进行定量诊断与识别，同时还可以为燃料泵送系统的性能优化提供依据。     

Prediction of the frictional coefficient between a hard protuberance and a soft metal surface

Sliding contact is investigated between a soft metal surface (duralumin) and a hard protuberance ball (steel). The frictional coefficient in this case does not obey Amonton's law of friction, and it increases with an increase of normal load. The experimental value of the frictional coefficient agrees well with the calculated one. In the calculation, the variation of work-hardened depth corresponding to normal force is taken into consideration. It is confirmed that the normal force dependence of the frictional coefficient is generated from the contact pressure determined by the work-hardened depth corresponding to normal force, and from the ploughing effect.     

音圈电机直驱水液压球阀的动态特性建模与仿真研究

音圈电机直驱水液压球阀由音圈电机和水液压球阀阀体两部分组成.电机轴与阀芯组件直接接触,所以阀芯组件受到的摩擦力、弹簧力、密封圈阻力和流体作用力等直接作用在电机上,是电机负载的一部分,而负载特性的不明确是限制直驱阀动态特性提升的因素之一.为了克服这个问题,对球阀进行了较为全面的数值和试验分析.在数值分析中,使用动量法计算...     

Investigation of the mechanical behavior of a flexible solid metal seal for a cryogenic butterfly valve

Seat tightness at the fully shut position should be a consideration in the development of a butterfly valve for use in a liquefied natural gas (LNG) vessel. A flexible solid metal seal offers sufficient tightness of the butterfly valve and meets the specifications for cryogenic temperature. In the present study, characteristics for a cryogenic butterfly valve, such as the flow coefficient and the pressure loss coefficient, were estimated by numerical fluid analysis carried out to simulate 3-D flow and to study performance as it was affected by the opening angles of the valve disc. A design criterion to ensure the seat tightness of the butterfly valve at the fully shut position was proposed, in which the contact pressure between the metal seal and the valve disc would be compared with the fluid pressure. Numerical structural analysis showed that the contact pressure can be calculated by simulation of the frictional contact behavior on the surface of the metal seal and the valve disc. As a result, an adequate flexibility of the metal seal and the valve disc was required in order to accomplish a contact pressure that would be high enough to satisfy the seat tightness requirement. Under cryogenic temperature, thermal shrinkage caused the metal seal to adhere closely to the valve disc periphery at both sides and raised the contact pressure to a relatively high value, though there was no contact across a small area at the center position, which is susceptible to leakage. An additional displacement of the metal seal and the valve disc appeared at an operating fluid pressure of 6.9 bar and produced sufficient contact pressure at the no-contact area. This was verified by experimental leakage tests performed at room and cryogenic temperatures.     

Theoretical Model for Friction-Induced Vibration of Ball Joint System under Mode-Coupling Instability

A theoretical model for the friction-induced vibration in ball joint systems is proposed. In a ball joint system, a small contact area is formed on the surface of the ball due to clearance between the ball and hemispherical cup. To analyze the dynamic instability induced by friction in the ball joint system, the dynamic beam-on-socket model with nonconformal contact under three-dimensional rotation was theoretically proposed. The results from stability analysis revealed that the mode-coupling type instability occurred for the lower bending modes at a specific combination of rotation components as well as an increase in the friction coefficient. In particular, the spinning component was essential in generating the mode-coupling instability between the doublet bending modes of the beam.     

A novel modular fretting wear test rig

A novel modular experimental apparatus was designed and developed to measure and visualize fretting wear and friction for Hertzian circular and elliptical contacts and flat on flat contacts. The experimental apparatus utilizes a magnetostrictive actuator to reciprocate a flat, ball, or cylinder between two fixed specimens. Two stationary flat or cylindrical specimens mounted on a rotary table clamp the reciprocating specimen from the top and bottom to generate the fretting contact. The two stationary test specimens installed on the rotary table perpendicular to the moving specimen form a crossed cylinder geometry which creates a well-defined circular contact. An elliptical contact with different aspect ratios can be obtained by varying the angle between the fixed and the moving specimens. Dead weights placed on top of the upper stationary specimen provide the normal load. A force sensor located in line between the actuator output shaft and the specimen is used to measure friction. The test rig's modular design allows it to be configured for Hertzian circular (ball-on-flat, crossed cylinder), elliptical (crossed cylinder), and conformal (flat-on-flat) contacts. In the ball on flat configuration a steel flat or sapphire window is used in contact with the reciprocating ball. When the sapphire window is used a microscope and high speed camera is employed for in situ visualization and recording of the contact.     

Lubrication of a rubber ball rolling with spin

Relative spin is present between surfaces at each point of contact when a ball is rolled between two circular contra-rotating plates. This gives rise to tangential frictional tractions transmitted across the contact surfaces which may result in a creep of the ball perpendicular to its direction of rolling. This paper reports a study made of rubber and steel balls rolling between plates of perspex lubricated with various oils and water.In dry contact an unrestrained ball, whether of rubber or steel, was found to creep radially outwards between the contra-rotating plates in a manner anticipated by earlier work, but when surfaces were lubricated with a viscous oil steel balls showed a neutral behaviour and rubber balls actually crept inwards. The inward creep was quite unexpected. Such behaviour suggests a greater traction, due to spin, over the back half of the contact zone arising by tilt between the contact surfaces. Estimates and actual measurements of tilt generated by elastohydrodynamic action were used to predict inward creep which could then be compared directly with experiment. The comparison shows that tilt clearly contributes to inward creep though does not fully explain the observed results.     

Numerical modeling of the thermal contact in metal forming processes

Heat flow across the interface of solid bodies in contact is an important aspect in several engineering applications. This work presents a finite element model for the analysis of thermal contact, which takes into account the effect of contact pressure and gap dimension in the heat flow across the interface between two bodies. Additionally, the frictional heat generation is also addressed, which is dictated by the contact forces predicted by the mechanical problem. The frictional contact problem and thermal problem are formulated in the frame of the finite element method. A new law is proposed to define the interfacial heat transfer coefficient (IHTC) as a function of the contact pressure and gap distance, enabling a smooth transition between two contact status (gap and contact). The staggered scheme used as coupling strategy to solve the thermomechanical problem is briefly presented. Four numerical examples are presented to validate the finite element model and highlight the importance of the proposed law on the predicted temperature.     

Study on the Boundary-Lubricated Sliding Contact with Subsurface Plastic Deformation

In this study, low-velocity oblique plastic impact-testing experiments were conducted at different angles of incidence to investigate the consequences of the short-distance sliding interaction between a very hard (En31) ball and a relatively softer (mild steel) metal specimen. The purpose was to understand the mechanism of boundary lubrication in the metalworking processes. The specimen was mounted on a specially designed inclined-plane-type fixture so that its surface could be oriented at any desired angle against the free-falling hard ball from a predetermined height. The experimental setup included sufficient details of instrumentation to record the post-impact travel distance and time from which the average coefficient of friction was calculated using a simple methodology. The specimen surfaces were studied using the SEM for different cases of sliding experiments with and without lubricants and two different additives in the lubricants. Marked difference was observed in the nature of surfaces produced in different cases. The oblique impact process was modeled using the equations of motion of the ball and its interaction with plastically deforming specimen material. A fourth-order Runge-Kutta method was used and variations of shear and normal forces during the sliding contact were estimated. The friction behavior showed by this model is in conformance with the experimental results. In addition to that, it has been shown by this model that the coefficient of friction cannot exceed the value of one in sliding. A finite element model has been prepared to estimate the plastic deformation component of friction. Considering the soft asperities of the workpiece deforming as a wave in front of hard asperities, the steady-state Galerkin finite-element model enabled estimation of friction. The trend of the results of the FEM model seems to substantiate the experimental results.     

密封介质对接触特性影响的建模分析

应用建模计算和性能试验相结合的方法对不同介质环境下车辆传动装置密封环的接触特性进行研究。以非牛顿流体的流变特性为基础,计及变黏度影响,模拟实际运行工况,运用有限差分数值解法,确定2种不同介质中密封摩擦副的摩擦因数和密封环温度等表达密封环接触特征的参数变化规律。通过试验进行对比论证,表明试验获取的摩擦因数和密封温升曲线与仿真曲线的基本变化规律保持一致,并且在密封系统中黏度小的介质在摩擦因数和密封温升方面较黏度大介质的数值小。通过建模和试验的双重评价方法,可以方便准确预估不同介质环境下的密封接触性能。     

Numerical simulation of wheel rolling over rail at high-speeds

In the paper, a contact element method was used to analyze a wheel rolling over a rail at high-speeds. The rolling contact of the wheel and rail was considered as a two-dimensional rolling contact in a pure rolling and steady state. The loads applied to the wheel are the different axle-loads of train and the inertia forces caused by accelerations of the wheel in its pure rolling state. The convergence of non-linear numerical analysis on frictional contact was reached through repeated contact calculations. The normal contact pressure and tangential traction on wheel/rail contact surface were obtained for the different axle-loads and the different rolling speeds. The highest rolling speed in the numerical simulation is 400 km/h. Through the detailed numerical simulation and analysis, it was found that there exist some differences between the traditional Hertzian contact pressure and the present normal pressure. With the speed increasing the normal contact pressure becomes larger in the leading area of the contact surface, and becomes smaller in the trailing area of the contact surface. However, in the trailing area the tangential traction become larger, and in the leading area becomes smaller with the speed increasing.     

A new method for determining the preload in a wire race ball bearing

This paper explores a numerical method to calculate the frictionless three-dimensional non-conforming contact problem associated with a wire race ball bearing used in a certain aircraft simulating rotary table, for challenging the conventional method on the determination of the preload magnitude. A computer program based on the Hertz elastic contact theory and a mathematical model of two critical loading conditions was performed in MATLAB^® by using an example of a wire race ball bearing having an approximately 900 mm diameter. The normal contact forces, the contact deformation, the maximum contact pressure, the semi-major axes and the semi-minor axes of contact ellipses of the ball-wire race were computed. The analytic results show that the overturning moment, the pitting corrosion and the shear failure due to combined stresses can be avoided by controlling preload values in the range 11.3–169.9 μm. The experimental results are closely in agreement with the theoretical results, and verify the availability of the numerical method. The research provides theoretical support for the development and further application of wire race ball bearings with large diameters.     

蹄-鼓式制动器热弹性耦合有限元分析

首先探讨蹄—鼓式汽车制动器的摩擦接触热弹性耦合非线性动力学问题及其分析方法,包括摩擦生热模型、多物理场中的弹性体有限元模型、接触问题模型的建立方法以及相应的数值分析方法。然后,利用有限元分析软件ADI-NA建立一种新型蹄—鼓式制动器热弹性耦合动力学分析的三维有限元模型,确定对模型求解的位移边界条件和热边界条件,设定材料物性参数、加载过程及模拟工况,探讨进行制动器热弹性耦合有限元分析的过程,通过仿真计算得到制动器工作过程中摩擦副间接触力分布、制动鼓瞬态温度场、应力场、变形场等重要信息。