Tapping Effect on Friction Between Slider and Disk

The effect of tapping on friction between slider and disk in a hard-disk drive was investigated by using a model active slider with a piezo-actuator. It was found that the tapping can reduce friction, especially when the disk is smooth and the load is light. It was also found that a certain vibration amplitude is necessary to reduce friction significantly. In addition, the resonant frequency of the piezo-actuator was found to shift to higher values at higher suspension load. This frequency-shift is considered to be an important factor in optimizing the drive frequency of the actuator.     

探头中心频率与摩擦副材质对超声膜厚测量范围的影响*

目前超声膜厚测量研究均是在固定探头中心频率(或单一摩擦副材质)下进行的,未考虑探头中心频率与摩擦副材质的变化对膜厚可测量范围的影响。为定量分析2种因素对膜厚测量范围的影响,设计一种压电陶瓷驱动的高精度微调式实验装置,基于弹簧模型利用不同中心频率探头对不同摩擦副材质间的水膜厚度进行测量。实验结果表明:膜厚的可测量值随探头中心频率的增大而减小,随摩擦副阻抗值的增大而减小;与理论值相比,利用超声探头测量水膜厚度的相对误差均低于10%,验证了实验装置及方法的可行性。提出一种根据摩擦副材质和期望测量膜厚范围来确定探头有效带宽的方法并进行试验验证,可为工程实际中不同膜厚测量时超声波探头的选型提供参考。     

干式摩擦元件的热弹不稳定性分析

针对干式摩擦元件热弹性失稳问题,通过理论和仿真计算相结合的方法,将系统扰动因素和系统结构因素相统一,从扰动频率对临界速度影响的角度,开展制动器干式摩擦元件的热弹不稳定分析。研究发现,系统失稳与扰动频率有关,造成系统失稳的临界速度存在一个极小值点,在该点系统最容易产生失稳;摩擦副局部热应力过大是造成系统失稳的主要原因,摩擦副整体温度的高低与系统失稳之间不存在必然的联系。提出的基于热固耦合扰动边界的干式摩擦元件热弹不稳定性分析方法,其计算结果可以直接用来指导摩擦片热弹性失稳的结构设计。     

变滑动磨擦系数振动系统最优化计算方法研究

研究了两自由度滑动摩擦系数随相对速度变化的干摩擦振动系统简谐激励响应计算问题,通过将干摩擦力中的理想干摩擦力（Coulomb dry friction)部分进行Fourier级数展开,取级数展开的第一项作为近似,结合一次谐波平衡法,推导出了系统的非线性频响方程组,运用最优化理论中求解非线性方程组的梯度算法,给出非线性频响方程组的数值迭代格式,最后,通过一个数值例分析讨论了干摩擦力对系统响应的重要作用。     

The effect of frequency of vibration and humidity on the coefficient of friction

Variation of friction coefficient with the variation of frequency of vibration and relative humidity is investigated experimentally on a mild steel disc. A pin-on-disc apparatus having facility of vibrating the disc at different frequency and amplitude is used for the experiment. During the experiment, normal load, speed and relative humidity were varied. The surface conditions of the mild steel base plate were ‘as-turned’ and ‘as-ground’. It is found that friction co-efficient under no vibration condition is higher than that under vibration condition, and the values of friction co-efficient decrease with the increase of frequency of vibration. Similarly, the friction co-efficient decreases with the increase of relative humidity. It is also observed that the rate of reduction of friction co-efficient has a particular relationship with the frequency of vibration and the relative humidity.     

25CrNi2MoV钢的微动磨损性能

采用微动摩擦磨损试验机在干摩擦条件下对新型高速重载传动轴用25CrNi2MoV钢进行微动磨损试验,研究了不同载荷(50~200N)和频率(15~30Hz)下该钢的微动磨损性能。结果表明:在频率为20Hz条件下,当载荷由50N增至200N时,25CrNi2MoV钢的平均摩擦因数由0.766减至0.661,磨损体积由19.65×10^-3 mm^3增至75.83×10^-3 mm^3;在载荷为30N条件下,当频率由15Hz增至30Hz时,平均摩擦因数由0.790增至0.905,磨损体积由11.43×10^-3 mm^3增至23.88×10^-3 mm^3;在不同试验参数下,25CrNi2MoV钢磨损表面均出现了氧化和犁沟现象,磨损机制包含氧化磨损和磨粒磨损;在频率为20Hz条件下,载荷为50,100N时,25CrNi2MoV钢的磨损机制以黏着磨损为主,载荷为150,200N时,主要磨损机制为疲劳磨损;在载荷为30N条件下,频率为15~25Hz时,磨损机制以磨粒磨损为主,当频率增至30Hz时,磨损机制以疲劳磨损为主。     

变滑动摩擦系数振子简谐激励Krylov-Bogoliubov 计算方法

研究了单自由度滑动摩擦系数随相对速度变化的干摩擦振动系统简谐激励响应计算问题，运用Krylov-Bogoliubov近似方法推导了相应的频响方程。通过一个数值例分析，考察了简化为理想干摩擦模型时带来的计算误差。     

界面摩擦过程黏滑行为特征研究

通过建立界面摩擦系统动力学模型,并利用原子力显微镜测试云母、石英以及单晶硅片界面摩擦条件下的黏滑行为特征,探讨摩擦系统内外因素对黏滑频率、幅值的影响。结果表明:同一实验条件下,不同材料的黏滑频率与黏滑波动幅值不同;缓慢滑动时,黏滑的频率主要取决于表面势场的频率,波动幅值取决于表面势场强度,随着滑动速度逐渐增大,黏滑频率同时取决于表面势场频率和探针系统的固有频率,波动幅值取决于表面势场强度和探针系统结构;滑动速度较大时,黏滑频率及波动幅值主要取决于探针系统,且随着滑动速度增大,波动幅值逐渐减小。     

Hybrid phenolic friction composites containing Kevlar® pulp Part 1. Enhancement of friction and wear performance

The friction and wear characteristics of control (without Kevlar® pulp) and hybrid (with Kevlar® pulp) phenolic composites containing milled E-glass or steel were determined at various counterface speeds and temperatures using a Chase friction tester. In general, Kevlar® pulp significantly improved the wear resistance and decreased the coefficient of friction for both types of hybrid composites. Kevlar® pulp also imparted excellent frictional stability at high speeds in steel-fiber composites and significantly reduced higher frequency ( > 5 kHz) noise at high speeds in both steel and glass-fiber composites. The stabilization of the coefficient of friction and reduction of noise was not due to the reduction of the coefficient of friction because it also occurred at constant frictional force. The addition of Kevlar® pulp to a steel-fiber-containing formulation significantly improved its overall performance.     

空调转子压缩机摩擦噪声的有限元分析

为探讨空调转子压缩机摩擦噪声的产生机制,提出一种利用有限元软件对空调压缩机相关摩擦副进行摩擦噪声预测的方法.利用复特征值分析法对空调转子压缩机摩擦系统的有限元模型进行模态分析,获得摩擦系统的固有频率以及相应振型的变化特性,据此推断可能导致摩擦噪声的频率.有限元模型计算结果与实测数据具有很好的一致性,验证了该预测方法的有...     

基于销/盘试验机的摩擦噪声试验与仿真研究

为了研究摩擦噪声的产生机制和影响因素,利用销/盘试验机对以转子式压缩机曲轴-法兰材料制成的销/盘试样进行摩擦噪声试验研究;应用ABAQUS有限元软件,建立销/盘试验机有限元模型,利用复特征值分析方法预测该系统摩擦噪声的主频,并与试验结果进行对比;讨论相关参数对系统的稳定性和摩擦噪声的影响。结果表明：销与盘法向和横向振动的耦合是引起系统自激振动和摩擦噪声的重要因素;当系统摩擦界面处的摩擦因数大于系统临界摩擦因数时,系统开始出现不稳定振动,且摩擦因数越大,系统越不稳定,越易出现摩擦噪声;法向载荷对系统稳定性的影响不大;选择具有合适弹性模量的摩擦副材料可以抑制摩擦噪声的产生。     

[轮轨磨耗及预测]地铁直线轨道钢轨波磨影响参数研究

基于车辆轨道耦合动力学模型和钢轨材料摩擦磨损计算模型,分析了不同轨道结构参数和车辆运营速度对地铁直线轨道钢轨波磨发生和发展的影响。结果发现,对于不同的变量参数,轮轨接触斑内摩擦功率随时间的变化都具有一定的波动性,且摩擦功率整体波动幅度较为均匀。同时,摩擦功率1/3倍频程图分析结果表明,摩擦功率的特征频率主要集中在中低频范围。在主要特征频率处,扣件纵向刚度、纵向阻尼、横向阻尼和垂向阻尼对钢轨波磨的影响较小,扣件横向刚度、垂向刚度、扣件间距、轮轨摩擦因数和车辆运行速度对钢轨波磨的影响较大。扣件垂向刚度和扣件间距的变化会导致摩擦功率的特征频率发生偏移,主要特征频率从80 Hz偏移至100 Hz,从而导致对应波长的钢轨波磨,说明扣件垂向刚度和扣件间距对特定频率处钢轨波磨的产生和发展具有重要的影响。其余变量的增大并未导致摩擦功率的特征频率发生改变,表明其余变量不影响钢轨波磨的特征频率。     

基于润滑降噪实验的车床挂轮噪声分析

以一台C630车床空转噪声的测试数据为依据,分析了齿面摩擦对车床挂轮噪声的影响,以及摩擦激励频率与齿轮啮合频率的关系,并通过涂油润滑降低挂轮噪声的实验对此进行了验证。结果证明:齿面摩擦对齿轮振动的激励频率是啮合频率的2倍,可以利用适当的润滑有效地抑制齿轮噪声的高频成分。     

Fluctuating flow of a viscoelastic liquid between two parallel plates with time-varying suction

The non-steady flow of a viscoelastic liquid between two parallel porous plates was studied when the suction velocity normal to the plate oscillates in magnitude but not in direction about a non-zero constant mean and one plate is at rest and the other oscillates harmonically about a non-zero constant mean. The response of skin friction to fluctuating flow and suction velocity was studied for variations in the suction parameter A, the elastic parameter Λ and the frequency parameter Ω. The effect of the elastic parameter is to decrease the amplitude of skin friction at the upper plate as the suction parameter increases and to decrease the amplitude of the skin friction at the lower plate as the suction parameter decreases.     

Experimental investigations of porous bearings under vertical sinusoidally fluctuating loads

There are many papers on the experimental investigations of porous bearings under static loads but there is no paper on the experimental investigations under dynamic loads. In the present paper, the results of experimental investigation of porous bearings under vertical sinusoidally fluctuating loads are presented. The friction force was measured under various conditions of fluctuating load/steady load ratio, journal frequency and load frequency. The investigations were carried out in the hydrodynamic lubrication regime in a specially designed and fabricated test rig. It was found that at any given rpm, as the fluctuating specific load/steady specific load ratio, P_f/P_s, increases, the mean coefficient of friction μ_m increases. It was also found that the mean coefficient of friction is not affected by the load frequency even when the load frequency is half of the journal frequency.     

GF/PTFE自润滑纤维复合材料磨损性能热衰退研究

针对高频摆动关节轴承摩擦热对自润滑纤维复合材料摩擦磨损性能的影响,研制了高频使用条件下的玻璃纤维增强聚四氟乙烯(GF/PTFE)自润滑纤维复合材料,利用MYB～500高频高载摆动摩擦磨损试验机,对其进行不同摩擦温度下的摩擦磨损性能测试,研究摩擦热作用下材料自润滑性能和磨损性能衰退特征,分析磨损产物和摩擦表面以及不同摩擦温度下材料的磨损机理。结果表明,摩擦热对材料自润滑性能影响显著,适当的摩擦温度范围能够保证材料的自润滑性能,摩擦温度和摩擦因数之间互为耦合作用,对材料的磨损性能具有一定的影响;高摩擦热作用于自润滑过程及机理的改变,造成材料的磨损性能衰退现象。因此,不同温度下材料的磨损特征具有明显的差异化,其中低摩擦温度下(60～120℃)材料自润滑性能优异,磨损率很低;140℃摩擦温度条件下材料摩擦磨损性能开始衰退;材料在高摩擦温度下(140～180℃)的磨损初期自润滑性能良好、磨损轻微,而中后期磨损严重。微观分析表明,低摩擦温度下材料的磨损机理以轻微粘着和疲劳磨损为主;高摩擦温度下材料的磨损以片状剥落、纤维剪切破坏为主,且磨损面局部损伤特征明显,磨损严重。     

Reduction of the sliding friction of metals by the application of longitudinal or transverse ultrasonic vibration

The influence on sliding friction of ultrasonic vibration both parallel and perpendicular to the sliding direction has been studied for samples of aluminium alloy, copper, brass and stainless steel sliding against tool steel. Experiments were performed at a mean sliding speed of 50 mm s⁻¹, and at mean contact pressures up to 0.7 MPa, with vibration amplitudes up to 10 μm at 20 kHz. Significant reduction in sliding friction was observed (up to >80%) and good agreement was found between the measured values and the predictions of two simple models for the effects of longitudinal and transverse vibrations. Longitudinal vibration produces greater reduction in friction than transverse vibration at the same amplitude and frequency. At high vibration amplitudes, the reduction in friction was less than that predicted by the models, because significant metallic transfer occurred from the softer metals to the tool steel counter surface.     

挤压型不锈钢向心关节轴承的摩擦磨损性能

研究挤压型不锈钢向心关节轴承在不同的试验参数下的摩擦磨损性能,分析其摩擦磨损形式。结果表明:不锈钢向心关节轴承的磨损形式以黏着磨损和磨粒磨损为主,磨损量随载荷的增大而增大,随摆动频率先减小而后增大;摩擦因数随载荷和摆动频率的增大而减小。     

Mechanism of energy dissipation in mechanical system with dry friction

Determination of the energy dissipative mechanism in a mechanical system composed of two elastic structures in dry contact is presented. The analysis is based on the measurement of displacement ratio of the contacting elastic structures as a function of frequency due to light impulse excitation at a single point on any of the two elastic structures. The theoretical analysis depends on a very simple model of a two-degree-of-freedom system where two solid friction models are adopted in the analysis of the mathematical model. Several experiments are presented to illustrate the dominant friction mechanism of contacting surfaces within the micro slip regime in a frequency range of oscillation up to 400 Hz. It was shown experimentally that the solid friction model behaves in a way that is described as structural (hysteretic) damping. In other words, the energy dissipated due to dry friction during micro slip regime does not depend on the relative velocity between the two contacting surfaces but it is proportional to their relative displacements. The determination of the contact stiffness and damping loss factor in addition to their variation with the applied normal load was also shown.     

Corrosion wear behaviors of micro-arc oxidation coating of Al2O3 on 2024Al in different aqueous environments at fretting contact

The fretting wear behavior of micro-arc oxidation (MAO) coating of Al₂O₃ on an aluminum alloy 2024Al flat against a 440C stainless steel ball was investigated in artificial rainwater, artificial seawater and distilled water by using a ball-on-flat configuration with 300 μm amplitude at room temperature for 1 h. The morphology of the wear scars were observed and analyzed using scanning electron microscopy; the 3D-morphology and wear volume-loss were determined using a non-contact optical profilometer. Potentiodynamic anodic polarization was used to measure the corrosion behavior of the MAO coating before and after the corrosion wear test. The influences of the load, frequency and aqueous medium on the friction coefficient and wear volume-loss of the coatings were also analyzed. Results show that the friction coefficient decreases generally with an increase of the frequency in the three aqueous solutions; whereas it presents different variation trends as the load increased. In addition, aqueous environment does significantly influence the friction coefficient, the friction coefficient was the largest when fretting occurred in distilled water, smaller when fretting occurred in rainwater, and the smallest when fretting occurred in seawater. Particularly the remarkable antifriction effect of the seawater is of note. The wear-loss of the MAO coating in the distilled water is the largest at low frequency; however, it increases rapidly in rainwater and seawater at high frequency due to the corrosion effect of Cl^? ion as well as its accelerating effect to the wear process, and results in larger wear-loss than that in distilled water, which implies a positive synergism between corrosion and wear.