伴随变阻尼作用的干摩擦下的车辆系统非线性动力学分析

对分段线性阻尼和干摩擦共同作用下的车辆悬挂系统进行了非线性动力学分析研究，阐述了判定系统周期运动稳定性的理论方法；利用数值模拟方法分析了具有不同阻尼参数组合的系统对简谐激励的振动响应，并分析了由干摩擦引起的粘-滑振动行为．结果表明：提高摩擦力对抑制响应有利，但车辆系统在低速下运行时会出现复杂的粘-滑振动，轮轨之间产生较大的瞬时刚性冲击；而通过增加轮对与侧架的弹性悬挂可以有效减弱这种瞬时刚性冲击．     

Nonlinear Vibration Control of a System with Dry Friction and Viscous Damping Using the Saturation Phenomenon

Application of saturation to provide active nonlinear vibration control was introduced not long ago. Saturation occurs when two natural frequencies of a system with quadratic nonlinearities are in a ratio of around 2:1 and the system is excited at a frequency near its higher natural frequency. Under these conditions, there is a small upper limit for the high-frequency response and the rest of the input energy is channeled to the low-frequency mode. In this way, the vibration of one of the degrees of freedom of a coupled 2 degrees of freedom system is attenuated. In the present paper, the effect of dry friction on the response of a system that implements this vibration absorber is discussed. The system is basically a plant with a permanent magnet DC (PMDC) motor excited by a harmonic forcing term and coupled with a quadratic nonlinear controller. The absorber is built in electric circuitry and takes advantage of the saturation phenomenon. The method of multiple scales is used to find approximate solutions. Various response regimes of the closed-loop system as well as the stability of these regimes are studied and the stability boundaries are obtained. Especial attention is paid on the effect of dry friction on the stability boundaries. It is shown that while dry friction tends to shrink the stable region in some parts, it enlarges other parts of the stable region. To verify the theoretical results, they have been compared with numerical solution and good agreement between the two is observed.This work was done while the authors were associated with the Mechanical Engineering Department, Sharif University of Technology, Tehran, Iran.     

Dynamic Study of a Structure with Flexion-Torsion Coupling in the Presence of Dry Friction

In aero engines, blade vibrations are frequently reduced by centrifugal flyweights, which exert a dry friction force per unit length under blade platforms. The response of this system to a periodic load has been analysed experimentally and theoretically. From a model having mode shapes similar to those of a blade, and a dry friction link per unit length, we show that the presence of the dry friction link is very effective in reducing vibrations for a range of excitation loads. The theoretical analysis is based on the Craig and Bampton mode synthesis, the rigid movement of the platform in its plane and the replacing of the linear dry friction link by several discrete parallel systems. Direct integration of the equations of motion is carried out by using the Newmark method. The comparison with experimental results is good. This method can easily be extended to more complex structures and shows that the dry friction link is effective when stick-slip occurs in the contact zone by limiting the energy provided to the system.     

三种结构陶瓷摩擦副的干摩擦磨损研究

对３种结构陶瓷摩擦副－Ｓｉ３Ｎ４／Ｓｉ３Ｎ４，Ｓｉ３Ｎ４／Ａｌ２Ｏ３和Ｓｉ３Ｎ４／ＳｉＣ的干摩擦磨损行为进行了对比试验研究，并且通过扫描电子显微镜和Ｘ射线衍义对试样的磨损表面形貌和磨屑进行了观察与分析，利用射线光电子能谱仪研究了磨屑健能和分析了表面摩化学过程。     

高强度铸造锌合金在干摩擦条件下摩擦磨损特性之研究

本文在干摩擦条件下对高强度铸造锌合金ZA-12和ZA-27的摩擦磨损特性进行了研究,并以锡青铜ZQSn6-6-3进行了对比试验。结果表明,这3种合金与45~#钢配磨时的摩擦系数相差不大,但前两者的磨损率都比后者的低2～3个数量级,表明高强度铸造锌合金在润滑失效时仍具有良好的拉伤抗力。     

环氧树脂在干摩擦过程中的表面化学效应研究

研究了环氧树脂在干摩擦下载荷为49 N和98 N时的摩擦磨损性能及其表面化学效应,利用扫描电子显微镜、X射线光电子能谱仪和傅立叶变换红外光谱仪对环氧树脂磨损表面的形貌和官能团进行观察与分析.结果表明:在载荷49 N下环氧树脂表现出良好的耐磨性能;在载荷98 N下,环氧树脂表面磨损较严重且呈脆性剥落;环氧树脂在干摩擦过程中发生的表面化学效应主要是其分子链的断裂和氧化降解,其磨损形式主要为疲劳磨损.     

Complex Oscillations Revisited

The problem of applying some approaches to approximate solutions and the asymmetry of closed phase trajectories in some domain of parameters are examined__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 2, pp. 81–90, February 2005.     

激光织构化TiN薄膜的干摩擦性能研究

采用固体Nd:YAG激光器对离子镀TiN薄膜进行织构化处理,表征了薄膜的结构、形貌及凹坑织构参数.通过UMT-2往复式球-盘摩擦磨损试验机评价了织构化薄膜的摩擦磨损特性,研究了织构形貌对TiN薄膜干摩擦条件下摩擦磨损性能的影响.研究结果表明:与未织构化的TiN薄膜相比,织构化TiN薄膜的平均摩擦系数降低,并且磨损率明显减小,这说明织构化TiN薄膜具有更好的耐磨损性能.摩擦过程中,凹坑织构既捕获了磨屑,又有利于摩擦过程中阶跃运动的发生,易于将磨屑带出磨痕,从而降低了摩擦磨损.     

45~#钢表面激光织构化及其干摩擦特性研究

采用声光调的固体Nd:YAG激光器在45#钢表面进行了织构化处理;采用栓盘摩擦试验机考察了织构化对其摩擦性能的影响;用三维轮廓仪及扫描电镜对摩擦试验前后试样的表面形貌进行了分析.研究结果表明:经过激光织构化的45#钢表面形成了较为规整的微坑型结构.在相同试验条件下与未织构面对比,织构面的摩擦系数均有不同程度减小且表现得更为稳定,并且磨损率也得到一定的降低,这是由于所制备的表面微坑起到了捕获磨屑的作用.对不同织构密度及织构尺寸样品摩擦性能的考察结果表明较大的织构密度及较大孔径更有利于减摩抗磨.     

Estimating the Largest Lyapunov Exponent in a Multibody System with Dry Friction by using Chaos Synchronization

Using the properties of chaos synchronization, the method for estimating the largest Lyapunov exponent in a multibody system with dry friction is presented in this paper. The Lagrange equations with multipliers of the systems are given in matrix form, which is adequate for numerical calculation. The approach for calculating the generalized velocity and acceleration of the slider is given to determine slipping or sticking of the slider in the systems. For slip–slip and stick–slip multibody systems, their largest Lyapunov exponents are calculated to characterize their dynamics.The project supported by the National Natural Science Foundation of China (10272008 and 10371030) The English text was polished by Yunming Chen     

激光表面织构对不同材料干摩擦特性的影响

采用环-块线接触摩擦磨损试验,研究了经激光处理后不同织构面密度的45钢和12Cr凹坑形织构试件的干摩擦磨损特性.借助高精度天平分析了试件磨损量,采用三维形貌仪和扫描电镜对试件表面形貌进行了分析.研究结果表明:激光表面织构化使得45钢试件表面形成可以改善摩擦性能的高硬度质点;在相同试验条件下,与无织构试件相比,45钢织构环试件磨损量明显降低,而12Cr织构环试件磨损量却有所升高;织构试件的磨损量在一定范围内随着织构面密度的增加而降低;激光织构化对摩擦系数的稳定值影响不大.     

干摩擦条件下3Cr13 涂层的加速磨损机理研究

在MM200摩擦磨损试验机上对高速电弧喷涂3Cr13涂层在干摩擦条件下的加速磨损机理进行了研究.涂层在加速磨损过程中经历了跑合磨损、稳定磨损、剧烈磨损这三个不同的阶段.采用扫描电镜、X射线衍射仪、显微硬度仪和纳米压痕仪对涂层磨损各阶段的截面形貌、残余应力、硬度和纳米力学性能进行了表征.结果表明:在加速磨损寿命3个阶段中,涂层的磨损机制和影响残余应力的主导因素是动态变化的,过分的冷作硬化加剧了涂层的失效,涂层磨损寿命长短关键在于稳定磨损时间的长短.     

一种高碳钢低温干摩擦行为的研究

在20 ℃至-55 ℃范围内以球-盘摩擦形式考察了一种1.08%C高碳钢在滑动速度0.319 m/s,载荷在0.5～2.5 N下与GCr15钢球干摩擦时的摩擦磨损行为,利用SEM、EDS、XPS等观察了磨痕形貌,考察了磨屑中氧含量的变化,分析了摩擦氧化反应.结果发现,与常温环境相比,在0 ℃以下的低温环境显著提高了该钢铁摩擦副之间的摩擦系数,且摩擦系数基本不随温度发生变化.随着温度的降低该高碳钢的磨损量增加,黏着磨损程度增强,屑中氧含量减小.分析认为温度的降低伴随着湿度的降低,低温、低湿度环境减弱了摩擦氧化反应,减少了起隔离作用的金属氧化物的生成,加剧了摩擦副之间的黏着,从而导致摩擦系数和磨损量增大.     

Dry Friction Model of Percussive Drilling

It is postulated that the main mechanism of the enhancement of material removal rate (MRR) in percussive drilling is associated with generating impact forces, which act on the workpiece and help to develop micro-cracking in the cutting zone. The inherent non-linearity of the discontinuous impact process is modelled as a frictional pair, to generate the pattern of the impact forces. A novel formula for calculating the MRR is proposed, which explains the experimentally observed fall in MRR at higher static forces.     

表面纳米化中碳钢在干摩擦条件下的摩擦磨损性能研究

采用高能喷丸方法对45#钢进行表面纳米化处理,在环-盘摩擦磨损试验机上评价表面纳米化处理45#钢与T10钢摩擦副在干摩擦条件下的摩擦磨损试验,通过分析其磨损表面形貌探讨表面纳米化对中碳钢磨损行为的影响.结果表明:在载荷为10～60 N条件下,表面纳米化中碳钢的摩擦系数较处理前有所降低;在载荷为10～40 N时,其磨损质量损失较处理前有所降低;表面纳米化能够减弱中碳钢的疲劳磨损效应,提高中碳钢的摩擦磨损性能.     

用外加电压控制摩擦力的机理与技术

用外加电压控制金属摩擦学磨损是摩擦领域很有发展前景的新技术之一，能够有效地降低干摩擦下金属间的摩擦与磨损，但国内外有关的研究报道却还少见．因此，利用特制的球－盘式摩擦磨损试验机，对几种配对金属的摩擦自生电势和摩擦力进行了测量，揭示了摩擦自生电势与摩擦力的相关性，并且考察了外加电压对金属间摩擦力的影响，发现在外加电压与摩擦自生电势相抵消时的摩擦系数最低，比无外加电压时的摩擦系数低１２％～２６％     

法向载荷和滑动速度对GCr15钢干滑动摩擦的影响

本文研究了在干滑动摩擦情况下,GCr15钢与YG8硬质合金对磨时的摩擦系数与法向载荷及滑动速度的关系。结果表明,摩擦系数是随着法向载荷和滑动速度的增加而降低。根据磨损表面发生的变化和磨损表面温度计算,作者认为法向载荷和滑动速度的增加使闪温增高,从而导致了摩擦磨损表面的局部熔化,即形成了边界润滑,故此摩擦系数降低,而且在较高的载荷和滑动速度条件下,不同显微组织材料的摩擦系数之差减小。     

Attractivity of Equilibrium Sets of Systems with Dry Friction

The dynamics of mechanical systems with dry friction elements, modelledby set-valued force laws, can be described by differential inclusions.An equilibrium set of such a differential inclusion corresponds to astationary mode for which the friction elements are sticking. Theattractivity properties of the equilibrium set are of major importancefor the overall dynamic behaviour of this type of systems. Conditionsfor the attractivity of the equilibrium set of MDOF mechanical systemswith multiple friction elements are presented. These results areobtained by application of a generalisation of LaSalle's principle fordifferential inclusions of Filippov-type. Besides passive systems, alsosystems with negative viscous damping are considered. For such systems,only local attractivity of the equilibrium set can be assured undercertain conditions. Moreover, an estimate for the region of attractionis given for these cases. The effectiveness of the results isillustrated by means of both 1DOF and MDOF examples.     

碳钢表面碳—氮共渗层在高速干摩擦条件下的摩擦学性能研究

对 2 0 # 钢试样进行碳 -氮共渗热处理 ,考察了共渗层在高速干摩擦条件下的摩擦学性能 ,并用扫描电子显微镜和X射线光电子能谱仪对其磨损表面形貌和元素化学状态进行了分析 .结果表明 :随着滑动速度的增加 ,2 0 # 钢表面碳 -氮共渗层的磨损率逐渐降低 ,当滑动速度达到 35m/s左右时 ,磨损率显著增大 .扫描电子显微镜和X射线光电子能谱分析结果表明 ,高速轻载干摩擦条件下 2 0 # 钢表面碳 -氮共渗层的摩擦学性能同磨损表面氧化物的形成和剥落密切相关 ,而磨损率的显著增加是由于磨损表面氧化物类型发生从Fe2 O3 到FeO的转变所致 .     

干摩擦条件下Si3N4基和Ti（CN）基陶瓷对1Cr18Ni9Ti不锈钢的磨损机理

研究了Ｓｉ３Ｎ４基陶瓷和Ｔｉ（ＣＮ）基陶瓷分别与１Ｃｒ１８Ｎｉ９Ｔｉ不锈钢在干摩擦条件下对摩时的磨损行为，并且通过销－盘磨损试验和磨损表面形貌分析等，提出了这２种陶瓷的磨损机理：Ｓｉ３Ｎ４基陶瓷主要是在磨损表面发生偶件材料１Ｃｒ１８Ｎｉ９Ｔｉ粘着层的粘着与剥落，同时陶瓷中的Ｓｉ向粘着层发生扩散转移，并在粘着层表面下２０～３０μｍ深度范围内产生裂纹和断裂而导致磨损；Ｔｉ（ＣＮ）基陶瓷在发生粘着层的粘着与剥落的同时，还由于摩擦温度很高引起陶瓷表面熔化，熔融状的陶瓷被挤走或冷凝收缩产生裂纹和断裂而导致磨损