PEEK摩擦信号分形维数与表面形貌相关性试验研究

为研究聚醚醚酮树脂/球墨铸铁摩擦副磨合初期摩擦信号分形维数与聚醚醚酮初始表面形貌分形维数的相关性,在UMT-3MT摩擦磨损试验机上对聚醚醚酮树脂/球墨铸铁摩擦副进行了摩擦磨损试验,运用结构函数测度法对初始表面形貌、摩擦力信号、摩擦因数信号进行了分形表征,计算得到了不同载荷下的分形维数。研究结果表明,聚醚醚酮初始表面和摩擦信号均具有显著的分形特征;在相同速度、相同初始表面下,摩擦信号的分形维数随着载荷的增大而增大;在相同速度、不同载荷下,磨合初期摩擦信号的分形维数均与初始表面分形维数负相关。     

载荷、相对湿度和气氛对硅表面及金表面纳米摩擦特性的影响

利用分子沉积技术 ,在不同修饰的硅表面上考察了载荷对纳米摩擦学性能的影响 ,同时在阴、阳离子化金表面上考察了湿度、气氛对纳米摩擦学性能的影响。结果表明 ,不同修饰的硅表面在较低的载荷下 ,摩擦力均随着载荷成线性增加 ,同时发现单层磺化酞菁铜MD膜修饰的硅表面没有改变硅的摩擦特性 ;试验表明 ,在阳离子化金表面上 ,相对湿度越大 ,摩擦力和摩擦系数越低 ;阴离子化金表面在氮气保护下 ,体系的摩擦学特性不同于大气环境。     

复合绝缘子芯棒疲劳断裂特性分析

在自制疲劳试验机上模拟了复合绝缘子实际运行时的疲劳损伤过程,分别讨论了摆动幅度和扭转角度对绝缘子疲劳寿命的影响。并采用超景深三维显微系统测量了绝缘子断口表面形貌,利用分形几何学理论定量表征了断口表面形貌。研究表明,芯棒疲劳断裂是在循环应力的作用下,芯棒裂纹逐渐深化直至大量纤维断裂的过程。断口表面分形维数介于2～3之间,且线性回归相关系数都在0.99以上,强的相关性表明断口表面分形维数具有明显的分形特征;断口形貌的形成不仅受载荷产生的形变影响,也与载荷循环次数有关,断口表面分形维数与其受到的载荷呈正相关,与应力循环次数呈负相关关系。     

苜蓿草粉对金属材料磨损表面的分形维数计算

基于分形理论和扫描电镜分析,采用差分计数盒法(DBC)计算了苜蓿草粉对金属材料磨损表面的三维分形维数。结果表明:基于DBC法和磨损表面SEM照片计算所得的分形维数,可以表征苜蓿草粉对金属材料磨损表面的形貌特征;相同加工条件下的金属加工表面具有相近的分形维数,但不能通过分形维数区分材料;苜蓿草粉磨损后的磨损表面分形维数与磨损体积损失有着密切的关系,体积磨损量越大,分形维数也越大。     

基于小波变换和分形维数的表面微观形貌分析

针对传统三维参数和单一分形维数在表面微观形貌分析中的不足,提出了一种基于小波变换和分形维数的表面微观形貌分析方法。该方法通过小波变换对表面形貌的灰度图像进行分解和单支重构,利用改进的差分盒维法计算原图像和重构子图像的分形维数,依据原图像和重构子图像的分形维数构成的数组对表面微观形貌进行分析。最后,利用本文提出的方法对一组零件的表面微观形貌进行了分析,结果表明原图像和重构子图像的分形维数不仅能够反映表面微观形貌的整体特征还能反映表面不同分辨率下的细节特征。     

超声磨削加工表面分形维数计算方法

基于盒维数法、差分盒维数法、结构函数法,用MATLAB模拟出已知分形维数的理论分形曲面,对其进行分形维数的计算,并计算其误差,结果表明:盒维数法的计算结果误差最小,可确定超声磨削加工表面分形维数的计算方法,为超声磨削加工表面形貌的特征分析奠定理论基础.     

基于分形理论的柱塞泵/马达配流副润滑特性研究

为研究配流盘表面形貌对配流副润滑特性的影响,采用分形理论模拟配流盘表面形貌,建立轴向柱塞泵配流副润滑模型,使用有限差分法对模型进行求解,探讨分形参数对表面轮廓的影响,并进一步分析分形参数和配流副工况参数对油膜承载力、摩擦力、摩擦转矩和摩擦因数的影响。结果表明：分形维数越大,表面轮廓形貌复杂度越高,且粗糙表面高度随尺度系数减小而降低;随着缸体倾角和转速的增大,油膜承载力提升,但摩擦力、摩擦转矩和摩擦因数也随之升高;配流副润滑性能与分形维数呈现正相关的关系,选取较大的分形维数有利于提升配流副的润滑性能;尺度系数越小其摩擦力越小,但承载力也减小,因此需选择适中的尺度系数。     

滑动轴承表面形貌的分形模拟及对摩擦学性能的影响

运用分形理论对滑动轴承粗糙表面进行模拟,研究粗糙表面对其膜厚、压力以及承载力的影响。进一步模拟两向异性粗糙表面,比较轴承圆周及轴向方向上粗糙表面对轴承承载及摩擦性能的影响。结果表明:在一定载荷下,轴瓦表面分形维数越小,尺度系数越大,则轮廓幅值越大,表面轮廓越简单,越难形成润滑膜;表面轮廓幅值对润滑膜压力影响明显,幅值越大,润滑膜压力分布越不平滑,润滑性能越差;表面分形维数越小,特征粗糙度值越大,则承载力越低,摩擦力越大,且圆周方向上的分形维数以及特征粗糙度的影响要比轴线方向的影响大。     

基于W-M分形函数的三维粗糙表面摩擦生热研究

将W-M分形函数引入风电制动器制动过程的摩擦生热研究中,根据W-M分形表面形貌的特点及利用其特有的自相似性,以Matlab软件模拟出粗糙表面的分形曲面形貌.通过Creo软件建立不同分形维数的粗糙表面模型,运用Abaqus有限元软件分析分形维数、相对滑动速度、施加载荷对粗糙表面制动过程中闪点温度和接触压力的影响.结果表明:随着分形维数增大,摩擦区域块状热区的数量减少,而点状热区的数量增多;相对速度越大时,接触区域最顶端的微凸体节点温度也越大,非接触区域温度上升速率也越快;施加载荷增大时,微凸体的最高闪温点的温度变化幅度不大,但会影响热区的数量大小与次闪温点和非接触点的温度.     

齿面形貌对动力学特性的影响规律研究

为了建立表面形貌特征参数对齿轮动力学性能的影响规律,开展不同润滑条件下的齿轮表面分形维数测定及效率和振动特性试验。选择3组同等齿面精度等级的齿轮箱,在相同的载荷和运转时间等工况下,对油润滑、脂润滑和干摩擦的齿面进行表面轮廓测量,通过结构函数法获得相应的分形维数。结果显示,油润滑的分形维数最大,且试验前后的分形维数变化最小,表明齿面磨损较低、从而能够获得较为稳定的动力学性能。通过效率和振动特性试验也发现,油润滑的传动效率最高、振幅最小,与分形维数的测量分析结论一致。本研究能够为后续进行齿面的微观形貌设计提供理论基础和应用前提。     

离子束增强沉积Ni、Ti纳米金属薄膜的表面形貌与摩擦特性研究

在原子力显微镜上对采用离子束增强沉积方法制备的Ni、Ti纳米金属薄膜的形貌进行了观察,应用分形理论分析了薄膜表面的分形特征,并且对金属薄膜的纳米摩擦特性进行了研究,分析了载荷和表面力对金属薄膜摩擦特性的影响。结果表明,Ti薄膜晶粒细小,表面平整,而Ni薄膜表面粗糙。Ni、Ti沉积薄膜表面具有显著分形特征,各向同性。Ni、Ti纳米薄膜的摩擦力均随载荷的增大而增大,并且都存在一个临界载荷值,超过这个值,摩擦力急剧增加。将分形理论和接触力学JKR模型结合,对纳米金属薄膜摩擦的临界载荷进行的预测与实验结果具有相同的趋势。     

Optimum film thickness of thin metallic coatings on silicon substrates for low load sliding applications

The frictional behaviour of thin metallic films on silicon substrates sliding against 52100 steel balls is presented. The motivation of this work is to identify an optimum film thickness that will result in low friction under relatively low loads for various metallic films. Dry sliding friction experiments on silicon substrates with soft metallic coatings (silver, copper, tin and zinc) of various thickness (1–2000 nm) were conducted using a reciprocating pin-on-flat type apparatus under a controlled environment. A thermal vapour deposition technique was used to produce pure and smooth coatings. The morphology of the films was examined using an atomic force microscope, a non-contact optical profilometer and a scanning electron microscope. Following the sliding tests, the sliding tracks were examined by various surface characterization techniques and tools. The results indicate that the frictional characteristics of silicon are improved by coating the surface with a thin metallic film, and furthermore, an optimum film thickness can be identified for silver, copper and zinc coatings. In most cases ploughing marks could be found on the film which suggests that plastic deformation of the film is the dominant mode by which frictional energy dissipation occurred. Based on this observation, the frictional behaviour of thin metallic coatings under low loads is discussed and friction coefficients are correlated with an energy based friction model.     

Frictional behaviour of Pb‐Sn thin‐film lubrication

The frictional properties of lead‐tin thin films (thickness of 0.05–0.19 μm) with two types of copper interlayer were investigated. The thin film and the interlayer were formed on a silicon wafer surface by vacuum deposition. Friction tests were carried out using a ball‐on‐disc apparatus in a vacuum chamber. The thin copper interlayer reduced the friction coefficient and prolonged the film life. The effect of load on the friction coefficient is explained by an equation derived using the Hertzian contact area between a sphere and a plate. The thicker copper interlayer did not reduce the friction coefficient but markedly extended the life of the film. In this case, the dependence of the friction coefficient on the load is explained by an equation derived using the Hertzian contact area between a sphere with surface roughness of second order and a plate.     

Nanofriction of silicon oxide surfaces covered with thin water films

A thin water film present on surfaces plays a central role in defining the micro- and nanotribological properties of a system. This paper presents a quantitative examination of the nanotribological effects of thin water films in ultra high vacuum (UHV) on OH-terminated (hydrophilic) and bare (no OH terminations, hydrophobic in vacuum) silicon oxide surfaces. Water film thickness was controlled by varying the water partial pressure in UHV. Friction was measured by scanning force microscopy (SFM) as a function of an external applied load. The surface energy and the shear stress of the nanotribological contact was then approximated by fitting the friction-load curves using the Derjaguin-Muller-Toporov (DMT) model. The surface energy as well as the adhesion force of the OH-terminated hydrophilic sample first decrease and later increase significantly at higher water partial pressures. No such dependence could be deduced from the friction-load curves at varying water pressures for the bare hydrophobic silicon oxide surface. However, at relatively high normal loads (pressures) and water partial pressures the bare hydrophobic silicon oxide is transformed to an OH-terminated surface. This transformation appears to occur only in the area of contact leading to the conclusion that it is friction-induced. This work shows that the chemical composition of the topmost surface layer defines the frictional behavior of the tribosystem.     

PECVD法硅基氮化硅薄膜的制备及其耐磨性研究

以N(111) 型的单晶硅片为基体,运用PECVD-2D等离子体化学气相淀积台在单晶硅片表面沉积氮化硅薄膜,通过薄膜颜色与厚度间的关系探讨了制备工艺参数对薄膜厚度的影响,用原位纳米力学测试系统对氮化硅薄膜的纳米硬度进行测定,在UMT-2型摩擦试验机上对不同制备工艺的硅基氮化硅薄膜进行耐磨寿命试验.结果表明:随着沉积温度的升高,薄膜厚度逐渐递减,SiH4和N2流量比越大,薄膜厚度越大;温度越高,薄膜硬度越大,耐磨寿命越长;随着SiH4和N2流量比的增加,薄膜硬度和耐磨寿命均先增加后减小.     

DPPC LB膜的摩擦学行为研究

通过LB技术,以镉离子水溶液为亚相在单晶硅表面制备DPPC不同层数的LB膜,并通过AFM、UMT-2对其表面形貌及摩擦学行为进行考察。摩擦学行为研究发现,DPPC LB膜表现出比花生酸(AA)LB膜更为优异的摩擦学性能。同时,DPPC LB膜的摩擦学性能存在最佳层数。分析认为,DPPC LB膜优异的摩擦学性能与DPPC分子有2个亲水极性基团有关,它可使DPPC分子与亲水基底结合更为牢固,而亚相中金属离子的加入使成膜性能有效提高。     

A Method for Studying the Effect of Extreme Pressure Additives on Rubbing Metal Surfaces

When a film of lubricant separates two moving metal surfaces, it may be subjected to radical changes in temperature as the severity of the forces changes. This paper is concerned with a technique which measures the temperature of the lubricant after it leaves the area of rubbing metal surfaces. Special attention was given to: (A) the changing load conditions, (B) the changes in frictional force, (C) the effect of phosphate coating of the metal surface, and (D) the effect of different lubricant compositions. A modification of the Shell Four-ball EP Lubricant Tester has been made which permits automatic recording of a temperature-load curve which registers the temperature and frictional forces with either constant or changing load.

The work has shown that as the load increases at a uniform rate, there may be drastic and sudden changes in lubricant temperature which depend on lubricant composition as well as on metal surface composition.     

Friction and Wear Studies of Octadecyltrichlorosilane SAM on Silicon

A self-assembled monolayer of octadecyltrichlorosilane (OTS) was prepared on a single-crystal silicon wafer (111) and its tribological properties were examined with a one-way reciprocating tribometer. The worn surfaces and transfer film on the counterface were analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that, due to the wear of the OTS monolayer and the formation of the transfer film on the counterpart ball, the friction coefficient gradually increases from 0.06 to 0.13 with increasing sliding cycles and then keeps stable at a normal load of 0.5N. The transfer film is characterized by deposition, accumulation, and spalling at extended test duration. Though low friction coefficients of the monolayer in sliding against steel or ceramic counterfaces are recorded, poor load-carrying capacity and antiwear ability are also shown. Moreover, the monolayer itself or the corresponding transfer film on the counterface fails to lubricate even at a normal load of 1.0N. Thus, the self-assembled monolayer of octadecyltrichlorosilane can be a potential boundary lubricant only at very low loads.     

An investigation of the tribological properties of thin KCl films on iron in ultrahigh vacuum: modeling the extreme-pressure lubricating interface

The frictional properties of thin KCl films deposited onto clean iron are measured in ultrahigh vacuum using a tungsten carbide tribotip, where the observed initial rapid decrease in friction coefficient with film thickness is proposed to be due to the formation of a complete KCl monolayer where the friction coefficient of this film is ∼0.27. A 1800 Å thick KCl film shows a hardness and friction coefficient similar to those for bulk KCl when the width of the surface height distribution of the tribotip measured by atomic force microscopy (AFM) is 2000–3000 Å. This implies that the KCl film behaves like the bulk material when the film thickness exceeds the roughness of the interfaces.