Evaluation of surfaces complementarity based on high definition metrology

The gap between two mating surfaces has a direct influence on sealing performance. However, traditional surface metrology rarely characterizes the gap between two mating surfaces. To solve this problem, a novel concept of surfaces complementarity is proposed in this paper. Surfaces complementarity measures how well two rough surfaces fit into each other. To make this concept applicable in engineering practices, a virtual assembly algorithm is developed. The automatic virtual assembly algorithm aligns the mating surfaces by maximizing the overlap ratio of the surface masks. Then, a sum surface which is complementary to the surface gap is constructed to represent the mating states. The top surface of a cylinder block and corresponding cylinder head surface measured by high definition metrology is mated by the virtual assembly algorithm. The differences of functional parameters between the mating surfaces and the sum surface are discussed thoroughly. Due to surfaces complementarity, parameters of the sum surface has a certain deviation from expected combined parameters from two individual surfaces. A case of square surface shows the practical application potential of the virtual assembly algorithm to optimize the sealing performance of the mating surfaces.     

Characterization of the surface functionality on precision machined engineering surfaces

The surfaces characterization of a component generated from the machining process is important as the surfaces have significant effects on the performance of the component and associated product. The work presented aims to investigate the surfaces functionality characterization of a component by using 3D surface parameters. The paper also investigates the surface generation in relation with the machining process and the associated functionality formation. The corresponding surface characterization is investigated with two case studies on typical engineering components. The generation of the sample surfaces and associated surface functionalities are also studied by MATLAB-based modelling and simulation. The relationship between surface characterization and surface functionality are further studied by the simulations. The paper concludes with discussions on the applications and potential of this approach for the achievement of high quality surfaces, optimization and control of their functional performance at the machining stage.     

Fractal-wavelet based classification of tribological surfaces

Classification of the topography of freshly machined, worn and damaged surfaces (e.g. damaged by adhesion, scoring, abrasion, pitting) is still a problem in machine failure analysis. Tribological surfaces often exhibit both a multiscale nature (i.e. different length scales of surface features) and a non-stationary nature (i.e. features which are superimposed on each other and located at different positions on a surface). The most widely used approaches to surface classification are based on the Fourier transform or statistical functions and parameters. Often these approaches are inadequate and provide incorrect classification of the tribological surfaces. The main reason is that these techniques fail to simultaneously capture the multiscale nature and the non-stationary nature of the surface data. A new method, called a hybrid fractal-wavelet method, has recently been developed for the characterization of tribological surfaces in a multiscale and non-stationary manner. In contrast to other methods, this method combines both the wavelets’ inherent ability to characterize surfaces at each individual scale and the fractals’ inherent ability to characterize surfaces in a scale-invariant manner. The application of this method to the classification of artificially generated fractal and tribological surfaces (e.g. worn surfaces) is presented in this paper. The newly developed method has been further modified to better suit tribological surface data, including a new measure of differences between initial and decoded images. The accuracy of this method in the classification of surfaces was assessed.     

Impact of Plateaued Surfaces on Tribological Performance

Plateaued surfaces are surfaces that have been machined to simulate those that result from normal running in and are said to have advantages over conventional or non-plateaued surfaces. However, the evidence is lacking. This study evaluates the tribological performance of plateaued and non-plateaued surfaces on a pin-on-disk tribometer. The honing pattern of an engine cylinder bore was simulated on the disks. These disks have similar average surface heights with either plateaued or non-plateaued surface finish. Friction, wear and scuffing resistance of plateaued and non-plateaued disks were evaluated. Results from the pin-on-disk tribometer show that in the hydrodynamic lubrication regime plateaued and non-plateaued disks have the same friction, while in the mixed lubrication regime the plateaued surface has less friction. The author's findings also reveal that plateaued surfaces tend to have higher wear resistance but lower scuffing resistance. It also confirms the conventional wisdom that plateaued surfaces have shorter running-in wear period.     

Studies on friction and transfer layer: role of surface texture

Friction influences the nature of transfer layer formed at the interface between tool and metal during sliding. In the present investigation, experiments were conducted using “Inclined Scratch Tester” to understand the effect of surface texture of hard surfaces on coefficient of friction and transfer layer formation. EN8 steel flats were ground to attain surfaces of different textures with different roughness. Then super purity aluminium pins were scratched against the prepared steel flats. Scanning electron micrographs of the contact surfaces of pins and flats were used to reveal the morphology of transfer layer. It was observed that the coefficient of friction and the formation of transfer layer depend primarily on the texture of hard surfaces, but independent of surface roughness of hard surfaces. It was observed that on surfaces that promote plane strain conditions near the surface, the transfer of material takes place due to the plowing action of the asperities. But, on a surface that promotes plane stress conditions the transfer layer was more due to the adhesion component of friction. It was observed that the adhesion component increases for surfaces that have random texture but was constant for the other surfaces.     

Classification of Tribological Surfaces Without Surface Parameters

Quantitative measures are obtained from images of tribological surfaces. Based on these data, decisions are made regarding manufacturing and maintenance processes, machine-condition monitoring and failure analysis of engineering components. These decisions are often guided by an automated pattern recognition system. Components of this system are: surface topography data acquisition, surface characterization, surface classification and performance evaluation. The characterization and classification of tribological surfaces are major challenges that make the development of a reliable pattern-recognition system difficult. The reasons are that: (i) tribological surfaces often exhibit a non-stationary and multiscale nature, while most surface characterization methods currently used work well with surface data exhibiting a stationary random process, (ii) changes in topography that might occur between the interacting surfaces usually need to be known in advance, and (iii) the selection of surface parameters that separate different classes of surfaces is usually time-consuming and cumbersome. Because of these difficulties, characterization and classification methods which do not use surface parameters have been developed. In the classification methods, a measure of dissimilarity (e.g., Euclidean distance) calculated between a surface to be classified and already classified surfaces was used, instead of surface parameters. The unclassified surface was assigned to the class (of classified surfaces) with the lowest value of dissimilarity measure. The suitability of different classifiers; such as k-nearest neighbour classifier, linear-discriminant-analysis based classifiers and different dissimilarity measures; for the classification of tribological surface topographies (without the need for surface parameters) is investigated in this paper. Recent developments in this area, i.e., a fractal measure and a hybrid fractal-wavelet measure, are also discussed. The most suitable method for the classification of tribological surfaces has been selected.     

基于状态转换的超疏水表面滑移特性研究方法

根据流体在大剪切速率下在超疏水表面上产生状态转换的现象,提出了通过转换后得到的参数来刻画转化前滑移特性的方法,这种方法能够去除大接触角对滑移特性测量值的影响。为验证方法的可行性,进行了水在光栅结构超疏水表面上、甘油水溶液在碳纳米管(CNTs)结构表面上以及甘油水溶液在ZnO纳米结构表面上的流变实验。结果表明:所研究的超疏水表面在大的剪切速率下产生了状态转化,而通过这种转化正好可以刻画表面的滑移特性。这种方法适合于衡量液体在超疏水表面的接触状态容易发生转换的情况。     

曲面数控加工中刀具干涉的检验

文章讨论了雕塑曲面数控加工中单张曲面产生刀具干涉的现象；相邻两曲面在凹向交线处的无干涉加工以及曲面拼接处刀具干涉的截面验证法，给出了具体算法和加工实例，取得了较好的干涉处理效果。     

超疏水光栅微结构表面减阻试验研究

为了研究超疏水固体表面的微结构对减阻特性的影响，首先利用飞秒激光加工技术在光滑K9玻璃基面上加工出微脊光栅结构，然后将光滑K9玻璃与光栅结构K9玻璃置于干燥箱内进行硅烷化处理，以降低表面自由能，最后用AR-G2流变仪测量两表面的流变特性，试验用流体为体积分数40%的甘油溶液和水。试验结果表明：两表面均存在明显滑移，即都具有减阻特性，且光栅结构的超疏水表面比光滑结构的疏水表面的减阻效果明显；减阻效果随着流体粘度的增大而增强。     

超声纵扭辅助铣削高强铝合金表面润湿性能研究

针对超声辅助加工在工件表面形成微刻划表面可以提高高强铝合金表面的微结构性能的现象,进行了单激励旋转超声纵扭复合铣削表面微观结构的试验,基于水接触角理论和纵扭铣削运动学理论分析了加工参数对水接触角的影响;搭建了单激励超声纵扭铣削试验平台,采用正交试验法研究了不同加工参数对表面粗糙度、铣削力以及表面润湿性能的影响。结果表明：超声振幅为4μm时表面质量最佳,切削速度和进给量与表面粗糙度和水接触角呈正相关的关系;超声加工方式下的表面水接触角较普通方式更大,而在超声加工时低振幅加工比高振幅加工的表面水接触角大,当转速达到一定值时,高振幅和低振幅所加工的表面水接触角差别不大。合适的加工参数条件下超声纵扭加工方式可以降低加工表面的粗糙度,改变表面的润湿性。     

A new approach to characterising aspheric surfaces

In this paper, a new approach to fitting aspheric surfaces in three-dimensional space is proposed, based on the nonlinear least-squares algorithm. For the conditions tested, there are good indications that this method provides better results than conventional solutions as all the surface parameters can be estimated simultaneously based on the design equation, thus allowing the result to be directly compared to design parameters. Conventionally, aspheric surfaces can be fitted with simplified surface models, such as a second order surface or polynomial model. Using this approach the estimated parameters cannot be compared with the design values, breaking the link between the designed and measured surface. The new method is developed here and tested on computer simulated aspheric surfaces. Both ideal surfaces and surfaces with random irregularities are considered. Issues regarding the application of the fitting method to real measured surfaces are discussed.     

粗糙表面仿真方法综述

粗糙表面在自然界普遍存在。在研究表界面现象时,粗糙表面往往是重要的输入信息。实际测量和数值仿真是获取粗糙表面的两种常用方法。与实际测量相比,数值仿真无需昂贵的测量设备和大量机时,即可根据给定的表面特征信息高效地批量生成粗糙表面。目前,表面仿真已有近五十年的发展历史,基于不同表面形貌特征形成了采用多种表面特征参数的多种仿真方法,在摩擦学研究中应用广泛。梳理和总结表面仿真方法利于方法的高效、准确应用以及进一步发展。考虑到表面仿真方法与表面形貌特征及其表征参数密切相关,为了系统全面地综述表面仿真方法,首先介绍与表面仿真相关的形貌特征表征方法及特征参数。随后,以不同特征为线索对相应的表面仿真方法的原理、算法、优缺点进行梳理,初步提出了方法选用建议,并整理了其在摩擦学研究中的典型应用,最后展望了未来粗糙表面仿真的可能研究方向。     

粗糙表面弹性微动接触数值研究

由于实际工程表面多为粗糙表面,这里研究了粗糙表面对微动接触中压力和切向应力的影响。研究接触过程中法向载荷保持不变,切向载荷为周期性的交变载荷。首先,建立接触算法和模型,其算法核心是利用共轭梯度法(CGM)计算微动接触中的表面压力及切向应力并使用快速傅里叶变换(FFT)加快计算速度。然后,在验证算法正确的基础上,分析正弦和非高斯粗糙表面接触的压力和切向应力的分布,通过对光滑与粗糙表面的研究对比,表明:(1)在正弦表面接触切向应力分布呈现尺寸效应;(2)在非高斯表面接触中,切向应力分布跟光滑表面形状类似;同时由于粗糙峰存在,粗糙表面下的切向应力比光滑表面下的要大,研究粗糙表面微动接触对实际工程具有重要意义。     

曲面间最小距离及其在曲面求交中的应用

为了计算曲面间的最小距离 ,首先在两曲面上分别划分网格 ,选择两曲面上对应于最小距离的一对网格点作为初始点 ,利用曲面的几何特性进行数值迭代求取两曲面间的最小距离。在此算法的基础上 ,对采用跟踪法求曲面交线时如何确定初始跟踪点进行了深入研究。为了获得用于跟踪全部交线的初始跟踪点 ,将一张曲面分割成一组小曲面片 ,利用曲面间的最小距离检测各曲面片与另一曲面的相交性 ,并采用二分法求初始跟踪点。计算结果表明 ,本文算法效率高 ,稳定性好 ,实用性强。     

Effects of surface texturing on friction and vibration behaviors of sliding lubricated concentrated point contacts under linear reciprocating motion

Friction and vibration behaviors of lubricated concentrated point contacts with surface texturing have been experimentally investigated under reciprocating motions. Ground, lapped and textured lapped flat surfaces are tested against polished ball surfaces. Coefficient of friction, surface temperature, electrical resistance and vibrations at the lubricated contacts have been measured and analyzed. In the presence of surface texture, the coefficient of friction reduces by 30% in some of the cases. Surface temperature distributions on reciprocating tracks have also been measured and compared. Vibrations associated with lubricated point contacts formed between textured surfaces/balls reduce significantly at resonance frequency in comparison to polished surfaces/balls.     

Adhesion and Friction Enhancement of Film-Terminated Structures against Rough Surfaces

A number of biomimetic and bioinspired micron-scale surface structures have been developed in recent years with unique surface properties such as highly enhanced and switchable adhesion and friction against smooth surfaces. However, few studies have examined the effect of roughness on mechanisms for property enhancement, although this is of critical importance for applications. Here, we investigate the effect of roughness on adhesion and friction of a family of film-terminated fibrillar and ridge/channel microstructures. Although increasing roughness uniformly attenuates adhesion and friction, we find that the film-terminated structures maintain their enhancement compared to flat controls against a variety of rough surfaces (including natural stones). The principal mechanisms underlying property enhancement against smooth surfaces remain operative against rough surfaces. We show how the effect of roughness on surface mechanical properties of structured surfaces can be understood as a combination of known effects due to structure and roughness.     

梯度辟水涂层表面上的流动分析

基于对荷叶表面辟水性能的仿生，首次提出了表面张力梯度的新型表面设计，并分析了液滴在这种梯度表面上的运动过程，得到了液滴运动速度与位移随时间的变化规律。研究结果表明：在表面张力各向同性表面的流动速度为零，而液滴在梯度表面上的运动速度在0．2s的时间内就可达到20m／s以上，液滴的运动特性与在各向同性表面显著不同；通过涂层材料设计可获得表面张力梯度涂层，这种涂层在防雨衣、鱼雷与汽车挡风玻璃等产品中有重要应用价值。     

The influence of stylus flight on change of surface topography parameters

Theoretical and experimental work on stylus flight is described. The paper describes the development of a simulation model for assessing the magnitude of surface topography distortion by stylus flight. Experiments on the surfaces support the theoretical model, which predicts stylus flight. The measurements of different surface topographies (including surfaces after grinding, turning, honing, milling) were done using Talyscan 150 measuring instrument with four traversing speeds (0.5, 1, 2 and 3 mm/s). The results of theoretical considerations and experiments were compared. The effect of stylus flight on surface topography parameters of measured surfaces basing on experimental investigation was assessed. The tendency was found that slope decreased, decrease of amplitude parameters and increase of horizontal parameters took place, but these effects were different for various surface types. The simulation procedure assured good accuracy of surface topography parameters changes.Based on theoretical investigation, the effect of stylus flight and stylus tip radius on parameters of computer-generated profiles was predicted. The choice of traversing speed to different types of surfaces was done. The parameters of biggest changes caused by error in measurement due to stylus kinematics were selected.