利用功率谱密度函数表征光学薄膜基底表面粗糙度

光学表面的表面粗糙度通常利用两个传统参数方根粗糙度σ和相关长度l来进行表征。主要就如何引入功率谱密度函数(PSD)表征表面微观形貌进行了初步研究。说明了一维和二维功率谱密度(PSD)函数的数学计算方法、PSD函数的物理意义,同时给出了PSD函数与传统的表面评价指标σ和l之间的关系。利用不同仪器对多种样品进行测试,在分析比较测试结果的基础上,总结了利用PSD函数评价光学表面粗糙度的优点。功率谱密度函数作为一个全面的光学表面评价参数,正得到越来越广泛的重视和应用。     

The filtering method to calculate the transmission characteristics of the low-pass filters using actual measurement data

The Gaussian filter and spline filter are low-pass filters used in surface roughness estimation methods, and their transmission characteristics are well known. However, the transmission characteristics of the Gaussian filter and spline filter used at actual sites may not be in agreement with their theoretical characteristics. Generally, the spline filter is used with an open profile. Although the transmission characteristics of the periodic spline filter are well known, these transmission characteristics are not those of a nonperiodic spline filter used with an open profile. In the case of a Gaussian filter, the filter width of the theoretical transmission characteristics is ∞. However, a Gaussian filter of filter width λ_c is used at actual sites. This fact is a major problem. To solve this problem, it is necessary that the transmission characteristics of a low-pass filter are obtained from actual measurement data and the filter output. However, it is not possible to calculate the transmission characteristics from actual measurement data owing to the end effect and the discontinuity at each end of the data, etc. In this paper, we propose a new method for exactly calculating the transmission characteristics of a low-pass filter. This method involves the process in which the open profile is considered as a closed profile by repeating it periodically. The transmission characteristics of a nonperiodic spline filter and a Gaussian filter (filter width λ_c) used at actual sites were confirmed by the proposed method. The transmission characteristics of the Gaussian filter of filter width λ_c were almost the same as the theoretical characteristics. However, the transmission characteristics of the nonperiodic spline filter were considerably different from those of a periodic spline filter with well-known characteristics. Moreover, the transmission characteristics of the nonperiodic spline filter were found not to be unique.     

A pulsed two-channel Nd:YAG laser with an improved spatial structure of IR radiation for prompt recording and development of photothermoplastic holograms

A two-channel Nd:YAG laser for high-speed recording and development of photothermoplastic holograms has been created. In two independent channels, the laser generates monopulse radiation of nanosecond duration (30 ns) at the second harmonic frequency (λ ₂ = 0.532 μm) and IR radiation (λ ₁ = 1.064 μm) produced by quasi-stationary free-running lasing of millisecond duration (4 ms). The radiations with wavelengths λ ₂ and λ ₁ are used, respectively, for exposure and development of photothermoplastic holograms. A method based on the use of a passive resonator is proposed to improve the spatial structure of IR radiation during lasing.     

Prediction of the thermal conductivity of petroleum products

One of the main functions of a lubricant is to cool the mating surfaces. Detailed studies of thermal behaviour of bearings and coolers requires a knowledge of the thermal conductivity of the lubricant. Thermal conductivity varies from one lubricant to another, and since it is a difficult property to measure, a prediction method has been developed. Over a wide range of temperature, thermal conductivity is described by the equation λ_t = λ₆₀ + α(t?60) and it is shown that λ₆₀ and α can be found from more readily available data. Thus the method allows thermal conductivity of lubricants and a wide range of other petroleum products to be calculated from the equation to within ± 5%.     

The behavior of an elastic-perfectly plastic sinusoidal surface under contact loading

The goal of this paper is to provide the foundation for an analysis of contact between elastic-plastic solids, whose surface roughness is idealized with a Weierstrass profile. To this end, we conduct a parametric study of the plastic deformation and residual stress developed by the two-dimensional contact between a flat, rigid platen and an elastic-perfectly plastic solid with a sinusoidal surface. Our analysis shows that the general characteristics of the deformation can be characterized approximately by two parameters: α = a/λ, where a is the half-width of the contact and λ is the period of the surface waviness; ψ = E^*g/σ_Yλ, where E^* and σ_Y are the effective modulus and yield stress of the substrate, respectively, and g is the amplitude of the surface roughness. Depending on the values of these parameters, we identify eight general types of behavior for the asperity contacts: (a) elastic, elastic-plastic or fully plastic isolated Hertz type contacts; (b) elastic, or elastic-plastic non-Hertzian isolated contacts; and (c) elastic, elastic-plastic or fully plastic, interacting contacts. Relationships between contact pressure, contact size, effective indentation depth and residual stress are explored in detail in each regime of behavior. Implications on rough surface contacts are discussed.     

Finite difference spectral moment estimation for profiles the effect of sample spacing and quantization error

The mean square slope m₂ and curvature m₄ of surface profiles are characteristics that depend upon the frequency content of the roughness. Together with the mean square profile height m₀ they determine the microgeometrical behaviour of contacting rough surfaces. It is shown that in the absence of quantization error, the error due to finite sample spacing in estimating these spectral moments for a sinusoid is negligible when more than 8 points per cycle are used. In the presence of quantization error, large potential overestimates of m₂ and m₄ can occur. The error decreases initially with increased sample spacing and then increases. The severity of the distortion is shown to increase as the peak-to-peak range of the sine wave decreases relative to the full range of the a/d converter used in the digitization process.     

Near infrared reflectance spectroscopy: Moisture content measurement for ceramic plaster

We measured moisture content of ceramic plaster using near infrared reflectance spectroscopy (NIRS) as required by the ceramic industry. The moisture content and the normalized spectral reflectance were measured and correlated at the wavelengths of the spectral absorptance peaks (α _λ ), spectral sensitivity peaks (S _λ ) and normalized sensitivity peaks (S _λn ), in the wavelength range of 900–2500 nm. The best model was obtained by the scanning method, normalizing the sensitivity and doing a minimization of the standard error of estimate (SE). The α _λ -peaks, s _λ -peaks and s _λn -peaks were not found at the same wavelength, for the three studied wavebands. The optimal model in terms of SE was the linear model at 1420 nm (s _λ -peak), for the ceramist drying range with a SE ₁₄₂₀ =1.25 (R²=0.96). The results indicate the feasibility of NIRS to non-contact moisture content measures of plaster in the studied range, even more for ceramist range.     

Sinusoidal profile precision roughness specimens

The design, specifications, fabrication, testing and potential use of a series of sinusoidal profile precision roughness specimens are described. These specimens were designed primarily to provide a means for optimum transfer of an accurate roughness average R_a value from primary to secondary laboratories. However, properties of the specimens also make them very useful for evaluating instrumentation and computational algorithms designed to measure the statistical parameters and functions now being investigated in many laboratories. Specimens with an R_a value of 1.0 μm and spatial wavelengths of 40, 100 and 800 μm are being fabricated. For the wavelength of 100 μm, specimens are also being fabricated with R_a values of 3.0 and 0.3 μm. Fabrication using numerically controlled diamond lathes has produced specimens with very high quality sinusoidal profile waveforms with uniform R_a values across the surfaces and with very low amounts of waviness over a test area of about 2 cm².     

Mathematical modeling of the thermal relaxation of nominally flat surfaces in contact using fractal geometry: Maxwell type medium

This work aims at studying the stress relaxation behavior of a nominally flat (rough) surface of a viscoelastic material in contact with a rigid half space. The effect of temperature will be included through the concept of activation energy using Arrhenius's equation. A synthesized Cantor-Borodich (C_B) profile is used to construct the rough surface. C_B profile has two scaling parameters, a and b, and different heights h_i for each generation of asperities. This simple model is applicable for fractal surfaces in which a single exponent (the fractal dimension) is enough to describe their quality.The surfaces in contact are viscoelastic, and they are assumed to behave according to the linear Maxwell model. An asymptotic power law is obtained, which relates the force and the bulk temperature acted on the punch to its approach. This model is valid only when the approach between the punch and the half space is in the range of the roughness size. The proposed model admits an analytical solution for the case when the deformation is linear thermo-viscoelastic. The obtained model shows a good agreement when compared with the experimental results obtained by Handzel-Powierza et al. [Handzel-Powierza Z, Klimczak T, Polijaniuk A. On the experimental verification of the Greenwood-Williamson model for the contact of rough surfaces. Wear 1992;154:115-24].     

Three-dimensional profile stitching measurement for large aspheric surface during grinding process with sub-micron accuracy

A novel measurement method is proposed to realize three-dimensional (3D) profile stitching for large aspheric surface. The proposed method is based on the multiple sub-regions stitching technology applying a four-axis fixture and a commercial small-range profiler. The partition of sub-regions is due to the effective profiler’s range and the characteristic parameters of aspheric surface, and the measurement for each sub-region within the profiler’s range is achieved through the fixture to translate and rotate the aspheric surface. Then a stitching algorithm including the multi-body theory, the invariability of curvature radiuses and the least square principle is established to reconstruct the full 3D profile. Simulations of multiple sub-regions stitching for different aspheric surfaces are performed to predict the stitching accuracy of proposed method and analyze the influence of alignment errors in Y direction caused by the rotation error along Z direction (Δβ_w,g). The stitching accuracy of proposed method is verified by measuring the 3D profile of an off-axis parabolic surface and an axisymmetric aspheric surface. The experimental standard deviations of stitching errors are 0.16 μm and 0.42 μm, which are less than the form errors of aspheric surface during grinding process. The results show that the proposed method achieves 3D profile stitching for large aspheric surface with sub-micron accuracy.     

Attenuation of ultrasonic Rayleigh–Lamb waves by small horizontal defects in thin aluminium plates

The present paper illustrates how horizontal symmetric crack-like defects can be detected rapidly in thin isotropic plates by using longitudinal ultrasonic waves. The use of such longitudinal waves offers the potential of being significantly faster for non-destructively detecting defects than conventional ultrasonic techniques, which rely on transverse waves propagating through the thickness of a plate. Computational and analytical methods are used to predict reflection coefficients due to the attenuation of a longitudinal ultrasonic wave by physically small defects. It is shown that detectable attenuation (>10%), i.e. reflection coefficients, of the lowest order symmetric Rayleigh–Lamb wave (S₀) occurs for a range of small defects (sub-millimeter in length) when using high-frequency waves (MHz range).     

Research on error averaging effect of hydrostatic guideways

Hydrostatic guideways can obtain high motion accuracy due to their error averaging ability. In order to optimize the structural and accuracy design of hydrostatic guideways, the mechanism and affecting factors of the error averaging effect are investigated in detail in this paper. A new method is proposed to quantitatively analyze the motion errors of a typical closed hydrostatic guideway with four pads, and the restrictor is also taken into consideration. A hydrostatic guideway in an ultra-precision grinding machine LGF750 is analyzed with the method. The results show that the wavelength of each profile error component is a main affecting factor on the error averaging effect. Fluid films usually show obvious error averaging effect on each profile error component when the wavelength λ is shorter than twice of the pad length 2l_u. However, for each component with the wavelength λ over 2l_u, the error averaging effect becomes obvious only when the ratio of the pad length to the evaluation length of motion straightness l_u/l_e is greater than 0.5. Furthermore, the instability of the oil supply system is taken into consideration, and possible influences on the error averaging effect due to the supply pressure fluctuation are investigated preliminarily.     

积屑瘤状态对微细切削表面轮廓特征的影响

研究了微细切削条件下,刀具前刀面上的积屑瘤状态对切削表面轮廓特征的影响,为合理选择和控制微细切削刀具的切削条件,以及评价微细切削的表面形貌特征提供实验依据.利用表面粗糙度仪分别提取了无积屑瘤、积屑瘤生长、稳定和脱落等4种积屑瘤状态下的切削表面轮廓,选取幅值密度函数(ADF)、自相关函数(ACF)和功率谱密度函数(PSD...     

Influence of the geometry and connection of electrodes on electromechanical characteristics of frequency-tuned disk piezoelectric elements

Amplitude-frequency and electromechanical characteristics of PZT-19 ceramic thin disk piezoelectric elements covered nonuniformly with electrodes are studied. It is shown that, in the case of in-phase connection of ring electrodes to one of the surfaces of a piezoelectric element, which enters the nonuniform stressed-strained state, mechanical vibrations can be excited at several resonance frequencies for which electromechanical-coupling coefficient k _d reaches 67% of that attained for the piezoelectric element covered completely with electrodes.     

A technique for forecasting the durability of rolling bearings and the optimum choice of lubricants under flood-lubrication and oil-starvation conditions

Effective conditions of friction in units that ensure performance and maximum longevity have been created by flood lubrication under the conditions of elastohydrodynamic (EHD) lubrication. In connection with this, prolonging the service life of friction units by ensuring local requirements to the amount of oil in the contact area and establishing the optimum choice of lubricating material in terms of its viscosity ratings is a topical problem for rolling bearings. Thus, it is suggested to determine the parameter of the lubricating layer (λ) values for the conditions of flood lubrication (λ_o) and progressing (λ_o.s ) and catastrophic (λ _c.s ) oil starvation for a wide spectrum of lubricating materials of different viscosity, since, in oil starvation mode, the efficiency of EHD conditions is violated, the lubrication mode is disturbed, and the bearing capacity of the EHD lubricating layer is lost.     

ELNES for boron, carbon, and nitrogen K-edges with different chemical environments in layered materials studied by density functional theory

Electron energy-loss near-edge fine structures (ELNES) were calculated for graphene, doped graphene, a hexagonal BN monolayer, and a hexagonal BC₂N layer using an ab initio pseudopotential plane wave method including the core-hole effect. Spectral features that can be used to distinguish different chemical environments are identified. The spectral features are closely related to the atomic species and arrangement. The connection between chemical environments and fine structures is discussed.     

Frictional response of precision finished surfaces in pure sliding

The functional performance of a component is closely tied to the geometric properties of its surface, which is an outcome of the finishing process used to make the component. This paper investigates the role of three-dimensional (3-D) surface topographic features of four precision finished surfaces (Ground, Hard Turned, Honed, and Isotropic) commonly used in the bearing industry on their frictional response. Experiments are conducted to investigate the effect of surface type, sliding speed, and normal contact load on the coefficient of kinetic friction under point contact. The effect of lay is also analyzed for the strongly anisotropic ground surface. Based on a detailed 3-D surface characterization, it is shown that the amplitude parameter S_q (rms deviation of surface), and spatial parameters S_ds (density of summits) and S_td (texture direction) play an important role in determining the frictional behavior of the surfaces studied. An empirical model for the coefficient of kinetic friction as a function of these parameters is proposed.     

Investigation on the polishing of aspheric surfaces with a doughnut-shaped magnetic compound fluid (MCF) tool using an industrial robot

Aspheric elements have become essential optical surfaces for modifying optical systems due to their abilities to enhance the imaging quality. In this work, a novel method employing a doughnut-shaped magnetic compound fluid (MCF) polishing tool, and an industrial robot was proposed for polishing aspheric surfaces. Firstly, investigations on the MCF tool, including the formation process and geometry, were conducted to form an appropriate polishing tool. The distribution of abrasive particles was observed using SEM and EDX mapping. Thereafter, a conic workpiece constructed from 6061-aluminum alloy was selected as the workpiece, which was used to discover the effects of the parameters on the polishing ability of aspheric surfaces. Finally, a polishing experiment was conducted with an aspheric element under the optimized conditions. The obtained results are shown as follows. (1) A relatively regular MCF tool was obtained when the eccentricity (r), amount of MCF slurry supplied (V), revolution speed of the MCF carrier and magnet (n_c and n_m, respectively) were given at appropriate values. (2) Abrasive particles entrapped in or attached to the clusters were observed abundantly on the MCF tool sample. (3) The surface profile of the conic workpiece after 60 min of polishing indicated that material was removed evenly, and an annular polishing area was attained. Meanwhile, a higher material removal rate and better surface roughness were achieved with a smaller working gap (h) and larger volume of the MCF slurry supplied (V). (4) The roughness (Ra) of the aspheric surface decreased from 49.81 to 10.77 nm after 60 min of polishing. The shape retention obtained a Pearson correlation coefficient (Pcc) of 0.9981, which demonstrated that this novel method is appropriate for polishing aspheric elements.     

掠入射X射线散射法测量超光滑表面

介绍了掠入射X射线散射法(GXRS)测量超光滑表面的原理及基于商业用X射线衍射仪改造而成的实验装置。选择3片不同粗糙度的硅片作为实验样品,根据一级矢量微扰理论对各个样品所测量的散射分布进行处理。结果表明,GXRS法得到的样品功率谱密度函数(PSD)与使用原子力显微镜(AFM)所测量的结果基本相符。分析了探测器接收狭缝的宽度和入射光发散度对实验结果的影响,结果表明,在其他实验条件理想的情况下,当探测器接收狭缝宽度0.02mm,入射光发散度43″时,在空间频率0.03μm-1的范围内,由其引起的PSD函数测量误差2%。随着探测器接收狭缝宽度和入射光发散度的减小,测量误差呈指数迅速减小。在所测量的空间频率范围内,PSD函数的误差随频率的增加而减小,仪器的重复精度优于2.6%。