The effect of tip size on the measured Ra of surface roughness specimens with rectangular profiles

When measuring rectangular and trapezoidal profile roughness specimens, the stylus tip increases the measured profile peak width and decreases the measured valley width. This can cause either an increase or a decrease in the apparent roughness average Ra, depending on the tip size and the ratio of peak width to valley width. Sometimes the change is larger than the combined measurement uncertainty from other sources. This raises the question as to whether measured surface parameters should be corrected for the effect of tip size.     

Discrimination between the move and stop of a lift based on accelerometer signals

Optoelectronics, Instrumentation and Data Processing - A solution to the problem of reliable discrimination between the move and stop states of a mine lift is proposed based on processing signals...     

Effect of surface roughness on the squeeze film between rotating porous annular discs with arbitrary porous wall thickness

The stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effect of surface roughness on the response of a squeeze film between two rotating annular discs when one disc has a porous facing. An exact solution, valid for arbitrary wall thickness is given for the film pressure and pressure in the bearing material. The results are compared with the approximate solution and the range of influencing parameters for which the approximate solution is satisfactory from a practical view point, is determined.     

An investigation on friction factors and heat transfer coefficients in a rectangular duct with surface roughness

An investigation on the fully developed heat transfer and friction factor characteristics has been made in rectangular ducts with one-side roughened by five different shapes. The effects of rib shape geometries as well as Reynolds numbers are examined. The rib height-to-duct hydraulic diameter, pitch-to-height ratio, and aspect ratio of channel width to height are fixed ate/De=0.0476,P/e=8, andW/H=2.33, respectively. To understand the characteristics of heat transfer enhancements, the friction factors are also measured. The data indicates that the triangular type rib has a substantially higher heat transfer performance than any other ones.     

基于同步挤压小波和脉冲压缩的钢轨踏面裂纹电磁超声表面波检测方法研究

钢轨踏面上的疲劳裂纹严重影响着列车行车安全。 针对如何快速有效地检测出踏面斜裂纹的问题,本文提出了一种快 速检测钢轨踏面裂纹的方法。 首先分别建立了含高斯白噪声、正弦信号加高斯白噪声干扰的数学模型,分析了编码脉冲压缩、 同步挤压小波变换和先同步挤压小波变换后脉冲压缩共 3 种信号处理方法的噪音抑制效果。 其次,为了验证上述方法对噪音 的抑制能力,使用激励频率为 1 MHz 的表面波电磁超声换能器对含裂纹的钢轨踏面进行检测。 最后,以检测得到裂纹的超声 回波为研究对象,比较了希尔伯特黄方法处理单一频率脉冲对应的超声回波信号和先同步挤压后脉冲压缩方法对应的降噪能 力和超声成像效果。 实验结果表明:本文所提方法可以获得钢轨踏面裂纹的位置信息及其数量。 希尔伯特黄变换在处理无同 步平均的原始超声回波时,由于回波信噪比低,经验模态分解(EMD)失效。 在以巴克码为激励信号且无同步平均采集的条件 下,先进行同步挤压小波变换后脉冲压缩处理,得到的超声回波信噪比相较于只采用相位编码脉冲压缩提高了 6. 82 dB,相比于 只做同步挤压小波变换提高了 11. 02 dB,能明显提升检测速度和 B 扫图像分辨率。     

Investigation of the relationship between the white layer thickness and 3D surface texture parameters in the die sinking EDM process

It is a well known fact that the EDM process results in the formation of a hard, brittle recast layer on the component's surface. Several investigations have been carried out in order to assess the nature of the recast layer in terms of its phase structure, the microhardness, presence and the density of cracks, and other surface features. Some researchers [Barash, Delpretti] have reported mathematical relationships between the thickness of the white layer and 2D amplitude surface roughness parameters (such as R_a and R_t). But so far no investigation has been reported which correlates the thickness of the white layer with 3D surface roughness parameters, especially those related to spatial parameters. This paper presents an experimental investigation of the effect of the EDM process factors (current and pulse on-time) on the thickness of the white layer. Empirical equations relating the thickness of the white layer with 3D surface texture amplitude, spatial and volume parameters are presented and their physical basis is discussed. The results of this study show that a better correlation can be obtained between the average thickness of the white layer (AWLT) and the spatial parameter, S_ds as compared to other 3D surface texture parameters. This is believed to be mainly due to the similar effect of the current and pulse on-time on both AWLT and S_ds. The possible effect of surface tension between the solid and liquid phases on the thickness of the white layer during erosion is also discussed.     

Fundamentals of electromagnetic-acoustic-transformation thickness measurements with attachable probes: III. Inverse and double electromagnetic-acoustic transformation in a normal polarizing field

Calculations are performed for projections of the induction of the secondary field in air, which appears after an inverse and double electromagnetic-acoustic transformation in a solid ferromagnetic conducting body via the induction and magnetic transformation mechanisms, for arbitrary values of this body’s macroscopic parameters and the radiation frequency lying in a quasi-stationary range. The experimental data obtained in measurements of the topography of the secondary field are compared to the calculation results, and their satisfactory agreement is shown. The presented calculated and experimental topography data show that, in the near radiation-field zone, shear waves propagate in the directions close to the normal to the object’s boundary and measured from the radiating elements. It is shown that, when the transmitter and receiver are spatially separated, the emf induced in the receiver is due to the peripheral part of the secondary field with a lower amplitude and a weaker dependence on the changes in the thicknesses of samples.     

Fundamentals of electromagnetic-acoustic-transformation thickness measurements with attachable probes: IV. Inverse and double electromagnetic-acoustic transformation in a tangential polarizing field

Calculations are performed for projections of the induction of the secondary field in air, which arises after inverse and double electromagnetic-acoustic transformations in a solid ferromagnetic conducting body via the induction and magnetic transformation mechanisms, for arbitrary values of this body’s macroscopic parameters and the radiation frequency lying in a quasi-stationary range. The distributions of the emf induced in the measuring coil by the normal projection of the secondary field upon the first and second sound reflections are presented. It is shown that these distributions are identical to the distributions observed in a normal polarizing field, and this identity is explained. Additional experimental and theoretical data are presented in favor of the use of the magnetostriction transformation mechanism during the construction of a thickness gage with spatially separated emitting and measuring coils that is placed on ferromagnetic articles.     

Determining the distance between antenna arrays and the speed of longitudinal waves in a test object when reconstructing the profile image of the bottom of a weld in ultrasonic testing

A method is considered for determining the distance between two wedges and the speed of longitudinal ultrasonic waves in a test object when measuring the profile of the surface of pipelines under the bead of a weld. The method makes it possible to reduce the error in determining the profile of the bottom of a pipeline in the course of testing by refining the distance between the wedges and the speed of sound using head-wave pulses. Results of numerical experiments are provided for the processing of echo signals calculated by the finite-difference method in the time domain. The efficiency of the proposed technique is demonstrated with some model experiments.     

高速车削工件表面形貌及其粗糙度特征的试验研究

借助于扫描电镜照片、已加工样品表面形貌轮廓描绘和试验数据处理等手段,对高速车削工件已加工表面形貌与其表面粗糙度之间的关系以及它们的形成特征进行了分析研究.研究结果表明,切削速度和被切削材料的硬度是决定高速车削过程中被切削层材料变形和已加工表面形貌及其表面粗糙度形成的主要因素,随着被切削材料硬度和切削速度的提高,工件已加工表面质量在一定程度上得到了改善.在已加工表面上出现了犁垄和高速加工所特有的熔融金属涂抹现象,由此决定着已加工表面粗糙度值的变化.     

Uncertainty evaluation and reduction in three-probe roundness profile measurement based on the system transfer function

The three-probe method for separating the spindle rotation error and the specimen form error is extensively described in the literature. An attractive feature is its application in in-process measurement. However, the resulting uncertainty is studied far less extensively. In this paper, an evaluation and propagation method for the uncertainty, as well as for an uncertainty reduction, is given based on the system transfer function (S-function). First, utilizing the Laplace transform, the measurement system model is developed and expressed by an S-function. Second, the propagation laws of input uncertainties are analytically deduced by computing the partial derivatives of the S-function of roundness. Then, the laws are numerically validated by Monte Carlo simulations. The uncertainty propagation laws show that the uncertainties propagate with varying amplification over the harmonic domain, and moreover, they enable the quantification of both the harmonic and the total uncertainty of roundness. Taking the roundness uncertainty as a decisive parameter, three approaches are proposed for uncertainty reduction: (1) the hybrid 3-PM, where two roundness estimates are combined by taking individual harmonic estimate with the lowest uncertainty, (2) the fusion 3-PM, where the weighted average is taken over the harmonic domain, and (3) the angle optimization, which minimizes the total roundness uncertainty by properly arranging the sensor angles. The angle optimization is applied to the conventional 3-PM, as well as to the hybrid and the fusion 3-PMs. The genetic algorithm is adopted to speed up the optimization process. Finally, practical roundness measurements are performed.     

机器视觉中基于彩色伪随机编码特征点匹配的研究

为研究基于单幅二维图像不标定欧氏重构三维场景的理论,介绍一种采用伪随机编码结构光照明主动视觉技术.利用伪随机序列的窗口特性,使被编码结构光照明的场景表面每一个特征点都具有唯一的代码,可以唯一地被辨识.实验表明,该编码结构光主动视觉系统,可以比较容易地解决被动视觉系统中难以解决的特征点匹配问题,实验效果良好.     

Investigation on the effects of ultrasonic vibration on material removal rate and surface roughness in wire electrical discharge turning

An investigation has been made to combine ultrasonic vibration and wire electrical discharge turning. Design of a submerged, precise, flexible, and corrosion-resistant rotary spindle is introduced. The spindle was mounted on a five-axis wire electrical discharge machine to rotate the workpiece in order to generate free-form cylindrical geometries. An auxiliary device that produces ultrasonic vibration was installed between the two wire guides. The ultrasonic system consists of an ultrasonic generator, a transducer, and a wire holder. When the wire is being driven, the transducer together with the wire holder vibrates under the resonance condition. Material removal rate (MRR) indicates efficiency and cost-effectiveness of the process. Experimental results show that wire vibration induced by ultrasonic action has a significant effect on material removal rate. This study has been conducted to evaluate the influence of four design factors: power, pulse off time, spindle rotational speed, and ultrasonic vibration over material removal rate. This has been done by means of design of experiments technique. Analysis of variance was used to determine significant effective factors and also to obtain an equation based on data regression. Experimental results indicate that ultrasonic vibration and power are the most significant influencing parameters on MRR. Rotational speed and pulse off time are the next in ranking. In order to study surface roughness, R _a is measured in different machining parameters.     

Crack localisation and sizing in a beam based on the free and forced response measurements

In the present paper, a method of the crack localisation and sizing in a beam from the free and forced response measurements is developed. The method gives crack flexibility coefficients as a by-product. Timoshenko beam theory is used in the beam modelling for transverse vibrations. The finite element method (FEM) is used for the cracked beam free and forced vibration analysis. An open transverse surface crack is considered for the crack model. The effect of the proportionate damping has been included. A harmonic imbalance force of known amplitude and frequency is used to dynamically excite the beam with the help of an independent exiting unit. The crack localisation and sizing algorithm is iterative in nature. The iteration starts with an initial guess for the crack depth ratio and iteratively estimates the crack location and the crack depth until getting the desired convergence for both the crack location and the crack depth. For estimation of bounded flexibility coefficients, a regularisation technique has been adopted. The method has been illustrated through numerical examples. The prediction of the crack location and size are in good agreement even in the presence of the measurement error and noise.     

Al2O3工程陶瓷超声振动钻磨表面质量的试验研究

通过超声振动钻磨与普通钻磨的对比试验,研究了缓进给超声振动钻磨对工件表面微观形貌和表面粗糙度的影响。结果表明,超声振动钻磨可明显地提高A l2O3工程陶瓷表面的质量,是陶瓷精密加工的一种新方法。     

Studies of the fracture process in composite structural elements based on strain measurements and the acoustic-emission technique

The results of cyclic tests of structural elements (SEs) with a stringer, which are made of the composite material (CM) Organit-10T and are parts of an aileron from an ë-80Éè aircraft, are considered. As SEs are broken, information is obtained simultaneously from acoustic-emission (AE) and tensometric equipment and measurements of the fatigue cracks opening are carried out. An insignificant increase (by 0.25 µm) of the crack opening generates a considerable flow of AE signals. These signals are processed using cluster analysis, which makes it possible to separate the signals emitted by a propagating fatigue crack in the stringer region from the signals arriving from the region of the fracturing gripping jaw.Translated from Defektoskopiya, Vol. 40, No. 9, 2004, pp. 11–18. Original Russian Text Copyright © 2004 by Sereznov, Stepanova, Lebedev, Chaplygin, Katarushkin, Kozhemyakin.     

基于曲面重构及刀具轨迹生成系统的实验研究

论述了重构NURBS曲面的方法及曲面插值的详细算法，介绍了一种适宜生成NURBS反求曲面的刀具轨迹方法，并对生成轨迹的优化问题进行了探讨。实验开发了一个基于Microsoft Windows系统的小型反求工程CAD／CAM软件。     

Theoretical foundations of ultrasonic nondestructive testing of multilayer articles manufactured from composites with rubbery coatings: II. Scattering of elastic waves at flaws involving poorly glued joints between plastic layers and between a plastic layer and a rubbery coating

The second part of this study is devoted to the solution of the following problems: (i) excitation of plate modes with a lumped force applied to the plate’s surface, (ii) scattering of a bending wave at a small crack parallel to the plate’s surface, and (iii) scattering at a flaw involving a poorly glued joint between a rubbery coating and a plastic layer. The final formulas and numerical dependences for calculating the parameters of a crack or a cleavage are presented. A mathematical model that describes the scattering of waves by flaws in a multilayer article made from a plastic composite material has been developed.     

Numerical and experimental studies on the mixing characteristics of two jets with inclined angles in a rectangular chamber

Mixing characteristics in a rectangular chamber are investigated using experimental and numerical methods. A mixing chamber with an axial inlet (representing fuel inlet) and a side inlet (representing air inlet) is designed. Two jets with different momentum ratios through the two inlets are mixed in the chamber. Computational fluid dynamic simulation is validated by experimental data of particle image velocimetry that measures flow velocity distribution. The momentum ratios of the two jets and the height of the axial inlet significantly influence the penetration depth of axial jet into the mixing chamber and the pressure drops at recirculation zones.