Boundary element analysis of moiré fields in anisotropic materials

A procedure for analyzing moiré fringe patterns using boundary elements is presented. The kernels of the boundary integrals are based on anisotropic elastic Green's functions developed for bimaterial problems. The interfacial boundary conditions are incorporated in the Green's functions so the interface does not require discretization. The bimaterial kernels are also appropriate for homogeneous problems as well as degenerate isotropic problems. The moiré fringe data provide full-field displacement information and are analyzed in a least-squares sense. The numerical procedure is shown to be a logical extension of the local collocation method developed for linear elastic fracture mechanics. An example is given to investigate convergence of the method, predictions of stress, and to investigate factors influencing the analysis. It is shown that moiré fields associated with both displacement components are needed for an accurate analysis.     

Estimation of the surface normal velocity of high frequency ultrasound transducers

This paper is concerned with the characterization of the true locally resolved surface normal velocity of an assumed piston-type ultrasonic transducer. Instead of involving a very complicated direct pointwise measurement of the velocity distribution, an inverse problem is solved which yields a spatially discretized weighting vector for the surface normal velocity of the transducer. The study deals with a spherically focused high frequency transducer, which is driven in pulse-echo mode. As a means of posing the inverse problem, the active transducer surface is divided into annuli of equal surface so that for each annulus the spatial impulse response can be calculated. An acrylic glass plate acts as a simple structured target. The resulting ill-posed nonlinear inverse problem is solved with an iterative regularized Gauss-Newton algorithm. The solution of the inverse problem yields an estimated weight for the surface normal velocity for each annulus. Experimental results for a thin copper wire target are compared to simulation results for both uniform and estimated surface normal velocities.     

编码发射技术在医学高频超声成像中的研究进展

高频超声成像以其高分辨和实时性好等优势成为近年来医学超声成像领域研究的热点。但由于超声的衰减随频率增加呈指数级升高,导致高频超声信号幅值小,图像信噪比低。为了增强高频超声成像的信噪比,近年来编码发射（又称编码激励）技术得到了越来越多的研究和应用。文章对近几年国内外编码发射技术在医学高频超声成像方面的应用和研究进展进行了综述,重点分析了Chirp码、巴克（Barker）码和格雷（Golay）码3种主要编码发射技术在高频超声成像方面应用的优缺点,并综合对比了各种编码发射技术在高频成像方面的应用前景。     

A single exposure reflection moiré interferometric technique for complete curvature analysis of bent plates

Most known moiré methods need to be repeated three times for getting curvature information in three different in plane directions, for the complete analysis. To overcome this difficulty, a new single exposure moiré interferometric technique is proposed that maps completely partial curvature contours in three different directions of laterally loaded specularly reflecting plate models. Converging HeNe laser light is diffracted by a lens plane cross grating. The 00, + 10 and the +01 diffraction orders are permitted through the Fourier transform (FT) plane and collimated to illuminate the plate model. The reflected light from the loaded model records the model with the inherent deformed interferometric cross grating superimposed on it. A posteriori Fourier filtering of the developed recording (moirégram) gives partial curvature contours pertaining to three different in plane directions from which the principal curvatures and the principal directions are obtained. Also, this technique, being a single exposure technique, has the potential for complete bending analysis of plates subjected to lateral impact loading and destructive loading applications, where the repeatability of the event may not be possible.     

The measurement of deformation of a bridge by moiré photography and photogrammetry

Optical techniques offer advantages over mechanical methods for displacement measurement. A comparative study has been made between photogrammetry and moiré photography during a destructive test applied to a bridge. The first provided accurate values for point displacements whereas the second revealed the whole field movements and indicated the region of eventual failure.     

Commercial applications of overlay coating techniques

As part of a panel discussion this paper was presented to review the wide variety of coating technologies available and the need for consideration of the number of materials, process and product variables in determining the applicability of a technology. Of particular concern is the lack of utilization of a “coating technologist” in the early stages of decision making. This often leads to expensive mistakes and misapplications.     

Application of moiré technique in the stress analysis of cutting tools

Knowledge of the stress field in cutting tools is necessary for their strength evaluation. However, the experimental analysis of stresses in cutting tools during machining poses a number of problems in view of the steep stress gradient present. Photo-elasticity and the 'built-up tool' methods are the common techniques used for this purpose. In the present paper results on the stresses in cutting tools obtained during actual machining through the successful application of the transmitted moiré technique, are presented. In these experiments transparent epoxy tools carrying moiré gratings were used to machine commercial lead alloy at low speeds. The tool rake angle was varied. The effectiveness of moiré method, basically a displacement analysis technique, in providing useful data on tool stresses comparable with the other direct stress analysis techniques such as photo-elasticity is also discussed in the paper.     

Measurement of strain concentration factor of composites plate using moiré interferometry

In this paper, using a 1200 lines/mm replicated grating, the moiré interferometry method was applied to study the strain concentration factor of a carbon fibre composites plate with a central hole. The rules of strain concentration factors were determined under different loads.     

Effects of temperature and normal load on tribological behavior of nickel-based high temperature self-lubricating wear-resistant composite coating

NiCr/Cr₃C₂–WS₂–CaF₂ mixed powders were designed and aimed to fabricate high temperature self-lubricating wear-resistant composite coating by laser cladding. The friction and wear properties of the coating were investigated under different temperatures and loads against Si₃N₄ ceramic ball. Results show that friction coefficient decreases with the increasing temperature while the wear rate firstly decreases and then increases with the increasing temperature. Both the friction coefficient and wear rate firstly decreases and then slightly increases with the increasing normal load. The coating exhibits relatively excellent tribological behavior under moderate temperature and moderate normal load.     

Ballistic nano-devices for high frequency applications

In this paper, we present a study on three-terminal ballistic junction and their applications to rectifiers and MUX/DEMUX. Rectifying effect is observed up to 94 GHz at room temperature. Although THz frequency performance has been demonstrated by Monte Carlo simulation, the high impedance of the nano-device combined with the parasitic capacitances is a limiting factor.     

D.C. glow discharge techniques for surface treatment and coating

Beam-generating d.c. glow discharges operating in a soft vacuum (about 10^?1 Torr) were investigated as means for depositing coatings by evaporation or by sputtering. A hot gas technique was developed which, in addition to avoiding homogeneous nucleation, permitted very clean conditions to be achieved in a simple vacuum system. The preliminary ion bombardment cleaning of substrates remained effective for a long time under these conditions. A wide variety of metals, alloys and ceramics were experimentally deposited as thick, dense and adherent coatings by one of the two methods. By sputtering we were able to deposit refractory alloy and compound coatings that could not be satisfactorily deposited by evaporation.     

Curvature contours of flexed plates by a multiple illumination moiré shearing interferometer

A new moiré method is proposed to map partial slope, partial curvature and twist curvature contours of laterally loaded specularly reflecting plate models. Converging HeNe laser light is diffracted by a lens plane cross grating, different combinations of orders are selectively permitted through the Fourier transform plane and collimated to illuminate the plate model. This technique eliminates the difficulties involved in Fourier filtering in the imaging optics, thereby extending the reflection moiré' interferomelry to general plate structures and loading. The slope contours are obtained still by double exposure.     

涂料用高浓度SiO2溶胶制备及改性研究

以TEOS为先体,在硫酸乙酯催化下初步水解,在碱性条件下,将水解液与钛酸四丁酯(TBOT)、甲基三乙氧基硅烷(MTES)按一定比例混合,继续缩聚反应至一定程度,得到高浓度改性SiO2溶胶,研究分析了水解、缩聚规律及pH、粒度、改性剂等因素与溶胶稳定性关系。     

高硅钢用半有机绝缘涂层的制备及其性能研究

为减少高硅钢铁芯叠片间的涡流损耗,以磷酸二氢铝、苯丙乳液、甘油及水为主要原料,制备出一种适合高硅钢用无铬环保半有机绝缘涂层.利用光电子谱仪、扫描电镜及能谱仪对高硅钢脱碳退火板的氧化薄膜、绝缘涂层的微观结构形貌及部分缺陷进行分析,并研究了该涂层的涂覆量对其附着性、硬度及绝缘性能的影响.研究结果表明:普通无取向硅钢磷酸盐环保半有机绝缘涂层同样适用于高硅钢;绝缘涂层的均匀性取决于高硅钢片表面的平整度、涂辊表面质量以及对涂覆速度的平稳控制;高硅钢的表面粗糙度及氧化膜厚度对绝缘涂层的附着性有着重要影响;本试验制备的半有机涂层每面涂覆量控制在0.8~1.2 g/m2,具有良好的附着性及绝缘性能,层间电阻在5Ω·cm2/片以上.     

A study on the production of 950°C moiré gratings in metal materials

In this paper, a new method for producing high temperature gratings is put forward. With two deposited metal layers on the specimen, the oxidation resistant ability of this grating was improved, and its applications were enlarged, to cover almost all metals. The procedure for producing a grating and the controlling factors of grating quality are discussed in detail.     

Recent advances in frequency domain techniques for electromagneticscattering problems

Some recent applications of numerical techniques for the analysis of electromagnetic scattering problems involving several general classes of geometries are reviewed. The solution procedures are all formulated directly in the frequency domain, using the method of moments or the finite-element method, in terms of an integral equation and/or a partial differential equation. Geometrical configurations discussed include three-dimensional conducting scatterers and two- and three-dimensional homogeneous and inhomogeneous dielectric scatterers     

Soft PVD Coatings — a new coating family for high performance cutting tools

The joint effort of a cutting tool manufacturer and a coating specialist led to the development of a soft solid lubricant based cutting tool coating (Patents pending!). It is applied by an advanced sputtering technique as a very thin uniform coating with a good adherence to the tools. It has a low coefficient of friction and a low affinity to alloy materials like aluminum, titanium and precious metals. These factors and others allow the machining at high spindle speed and feed rates with an excellent workpiece surface finish. Values can be maintained which are far superior to even those permitted for cemented carbide tools. In some cases, productivity and tool life can be increased by a factor of up to 20.     

Two-stage high frequency pulse tube cooler for refrigeration at 25 K

A two-stage Stirling-type U-shape pulse tube cryocooler driven by a 10 kW-class linear compressor was designed, built and tested. A special feature of the cold head is the absence of a heat exchanger at the cold end of the first-stage, since the intended application requires no cooling power at this intermediate temperature. Simulations where done using Sage-software to find optimum operating conditions and cold head geometry. Flow-impedance matching was required to connect the compressor designed for 60 Hz operation to the 40 Hz cold head. A cooling power of 12.9 W at 25 K with an electrical input power of 4.6 kW has been achieved up to now. The lowest temperature reached is 13.7 K.     

Colorimetric method for high frequency treated bandsaw blades

An ndt technique has been developed in which the hardness of high frequency hardened bandsaw blades can be determined using a non-destructive colorimetric method. The novel concept is based upon the linear relationship existing between the variation in coloured bands produced by thermal induction and the corresponding DPN hardness. It is suggested that this technique can be applied to all HF treated steel plates.