Showing papers by "Xi'an Jiaotong University published in 1993"
TL;DR: The technique retains all the advantages of optical speckle photography and provides an extended range of measurement and was applied successfully to the study of crack-tip deformation fields.
Abstract: An alternative approach to fully automatic speckle-displacement measurement is described. Two speckle patterns of a specimen, one before and one after deformation, are captured by a CCD camera and registered by a frame grabber. Two series of small subimages are obtained by segmenting the two speckle patterns. The corresponding subimage pairs extracted from both series are analyzed pointwise. The interrogation of each subimage pair involves a two-step fast-Fourier transform. While the first-step fast-Fourier transform achieves a complex spectrum characterized by the local displacement information, the second-step one generates a signal peak in the second spectral domain that resolves the local displacement vector. A rough estimate of the displacement vector is achieved by detecting the maximum pixel of the discrete spectrum. A more accurate determination is attained by a subpixel-maximum determination through a biparabolic fitting near the signal peak. The u- and v-displacement fields are deduced by analyzing all subimage pairs. A large rigid-body displacement can be overcome by introducing an artificial rigid shift of the two speckle patterns toward each other before the numerical process. The technique retains all the advantages of optical speckle photography and provides an extended range of measurement. Dynamic incremental deformations can be inspected by registering more speckle patterns at many consecutive deformation stages by using a high-speed CCD camera. The system was applied successfully to the study of crack-tip deformation fields.
306 citations
TL;DR: In this article, the structure of singular stresses and strain fields at the border of three dimensional cracks in a tension field is investigated for elastoplastic materials treated by a deformation theory.
208 citations
TL;DR: In this paper, the authors studied the distribution of crack border stresses and strains in strain hardening materials under a triaxial stress constraint Tzϵ[0,0.5] and proved that single parameter dominance is lost and a two parameter system including Tz should be adopted to describe the 3D crack border field.
153 citations
TL;DR: In this article, phase structures and dielectric properties of the compounds with formulas BixZn2/3Nb4/3O4+3x/2 (group M), BixN8/3-x Nb 4/5O6+3O7 (group W) have been investigated, and the results indicate that a cubic pyrochlore structure is the predominant phase of these compounds.
Abstract: Phase structures and dielectric properties of the compounds with formulas BixZn2/3Nb4/3O4+3x/2 (group M), BixZn8/3-x Nb4/3O6+x/2 (group V), and BixZn2-2x/3Nb2-x/3O7 (group W) have been investigated. Initial results indicate that a cubic pyrochlore structure is the predominant phase of these compound. Most of the measured ceramic specimens exhibit dielectric properties suitable as temperatures-stable and temperature-compensating dielectrics in the capacitor industry. The values of the dielectric constant K are 80-160, while those of the temperature coefficient are–500 to + 160 ppm/°C. The composition limits of the single pyrochlore phase are determined mainly by Bi2O3 additives.
130 citations
TL;DR: In this article, the melting of n- octadecane that is discretely heated at a constant rate from one side of an enclosure with inside dimensions of 100 mm × 60 mm × 50 mm was investigated experimentally.
70 citations
01 Jan 1993
TL;DR: The finite difference method (FDM) is an approximate method for solving partial differential equations that has been used to solve a wide range of problems, including linear and non-linear, time independent and dependent problems.
Abstract: The finite difference method (FDM) is an approximate method for solving partial differential equations. It has been used to solve a wide range of problems. These include linear and non-linear, time independent and dependent problems. This method can be applied to problems with different boundary shapes, different kinds of boundary conditions, and for a region containing a number of different materials. Even though the method was known by such workers as Gauss and Boltzmann, it was not widely used to solve engineering problems until the 1940s. The mathematical basis of the method was already known to Richardson in 1910 [1] and many mathematical books such as references [2 and 3] were published which discussed the finite difference method. Specific reference concerning the treatment of electric and magnetic field problems is made in [4]. The application of FDM is not difficult as it involves only simple arithmetic in the derivation of the discretization equations and in writing the corresponding programs. During 1950–1970 FDM was the most important numerical method used to solve practical problems ([5–7]). With the development of high speed computers having large scale storage capability many numerical solution techniques appeared for solving partial differential equations. However, due to the ease of application of the finite difference method it is still a valuable means of solving these problems ([8–11]).
57 citations
TL;DR: In this paper, an exact elastic-plastic solution is obtained for the residual stress and strain field in a finite circular sheet having a cold-worked or interference fitted hole on the basis of J2 deformation theory together with a modified Ramberg-Osgood law.
57 citations
TL;DR: In this paper, heat/mass transfer and pressure drop characteristics for arrays of nonuniform plate length, aligned at an angle of 25 degrees to the flow direction, are investigated experimentally via a naphthalene sublimation technique.
Abstract: In this paper, heat/mass transfer and pressure drop characteristics for arrays of nonuniform plate length, aligned at an angle of 25 deg to the flow direction, are investigated experimentally via a naphthalene sublimation technique. The measurements of cyclic average Sherwood numbers and friction factors in the fully developed regime are conducted for nine geometric configurations. The following parameter ranges are studied: length ratio of successive plates; ratio of the transverse pitch to the longitudinal pitch, and Reynolds number based on shortplate length. Comparisons with the results for arrays with uniform plate length are conducted
33 citations
TL;DR: In this paper, a formulation for the dyadic Green's function of cylindrical multilayered chiral media is presented at first using the methods of eigenfunction expansion and scattering superposition.
Abstract: In this paper, a formulation for the dyadic Green's function of cylindrical multilayered chiral media is presented at first using the methods of eigenfunction expansion and scattering superposition. The specific expressions of the dyadic Green's function are also found in terms of normalized cylindrical vector wave functions, when the electric current sources are placed both inside and outside of a chiral circular cylinder and a cylindrical chirodome. The radiation characteristics of a point dipole antenna on the axis of chiral circular cylinder and cylindrical chirodome are analysed. For both cases, the results show that by changing the size of chiral circular cylinder, the thickness of cylindrical chirodome and the parameters of chiral media, purely circular and linear polarization can be obtained in the far field. Also, the expressions of dyadic Green's function given in this paper can be directly used to analyse the radiation characteristics of cylindrical chirostrip antennas.
32 citations
TL;DR: In this article, a disc cutter with a concave end instead of traditional ball-ended or drum-shaped tools is used for machining sculptured surfaces, and a series of strict proofs of the theoretical foundation of this method is presented in this first part of the paper, whilst some essential algorithms are to be discussed in the second part.
32 citations
TL;DR: This paper describes several fitting algorithms intended to facilitate extraction of parameters describing the recorded impulses, including peak value, front time, and time to half-value, from recorded data.
Abstract: Standard analysis of high voltage impulses comprises determination of parameters describing the recorded impulses. These include peak value, front time, and time to half-value. This paper describes several fitting algorithms intended to facilitate extraction of these parameters from recorded data. These algorithms were used to fit bi-exponential models to smooth lightning and switching impulses, to lightning impulses having oscillatory fronts or peaks where the evaluation of the waveform parameters is based on the construction of a smooth curve, and to tail-chopped lightning impulses. The overall effectiveness of these algorithms and their influence on parameter estimates are presented and discussed. >
TL;DR: A numerical model of a double-inlet pulse tube refrigerator (DPT) has been developed and the equations of continuity, momentum and energy (for both gas and solid) are solved numerically as discussed by the authors.
TL;DR: In this article, the response and long-term stability of the humidity sensor are investigated. And the resonant frequency of the coated quartz resonantors decreases with increasing relative humidity.
Abstract: Porous silica coating on AT-cut quartz crystals are derived from the sol—gel process. Hydrochloric acid catalyst it used to accelerate hydrolysis and polymerization of a silica solution. Experimental results show that the non-crystalline silica material has a lot of nanonometer pores. The resonant frequency of the coated quartz resonantors decreases with increasing relative humidity. The maximum frequency shift of 3.72 kHz due to humidity is achieved. The response and long-term stability of the humidity sensor are investigated.
TL;DR: In this article, a multivariable linear model is developed to analyse the system stability in the frequency domain by means of multivariability control system theory, which includes feedback on the two-phase pressure drop and external loop pressure drop.
28 Oct 1993
TL;DR: The wavelet transform(WT) is used for QW detection with some results in QRS detection with the WT, andvantages have been found in its use to locate signal singularities.
Abstract: In this paper, the wavelet transform is used for QW detection. Some detection strategies are applied to decrease the fake detection succes~fully. The correct QRS detection rate reaches to 99. 8% in the experiment with the bflT/BLH arrhythmia database. INTRODUCTION ECG signal has been extensively studied because of its great clinical significance in diagnosing heart diseases. QRS detection is the most important problem in ECG signal analysis. A number of QRS detectors have been designed, but none of them is perfect. The wavelet transform(WT) is a recently introduced thefrequency Id i za t ion tcdmique which has already found applications in a variety of fields. In essence, the WT in different scale represents the information of signal in different frequency domain. Advantages have been found in its use to locate signal singularities. This paper gives some results in QRS detection with the WT. METHODS I . Wavelet Transform The W T of a signal f (x) is defined as where s is scale; Jl(x) is named a wavelet, Js (x> =~41(:)is the dilation of $(XI by scale factor In order to calculate the WT by computer, the WT should be discretization WT , so lead to a dyadic wavelet transform as Wif (x) = f * @(x), where s= 2’. The dyadic WT can be calculated by Mallat algorithmC31, as described as Spff(n) = x h , S p l f ( n 2J ’ lk ) 1
TL;DR: The concept of identical problemsn of natural convection in enclosures is introduced in this article. But the concept is restricted to problems with identical geometric configurations and identical dimensionless governing equations and related boundary conditions.
Abstract: In this paper, a concept of “identical problemsn of natural convection in enclosures is presented. A pair of problems of natural convection in enclosures is said to be identical if they look different in appearance but with appropriate selection of coordinates and appropriate definition of dimensionless variables for each problem; they will have identical geometric configurations and identical dimensionless governing equations and related boundary conditions. The identical characteristics of a pair of problems of natural convection in enclosures with an internal isolated island are demonstrated via dimensionless mathematical formulation and flow visualization results. Numerical computations are performed and the predicted streamlines agree with the flowvisualization results. A number of other possible pairs of identical problems are also presented. Applications of the identical character are provided and assumptions under which the identical problems may exist are discussed.
TL;DR: In this paper, the heat transfer and pressure drop characteristics in the developing region for arrays of plates of nonuniform length positioned obliquely to the direction of airflow in a rectangular duct have been investigated experimentally via the naphthalene sublimation technique.
27 Sep 1993
TL;DR: In this article, the effects of additives on the wettability between liquid silver metal and the contact surface, the distribution and the thermal stability of additives are critical in the determination of erosion characteristics and the morphological features of the contact surfaces.
Abstract: The switching performances of several improved silver tin-oxide materials with several kinds of additives, including WO/sub 3/,Bi/sub 2/O/sub 3/,In/sub 2/O/sub 3/, were conducted in an accelerated testing machine. Based on the experimental results and the observations of the contacts surface microstructure, the effects of additives on the silver tin-oxide contacts erosion behavior are studied. It is indicated that the effects of additives on the wettability between liquid silver metal and the contact surface, the distribution and the thermal stability of additives are critical in the determination of erosion characteristics and the morphological features of the contact surface. The erosion behaviors of silver-tin oxide materials with different additives are compared, and the doping effect on surface morphology is presented.
27 Sep 1993
TL;DR: In this paper, the effects of phase change, viscosity and surface tension on erosion losses of AgMeO contact materials are analyzed during arcing in the current range up to 1000 A rms.
Abstract: Based on switching experiments with cylindrical contacts of different diameters by high speed camera observations and SEM micrographs, the effects of phase change, viscosity and surface tension on erosion losses of AgMeO contact materials are analysed during arcing in the current range up to 1000 A rms. The erosion model of AgMeO is used for expressing the heat-force function during arc-electrode interaction and the liquid-solid, liquid-gas boundary corresponding to the upper and lower erosion limit respectively for the reason that erosion is composed of two modes: evaporation and minute molten droplets losses. Furthermore, supposing that the arc column is a hypothetical "point heat source" in middle of the gap, a new erosion mathematical model is established by the finite differential method and the results coincide well with those of experiments.
TL;DR: In this article, a double-inlet reversible pulse tube refrigerator (DRPTR) is proposed and two important parameters which affect the performance of the DRPTR are discussed.
TL;DR: In this paper, the electromagnetic properties of radially stratified spherical chirolenses were examined using the dyadic Green's function, and a general formulation was presented for determining the focal points of in-homogeneous spherical Chirolenses.
Abstract: The electromagnetic properties of radially stratified spherical chirolenses are examined using the dyadic Green's function, and a general formulation is presented for determining the focal points of in-homogeneous spherical chirolenses. Also, the focal points of Luneberg chirolenses are calculated. It is shown that chirality admittance has strong influence on the location of focal points. © 1993 John Wiley & Sons, Inc.
TL;DR: In this paper, stress intensity factors of corner cracks emanating from fastener holes in finite plates subjected to biaxial load and three types of pin load were obtained on the basis of SIFs for through cracks by introducing of modifying factors for corner crack geometries, which are evaluated by empirical fit for some carefully selected numerical results.
TL;DR: In this article, the stress condition and wear failure mechanisms of a flour milling roller have been investigated, and the wear mechanism of the roller consists of plastic fatigue and multi-impact fatigue wear in the matrix and brittle spalling in the carbides.
TL;DR: In this paper, lead titanate fine powders derived from the metal alkoxide hydrolysis precipitate precursor treated under hydrothermal conditions have been obtained and three kinds of lead titanates with different structures have been formed and fine particles with different morphologies have been successfully obtained.
Abstract: This paper reports lead titanate fine powders derived from the metal alkoxide hydrolysis precipitate precursor treated under hydrothermal conditions. The influences of pH value, Pb/Ti mole ratio, reaction temperature and time on the hydrothermal synthesis of the phase transformation and particle morphology have been investigated. As a result, three kinds of lead titanates with different structures have been formed and fine particles with different morphologies have been successfully obtained.
TL;DR: In this article, the authors show that when water is supplied to a dry specimen surface, small scale topographic irregularities (up to about 0.2 μm) are smoothed and characteristic changes are observed in the tunneling barrier signals of the investigated materials.
TL;DR: In this article, the authors studied the Laminar flow and heat/mass transfer of a slot jet impinging in a rectangular cavity, and the discretization equations were formed by the finite-volume approach.
TL;DR: The authors points out that Housner's equation of bending vibration of a pipe line containing flowing fluid is approximate and makes correction to it and gives an exact form of the vibration equation.
Abstract: This paper points out that Housner's equation of bending vibration of a pipe line containing flowing fluid is approximate and makes correction to it. An exact form of the vibration equation is given.
01 Jan 1993
TL;DR: The main idea behind FDM is the approximation of the derivative operations ∂u/∂x and ∂ 2 u/ ∂x 2 by the difference quotients Δu(x)/Δx and Δ 2 u(x/Δ) 2, which reduces the partial differential equation to a set of algebraic equations as mentioned in this paper.
Abstract: The main idea behind FDM is the approximation of the derivative operations ∂u/∂x and ∂ 2 u/∂x 2 by the difference quotients Δu(x)/Δx and Δ 2 u(x)/Δx 2 , which reduces the partial differential equation to a set of algebraic equations. The application of FDM has two serious limitations. First, the regular steps of h x , h y , h z which construct an array of grid nodes in the x, y, z directions are not suitable for a field with a rapidly changing gradient or for problems having a curved boundary. Second, different formulae must be derived for specific interfaces between different media and for the various shapes of boundaries.
TL;DR: In this paper, the singularity at a crack tip for the homogeneous brittle crack problem is not convincing from a physical point of view, and it is assumed that the cohesive zone appears ahead of the crack tip and the normal cohesive stress acting on the surface of the zone makes the stress intensity factor at the zone tip equal zero.
Abstract: From a physical consideration, the mathematical singularity at a crack tip for the homogeneous brittle crack problem is not convincing. To avoid this drawback Dugdale assumed that the cohesive zone appears ahead of the crack tip and the normal cohesive stress acting on the surface of the zone makes the stress intensity factor at the zone tip equal zero. As a consequence, the singularity at the zone tip disappears and opening-displacement at the crack tip (CTOD) exists.