Simplified determinations of heat transfer data for solids, applications to quality testing of electrical insulations

Summary The first part of the paper describes a simple steady state apparatus for measuring the thermal conductivity of plates of electrical insulations, plastics, etc. The measurement is quick, requiring approximately 5 min. The apparatus also enables one to determine the thermal capacity of the sample. The second part of the paper describes the k-meter, a new device for measuring the heat transfer coefficient through the insulation on metal bars such as generator coils. The method does not require any access to the inner conductor. The suitability of the k-meter for nondestructive thermal ageing investigations of e.g. generator insulations and for quality control, is demonstrated. In this respect k-value measurements might be a valuable complement to dielectric loss measurements.An Appendix gives details of the theory and error estimates.     

A TEST OF CLOSE-RANGE PHOTOGRAMMETRY

Care was taken to generate high-contrast targets for calibration and measurements. These target coordinates were documented with an order of magnitude more accuracy than achievable using photogrammetry. The repeatability of the film measurements was also an order of magnitude more accurate than photogrammetric coordinate determinations.
The best accuracy for in-plane measurements of X or V was approximately 0.2 percent (1 part in 500) and 0.4 percent (1 part in 250) for range Z measurements.
It is not obvious how the accuracy can be easily increased using this hardware; measurements for the purpose of quality control of typical parts manufactured by machining and grinding is out of the question.
Measurements for quality control of bent sheet metal may be possible. Certainly automobile accident reconstruction scenes, general archiving, and similarly relaxed environments have applications for this accuracy.
This fine-grain film with its 35-mm format has an order of magnitude more resolution than a typical solid state CCD imager. Furthermore, it is difficult to perceive object targets which result from features of the part itself that would even approach the contrast of the special targets used here.
More accuracy is, however, obtainable from convergent cameras, redundant cameras, calibrated optics/principal points, large-film format, stereo-plotter measurements, and error minimization techniques.     

Thickness effects in birefringent coatings with radial symmetry

One method of determining the strains on the surface of a metal part is by the use of a birefringent coating. Because of the thickness of the coating, however, the observed fringe order depends not only on the surface strains but also on two other factors, namely, the curvature that the surface undergoes and the variation of strain acrose the thickness of the coating. These thickness effects have already been studied in a paper dealing with one dimensional variations in strain. In the present paper, the solution is extended to a two-dimensional deformation with radial symmetry. An experiment is described in which the surface strains produced by the impact of a bullet on a flat plate are determined from the birefringence of a surface coating taking into account the effects of strain gradients and curvature. The values of surface strain are compared with measurements made by means of a square grid inscribed on the metal surface. A procedure is suggested for determining an unknown surface strain having radial symmetry from the total birefringence of the surface coating when the change in curvature of the metal surface under load is known or can be determined separately.     

Dual-plane stereo particle image velocimetry (DSPIV) for measuring velocity gradient fields at intermediate and small scales of turbulent flows

A two-frequency dual-plane stereo particle image velocimetry (DSPIV) technique is described for highly resolved measurements of the complete nine-component velocity gradient tensor field u_i/x_j on the quasi-universal intermediate and small scales of turbulent flows. The method is based on two simultaneous, independent stereo particle image velocimetry (PIV) measurements in two differentially spaced light sheet planes, with light sheet characterization measurements demonstrating the required sheet thicknesses, separation, and two-axis parallelism that determine the measurement resolution and accuracy. The present approach uses an asymmetric forward–forward scatter configuration with two different laser frequencies in conjunction with filters to separate the scattered light onto the individual stereo camera pairs, allowing solid metal oxide particles to be used as seed particles to permit measurements in nonreacting as well as exothermic reacting turbulent flows.     

Perturbing effects of electric potential probes on MHD duct flows

Data for local velocity in liquid metal duct flows exposed to an external uniform magnetic field may be obtained from measurements of electric potential differences recorded by probes that are moved along the channel width. Experiments show an asymmetry in the distribution of the measured transverse potential gradient and its underestimation compared with the one expected from flow-rate measurements. A numerical analysis of magnetohydrodynamic flows around a probe in a rectangular duct has been performed to support the physical interpretation of potential measurements and to study the influence of the instrument itself on the readings. A calibration procedure is suggested, which allows using measurements of potential differences to get reliable data for velocities in the duct.     

Numerical and experimental study of the traveling magnetic field effect on the horizontal solidification in a rectangular cavity part 2: Acting forces ratio and solidification parameters

In recent decades, many phase change processes in metals have been optimized using traveling magnetic fields due to a better understanding of their electromagnetic impact in such applications. In this paper, numerical and experimental study of the effect of traveling magnetic field on the solidification process was evaluated. A three-dimensional numerical model based on the multi-domain method was used to analyze the process of gallium horizontal solidification under the electromagnetic impact in a laboratory-size rectangular cavity. A linear inductor creating traveling magnetic field was designed and built for appropriate measurements and validation the calculations. The analysis was focused on the influence of the ratio between the applied electromagnetic forces and natural convective forces on the solidification front location and shape and on the velocity field. Since the overall electromagnetic force impact on the melt reduced during the solidification, when the melt area was converting into a solid, a new approach to control the solidification parameters was analyzed. In this approach, the value of electromagnetic force acting on the remaining melt during the process was maintained. The main result is the development and improvement of an effective tool for the analysis of direct solidification parameters.The experimental setup included an ultrasonic Doppler velocimeter (UDV) for noninvasive measurements of the velocities in the liquid part of the metal and the liquid-solid interface position, its profile and displacement. All important characteristics of the process were measured, and the results of computations agreed well enough with experimentally obtained data.     

Data assimilation for non-linear tidal models

A data assimilation procedure to incorporate measurements into a non-linear tidal model by using Kalman-filtering techniques is developed. The Kalman filter is based on the two-dimensional shallow water equations. To account for the inaccuracies, these equations are embedded into a stochastic environment by introducing a coloured system noise process into the momentum equations. The continuity equation is assumed to be perfect. The deterministic part of the equations is discretized using an ADI method, the stochastic part using the Euler scheme. Assuming that the system noise is less spatially variable than the underlying water wave process, this stochastic part can be approximated on a coarser grid than the grid used to approximate the deterministic part. A Chandrasekhar-type filter algorithm is employed to obtain the constant-gain extended Kalman filter for weakly non-linear systems. The capabilities of the filter are illustrated by applying it to the assimilation of water level measurements into a tidal model of the North Sea.     

倾斜非均匀磁场下导电方管磁流体管流的数值模拟研究

热核聚变反应堆液态金属包层应用中的一个重要问题是液态金属在导电管中流动和强磁场相互作用产生的额外的磁流体动力学压降.这种磁流体动力学压降远远大于普通水力学压降.美国阿贡国家实验室ALEX研究小组,对非均匀磁场下导电管中液态金属磁流体动力学效应进行了实验研究,其实验结果成为液态金属包层数值验证的标准模型之一.液态金属包层在应用中会受到不同方向的磁场作用,本文以ALEX的非均匀磁场下导电方管中液态金属管流实验中的一组参数为基础,保持哈特曼数、雷诺数和壁面电导率不变,采用三维直接数值模拟的方法,研究了外加磁场与侧壁之间的倾角对导电方管内液态金属流动的速度、电流和压降分布的影响.研究结果表明:沿流向相同横截面上的速度、电流以及压力分布均随磁场的倾斜而同向旋转.倾斜磁场均匀段,横截面上的高速区位于平行磁场方向的哈特曼层和平行层交叉位置,压力梯度随磁场倾角的增大先增大后减小.倾斜磁场递减段,在三维磁流体动力学效应作用下,横截面上的高速射流位置向垂直磁场方向偏移.磁场递减段的三维磁流体动力学压降随磁场倾角的增大而增大.随磁场倾斜,截面上的射流峰值逐渐减小,二次流增强,引发层流向湍流的转捩.      

Assessment of Primary Slice Release Residual Stress Mapping in a Range of Specimen Types

This paper further explores the primary slice removal technique for planar mapping of multiple components of residual stress and describes application to specimens with a range of alloys, geometries, and stress distributions. Primary slice release (PSR) mapping is a combination of contour and slitting measurements that relies on decomposing the stress in a specimen into the stress remaining in a thin slice and the stress released when the slice is removed from a larger body. An initial contour method measurement determines a map of the out-of-plane stress on a plane of interest. Subsequently, removal of thin slices and a series of slitting measurements determines a map of one or both in-plane stress components. Four PSR biaxial mapping measurements were performed using an aluminum T-section, a stainless steel plate with a dissimilar metal slot-filled weld, a titanium plate with an electron beam slot-filled weld, and a nickel disk forging. Each PSR mapping measurement described herein has one (or more) complementary validation measurement to confirm the technique. Uncertainty estimates are included for both the PSR mapping measurements and the validation measurements. Agreement was found between the PSR mapping measurements and validation measurements showing that PSR mapping is a viable technique for measuring residual stress fields.     

SECTIONAL FINITE ELEMENT ANALYSIS OF COUPLED DEFORMATION BETWEEN ELASTOPLASTIC SHEET METAL AND VISCO-ELASTOPLASTIC BODY

The present paper is devoted to developing a new numerical simulation method for the analysis of viscous pressure forming (VPF), which is a sheet flexible-die forming (FDF) process. The pressure-carrying medium used in VPF is one kind of semisolid, flowable and viscous material and its deformation behavior can be described by the visco-elastoplastic constitutive model. A sectional finite element model for the coupled deformation analysis between the visco- elastoplastic pressure-carrying medium and the elastoplastic sheet metal is proposed. The resolution of the Updated Lagrangian (UL) formulation is based on a static explicit approach. The frictional contact between sheet metal and visco-elastoplastic pressure-carrying medium is treated by the penalty function method. Coupled deformation between sheet metal and visco-elastoplastic pressure-carrying medium with large slip is analyzed to validate the developed algorithm. Finally, the viscous pressure bulging (VPB) process of DC06 sheet metal is simulated. Good agreement between numerical simulation results and experimental measurements shows the validity of the developed algorithm.     

Condensation of zinc vapor in a supersonic carrier gas

A study of the condensation of a metal vapor in an inert carrier gas is made. Superheated zinc vapor is generated in a hot shot wind tunnel in a helium carrier gas and expanded in a converging-diverging nozzle. Static pressure measurements along the length of the nozzle are made to determine the location of the onset of condensation. A conical nominal Mach 5 (helium) nozzle is employed. The amount of supercooling before the onset of condensation is found to be approximately 430 K, measured along the isentrope over a range of initial zinc mass fractions of .35 to .70 for saturation partial pressures of zinc between 10 psia and 70 psia. The measurements are compared with results of an analysis based on the classical liquid drop model of nucleation. The computed results agree reasonably well with the measurements.     

Laser surface-contouring and spline data-smoothing for residual stress measurement

We describe non-contact scanning with a confocal laser probe to measure surface contours for application to residual stress measurement. (In the recently introduced contour method, a part is cut in two with a flat cut, and the part deforms by relaxation of the residual stresses. A cross-sectional map of residual stresses is then determined from measurement of the contours of the cut surfaces.) The contour method using laser scanning is validated by comparing measurements on a ferritic steel (BS 4360 grade 50D) weldment with neutron diffraction measurements on an identical specimen. Compared to lower resolution touch probe techniques, laser surface-contouring allows more accurate measurement of residual stresses and/or measurement of smaller parts or parts with lower stress levels. Furthermore, to take full advantage of improved spatial resolution of the laser measurements, a method to smooth the surface contour data using bivariate splines is developed. In contrast to previous methods, the spline method objectively selects the amount of smoothing and estimates the uncertainties in the calculated residual stress map.     

Evaluation of the performance of high-speed PIV compared to standard PIV in a turbulent jet

In this paper, a comparison between two particle image velocimetry (PIV) systems, one based on a standard cross-correlation charge coupled device (CCD) camera with pulsed laser and another using high-speed complementary metal oxide semiconductor (CMOS) camera with continuous laser is performed. The objective of the paper is to point out advantages and disadvantages of the two systems when computing large and small flow scale statistics. The comparison is performed on velocity measurements in the near and far fields of a circular water jet: on this flow several experimental data and empirical self-similarity laws are available for comparisons. The results show that both systems are suitable for measurements with a preference for the standard one when investigating small-scale statistics. This result depends on the lower number of effectively independent samples acquired by a high-speed system and on the higher noise levels of CMOS sensors in comparison to CCDs.     

Experiments on the magnetic damping of an inductively stirred liquid metal flow

This work is concerned with the stabilisation of both bulk liquid metal flow and free surface shape in inductively heated melts. Static magnetic fields in different orientation were used to damp the fluctuations generated by the alternating magnetic field of an induction heater. This superposition of a driving alternating with a braking static magnetic field was investigated experimentally in a low temperature isothermal model utilising a rectangular fluid volume in an induction-furnace-like setup fed by a current of intermediate frequency. Local velocity measurements in the liquid metal showed different damping characteristics for static fields aligned either normal or parallel to the melt surface.     

金属板料成形的快速有限元分析

研究了基于形变理论的金属板形成快速有限元分析的方法－反向方法,并实现了计算程序。通过实例的计算结果和实验以及增量方法进行了比较,表明此方法能够定性地分析成形工件中的变形情况。由于计算速度快、建立分析模模型简单,此方法可用于设计早期估计零件的可成形性,以及部分工艺参数对形的影响。     

Rheology of transient networks containing hydrophobically modified cellulose,anionic surfactant and colloidal silica: role of selective adsorption

Rheology and adsorption studies are performed on a model multicomponent system of hydrophobically modified cellulose (hmHEC), anionic surfactant (SDS), and negatively charged silica. Optical reflectometry measurements on silica quantify the total adsorbed mass from polymer-surfactant mixtures and indicate that the adsorption is irreversible. Linear and nonlinear rheological measurements show that the addition of colloidal silica to polymer-surfactant mixtures leads to complex and unexpected changes in behavior that cannot be explained simply as depletion of the bulk solution via adsorption to the colloidal surface. Instead, the combination of rheology and adsorption measurements indicates that the colloidal silica becomes an integral part of the transient network shifting the dynamics of the system.     

Anti-Buckling Device for Ultra-Thin Metallic Sheets Under Large and Reversed Shear Strain Paths

The kinematic contribution to the hardening of ultra-thin metallic sheets characterized by monotonic and reversed simple shear tests is of high interest in the sheet metal forming industry, because of its influence on the accurate prediction of springback. However, ultra-thin sheets are very sensitive to buckling when submitted to shear stress because of the large gauge width to thickness ratio, the stress perturbations induced by the clamping and the alignment of sample, which thus limit the attainable strain levels using conventional simple shear devices. In this paper, a new simple shear test dedicated to ultra-thin metallic sheets is proposed through the development of a specific support. A transparent glass part enables the application of a normal tightening force to prevent the out-of-plane buckling of the sheets whilst also allowing full field strain measurements to be taken. Firstly, the capabilities of the device are shown by comparing the mechanical behavior in a simple shear test on an austenitic stainless steel with and without the support. A good reproducibility of the flow curves is observed with the support and large shear strains are reached without buckling. Secondly, the influence of friction due to the contact between the sample and the support is checked by finite elements simulations and shown to be negligible compared to the shearing force. Finally, monotonic and reversed shear tests on a pure copper sheet with a thickness of 0.1 mm were performed up to rupture without buckling, these were not previously conceivable on such a low thichness, and demonstrate the potential of the proposed device.     

Dynamic Analysis of Human Gait Disorder and Metabolical Cost Estimation

For the design and improvement of orthotic and prosthetic devices the biomechanical effort is an important criterion to obtain a more comfortable and natural gait of humans with gait disorders. In the first part of the paper the inverse dynamic analysis based on measurements of the human gait for subjects with different kinds of disorders is presented. The second part is devoted to a method to estimate the energy expenditure for human motions. This approach allows the computation of metabolical cost for human locomotion using Hill-type muscle models.     

Extension of Stoney's formula to non-uniform temperature distributions in thin film/substrate systems. The case of radial symmetry

Current methodologies used for the inference of thin film stress through curvature measurements are strictly restricted to stress and curvature states which are assumed to remain uniform over the entire film/substrate system. By considering a circular thin film/substrate system subject to non-uniform, but axisymmetric temperature distributions, we derive relations between the film stresses and temperature, and between the plate system's curvatures and the temperature. These relations featured a “local” part which involves a direct dependence of the stress or curvature components on the temperature at the same point, and a “non-local” part which reflects the effect of temperature of other points on the location of scrutiny. Most notably, we also derive relations between the polar components of the film stress and those of system curvatures which allow for the experimental inference of such stresses from full-field curvature measurements in the presence of arbitrary radial non-uniformities. These relations also feature a “non-local” dependence on curvatures making full-field measurements of curvature a necessity for the correct inference of stress. Finally, it is shown that the interfacial shear tractions between the film and the substrate are proportional to the radial gradients of the first curvature invariant and can also be inferred experimentally.