Showing papers by "National Physical Laboratory published in 1989"
210 citations
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01 Nov 1989TL;DR: Data security ciphers and their properties the data encryption standard using block cipher in practice authentication and integrity key management identity verification public key Ciphers digital signatures electronic funds transfer and the intelligent token data security standards as discussed by the authors.
Abstract: Data security ciphers and their properties the data encryption standard using block cipher in practice authentication and integrity key management identity verification public key ciphers digital signatures electronic funds transfer and the intelligent token data security standards.
178 citations
TL;DR: In this paper, a new analytical method has been developed that can predict the stress transfer between fibre and matrix in a uniaxially fiber-reinforced composite associated with either a single matrix crack or a fibre break.
Abstract: A new analytical method has been developed that can predict the stress transfer between fibre and matrix in a uniaxially fibre-reinforced composite associated with either a single matrix crack or a fibre break. Account is taken of thermal residual stresses arising from a mismatch in thermal expansion coefficients between the fibre and matrix. In addition Poisson ratio mismatches are also taken into account. The theoretical approach retains all relevant stress and displacement components, and satisfies exactly the equilibrium equations, the interface conditions and other boundary conditions involving stresses. Two of the four stress-strain-temperature relations are satisfied exactly, whereas the remaining two are satisfied in an average sense. The required non-interface displacement boundary conditions are also satisfied in an average sense. The general representation is used to solve three types of stress transfer problem. A matrix crack and a broken fibre are analysed for the case when there is perfect bonding between fibre and matrix. The third type of problem takes account of frictional slip at the interface governed by the Coulomb friction law. The approximate analytic approach described in this paper, and the preliminary numerical predictions presented, indicate that the stress transfer between fibres and matrix in a unidirectional fibre-reinforced composite, loaded in tension, can now be investigated theoretically in more detail than before. The paper includes some discussion of singularities in the stress fields, which are smoothed by the averaging techniques employed in the analysis. The analytical approach has enabled the development of a micro-mechanical model of frictional slip at the fibre-matrix interface based on the Coulomb friction law, which is more realistic than assuming that the interfacial shear stress is a constant. Predictions are presented of the stress distributions along the fibre-matrix interface and, in particular, it is shown how the length of the frictional slip zone is related to applied strain, friction coefficient, fibre volume fraction and the difference between the test and ‘manufacturing’ temperatures. An indication is given of many other areas of composite modelling where the new theory will be applied.
173 citations
TL;DR: In this paper, a machine tool of very high stiffness has been constructed and used for single-point diamond grooving of blanks of soda-lime glass and optical glassy quartz.
Abstract: A machine tool of very high stiffness has been constructed and used for single-point diamond grooving of blanks of soda-lime glass and optical glassy quartz. Results show that below a critical depth of cut predicted in order of magnitude by a fracture mechanics analysis, material is removed by the action of plastic flow, leaving crack-free surfaces. Subsequent observations by scanning electron microscopy indicate that a crucial part in the detachment of ribbons of swarf is played by the operation of residual stresses after the passage of the tool, particularly in the case of the amorphous ceramic.
138 citations
TL;DR: In this article, a theoretical analysis has been made of the combined effects of reversible and irreversible trapping on hydrogen transport in steels, coupled with repetitive electrochemical permeation measurements to characterise the diffusion and trapping parameters associated with a 13% Cr martensitic stainless steel commonly used for oil production tubing.
127 citations
TL;DR: In this article, the large scatter found in the intercomparison of spectroradiometric scales maintained by standards laboratories is attributed to the spectral shifts, due to source correlation and violation of scaling law.
81 citations
TL;DR: In this article, the thermal properties of coal slags formed in the British Gas/Lurgi slagging gasifier have been measured for temperatures between 298 and 1800 K. The authors derived values of heat capacity and enthalpy using a model relating the property value to the chemical composition of the slag and these were found to be in good agreement with experimental data.
81 citations
TL;DR: In this article, the authors measured the hydrogen permeation in AISI 410 stainless steel in 5% NaCl containing varying levels of dissolved H 2 S at pH values between 2.6 and 4.6.
80 citations
TL;DR: In this article, an analysis of the glass-rubber β-relaxation as a function of temperature has been carried out for isotactic polypropylene over a wide frequency range (10−2−107 Hz) at temperatures between −10°C and 50°C.
77 citations
TL;DR: In this paper, the physical properties of coal slags relevant to the fluid flow in the British Gas/Lurgi slagging gasifier were measured for temperatures between 1400 and 1800 K. Mathematical models for the estimation of these properties on the basis of the chemical composition of the slag have been developed and compared with experimental data.
72 citations
TL;DR: In this article, it has been found that fiber-matrix bonding in polymer composites has great influence on the pyrolysis shrinkage, macrostructure, flexural strength and fracture behaviour of the final carbon-carbon composites.
TL;DR: In this paper, the superconductivity of a Bi-based 2-1-2-2 cuprate was studied as a function of processing parameters. And the results were compared with those of a Y-based cuprate and a 1-2 -3 cuprate.
Abstract: Superconductivity in the low T c Bi-based 2-1-2-2 cuprate has been studied as a function of processing parameters. T c ( R =0) above 91 K has been realized through the optimization of process conditions. XRD of the samples indicate subtle changes in respect of intensity and splitting of certain peaks. The results are compared with those on Bi-based 2-2-2-3 and Y-based 1-2-3 cuprates. The enhanced T c and the reduced δT c of the 2-1-2-2 compound have been suggested to be the consequence of improved atomic ordering and orthorhombicity.
TL;DR: In this article, the electrochemical properties of BF 4 -doped poly-α-naphthalene oxide-pyrrole, a new conducting copolymer, are reported.
TL;DR: In this paper, the effect of molecular weight and thermal history on the heat capacity of amorphous polystyrene over the temperature range from 200-440 K has been measured using differential scanning calorimetry.
TL;DR: In this article, a systematic study on liquid phase sintering of barium titanate ceramics with low melting glasses has been done, which has the potential of reducing the sinting temperature of the material and avoiding the use of expensive metals (Pt, Pd etc.) as electrodes in multilayer capacitors.
TL;DR: In this paper, the Bureau International des Poids et Mesures has initiated world-wide intercomparisons of pressure standards, i.e., 10-4 to 1 Pa, using Ar as the test gas, with the participation of laboratories in nine countries (in alphabetical order): Czechoslovakia, Federal Republic of Germany, France, India, Italy, Japan, People's Republic of China, UK and United States of America.
Abstract: The Bureau International des Poids et Mesures has initiated world-wide intercomparisons of pressure standards. The intercomparison in the regime of very low pressures, i.e. 10-4 to 1 Pa, using Ar as the test gas, has now been completed with the participation of laboratories in nine countries (in alphabetical order): Czechoslovakia, Federal Republic of Germany, France, India, Italy, Japan, People's Republic of China, UK and United States of America. In addition, five of these laboratories made measurements using H2 as the test gas. Four spinning-rotor gauges were employed as transfer standards. The achieved transfer uncertainty between the pilot laboratory (Physikalisch-Technische Bundesanstalt) and a participating laboratory lies between 0.16% and 0.30% (1σ) for Ar and has allowed an intercomparison at this level of accuracy. At all investigated pressures the standards in the various laboratories lie within an interval of ±3% around the standard of the pilot laboratory. For a brief synopsis of the intercomparison results, the calibration data of each laboratory for one gas species are reduced to a single number, i.e., the average over the pressure range 10-3 to 1 Pa, although this procedure is somewhat arbitrary and obscures scatter and pressure-dependence of some calibration results. These averages deviate from their mean by not more than about 1%. Systematic deviations between some laboratories are clearly identifiable: however, for most of the laboratories it appears that these are compatible with the estimated uncertainties of the pressure generation and the transfer uncertainty.
TL;DR: A simple, reliable and rapid technique for the assessment of bone fracture is reported and the natural frequency and intensity of sound in the injured bone was reduced while the output voltage increased with respect to the normal bone.
TL;DR: Caracterisation detaillee des intensites emises par des feuilles de cuivre et dargent, nettoyees par pulverisation ionique, dans le spectre direct afin de mieux comprendre les processus dans l'echantillon controlant ces intensites.
Abstract: Caracterisation detaillee des intensites emises par des feuilles de cuivre et d'argent, nettoyees par pulverisation ionique, dans le spectre direct afin de mieux comprendre les processus dans l'echantillon controlant ces intensites. Les caracterisations des dependances des intensites avec l'angle d'incidence du faisceau electronique et avec l'angle d'emission des electrons detectes fournissent des regles permettant le transfert des spectres de reference entre differentes configurations d'instruments et differentes conditions de mesure
TL;DR: In this article, it is shown that the setting chosen in this way depends on the incident electron energy in such a way that a higher voltage is required for lower energy electrons, and that if too low voltage is chosen, not only is the counting efficiency less than it should be, but the intensity in the low energy part of the spectrum is progressively lost.
TL;DR: In this paper, it has been found that gravity waves can be generated by a total solar eclipse but their detection at ionospheric heights is critically dependent on the location of the observing station in relation to the eclipse path geometry.
TL;DR: An optical fiber vibration sensor capable of measuring vibration amplitudes ranging from 1 mm down to 0.1 mu m with a wide range of frequencies form 0.5 Hz to 100 kHz is described in this article.
Abstract: An optical fiber vibration sensor capable of measuring vibration amplitudes ranging from 1 mm down to 0.1 mu m with a wide range of frequencies form 0.5 Hz to 100 kHz is described. The proposed method can be used to calibrate accelerometers. In this method the light from a tungsten halogen lamp is made to pass through an optical fiber whose exit end is mounted on the object under test. The emergent light is detected by a lock-in amplifier and then measured by a digital panel meter which can be made to give direct reading of the vibration amplitude. The main advantages of this method are wide dynamic range, wide frequency range, linearity, noise reduction, ruggedness, and light weight. The ultimate detectability can be as much as 0.5 AA/ square root Hz at 1 kHz. >
21 Mar 1989
TL;DR: In this article, the amplitude-wavelenyth (AW) space is used to measure sinusoidal profiles and the performance of stylus profilometers is compared by mapping their limits in AW space.
Abstract: The performance of stylus profilometers can be defined by modelling their abilities to respond to sinusoidal profiles, and can be compared by mapping their limits in amplitude-wavelenyth (AW) space. The performance of traditional stylus profilometers fall within well-defined limits; but new applications are requiring new capabilities beyond these traditional limits. At low amplitudes and wavelengths the tip radius of practical styli has been a limiting factor. Development of the scanning tunnelling and atomic force microscopes has opened up this area of AW space, which extends to the resolution of individual atoms. At low amplitudes and long wavelengths, temporal stability and quality of the datum are critically important. Advances into this area of AW space, which is important to X-ray optical and other super-smooth surfaces, have been made at NPL with the Nanosurf-2 instrument. A description of the instrument and its design philosophy are given, along with examples of precision surfaces that have been measured with it.
TL;DR: In this article, the Savizky and Golay cubic/quadratic, quartic/quintic and Gaussian convolutional functions were investigated and it was shown that the most effective smoothing is achieved with a single pass with a number of points in the smooth equal to 1.7 times the FWHM (N channels) of the peak to be smoothed and that this improves the signal-to-noise ratio by 0.69 N0.5.
TL;DR: Dow Corning 710 silicone fluid has been investigated to establish its suitability as a reference liquid for ultrasonic attenuation Measurements made in the megahertz frequency range with overall uncertainties of 4-5% at a confidence level of 95% are compared with previous values given in the literature as discussed by the authors.
TL;DR: In this article, four uncoated superalloys, IN738LC, IN939, IN100 and IN713LC, were be-en exposed in both high and low velocity burner rigs for times of up to 1500 h at temperatures in the range 700-950°C.
Abstract: Four uncoated superalloys, IN738LC, IN939, IN100 and IN713LC have be-en exposed in both high and low velocity burner rigs for times of up to 1500 h at temperatures in the range 700–950°C. V...
TL;DR: In this paper, the authors propose an algorithme des moindres carres avec des ellipses d'incertitude specifiees to solve the problem of solving un probleme d'ajustement d'un cercle a un ensemble de mesures.
Abstract: On traite un probleme d'ajustement d'un cercle a un ensemble de donnees de mesures. On propose un algorithme des moindres carres avec des ellipses d'incertitude specifiees
TL;DR: In this article, the benefits of laser soldering on the solder fillet microstructure and how this relates to in-service performance were discussed. And the criteria for selection of a CO2 or a Nd:YAG laser are discussed.
Abstract: Laser soldering, as a viable technique for surface mounting assemblies, is reviewed. The criteria for selection of a CO2 or a Nd:YAG laser are discussed. New data are given that quantify the beneficial effects of laser soldering on the solder fillet microstructure, and how this relates to in‐service performance.
TL;DR: In this paper, the slow strain rate method has been used to characterize the cracking resistance of AISI 410 stainless steel (commonly used for downhole applications) in 5% NaCl containing varying levels of dissolved H2S at pH values of 2.6 and 3.6.
TL;DR: In this article, the authors studied the charge transfer during bromine desorption, using an empirical relationship based on CC bond lengths, and showed a maximum of charge transfer for stage-4 samples, which could correspond to the presence of Br2− entities.
21 Mar 1989
TL;DR: A wide range of noncontact optical profilometers have been described in recent years, based on a variety of principles such as interferometry, local slope measurement, and focus detection as discussed by the authors.
Abstract: A wide range of non-contact optical profilometers has been described in recent years, based on a variety of principles such as interferometry, local slope measurement, and focus detection. The performances of these instruments can be compared by considering their ability to measure sinusoidal profiles, and mapping the limitations in amplitude-wavelength (AW) space.Relevant parameters depend on the design of the particular instrument. The numerical aperture of an objective lens, the maximum density of fringes that may be resolved, and the directional (angular) stability of a laser beam are examples of parameters that directly affect performance. Other relevant factors in optical, just as stylus, instruments are the ranges and resolutions of scanning motions, and the quality of a straight datum. AW maps are presented and compared for a number of different types optical probes instru ments, and comparisons are made with conventional stylus instruments. 1. INTRODUCTION