Showing papers by "National Physical Laboratory published in 1992"
TL;DR: In this article, two analytical methods have been developed that can predict the stress transfer between the 0 and 90° plies in a 0°-90°-0° cross-ply laminate containing transverse cracks.
Abstract: Two new analytical methods have been developed that can predict the stress transfer between the 0 and 90° plies in a 0°—90°—0° cross-ply laminate containing transverse cracks. Account is taken of thermal residual stresses arising from a mismatch in thermal expansion coefficients of the 0 and 90° plies. The first method is based on a 2-D model which assumes that generalised plane strain conditions prevail. 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. The stress—strain—temperature relations are satisfied either exactly or in an average sense. The 2-D representation can be used to predict the stress and displacement fields for a laminate containing parallel transverse cracks. In this paper the solutions are used to estimate the dependence of the longitudinal values of Young's modulus, Poisson's ratio, and thermal expansion coefficient on the density of transverse cracks. The second analytical method extends the 2-D model so that it can apply to 3-D problems which arise, for example, when edge effects or orthogonal cracking are to be taken into account. For the special case of very large laminate widths the 2- and 3-D models predict results which are very close to each other for both glass fibre/epoxy and carbon fibre/epoxy laminates. It is shown how the 3-D model can be used to predict the transverse Young's modulus and thermal expansion coefficient. Theoretical predictions of the dependence of Poisson's ratio on transverse crack density indicate that experimental measurements can be sensitive to the strain measurement technique used, and to specimen width when using a transverse extensometer. Theoretical predictions, for glass fibre/epoxy and carbon fibre/epoxy laminates, of the dependence of Young's modulus and Poisson's ratio on the crack density are compared with some experimental results.
201 citations
TL;DR: In this paper, the development of aluminium hydroxide interfacial layers in the wear of alumina at intermediate wear rates and the effect of these layers on wear and friction was examined and it was found that alpha-alumina reacts directly to form boehmite (Al(OH)) under moderate pressures and high temperatures.
120 citations
TL;DR: In this article, the application of the compound energy model to crystalline ionic phases is discussed and compared with the regular solution model, with special reference to oxides, and problems connected with the choice of a state of reference for charged components in a multicomponent solution are addressed.
Abstract: The application of the compound energy model to crystalline ionic phases is discussed and compared with the regular solution model. Its application to solutions with reciprocal reactions between cations on different sublattices is discussed with special reference to oxides. Examples are taken from various solutions between spinels, including cases with vacancies and interstitials. Problems connected with the choice of a state of reference for charged components in a multicomponent solution are addressed. This paper was presented at the International Phase Diagram Prediction Symposium sponsored by the ASM/MSD Thermodynamics and Phase Equilibria Committee at Materials Week, October21-23,1991, in Cincinnati, Ohio. The symposium was organized by John Morral, University of Connecticut, and Philip Nash, Illinois Institute of Technology.
95 citations
TL;DR: In this paper, the industrial possibilities and alternative products which might benefit from the use of carbonitride cermets have been examined and a number of alternative products have been suggested.
Abstract: Titanium carbonitride cermets have been largely developed as cutting tool materials. However, their properties indicate that there is potential for extending the application areas to other tools. This report examines the industrial possibilities and indicates a number of alternative products which might benefit from the use of cermets.
92 citations
TL;DR: In this paper, the mechanism of grain boundary (GB) cracking in fatigued polycrystalline copper, specimens were fatigued in symmetrical push-pull at an intermediate constant plastic strain range at room temperature in dry air.
Abstract: In order to study the mechanism of grain boundary (GB) cracking in fatigued polycrystalline copper, specimens were fatigued in symmetrical push-pull at an intermediate constant plastic strain range at room temperature in dry air. The intergranular cracks were examined under the scanning electron microscope. Many GB cracks were found to have been formed by the impingement of persistent slip bands (PSBs) against the grain boundaries (PSB-GB cracks). The orientations of the grains adjacent to the cracks were determined by electron back-scattering patterns. The misorientations of the cracked boundaries were calculated and the boundary plane orientations were also determined. High-energy grain boundaries were found to be preferred sites for cracking. The activated slip systems in the component grains adjacent to the cracks were determined and analyzed. With these data, the cracking stresses due to the interaction between the PSBs and the boundaries were calculated for the observed PSB-GB cracks in a pile-up type dislocation model in a three-dimensional analysis. The results confirmed that, with reasonable assumptions, the estimated minimum theoretical shear stresses which are required to act in the PSBs for causing PSB-GB cracks were always smaller than the real shear stresses operating in the PSBs.
80 citations
TL;DR: In this article, the authors developed equations for numerically evaluating random uncertainties in Auger and x-ray photoelectron spectroscopies and applied them to peak synthesis to determine the standard deviation uncertainties in quantities such as peak intensity, peak energy and peak width.
Abstract: We develop equations for numerically evaluating random uncertainties in Auger and x-ray photoelectron spectroscopies. First, the general statistical theorems involving the chi-squared (χ 2 ) distribution are clearly stated. These are applied to peak synthesis to determine the standard deviation uncertainties in quantities such as peak intensity, peak energy and peak width. General methods for their incorporation in new software are discussed. In the mean-time, we suggest a new method for determining these uncertainty values using existing software provided by instrument manufacturers
77 citations
TL;DR: In this article, an additional exothermic peak at about 350°C has been observed in PAN fibres and it has been proposed that this peak is associated with certain intermolecular crosslinking reactions as well as with the aromatization of the structure during thermal stabilisation.
73 citations
TL;DR: An optical radiation source has been developed by coupling a dye laser to a small integrating sphere with an optical fiber and has been successfully used in a spectrophotometer to measure the transmittance of a large lens and the spectral responsivity of a filter radiometer.
Abstract: An optical radiation source has been developed by coupling a dye laser to a small integrating sphere with an optical fiber. The radiant power from this source, which is monochromatic and spectrally tunable, has been stabilized to +/-0.02%. Nonuniformities in the emitted optical radiation field caused by speckle have been overcome by vibrating the fiber at ultrasonic frequencies. The source has been successfully used in a spectrophotometer to measure the transmittance of a large lens with an uncertainty of +/-0.01%, and the spectral responsivity of a filter radiometer with an uncertainty of +/-0.04%.
63 citations
TL;DR: In this article, the far-infrared optical constants of polypropylene, PTFE and polystyrene have been determined in the spectral region between 50 and 500 cm −1 at a temperature of 290 K by the method of dispersive Fourier transform spectroscopy.
57 citations
TL;DR: Three of the two-photon annihilation operators possess eigenstates that are analogous to the often-used coherent and squeezed states, and it is hoped that these states will find applications in quantum optics and quantum mechanics in general.
Abstract: We introduce the inverse of the harmonic-oscillator creation and annihilation operators by their actions on the number states. We then show that three of the two-photon annihilation operators, a^ $^{\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\mathrm{\ensuremath{-}}1}$a^, a^a^ $^{\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\mathrm{\ensuremath{-}}1}$, and a^ $^{2}$, possess eigenstates that are analogous to the often-used coherent and squeezed states. A family of the eigenstates of the operator a^ $^{\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\mathrm{\ensuremath{-}}1}$a^ is the customary squeezed vacuum S(\ensuremath{\sigma})\ensuremath{\Vert}0〉 while another family of the eigenstates of a^a^ $^{\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\mathrm{\ensuremath{-}}1}$ is the state S(\ensuremath{\sigma})\ensuremath{\Vert}n=1〉. We find some interesting properties related to squeezing, bunching, and antibunching exhibited by these states. An alternative method of summing some series by using these states is also considered. It is hoped that these states will find applications in quantum optics and quantum mechanics in general.
56 citations
TL;DR: The measured mass losses have been fitted to a variety of simple multivariate correlation functions as discussed by the authors, showing that the rate of corrosion of steel is controlled in British conditions mainly by the long-term average sulphur dioxide concentration, and scarcely responds to short-term SO2 episodes.
TL;DR: The electrochemical permeation technique has been used to characterize hydrogen transport and trapping in pure nickel and in alloys 600, X-750, and 718 at a temperature of 80 °C as mentioned in this paper.
Abstract: The electrochemical permeation technique has been used to characterize hydrogen transport and trapping in pure nickel and in alloys 600, X-750, and 718 at a temperature of 80 °C. The “effective diffusivity” of hydrogen atoms in alloy 600 is reduced by a factor of about 5 compared to pure nickel. This is attributed to both compositional changes and the presence of [(Ti, Nb)C] carbides. Aging of alloy 600, with subsequent M23C6 carbide precipitation, does not significantly influence the measured “effective diffusivity,” which is explained by the dominant effect of preexisting [(Ti, Nb)C] carbides. The “effective diffusivity” of hydrogen atoms in solution-annealed alloy X-750 is reduced by a factor of about 9 compared to that of pure nickel. This is also attributed to compositional changes and [(Ti,Nb)C] carbides. Aging of alloy X-750, which causes precipitation of γ’[Ni3(Al, Ti)], reduces the “effective diffusivity” by an additional factor of 5 or more. Double aging at 885 °C/24 hours, 704 °C/20 hours following hot working yields the greatest reduction in “effective diffusivity.” Analysis of permeation transients using a diffusiontrapping model indicates a binding energy associated with trapping due to the γ’ phase of between-31 and -37 kJ/mol. The “effective diffusivity” of hydrogen in alloy 718 is about 40 pct greater than for alloy X-750 for the same double and direct aging treatments. The average “effective diffusivities” of the double-aged and direct-aged alloy 718 are comparable, but the permeation transients for the double-aged treatment are significantly steeper. The double-aged treatment with predominantly S phase (orthorhombic Ni3Nb) yields a binding energy of about-30 kJ/mol. Analysis of the direct aged-treated 718, which contains predominantly γ′ phase (body-centered tetragonal Ni3Nb) gave a binding energy between -23 and -27 kJ/mol. Segregation of hydrogen atoms to the γ′/matrix interface, combined with a large volume fraction ofγ at grain boundaries, provides the most likely explanation for the enhanced cracking associated with the double-aging treatment in alloy X-750.
TL;DR: In this article, the cyclic fatigue crack growth behavior in two aluminas with different grain sizes and purities was investigated using tapered cantilever beam specimens, and it was concluded that the fatigue cracks in these materials were strongly bridged by both rigid and elastic loadbearing ligaments.
Abstract: The cyclic fatigue crack growth behavior in two aluminas with different grain sizes and purities has been investigated using tapered cantilever beam specimens. The curves of load–crack opening displacement revealed a hysteretic loss behavior, in both aluminas, produced by frictional forces generated in the crack wake. From measurements of the specimen complinces it is concluded that the fatigue cracks in these materials were strongly bridged by both “frictional” and “elastic” load-bearing ligaments. It is shown that the “elastic” contribution to the total crack-bridging force is far greater than that produced by fristional sliding ligaments. The results support the view that cyclic loads produce degradation of the strength of the bridging ligaments. The effect of grain size and compressive loads on the magnitude of the bridging forces is discussed.
01 Jan 1992
TL;DR: In this article, a relatively simple shear-lag approach to understand stress transfer between fibres and matrix is presented, and a more realistic model of stress transfer for unidirectional composites must be modified for transverse isotropic solids.
Abstract: Many unidirectional composites are made using carbon fibres which have anisotropic thermo-mechanical properties. There is a need, therefore, to take account of this anisotropy when making predictions of the properties of damaged composites. For the more general case when the fibres and matrix are both transverse isotropic solids, a relatively simple shear-lag approach to understanding stress transfer between fibres and matrix is presented. A similar approach is used to develop a shear-lag model of stress transfer between neighbouring plies in a cross-ply laminate containing transverse cracks. As to be expected stress transfer is governed by second order ordinary differential equations which are easily solved. It is shown how a more realistic model of stress transfer for unidirectional composites must be modified when the fibres and matrix of the composite are transverse isotropic solids. Reference is made to more realistic models of stress transfer in cross-ply laminates containing transverse cracks in the 90 ply. The more realistic models lead to fourth order differential equations. Such models are thus more flexible than shear lag models in that a greater variety of boundary conditions can be satisfied.
TL;DR: In this article, an attempt has been made to estimate various electronic parameters such as work function, barrier height, and ideality factor through I-V measurements carried out on metal/polyaniline Schottky junctions.
Abstract: An attempt has been made to estimate various electronic parameters such as work function, barrier height, and ideality factor through I-V measurements carried out on metal/polyaniline Schottky junctions. The results of optical studies conducted on chemically synthesized polyaniline used in the fabrication of such Schottky devices have been presented.
TL;DR: In this paper, the intrinsic competition between superconductivity and localization in an essentially localized system is discussed in terms of a theoretical model which determines the intrinsic competitiveness between supercondivity and localized system.
Abstract: Electrical resistivity measurements have been performed on the Bi 2 Sr 2 Ca 1−x M x Cu 2 O 8+y (M=Eu, Dy, Tm) system with various heat treatments. A gradual change in normal state resistivity ( ϱ n ) and T c has been observed with increasing dopant concentration. The results provide experimental evidence for a transition from a metallic behaviour to a variable range hopping regime at low temperatures. In the insulator regime (highly semiconducting-like) the resistivity behaviour is found to turn from 2D to 3D variable range hopping for x ⩾0.6. The results are discussed in terms of a theoretical model which determines the intrinsic competition between superconductivity and localization in an essentially localized system. T c data are compared with the earlier reported findings.
TL;DR: In this article, the first measurements of toluene by differential-absorption LIDAR in the near-ultraviolet spectral region were reported, generated by frequency doubling the output from a tunable dye laser in beta-barium borate.
Abstract: The first measurements of toluene by differential-absorption LIDAR in the near-ultraviolet spectral region are reported. A pulse energy of 4.5 mJ was used for the measurement, generated by frequency-doubling the output from a tunable dye laser in beta-barium borate. The magnitude of spectral interference from other pollutant species has been calculated and the extension of the system to measure other aromatic hydrocarbons in the same spectral region is discussed.
TL;DR: On etudie la forme et l'etendue des transformations and la presence de fissurations aux alentours des indentations Vickers dans des ceramiques Y-TZP and Ce TZP as discussed by the authors.
Abstract: On etudie la forme et l'etendue des transformations et la presence de fissurations aux alentours des indentations Vickers dans des ceramiques Y-TZP et Ce-TZP.
TL;DR: In this article, the tensile creep compliances have been determined for PVC over a wide range of times ( t = 10 −8 to 10 6 s) at 23°C.
TL;DR: A critical assessment of the thermodynamic and phase diagram data for the crystalline and liquid phases of the Ge-O system at ambient pressures has been carried out to provide a set of parameters which can be used as a basis for the calculation of ternary and multicomponent phase equilibria.
Abstract: A critical assessment of the thermodynamic and phase diagram data for the crystalline and liquid phases of the Ge-O system at ambient pressures has been carried out to provide a set of parameters which can be used as a basis for the calculation of ternary and multicomponent phase equilibria The phase diagram reported by Massalski (Binary Alloy Phase Diagrams, ASM International, Materials Park, 1990) does not correctly reproduce the rather limited experimental information for the system There is some inconsistency between the rather more extensive experimental thermodynamic data for the three phases of GeO2 stable at ambient pressures
TL;DR: In this paper, an analysis of the non-linear effects of channel electron multipliers (CEMs) in both the analogue amplification and pulse counting modes was presented, with supporting experimental measurements, and it was shown that the output current should not exceed 0.8r% of the wall current for the linearity to be maintained within r%.
Abstract: An analysis is presented, with supporting experimental measurements, of the non-linear effects in electron intensity measurements using channel electron multipliers (CEMs) in both the analogue amplification and pulse counting modes. It is shown that for Auger electron spectroscopy, where the CEMs may be used in the analogue mode, the output current should not exceed 0.8r% of the CEM wall current for the linearity to be maintained within r%. In the pulse counting mode, used more generally, simple dead time corrections are possible over a limited range of counting rates. This range is defined theoretically and experimental procedures are demonstrated to show how the range may be defined, and the necessary corrections made, to retain accurate linearity within 0.5%.
TL;DR: In this article, spectral changes are produced on superposing partially coherent light emerging from two pinholes in Young's interference experiment, and these changes have been studied for on-axis and off-axis points of observation.
TL;DR: A review of the major developments over the past two decades of alkaline earth sulphides as luminescent emitting and energy storage materials can be found in this article, where an ionic model with an ionicity of 0.9 is proposed.
TL;DR: The 4f13 6s2 2F7/2 467 nm ultra-narrow transition in laser-cooled Yb+ was determined by probing a cloud of 172Yb+ ions held in a radiofrequency trap in the presence of helium buffer gas as discussed by the authors.
Abstract: The 4f13 6s2 2F7/2–4f14 5d 2D5/2 3·43 μm infrared transition in 172Yb+ has been driven for the first time and measured to be 87 360 087(4) MHz The frequency was determined by probing a cloud of 172Yb+ ions held in a radiofrequency trap in the presence of helium buffer gas The infrared radiation was generated by difference frequency mixing in LiNbO3 The frequency measurement is part of a programme to locate the 4f14 6s 2S1/2–4f13 6s2 2F7/2 467 nm ultra-narrow transition in laser-cooled Yb+
01 Jan 1992
TL;DR: Differential scanning calorimetry (DSC) is a simple and rapid method for determining the heat capacities of small samples over a wide range of temperature as discussed by the authors, and it is applicable to materials in general and a variety of forms (bulk, powder, film, granular, and liquid).
Abstract: Differential scanning calorimetry (DSC) is a simple and rapid method for determining the heat capacities of small samples over a wide range of temperature. It is applicable to materials in general and a variety of forms (bulk, powder, film, granular, and liquid). Although easy to operate, the relevant instrumentation is of complex construction and it is normal to use commercial, rather than home-made, equipment. In this chapter, following a brief general introduction, the remarks will refer specifically to Perkin-Elmer power-compensation calorimeters—although they can usually be generalized to include other makes. The performance of most currently available DSCs is such that an accuracy of ±1-2% should be routine but this can be undermined by unsuitable samples, incorrect calibration, or by inadequate data treatment. Particular emphasis will therefore be placed on these aspects rather than on the setting-up and basic operation which are fully described in the manufacturers’ manuals.
TL;DR: This paper demonstrates how a syntax-directed editor, designed as an entry fool for VDM specifications, can produce executable prototypes by the automatic translation of V DM specifications into Standard ML programs.
Abstract: This paper demonstrates how a syntax-directed editor, designed as an entry fool for VDM specifications, can produce executable prototypes by the automatic translation of VDM specifications into Standard ML programs. A small example of this translation process is given
TL;DR: The electrochemistry of relevance to environment-assisted cracking in high temperature, low conductivity water is critically reviewed in this article, which covers corrosion potential and electrochemical polarisation measurements, thermodynamics, and also experimental measurements and mathematical modelling of the Electrochemistry in cracks and crevices.
TL;DR: In this article, a silicon nitride films produced by plasma enhanced chemical vapor deposition (PECVD) have been studied as antireflection (AR) coating on polycrystalline silicon solar cells.
TL;DR: In this article, the residual stress measurements and distortion analyses have been conducted on injection molded plaques made from polypropylene (PP) and a short glass-fiber filled polypropylon (GFPP) and the residual stresses are very anisotropic in GFPP, but not in PP.
Abstract: Residual stress measurements and distortion analyses have been conducted on injection molded plaques made from polypropylene (PP) and a short glass-fiber filled polypropylene (GFPP). The residual stress analyses include measurements both parallel and perpendicular to the direction of flow during mold filling. Residual stresses are very anisotropic in GFPP, but not in PP. The residual stress levels in PP fall on aging at room temperature, whereas in GFPP the proportion of stress relaxation is smaller, and significant stresses remain even after heating to elevated temperatures. A significant contribution to distortion has been linked to the ejection process, and the long- and short-term distortion of moldings is discussed within the framework of the properties of the materials measured here.
TL;DR: In this paper, it was demonstrated that this non-collinear geometry corresponds to the tangential phase-matching condition which increases the acceptance angle of a second-order nonlinear interaction over that achieved in a non-critically phase-matched geometry.