National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

Interface effects and the work of fracture of a fibrous composite

Abstract: The stresses near the tip of a crack which lies normal to a set of alined fibres is discussed when the elastic properties of the composite are appropriate to those of a carbon reinforced epoxy resin. Splitting parallel to the fibres is expected to occur before fibre fracture only if an interface parallel to the fibres of one fiftieth the strength of the composite parallel to the fibres is present. The two mechanisms of energy dissipation which have been suggested to occur in a fibre composite of brittle fibres in a brittle matrix, namely pull out and debonding, are discussed. Experiments to measure the latter are described. The work of debonding ( 4 J m -1 ) is usually less than the work of pull out. The theory of pull out is described and experiments to support it noted. An important result is that the work of pull out increases linearly with fibre diameter, and is likely to be inconveniently small for fibres of diameter ≾ 10 μ m. The relative advantages and disadvantages of fibres of various diameters are discussed. Fibres of diameter ≿ 25 μ m lead to large works of pull out and are stable and easily handled. Thinner fibres ( μ m diameter) give rise to constraint effects which are important in metallic matrices.

The Colorimetric Properties of the Spectrum

Abstract: Those properties of the eye which determine its behaviour in the measurement of luminous intensity and colour are completely defined by two sets of numerical data which express, as functions of wave-length, its behaviour to monochromatic radiation throughout the visible spectrum in respect of these two aspects of the visual effect of a stimulus. The first of these functions is embodied in the “ Relative Visibility ”* curve of the spectrum, and the second is embodied in a curve showing the locus of the spectrum on the “ colour triangle ” of some trichromatic system. These two functions may be combined to give the “ mixture curves ” of the spectrum, by means of which we can calculate both the photometric and colorimetric values of any stimulus from its spectral energy distribution. The nature and significance of these various functions are sufficiently well understood to need no explanation here.

On the effects of boundary-layer growth on flow stability

Abstract: The stability of small travelling-wave disturbances in the flow over a flat plate is discussed. An iterative method is used to generate an asymptotic series solution in inverse powers of the Reynolds number Rx = Ux/v to the power one half. The neutral-stability boundaries given by the first two terms of this series are obtained and compared with experimental data. It is shown that the parallel flow approximation leads to a valid solution at very large Reynolds numbers.

The use of the PeakForceTM quantitative nanomechanical mapping AFM-based method for high-resolution Young's modulus measurement of polymers

Abstract: PeakForceTM quantitative nanomechanical mapping (QNMTM) is a new atomic force microscopy technique for measuring Young's modulus of materials with high spatial resolution and surface sensitivity by probing at the nanoscale. In this work, modulus results from PeakForce™ QNM™ using three different probes are presented for a number of different polymers with a range of Young's moduli that were measured independently by instrumented (nano) indentation testing (IIT). The results from the diamond and silicon AFM probes were consistent and in reasonable agreement with IIT values for the majority of samples. It is concluded that the technique is complementary to IIT; calibration requirements and potential improvements to the technique are discussed.