Residual stresses in continuous-tungsten-fibre-reinforced Kanthal-matrix composites

Residual stresses were measured in four Kanthal matrix-continuous-tungsten-fibre composites (with different tungsten fibre volume fractions V f = 10, 20, 30 and 70 vol.%) using neutron diffraction. Parallel to the fibres the stress in the Kanthal ranged from 40 MPa ( V f = 10 vol.%) to 1100 MPa ( V f = 70 vol.%) compared with m1877 MPa ( V f = 10 vol.%) to m400 MPa ( V f = 70 vol.%) for the tungsten. Perpendicular to the fibres the stress ranged from m52 MPa ( V f = 10 vol.%) to 620 MPa ( V f = 70 vol.%) in the Kanthal compared with m778 MPa ( V f = 10vol.%) to m195 MPa ( V f = 70 vol.%) in the tungsten. Assuming that the measured residual stresses were solely thermal in origin, predictions were made using concentric cylinder and finite-element models. In the absence of hardening data the assumed material behaviour was elastic-perfectly plastic and the predictions underestimated the measured stresses for all volume fractions. Nevertheless the model results were consistent with the experimental measurements. The transverse stress in the fibres is discussed in the context of the interface normal stress, which is significant to the global mechanical response.     

Operator algebras and a theorem of Dieudonne

LetA be aC*-algebra with second dualA″. Let (φ _n)(n=1,...) be a sequence in the dual ofA such that limφ _n(a) exists for eacha εA. In general, this does not imply that limφ _n(x) exists for eachx εA″. But if limφ _n(p) exists whenever p is the range projection of a positive self-adjoint element of the unit ball ofA, then it is shown that limφ _n(x) does exist for eachx inA″. This is a non-commutative generalisation of a celebrated theorem of Dieudonné. A new proof of Dieudonné’s theorem, for positive measures, is given here. The proof of the main result makes use of Dieudonné’s original theorem.     

Finite difference method calculations of X-ray absorption fine structure for copper

The finite difference method is extended to calculate X-ray absorption fine structure (XAFS) for solid state copper. These extensions include the incorporation of a Monte Carlo frozen phonon technique to simulate the effect of thermal vibrations under a correlated Debye–Waller model, and the inclusion of broadening effects from inelastic processes. Spectra are obtained over an energy range in excess of 300 eV above the K absorption edge—more than twice the greatest energy range previously reported for a solid state calculation using this method. We find this method is highly sensitive to values of the photoelectron inelastic mean free path, allowing us to probe the accuracy of current models of this parameter, particularly at low energies. We therefore find that experimental data for the photoelectron inelastic mean free path can be obtained by this method. Our results compare favourably with high precision measurements of the X-ray mass attenuation coefficient for copper, reaching agreement to within 3%, and improving previous results using the finite difference method by an order of magnitude.     

High X-ray conversion efficiency with target irradiation by a frequency tripled Nd : Glass laser

High conversion efficiency of laser energy into X-rays from a laser irradiated target is of great interest for a variety of dynamical (pulsed) studies, e.g.: radiography of laser-imploded targets, structure determination by diffraction and absorption fine-structure, and X-ray laser pumping. We report here on a frequency tripled Nd : glass laser used to irradiate targets of various materials at ～5 x 10¹⁴W/cm². We find conversion efficiencies of between 1% and 0.1% (with respect to the incident laser energy) for individual X-ray lines between 1.8 and 7.8 keV. These efficiencies are more than an order of magnitude higher than whose achieved with 1.06 μm lasers.