Distribution of critical current density in large YBa2Cu3O7-δ grains fabricated using seeded peritectic solidification

High quality large grain high Tc superconducting ceramics offer enormous potential as 'permanent' magnets and in magnetic screening applications at 77K. This requires sample dimensions -cm with uniform high critical current densities of the order 105 A/cm2 in applied magnetic fields of IT. We report a study of the magnetic characterisation of a typical large YBa2Cu3O7-δ grain, prepared by seeded peritectic solidification, and correlate the magnetically determined critical current density, Jc, with microstuctural features from different regions of the bulk sample. From this data we extract the temperature, field and positional dependence of the critical current density of the samples and the irreversibility line. We find that whilst the bulk sample exhibits a good Jc of order 104 A/cm2 (77K, 1T), the local Jc is strongly correlated with the sample microstructure towards the edge of the sample and more severely at the centre of the sample by the presence of SmBa2Cu3O7-δ seed crystal. © 1997 IEEE.

Microstructure, strain fields and flow stress in deformed metal matrix composites

An experimental study of local orientations around whiskers in deformed metal matrix composites has been used to determine the strain gradients existing in the material following tensile deformation. These strain fields have been represented as arrays of geometrically necessary dislocations, and the material flow stress predicted using a standard dislocation hardening model. Whilst the correlation between this and the measured flow stress is reasonable, the experimentally determined strain gradients are lower by a factor of 5-10 than values obtained in previous estimates made using continuum plasticity finite element models. The local orientations around the whiskers contain a large amount of detailed information about the strain patterns in the material, and a novel approach is made to representing some of this information and to correlating it with microstructural observations. © 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.

INFLUENCE OF MICROSTRUCTURE ON THE TOUGHNESS OF CARBON FIBRE/PLASTIC COMPOSITES.

A preliminary study is presented of the relationship between the microstructural aspects of failure and the fracture energy G//1//C for cracking parallel to the fibres in long-fibre/thermoplastic matrix composites. Fracture energies are measured by a new technique, and fracture surfaces generated by the test are examined by scanning electron microscopy.

INFLUENCE OF MICROSTRUCTURE ON THE TOUGHNESS OF CARBON FIBRE/PLASTIC COMPOSITES.

A preliminary study is presented of the relationship between the microstructural aspects of failure and the fracture energy G//l//C for cracking parallel to the fibres in long-fibre/thermoplastic matrix composites. Fracture energies are measured by a new technique, and fracture surfaces generated by the test are examined by scanning electron microscopy.

Model for solidification cracking in low alloy steel weld metals

Data on the occurrence of solidification cracking in low alloy steel welds have been analysed using a classification neural network based on a Bayesian framework. It has thereby been possible to express quantitatively the effect of variables such as the chemical composition, welding conditions, and weld geometry, on the tendency for solidification cracking during solidification. The ability of the network to express the relationship in a suitably non-linear form is shown to be vital in reproducing known experimental phenomena. © 1996 The Institute of Materials.