No abstract

Departures from the theoretical behavior of a Schottky barrier are reported in the case of gold on gallium arsenide. It is shown that the empirical introduction of a single temperature-independent parameter takes care of all the observed departures.

The crystal structure of zinc salicylate dihydrate has been determined by two-dimensional Fourier methods. The molecule, Zn(CTHsO3) 2. 2 H20, possesses a twofold axis, and exists as a unit in the structure. Except for two oxygen atoms, the entire salicylate radical is planar. Oxygen coordination about the zinc is tetrahedral. The water molecules play a dominant role in the framework structure. Their oxygen atoms are a part of the primary coordination sphere around the zinc atoms, and through hydrogen bonds they hold the crystal together in the a and b directions. Binding forces in the c direction are van der Waals in character.

This paper comprises the text of a code of testing practice prepared under the auspices of a British High Temperature Mechanical Testing Committee. The code makes recommendations concerning equipment, test specimens and procedures; it includes several explanatory and cautionary notes and references to related standards and publications. It was considered that the American National Standard ASTM E606-80 [l] contained much of the required material and in order to avoid unnecessary divergence of practice the recommendations therein have been used as far as possible but with specific modifications and additions to account for current UK needs and practice. It is anticipated that this document may form the basis of a future BSI publication and consequently, the general format is similar to that recommended by BSI in BS 0 1981 [2]. Currently a programme of intercomparative Low Cycle Fatigue testing is being carried out under the auspices of and with support from the Community Bureau of Reference (BCR) of the Commission of European Communities. This programme will shortly be widened to include non-European countries as part of a broader initiative in the field of Materials and Standards (VAMAS). In consequence it is intended to consider and, if necessary, revise the Code of Practice in the light of results from this programme and of other on-going work in the field.

Fatigue failure at room temperature in most structural metals and alloys occurs by the rapid initiation and subsequent controlled propagation of a surface crack. Propagation is transgranular and is controlled to a large extent by continuum plasticity effects ahead of the crack. With increasing temperature, other factors affect this simple fatigue process; namely, the weakening of grain boundaries leading to intergranular propagation, the initiation and growth of other cracks in the bulk of the material by creep processes, and the more rapid oxidation effects which can occur at elevated temperatures. This paper shows the extent to which continuum material properties still control fatigue failure in elevated temperature situations, by reference to recently developed theories and the observed fatigue behavior of a stainless steel and a magnesium alloy over a range of temperatures (up to 0.73 Tm) and strain rates. The influence of secondary creep fracture is examined in the light of results of holdtime tests.