Wyraźna granica plastyczności metali w ujęciu teorii atmosfer Cottrella

W artykule podane są podstawowe zagadnienia z zakresu teorii atmosfer Cottrella w zastosowaniu do wyraźnej granicy plastyczności w metalach. Artykuł ma na celu wprowadzenie czytelnika w podstawy teorii granicy plastyczności ujętej z punktu widzenia klasycznej teorii dyslokacji.

YIELD POINT PHENOMENON IN THE LIGHT OF COTTRELL ATMOSPHERES THEORY

The Cottrell atmospheres theory belongs to the classical chapters in the theory of dislocations and plays a significant part in many considerations concerned with the properties of metals. The present paper deals with the sharp yield point described on the ground of the atmospheres theory. The first part of this paper outlines the yield point phenomenon from the experimental point of view. The conditions of its appearance and the influence of such factors as temperature, deformation rate and testing machine rigidity are described. Several types of the stress-strain curves are given. The former yield point theories, namely the theory of membranes and precipitations theory are discussed in the second part of paper. The third part contains the basic problems concerned with the atmospheres of foreign atoms assembled near the dislocations. Subsequently, the formation of Maxwell’s atmospheres and their transition into condensed atmospheres is described. Finally, both the derivation of the principal formulae expressing the yield point value and the influence of thermal fluctuations are discussed.