Open AccessThe influence of phase changes on the tenacity of ductile metals at the ordinary temperature and at the boiling point of liquid air
Author(s) -
George Beilby,
H. N. Beilby
Publication year - 1905
Publication title -
proceedings of the royal society of london. series a, containing papers of a mathematical and physical character
Language(s) - English
Resource type - Journals
eISSN - 2053-9150
pISSN - 0950-1207
DOI - 10.1098/rspa.1905.0052
Subject(s) - tenacity (mineralogy) , boiling , materials science , freezing point , ultimate tensile strength , cohesion (chemistry) , boiling point , composite material , metallurgy , chemistry , thermodynamics , physics , organic chemistry
The study of tenacity in metals has had so direct a bearing on the practical problems of metallurgy and engineering, that there is some risk that its scientific importance may be overlooked or lost sight of. It has occurred to us that the measurement of tenacity in solids may supply a direct means for the estimation of the cohesive force of the molecules at any given temperature, so that by the multiplication of observations at a variety of temperatures, it may become possible to estimate more and more closely the molecular cohesion at the absolute zero. The early observations of Dewar on the increase of tenacity at the boiling point of liquid air made it clear for the first time that the nature of the relation between tenacity and temperature continues unchanged even at the lowest attainable temperatures. The recent experiments of Hadfield supply further confirmation of this continuity. The metals used by these observers were almost always in the annealed or crystalline condition. Tenacity in metals is measured, as is well known, by the tension required to tear asunder a rod, bar, or wire of the material. In ordinary mechanical tests of this kind it is assumed that the tensile stress is uniformly distributed over the whole surface at which rupture occurs; but this is only approximately true in the most favourable cases, while in many cases it is obviously untrue, as, for instance, when the surface of fracture is large relatively to the length of the specimen, or when the material is not homogeneous. It is not possible to experiment with a chain of single molecules, for even in the thinnest wire its smallest cross-section contains many millions of molecules. It follows, therefore, that only in a perfectly rigid body can all the pairs of molecules be pulled directly apart as they would be in a single chain. Any departure from perfect rigidity must involve that the molecules under strain will move over each other with a certain degree of freedom, as in the liquid state, and the rupture will become to some extent like that of a highly viscous liquid,e. g. , molten glass, in which the molecules evade any direct pull by slipping over each other.