Nomenclature in Elasticity

Abstract

IN reference to a communication of mine which you published not long ago (see NATURE, vol. xxxi. p. 504) on this subject, I have pleasure in enclosing for publication, should you think fit, photos from three automatically recorded stress-and-strain diagrams made in my laboratory. The originals were traced on smoked glass, the glass plate then varnished to fix it, and used at once as a negative. Test-piece No. 9461, of which Fig. 1 shows the behaviour, was a very ductile piece of Swedish bariron, turned to ¾-inch diameter. The extensions were measured on a length of 10 inches, and recorded double full size; they are to be measured from the curved base-line, distances along which measure the total load on the piece (on a scale, as recorded, of about 1.9 tons per inch), and therefore the load per unit area (or, as I prefer to call it, the intensity of stress) up to the limit of elasticity, to which point the cross-section remains practically unchanged. The point where instability comes in is very marked, and also the release or going back of the stress after the material has “broken down.” Lastly, the condition of local flow, or whatever it is to be called, is excellently shown. The material draws down in one place, so that the increase of extension, being confined to that place, is very small, and the total load diminishes, although the intensity of stress, on the now greatly reduced area, is much increased, as is shown further on in Fig. 4.