Behaviour of Actual Materials

Abstract

The notions of stress and strain developed quantitatively in Chapter I are universal notions, the one being essentially a part of statics and the other a part of geometry. Any substance may be regarded as being in a state of stress and strain, the relationship between them depending on the nature of the substance. The procedure for finding this relationship is the same as that at the outset of any branch of mathematical physics: certain simple experiments are made (for example in a tensile testing machine) in which both the stress and strain are measured and the connexion between them is determined; this is idealized into a simple mathematical formula connecting stress and strain on the basis of which the behaviour of bodies under more complicated conditions can be calculated and in some cases (e.g., hollow cylinders under tension or torsion combined with internal pressure) compared with experiment.