Home › S › Strength of Materials

Strength of Materials

in mechanics, an important part of the theory of structures, and includes the consideration of all questions relating to the straining of solids. A solid is said to suffer strain when it is in any way altered in volume or figure, and to effect such an alteration external force must be applied. If the strain is not carried so far as to cause disintegration of the solid - that is, if no fracture results the force or resultant of the forces which produce the strain must be balanced by an internal force conditioned by the molecular structure of the solid.

This internal force called into existence by the strain is the one aspect of the stress, of which the original force producing the strain is the other. To every strain, then, there corresponds a stress, which is regarded as the resultant of the stresses which act between the elementary portions into which the solid may be supposed to be divided. When the strain is proportional to the stress other words, when Hooke's law holds the body strained is said to be perfectly elastic; and the elasticity of every solid,. even for such cases as moistened clay, is sensibly perfect when the strain does not exceed a certain limit. For every solid, however, there are limits of strain which, if exceeded, give to the body a set or permanent alteration of volume or figure. Hodgkinson has proved that these limits depend on the duration of the strain, so that in all probability any strain if sufficiently long-continued would give a set to any body. in