Stress and strain

Stress and strain

Related terms defining the intensity of internal reactive forces in a deformed body and associated unit changes of dimension, shape, or volume caused by externally applied forces. Stress is a measure of the internal reaction between elementary particles of a material in resisting separation, compaction, or sliding that tend to be induced by external forces. Total internal resisting forces are resultants of continuously distributed normal and parallel forces that are of varying magnitude and direction and are acting on elementary areas throughout the material. These forces may be distributed uniformly or nonuniformly. Stresses are identified as tensile, compressive, or shearing, according to the straining action.

Strain is a measure of deformation such as (1) linear strain, the change of length per unit of linear dimensions; (2) shear strain, the angular rotation in radians of an element undergoing change of shape by shearing forces; or (3) volumetric strain, the change of volume per unit of volume. The strains associated with stress are characteristic of the material. Strains completely recoverable on removal of stress are called elastic strains. Above a critical stress, both elastic and plastic strains exist, and that part remaining after unloading represents plastic deformation called inelastic strain. Inelastic strain reflects internal changes in the crystalline structure of the metal. Increase of resistance to continued plastic deformation due to more favorable rearrangement of the atomic structure is strain hardening.

A stress-strain diagram is a graphical representation of simultaneous values of stress and strain observed in tests and indicates material properties associated with both elastic and inelastic behavior (see illustration). It indicates significant values of stress-accompanying changes produced in the internal structure. See Elasticity

References in classic literature ?
As the whole dark earth bows before some tempest on an autumn day when Jove rains his hardest to punish men for giving crooked judgement in their courts, and arriving justice therefrom without heed to the decrees of heaven--all the rivers run full and the torrents tear many a new channel as they roar headlong from the mountains to the dark sea, and it fares ill with the works of men--even such was the stress and strain of the Trojan horses in their flight.
He felt the stress and strain of life, its fevers and sweats and wild insurgences - surely this was the stuff to write about
He was a large, powerful man, prone to sudden rushes of anger over little things, and of unfailing good-humor under the stress and strain of big things.
It is important to remember that even if a data sheet gives stress and strain values at both yield and break, these simply represent points on a curve, just as the modulus we discussed last month is a point on a curve.
Hence we define the stress and strain value at the failing moment as failure stress and strain.
The finite-element method analysis also shows that during triaxial, oedometer, shear box tests distribution of stress and strain in the sample is non-uniform.
Some more parameters such as Von Mises stress and strain energy values of belt edges for both types of analysis have been reported in table 4, keeping in mind that this region is highly prone to failure during service.
Finite element analysis was used in order to get deeper insight into stress and strain distribution and to identify positions for strain gages.
By summing the relative standard uncertainties in quadrature, the combined standard uncertainty of the stress and strain measurements is about 4%.
Neurasthenia] was first described in 1869 by the eminent neurologist Beard, who thought it was entirely caused by the stress and strain of American life.
For instance, he adds, "frequent short breaks or job rotation can reduce repetitive hand and body movement to avoid stress and strain.