Strain

A measure of the relative change in the size or shape of a body. Linear strain is the change per unit length of a linear dimension. True strain (or natural strain) is the natural logarithm of the ratio of the length at the moment of observation to the original gauge length. Conventional strain is the linear strain over the original gauge length. Shearing strain (or shear strain) is the change in angle (expressed in radians) between two lines originally in right angles. When the term “strain” is used alone it usually refers to the linear strain in the direction of applied stress.