2.3. Strain Defined

For purposes of defining normal strain, refer to Fig. 2.2, where line AB of an axially loaded member has suffered deformation to become A′B′. The length of AB is Δx (Fig. 2.2a). As shown in Fig. 2.2b, points A and B have each been displaced: A an amount u, and B, u + Δu. Stated differently, point B has been displaced by an amount Δu in addition to displacement of point A, and the length Δx has been increased by Δu. Normal strain, the unit change in length, is defined as

Equation 2.1