**Stress**

Force per unit area, often thought of as force acting through a small area within a plane. It can be divided into components, normal and parallel to the plane, called normal stress and shear stress, receptively. True stress denotes the stress where force and area are measured at the same time. Conventional stress, as applied to tension and compression tests, is force decided by the original gauge length. Shearing strain (or shear strain) is the change in angle (expressed in radians) between two lines originally at right angles. When the term strain is used alone it usually refers to the linear strain in the direction of the applied stress.