Experience shows that when a straight bar (or wire, cable, rubber band or the like) is subjected to a tensile axial force, it stretches and, as the force is increased, eventually breaks. Depending on the material of which the bar is made, the bar may or may not undergo a considerable amount of permanent elongation, with relatively little resistance, before it breaks. The onset of this elongation is known as yielding, and a material that allows it is called ductile. These properties will be discussed further in Chap. 11.