The stress-strain graph for a metal wire is as shown. In the graph, the region in which Hooke’s law is obeyed, the ultimate strength, and fracture points are represented by

In the region OA, the graph is linear showing that stress is proportional to the strain. Thus, in this region Hooke’s law is obeyed. The point D on the graph is known as ultimate tensile strength.
The point E on the graph is known as fracture point.