Hooke's Law states that stress is directly proportional to strain, which is valid in the linear elastic region of the stress-strain curve. In the given stress-strain graph:
- The x-axis represents strain, and the y-axis represents stress.
- Point O is the origin, A is within the linear region, B is the elastic limit, C is beyond the elastic limit, and D is in the plastic region.
- The region where stress is proportional to strain (a straight line) is from O to A.
Thus, Hooke's Law is valid in the region OA.