Explanation: As per the stress-strain curve, The occurrence of the following points are given below: Proportional limit: It is the highest stress at which stress and strain are directly proportional so that the stress-strain graph is a straight line and follows the Hooke's law. Elastic limit: It is the greatest stress that can be applied to it without causing plastic (permanent) deformation. When a material is stressed to a point below its elastic limit, it will return to its original length once the stress is removed.