As the specimen continues to elongate under increasing load beyond Y. its cross-sectional area decreases permanently and uniformly through its gage length. If the specimen is unloaded from a stress level higher than Y, the curve follows a straight line downward and parallel to the original elastic slope (fig.2.3.)As the load, hence the engineering stress, is further increased, it eventually reaches a maximum and then begins to decrease. The maximum stress is known as the tensile strength or ultimate tensile strength (UTS) of the material (table 2.1).ultimate tensile strength is a practical measure of the overall strength of a material.