STRESS-STRAIN RELATIONSHIPDOE-HDBK-1017/1-93Properties of MetalsThe area between Points 1 and 2 is called the elastic region. If stress is removed,the material will return to its original length.Point 2 is the proportional limit (PL) or elastic limit, and Point 3 is the yieldstrength (YS) or yield point.The area between Points 2 and 5 is known as the plastic region because thematerial will not return to its original length.Point 4 is the point of ultimate strength and Point 5 is the fracture point at whichfailure of the material occurs.Figure 3 is a stress-strain curve typical of aFigure 4 Typical Brittle Material Stress-Strain Curveductile material where the strength is small,and the plastic region is great. The materialwill bear more strain (deformation) beforefracture.Figure 4 is a stress-strain curve typical of abrittle material where the plastic region issmall and the strength of the material is high.The tensile test supplies three descriptive factsabout a material. These are the stress atwhich observable plastic deformation or"yielding" begins; the ultimate tensile strengthor maximum intensity of load that can becarried in tension; and the percent elongationor strain (the amount the material will stretch)and the accompanying percent reduction ofthe cross-sectional area caused by stretching.The rupture or fracture point can also bedetermined.MS-02Page 18Rev. 0
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