YOUNG'S MODULUSDOE-HDBK-1017/1-93Properties of MetalsPreviously, we learned that tensile stress, or simply stress, was equated to the load per unit areaor force applied per cross-sectional area perpendicular to the force measured in pounds force persquare inch.(2-4)s PAWe also learned that tensile strain, or the elongation of a bar per unit length, is determined by:(2-5)e dThus, the conditions of the experiment described above are adequately expressed by Hooke's Lawfor elastic materials. For materials under tension, strain (e) is proportional to applied stress s.(2-6)e sEwhereE=Young's Modulus (lbf/in.^{2})s=stress (psi)e=strain (in./in.)Young's Modulus(sometimes referred to as Modulus of Elasticity, meaning "measure" ofelasticity) is an extremely important characteristic of a material. It is the numerical evaluationof Hooke's Law, namely the ratio of stress to strain (the measure of resistance to elasticdeformation). To calculate Young's Modulus, stress (at any point) below the proportional limitis divided by corresponding strain. It can also be calculated as the slope of the straight-lineportion of the stress-strain curve. (The positioning on a stress-strain curve will be discussedlater.)E = Elastic Modulus =stressstrainpsiin./in.psior(2-7)E seMS-02Page 12Rev. 0

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