n (1) (elastic modulus, tensile modulus, Young’s modulus) The ratio of nominal tensile stress to the corresponding elongation below the proportional limit of a material. Since elongation is dimensionless, modulus has the units of stress. The relevant ASTM test is D 638. In contrast to structural metals such as mild steel, the stress-strain graphs for many plastics exhibit some curvature, even at very low strains. Since there is then no significant linear region whose slope would give the modulus, a Secant Modulus at 1–3% elongation may be reported for stiff materials. (2) More generally, any of the several elastic moduli characterizing behavior in shear (torsion), flexure, or change in volume under pressure. See Bulk Modulus. In SI, all types of elastic moduli are reported in pascals, usually megapascals (MPa). 1,000 psi = 6.894,757 MPa. Also known as Elastic Modulus or Young’s Modulus. See Hardness.
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