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EAS 209-Spring 2008 Instructors: Christine Human Gilberto Mosqueda 1/23/2008 1 Lecture 05-stress and strain Lecture 5: Chapter 2 Stress and Strain under Axial Loading Design of machines and structures that are safe and function properly requires an understanding of the mechanical behavior of the materials being used. These properties of different materials are ordinarily measured in the laboratory. The most common test is the uniaxial tension test. Of interest is the stress-strain relationship. Recall Stress: AP=σ, Strain: Lδε=Tests are conducted in accordance with standard protocols. In the U.S. one of the major standards organizations is the American Society of Testing and Materials e.g. ASTM E8-04: Standard Test Methods for Tension Testing of Metallic Materials.EAS 209-Spring 2008 Instructors: Christine Human Gilberto Mosqueda 1/23/2008 2 Lecture 05-stress and strain •Uniaxial Tension Test •Apply a force P •Measure the elongation δwith an extensometer •2nddial gage often measures change in diameter From P and δplot the stress-strain curve 0AP=σ0Lδε=Standard coupon D=0.505 in L (gage length) = 2.0 in The elongation is measured over the gage length
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