EAS209 L04_Stress and Strain-spring 11

EAS209 L04_Stress and Strain-spring 11 - EAS 209-Spring...

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EAS 209-Spring 2011 Instructors: Christine Human 1/18/2011 1 04-Mechanical Properties Lecture 4: Mechanical Properties of Materials: Stress and Strain under Axial Loading ( Chapter 2) Design of machines and structures that are safe and function properly requires an understanding of the mechanical behavior of materials. Today’s Objectives: Stress was defined in chapter 1. After defining strain today’s objectives are to understand: Stress-strain curves Elastic versus plastic deformation Brittle versus ductile behavior Engineering stress-strain versus true stress- strain Tension versus compression Fatigue failure Today’s Homework: EAS 209-Spring 2011 Instructors: Christine Human 1/18/2011 2 04-Mechanical Properties Stress –Strain Under Axial Loading Laboratory 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 Uniaxial Tension Test : ASTM E8-04: Standard Test Methods for Tension Testing of Metallic Materials. Normal stress is load P by dividing the initial area, A P We can also normalize the elongation by dividing by the gage length, this is the strain, ε L Each material has a unique stress-strain curve Standard coupon D=0.505 in, L (gage length) = 2.0 in Apply P, measure elongation δ The elongation is measured over the gage length, L, using an extensometer
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EAS 209-Spring 2011 Instructors: Christine Human 1/18/2011 3 04-Mechanical Properties Typical Stress-Strain for Low Carbon Steel Elastic Region (OB) Stress is proportional to strain up to the proportional limit, σ PL . Hooke’s Law E For steel, E=29x10 6 psi (200 GPa) A PL L A P E / / Rearranging E is Young’s Modulus or Modulus of Elasticity NOT TO SCALE Ductile Behavior We will use this equation next lecture EAS 209-Spring 2011 Instructors: Christine Human 1/18/2011 4 04-Mechanical Properties In the
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EAS209 L04_Stress and Strain-spring 11 - EAS 209-Spring...

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