L27MechI145s09

L27MechI145s09 - Lecture 27: Mechanical Properties I -...

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Lecture 27, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Reading assignment : C&R §7.1-7.5; 7.11 Learning objectives: Know how to compute engineering stress and strain Understand properties related to elastic behavior: Elastic modulus Poisson’s ratio Proportional limit Modulus of resilience Understand the relationship of elastic modulus to bonding and the interatomic potential Distinguish the elastic behaviors of metals, ceramics, and polymers Lecture 27: Mechanical Properties I — Elastic Behavior 1
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2 Lecture 27, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Engineering Stress & Strain [C&R §7.2] C&R Fig. 7.1 σ≡ F A 0 ε≡ L L 0 tension
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3 Lecture 27, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Engineering Stress & Strain [C&R §7.2] σ≡ F A 0 ε≡ L L 0 compression tension C&R Fig. 7.1
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4 Lecture 27, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Poisson’s Ratio [C&R §7.5] v ≡ - ε x z = - y z Poisson’s ratio Elastic dimensional change will occur transverse to applied uniaxial load: 0.20-0.35 for most inorganic materials; 0.30-0.46 for most polymers C&R Fig. 7.9
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5 Lecture 27, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University C&R Figs. 7.2 & 7.3 Tensile Test Specimen [C&R §7.2] C&R Fig. 7.2
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6 Lecture 27, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Measure force w/load cell compute stress Measure elongation w/extensometer compute strain Tensile Test Apparatus [C&R §7.2] C&R Fig. 7.3
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Lecture 27, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Elasticity vs. Plasticity [C&R §7.2] Elastic behavior ε 0 when σ 0 I.e., reversible deformation — no permanent shape change after load is removed Plastic behavior ε≠0 when σ 0 I.e., some strain remains after load has been removed — more about this later 7
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This document was uploaded on 07/21/2009.

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L27MechI145s09 - Lecture 27: Mechanical Properties I -...

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