lecture 4 - ME 330 Engineering Materials Lecture 4 Material...

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Lecture 4 Material Structure Stephen D. Downing Mechanical Science and Engineering © 2001 - 2010 University of Illinois Board of Trustees, All Rights Reserved ME 330 Engineering Materials
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ME 330 - Lecture 4 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 1 of 30 This Lecture . .. ± Interatomic Bonding ± Crystalline vs. Amorphous ± Crystals and Crystallographic planes ± Metallic structures (BCC, FCC, HCP) ± Single Crystal vs. Polycrystalline Structure
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ME 330 - Lecture 4 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 2 of 30 Next Lecture . .. ± Theoretical Strength ± Point Defects ± Linear Defects ± Planar Defects ± Volume Defects ± Microscopy Please read chapter 4 Please read chapter 4
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ME 330 - Lecture 4 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 3 of 30 Strength of Carbon Graphite 10 – 15 MPa Diamond 10 GPa Nanotube > 100 GPa Why ?
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ME 330 - Lecture 4 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 4 of 30 Why Atomic Structure? ± Atomic level structure can strongly influence material performance ± We found that modulus, melting point, coefficient of expansion all depend on interatomic forces ± Will now demonstrate how to understand properties based on bonding potentials ± Different bond types have different potentials ± Constructionist approach ± Look at most basic level to begin our understanding ± Today we’ll look (in detail) at: ± How atoms pack together ± How atoms bond together ± See how these effect macroscopic properties
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ME 330 - Lecture 4 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 5 of 30 Atomic Bonding in Solids ± Primary ± Ionic ± Covalent ± Metallic ± Secondary ± Van der Waals ± Hydrogen ± Interatomic potential energies ± Function of separation, r ± Attractive - depends on bond ± Repulsive - atomic scale overlap ± Bonding energy (E o ) is strongly dependent on bond type ± Effect on modulus ??? ± Effect on thermal expansion ??? Energy φ (r) r o dr d ) r ( F φ = Force r E o
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ME 330 - Lecture 4 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 6 of 30 Ionic Bonding Na + Cl - Ions Ionic Bond NaCl Na Cl Atomic Structure Metal Nonmetal
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ME 330 - Lecture 4 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 7 of 30 Notes on Ionic Bonding ± To be stable, all positive ions must be near negative ions ± Bond strength is equal in all directions (nondirectional) ± Energy considerations ± Coulombic attractive force ± Repulsive force: ± Generally, very high bonding energies ± Typically hard, brittle, thermally and electrically insulative ± Ceramics Cl - Na + Cl - Cl - Cl - Na + Na + Na + Cl - Separate Ions Atoms 0 r Energy φ (r) “Stable” Electrostatic Attraction r E A α = Repulsion Curve 8 R r E β = r A 1 ) 8 ( 1 n r n R 8 r r + =
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ME 330 - Lecture 4 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 8 of 30 Covalent Bonding ±
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This note was uploaded on 10/03/2011 for the course ME 350 taught by Professor Staff during the Spring '08 term at University of Illinois, Urbana Champaign.

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lecture 4 - ME 330 Engineering Materials Lecture 4 Material...

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