lecture 5 - ME 330 Engineering Materials Lecture 5...

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Lecture 5 Theoretical Strength, Defects 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 5 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 1 of 34 This Lecture . .. ± Crystal Structure Review ± Theoretical Strength ± Point Defects ± Linear Defects ± Planar Defects ± Volume Defects
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ME 330 - Lecture 5 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 2 of 34 Next Lecture . .. ± Dislocations ± Strengthening Mechanisms Please read chapter 7 Please read chapter 7
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ME 330 - Lecture 5 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 3 of 34 Body Centered Cubic Structure ± Atoms “touch” along body diagonal <111> ± Cubic unit cell ( ) ± n = 2 ± N c = 8 ± APF = 0.68 ± “ABAB” stacking ± Iron (RT), Tungsten, Molybdenum, Chromium 3 R 4 a = {110} ² {110} is the closest packed plane From Callister, p. 34
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ME 330 - Lecture 5 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 4 of 34 Face Centered Cubic Structure ± Atoms “touch” along face diagonal <110> ± Cubic unit cell ( ) ± n = 4 ± N c = 12 ± APF = 0.74 ± A “close-packed” structure ± “ABCABC” stacking ± Aluminum, Copper, Gold, Silver, Iron (high temp)* 2 2 R a = {111} ² {111} is the close packed plane From Callister, p. 32 *Allotropic form- crystal structure depends on temperature and pressure
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ME 330 - Lecture 5 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 5 of 34 Hexagonal Close-Packed Structure ± Hexagonal unit cell ± n = 6 ± N c = 12 ± APF = 0.74 ± A “close-packed” structure ± “ABAB” stacking ± Cadmium, Magnesium, Titanium, Zinc {001} ² {0001} is the close packed plane From Callister, p. 35
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ME 330 - Lecture 5 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 6 of 34 Crystal Characteristics** ± Cube length (a)- dimension of unit cell ± Volume of unit cell -V c = a 3 ± Coordination number (N c ) - number of atoms in contact with a single atom (nearest-neighbors) ± Atomic Packing Factor (APF) - fraction of solid sphere volume in a unit cell where ± n = number atoms in a unit cell, R is radius of atom ± True Density - weight per unit volume ( ) 3 3 3 4 * a R n V V APF c atoms π = = A c N V nA cell Volume atoms Mass = = ρ
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ME 330 - Lecture 5 © 2010 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved 7 of 34 ± Deformation depends on density ± Examples for BCC crystal ± Linear Density : Fraction of line length filled by atoms. ± Planar Density
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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 5 - ME 330 Engineering Materials Lecture 5...

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