chp6 - CHAPTER 6: MECHANICAL PROPERTIES ISSUES TO ADDRESS....

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1 Chapter 6- Slides adapted from J Wiley material ISSUES TO ADDRESS. .. Stress and strain : What are they and why are they used instead of load and deformation? Elastic behavior: When loads are small, how much deformation occurs? What materials deform least? Plastic behavior: At what point do dislocations cause permanent deformation? What materials are most resistant to permanent deformation? 1 Toughness and ductility : What are they and how do we measure them? CHAPTER 6: MECHANICAL PROPERTIES Chapter 6- Slides adapted from J Wiley material F ! bonds stretch return to initial 2 1. Initial 2. Small load 3. Unload Elastic means reversible ! ELASTIC DEFORMATION (Small loads at lower temperatures, T < T melt /3)
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2 Chapter 6- Slides adapted from J Wiley material 3 1. Initial 2. Small load 3. Unload Plastic means permanent ! F ! linear elastic linear elastic ! plastic PLASTIC DEFORMATION (METALS) (larger loads at lower temperatures, T < T melt /3) Chapter 6- Slides adapted from J Wiley material 4 Tensile stress, σ : Shear stress, τ : ! = F t A o original area before loading Stress has units: N/m 2 or lb/in 2 ENGINEERING STRESS
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3 Chapter 6- Slides adapted from J Wiley material 5 Simple tension: cable o ! = F A Simple shear: drive shaft o ! = F s A Note: τ = M / Ac R here. Ski lift (photo courtesy P.M. Anderson) COMMON STATES OF STRESS Chapter 6- Slides adapted from J Wiley material Canyon Bridge, Los Alamos, NM 6 Simple compression: A o Balanced Rock, Arches National Park Note: compressive structure member ( σ < 0 here). (photo courtesy P.M. Anderson) (photo courtesy P.M. Anderson) OTHER COMMON STRESS STATES (1)
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4 Chapter 6- Slides adapted from J Wiley material 7 Bi-axial tension: Hydrostatic compression: Fish under water Pressurized tank ! z > 0 ! " > 0 σ < 0 h (photo courtesy P.M. Anderson) (photo courtesy P.M. Anderson) OTHER COMMON STRESS STATES (2) θ z Chapter 6- Slides adapted from J Wiley material Which has the most positive stress? 1. A 2. B 3. C F = 10 N F = 5 N F = 20 N A 0 = 10 mm 2 A 0 = 4 mm 2 A 0 = 10 mm 2 A B C
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5 Chapter 6- Slides adapted from J Wiley material 8 Tensile strain: Lateral strain: Shear strain: ! /2 " /2 " /2 - !
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chp6 - CHAPTER 6: MECHANICAL PROPERTIES ISSUES TO ADDRESS....

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