2-Chapter_06--Mechanical Properties

2-Chapter_06--Mechanical Properties - CHAPTER 6: MECHANICAL...

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1 Chapter 6 - 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? Toughness and ductility : What are they and how do we measure them? CHAPTER 6: MECHANICAL PROPERTIES
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2 Chapter 6 - MECHANICAL BEHAVIOUR is the respons of a MATERIAL to an APPLIED LOAD The nature of this respons is determined by the MICROSTRUCTURE [INTERNAL FEATURES] of the material as well as its dimensions
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3 Chapter 6 - 1. Initial 2. Small load 3. Unload Elastic means reversible ! ELASTIC DEFORMATION F δ Bonds stretch return to initial F δ Linear- elastic Non-Linear- elastic
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4 Chapter 6 - 1. Initial 2. Small load 3. Unload Plastic means permanent! F δ linear elastic linear elastic δ plastic PLASTIC DEFORMATION (METALS) planes remain sheared F δ elastic + plastic Bonds stretch & planes shear δ plastic
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5 Chapter 6 - Since the magnitude of deformation at a given load and the load to deform by a given amount depends on component dimensions, in place of quoting the dimensions every time even for the same material, the load and deformation can be normalized with respect to cross sectional area and initial length, respectively, for the sake of clearity and simplicity. These normalized values of load and deformation are called as STRESS and STRAIN
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6 Chapter 6 - Tensile stress, σ : Shear stress, τ : Area, A F t F t F s F F F s Stress has units: N/m 2 = Pascal (Pa) Mpa=10 6 •Pa kg/mm 2 =10 MPa ENGINEERING STRESS σ = F t A o original area before loading Area, A F t τ = F s A o
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7 Chapter 6 - Ski lift Cable Drive shaft Motor Applied Moment M F F
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8 Chapter 6 -
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This note was uploaded on 09/25/2011 for the course METE 227 taught by Professor Ali during the Spring '10 term at Middle East Technical University.

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2-Chapter_06--Mechanical Properties - CHAPTER 6: MECHANICAL...

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