Chapter5_lecture

Chapter5_lecture - Chapter 5 Linear, Planar, and Volume...

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Chapter 5 Linear, Planar, and Volume Defects Introduction Linear Defects, Slip and Plastic Deformation Planar Defects Volume Defects Strengthening in Metals
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Introduction Chapter 5 In the previous chapter, point defects were shown to strongly influence properties. It was hypothesized in the 1930’s and demonstrated experimentally in the 1950’s that crystals contained line defects and the mobility of the defects controls strength. The line defects account for the dramatic difference between the strength of perfect crystal and a real crystal with defects.
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Introduction Chapter 5 In addition to line defects, there are also planar and volume defects that also affect the strength and other properties of a material. The emphasis in this chapter will be on metallic and ceramic materials because of their highly crystalline nature.
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Normal Force Shear Force
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Model to Calculate Theoretical Critical Resolved Shear Strength Macroscopic view Atomic scale view Broken plane of atoms
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Shear Stress 1 1 1 cos sin cos cos sin sin z z z Shear force on the plane F A Area of the rotated plane F F A A φ τ = = = = σ z φ F z cos F z sin A 1 σ z 0 0.1 0.2 0.3 0.4 0.5 0.6 0 45 90 φ Shear stres For a unit stress, σ z
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Edge Dislocation Edge dislocation line Extra half plane of atoms
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Edge Dislocation Dislocation glide
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Role of Dislocations in Plastic Deformation τ τ
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Transmission Electron Microscopy (TEM) Image of a Collection of Dislocations
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Burgers and Burgers Vector for an Edge Dislocation Dislocation line Start=End Burgers Vector End Start
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Types of Dislocations Edge Screw Mixed Loop
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Rug Axis of the ripple Direction of applied force Ripple in the Rug Analogy to a Dislocation Dislocation line Burgers vector
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Tensile axis Force Normal Slip plane Slip direction τ = σ cos θ cos φ Extensive variable Intensive variable F s /A s = ( F / A )cos θ cos φ
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Chapter5_lecture - Chapter 5 Linear, Planar, and Volume...

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