Chapter5 - Chapter 5 Linear, Planar, and Volume Defects...

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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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Burgers Vectors and Slip in FCC Crystals These vectors are the Burgers vectors in the FCC system since they connect the atoms of closest approach. { } 111 These planes correspond to the planes of densest packing in the FCC structure. 110 2 o a
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Burgers Vectors and Slip in FCC Crystals 110 2 o a 110 2 o a 011 2 o a 2 o a 101 2 o a 101 2 o a
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Burgers Vectors and Slip in FCC Crystals These vectors are the Burgers vectors in the FCC system since they connect the atoms of closest approach. { } 111 These planes correspond to the planes of densest packing in the FCC structure. 110 2 o a
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Tetrahedron in a Cubic Unit Cell- Geometry of FCC Deformation x y z Geometry There are 4 faces on the tetrahedron these are the dense packed planes The six edges of the tetrahedron are the directions of closest approach of the atoms
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Tetrahedron in a Cubic Unit Cell- Geometry of FCC Deformation x y z Using intercepts the plane is (111) In a cubic crystal the vector normal to the plane has the same indices as the plane.
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This note was uploaded on 09/12/2011 for the course MSE 2001 taught by Professor Tannebaum during the Fall '08 term at Georgia Institute of Technology.

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Chapter5 - Chapter 5 Linear, Planar, and Volume Defects...

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