Lecture 8 Dislocations

Lecture 8 Dislocations - Elasticity dislocations Image...

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Elasticity –dislocations Image forces
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Comment about forces between dislocations Stress field for a dislocation scales as b 1 For other dislocation, displacement to create is b 2 Nett force therefore has to scale as b 1 b 2 ; b 2 for an image force Discuss case of a dislocation at an interface Strain energy density scales with elastic constants, decays with distance from interface At interface: More energy in material with larger elastic moduli Move dislocation away from interface Reduces energy stored in material of larger moduli Dislocation standoff – analogous to image force but now repulsive Concept is general Strains will tend to localize in material with lower elastic constants – less energy Example of Energy Balance Pseudomorphic Growth Consider an example, pseudomorphic growth. We consider a thin layer on top of a bulk material. We will assume little to no strain in the substrate (an approximation). If there is a difference in the lattice parameters if the layer is thin enough it can expand/contract to fit the bulk. If we do this in 1D (along z), we get back to the problem of a bar. The energy per unit
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This note was uploaded on 04/13/2010 for the course MAT SCI 404 taught by Professor Matsci during the Winter '10 term at Northwestern.

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Lecture 8 Dislocations - Elasticity dislocations Image...

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