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Transcript
Ideal Mechanical
Strength
Lindsay O’Brien, Course 22
9/27/12
Clarification of Variables
Variable
Units
Description
eV/atom
Binding energy per atom
--
Shear elastic strain
--
Hydrostatic invariant
GPa
Shear modulus
GPa
Bulk modulus
m2
Slip plane area
--
Bravais translational vector
energy/area
Generalized stacking fault
energy/area
Unstable stacking energy
Potential Learning Landscape
Metallic Bonding
Ideal Strength
Dislocations
• Explanation of Metal
Properties
• Metastable State of
Matter
• Binding Energy
• Potential Energy
Landscape
• Thought Experiment
Versus Frenkel
Sinusoidal
• Shear Modulus G,
Bulk Modulus B
• Types of Dislocations
• Explanation of
Strength
Discrepancies
Potential Energy Landscape
Activation
Energy
Turning Point
Things to Remember:
• First derivative of potential is force
• Force = 0 corresponds to minimum or saddle
point
• When the second derivative of potential is zero, you’re
at a turning point
Concave
Convex
http://www.engr.ucsb.edu/~shell/che210d/Exploring_the_energy_landscape.pdf
Shear and Bulk Moduli
Hydrostatic!
Measurement of Ideal Stress
• Assumptions
• Perfect lattice with no defects
• Temperature = 0 K
Oh no!
ɛ hydro
ɛ shear
Prove it!
• Electron glue is local
(only care about atomic
planes directly below and
above)
Further Simplification
Small Deformation (Small x)
Large Deformation (Large x)
Thanks!