How Bonds Break in Shear and Why It Matters

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How Bonds Break in Shearand Why It Matters

• Ju Li
• Ohio State University

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Shigenobu Ogata Osaka University, Japan
Sidney Yip Ting Zhu Krystyn J. Van Vliet Subra
Suresh M.I.T.
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basal plane
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Multiplane Generalized Stacking Fault Energy
n8

n1
n2
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Charge density distributions during affine shear
Cu
Al
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Charge density iso-surfaces during affine shear
Cu
Al
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Affine Shear Stress-Strain Curve
S. Ogata, J. Li and S. Yip, Science 298 (2002)
807.
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Anomalous Atomic Relaxation Patterns
sphere-in-glue muffin-tin embedded atom
hinged-rod
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Different Pressure-Hardening Behaviors
very anisotropic
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Plotting g1(x) vs. g8(x)
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• Abnormal ideal shear strength and abnormal
  intrinsic stacking fault energy of Al are two
  sides of the same coin - directional bonding.
• Non-shear stress components under the nano-
  indenter reach scale that can cause significant
  pressure-hardening.
• Because hardening is very anisotropic, effect
  cannot be easily ascertained without carrying out
  detailed calculations.

T. Zhu, J. Li, K.J. Van Vliet, S. Ogata, S. Yip,
S. Suresh, J. Mech. Phys. Solids (in print,
2003). http//164.107.79.177
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Theoretical Prediction of Onset of Yield
trz
trz, max
2-D Hertzian indentation theory
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Equivalence between Phonon Softening and
Stress-Strain Catastrophe
Direct MD Simulation at 10K
Static Phonon Dispersion Calculation
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Hydrostatic Tension of 3-D Mo Crystal
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J. Li, K.J. Van Vliet, T. Zhu, S. Yip and S.
Suresh Nature 418 (2002) 307. Phys. Rev. B 67
(2003) 104105.
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atomistic distribution
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How does a continuum wave evolve into an atomic
defect, e.g., dislocation or twin?
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2-D Morse potential solid
x
y
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Stage I Linear Growthcontinuum description
shape maintains, amplitude increases?-criterion
controls initiation
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Stage II Non-linear Growthcontinuum
description wave front steepens due to
nonlinearity
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Stage III Shear Shock Formationwave front
shrinks untilatomically sharp shock is formed
transfer continuum ? atomistic
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Stage IV Shock Arrested
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As length scale shrinks, ruggedness of atomic
energy landscape becomes visible. The atomically
sharp shock front will be arrested.
If three atomic layers can arrest the shock, it
is a twinning system. If not, and the shock
progresses to one layer, it is a dislocation
system.
Dislocation is the bounding rim of a one-layer
shear shock.
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Coupling between Chemistry and Mechanics
dry SiO2 nanorod
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SiO2 nanorod attacked by water
minimum energy paths