Comparative Analysis of Microstructural Defects in Monocrystalline Copper:
Comparative Analysis of Microstructural Defects in Monocrystalline Copper: Shock
Compression Versus Quasi-isentropic Compression
H. Jarmakani, M. Meyers, M. Schneider, B. Cao and B. Kad, Materials Science and Engineering, UCSD, La Jolla, CA.
Mc Naney, J Nguyen, and D. Orilkowsi, Lawrence Livermore National Laboratory, Livermore, CA.
Understanding deformation mechanisms of  Cu
under various high-pressure and high-strain rate loading
Develop constitutive models to determine slip-twinning
transition in Quasi-ICE and shock compression.
The Prenston-Tonks-Wallace (PTW) constitutive description is used to
determine critical twinning pressure in both shock and quasi-isentropic
PTW equation takes into account both thermal activation regime and
dislocation drag regimes.
The instantaneous flow stress is given by:
Slices cut from
Cell size vs. pressure: quasi-ICE,
laser shock and flyer-plate
Dislocation cell size vs. distance from sample free surface:
s s 0 y ln 1 1 exp p
s 0 y
s 0 y exp p s 1
Where s and yare work hardening saturation stress and yield stress, respectively.
s0 is the value of taken at zero temperature, , are the strain and work
hardening rate, respectively, and p is a dimensionless material parameter.
Thermal Activation Regime
Strain-rate regimes in shock and Quasi
s s0 s0 s erf T ln
y y0 y0 y erf T ln
Strong Shock Regime
Flow stress is normalized to shear modulus and twinning threshold
assumed to vary with pressure:
G T , P
Source: M.Pullington et al., Discovery.
Temperature rise in shock and ICE (gas-gun)
Hardness, Temp. vs. Peak Pressure: Gas-gun quasi-ice
Dislocation sell size vs. distance from sample free surface:
TRANSMISSION ELECTRON MICROSCOPY (TEM) OF KEY FEARURES AT:
Twinning at 52GPa
Dislocated laths at 34GPa
Stacking faults at 26GPa
Flow stress vs. peak pressure: gas-gun modeling
CONCLUSIONS AND FUTURE WORK
Twins/laths at 59GPa
Dislocation cells and stacking
faults at 24GPa
Dislocation cells at 18GPa
Micro-twins at 57GPa
Stacking faults at 30GPa
Flow stress vs. peak pressure: laser modeling
(Experimental data unavailable)
Micro-twins at 55GPa
Staking faults at 40GPa
Dislocation activity decreased away from impact surface in
TEM revealed twinning at higher pressures, stacking faults
and dislocated laths at intermediate pressures and mostly
dislocation cells at relatively lower pressures.
Modeling revealed twinning threshold lower for higherstrain rate compression experiments and reasonable
agreement with experimental data.
Future work will incorporate nanocrystalline materials (e.g.
nc Ni and nc Ni%Fe).
Understanding deformation mechanisms in nc materials:
Dislocation interactions with grain boundaries.
Grain boundary sliding.
Pressure effects on hardness.
Twinning thresholds modeling.
Molecular dynamics (MD), specifically LAMMPS, will be
used to simulate and study shock and high-strain-rate
phenomena in nc materials and compare with experiments.
High strain rate phenomena in bulk metallic glasses
(BMGs) will also be integrated into study.
Dislocation cells at 20GPa
This work was performed under the auspices of
the U.S. Department of Energy by University of
California, Lawrence Livermore National
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