Los Alamos NATIONAL LABORATORY LA-UR- Approved for public release; distribution is unlimited. Title: Author(s): Submitted to: Form 836 (10/96) Los Alamos National Laboratory, an affirmative action/equal opportunity employer, is operated by the University of California for the U.S. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the U.S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for U.S. Government purposes. Los Alamos National Laboratory requests that the publisher identify this article as work performed under the auspices of the U.S. Department of Energy. Los Alamos National Laboratory strongly supports academic freedom and a researcher’s right to publish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness. 99-3435 Damage Initialization for Modeling of Dynamic Shear Banding Michael B. Prime, ESA-EA Rick L. Martineau, DX-5 Carl R. Necker, Jr., MST-6 ASME Mechanics and Materials Conference June 27-30, 1999, Blacksburg, Virginia USA
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Los AlamosNATIONAL LABORATORY
LA-UR-Approved for public release;distribution is unlimited.
Title:
Author(s):
Submitted to:
Form 836 (10/96)
Los Alamos National Laboratory, an affirmative action/equal opportunity employer, is operated by the University of California for the U.S.Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the U.S. Governmentretains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for U.S.Government purposes. Los Alamos National Laboratory requests that the publisher identify this article as work performed under theauspices of the U.S. Department of Energy. Los Alamos National Laboratory strongly supports academic freedom and a researcher’s right topublish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness.
99-3435
Damage Initialization for Modeling of Dynamic Shear Banding
Michael B. Prime, ESA-EARick L. Martineau, DX-5Carl R. Necker, Jr., MST-6
ASME Mechanics and Materials Conference June 27-30, 1999,Blacksburg, Virginia USA
ASME 1999ASME 1999
Modeling of Dynamic Shear Banding
Michael B. Prime1, R. L. Martineau2, & C. R. Necker, Jr3.
Los Alamos National LaboratoryEngineering Sciences & Applications
9.2 mm) wall, inner copper cylinder
ASME 1999ASME 1999
Engineering Analysis
Los Alamos National LaboratoryEngineering Sciences & Applications
ASME 1999Experiments - Diagnostics
ASME 1999
• Diagnostics:g– Fast framing camera (used 3-5 s frame time)
– Visar/Fabry-Perot interferometry
• Uses:– Validate finite element model with disps, velocities
– Observe shear banding formation on surface, final fracture
Engineering Analysis
Los Alamos National LaboratoryEngineering Sciences & Applications
ASME 1999Experiments - Recovered Fragments
ASME 1999
Failed shear band
Shear band
30 mm
• Cross-Section of soft-catch fragment, smaller cylinders only
• Many Shear bands evident
• Data– Shear band spacing
– fragment thickness gives upper bound on final failure
Engineering Analysis
Los Alamos National LaboratoryEngineering Sciences & Applications
failure
ASME 1999Experiments - Recovered Fragments
ASME 1999
• Same test, 20% thicker cylinder
• Void plane
• Less developed shear bandsLess developed shear bands
• lower strain at failure
Engineering Analysis
Los Alamos National LaboratoryEngineering Sciences & Applications
ASME 1999Modeling Approach
ASME 1999
• Axisymmetric FEM• Axisymmetric FEM model
– ABAQUS Explicit + VUMAT
– Adiabatic Heatingg
– HE burn, JWL EOS
– Matches data
– Wrong plane for shear bands
Engineering Analysis
Los Alamos National LaboratoryEngineering Sciences & Applications
ASME 1999Plane Strain Model
ASME 1999
• Pressure load instead of HE elements– carefully extracted from axisymmetric contact forces
• Refined mesh to capture shear banding• Refined mesh to capture shear banding
Engineering Analysis
Los Alamos National LaboratoryEngineering Sciences & Applications
ASME 1999
Quantifying Model ResultsASME 1999
•Track final fragment thicknesses•Plateaus quickly•Unambiguous•No fragments for energetic shots
•tmin/tmax = 0.9•Compare with optical record of perturbation appearance
Engineering Analysis
Los Alamos National LaboratoryEngineering Sciences & Applications
perturbation appearance
ASME 1999Model Predictions - Johnson-Cook
ASME 1999
4
4.5
experiment
JC
Big cylinders
necking too late
2.5
3
3.5
r/r0
at
neck
JC necking too late
2
thin thick
0.17
0.18
Small Cylinders
0 11
0.12
0.13
0.14
0.15
0.16
ag
me
nt t
hic
kne
ss
(in
ch)
i t
fragments too thin (=necking too late)
0.08
0.09
0.1
0.11
3 4
fra experiment
J-C
FEM with Johnson-Cook constitutive law predicts shear banding too late in time
Engineering Analysis
Los Alamos National LaboratoryEngineering Sciences & Applications
ASME 1999MTS constitutive model
ASME 1999
• Physically realistic • Mechanical Threshold Stress is internal state variable
(as compared to just strain strain rate temperature)(as compared to just strain, strain rate, temperature)
• Evolution controlled by thermally activated interaction of dislocations with obstacles
ˆ)(
ˆ)(
TSTS ia 00
),(),(
TSTSi
is shear modulus = f(T)a is athermal, rate independent term (interaction of dislocations with long-range barriers like g b ’s)dislocations with long range barriers, like g.b. s)