Summer Internship 2011
Peter M. Mancini
Los Alamos National Laboratory, XTD-1
Los Alamos, New Mexico USA
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LA-UR-11-04080
What is LANL?
• Los Alamos National Laboratory
• Founded in 1943 in Los Alamos, New Mexico
• Manhattan Project
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First Atomic Bombs
Fat Man
Little Boy
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What Do You Want To Do?
• Research
- Government/University Lab
- Novel topics, laboratory work environment, no right or
wrong answer
• Industry
- Quality control
- Improve/develop current designs
- Manufacturing
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Where Do You Live?
• Companies in your city/state
~ 75% of the interns at LANL are from New Mexico
Cheaper for the company: no travel expenses to go out there
Companies here in Florida:
Lockheed Martin (Orlando)
Siemens (Orlando)
Pratt and Whitney (West Palm Beach)
o
Certain hot spots for engineering
i.e. Southwest U.S. has Sandia, LANL, Lawrence-Livermore
National Lab
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Who Do You Know?
• Networking
- Find and meet people who have jobs in your desired field or
at the company you would like to work for
- Ask around for open positions that are often not posted on a
career website
• With the huge amount of “John Smiths” applying for
these positions, a personal recommendation to an
employer can do you wonders
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Stand Out
• Words from my mentor (who is also the recruiter for X-Division):
“I would take a student with a lower GPA from a decent, top 50
school with some research over a 4.0 from MIT with no real
experience.”
 Most kids weren’t exceptionally qualified
 Low GPA? No worries. There are openings for you
 Worked with a UF sophomore
 You may feel like you don’t know enough to contribute to the research, but
most of what you need for the job will be taught to you or you will have to
read up on in textbooks and papers
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Government Labs
•
•
•
•
Unique projects
Tons of interesting, optional lectures
Friendly work environment
Plenty of students (undergraduate and graduate) to
interact with
• Mentors to guide you in your research
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Adventures
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Overview of Project
Long Rod Penetrators (LRP) - armor-piercing ammunition generally
used as anti-tank rounds
 Uses high kinetic energy to penetrate target
KE  12 mV 2
 Applies large force over small area to significantly exceed target’s yield
strength
g
 Generally use Tungsten or Uranium alloys, due to high density (~18 cm3 )
Uniqueness of problem:
• Semi-infinite target to model final penetration
P  Lo
P
T
• No residual velocity
• Due to normal impact of penetrator, simulation can be run as a quarter of the
model
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Experimental Data
1.8
1.2
1.6
1
1.4
1.2
0.8
P/L
Experimental
1
Predicted
0.6
0.8
0.6
0.4
0.4
Penetration/Length (P/L) of
Tungsten Rod on RHA Steel Target
0.2
0
0
0
G. Silsby, Penetration of Semi-Infinite Steel Targets By Tungsten
Long Rods at 1.3 to 4.5 km/s, Eighth International Symposium on
Ballistics (October 1984)
0.2
2
4
Striking Velocity (km/s)
P  Lo
P
T
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PAGOSA
 PAGOSA is a multi-dimensional / multi-material Eulerian hydrocode

Accurately models high strain rate deformation

Staggered mesh (U V W at vertices, P ρ e Sik at cell centers)

Multi-material (arbitrary number of materials per cell)

Young’s interface reconstruction for each material in each cell
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PAGOSA Equations of State
• Void
• Ideal gas analytic equation
• Polynomial
• Mie-Grüneisen ( Us / Up )
• Osborne analytic
• Becker-Kistiakowsky-Wilson (BKW)
• SESAME, tabular EOS including phase changes
• Jones-Wilkins-Lee (JWL), analytic EOS for explosive materials
• Reactive High Explosive (HE) Burn Models : BKW-HE, JWL-HE
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PAGOSA Strength Models
• “Hydrodynamic” (no strength)
• Elastic-Perfectly-Plastic
• Johnson-Cook (JC)
• Modified Steinberg-Cochran-Guinan (mod SCG)
• Steinberg-Cochran-Guinan (SCG)
• Kospall (SCG with additional thermal softening terms)
• Preston-Tonks-Wallace (PTW)
• Modified Preston-Tonks-Wallace (mod PTW)
• Mechanical Threshold Stress (MTS)
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Example of Mesh…(1mm cell size)
RHA Armor
Void
Vo
Tungsten Penetrator
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Visual
Void
Target Interface
Penetrator
Model Space
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Mesh Convergence
• Decreasing cell size increases accuracy but also increases computational
run time
• Computational cost increases nonlinearly with decreasing cell size due to
several factors:
 Increased number of elements
 Decreased integration time steps
 Increased total number of integrations performed
 Communication between the parallel processors
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Mesh Convergence
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Equation of State Comparison
• Maintained constant strength model:
o Target – Elastic Perfectly Plastic
o Projectile – Elastic Perfectly Plastic
EOS Evaluated:
o Target – Us/Up, Polynomial
o Projectile – Us/Up, Polynomial
 Results relatively insensitive to EOS
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Flow Stress Models
Elastic Perfectly Plastic:
 Material is linearly elastic
 After yield, stress remains constant
with increasing load
 2 constants required for PAGOSA
Steinberg-Guinan and Johnson-Cook:
 Includes strain, pressure, and thermal softening
 Function of strain rate
 Accounts for strain hardening
 7 constants required for PAGOSA
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Strength Model Comparison
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Hole Diameter
Simulation of hole created
at 3.335 km/s
Differently sized hole diameters
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Simulation Examples
Simulations
• Low/High Velocity Shots
• Wave Propagation
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Low velocity: 1.291 km/s
*Time in microseconds (µs)*
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High Velocity: 4.525 km/s
*Time in microseconds (µs)*
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Wave Propagation
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Conclusions
•
1 mm cell size provides converged data in a reasonable run time.
Equation of State
Low Velocity
Projectile:
Target:
Polynomial
Mie-Grüneisen (UsUp)
High Velocity
Polynomial
Mie-Grüneisen (UsUp)
Strength Form
Low Velocity
Projectile:
Target:
•
•
•
•
Johnson-Cook
Johnson-Cook
High Velocity
Steinberg-Guinan
Elastic Perfectly Plastic
Simulation data are generally insensitive of EOS
At low velocities, results are sensitive to strength model
At high velocities (> 3 km/s), the different models converge within 2% of each
other and 5% of experimental data
Hydrocode simulation accurately models actual physics of the penetration, i.e.
residual material and stress wave propagation
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Future Work
 Run more data points to get a smooth curve
 Search for different and/or more accurate EOS, strength, and fracture
models, i.e. SESAME, Osborne, Johnson-Cook Damage
 Compare other experimental data.
 Add different shaped tips to penetrator to see how it effects penetration
geometry (depth, hole diameter, etc..)
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References
1. Wayne N. Weseloh, Sean P. Clancy, and James W. Painter, “PAGOSA
Physics Manual,” Los Alamos National Laboratory report LA-14425-M
(August 2010).
2. Wayne N. Weseloh, “PAGOSA Sample Problems,” Los Alamos National
Laboratory report LA-UR-05-6514 (August 2005).
3. G. Silsby, Penetration of Semi-Infinite Steel Targets By Tungsten Long
Rods at 1.3 to 4.5 km/s, Eighth International Symposium on
Ballistics (October 1984)
4. Marc A. Meyers, “Dynamic Behavior of Materials,” John Wiley & Sons,
Inc., 1994
5. Private communication, Shuh-Rong Chen (MST) and Wayne Weseloh
(XTD-1), 8 July 2011
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Outline
•
Introduction / Overview
•
PAGOSA
•
Mesh Convergence
•
EOS Comparison
•
Strength Model Comparison
•
Simulation Examples
http://www.dtc.army.mil/tts/1997/proceed/walton/walton.html
i.
Low/High Velocity Shots
ii. Wave Propagation
•
Conclusions
•
Future Work
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Materials
Experimental: Silsby (1984)
Simulation: PAGOSA
Projectile:
Projectile:
• 90W-7Ni-3Fe alloy
• matname = “Tungsten”
• Yield Strength - 0.0119 Mbar (174 ksi)
• Yield Strength - 0.0119 Mbar (174 ksi)
• Rockwell C 40.6 hardness
• Shear Modulus - 1.6 Mbar
g
g
• Density – 17.3 cm3
• Density – 17.3 cm3
• L/D = 23
- Initial Length (L) – 15.83 cm
- Diameter (D) – 0.683 cm
• L/D = 23
- Initial Length (L) – 15.83 cm
- Diameter (D) – 0.683 cm
Target:
• Rolled homogeneous armor (RHA)
• 6 inch plate – BHN 270.4
• 8 inch plate – BHN 231.6
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Target:
• 6 inch plate - BNH 270.4
 Yield Strength - 0.00917 (133 ksi)
 Shear Modulus – 0.88 (88 GPa)
• 8 inch plate - BNH 231.6
 Yield Strength - 0.007 (101 ksi)
 Shear Modulus – 0.88 (88 GPa)
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