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Kristen John
Graduate Student, Caltech, Aerospace Engineering
Fellowship Field of Study: Properties of Materials Under Extreme Conditions
Tuesday, June 25 th , 2013
2013 DOE NNSA SSGF Annual Program Review
Santa Fe, New Mexico

Outline
• Motivation
• Objectives
• Omega Laser RT Experiments
• Omega Laser RM Experiments
• Caltech Gas Gun Experiments
• Multiscale Model Validation
• Future Work
• References

Motivation
• Question: What’s the most pressing scientific
challenge facing humanity?
• Stephen Hawking’s Answer: producing electricity
from fusion energy
• The prize is enormous: a near-limitless, pollution-free,
cheap source of energy that would power human
development for many centuries to come.

Hypervelocity impacts,
space shielding
Astrophysics,
Planetary impacts, bodies
ICF, Fusion Energy
RTI’s
Iron,
Earth core conditions (3.5 Mbar)
phase transition
strength at high pressures
New measurement
of strength

Objectives
Omega Laser
Experiments
Multiscale
Model
Caltech Gas
Gun
Experiments

Objectives
Omega Laser
Experiments
-measure of strength at high
pressures for Ta, Fe, and other
materials
Caltech Gas
Gun
Experiments
-measure of strength using
growth of RTI for soft materials
Multiscale
Model
-validate
experiments and
model
-run simulations
to aid in design
of future
experiments
-predict
material
behavior

Omega Laser Experiments

A Collaboration w/ LLNL
• Lawrence Livermore National Laboratory (LLNL)
• My group: NIF Directorate; ICF & HED Science
• Collaborators: Hye-Sook Park, Bruce Remington, Jon Belof,
Rob Cavallo, Brian Maddox
• Practicum: Summer 2011
• Learn how to design laser experiments which will be used to
study the solid-state material properties under high pressure
and high strain rates.
• Participate in laser experiments on the Omega Laser at the
Laboratory for Laser Energetics (LLE) at the University of
Rochester and at the National Ignition Facility (NIF) at LLNL.
• Analyze data from these experiments.

Omega Experience
• Experiments I participated in over
the summer
• RT
• DblPulse
• LattDyn, DynDiff
• ASCEL
• Had to learn how Omega worked
• Diagnostics
• Operations
• Preparation
• OLUG
• Metrology
• Readiness Review Meetings
• Weekly LowT Meetings
• Trips to LLNL

Omega
Rayleigh-Taylor (RT) Laser
Experiments

Omega RT Laser Experiments
• What?
• Studying the strength of Iron & Tantalum at high pressures
(>1 Mbar) and high strain rates (>100 s -1 )
• Quasi-isentropic ramped drive
• Utilizes a reservoir-gap-sample configuration
• Where?
• Omega & Omega EP at LLE in Rochester, NY
• When?
• Past: August 2011, December 2011, August 2012, April 2013
• Future: August 2013

Omega RT Laser Experiments
• Why?
• To determine the strength of Tantalum & Iron (and
eventually other materials) at high pressures and high
strain rates
• Stabilize/reduce RTI growth (via the material strength)
• How?
• By measuring the growth of Rayleigh Taylor instabilities
• Accomplished by putting a ripple in the material and
measuring the growth of the ripple
• Measure the RT growth using face-on radiography

Rayleigh Taylor Instabilities (RTI)
• Instability that occurs when lighter fluid
pushes heavy fluid
• Determine the strength of Ta, Fe at high
pressures and high strain rates by
measuring the growth of RTI
• Accomplished by putting ripple in material
and measuring the growth of the ripple
• Measure RT growth using face-on radiography
λ= 50 µm
η=2 µm
Ref: ICETaRT-09A, HS Park
Ref: SCCM 2011, Ta, HS Park
• Strength can stabilize, reduce RTI growth
Ref: ICETaRT-11A Shot Plan, HS Park

Omega Laser
Ref: Paul Drake, HEDP Summer School
• one of the most powerful and highest
energy lasers in the world
• 60-beam ultraviolet frequency-tripled
neodymium glass laser
• capable of delivering 30 kilojoules at up
to 60 terawatts onto a target less than 1
millimeter in diameter

Experimental Platform
• Laser-driven high pressure platform to compress materials
under near isentropic conditions by ramp compression
• The ripple sample is driven by a ramped drive from a
reservoir-gap-sample configuration. The ripple growth
from the Rayleigh-Taylor instability is measured using faceon
radiography.
• Observational parameter – RTI
• Compare growth measurements with constitutive strength
models
• Deformation under compression
• Macroscopically: can change their yield strength, tensile
strength, ductility, toughness, work hardening
• Microscopically: can change atomic lattice arrangement;
lattice structure can undergo phase transitions when
subjected to high P, T; micro changes have impact on macro

Omega Experiments: Design
• Laser (up to 20 kJ of laser energy) drives strong shock through
low-Z reservoir, which unloads across a vacuum gap, and
stagnates on the sample, generating a nearly isentropic pressure
profile in the sample
Ref: SCCM 2011, Ta, HS Park

Reservoir-Gap-Sample
• Up to 20 kJ of laser energy creates a ramp drive in a reservoir-gap configuration that is
mounted on the side of a hohlraum.
• Reservoir :
• 25 μm thick beryllium ablator
• 200 μm thick 12.5% bromine-doped polystyrene
• Gap
• 400 μm gap
• Ta sample
• 50 μm mean substrate thickness
• preimposed sinusoidal ripple on the driven side
• wavelengths of 50 to 100 μm and 2 μm amplitudes
• sample backed by a 100 μm thick LiF tamper
• Backlighter
• ripple growth measured by face-on radiography
• to probe thickness of sample, we developed a high energy backlighter using the highintensity
short pulse lasers
• for Omega experiment, 22 keV energy was optimal to produce best contrast from our
ripples
• since ripples are 1-D features, we utilize a micro-flag edge-on a 1-D x-ray source aligned to
ripple orientation to generate a bright x-ray source

Omega Experiments
• ICETaRT-11A (8/4/2011)
• Study of Ta material strength dependence on the sample grain sizes
• Why Ta? High density, high melting point, relatively high ductility,
interesting to impact engineering area
• ICETaRT-12B (8/21/2012)
• Study single crystal and Ta material strength at high
strain rates (side-by-side comparison)
• Study Ta material strength and Rayleigh-Taylor growth in a
multimode configuration.
• ICEIronRT-12A (8/22/2012)
• Study of Fe material strength at high strain rates.

Omega Experiments:
Preliminary Results
• Lineouts of the driven and undriven
ripples from λ=50μm ripple region.
The driven ripple growth is evident.
• Ta Rayleigh-Taylor growth factors as a
function of time. Omega data points
are the blue squares. Various material
strength models are plotted for
comparison.

Omega
Richtmyer-Meshkov (RM) Laser
Experiments

Laser Compression Recovery
Experiments for Measuring Strength
of Metals at High Pressures
• Collaborators: Caltech, LLNL, & General Atomics (GA)
Caltech
Aaron Stebner
Kristen John
G. Ravichandran
Bo Li
Brandon Runnels
Michael Ortiz
LLNL
Chris Wehrenberg
Brian Maddox
Bruce Remington
Hye-Sook Park
GA
Greg Randall
Mike Farrell
Paul Fitzsimmons
Abbas Nikroo
Support provided by DOE NNSA through the HEDLP program.

Omega RM Experiments
• Objective: to characterize the strength of metals at pressures
greater than 1 Mbar
• New Richtmyer-Meshkov (RM) and Rayleigh-Taylor (RT)
instability experiment platforms
• Being developed for laser compression recovery experiments to
characterize instabilities, yield strength, and phase transformations
at high pressures
• The multi-scale strength model and code (Eureka) of the Ortiz
group is being used together with 1D hydrodynamic software
(Hyades) to design and analyze RM and RT experiments for Ta &
Fe using these new platforms.
• Through combined analysis of the numerical and empirical data,
fundamental understanding of Ta & Fe strength at high
pressures as it correlates to the development of RT and RM
instabilities, yield strength, and phase transformations will be
advanced.

Omega RM Experiments
• April Experiments
• We performed RM experiments on Ta targets with a single
wavelength rippled surface
• August Experiments
• We will study both Ta and Fe targets with a multi-mode ripple
pattern to study the non-linearity of the ripple growth. The
modes grow independently while the deformation is linear,
then couple in the non-linear growth regime.

Experimental Platform:
“Ride-Along” Recovery Tube
• The basis of the new experimental platforms is a universal “ridealong”
recovery tube.
• The reusable recovery tubes accommodate both RM and RT
target stack configurations developed by the LLNL team for
studying strength of materials at high pressure.
• The tubes are designed to allow these experiments to “ridealong”
next to a primary experiment that does not require all 60
of Omega’s beams. The tube geometries do not interfere with the
primary experiment, and one of the unused beams is used to
drive a shock wave through the target.
• Aerogel catchers enable post-shot target recovery and analysis.

Experimental Platform:
“Ride-Along” Recovery Tube
• Recovery Tube (Cross Section)
• Modeled using SolidWorks; machined at Caltech

Target Stacks
RM Target Stack
(Cross-Section)
RT Target Stack
(Cross-Section)

Target Fabrication
• Rippled surfaces are coined (by General Atomics) into the targets
and characterized pre and post shot. Deformation of the ripples
and changes in material microstructure will be used to
characterize the material strength and deformation mechanisms.
• Single and multimode ripple patterns are designed and coined
into the driven surface of Ta and Fe targets. Deformation of
multimode targets will be used to assess if the drive remained in
the linear vs. nonlinear instability growth, as the modes grow
independently in the linear regime, but become coupled in the
nonlinear regime.

Experiment Design via Simulations
• Experiments are designed by calibrating simulations to drive
shots of similar heat shields and ablators and then predicting
peak pressure and ripple growth as a function of laser energy.
• HYADES Simulations
• Cascade Applied Sciences Inc.
• Radiation hydrodynamics simulation codes for the design and
analysis of laboratory high energy-density experiments
• 1D simulations – design ablators, heat shields, laser energies
• Match VISAR/drive info to produce pressure, velocity, temp profiles
for Eureka
• Eureka Simulations
• Caltech multi-scale model (utilizes engineering model)
• 2D simulations - predict strength and ripple growth

HYADES Simulations
• 1D HYADES simulations are
calibrated to VISAR
measurements, then used to
design ablators, heat shields,
and laser energies.
• In calibrating 1D hydrodynamic
simulations, VISAR velocity
profiles and breakout times at
the rear surface of samples are
matched. Once calibrated, the
1D software is used to calculate
pressure, velocity, and
temperature profiles at the
Heat Shield – Ablator (RM) or
Heat Shield – Reservoir (RT)
interface for laser energies that
correspond to peak pressures of
0.500 – 3.500 Mbar in the
targets.

Eureka Simulations
• Profiles from HYADES used as inputs to the multi-scale strength code
• 2D simulations are run:
• to study predictions of strength
• to ensure the expected ripple growth at the target surfaces will be measurable
in the post-shot target analyses
• to gage limitations in recovery of targets, such as critical energies for melt and
spallation
t = 0.0 ns t = 21.6 ns t = 38.4 ns
2D Eureka simulations predicting strength and ripple growth (GF = 1.4) for the 120 J RM shot.

Target Characterization
• Characterization of the ripple
pattern and microstructure is
done pre- and post-shot using
Wyko
• Provides growth factor
measurements -> used to
gage strength of material
• Insight into active
deformation mechanisms in
metals at pressures 1-4 Mbar
• Comparison with simulated
predictions also validates the
models and experiment
design.
• Post shot simulations used to quantify the drives experienced by
the targets and to correlate the drive characteristics to material
strength including analysis of the role of RT/RM instabilities and
phase transformations.
Characterization of peak-to-valley (PV) amplitudes of ripples

Target Characterization
• As was done for driven
copper (shown left),
microscopy comparing
pre and post shot
microstructures to
characterize dislocation
density, slip system
activity, grain growth,
and twinning is being
performed.
Slip system identification Twin identification
Myers, M.A. et al. Acta Mat. 2003 51 1211-1228.
• White light
interferometry is used to
characterize the ripple
patterns pre and post
shot. From these
measurements, total
growth factor may be
analyzed and used to
gage trends in the
strength of the material.
+70
0
-50
μm

Growth Factor
Analysis Procedure
1. Ripple peaks & valleys are
identified in pre and post shot
interferometry measurements.
2. Wave heights are calculated by
averaging the distance between
neighbor peaks and valleys.
3. Growth factors are assessed by
normalizing post shot wave by
preshot wave heights.
4. Error of the growth factors is
assessed using the mean and
standard deviation of multiple
“line-outs” across the driven
sample.

Simulation & Experimental Results
Shot
Energy (J)
Request/
Actual
Laser λ= 350 nm, 1 ns pulse
800 μm diameter spot
Predicted
Peak
Pressure:
HYADES
(Mbar)
Measured
Growth
Factor
Value(err)
Predicted
Growth Factor:
EUREKA
250/252.9 3.41 1.97(3) NA
200/202.3 2.68 1.72(3) NA
150/153.5 1.96 1.58(7) 1.60
120/118.9 1.52 1.43(6) 1.41
100/95.4 1.23 1.43(4) 1.38
70/56.6 0.98 1.26(4) 1.13
• Resulting expected laser energy – peak pressure relations calculated
using HYADES for our April 26, 2013 RM experiments are listed
together with predicted and measured growth factors.

Simulation & Experimental Results
Peak growth factors exhibited by Ta. The experimental
observations agree with simulated predictions of strength trends.

Caltech Gas Gun Experiments

Gas Gun Experiments: Background
• Goal: Impact sample with ripples, watch ripple
growth, correlate to strength
• Goal: to be able to reproduce RTI’s in an
experimental setup
• Resulting instabilities to be photographed to visually
determine presence of these instabilities
• Can we see growth of instabilities?
• Show that RTI are reproducible in consecutive experiments
• Recreate Omega experiments at Caltech
• Material?
• Ballistic gelatin

Gas Gun Experiments: Objectives
• Mission Statement: Correlate strength to the growth of the
Rayleigh-Taylor instability by recreating the Omega RT
experiments at Caltech.
• Advance the understanding of the current mechanics
exhibited in experiments
• Show through experiments that correlation exists between strength
and ripple growth/RTI
• Show that increasing strength suppresses growth
• Show effects of strain rates vs. growth
• Use different materials to begin understanding other
mechanics in experiments
• Potentially use soft crystalline material
• Determine effect of crystal structure/dislocations on growth
• Surface to volume issues; size scale effects

Gas Gun Experiments: Setup

Computer
& Software
Lighting
Catching
Mechanism
LED Trigger
Pressure
Gauge
Camera
Holding Mechanism,
Gel Samples,
Projectile
Gas Gun
Oscilloscope

Gas Gun
• Dynamic Materials Testing Facility
• sub-basement of Guggenheim
• Gas gun (setup to use air or helium)
• A projectile-firing gun powered by compressed gas
• Impact speeds: 5 to 200 m/s
• Projectile masses up to 2 kg
• Operations
• How it works…

Lighting & Catching Mechanism
Lighting:
• Can’t melt sample
• Aperture limitations => lots of light
• Future: fluorescent
Catching
Mechanism:
• To stop
projectile
• To catch
samples

Gel Samples
• SolidWorks
• 3D Printer
• Making ballistic gelatin
• Gel cube: 1 in x 1 in 1 in
• The perfect ripples
• 8 ripples
• Dimensions:
• λ = 1/8 in = .125 in = .3175 cm
• η = .458 cm
η=.458 cm
λ=.3175 cm

Gel Concentrations
• Goal
• to show ripple growth
• to see effect of strength on ripple
growth
• Ballistic Gelatin ingredients:
• Water
• Gel powder packets
• refined from any collagen-based tissue
• 1 packet = .25 oz. = 7 grams
• Concentrations
• C8: 1 cup cold water, 1 cup hot water,
8 gel packets
• C12: 1 cup cold water, 1 cup hot water,
12 gel packets
• C12 is 1.5 times “stronger”

Gas Gun Experiments:
Operating Conditions
• Pressure & velocity – 10 psi (12.5 m/s), 20 psi (22.3 m/s)
• Gel Samples: C8, C12 (C12 is 1.5 x stronger)
• Gas: air
• Projectile: metal, 40.13 mm long, 1 inch diameter
• Lens zoom: 200 mm (3.6x)
• fps: 1000-2000 fps
• Holding Mechanism: clamped metal impact plate

Gas Gun Experiments: Video

Gas Gun Experiments:
Preliminary Results
V1
~10 psi
~12.5 m/s
V2
~20 psi
~22.3 m/s
C8 (Softer)
C12 (Stiffer)
Data 1 Data 2 Data 3 Data 1 Data 2 Data 3
test5 (9/11) test6 (9/11) test9 (9/12) test2 (9/11) test7 (9/11) test13 (9/12)
test15 (9/12) test18 (9/13) N/A test16 (9/12) test17 (9/12) N/A
Concentrations
-C8: 1 cup cold water, 1 cup hot water, 8 gel packets
-C12: 1 cup cold water, 1 cup hot water, 12 gel packets
-C12 is 1.5 times “stronger”

Ripple Growth
C8V1
C12V1
C8V2
C12V2

Ripple Growth
GF=2.2
GF=1.4
GF=2.6
GF=1.8
Growth factor is the ratio of the ripple amplitude to its initial value
GF = perturbed amplitude / initial amplitude
GF = ηfinal/ηinitial

Ripple Growth
Stiffer
GF=2.2
Faster
GF=1.4
Faster
Stiffer
GF=2.6
GF=1.8
-faster impact = more growth
-stiffer material = less growth

Ripple Growth
C8V1
GFavg=2.3
C12V1
GFavg=1.4
GF=2.4 GF=2.2 GF=1.4 GF=1.4
C8V2
GFavg=2.6
C12V2
GFavg=1.9
GF=2.6 GF=2.6 GF=2.0 GF=1.8

Growth Factor
C8V1
GF=2.3
C8V2
GF=2.6
C12V1
GF=1.4
C12V2
GF=1.9

Multiscale Model Validation

Multi-scale Model
• Multi-scale dynamic strength model
• Use this to compare to experimental strength data
• Use this to improve design of experiments, and thus
improve model itself
• How does it compare?
• Model for Tantalum, Iron, other metals
• Validation for Omega Experiments LLNL interest
• Validation for Caltech Experiments
• Validation for model
• Validation against other experiments (pRad, etc)

Multiscale Model: Objectives
• Mission Statement: Use multiscale model to
understand/validate results of Omega experiments,
and to aid in design of future experiments.
• Understand mechanics effects on growth
• Dislocation dynamics effects
• Diffraction effects
• Predict/plot simulations vs. experiments
• Understand material choice options for experiments
• What is max shear modulus that will still be able to create
exp. in lab

Simulation: Single Ripple
RM – 200J

Simulation: Multimode Ripple
RM – 150J

Simulation Results
Peak growth factors vs.
laser energy
Nodal Displacement Analysis
GF vs. time

Melt Layer Analysis
• LLNL Question: What is the critical length scale for a
melt layer adversely affecting ripple growth?
• OTM simulations of RTI tests using the variational
thermomechanical coupling material model
• OTM – Optimal Transportation Meshfree method for
simulating general solid flows
• variational thermomechanical coupling material
model – Bo Li

Slide Courtesy of Bo Li

OTM simulation of the RTI tests
with or w/o melted layer
Two drivers calculated by HYADES rad-hydro code:
(Driver 1 – 800 kbar)
(Driver 2 – 1.2 Mbar)
Velocity[um/s] vs. Time [s] as the driver for the OTM simulations of RTI
Courtesy of Bo Li

OTM simulation of the RTI tests
with or w/o melted layer
(Driver 1) (Driver 2)
OTM simulation of the RTI tests with or w/o melted layer, in both movies: Left ripple
without melted layer; right ripple with a 10um melted layer at the bottom.
Courtesy of Bo Li

OTM simulation of the RTI tests
with or w/o melted layer
Conclusion:
• The peak pressure calculated in the OTM
simulations matches well with the results from
Hyades, i.e., 800kbar with driver 1 and 1.2Mbar
under driver 2;
• Ripple grows using both drivers and growth factor
increases as the intensity of the driver increases;
• Melted layer doesn’t affect the ripple growth.
Courtesy of Bo Li

Future Work
Gas Gun
Experiments
Multiscale
Model
Validation
Omega
Experiments

Future Work – Gas Gun Experiments
• Other materials besides gelatin
• Tin
• Soft metals
• Poor metals
• melting and boiling points are generally lower than that of
the transition metals, electronegativity higher, and they are
also softer
• Other Materials? Indium? Suggestions?
• Need EOS
• Use multiscale model as tool to decide what meaningful
experiments to perform
• Are ripples necessary? Can we use nano-indenter to create
other shapes that will give us the same result?

Future Work – Omega Experiments
• August Ride-along Experiment at LLE
• Ta, Fe
• RM shots
• Multimode configuration
• Recovery tube design modeling, construction
• Assembly
• Microscope analysis of Ta samples
• Catcher material experiment
• Post experiment analysis
• Won’t have drive profile
• Can use multiscale model to estimate it

Future Work – Multiscale Model
• August Omega Experiments analysis
• Pre-experiment predictions of growth
• Post experiment analysis of drive
• Iron – EOS
• Tin – EOS
• Parametric studies of drives
• Sensitivity analysis

References
• Park, H. S., Barton, N. et al., AIP Conf. Proc. 1426, 1371, 2012. Experimental results of tantalum
material strength at high pressure and high strain rate.
• Remington, B. et al., Met. Mat. Trans. A 35A, 2607, 2004. Materials Science Under Extreme
Conditions of Pressure and Strain Rate.
• Mikaelian, K. Phys. of Plasmas 17, 092701, 2010. Design of a Rayleigh–Taylor experiment to measure
strength at high pressures.
• Park, H. S., et al., Phys. of Plasmas 17, 056314, 2010. Strong stabilization of the Rayleigh-Taylor
instability by material strength at megabar pressures.
• Plechaty, C. ICETaRT-12B Readiness Review Slides, 2012.
• Plechaty, C. ICEIronRT-12A Readiness Review Slides, 2012.
• Park, H. S., Maddox, B. ICETaRT-11A Readiness Review Slides, 2011.
• Barton, N. et al., LLNL-JRNL-448591, 2010. A multi-scale strength model for extreme loading
conditions.
• Becker, R. et al., LLNL-TR-417075, 2009. A tantalum strength model using a multiscale approach:
version 2.
• Ortiz, M. PSAAP Peer Review Presentations, 2010 & 2011.
• Bhattacharya, K. PSAAP Peer Review Presentations, 2010 & 2011.
• Ravichandran, G. PSAAP Peer Review Presentations, 2011.
• Ortiz, M. and Stainier, L. Comput. Methods Appl. Mech. Engrg. 171 419-444, 1999. The variational
formulation of viscoplastic constitutive updates.
• Stainier, L., Cuitino, A.M., and Ortiz, M. Jrnl of Mech. Phys. of Solids 50 1511-1545, 2002. A
micromechanical model of hardening, rate sensitivity and thermal softening in bcc crystals

• G. Ravichandran
SSAP Poster Plug
• Laser Compression Recovery Experiments for
Measuring Strength of Metals at High Pressures

Acknowledgements
• DOE NNSA SSGF
• Caltech PSAAP
• LLE
• LLNL
• Krell Institute
• Lucille
• John Ziebarth
• James Corones
• Bill Cannon
• Michelle
• Other Fellows
• Advisor
• G. Ravichandran
• Mentor/“Go-to” Guy
• A. Stebner
• Modeling Guru
• Bo Li
• Committee
• K. Bhattacharya
• D. Kochmann
• M. Ortiz
• LLNL Collaborators
• Hye-Sook Park
• Bruce Remington
• Jon Belof
• Brian Maddox
• Chris Plechaty
• Chris Wehrenberg
• Caltech Folks
• Petros
• Cheryl
• Leslie

Back-up
• OTM simulations of RTI tests using the variational
thermomechanical coupling material model – Bo Li
• Omega RT Experiments Backup
• Gas Gun Details
• Gas Gun Air Test
• Multiscale Model Objectives

The variational thermomechanical
coupling material model
•Variational updates for a dissipative system:
⎡ ρ0
2
Φ[ ϕn→n+
1]
= ∫ n→n+
Wn
Fn
+
F
Ω ⎢ ϕ
1
+ (
1;
2
0
⎣2∆t
n
, T
n
, Z
n
⎤
) ⎥dV
⎦
• The incremental energy density:
Helmholtz free energy
Entropy per unit volume
Rate sensitivity, dissipation pseudopotential:
it determines the evolution
of the Taylor-Quinney factor.
Viscous dissipation potential

The variational thermomechanical
coupling material model
We assume an additive decomposition of the Helmholtz free energy
Stored energy
of plastic
work
Stored heat
Hardening Law
Thermal Softening
Elastic strain
energy EOS Deviatoric elastic response

The variational thermomechanical
coupling material model
Testing of the material model:
Stress–strain curves for pure polycrystalline Ta (no annealing), in the quasi-static range
(isothermal conditions) and dynamic range (adiabatic conditions) from Stainier and Ortiz
2010. Experimental results taken from Rittel et al. (2007).

OTM
• OTM – Optimal Transportation Meshfree
• Bo Li, PSAAP, Feb. 2010
• Optimal Transportation Meshfree (OTM) method for simulating
general solid flows including multi-body system and fracture and
fragmentation. The method combines concepts from Optimal
Transportation theory with material-point sampling and max-ent
meshfree interpolation. The proposed OTM method generalizes the
Benamou-Brenier differential formulation of optimal mass
transportation problems to problems including arbitrary geometries
and constitutive behavior. The OTM method enforces mass transport
and essential boundary conditions exactly and is free from tension
instabilities. The OTM method exactly conserves linear and angular
momentum and its convergence characteristics are verified in standard
benchmark problems. We also develop a dynamic contact algorithm
and energy-based material-point erosion algorithm for the simulation
of impact and discontinuous material failure phenomena. The
convergence of this algorithm to Griffith-fracture solutions is ensured
by means of Gamma convergence.

Omega RT Experiments Backup

Omega Experiments: Background
• ICETaRT Experiments
• Platform for RT Experiments
• study of more materials: Ta, Iron, V, Be
• ICE = isentropic compression experiments
• Quasi-isentropic drive used to study material properties such as strength, equation of
state, phase, and phase-transition kinetics under high pressure
• Measure Ta Rayleigh Taylor (RT) ripple growth to test models of Ta material
strength at >1 Mbar pressures and high strain rates >100 s -1
• Quasi-isentropic ramped drive
• To keep Ta sample below the melt temperature
• Utilizes a reservoir-gap-sample configuration
• Determine strength of Ta
• By measuring the growth of Rayleigh Taylor instabilities
• Measure the RT growth using face-on radiography
• Stabilize/reduce RTI growth (via the material strength)
• Deformation under compression
• Macroscopically: can change their yield strength, tensile strength, ductility, toughness,
work hardening
• Microscopically: can change atomic lattice arrangement; lattice structure can undergo
phase transitions when subjected to high P, T; micro changes have impact on macro

Gas Gun Details Backup

Camera & Lens
Camera Specifications:
• Model: Dalstar 64K1M
• Resolution: 240 x 240 pixels
• Pixel size: 56 μm x 56 μm
• Pixel Depth: 12-bits
• Frame rate: Up to 1 Million fps but limited to 17 images
• Technology: the ultra high speed is made possible by
masking a 1024 x 1024 image to allow only 1 in 17 frames
to be exposed at a time. The 17 frames are captured by
quickly shifting exposed frame pixels into the mask
area.
Lens:
• Model: Nikon DX AF-S Nikkor
• Focal Length Range : 55-200mm
• Zoom Ratio: 3.6x
• Aperture range: f/4 - 22 at 55 mm; f/5.6 - 32 at 200 mm

Computer & Software
• EPIX XCAP SOFTWARE
• “Ready-to-Run Image Analysis Software for PIXCI®
Imaging Boards”
• PIXCI frame grabber
• Image processing software
• Video capture or frame capture
• Hardware
• Installation
• Learning the software

Holding Mechanism & Projectile
Holding Mechanism:
• Impact plate
• Positioning of sample
• Timing/triggering
Projectile:
• 1 inch diameter
• Metal
• Length: 40.13 mm (1.58 inches)

LED Trigger & Scope
• aka….Velocity Measurements
• Oscilloscope records constantly varying signal voltages
• 2 LED sensors at end of barrel of gun
• As projectile passes sensors, it sets off trigger, scope
• Knowing length of projectile & Δt from scope, we can back out
velocity

Gas Gun: Air Test

Multiscale Model: Objectives
• Mission Statement: Use multiscale model to understand/validate results of
Omega experiments, and to aid in design of future experiments.
• Understand mechanics effects on growth
• Show correlation between strength and ripple growth/RTI
• Show effects of strain rates vs. growth
• Parametric study of drives
• Understand the effect of strain rates on the ripple growth; as we vary the strain rates,
how does that change GF, how does this compare with Omega experiment (ride-along)
results; provide estimate of drive for experiments
• Sensitivity analysis: understand what’s happening in ripple throughout impact; where is
growth happening; what parameters really effect ripple
• Dislocation dynamics effects
• Vary initial dislocation densities and see how that effects strain rates, growth factors
• Run numerical experiments where we keep geometry and drive the same, but change
dislocation in material
• Diffraction effects
• Simulate diffraction patterns with model
• In experiments, can we see RTI while still having strength, otherwise if it’s truly a fluid
then we can’t do diffraction, can’t see phase transformation
• Predict/plot simulations vs. experiments
• Understand material choice options for experiments
• What is max shear modulus that will still be able to create exp. in lab