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Small Scale Testing of Energetic Materials
Nick Glumac Mechanical Science and Engineering Department, UIUC
Energetics Workshop, Rutgers University February 28, 2008
Testing new energetics candidates – What do we want to know?
For an RM or propellantTemperature dependent ignition characteristics (kinetics)Rate of energy releaseRate of gas releaseSensitivity
For an HEDetonation performance
TNT equivalenceSensitivity
Why small scale testing?Much easier to make 1 mg than 1 g or 1 kgRapid screening of new materialsParametric studies
Elucidate underlying physicsKeep costs down
MaterialsHandlingCapital costs
Minimize handling and safety issues
Main issue w/small scale tests - SCALABILITY
Does what we learn from 50 mg test samples translate to 50 kg devices???
Do generic scaling laws really translate to the miniature scale?
Ideal explosives scale better than non-ideal explosives
Residence times and time/temperature histories typically do not.
Velocities don’t increase with charge diameter.
Scalability must be addressed before planning a matrix of small scale tests.
If results don’t scale directly, what good are small scale tests?
Reaction kinetics should remain independent of scale
Ignition delays, combustion times
Small scale results can validate key kinetics in numerical models, which can then address scaling issues
Critical Reaction Measurables for Novel (non-ideal) Energetic Materials
Ignition delay as a function of Temperature & rate of temperature increaseAmbient pressureAmbient oxidizer concentration
Rate of energy releaseSame independent variables as ignition
Information on reacting systemIntermediate species & sequence of appearanceTemperature distribution around system
Some small scale approaches of note using m < 1 g (incomplete list)
Brill’s T-jump + FTIR methodsDreizin’s hot wire and laser ignition techniquesZachariah hot wire in mass spectrometerSettles HE shadowgraph blast scaling Kuo, Parr and others using flame insertion
Our Approach to Measuring Relevant Kinetics
Heterogeneous shock tube1 mg sample sizeHigh heating rates 107/K sec.High temperatures possible (3000 – 4000 K)Microsecond or better time resolutionFully controllable oxidizer composition
Sample Trajectory Modeling
Dis
tanc
e fro
m E
ndw
all (
m)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Time (µs)
0 200 400 600 800 1000 1200 1400
Velo
city
(m/s
)
0
200
400
600
800
1000
1200
1400
1600
Tem
pera
ture
(K)
500
1000
1500
2000
2500
SHOCK
PARTICLES
Shoc
k H
its E
ndw
all
Shoc
k H
its P
artic
les
IGNITION
Shock Tube Diagnostics
High PowerFlashlamp
AbsorptionSpectrometerEmission
Spectrometer
Streak CameraSpectrograph
Photometer
3-colorPyrometer
High Speed Pyrometry & Photometry
Time (µs)
0 200 400 600 800 1000
Nor
mal
ized
Inte
nsity
(a.u
.)
0.0
0.5
1.0
1.5
2.0
Tem
pera
ture
(K)
1000
1500
2000
2500
3000
3500
3-color Temperauture
514 nm
InductionTime
Burn Time
Spectroscopic Measurements of Al & AlO
Time
Wav
elen
gth
2D Graph 1
Wavelength (nm)510 515 520 525
300 350 400 450 500
AlO C-X
Al
AlO B-X
AlO ∆v = -1
Ignition tests in shock tube
The shock tube is an extremely accurate means to evaluate ignition thresholds of advanced EMs.
Time (µs)
0 100 200 300 400 500 600
Nor
mal
ized
AlO
Em
issi
on In
tens
ity
0.0
0.2
0.4
0.6
0.8
1.0
1.2
n-AlH-2 (~2 µm)H-5 (~5 µm)10 µm
Small Scale Explosives Testing
Explosives testing is not confined to DoD and DoE labs
UIUC, PSU, Purdue, URI, and many others have well established explosives programs.Typically 50g and smaller tests are routineCompared to DoD facilities, university costs are typically lower and lead times are shorter.Still, tests are typically small scale, but diagnostic capabilities are extensive.
Instrumented Small Scale HE tests
Reaction front tracking
Emission/Absorption spectroscopy
Velocimetry in plume
Dynamic pressures for blast characterization
Blast Chamber
Light Source(s)UV, Vis, NIR
Imaging & PIV cameras Spectrometers
Pressure taps
Windows
Streakcamera
Key issues with small scale tests
Focus on fundamental physics immune to scaling – e.g. chemical kinetics
Detailed and accurate measurements of relevant parameters under relevant conditions in appropriate time scales
Modeling support to assist in scaling results
Test configuration
Vent
PETNBooster
RDX + 20%Al
Fireball
Fast KineticsSpectrometer
RDX
Al loosepowder
Case A: Al Powder in Detonator
Case B: Al powder outside HE
BEFORE AFTER
UIUC Fast Kinetics SpectrometerAndor FK Camera
Up to 128 spectra in a sequenceSpectra taken every 1 us
Custom f/1.4, volume phase holographic (VPH) grating (90% efficiency).
4 A resolution over 450 – 580 nm range
UV version f/2 10 A resolution 200-600 nm
Emission & Absorption Spectroscopy
Detailed spectral modelCalibrated by experimentTime-resolved or time integrated2σ temperature uncertainties below 150 K. Wavelength (nm)
508 510 512 514 516 518 520
Em
issi
on In
tens
ity (a
rb. u
nits
)
Experiment
Model: Fit to 3185 K
Shock Induced Ignition Curves: Al/MoO3 Alloys from NJIT
1500 K
Time (µs)
-1000 -800 -600 -400 -200 0 200
Nor
mal
ized
Inte
nsity
0.0
0.2
0.4
0.6
0.8
1.0 Nano-Al4:116:18:12.7 µm Al10 µm Al
Low Temperature Ignition Behind an Incident Shock
At 965 K, 4:1 and 8:1 alloys ignite within 200 us.
16:1 alloy shows a thermal signature, but at best incomplete ignition.
965 K, Al/MoO3 Nanocomposites
Time (us)-1000 -500 0 500
Rel
ativ
e In
tens
ity
0.0
0.2
0.4
0.6
0.8
1.0
1.24:18:116:1
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