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Recent Results from Dragonfire Armor Simulation Experiments
Farrokh Najmabadi, Lane Carlson, John PulsiferUC San Diego
HAPL Meeting,Naval Research LaboratoryOctober 30-31, 2007
Summary of Previous Results
Small changes in sample when maximum temperature < ~2500K.
103 shots 105 shots104 shots
14A, 150mJ, RT, Max: 2,500K (~2,200K T)
11A, 200mJ, 773K, Max: 3,000K (~2,200K T)
It appears that material response (powder metallurgy samples) depends on the maximum sample temperature and not on temperature rise
New Experimental Setup
Previous Experimental Setup Was Dictated by the High-Temperature Sample Holder
High-Temperature Sample holder
Thermometer head
RGA
Laser entrance All alignment had to be done in
air. Laser/thermometer head had to
be realigned for exposure of new portion of the sample.
No control of diagnostics during the run.
No external diagnostics capability because sample was too far from windows.
All alignment had to be done in air.
Laser/thermometer head had to be realigned for exposure of new portion of the sample.
No control of diagnostics during the run.
No external diagnostics capability because sample was too far from windows.
New Experimental Setup -- Most diagnostics are outside the chamber
New in-situ microscopy <25 m resolution large standoff K2 Infinity
optics
translator electronics
New heater halogen lamp 100 W (300 W available) ~500˚C base
temperature
New external thermometer head locationReplaced by a “free-space” head
New sample manipulator
xy translation external control located closer to window
The size of thermometer spot size was not known
Target
Laser intensity
distribution
Object spot
Objective lens
h1 h2
s1 s2d
m = h2/h1 = s2/s1 = NA1/NA2 f = (s1+s2) x m/(m+1)2
optical system
= 2.44 f/d
Two-lens formulas and fiber diameter were used to roughly size the thermometer head and compute the spot size (~100 m).
The thermometer head was focused on the sample by coupling a diode laser to the fiber and adjusting the objective to get a sharp image. The diode laser spot was roughly centered in the middle of drive laser foot-print.
Two-lens formulas and fiber diameter were used to roughly size the thermometer head and compute the spot size (~100 m).
The thermometer head was focused on the sample by coupling a diode laser to the fiber and adjusting the objective to get a sharp image. The diode laser spot was roughly centered in the middle of drive laser foot-print.
Similar arrangement to couple fiber to PMT Similar arrangement to couple fiber to PMT
An image relay optical train was to used to obtain an accurate thermometer field of view
The thermometer field of view is controlled with the size of the aperture.
A CCD camera was used to verify the theoretical calculation of the spot size.
The thermometer field of view is controlled with the size of the aperture.
A CCD camera was used to verify the theoretical calculation of the spot size.
h1 h2
s1 s2d
m = h2/h1 = s2/s1 = NA1/NA2 f = (s1+s2) x m/(m+1)2
optical system
= 2.44 f/d
h1 h2
s1 s2d
m = h2/h1 = s2/s1 = NA1/NA2 f = (s1+s2) x m/(m+1)2
optical system
= 2.44 f/dAperture
PMT Head
Image of calibration lamp filament
280 mimage
M=0.2
All results reported are based on a 1-mm aperture (2 mm thermometer field of view)
Reported temperatures are heavily weighted toward “hot spots” because of T3 dependence of radiation.
All results reported are based on a 1-mm aperture (2 mm thermometer field of view)
Reported temperatures are heavily weighted toward “hot spots” because of T3 dependence of radiation.
Spatial profile of sample temperature is obtained
The objective of the thermometer head is mounted on a translation stage which would allow sweeping the thermometer spot over the laser beam spot and measure temperature profile of the target in real time.
The objective of the thermometer head is mounted on a translation stage which would allow sweeping the thermometer spot over the laser beam spot and measure temperature profile of the target in real time.
New Exposure ResultsPowder Metallurgy W
For a fixed laser energy, sample temperature changes in time
Above >2500-2700K, a “run-away” condition occurs leading to localized surface melting
Above >2500-2700K, a “run-away” condition occurs leading to localized surface melting
At around 2000-2500K, Some surface damage occurs to relieve thermal stresses, reaching a new equilibrium but at a “higher” temperature
At around 2000-2500K, Some surface damage occurs to relieve thermal stresses, reaching a new equilibrium but at a “higher” temperature
At low laser energy, temperature remains constant (little surface damage)
At low laser energy, temperature remains constant (little surface damage)
This behavior is repeatable
Sample temperature as a function of time 3 different experiments, same laser energy
Sample temperature as a function of time 3 different experiments, same laser energy
It appears that some surface damage occurs to relieve thermal stresses, reaching a new equilibrium but at a “higher temperature.”
It appears that some surface damage occurs to relieve thermal stresses, reaching a new equilibrium but at a “higher temperature.”
Material response seems to be better correlated to final temperature than laser energy (all 104 shots)
21C4, 150 mJ, T= 2000→2145K
21C6, 150 mJ, T= 1925→1840K
21C5, 175 mJ, T= 2050→2680K 21C2, 250 mJ, T= 2500→3025K
21C3, 350 mJ, T= 2900 – 3100K21C8, 200 mJ, T= 2194→2580K
Initial Exposure ResultsSingle Crystal W
Similar to power Met. Samples, for a fixed laser energy, sample temperature changes in time
Surface morphology, however, is very different than power met. samples
X1-C4, 300 mJ, T= 2100→3700K
X1-X2, 200 mJ, T= 2400→2400K
X2C6, 250 mJ, T= 2200→3000K
Summary
For powder met. Samples: For T < ~2,000K no change in the sample, For T > ~2,500K, sample surface morphology to
accommodates thermal stresses. Localized hot spots develop and evolve.
Operation at high temperature (~3,000K) may lead automatically to an “engineered” surface with < 5 m features.
Initial results with single crystal samples indicate similar “general” behavior. However, surface morphology appears to be very different than powder met. samples.
SEM of single crystal samples will be posted on the HAPL Web site.
For powder met. Samples: For T < ~2,000K no change in the sample, For T > ~2,500K, sample surface morphology to
accommodates thermal stresses. Localized hot spots develop and evolve.
Operation at high temperature (~3,000K) may lead automatically to an “engineered” surface with < 5 m features.
Initial results with single crystal samples indicate similar “general” behavior. However, surface morphology appears to be very different than powder met. samples.
SEM of single crystal samples will be posted on the HAPL Web site.
Thank you,Any Questions?