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Recent Results from Dragonfire Armor Simulation Experiments

Recent Results from Dragonfire Armor Simulation Experiments . Farrokh Najmabadi, Lane Carlson, John Pulsifer UC San Diego HAPL Meeting, Naval Research Laboratory October 30-31, 2007. Summary of Previous Results. Small changes in sample when maximum temperature < ~2500K.

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Recent Results from Dragonfire Armor Simulation Experiments

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  1. Recent Results from Dragonfire Armor Simulation Experiments Farrokh Najmabadi, Lane Carlson, John Pulsifer UC San Diego HAPL Meeting, Naval Research Laboratory October 30-31, 2007

  2. Summary of Previous Results

  3. Small changes in sample when maximum temperature < ~2500K. • It appears that material response (powder metallurgy samples) depends on the maximum sample temperature and not on temperature rise 14A, 150mJ, RT, Max: 2,500K (~2,200K DT) 11A, 200mJ, 773K, Max: 3,000K (~2,200K DT) 105 shots 103 shots 104 shots

  4. New Experimental Setup

  5. RGA Laser entrance Previous Experimental Setup Was Dictated by the High-Temperature Sample Holder High-Temperature Sample holder • 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. Thermometer head

  6. New heater • halogen lamp • 100 W (300 W available) • ~500˚C base temperature • New sample manipulator • xy translation • external control • located closer to window • New in-situ microscopy • <25 m resolution • large standoff K2 Infinity optics • New external thermometer head location • Replaced by a “free-space” head New Experimental Setup -- Most diagnostics are outside the chamber translator electronics

  7. The size of thermometer spot size was not known • Two-lens formulas and fiber diameter were used to roughly size the thermometer head and compute the spot size (~100 mm). • 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

  8. M=0.2 280 m image Image of calibration lamp filament 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. • 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. Aperture PMT Head

  9. 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.

  10. New Exposure ResultsPowder Metallurgy W

  11. For a fixed laser energy, sample temperature changes in time 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 low laser energy, temperature remains constant (little surface damage)

  12. 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.”

  13. Material response seems to be better correlated to final temperature than laser energy (all 104 shots) 21C2, 250 mJ, T= 2500→3025K 21C5, 175 mJ, T= 2050→2680K 21C4, 150 mJ, T= 2000→2145K 21C3, 350 mJ, T= 2900 – 3100K 21C8, 200 mJ, T= 2194→2580K 21C6, 150 mJ, T= 1925→1840K

  14. Initial Exposure ResultsSingle Crystal W

  15. Similar to power Met. Samples, for a fixed laser energy, sample temperature changes in time

  16. Surface morphology, however, is very different than power met. samples X1-X2, 200 mJ, T= 2400→2400K X2C6, 250 mJ, T= 2200→3000K X1-C4, 300 mJ, T= 2100→3700K

  17. 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 mm 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.

  18. Thank you,Any Questions?

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