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 shots 10 5 shots 10 4 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 location Replaced 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  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

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. Aperture PMT Head Image of calibration lamp filament 280  m image 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 T 3 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 T 3 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.

New Exposure Results Powder Metallurgy W

For a fixed laser energy, sample temperature changes in time Above > K, a “run-away” condition occurs leading to localized surface melting At around K, 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)

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.”

Material response seems to be better correlated to final temperature than laser energy (all 10 4 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 – 3100K 21C8, 200 mJ, T= 2194→2580K

Initial Exposure Results Single 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?