CP620, Shock Compression of Condensed Matter - 2001edited by M. D. Furnish, N. N. Thadhani, and Y. Horie© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00

RE-SHOCK EXPERIMENTS IN LX-17 TO INVESTIGATE REACTEDEQUATION OF STATE

Kevin S. Vandersall, Jerry W. Forbes, Craig M. Tarver,Paul A. Urtiew, and Frank Garcia

Lawrence Livermore National Laboratory, Energetic Materials Center, 7000 East Avenue, L-282, Livermore,CA 94550

Abstract. Experimental data from measurements of the reacted state of an energetic material aredesired to incorporate reacted states in modeling by computer codes. In a case such as LX-17, where thetime dependent kinetics of reaction is still not fully understood and the reacted state may evolve overtime, this information becomes even more vital. Experiments were performed utilizing a 101 mm gun tomeasure the reacted state of LX-17 using a re-shock method. This method involves backing theenergetic material with thin plates (of a known equation of state) that reflect a shock back into thedetonated material. Thus, by measuring the parameters of this reflected wave, information on thereacted state can be obtained. The experiments were driven by a projectile to near the CJ state ensuringa quick transition to detonation near the front of the sample. Embedded manganin piezoresistive gaugeswere used to measure the pressure profiles at different Lagrange positions during the event. Adiscussion of this work will include the experimental setup utilized, pressure gauge profiles, datainterpretation, and future experiments.

INTRODUCTION

The main question posed by this research is: whatrole does kinetics play in the reacted state of anenergetic material? A TATB based energeticmaterial, LX-17 (92.5% TATB/ 7.5% Kel-F), wasselected to help answer this question, becauseTATB-based explosives are considered somewhatnon-ideal due to the presence of a 3-4 mm reactionzone. The re-shock technique was chosen because itprovides a method for gaining a measure of thereacted state via the re-shock wave speed andpressure profiles. If the reaction in the initial shockis fast and complete, then the measured re-shockvelocity should be equal to the isentropic (sound)wave speed in the material [1]. However, if reactionis incomplete, interpretation is necessary tocorrelate the re-shock wave speed to the trueisentropic wave speed in the material. This data willbe used to provide an accurate isentrope of LX-17

reacted products, which can then be incorporatedinto the computer codes for improved models.

Previous reflected wave experiments have beenperformed by McQueen and Fritz [2-4], in whichthey characterized the point at which the rarefactionrelease wave catches up with the reacting energeticmaterial using an optical technique. Transienteffects and structure in the release profiles wereobserved and a ratio of the shock wave velocity tothe rarefaction velocity was obtained. Somereflected wave experiments have also beenperformed above the Chapman-Jouguet (CJ)pressure (referred to as "supracompression" or"overdriven") [5-6]. Additional work by Tarver et.al. investigated the initiation of energetic materialby reflected shocks at pressures driven below the CJpressure [7-8]. This work, however, focuses on theregion at or near the CJ pressure in the energeticmaterial. This paper will discuss experimental setup

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used, pressure gauge profiles, data interpretation,and future work.

EXPERIMENTAL PROCEDURE

Experiments were performed using the 101 mmdiameter propellant driven gas gun at LawrenceLivermore National Laboratory (LLNL). Figure 1shows a schematic of the rear reflector re-shocksetup that was used. The projectile consisted of apolycarbonate sabot with a 15 mm thick siliconcarbide (SiC) flyer plate. The target included a3.2 mm thick SiC buffer plate in contact with13 mm of LX-17 (TATB based high explosive) nextto another 5 mm thick plate of SiC with 5 mm ofA12O3 at the rear. Manganin gauges were placed (2at each level) at the buffer interface (0 mm), 4, 7, 9,11, and 13 mm within the LX-17 sample with125 fim Teflon insulation on each side of the gauge.The SiC plates were SiC-'B' produced by Cercom,Inc. and the A12O3 plate was AD998 produced byCoors Ceramics. In the experiment, the first SiCplate at the back of the LX-17 acts as the firstreflector plate since it has shock impedance(product of the shock wave speed at pressure andthe density) higher than the LX-17, and the A12O3will act as a second reflector material since it has aslightly higher shock impedance than the SiC plate.Because of this, the manganin gauges will measurethe initial increase in pressure from the initial shocktraveling through the target and then bothreflections from the LX-17/SiC and SiC/Al2O3interfaces respectively. Using two reflectormaterials ensures that a double re-shock is observedand enables two measurements to be made in thesame experiment.

In this experiment, the impact velocity waschosen to result in a pressure at or very near to theCJ pressure for the LX-17 sample. Therefore, withthe LX-17 driven near CJ state and the 15 mm thickSiC flyer acting as a piston, a supported shockpropagates through the sample. As shown inFigure 1, PZT Crystal pins were used to measure theprojectile velocity and tilt (planarity of impact). Themeasured impact velocity was 2.33 mm/us with thecrystal pins located at the impact surface and at a15 mm standoff. The manganin gauges wereanalyzed using a hysterisis corrected fit publishedelsewhere [9,10]. An experiment was first

performed with just SiC plates backed by a A12C>3reflector material to show the feasibility of the re-shock method, however, the results are not includedhere for brevity.

SiC Flyer LX-17 HE SampleTilt Crystal Pins

SiC Buffer Plate(round with flat edges)

AI203Reflector

Plate

SiCReflector

Plate

Velocity Crystal Pins

FIGURE 1. Schematic of rear reflector re-shockexperiment setup.

so -.[Modeling Results. EXPT 4557 |

- - - Model, Gauge 1 (0 mm)Model. Gauge 2 (4 mm)Model. Gauge 3 (7 mm)

-Model. Gauge 4 (9 mm)- - - Model, Gauge5 (11 mm) .........- - - Model, Gauge 6 (13 mm) -It-

10 11time, MS

FIGURE 2. Modeling results of LX-17 rear reflector re-shock experiment.

RESULTS AND DISCUSSION

Figure 2 displays the modeling results (shown asdashed lines). The initiation and growth model [8]was used along with a model developed bySteinberg [11] for SiC. In short, the re-shock wavespeeds are determined from the travel time between

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the reflected shock peaks at the gauge locations.The modeling was performed before the experimentto ensure that the reflected re-shock states could bemeasured before any release waves arrive. TheTeflon gauge packages were inserted into themodel.

Figure 3 (a) shows the results from theexperiment (solid lines) and modeling (dashed lines)combined together in one trace with only the gaugesat 7, 9, 11, and 13 mm shown in Figure 3 (b) forclarity of the region of interest. It can be observedthat the model and experiment do not match exactly,but the main features are reproduced reasonablywell. The model predicts earlier initiation and fasterdetonation than the experiment. This is most likelydue to the interference of the teflon gauge packageswith the developing reactive flow [12]. Thinner andfewer gauge packages and longer LX-17 chargeswill be used in future experiments. Aligning theinitial wave arrival times in Fig. 3 (b) shows that thecalculated and measured reflected shock velocitiesare in good agreement.

The re-shock wave speeds were calculated forboth the modeling and experimental results fromtravel time between reflected shock peaks in gaugetraces. To be consistent, the wave speed wascalculated from the times at 1/2 the maximum timefrom the toe to peak of the increase in pressure there-shock event provides. The propagation timethrough the Teflon insulation was subtracted usingthe insulation thickness and shock wave speed atpressure. The average pressure value from the firstre-shock peak value to the second re-shock peakwas used. The re-shock wave speeds and pressuresfrom the modeling are 6.63 mm/|Lis at 31.5 GPa,6.74 mm/^s at 32.3 GPa, 7.24 mm/^s at 35.5 GPafrom gauges located from 7 mm to 9 mm, 9 mm to11 mm, and 11 mm to 13 mm, respectively. Fromthe experiment, the calculated wave speeds from 7mm to 9 mm and 9 mm to 11 mm respectively are6.9±0.2 mm/^is at 31.9±0.2 GPa and 7.8±0.2 mm/^sat 39.4±0.1 GPa. A complete analysis of the errorsassociated with the experiment will be done later. Itwill include factors such as gauge performanceduring the re-shock environment and effects of thegauge insulation thickness.

Impacting future experiments at a slightly highervelocity than was used in this experiment to allowsteady state to be reached faster would be beneficialto allow measurement where time dependent flow isnot occurring.

(a)—— EXPT, Gauge 1 (0 mm)

EX FT, Gauge 2 (4 mm)EXPT. Gauge 3 (7 mm) •

—— EXPT. Gauge4 (9 mm)—— EXPT, Gauge S (11 mm)—— EXPT, Gauge 6 (13 mm)-- Model. Gauge 1 (Omm)

Model, Gauge 2 (4 mm)Model, Gauge 3 (7 mm)

-- Model.Guage4(9mm)-- Model, Gauge 5 (11 mm)-- Model. Guage6(13mm>

-r

EXPT, Gauge 3 (7 mm)EXPT. Gauge 4 (9 mm)EXPT. Gauge 5 (11 mm)EXPT. Gauge 6 (13 mm)Model, Gauge 3 (7 mm)Model,Guage4(9mm)Model, Gauge 5 (11 mm)Model,Guage6(13mm)

FIGURE 3. Results of LX-17 rear reflector re-shockexperiment showing experiment with (a) all of the gaugelevels and (b) the gauges in the region of interest showingthe reflected shock characteristics.

SUMMARY AND FUTURE WORK

The re-shock method was used to measure re-shock wave speeds in LX-17. Further analysis isneeded to analyze and minimize the errors involvedand correlate the re-shock wave speeds with theisentropic (sound) speed in the reacted products.

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Figure 4 outlines a schematic design of a futureexperiment in which the re-shock is directed fromthe rear of the flyer plate instead of reflecting off therear of the sample. Ongoing work to validate thecurrent research is in progress to conduct a similarset of experiments using electromagnetic velocity(EMV) gauges.

LX-17 HE SampleSiC Flyer Plate Tilt Crystal Pins

SABOT

Air Gap

VelocityCrystal

Pins

SiC Buffer Plate(round with flat edges)

AI2O3 Reflector Plate

FIGURE 4. Schematic of experiment for future workwhere the shock is reflected from the front behind theflyer plate.

ACKNOWLEDGEMENTS

Dan Greenwood is greatly acknowledged forimplementing the data acquisition system andplaying a key role in research to reduce noise inmanganin gauge recording. Ernie Urquidez, GarySteinhour, and Mike Martin assisted with theexperiments. Funding was provided through LLNLby the Chemistry and Materials Science DirectorateWR&D and Postdoctoral (for KSV) programs. Thiswork was performed under the auspices of theUnited States Department of Energy by theLawrence Livermore National Laboratory underContract No. W-7405-ENG-48.

2. R.G. McQueen, J.W. Hopson, and J.N. Fritz, Rev.Sci. Instrum. 53 (2), Feb. 1982, pp. 245-250.

3. Joseph N. Fritz, "Waves at High-Pressure andExplosive-Products Equation of State," ShockCompressrion of Condensed Matter-1999, M.D.Furnish, L.C. Chhabildas, and R.S. Hixson eds., AIPPress, New York, 2000, pp. 239-244.

4. J.N. Fritz, R.S. Hixson, M.S. Shaw, C.E. Morris, andR.G. McQueen, J. Appl. Phys. 80 (11), December1996.

5. L. Green, E. Lee, A. Mitchell, and C. Tarver, inEighth Symposium (International) on Detonation,Office of Naval Research NSWC MP 86-194, editedby J.M. Short (Naval Surface Weapons Center,White Oak, Maryland, 1985), pp. 587-595.

6. L.G. Green, C.M. Tarver, and DJ. Erskine, in NinthSymposium (International) on Detonation, Office ofNaval Research OCNR 113291-7, edited by W.J.Morat (office of Naval Research, Arlington,Virginia, 1989), pp. 670-682.

7. Craig M. Tarver, Paul A. Urtiew, and William C.Tao, Effects of Tandem and Colliding Shock Waveson the Initiation of Triaminotrinitrobenzene," J.Appl. Phys. 78 (5), 1 September 1995.

8. C.M. Tarver, T.M. Cook, P.A. Urtiew, and W.C.Tao, "Multiple Shock Initiation of LX-17," TenthSymposium (International) on Detonation, ONR33395-12, (Boston, MA, 1993), pp. 696-703.

9. Vantine, H.C., Erickson, L.M. and Janzen, J.,"Hysteresis-Corrected Calibration of Manganinunder Shock Loading", J. Appl. Phys., 51 (4), April1980.

10. Vantine H., Chan J., Erickson L. M., Janzen J., LeeR. and Weingart R. C., "Precision StressMeasurements in Severe Shock-Wave Environmentswith Low Impedance Manganin Gauges," Rev. Sci.Instr., 51. pp. 116-122 (1980).

11. Daniel Steinberg, "Computer Studies of the DynamicStrength of Ceramics," Lawrence LivermoreNational Laboratory Report, UCRL-ID-106004,September, 24, 1990.

12. A. W. Campbell and Ray Engelke, "The DiameterEffect in High Density Heterogeneous Explosives,"Sixth Symposium (International) on Detonation,Office of Naval Research ACR-2221, (Coronado,CA, August 24-27,1976), pp. 642-652.

REFERENCES

W. Fickett and W.C. Davis, Detonation, Los AlamosSeries in Basic and Applies Sciences, edited byDavid J. Sharp and L.M. Simmons, Jr. (University ofCalifornia Press, Berkeley, California, 1979).

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