Susan H. Fischer and Mark. C. Grubelich- The Use of Combustible Metals in Explosive Incendiary...

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To be presented at the D efense Exchange Agreement 5642 (Pyrotechnics)Meeting, Lawrence Livermore National Laboratory, July 22-23,19 96

u..

The Use of Combustible Metals in Explosive Incendiary Devicest

Susan H. Fischer and Mark. C. Grubelich

Explosive Components Department

Sandia National Laboratories

Albuquerque, NM 87185-1453

(505) 845-8092,844-9052

Abstract

We have investigated tailoring damage effects of explosive devices by the addition of

unconventional materials, speciJically combustible metals. Initial small-scale as well asfull-scale testing has been performed. The explosives inction ed to disperse and ignite

these materials. Incendiary, enhanced-blast, andfiagm ent-damage effects have beenidentiJed. These types of effects can be used to extend the damage done to hardened .

facilities. In other cases it is desirable to disable the target with minimal collateral

damage. The useof

unconventional mater ials allows the capability to tailor the dam ageand effects of explosive devices o r these and other applications. Current work includesthe testing of an incendiary warhead o r apenetrator.

Background

There is interest in enhancing or selectively damaging specific targets. For example,hardened targets may suffer minimal overall damage when breached by a conventionalpenetrator. It would be advantageous to extend the damage beyond the room in which the

penetrator detonated. On the other hand, sometimes strategically limited damage isdesirable. For instance, it can be useful to disable a power grid in such a manner that

necessary utilities can be restored relatively quickly to the populace. In som e cases, adevice is needed that can be quickly installed by military personnel to breach a barrier orwall and then spread secondary effects inside the targeted strucfxre.

f This work was supported by the United States Department of Energy under ContractDE-AC04-94-AL85000.



Materials

,Combustible metals were chosen as the baseline materials for an incendiary effect.Magnesium, aluminum, titanium, zirconium, and hafhium were considered. Magnesium,aluminum , titanium, and zirconium were tested. Titanium and zirconium are more dense

than m agnesium and aluminum (4.53 and 6.4 vs 1.74 and 2.7 g/cm3), a desirable factor forsome explosive devices, e.g., penetrators. We expected hafhium to perform w ell as anincendiary but ruled it out because of cost and availability. (Hafhium exists as about 2% ofzirconium ore).

Experimental ConfigurationThe experimental configurations are shown in Figure 1.

combustible

monolithic combustiblefillmaterial

steel casing

combustible HE pellets fillmalerialmetal sleev

Figure 1. Monolithic and fill-material experimental configurations.

The len gth of the test unit was from three to twenty-four inches. The three-inch lengthsimplified the assembly and testing, bu t was more susceptible to end effects. The OD(outer diameter) varied from 1.5 to 4.0 inches.

The m onolithic configuration consisted of a thick-walled sleeve of a combustible metal

with a column of high-explosive (HE) pellets in the center. The second configurationconsisted of a cylindrical steel casing, an annulus of a f ill material pressed in the cylinder,

and a central column of HE pellets. The steel casing was made of 4340 heat-treated to aRockwell hardness of 40 R,or a 1018 carbon steel. The combustible fill materials that

were tested in th is configuration included: ,

0 titanium sponge with an average particle size of 0.8 mm;0 zirconium gravel with an average particle size of 3 mm;

0 zirconium sponge with an average.particle size of 1 mm;0 zirconium w ashers 2 mm thick.

I .

I2



DISCLAIMER

This report was prepared as an account of work sponsored by an agency of theUnited States Government. Neither the United Sta tes Government nor any agency

thereof, nor any of their employees, makes any warranty, express or implied, orassumes any legal liability or responsibility for the accuracy, completeness, or use-fulness of any information, apparatus, product, or process disclosed, or representsthat its use would not infringe privately owned rights. Reference herein to any spe-

cific commercial product, proctss, or service by trade name, trademark, manufac-turer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof.Th e views and opinions of authors expressed herein do not nectssarily sta te orreflect those of the United Sta tes Government or any agency thereof.



DISCLAIMER

Portions of this document may be illegible

in electronic image products. Images are

produced from the best available original

document.

.



16’2”

..

Figure 3. Arrangement in the tes t cell us ed for the full-scale penetrator tes ts.

Experimental Resu ltsThe experimental results are listed in Table 1.

Data tabulated fo r each experiment include:

the material and dimensions of the metal sleeve or casing;

the type, density,%TMD, and mass of the fill material (if present);

the type, dimensions, number, and mass of the explosive pellets used; andthe ratio of the mass of nonexplosive material to that of explosives (ME).

The resu lts and comments are listed in the last column.

Fires were started inside the test cell in tests using zirconium in the forms of washers,

gravel, and sponge. Following the detonation of the explosives, the burning Zirconium wasdispersed throughout and outside the test cell. The wood in the test cell was fiactured and

splintered, which enhanced ignition qualities. In Test 23, fires were started up toapproximately70meters away fiom the test cell.

In the full-scale tests, the case broke up in a unique pattern that led to a very large numberof fiagments. Thiswas due to the axially segmented porous zirconium sleeve. Bychanging the configuration of the explosive and the incendiary fill, fragment size and shapecan be tailored to a given application without compromising the integrity of the penetratorcase.



Table I Test Results

material

~~

OD, n

0.375

0.375

0.625

0.75

0.75

1o

3.375

3.375

Ms

Mg

plastic

Zr

Zr

1.5

2.5

3.O

3.O

PBX-

9501

PBX-9501

49.29'

96.7'

__ _

metal sleevelcasing HE elletsill materia1date of

testM/C

ratio'ID, in. L,in.- material %TMD resultslcomments-

/9/94

--74on e --- burning streamers; several

large pieces recovered

8/9/94 none ----e -49 smaller pieces; no evidence ofcombustion

8/10/94 none sooty cloud due to C-4explosive; glowing particles;small melt marks on Lexan;small pieces (<1/16")recovered

8110194 none --- no combustion

8/10/94 30ipowder

(0.030 4)

-10 Ti pellets secured in a small

plastic container; many hotparticles, som e hitting Lex anshield

detonator at each end; manyparticles, m ore damage; -1-in

particles hot after 10 min

6

-78110194 none

none --- I detonator; many burningpieces; mJmm -23.5; paperset on fire

8111/94 23.5

' M is the total mass of nonexplosivematerial (e.g., the sum of the masses of the casing and fill material); C is the m ass of explosive used.

2 Total explosive weight.

Explosive weight of interior pellets only.

5



Table I continued)

13-14

-

-WC

ratio'

-

-93

-at e of

test

-test

#

-8

HE pellets c

resultdcomments

metal sleevelcasing fill materia l

HE OD ,in.

material-1 Cokecan

OD, n ID, in. material wt, g

-20.722

20.72'

L, n.-4.0

3.375

3.375

3.375

6.0

PETN 0.5 PETN pellets held in plastictube; RP-2 detonator; can hung30 in above floor; burning Tiparticles

Ti sponge/7/94

Ti sponge 0.99 22% 21 5 PETN 0.59-10

9/7/94 1018steel

3.O 2.0 PETN pellets held in plastic

tube; burning Ti andexplosively compacted T irecovered

20 6 PBX-9404

0.75

(4)

PBX-9404 pellets held inplastic sleeve; burning Ti andexplosively compacted T irecovered

3.O 2.0 Ti sponge

- .

0.94 21%9/8/94 1018steel

52.62

42.2'

-36

-55r lumps(pressed)

2.69 42% 589 PBX-9404

0.75

(3)9/22/94 1018

steel

3.O 2.0 three PBX-9404 pellets with 2booster pellets; more vigorousburning of papers for -5 min

1081 PBX-9501

127.33

. .. .

4340 3.O 1.75 Zrwashers

5.95 93 %10/3/94 interior pellets extendedbeyond the ends of the casing;paper set on fire; lots of

fragment damage (embeddedin wood, a few welded tosteel); unreacted Zr recovered

' M is the total mass of nonexplosiv e material (e.g., the s um of the masses of the casing and fill material); C is the mass of explosive used.

2 Total explosiv e weight.Explosive weight of interior pellets only.

6



Table I continued)

test

#

15

17

20

21

date of

test

1014194

10/12/94

11/4/94

10/5/95

material

4340

1018steel

4340

4340

OD, in

3.0

3 O

3.0

4.0

-M/C

ratio '

metal sleevelcasing fill material HE pellets f

ID,n. material %TMD HE OD,in.

1.0 (6)

-L, in.

-6.0

results/comments

-30.75 Zr sponge 3.8298 60%

~

PBX-9501

fireball saturated video for 1.2s; fewer hot particles seen;paper blown awa y by blast, allburned; plywood ignited after-1 s

interior pellets recessed at oneend; initiated at the flush end;many glowing particles; paperstarted to bum at 5 ms, wood a50 ms, strong fire put out after10 min

lots of hot particles seenbouncing in the box an d

spraying out; paper firesstarted; casing was broken intolarge pieces

many fragments (>1000) -1 1g; some larger, many smaller;

fragment velocity -1480 f p s(1543 fps from Gurney); verystrong fire throughout test cell

2.0 3.375 Zr sponge 3.9308 61% 38 1 40.03BX -9404

0.75

(3)

52

1.75 6.0 Zr sponge 3.60 56% LX- 15 1 o 325 1 135.1

2.0 24 . Zr sponge 4.03 63% 2179 Comp.c - 4

-1.5 1106 28

M is the total mass of nonexplosiv e material (e.g., the sum of the masses of the casing and fill material); C is the m ass of explosive used.

Explosive weight of interior pellets only.2 Total explosive weight.

7



0

d

co

0

m

H

sm

\o \o

s

.-( m

-3 z

z z

z 9m

aP=r

cu0

ME:

0

.*

W

cu0

E

- N P ,



Discussion

The feasibility o f coupling additional effects with an explosive device has been

'Ldemonstrated n these tests. The performance depends on a number of parameters. We

have observed the effect of changing some of the parameters, but much more needs to bedone to validate our conclusions and to optimize the design of an explosive device withadditional effects due to the addition of unconventional energetic materials.

explosivedesignation

Cornp C-4

HMX

HNS

LX - 1

PBX-9404

PBX-950 1

PETN

One important parameter is the type of explosive used. The formulation, density, oxygenbalance, and detonation properties of the explosives used in the tests are summarized in

Table 2. HMX, hich was used in Gurney and hydrocode calculations (discussed below),is also listed. The explosive properties are from Dobratz and Crawford 1985, b e y nd

Graham 1985, and Mader 1979.

Table 2. Explosive Properties

explosive composition density, oxygen (0 ) detonation p ropertiesingredients w t % g/cm3 balance P,kb D , m m / p

RDX 91 1.65l very 0 2572 8.37di(2-ethylhexyl) deficient

sebacate 5.3

polyisobutylene 2.1

fue l oil 1.6

-_ - 1.84' slightly0 390 9.1 1

deficient

deficient

Kel-F 800 5 deficient

--- --- 1.72' very 0 zoo2 7.00

HNS-I 95 1753 very 0 188' 6.84

HMX 94 1.84' 0 deficient 375 8.80

CEF 3

NC (12.0% N) 3

HMX 95 1.84' sligh tly0 363' 8.83Estan e 2.5 deficient

BDNPA-F 2.5

--- --- 1.76' balanced 335 8.26

The pow er of the detonation, indicated by the detonation pressure and velocity, is animportant characteristic for the design of the explosive device. Gurney and hydrocodecalculations, discussed below, were done withHMX s he explosive, which has very high

Nominal density.

Calcula ted detonation pressure.

Theor etical maximum density.

9



detonation pressure and velocity. PBX-9404 and PBX-9501 are 94 to 95% HMX nd are

the most powerful explosives we used in these tests. LX-15 is a much less powerful

,explosive. The effect of the power of the explosive can be seen by comparing Tests 15 and20, bo th of which contained zirconium sponge as the combustible fill material. In Test 15,PBX-9501 pellets were used. The casing was broken into small pieces, the zirconium was

well dispersed, and the wood in the test cell was ignited. In Test 20, which used LX-15pellets of the same diameter as the PBX-9501 pellets in Test 15, the casing was broken into

very large pieces, m uch of the zirconium was found unreacted and in large explosivelycompacted pieces, and none of the wood was ignited. This effect is even more noticeablein a comparison of Tests 17 and 20. In Test 17, even though the PBX-9404 pellets were0.75 inches in diam eter and there was only about 30% asmuch zirconium as there was in

Test 20, the wood ignited and grew into a vigorous fire that had to be extinguished by testpersonnel.

Also tabulated in Table 2 is the oxygen balance of the explosive. Oxygen-rich explosivesshow molecu lar oxygen in the nominal products and generate little smoke or soot.

Oxygen-deficient explosives show combustible products such as carbon, carbon monoxide,or hydrogen and generate large amounts of smoke or soot. Oxygen-balanced explosivesshow oxidized products such as COYCO,, and H20. We used the highest oxygen-balanced

explosives available for our tests when possible; with less smoke and soot the videocoverage was better. This made it possible to view ignition and burning after the explosive

was detonated. This is why Comp C-4 was not used in most of the tests, even though it

may be th e explosive of choice for certain applications. (Comp C-4 was used in the full-scale tests because of time constraints.)

The products of oxygen-rich explosives may also assist in the ignition and burning of thecombustible fill. To determine if this affected the ignition of the zirconium, w e performed

Test 20 with LX-15 explosive pellets and zirconium sponge fill material to com pare to Test15, which was done with PBX-9501 pellets. LX-15 is an oxygen-deficient explosive andproduces less of the oxidized products (e.g., steam and C 02 ) hat would aid the ignition ofthe zirconium particles. Although the one-inch-diameter LX-15 pellets did not disperse thezirconium well, there were many visible burning particles in the videotape coverage of Test20. This indicates that the zirconium can function well as an incendiary with an oxygen-deficient explosive.

Zirconium performed the best as an incendiary in the tests discussed here. We obtained thebest results from zirconium sponge, but zirconium in the form of thindisks also performed

well. In Test 1 4 with 3- m -t h ic k zirconium disks, the wood was scorched but did notburn. Large partially reacted pieces of zirconium were recovered. These larger fragmentspenetrated the wood, scorching the wood but not depositing enough energy for ignition.Modifications such as scoring the washers, using thinner washers, and changing the 1

amount and type of explosive used should be considered.

Fragment velocities were calculated for the last three tests using the Gurney method(f3enry 1967, Kennedy 1972) with some modification. The Gurney method assumes that

10



the potential energy in the explosive charge before detonation is equal to the kinetic energyof the charge and casing after detonation and expansion. In the calculations done here, the

the explosive. The predicted fiagment velocities agreed within 5% of the measured

fragment velocity measured inTest 2 1 and 13% of that measured in Test 22.

',energy used to compact the porous zirconium was subtracted fiom the G urney energy for

Conclusion and RecommendationsThe experiments described in this report have demonstrated the feasibility of addingenhanced effects to an explosive device by the addition of combustible metals.

The incendiary performance depends on a number of parameters. From the tests described

here, we have come to the following conclusions:

0 there must be enough explosive (the amount needed depends on the detonation

properties of the explosive) to adequately break up the casing and disperse the

combustible fill material in effective particle sizes;0 the monolithic test configuration, with a thick-walled sleeve of combustible metal,

does not work well as an incendiary;zirconium was the best incendiary material;

the breakup o f the material in the test cell due to blast and fragmentation

contributed to the ignition process.

Additional work needs to be conducted to optimize the choice of materials, relative amount

of explosive, and penetrator configuration. If the com bustible fill is porous, more

explosive may be needed to attain fragment damage. For the combustible fill materials,other metals, such as a mixture of zirconium and aluminum which exothermically alloy,

may further enhance the incendiary effect.

We recommend that future experimental work include the following:

additional tests with zirconium washers to better determine incendiary

performance;optimization of the type, amount, and oxygen balance of the explosive;optimization of the type, morphology, and density of the combustible fill material;

tests with other combustible metals and intermetallic compositions.

Our results indicate that a metalized incendiary explosive device is feasible and capable ofstarting massive fires at the target site.

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References

B. M. Dobratz and P. C. Crawford, LLNL Explosives Handbook, UCRL-52997 Change 2,January 1985.

L

I. G. Henry, 1967, The Gurney Formula and R elated Approximationsfor the High-Explosive Deployment of Fragments, Report No. PUB-1 89.

J. E. Kennedy, 1972, Explosive Output for Driving Metal, Behavior and UtiZization of

Explosives in Engineering Design, Albuquerque, NM, March 1972.

G. F. Kinney and K. J. Graham, 1985, Explosive Shocks in Air, 2nd Ed ition, Springer-Verlag.

' _

C. L. Mader, 1979, Numerical Modeling of Detonations, University of California Press.

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