Cast PBX B2238 for Small-Calibre High Performance Insensitive Munitions

65 Propellants, Explosives, Pyrotechnics 22, 65-70 (1 997)

Cast PBX B223 8 for Small-Calibre High Perforrnance Insensitive Munitions Ralph Kent

INEXCO, 45240 La FertC-Saint-Aubin (France)

Ein gegossener kunststoffgebundener Sprengstoff B2238 fiir kleinkalibrige unempfindliche Hochleistungsmunition

Im allgemeinen wird die heutige kleinkalibrige Munition, die gefiillt 1st rnit konventionellen schmelzgegossenen oder geprefiten Spreng- stoffen, klassifiziert rnit der Gefahrlichkeitsstufe 1.1 oder 1.2, da sie explodiert, wenn sie verschiedenen Einfliissen ausgesetzt wird, wie z.B. Fuel Fire und sympathetischer Detonation. Die Komposition B2238 auf der Basis RDX ist ein preiswerter und wenig empfindlicher gegossener PBX und wurde urspriinglich von der SNPE entwickelt fiir die Ziindung von gegossenen PBX-Hauptladungen. Da B223 8 leicht zu ziinden ist mit konventionellen Ziindem, bietet es denselben Grad an Unempiindlichkeit wie andere gegossene PBXe, die fiir Hauptla- dungen venvendet werden (2.B. Hexabu 88A oder Octorane 86B), und explodiert nicht, wenn es Feuer undoder Kugelaufschlag ausgesetzt wird. Machbarkeitsstudien wuden durchgefiihrt an verschiedenen Arten von Kleinkalibermunition und haben gezeigt, dal3 B2238 als Sprengstofffiillung eine hervorragende Losung darstellt fi die Her- stellung kleinkalibriger Munition mit hoher Leistung (bezogen auf Splitterwirkung und Hohlladungsstachel) und vergleichbar ist rnit den meisten konventionellen Hochleistungssprengstoffen wie RDW Wax(98/2). Ergebnis ist, dab der neue IM-standard, der z.Zt. definiert wird, in Zukunft eine Ruckstufung von Kleinkalibemunition hei Fiillung rnit B2238 in eine andere Gefahrenklasse als 1.1 und 1.2 erlauben sollte.

Un explosif coulk d liant plastique B2238 pour des munitions ir hautes performances, insensibles et de petit calibre

En rhgle ginirale, les munitions de petit calibres actuelles, qui sont remplies d’explosif conventionel code par fusion ou comprimk, sont classkes dans les groupes de risque 1.1 ou 1.2, car elles explosent lorsqu’elles sont exposees a diffirentes influences telles que le feu de fuel et la detonation par influence. La composition B2238 a base de RDX est un PBX cod&, de faible coilt et peu sensible et a Btk developpie a l’origine par la SNPE pour l’amorqage de charges principales RDX coulees. Etant donnk que le B2238 est facilement amorqable avec des dktonateurs conventionnels, il offre Ie mdme degrk d’insensibilite que d’autres PBX coules utilises pour les charges principales @.ex. Hexabu 88A et octorane 86B) et n’explose pas lorsqu’il est expose au feu et/ou a un impact de bille. Des itudes de faisabilitb ont eti effectuies sur differents types de munitions de petit calibre et ont montrh que le remplissage de B2238 reprksentait une excellente solution pour la fabrication de munitions de petit calibre a performance BlevBes (par rapport a I’effet des klats et au jet de charge creuse) et Btait comparable a la plupart des explosifs a hautes performances conventionnels tel que le RDWcire (98/2). Le rksultat est que le nouveau standard IM actuellement dkfini devrait permettre a l’avenir de reclasser les munitions de petit calibre remplies de B2238 dans un autre groupe de risque que 1.1 et 1.2.

Summary

Generally speaking, today’s small-calibre munitions, filled with conventional melt-cast or pressed high explosives, are classified in the 1.1 or 1.2 Hazard Divisions because they explode when exposed to various threats, such as fuel fire and sympathetic detonation. The RDX-based B2238 composition is a low-cost and less sensitive cast PBX originally developed by SNPE for the initiation of cast PBX main charges. While it is easily initiated with conventional detonators, 82238 offers the same degree of insensitivity as other cast PBXs used for main charges (HEXABU 88A or OCTORANE 86B for example) and does not explode when exposed to fire and/or bullet impact. Feasibility tests carried out on several types of small-calibre munitions have shown B2238 explosive filling to be an excellent solution in the design of small calibre insensitive munitions with a high performance (in terms of fragments and shaped charge jet) comparable to that of the most energetic conventional high explosives such as 98RDW2wax. As a result, the new IM standards, currently being defined, should allow in the future to reclassify the small- calibre munitions filled with B2238 in Hazard Divisions other than 1.1 and 1.2.

high explosive filling alone is not sufficient to ensure low insensitivity. The use of less sensitive booster is also of critical importance. Consequently, SNPE has also developed the B2238 composition for booster charge applica- tions.

B2238 is composed of an HTPB inert binder and only 85% RDX. Careful selections in the quality and the size of the RDX particles have enabled the development of a cast PBX that is both low-cost and offers the best compromise between easy initiation by currently available detonators and a high degree of insensitivity to intense shock waves.

Cast PBX B2238 has obtained STANAG 4170 Certifi- cation, and is currently being mass-produced at SNPE. A description of the B2238’s characteristics follows. It includes, in some instances, a comparison with the characteristics of conventional high explosives such as TNT and/or Composition B.

1. Characteristics of B2238 Composition(’) 1.2 Physico-Chemical Properties

1. I Introduction

Even though it is a prerequisite for the development of Insensitive Munitions, the availability of a less sensitive

The B2238 composition exhibits the usual physico-che- mica1 properties specific to most cast PBXs, as well as excellent mechanical properties (see Table 1):

0 VCH Verlagsgesellschafi, D-6945 1 Weinheim, 1997 0721-31 15/97/0204-0065 $17.50+.50/0

66 Ralph Kent Propellants, Explosives, Pyrotechnics 22, 65-70 ( 1 997)

Table 1. Mechanical Properties (traction) of B2238 Table 3 shows that the B2238 composition can be initi-

emax. (%) T ("C) Smax. (MPa) E (Mpa)

-34 1.60 64.0 18.0 +20 0.98 15.0 13.9 i-70 0.64 9.2 11.1

Smax., maximum strength; E, Young's modulus; emax., maximum elongation; Note that, if necessary, these values can be modified.

- density 1572 kg/m3 - thermal expansion coefficient - thermal diffusivity 0.13 mm2/s - decomposition (DSC)

81.10-6 "C--'

200 "C =weak endo- thermic peak 207 "C =exothermic peak 0.7 cm3/g (193 hours at 100 "C)

- vacuum thermal stability

1.3 Detonic and Initiation Characteristics

B2238's main detonic and initiation characteristics are:

- unconfined failure diameter - detonation velocity 8040 m / s - detonation pressure 25.4 GPa

The Gurney constant was determined, using Xray film, based on the average velocity of the fragments resulting from the explosion of 1.94 kg of B2238 in a pre-scored steel tube @re-machined circular and longitudinal notches). The main characteristics are:

- inside diameter 75 mm - thickness 12.5 mm - length 280 mm - number of cubic fragments 380

- B2238 weightlsteel weight 0.4

Table 2 provides a comparison between the values of B2238's and Composition B's Gurney constants, under identical test conditions:

< 2 mm

- weight of fragments 12 g

Table 2. Detonation Velocity (D) and Gurney Constant (TQ HE Density D (m d B ( d s )

Composition B 1.71 7900 2130 B2238 1.57 8000 2030

ated using conventional detonators. For comparison pur- poses, Composition B tested under UN 7a also detonated(2).

When tested according to the French initiation test (reference: FMD.210.A1), B2238 shows a lesser degree of ignitability than other conventional high explosives used in boosters (Table 4). This is not surprising because cast PBX B2238 is a less sensitive composition. This test, whereby an aluminium plate is placed between the high explosive sample ($3 10 mm, L 18 mm) and the detonator (ADFO- 12 EAB T030), is designed to determine the plate thickness above which the sample no longer detonates.

Tests carried out to determine the initiation power of B2238 have shown that a B2238 cylindncal sample ( 0 9 mm, L10 mm) is capable of initiating a PETN sample ( 0 9 mm, L18 mm) with a 20 mm thick aluminium plate placed between the samples (French test reference: FMD.211.A2). This is slightly higher than the initiation power of tetryl (plate thickness of 18 mm).

1.4 Safety and Vulnerability Data

The results from the standard safety and vulnerability tests are listed in Table 5.

The above test results are used in Table 6 to provide a comparison between B2238 and Composition B, in terms of the criteria set forth for the UN Series 7 tests on substances (according to the new UN 1.6 Hazard Division). B2238, like most of SNPE's cast PBXs, is less sensitive to threats from fire and bullet impact. B2238 is especially resistant to bullet impact due to its very low friability (2.5 MPdms). In comparison, the friability of Composition B is 40 MPdms. As a matter of fact, B2238 has a low burning rate and high resistance to fragmentation. However, Composition B2238, originally formulated as a booster, cannot be classified as EIDS, as it fails the intense shock wave tests (Cap and Gap tests).

Table 7 shows, however, that B2238 was found less sensitive to gap and sympathetic detonation tests than melt- cast and pressed high explosives. The sympathetic detona-

Table 4. French Initiation Test Results

HE Thickness (mm)

B2238 < 1 95RDW5wax 2.9

_______ ____ ____. ___ ~ _ _

Tetryl 3.4

Table 3. Detonator Test Results

B2238 sample Detonator dimensions (mm)

0 1O,L7 ADFP-12 EAB M030 @ 30, L70 DBS 420A 0 80, L200 EUROPEEN 0 30, L200 BRISKA

+ : detonation

Results

_____ - (0.15 g PETN) (in contact) + (0.15 g PETN) (in contact) + (0.60 g PETN) tm 7 4 + (0.80 g PETN) (in contact) +

Propellants, Explosives, Pyrotechnics 22, 65-70 (1997)Cast PBX B2238 for Small-Calibre High Performance Insensitive Munitions 67

Table 5. B2238 Safety and Vulnerability Data

Tests

30 kg fallhammer: no reaction height non-propagation height

BAM friction apparatus French ESD test Gap test EIDS Gap test Friability test Self-ignition temperature Cook-off temperature Thermal stability test at 75 “C Small-scale burning test Fuel fue Slow cook-off test with French 3L case 12.7 mm AP bullet impact test with French 3L case

Test references

UN 3a)iv

UN 3b)i

UN 2a)iv UN 7b) UN 7d)

AOP 7-201.03.002

AOP 7-202.01.004 AOP 7-202.01.01 1 UN 3c) UN 3d) AOP 7-202.01.003 AOP 7-202.01.003 AOP 7-201.05.002

Results

2.5 m > 4 m 230 N no sensitive 220 cards 110 mm 2.5 MPa/ms at 150 d s 210 “C < 125 “C stable no explosion no explosion reaction type IV reaction type V at 850 d s

Table 6. UN Sene 7 Tests on Substances ~~ ~ ~~~

Tests (French alternative) Composition B B2238 (Ref. 2)

7a) EIDS cap test + + 7b) EIDS gap test + + 7c)ii) Friability test + 7e) EIDS external fire test + 7f) EIDS slow cook-off test (*) + -

- -

__..__ ___ ~ _ _ (-) passes and (+) fails the criteria (*) with French 3L case (see Table 5 )

tion test was performed on two B2238 charges, donor and acceptor. In the case of the donor, the B2238 filling was confined in a steel tube, as described in paragraph 1.3. For the acceptor, the B2238 filling was also confined in a similar type of tube, without the pre-scoring however.

2. Feasibility Tests on Small-Calibre Munitions

2.1. Hand Grenades

In the past, tests designed to determine the storage classification for packages of French DF (defensive) and OF (offensive) hand grenades, known as “Model 1937”, have been carried out at GERBAM, a French Proving Ground(4’.

The main characteristics of these hand grenades are:

Table 7. Shock Sensitivity of Conventional High Explosives and B2238

High explosives UN gap test 7b Sympathetic detonation test

t(mm) P(GPa) a(mm)

110 2.0 - TNT (D) B2238 110 2.0 - -= 25 65RDW35TNT 155 0.7 - Composition B - - > 50

e, PMMA gap threshold. P, shock pressure corresponding to t (Ref. 3). a, air gap between tube walls to prevent sympathetic detonation.

(3L=3 litres)

- OF hand grenade

-DF hand grenade

ovoid aluminium body filled with 90 g of TNT, ovoid cast iron body filled with 56 g of TNT

A package consists of a metallic, water-proof inner box divided in three cells with wooden exterior. One package holds 20 hand grenades. One cell holds 20 igniter sets (“Model 1935”), packed head-to-tail, two to a cardboard case. In the other two cells, the grenades are stacked in individual cardboard cases, in two rows of five grenades each.

The tests were performed in 1972 in accordance with STANAG 4123 requirements, which are similar to the tests required by the UN Recommendations on Transport of Dangerous Goods(2):

- UN test 6a - UN test 6b - UN test 6c

single package test, stack test (5 packages), external fire test (5 packages).

The results of these tests are shown in Table 8. Based on these results, hand grenades are assigned to 1.1 or 1.2 Hazard Divisions because mass detonation occurred in tests 6a and 6b, and sporadx detonations in test 6c, lasting 44 minutes.

Ruggieri has developed a new, safer OF/DF hand grenade, designed to replace “Model 1937” hand grenades. This hand grenade, based on a highly innovative fragmentation concept, consists of an ovoid plastic body, with an inner dented copper liner, 0.5 mm thick (multi-micro shaped charges), and a safe igniter set containing 1.8 g RDX booster located at the center of the explosive charge. Ruggieri performed comparative performance and vulnerability tests with hand grenades filled with Composition B and B2238. The results of these tests are shown in Table 9. The test results demonstrate the definitive advantages in using B2238 filling for this type of small-calibre munitions, i.e., higher performance without sympathetic detonation. Based on these test results, the Ruggieri hand grenade can therefore be assigned to 1.4 Hazard Division according of the UN classification(2).

68 Ralph Kent Propellants, Explosives, wrotechnics 22, 65-70 (1997)

Table 8. Safety Tests on “Model 1937” Hand Grenades

UN tests

6a: single package test

6c: external fire test (5 packages) no detonation detonation of 50 grenades11 00

( 1 ) Test not performed because no mass detonation occurred in test 6a.

OF hand grenade

mass detonation

DF hand grenade

no detonation of 19 grenades 6b: stack test (5 packages) mass detonation of 4 packages (1)

Table 9. Performance and Vulnerability Tests on the New Ruggieri Hand Grenade ~

Tests Composition B (90 g) B2238 (87 g)

Performance (Pk) 0.57 0.62 Sympathetic detonation on 2 grenades with igniter set (1) fragmented)

partial deflagration of the acceptor no reaction of the acceptor (explosive filling only

no reaction of the 19 acceptors (10 only fragmented and 9 not fragmented)

UN 6a: single package (2) (3)

~~ ~ ~

Pk, probability to kill. (1) 10 mm air gap between walls (packaging configuration). (2) natural wood box containing 20 grenades without igniter set (sheet of cardboard between grenades) (3) test not performed.

2.2. Rife Grenades

ALSETEX and MECAR, developers and manufacturers of rifle grenades; also performed comparative performance and sympathetic detonation tests on rifle grenades filled with conventional high explosive and B2238. These rifle grenades consist of a pre-scored steel body (fragments) and a copper liner (shaped charge). The main dimensions are given in Table 10.

Sympathetic detonation tests were conducted on two rifle grenades, a donor equipped with its own igniter set, and an acceptor without igniter set. The rifle grenades are placed in a vertical position on a steel plate, and spaced to replicate the storage configuration. The test results in Table 1 1 show that B2238 composition yields the same performance as conventional high explosives 70RDW30TNT or Composi- tion A3, while being insensitive to sympathetic detonation.

Table 11. Performance and Vulnerability Tests on Rifle Grenades

2.3 Rocket Warheads and Anti-Personnel Munitions

Forges de Zeebrugge (FZ)/Thomson Brandt Armements (TBA) and Ruggieri, developers and manufacturers of rocket warheads and anti-personnel munitions, also performed comparative performance and sympathetic detonation tests on these types of munitions. The main dimensions of both munitions tested are given in Table 12. Cluster

Table 10. Rifle Grenade Dimensions

Dimensions ALSETEX grenade MECAR grenade (1)

Calibre (mm) 38.0 35.0

Length (mm) 100.0 60.0 Cone angle (“) 90.0 60.0

Thickness (mm) 4.0 3.5

(1) grenade under development.

Tests ALSETEX grenade ~ ~ _ _ _ ~

MECAR grenade

70RDN30 TNT B2238 (95 g) (89 g)

Compo. A3 B2238 (55 €9 (46 g)

P -fragments: e r 0 number of perfora. f 0Pk o -jet penetration: r 0 number o f tests m oaverage (mm)

deviation (mm)

0 target (at 10 m) 1.5+1.0+1.5 mmalu.

0.27 0.26 23 20

2 92

1

5 90 3

25 mm wood 27 26

Sympathetic detonat. - g (mm) 17 17 20 20 - reaction of the acceptor DEF NR DEF NR (l), target= 100 mm steel; NR, no reaction; Pk, probability to kill; DEF, deflagration; g, air gap between walls; Compo. A3 = 91RDW9wax.

Propellants, Explosives, Pyrotechnics 22, 65-70 (1 997)Cast PBX B2238 for Small-Calibre High Performance Insensitive Munitions 69 Table 12. FZlOl Rocket Warhead and Ruggieri Anti-Personnel Munition

Dimensions FZlOl Ruggieri munition ~~-

Calibre (mm) 70.0 31.0 Thickness (mm) 4.0 1.5 Length (mm) 45.0 80.0 Cone angle (“) 60.0 -

rocket FZlOO contains 9 sub-munitions FZ101. The FZlOl warhead consists of a conical pre-scored steel body (fragments) and a large copper liner (shaped charge). The liner cone measures 35 mm in length, with a flattened top mea- suring 20 mm in diameter. The Ruggieri anti-personnel munition consists of a double cylindrical case, 0.5 mm thick steel on the outside and 1 mm thick aluminium on the inside (fragments).

Sympathetic detonation tests were carried out on two similar types of munitions, placed in a vertical position on a steel plate: a donor equipped with its own igniter set and an acceptor without igniter set. The munitions were spaced to replicate the storage configuration. The test results in Table 13 show B2238 composition yields the same performance as energetic high explosive, 98RDX/2wax, while being insensitive to sympathetic detonation. In the sympathetic detonation test carried out on the FZlOl rocket warhead, the B2238 composition of the acceptor showed no reaction whatsoever (filling fragmented only into several large pie- ces).

3. Conclusions

For small munitions with calibres of less than 70 mm, a B2238 filling, weighing up to 100 g, greatly assists in meeting IM requirements, i.e., no violent reaction to the four basic tests of fuel fire, slow cook-off, bullet impact and

sympathetic detonation. Furthermore, B2238 performs as well as the most energetic conventional high explosives, such as 98RDW2wax for example, in terms of fragments and shaped charge jet.

Insofar as the igniter set has also been designed to be safe in all conditions, these munitions could conceivably be classified as insensitive munitions, and be assigned to the 1.4 Hazard Division of the UN protocol(2). In France, for example, the new hand grenade developed by Ruggieri, filled with B2238, should be granted the French “MURAT” (i.e. Insensitive Munitions) label, and be assigned to the 1.3 Hazard Division, according to the new French regulations(576).

A classification in the 1.3 or 1.4 Hazard Division would represent a significant improvement. Furthermore, a B2238 filling offers other very attractive advantages. For example, the manufacturing process allows the casting of PBX directly in the munition case, at the low temperature of 60°C. The rear section of the filling can also be moulded into a complex shape, using a specific mould, or simply the munition’s closing cap.

This technology, combined with the excellent properties of B2238, such as its chemical compatibility with the materials currently used in munitions, allows the following:

- to eliminate a number of current manufacturing steps including the coating of the munition cases with anti-acid varnish, the casting of a lost head necessary for melt-cast high explosives, or the machining of a fuse well in the explosive filling,

- to guarantee a perfect adhesion of the explosive filling to copper liners,

- to remove the booster, or reduce its size, - to guarantee excellent thermomechanical properties, at

low as well as high temperatures above 100 “C. Exudation or melting at 80°C does not occur as is the case with melt-cast high explosives. Consequently, performance is stable throughout the life duration.

Table 13. Performance and Vulnerability Tests on FZlOl Rocket Warhead and Ruggieri Munition

Tests FZlOl Ruggieri munition

95RDW5wax B2238 (100 €9 (97 g)

P - fragments: e target r number of perfora. f -jet penetration: 0 0 number of tests

0 deviation (mm) K 0 average (mm)

1.5 mm steel (at 10 m) 13 1 1

12 85 4

6 87

3

2.5 + 1.5 mm ah. (at 5 m) 50 50

Sympathetiddetonat. : I 1 1 (2)

NR NR (2) - g (mm> (1) - reaction of the acceptor (1)

(1) test not performed. (2) test not performed because NR with 98RDN2wax. g, gap between walls: FZlOl =air, Ruggieri munition =aluminium and plastic (launch tube). NR, no reaction.

70 Ralph Kent

In conclusion, the use of a cast PBX such as B2238, will allow manufacturers to offer, at equal cost and performance, small calibre munitions fulfilling a very critical function: immunity. (5)

(3)

(4)

4. References (6)

(1) SNPE data. (2) “Recommendalions on the Transoort of Dangerous GoodsTests

Propellants, Explosives, Pyrotechnics 22, 65-70 (1 997)

J. Isler (SNPE), “Classification Tests for Assignment to Hazard ClasslDivision 1.6: SNPE Two Years Experience”, 25th Explo- sives Safety Seminar, Anaheim, California, 1992. NIMIC informations. P. Lamy and J. Guillien, “The French National Doctrine with Regard to Less Hazardous Munitions (MURAT)”, Insensitive Munitions Technology Symposium, June 6-7, 1994, [Proc.], p 41.- 51. P. Lamy and J. Isier, “The MURAT Labels: a Good Answer to IM Policies, the Example of the French Doctrine”, 26th Explosives Safety Seminar, Miami, Florida, August 1 &18, 1994.

\ I , Y

and Criteria ”. STISGIAC. 1011 I/Rev. 1. (Received August 30, 1995; Ms 46/95)

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Cast PBX B2238 for Small-Calibre High Performance Insensitive Munitions