Sci. Tech. Energetic Materials, Vol．７１, No．５,２０１０ 129

Research paper

Card gap tests of plastic high by using mortar, light weight concrete and sand as gap materials

Tomoharu Matsumura＊†, Koki Ishikawa＊＊, Tomotaka Homae＊＊＊, Kunihiko Wakabayashi＊, and Yoshio Nakayama＊

＊Research Core for Safety,National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1Higashi, Tsukuba, Ibaraki 305-8565, JAPAN TEL +81-29-861-4793 FAX +81-29-861-4783 †Corresponding address : [email protected]

＊＊Civil Engineering Research & Environmental Studies, Inc. (CERES), 1646 Abiko, Abiko, Chiba 270-1166, JAPAN

＊＊＊Department of Maritime Technology, Toyama National College of Technology, 1-2 Ebie-neriya, Imizu, Toyama 933-0293, JAPAN

Received : October 31, 2008 Accepted : August 3, 2010

Abstract The series of card gap test like experiments were carried out to examine the relation between gap length and sympa- thetic detonation of plastic high explosive, and the scale effect of shock initiation sensitivity of the explosive. Composition C-4 explosive charges (1400kg·m－３ in density) of cylindrical shape and with same weight, were used as donor and accep- ter charges. The ratio of charge length to diameter (L/D) was set to be one. The experiments have been conducted with five explosive weights ; 10g, 40g, 320g, 2.5kg, and 20kg. Three kinds of gap materials, i.e., mortar, light weight concrete and sand with various thicknesses, were used. The sand layer was sandwiched by two thin mortar disks. Detonation or no-detonation of accepter charge was determined by observing the situation of a mild steel witness plate after the ex- periment. It became clear that, even in the case for 20kg charge, the critical gap length of detonation and no-detonation can be evaluated in the range of 20mm or so. Furthermore, in log-log coordinate system of gap length as a function of ex- plosive weight, it was found that all three gap materials showed good linear relationship, and those inclinations were larger than the value of the scale factor of explosive weight ( = 0.333). It was obtained a tendency that the material with higher density showed higher obstruction effects to prevent the sympathetic detonation.

Keywords : , sympathetic detonation, gap test, scale effects, composition C-4

1. Introduction In case of breakup and dispersion of debris from the par- In theassessment of the safety of storage facilities for tition wall caused by the explosion accident of the adjacent , it is necessary to investigate the blocking ef- storage bay, it is important to consider the selection of the fects of sympathetic detonation by obstacle, such as a par- partition wall material. That is, when thinking about the tition wall. If the sympathetic detonation of the adjoining influence by the collision of the secondary fragments, the storage bay can be obstructed by the partition wall, the wall must be covered by energy absorbing material, rela- safety distance can be decreased because the explosive tively low-strength and porous in comparison with nor- amount is considered to be a half of the net total amount. mal weight concrete, to reduce the impulse loading of the Acomposite structure which consists of sand fills in be- acceptor charge and to prevent the scenario of sympa- tween two concrete or mortar walls can contribute to the thetic detonation. strength of the concrete or mortar and the sand itself can In this study, a composition C-4 plastic high explosive reduce the shock pressure１，２）. with high shock sensitivity, was chosen from among the 130 Tomoharu Matsumura et al. commercial explosives currently being used and based on charge length to the diameter (L/D) was set to one. A the scale rules for the gap tests with mortar, light weight booster holder made of polyethylene with Comp. C-4 concrete and sand were conducted. In order to clarify the booster explosive, 2 wt. % exclude of charge amount, was scale effects in the shock sensitivity, laboratory scale ex- set on the donor charge３）. In the laboratory scale experi- periments with 10g, 40g, and 320g of composition C-4 ex- ments, the donor charge was detonated by one electric plosive for the donor and accepter charges and medium detonator. In the field explosion experiments, the donor scale explosion experiments with 2.5kg and 20kg of com- charge was detonated by two electric detonators. position C-4 explosive for the donor and accepter charges were carried out.

Detonator 2. Experiment 2.1 Explosives and assembly Booster explosive The composition C-4 (hereafter, abbreviated as Comp. PMMA tube C-4) explosive (Nippon Koki Co., Ltd.) was used for the do- Donor explosive

nor and acceptor charges. Schematic drawings of the gap PVC tube L Gap material (sand) test assembly are shown in Figure 1, and sizes of the de- (Unpolished side) D vices are listed in Table 1. According to the amount of charge, two types of assembly were used for the sand gap Mortar disc Gap length experiments. The donor and acceptor charges were set re- spectively at the top and bottom of the gap material, and (Polished side) Acceptor explosive the lower side of the acceptor charge was set on the two- PMMA tube ply mild steel witness plates that could touch it. Witness plate The Comp. C-4 stuffed into PMMA tube was used and itsdensity was adjusted to 1400kg·m－３. The ratio of the

Fig.１(b) Experimental setup for sand gap (explosive weight up to 2.5 kg). Detonator

Detonator Booster explosive

Booster explosive PMMA tube D onor explosive L Gap material PMMA tube Donor explosive

(Unpolished side*) D (mortar or LW C) L Gap material (sand) (Unpolished side) D G ap length PVC tube Mortar disc Gap length (Polished side*) Acceptor explosive PMMA tube (Polished side) Acceptor explosive Witness plate PMMA tube Witness plate

* LW C gap was used upside down. Fig.１(a) Experimental setup for mortar or light weight con- Fig.１(c) Experimental setup for sand gap (explosive weight crete gap. of 20 kg).

Table１ Sizes of each part of test devices.

PMMA tube for donor / acceptor PVC tube for Mortar / LWC gap Mortar disk for sand gap Explosive charge sand gap Witness plate weight Inner diameter Inner diameter (mm) Length (mm) Diameter (mm) Diameter (mm) Thickness (mm) (mm) (mm)

10g + 10g 20 20 33 35 33 3.5 60×60×2.3

40g + 40g 32 32 53 67 53 5.5 100×100×4.5

320g + 320g 65 65 108 125 108 11.5 200×200×8

2.5kg + 2.5kg 126 126 208 240 208 23 400×400×16

20kg + 20kg 260 260 442 395 442 45 800×800×32 Sci. Tech. Energetic Materials, Vol．７１, No．５,２０１０ 131

Table２ Specification ofgap materials.

Gap material Mortar Light weight concrete Sand

Water, Cement, Coarse Composition Water, Cement, Aggregate Soma sand aggregate, EPS

Mixing ratio 0.4 : 1.0 : 2.0 0.45 : 1.0 : 1.19 : 0.1 1.0

Apparent density 2200 1400 1520 (kg·m－３)

Compressive strength 35.0 16.4 - (N·mm－２)

Grain size (mm) 0.15―2.5 <3 0.425―1.7

EPS : Natural silica sand. Remarks - Expandable polystyrene Standard sample of strength test etc. on cement.

2.2 Gap material 3. Results and discussion The specifications of each gap material are tabulated in 3.1 Damage states of the witness plates Table 2. Three kinds of gap materials, mortar, light weight After the explosion experiments, three types of reaction concrete (hereafter, abbreviated as LWC) and sand were phenomena of the accepter charge were obtained from the used in this study. It was decided to make the diameter of damage states of the witness plates as following. 1) Sympa- the gap materials 1.66 times that of the explosive charge in thetic detonation of the accepter charge ; the witness accordance with the Japan Explosives Society standard４）. plates were greatly distorted, and the hole were opened on The sand gap was produced by loading the sand in be- both plates. In addition, no remaining unexploded explo- tween two mortar disks with same thickness. The loading sive was discovered on the witness plate or in its vicinity. densityofthe sand was adjusted to 1600kg·m－３.The side 2) No-detonation of the accepter charge ; neither of the surface of sand gap was supported by using a polyvinyl two witness plates was distorted. In addition, remaining chloride (PVC) tube. As mentioned in the previous section, unexploded explosives were discovered on the witness two types of assembly were used for the sand gap experi- plate and in its vicinity. 3) Incomplete detonation of the ac- ments. In case that charge weight of less than or equal to cepter charge ; distortion of the witness plates was obvi- 2.5kg, the thickness of sand layer was adjusted by chang- ously less than in case of sympathetic detonation, and no ing the location of two mortar disks set inside the PVC hole was opened to either witness plate. However, no re- tube. And in case that charge weight of 20kg, the thick- maining unexploded explosives were discovered on the ness of sand layer was adjusted by using the PVC tubes of witness plate and in its vicinity. The reaction appears to various lengths. The total gap length was therefore de- be an incomplete detonation, though the acceptor charge fined by adding the thickness of two mortar discs to the reacted in this case. It was difficult to categorize the dam- length of sand layer. age to the witness plates either sympathetic detonation or There was a difference in surface roughness on the no-detonation, and the result was judged to be incomplete front side and the back side of the mortar and LWC gaps. detonation. In that sense, the gap length in the result One side of the gap was polished to fine-tune the thick- judged to be incomplete detonation is thought to be very ness and to smooth its surface, and the aggregate section close to the critical gap length. was exposed. On the other hand, small holes due to bub- If the shortest gap length judged to be no-detonation is bles were apparent, but hardly any aggregate was visible shown to be Ln,and the longest gap length judged to be on the other side (unpolished). In this study, the polished sympathetic detonation is shown to be Ld, the critical gap side was made the back side of mortar gap which con- length (Lc)isexpressed as tacted with the top surface of the accepter charge, and the !!"#!#!!" other side was made the front side of mortar gap which contacted with the bottom surface of the donor charge. In In addition, the length judged to be incomplete detona- case of LWC gap, however, unpolished side was rougher tion is assumed to be the critical gap length in this study. than polished side ; the gap material was used upside down. 3.2 Effect of the weight of explosive on shock Natural silica sand was used as sand gap material. The sensibility particle size of the sand has been adjusted by sifting out to The scale effects on the shock sensitivity of Comp. C-4 0.425-1.7mm though it was considerably all of a size at explosive are indicated in Table 3. When pay attention to this point. The foreign object such as clay was removed the longest gap length of sympathetic or incomplete deto- from the mined original sand by washing in clear water. nation (Ld), the scale effect of the explosive could realize for all three gap materials. In case of the LWC gap for exam-

ple, the Ld of 320g (39.9mm) is longer than 2 times of the Ld

of 40g (17.5×2=35mm), the Ld of 2.5kg (110.3mm) is longer ie fthe of times no-det materials. gap two other for ( loraiefraltregpmtras ncs ftesand the of the case In example, materials. for gap gap three all for realize also ie fthe of times 0m) n the and 100mm), Table３ 132 f2k 291m slne hn2tmso the of times 2 than longer is (299.1mm) 20kg of the of times 2 than ( (0.01kg≦ length approved. gap was the explosive of between in weight law the shown power and as The plane, 4. log through - 2 length log Figs. gap be- the critical in the lines relationship and straight exhibited explosive the of weight Moreover, the tween respectively. gap) sand mort de- (for incomplete to or possible no-detonati sympathetic was and each detonation it of 20kg, the boundary of in the Even amount termine explosive. charge C-4 the Comp. of 20kg experi- case through - 20.9mm 10g - with 1.6mm ments of mate- range gap the incomplete of within kinds rials or three for sympathetic no-detonation and between de- detonation to boundary possible was the It limit re- experiments. the these for in reason obtained a as sults erated enum is explosives of nomena materials. gap two other for result the realize can trend ○:dtnto,×:n-eoain△:icmlt detonation incomplete : no-detonation,△ : × detonation, : ※○ 1.×=2.m)as.Sm rn a elz h result the realize can trend Same also. 110.3×2=220.6mm) 2. m slne hn2tmso the of times 2 than longer is mm) 126.4 Explosive .k 2.5kg + 2.5kg 0k 0kg 20 + kg 20 2g+320g + 320g 0 40g + 40g n,we a teto otesots a eghof length gap shortest the to attention pay when And, If phe- explosion the on scale the of effect peculiar The 0 10g + 10g wei L sgplnt i m and mm) (in length gap is ght nto ( onation ooauMatsumura Tomoharu rgp,2.m frL (for 20.9mm gap), ar W cl feto h hc estvt fteCm.C-4 Comp. the of explosive. sensitivity shock the on effect Scale 2k) h prxmto sepesdas expressed is approximation the ≦20kg), L L Mo Sand Sand Sand Sand Mortar ih egtconcrete weight Light concrete weight Light Mo concrete weight Light Mortar Sand concrete weight Light concrete weight Light Mortar n n L f4g(0724.m) the (20.7×2=41.4mm), 40g of n f25g(2.×=5.m)as.Same also. (126.4×2=252.8mm) 2.5kg of rtar rtar a material Gap ,tesaeefc fteepoiecould explosive the of effect scale the ), L L n d f2k 296m slne hn2 than longer is (279.6mm) 20kg of f30 3.×=98m,adthe and (39.9×2=79.8mm), 320g of L n f30 5m)i ogrta 2 than longer is (50mm) 320g of nwti h ag f17.3mm of range the within on tal. et Cgp,ad1m (for 19mm and gap), WC W 6. ○ 296(×) -279.6 (○) 260.6 (×) -126.4 (○) 107.7 9. ○ 300(×) -320.0 (○) 299.1 (×) -119.0 (○) 110.3 (×) -50.3 (○) 39.9 (×) -20.2 (△) -17.5 (○) 15.1 (×) -24.8 (△) -19.8 (○) 14.9 (×) -12.0 (△) -10.4 (○) 9.4 (×) -12.0 (○) 10.1 4. ○ 278(×) -257.8 (○) 240.5 gh(m and (mm) length Gap 02()-20(×) -12.0 (○) 10.2 03()-00(×) -50.0 (○) 40.3 1. ○ 187(×) -118.7 (○) 110.0 00(○) 40.0 78(○) 17.8 swih fexplosive of weight is L n 5. (×) -50.0 2. (×) -20.7 Judge※ f30 (50×2= 320g of L L n d f2.5kg of f2.5kg of L d Fig.３ n h omlsof formulas the and rse as pressed ae.Bcuetedsrcinstaino the ex- of situation the destruction of the amount Because the increases. as plosive much im- gap so the the change to and doesn’t pressure long material shock incident becomes the wave though grows shock pulse the of time ration va " " " Fig.２ /!5.20 /!, /! twscerta hs nlntoswr agrta the than larger were inclinations those that clear was It 13 lu Gap length (mm) Gap length (mm) -+ 46.4 eo 1000 1 ! ! 100 100 000 ! ft eaino xlsv egtadgplnt o light for length gap and weight wei explosive of Relation 10 10 () eaino xlsv egtadgplnt o mortar. for length gap and weight explosive of Relation )# (' 1 1 .0 .10111 100 10 1 0.1 0.01 0.001 .0 .10111 100 10 1 0.1 0.01 0.001 he ! ! % " h concrete. ght ! $ ( $ sc $ 䕧 㽢 䕿 䕧 㽢 䕿 " " l atro xlsv egt( .3) Du- 0.333). (= weight explosive of factor ale ! ! &$( " &&# : incompletet de : no-det : det : incomplete : no-det : det ! &## , , # # , # onation onation $ ightExplosive we (kg) Explosive $ L $ ! ! c onation onation ! eex- re a materials gap three all for " " ! " " ! *** **) ! ***

! detonation !& o sand. for o ih egtcnrt,and concrete, weight light for onation o mortar, for weight (kg) Mortar ih weight concrete Light % , R R c c 2 2 = = = = 76 81 .0 .0 999 998 7. 0. WL WL .0 .0 441 411 bandb h a et.Ta s h W hwdthe showed LWC Th the length. is, gap That critical were tests. longest gap results the different by the obtained however, detonation, p pathetic to and charge acceptor the of b to seems in- LWC the about thinking fl When detonation. with prevent sympathetic material to the effects the obstruction that higher shows seems density higher It respectively. (sand), mm h ofiin fdtriain( determination shown. of were coefficient explosive The the of sensitivity initiation shock of the f of scale amount the on depending e different is material gap le larger much experiments. the se for from presumed extrapolation explosive of the amount enabled rule scale this ie sti au prahst one to curve approaches approximated value the this of as accuracy rises the and th curve, to mate value predictive the of poie ti huh htdfeetrslsbsdsthe besides results different that thought is it xplosive, Fig.４ ec ytecliino h eodr rget,the fragments, secondary the of collision the by uence ngths

ncs ftecag egto 0g h rtclgap critical the 20kg, of weight charge the of case In Gap length (mm) 1000 co eeotie.I em httesaeeffects scale the that seems It obtained. were actor 100 10 r 6.m mra) 0.m LC,ad281.4 and (LWC), 303.6mm (mortar), 262.7mm are eaino xlsv egtadgplnt o sand. for length gap and weight explosive of Relation 1 .0 .10111 100 10 1 0.1 0.01 0.001 㽢 䕿 䕧 : no-det : det : incomplete fetv ordc h mus loading impulse the reduce to effective e onation Expl onation osive (kg) weight

detonation culdt b data actual e rfr,t eino evalu- or design to erefore, eetteseai fsym- of scenario the revent Sand R ２ ５ hw th shows ) ） .I ti ss R c getdthat uggested 2 napproxi- an y = = 78 ea .0 999 3. ccuracy WL .0 427 tchg xlsvsadb sn three using by and ca were explosives materials gap of high kinds plastic of amounts opeettesmahtcdetonation. sympathetic the prevent to mate- densi the higher that with tendency rial the obtained was it study, present initi ex- shock of factor scale all the of for pl value the length than larger gap lo were nations the critical in the materials gap and three explosive of amount respec- gap), sand (for 19mm and tively. gap) concrete weight of range de or sympathetic each incomplete of boundary the determine to possible as are obtained ex- results the The : of follows sensitivity. amount shock the sympa- on of and effects plosive length the to and charges, gap detonation accepter between thetic and relationship donor the the clarify for used was plosive t h piu eghfrec aeil ftecompos- encouraged. the of materials parti each ite for length optimum the ate .Conclusions 4. References 4) Ishi K. 3) Ha K. Ishida, T. Hirosaki, Y. 2) Ishi M. 1) 5) sv egt(=033.I em httesaeefcsof effects scale the that seems It 0.333). = ( weight osive )I h ag fteaon fepoie sdi the in used explosives of amount the of range the In 3) the between relationship linear a have to found was It 2) was it 20kg, of amount charge the of case the in Even 1) iet ihfive with experiments like tests gap card of series A aauakiiau S3 1,JpnEpoie Society Explosives Japan (1), ES-33 Kayakugakkaikikaku, .Izk,M hr,adH wsk,”akbnei,p.10- pp. ”Kaikibunseki”, Iwasaki, H. and Ihara, M. Iizuka, Y. aku ua .Nkym n .Ysia cec n Technol- and Science Materials Energetic Yoshida, of Y. ogy and Nakayama Y. mura, Gakkaishi (2000). Kayaku 249 Ogawa, T. and Miyake, A. Takahashi, ( 4(99,Uino aaeeSinit n Engineers. and Scientists Japanese of Union (1999), 14 2001). c.Tc.EegtcMtras Vol． Materials, Energetic Tech. Sci. 43, inwl tutr,frhrivsiainsol be should investigation further structure, wall tion aa .Ae .Kbt,K aaaah,T Matsu- T. Wakabayashi, K. Kubota, S. Abe, T. kawa, to estvt fteepoiewr shown. were explosive the of sensitivity ation uh,M ohd,Y aaaa .Mtuua I. Matsumura, T. Nakayama, Y. Yoshida, M. guchi, 73m(o otrgp,2.m frlight (for 20.9mm gap), mortar (for 17.3mm 2 (1982). 323 oainadn-eoainwti the within no-detonation and tonation ysoe ihrosrcineffects obstruction higher showed ty 67, o ln n hs incli- those and plane log - g tr,and ttori, rried 9 (2006). 199 u.TeCm.C4ex- C-4 Comp. The out. ７１ .Ski oy Kay- Kogyo Sakai, H. No． , ５ , ２０１０ 133 61, 134 Tomoharu Matsumura et al.

モルタル，軽量コンクリート，砂をギャップ材に用いた 可塑性爆薬のカードギャップ試験

松村知治＊†，石川弘毅＊＊，保前友高＊＊＊，若林邦彦＊，中山良男＊

可塑性爆薬のギャップ長と殉爆の関係，また，当該爆薬の衝撃起爆感度の規模効果を調べる目的で，カードギャップ 試験に類似したシリーズ実験を行った。励爆薬と受爆薬には，同薬量の円柱形コンポジションC４爆薬（密度1400kg・m‐３） を使用した。爆薬長さと直径の比（L/D）は１とした。５水準の薬量（10g，40g，320g，2.5kg，および20kg）で実験 を行った。様々な厚さの３種類のギャップ材（モルタル，軽量コンクリート，砂）を使用した。砂の層は２枚の薄いモ ルタル板でサンドイッチにした。受爆薬の爆・不爆は，軟鋼製の証拠板を観測することで判定した。本実験により，薬 量20kgの場合でも，爆・不爆の限界ギャップ長を20mm程度の範囲で評価できることが分かった。加えて，３種類のギャッ プ材全てについて，爆薬量と限界ギャップ長は両対数座標系で良好な直線関係を示すこと，それらの傾きは爆薬のスケー ル則の値（１／３＝0.333）より大きいことが分かった。また，本実験で用いた薬量の範囲では，密度の高い材料ほど，殉爆 阻止効果が大きくなる傾向が得られた。

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