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TITLE: Deflagration-to-lletonation Transition in Granular HMX

MIBTERAUTHOR(S): A, H. Campbel 1

SUBMIITED TO: JANNAF Propulsion Systems Hazards Committee

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L%? LOS ALAMOS SCIENTIFIC LABORATORYPcJstOff Ice Box 1693 Los Alamos, New Mexlco87545An AffkrnattveAction/EqualOpportunityEfr@uya

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Deflagration-to-Detonation Transition in Granul~r HMX*

A. W. Campbell

Introduction

For the past three decades the study of the deflagration-to-detonation

transition (DOT) has been strongly influenced by the views of G. B..

Kistiakowsky. 1 Very briefly stated, he postulated the origin of th’

enon as localized burning in a mass of subdivided explosive, with the

ity of confinement either by a strong container or by th? inert

s p?enom-

poss(bil.

a of the

, 3.

burning. Finally, the amplitude of the shock wave is large enough to initiate

detonation.4 Jacobs has shown that Macek’s treatment of shock formation is

inadequate.

Another hypothesis, widely investigated, is that convective combustion

pl~ys a central role in bridging the gap between conductive burning and the

transition to detonation.5 Driven by the pressure gradient generated by

burning,

mately,

hnt combustion products spread burning at an ever faster rate. Ulti-

under favorable conditions of inertial or other confinement, the ra~e

of energy reledse is sufficient to cause shock formation and the ir)itiation of

detonation. I-nr this process the pwmeability of the explosive to gases is a

factor of prime importance. Several workers hav~ shown that inded the

distance to the onsrt of a~tnnation dcpcn+; strorlgly on the permeability.

Griffiths and (%oocnck6 sturtid tht’ distancp tn detonation whrn burning was

initiatd in granular tt’tryl, R13X, HMX, and TNT undI?r hrilvy confir)cmr!nt. S(JIW

of ttieir data for }{;”1ar;? shown in Fig. 1, Whl?r,.distanrt? to transitiorl is

plnttnct fir a function of th(? pm~l~,lbllity, which was ch(]ngwi by varyirlg th(?

p.lrticle si?eo Price, ~(!r.rl~?l:k~~r,~n(l their coworkers havf? explored II(I1”irld

varirty of f?XplnSiVi’~ anti pro[.’’llant5nvw (1wid(? r(~ngr”of cien’.i’.i~’~and hav!’

pIIl)lls}IO:t a s~ri~’< of rrpr,rt< rio’,rril)ifl~ltill’irwnrk. In agrm?lw’irll.with Lh!~

rt?slllt,.’shovm iI Fig, 1, thfy P1V3 Ol~I;IV-VIIIla mlnillllwlin till’trrlrl’;ihlo!l

dlst.,~rlc~’[rl grar!!llar t!’lryl’ as a f{lrl~l1o11 frf thl’ riI’fl+ity or po’rml.!!)i1ty.

MudI ar’dltionll wnrk hn’; 1)1-I,I!Irl171111,C(lIIVIII.t ;VO c{vr~)liitiofl Ii:,.I)l:llfld k13y

tho crw’lIIII,t.i,lrlpD’I)I!III 1,-:,

It i’j ftl(litlllt,t.1)r.,ll~l,ill’tlIl f.f)Il,.1~1 lVIJCIIIVl\II .! i(lflpi( l,IIrlI wif.h %1111:11

CX;Y*J. iiu,~r)l.!I r)l)’.l’!’vj!f.illll,,nl..lll!’,lf,flol,,.ll~,!: irl work Wil.il gf’dlllll.lfl’,i

— -.. . . . . .._

4,

8

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-. . !11 1! 11111111! 1!

o 0,5 1.0 1.5

Perrncabilily (1/1)

Fig, 1, DUI dist,I!Icuin IIMX. Pcrm{’ll~iliLyv(lri(?l!I)yparticle silLI. [ irl(!Ilhlldl, Ltll’lvft.,cf),II’,,11PCr71ivl)l)iliLy it)dr.!)ilr’dry uflil,,,

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a—

,~

,... ..L. I .

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5.

propellant that the onset of detonation could occur well beyond the burning

front, separated frcnn it by a region that emitted no light, and that sometimes

resonation ran backward from the detonation to the burning zone. This “dark

zone” and the (~ccurrence of resonation were also reported by Griffiths and

Grcocock. Price, Bernecker, and coworkers observed that their ionization pins

that a second wave, stronger

originated in the combustion

were triggered by a rapid wave which swept through much of the explosive.

They also found, from records of strain gau4es,

and nme significant for leading to detonation,

zone and followed the first wave.

In this paper the following hypothesis is presented. When burning starts,

the hot combustion products flow away through the porous explosive, heating

and igniting additional eaplosive and being cooled in the process. As the

burning Increases, drag forces on the combustion prodllcts cause tile pres~ure

to rise in the burning zone, and the pressure rise causes the rate of coitlhlJs-

tlon to increase. As the pre$sur~ rises further, the bed begins to compact

anti the p~rrnenhility starts to dccrea’o and to furthelq imped(? th~? Iiow of

6.

●

by plugs sealed with epoxy. Steel masses of several kilograms were placed

over the ends of the tube for inertial containment of the plugs. Burning was

ignited at one end of the column of explosive, and the course of events was

evaluated frmn measurement of the changes in the internal diameter of the steel

tube or in the wall th+ckness of the tube fragments. DDT was assumed to be

complete when the internal diameter reached a maximum, or the tube wall thick-

ness reached a minimum.

Ian+ter.—

In most of the experiments, 200 mg of a mixture of finely divided titanium

powder and amorphous boron, ignited with an exploding briage-wire, formed the

Igniter. This mixture

formed a plug 9,6 mn in

thickness of 3,8 mrr,

was tamped in place to a density of 1.3 g/cm3 and

diameter, tapering to 6.3 mm In diameter, and having a

From data in the lit~rdtl~reg this igniter r~l~?s,?ci

abnllt ?20 calories, but when on~ considers thr slow rate of fu~icm (cam

3cmls), the measured rclc,]w of six cubic centirnl?tcrs of per-:’”,!llcrltga5

(probably mostly hydrogrrl), and tk,~ ratr of hclt Iu$s (alii,~b.ltict,-,.?r-,~tlir~?

cd. 3770rCl, it seems prollable thdt, only a w1,III part of the ignitr h~~at,

\131paI:rIw,]< inv~lvert in an,)’cxp~’riml’t!f,,

ttl(?pl-w’!$’r’., (’l)lll(i Il,lv,! l),- $:1 l’l}ljl:l”lil~,

III rlt “; t,tl~’ywili h,lB 1“,)(,1’1’,’1 to by

7.

SieveOpening

(Urn)

14(M

1000

710

500

350

250

177

?25

44

$s

TABLE I

HMX PARTICLE-SIZE DATA

Class A(HOL7&4-3) (HOL-:20-32)

1

7

92

1.3

4.0

15,6

18 2

27.8

11.8

12.1

4.9

4,3

Class C(HO:.~;03-9 )

0.3

2.8

8.6

17.9

19.6

18.2

9.3

5.0

5.4

9.9

specificSurface drea “

(cm2/ql

8.

TABLE II

SHOT SUMMARY

Expt .No.

——

1

2

3

4

5

6

7

8

9

10

11

1?

‘3

Shot No.

C-5009

C-5004

C-4983

B-8500

C-5002

C-4998

C-4958

c-4997

C-5013

C-50CXI

C-5014

C-5015

C-5005

HMX

F

F

A

A

C/Aa

c

c

c

c

c

c/ca

A/Ca

F/Ca

(Mnll

o1.8

0

0.8

1.8

0

0.8

1.9

1.8

1.8

1.8

1,8

1.8

Oisks(No.)

15 (27)b

6 ( 4.8)

1 ( 1.8)

13 (10.4)

12 (22.8)

8 (14.4)

18 (3?.4)

1 ( 1.8)

1 ( 1.8)

1(1.8)

Booster

-@Q__

220

685

220

220

220

440

220C

220

220

2?0

HMXd00T

m

72

83

45

46

99

50

67

67

52

106C

48

43

37

aThe left s@ol denotes the HMX type USPCI for the ??O-mg combustion incrt?mcnt;the second ~ymlml ldcntlfles the HMX typ~’ filling in remainclrr of tube,

hNumhcPs In parenthest?s are the totzl thickness of disks traversl?d Iw?for(?DD1”occurr~~ am+ :r~ obtalnd as th~ profillctof disk thickrl~’:sand th(? numl!w ofdisks travcrsl?d.

~LoiIIjI?dat 0.6 gI/cc.

dEntries arc the net length of HMX collmlrltrdVf7i”51?r! fron] igniter to tht?pointat which clctonatlon cccllrrml,

‘Mu,lsilr(:dfrom disk at,tol)of I)rils$tlil’1’.

9.

Experimental Results

Experiments 3,4. Experiment (4) is diagramed in Fig. 2. A series of

diaphragms cut from neoprene sheet 0.S inn thick was arranged throughout a

column of HMX-A, and burning was Ignited at one end. The diaphragms in this

experiment and those in (7) were cut with a cork borer and were somewhat

ragged: however, it appears that when all of the results are considered

together, these disks were adequate for the purpose.

The purpose of (4) was to interfere as much as possible with convective

combustion and then to observe whether DDT still occurred. It did occur and

at a distance in HMX-A of 46 mm. (See footnote to Table II. ) This result was

encouraging in that the distance to DDT was in the range found by Griffiths

and Groocock (Fig. 1).

For comparison, experiment (3) was fired (Fig. 3). With no diaphragms

present, the distanc~ to DllT was found to be indistinguishable from that of

(4). (Frag~ents of the steel tube are shown in Fig. 4.) This agreement was

puzzling at the time, and proved later to depend partly on the size of the

initial HMX increment In (4).

Excwimf!nts 1,2 and 6,7, In th~si’experiments the effect of diaphragms on the-—.—

DDT distance was explored in HMX-F and HMX-C. A standard initial increment

size of ??0 mg of HMX wa$ adopted and, where the diaphragm thickness of 1.8 or

1.9 Inn was Use(l, the disks were machintwl on a lathe to a precfsion ~

so as to show a slight Intt?rfcrence ftt when tamped in plac~!.

t In expcrimeni (1) (Fig. 5) the ~tcel tube was increased in d

f 0.0? mm

ameter to

76,2 IIM. At this diatnet~’rthe tllh~ did not bllrst during firing and a mor~t

desirable rt?cnrd ws oht.alndblc (Fig. 6); howwcr, because of the long wait

r~quired for thr m,lchinr work this 517P tube WY? not ust!d in other exp}!rlm~nts,I

10.

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12,7 MM

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6,35 MM I,D,

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Experiment (6) was as diagramed in Fig 3. From the results of experim~nts

(1), (3). and (6) It is evident that there is a llini~lJM in the DDT distance az

a function of th~ average particle SIZQ, of specific surfac@ area, or Prp~um-

ably, of pmneahillty as found by Griffiths md Wmcock.

Tt-Ie [!ffect of didphraqms in HMX-Cwas te<t~~d {n exp~riment (7) (Fig. 7)

and In HMX-F in exp~rimmt (2) (Fiq. 8). When th~ rr%ults of thoso exp~rlmcnts

are compared with thr)%p frnm i,1) and (6), it is som that th~ DOT distances

thl~

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shorter than the result for (6)(58 rrrn),wtl~re no diaphragms were employed.

Comparing this rt?qult with thn flndirrq nf Gr~fFith and Groocock that venting

of thPil’ tubes cauwd an incrl.lrit?in the DOT distance, one is led to the con-

jecture that the first diaphragm prevents the t?~capt?of combustion prwhcts

frr.xn the cr)mbustlnn 7r’)ne and thu< incrca~rs the rate of pre~$urf! rise and its

tIttW’Idant effc%t on the hurninq ratf! in the COmhlJ$tiOn zrlno.

Ex~Frimcnt 10. An illustration of the offcct of rcducod rate of prt;~>urc risi!—..—.—

in the combllstion zr)nr?is nffertvl in this ~xporimnnt (Fig. 10), A smdll br~f;s

tllh~ was in%rrtcri into the stwl tl~hl?and wat lmrtrd with ?70 mg of HMXat a

loadinq rinnsit.y of half t.htll,nf hlilk drn’;it.y-- 0.6 q/cn13. The 111~ di~t.lnc”,

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doubled. This result \s attributed to the decreased specific surface area of

tU4X-C relative to that of HMX-8 and the slower pressure rise during combustion.

Discussion

The Combustion Zone

Combustion begins as a conductive process. As the pressure rises it passes

into convective combustion, which more rapidly ignites additional explosive.

Experiments (5), (11), (12), and (13) show that the rate of pressure rise is

important; any leakag~ of combustion products from the combustion zone slows

the rate of pressure rise and increases the distance to detonation. The

diaphragms keep the products in place and thus cause th~ distance to detonation

to decrease. Griffiths and Groocock also found that venting of their tubes

resulted in longer runs to detonation than wh~rl the tubes were closed.

Convectiv~ combustion of explosives over long distanc~s is not nec~s~ary

cr impnrtant for DOT, as is shown by the exprrimcnt,s with di~l>hragms positioned

every 7 mm, GasI’% COIJlri not. p(l~s thr di~i)}~r,]gmsto prop,~g(~t,tzconvcct,ivc

combll$tion heyoncl thrm.

Thr rapid wavI_Iohsl~rv~ldby PI-iI-l~anflR~~rl]~(:k~rIII(Iynrigirl,]tcin thr colIIl~II:,-

tiorl~nnoo It ‘Iigllt})(’driv((l hy (IgllI;I,yig”lil(’r,or it might, btt rlII~J to r~,]f:-

tlon of p,yrol,y5i:-1prOflIICt,’;,9 The ot’igi~lof thl? W,IV{?h,ls not, IJPPI)clpt.(~rmillc~l,

in p,lrt b(I(:,~lJrl~ioni~llt,inllsifjllll?frml any Wf7VI~Sill ttlo itliti{~lpflr’l,of thr

nor pIW~-lVl<h;lv~ lII~I?IIvoI,y clifficllll,I(Iohhin, an~l w!lrrlol~l,,lin(~,l,I1;ILJITI)PP!!

dlffimllt to i’t.~’rpr-~t,(If cvi[ll~rl[:r(lin thi’ wot.k of Pricv arltlBormckIIr,

, Grlffittl’;,3nllGrotll:(l(-$,arl(lttl;! pr(’f;l’flt,Illttlor.

25.

fran the right-hand edge of Fig. 1 toward the minimum. The upturn at the left

is caused by behavior in the build-up zone to be di~~ussed below.

Dark Zone

The combustion zone is often terminated by a region which emits little or

no light. Brandon, in early work with I ~,~pellant, and Griffiths and

Groocock with high explosive, have observed the dark region. Sometimes resona-

tion has been seen to propagate backward through it while the detonation goes

forward. In M-7 propellant, resonation without simultaneous forward-going

detonation has also been observed.

Figure i4 is ‘n example of the occurrence of the dark zone i;,M-7 propel-

lant. Viewing the record with time horizontal, OIIV sees the record of light

frcrn the burning !t,~rting at early time at the lower left and progressing

slowly upward. The light has d fu.!zy outline because the propellant is granu-

lated. Abruptly, th~ light

region spre(?tlsboth fovward

wave arises at some di~ltance

ter-minate$ at its leading (upper) edg~ and a dark

and hackw(lrd. After a lapse of time a lumino~ls

ficw the beginning of the dark region and proceeds

wit;) an initial velocit.f much higher tll,lnth,~t of the burning wave before the

onset of the dark zone. The nc’,vIuminolls wave accpleratps and b.womrs a

det~nation wav?.

This dark Zon(} is intcrprpted as a region of b~ri cmllp~ction. Ar the pres-

sure rises in tht~ cmthustion zon!?, a critical prcssllt.uis relched at which the

grdnular brci of explosivo begins to collapsr and to re~trict the f[lrther flow

of cooled crmdlllstiorlprodltcts prt?ccw!ing thr flame front. At (irst the masst

velocity and ratv of comp~ction are $0 smr~ll th~t no hl.lrningis ignited by the

compaction, CIrl(da pll.igof unrr(~ctiflqexplo’;ivt>is forml-?d, As bt)rrllngcontinues

in th(~ collll~lictior]717fI(I I.}111 r !S iflij lIf’I~;TIir(’ dcf:I!lPrdt.P9 ttlt? plug and tht’ plllg

26.

“8A++i’.’,.&. .’a$u~

27.

grows at the front at an Increasing rate. When compaction of the explosive at

the front of the plug becomes sufficiently rapid, friction between the grains

and adiabatic shear within the grains reignite burning at the front of the

plug. This burning develops into a detonation,

Bl~rning may also be ignited by friction betw:ell tk,eplug and the confining

wall. When this happens, photographic observation of the dark zone is impos-

sible. This burning may produce random ionization signals, but however confus-

ing to observation, it is inconsequential for the events leading to detonation,

because of the small surface area involved.

In experiment (10), Fig. 11, and experiment (l), Fig. 13, long regions of

little or no exp~nsion of the internal bore of the steel tubes indicate the

occurrence of plugs. If the pressure in the combustion zone rises rapidly

enough, the plug may be v(lryshort or may not occur at all. It is not etident

in experiment (13), Fig. 130

The BIJilciu~to iletnnation— ---....—.—..

Reign ition of burning hi’yonclthe dark

tion becolll~~shigh enoligh. IntPrcrystdll

two hc(lting mecllf?nlsmswhich ar[? import,!n!

long been important in the study of the

zone occurs wht?n the rate of compac-

nc frictio’1 and aciiabatlc shear arc

in this rcglon, Adi~hatlc stle,]rhas

brhavior of metals 10and has become

of intcrt:rt for cxplo~ivr~ in rccl~nt ycnrs. 11,1?In this form of shci~r,

occllrring within the cry$tl~llltf’$,tht? rclt,rof cflPrgy ri(?posItIon in thl?sI1(,Ir

zone greatly cYcI~t~Ilsthe crlt?rgy loss by corlfillctir)ll.ThermJl soft~!n(ng

, Cii$plt?c(”;work hl~rdmlrlg a~ tllI’Aminl)fl( Cll[irlgI’in 10(~,11str(}n~;th. Corll,lnllO(l

stres~ cllllf117 conl.inuf7(islip vII1.hfurtll(lr10(:,11cn(?r”gydt’~J{J5ittClH dn[lFlt.ll?n[!rlrlt.

trwyl~r(llllr>rrls(l, Thus, t,tll’pr’ol:’?’,;lof locl]l Il[?llf.lf)gcolltInlll’sarul ignIt1011

may Crl’)lll’.Aflil~llif-st~,l,it’is of prlrl.iclllllrirll.1’r~’’;l.1)1’1’1111’1(’it ifl[:r-l’ll’~ll’;tht’

28.

There Is as yet little evidence for the effect of adiabatic shear in the

explosive literature, but an implication of its effect occurs in the work of

the Cavendish Laboratory. 13Lead azide was initiated by aluminum spher,.s

200 + 30 pm in dian,eter impacting at. a velocity of 200 m/s. Because the

energy delivered in the impact was insufficient to cause significant bulk heat-

inq of the lead azide, persuasive arguments point to adiabatic shear, occurring

during rapid plastic deformation of the explosive at the point of impact, as

the most. plausible cause, This result is the more dramatic wl~en, in a drop-

weight impact test where the energy delivered to a sample of lead azide was

orders of magnitude greater, the lead azlde failed to react. Because ~nerqy

was delivered slowly hy the drop wplght, apparently acilahatic shear was absrnt.

The occurrence of acliahatlc shear in the buildup procc$s offers an explana-

tion of tht?minimum In thr DOT dist[lncc in Fig. 1. Two @ppoL~ing p~”Ot-~?S$P~arp

.-

29.

as low as 1.3 rrrn/psIn steel tubes, Stable ”velocities both below and above

that of sound in either the explosive or the steel confinement were observed.

The value of the velocity ol)talned depcnried on the degree of confinement; heavy

confinement always rcslllted in hiqh-order detonation. Pressures were measured

with quartz qauqps in the wall of the conflninq tut)~, and it appeared th~t

stable low-velocity ci~tonation could i)~obtained below about 10 Lh,tr. Ermolapv

e‘: al, and Slllimov et al.19

have attempted theoretical treatments of tl~ese

reslllts.

Thu~, alt,hnllqhtht? huilrhip procos~ may start as a subsonic, plastic wave

with sllfficicnl.cnnfinrvn~nt.,en~rqy los~ is redllc~d so that pressure in tht~

reaction region rlzrt to Snnlllcritical value, as ~iJsr.r’vrdby Obm(!r]lnpt al.,

and

comp’

30.

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1971{),

0. W, W, llrdrl(!l~n,Jr, , i3,11ii’;fics Snrl,lt)f]l)rol)tl),;Rt?~~llrl.N(), 64, NOVIIIIIIII-

l~’\fi- Fr?tlt”ll,lr’.y 194/, RPIl,tI~mJArI-i IrIIl R(’’;l’!rrllDivisinll, Rnll:l,1!)(I11.1~;

Cmp!lf)y ,

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Wt~41i}r)rl’;cPlll,l’t’in Sllpllllf’1, nf Ilif)ll rr~l~f’lly PI* IIp IIll,lrIl ,vfl)t,y (iII v’.i) Pl,)(ltMllI

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(l(~til),

31.

11.

12.

13,

14,

15,

16,

R. E. Winter and J. E. Field, “The Role of Localized Plastic Flow in the

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(1975)0

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C. L, Scott., “Effcc~ of Part lc]f? Silo on Shof:k Initiation of PEtN, ROX,

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lfl-?lAIIqII-,l,10/’),l)p, ?47-t5r).

R. H. Pinl’!~,!r,R, Il. llnt,t~l’,1.l’r,anfl M, S, Mill ic,)nt “[h(; [)flv:l.or

Sp~~clfic Stlrf,lrt-on 1,111’71~f)l:kSf’rl(,lt,iv{ty of PI(’I,*,o~l(ir,lrlljl,~)PI IN,”

Expln~lv’,loff(~~, 1}1!1-1!!’7(lqh’1~,

R. W, GIIII,~~Il,Ir]llh, MiI(I’k, “1 l,IItl~’~r(lr~l,’,,In(!Cr)InjJrt’,1,I)n WrvIJ’,IIIJIln,~

It’llrl’’litfl)l) ft’wt nl’rllll)r’llf ilMl tn [11’!olll!I(w) in $oi i~l’,,F i!~l~l,l~5ylll~)[~,il~l!

(lnttIrn,Il10II!l)nrl Cnml!ll,lif)fl,11,1/-S’,~l,WI IIi,ImI; ,Iml Wi 14iIIIl:ill!lt,illl(~rl’

]qf;”,

0, Pt’irl’Ilnll!1,F, W(’hrl!’l’,“1 Trll III; il. infl fIIIIU f\llr II II to rlf’f I}rlllt Il)rl irI

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A, V, CI)IIIIIIIIII,A, 1, Km’(llkov, arl(!A, A, SIIIIIIII)V, “PrqL)~)I,jIliOII of i,.rw-

v~lol:lly p,, r,,,,,,,t i(,~, RI’IJ1111,’i I 11 lliqh D(IrI\ iLy Sfllld r~p](ljlivlll],ll

clll!f’llotj(~lov(ll:” Ak lf~,hl~llkS!1{ ,InllAk.\(l,N:~lllAtl;l,$’;1{,19/’1,pi),343-3,!),

Fng, Ir,ltl;, f(lr’ s,7111ill I ,lll(~tllI}IIIII; 1’,11, 4(!I ‘~~],1, L“;-~llrlo/}’)/fiti,

32.

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?0 , A, A. Sulimov, B, S. Ermolaev, A. A. Borisov, A. I. Korotkov, B. A.

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