(P.0, NO ) FINAL RZPOPT

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NOTICE

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1 their Research cmployeer~lopm~nt and De Administration nor any

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A p r i l - &Time 1 9 7 5

ABSTRACT

A t e c h n i q u e has been d e v i s e d t o determine t h e c o n f i g u r a t i o n dependent i n d u c t i o n t i m e f o r t r a n s f e r o f d e t o n a t i o n from a small diameter c o n f i n e d donor t o a l a r g e d i a m e t e r unconfined a c c e p t o r v i a t h e d e t o n a t i o n e l e c t r i c e f f e c t . T h i s r e p o r t e x p l a i n s some o f t h e a t t r i b u t e s and l i m i t a t i o n s o f t h e t e c h n i q u e and i n c l u d e s t e s t d a t a f o r PETN, RDX/Sylgard, and HNS e x p l o s i v e assemblies.

DISCUSSION

E x p l o s i v e t r a i n s a r e f r e q u e n t l y used i n ERDA components f o r t i m e sequencing

,

o r i n f o r m a t i o n t r a n s m i t t a l requirements. A t y p i c a l e x p l o s i v e t r a i n may

c o n s i s t o f a d e s i r e d l e n g t h o f small diameter MDF, which i s t e r m i n a t e d w i t h a much l a r g e r d i a m e t e r b o o s t e r s e c t i o n f o r a c t i v a t i o n o f downstream components. - P r o p a g a t i o n c h a r a c t e r i s t i c s a r e determined by i n t e r a c t i o n s between geometry and m a t e r i a l dependent waves generated a t t h e i n t e r f a c e between t h e MDF and b o o s t e r .

The purpose o f work r e p o r t e d here i s t o e s t a b l i s h a technique s u i t a b l e f o r p r e d i c t i o n o f these geometry and m a t e r i a l induced e f f e c t s thereby a i d i n g component design. T r a n s i t t i m e v a r i a t i o n as a f u n c t i o n o f t h e i n t e r f a c e c o n f i g u r a t i o n was s e l e c t e d as t h a t p r o p a g a t i o n c h a r a c t e r i s t i c t o be measured. T h i s v a r i a b l e p r o v i d e s i n s i g h t i n t o t h e e f f e c t s o f wave i n t e r a c t i o n s and i s c e r t a i n l y t h e most convenient and l e a s t expensive of t h e dynamic c h a r a c t e r i s t i c s t h a t c o u l d be measured.

EXPERIMENTAL TECHNIQUE A N D RESULTS

The experimental technique i s i l l w t r a t e d i n F i g . 1.. The small diameter c o n f i n e d donor i s segmented i n t o known l e n g t h s , which a r e i n t u r n

. . separated by a i r gaps o f known thicknesses. The a i r gaps p r o v i d e . heterogeneous i n t e r f a c e s which, ,when shocked, generate e l e c t r o m a g n e t i c d i s t u r b a n c e s d e t e c t a b l e byathe antenna(1). O f those m a t e r i a l s t e s t e d ( w a t e r , P l e x i g l a s , Krylon, and a i r ) t h e a i r gap produced both. t h e f a s t e s t r i s e and h i g h e s t a m p l i t u d e s i g n a l s .

The p i e c e s o f t h e e x p l o s i v e t r a i n a r e supported by a hardwood b l o c k which has been p r e c i s e l y machined t o c o n f i n e each p i e c e halfway around.

i t s c i r c u m f e r e n c e . The donor segments were h e l d i n a s p e c i a l l y made f i x t u r e w h i l e b e i n g c u t t o l e n g t h w i t h a r a z o r blade. Of t h e v a r i o u s methods t r i e d , t h i s produced t h e most p e r p e n d i c u l a r c u t w i t h t h e l e a s t 'gouging o f t h e e x p l o s i v e c o r e m a t e r i a l . The a i r gap thicknesses were

c o n t r o l l e d by punching c i r c u l a r holes i n ' p l a s t i c shim s t o c k and i n -

s e r t i n g t h e s e shims between t h e segments o f t h e donor w i t h proper alignment o f t h e h o l e s .

a

Since a f i n i t e t i m e i s r e q u i r e d f o r a shock wave t o t r a v e r s e an a i r gap and r e i n s t i t u t e d e t o n a t i o n , i t was a t f i r s t t h o u g h t necessary t o d e t e r - mine t h i s t i m e f o r each t y p e of donor. One method used was t o v a r y t h e

l e n g t h s o f t h e donor segments, w h i l e h o l d i n g t h e a i r gap t h i c k n e s s e s c o n s t a n t . The excess t r a n s i t t i m e due t o gap e f f e c t s equals t h e t i m e a x i s i n t e r c e p t o f a l i n e a r f i t t o t h e d i s t a n c e - t i m e data. Another

method used t o d e f i n e a i r gap excess t r a n s i t t i m e s was t o h o l d t h e donor l e n g t h s c o n s t a n t w h i l e v a r y i n g t h e a i r gap t h i c k n e s s e s . An a n a l y s i s s i m i l a r t o t h a t o f t h e f i r s t method i s t h e n used t o f i n d t h e excess t r a n s i t times. F i g . 2 shows r e s u l t s f r o m such an e v a l u a t i o n . Here t h e donor, e i t h e r 0.21 g/m o r 2.1 g/m commercially a v g i l a b l e PETN MDF, was segmented i n t o 6.35 mm l e n g t h s . A sequence o f a i r gaps w i t h t h i c k n e s s e s o f 25, 51, 127, 51, and 25 pm, r e s p e c t i v e l y , were i n t r o d u c e d between segments o f t h e donor. The r e s u l t a n t i n t e r f a c i a l s i g n a l s were t h u s separated by t h e t i m e r e q u i r e d f o r d e t o n a t i o n o f a 6.35 mm segment p l u s t h e t i m e t o t r a v e r s e an a i r gap. Average i n t e r f a c i a l times correspond- i n g t o t h e sequence noted above were 917, 925, 938, 925 and 917 ns f o r t h e 0.21 g/m MDF and 900, 908, 921, 908 and 900 ns f o r t h e 2.1 g/m MDF. Since t h a t t i m e i n t e r v a l which i n c l u d e s t h e t r a n s i t t i m e o f t h e 127 pm

gap should be maximum, these d a t a i n d i c a t e t h a t t h e s t a r t o f an i n t e r - f a c i a l s i g n a l i s generated when t h e shock wave e x i t s r a t h e r t h a n e n t e r s a donor segment. As may be seen from t h e curves o f F i g . 2, t h e t i m e r e q u i r e d f o r a shock t o t r a v e r s e an a i r gap i s n o t a l i n e a r f u n c t i o n of t h i c k n e s s . I n f a c t t h e e f f e c t i v e v e l o c i t y a t which t h e d e t o n a t i o n

process propagates across an a i r gap, a p ~ a r e n t l y i n c r e a s e s w i t h i n c r e a s i n g gap t h i c k n e s s . T h i s anomaly, a l t h q u g h i n t e r e s t i n g , was n o t pursued here s i n c e a knowledge g f t h e t r a n s i t t i m e f o r an a i r gap i s i n f a c t n o t necessary t o determine excess t r a n s i t times i n a c c e p t o r s as w i l l be e x p l a i ned be1 ow.

P r e l i m i n a r y v e r i f i c a t i o n t e s t s were conducted u s i n g PETN as b o t h donor and a c c e p t o r . F i g . 3 shows a t y p l c a l r e c o r d f g r t h i s work, and F i g . 4 i l l u s t r a t e s t h e method used t o determine excess t r a n s i t times. F i g . 3 i s d e r i v e d f r o m t h e assembly o f an EX-12B d e t o n a t o r , a 5.1 mm diameter by 2.0 mm PBX 9407 p e l l e t , 6.35

mm

l o n g donor segments, and a 12.7 mm diameter by 6.35 mm a c c e p t o r p e l l e t . The donor was 2.1 g/m PETN MDF, and t h e a c c e p t o r was PETN a t a d e n s i t y o f 1.53 Mg/m3. Each donor s e y ~ r ~ e n t and t h e i n t e r f a c e between a c c e p t o r and antenna were separated w i t h 25 pm a i r gaps. However, t h e l a s t donor segment was i n d i r e c t

.contact w i t h t h e a c c e p t o r s i n c e a gap a t t h i s i n t e r f a c e would p e r t u r b p r o p a g a t i o n c h a r a c t e r i s t i c s . Eleven s i g n a l s a r e v i s i b l e I n F i g . 3. The f i r s t two s i g n a l s a r i s e from t h e d e t o n a t o r w h i l e t h e t h i r d one i s

generated by a 25 pm a i r gap between t h e PBX 9407 p e l l e t and t h e f i r s t

between t h e l a s t two s i g n a l s . I f s i g n a l s were generated as t h e shock e n t e r e d a donor segment t h i s s u b t r a c t i o n would' not. be v a l i d and a know- l e d g e o f a i r gap t r a n s i t times would be necessary f o r d a t a r e d u c t i o n . The expected v e l o c i t y f o r PETN a t a d e n s i t y o f . 1.53 Mg/m3 i s 7.482

km/sec(2). The curves o f F i g . 4 a r e least-squares f i t s assuming a slope o f 7.482. These l i m i t e d da'ta thus i n d i c a t e excess t r a n s i t times (equal t o t h e t i m e a x i s i n t e r c e p t s ) of .40 .ns and 130 ns, r?espective.ly, f o r t h e

2.1 g/m and 0.21 g/m donor systems. . , .

Tests u s i n g an RDXjSylgard e x p l o s i v e as donor and acceptor were a l s o conducted.' F i g . 5 shows a t y p i c a l r e c o r d . Here t h e donor c o n s i s t e d o f f o u r each.19.05 mm l o n g segments which were e x t r u s i o n loaded s t a i n l e s s s t e e l tubes w i t h w a l l t h i c k n e s s . o f 0.25 mm. The acceptor was an uncon- f i n e d 12.7 mm.diameter by 6.35 mm extrusi.on formed p e l l e t . As above t h e donor segments and t h e i n t e r f a c e between acceptor and antenna were

separated w i t h 25 pm a i r gaps, a n d . t h e l a s t donor segment was i.n d i r e c t

c o n t a c t w i t h t h e acceptor. These t e s t s , however, proved u n s a t i s f a c t o r y because o f e l e c t r i c a l p o 1 a r i z a t i o . n w i t h i n , t h e acceptor. . As may be seen immediately b e f o r e t h e seventh s i g n a l i n ,Fig. 5, t h e s i g n a l s due t o shock induced p o l a r i z a t i o n a n d . t h e a i r gap i o n i z a t i o n s i g n a l a r e super- imposed. An a c c u r a t e knowledge o f shock wave. a r r i v a l a t t h e acceptor p e l l e t o u t p u t s u r f a c e i s t h u s n o t o b t a i n a b l e f o r t h e c o n f i g u r a t i o n used. F i g . 3 a l s o shows t h e e f f e c t o f p o l a r i z a t i o n . . . However, f o r PETN systems t h e r e l a t i v e s i g n a l amplitudes f o r p o l a r i z a t i o n . a n d a i r gap were such t h a t t i m i n g i n f o r m a t i o n was o b t a i n a b l e ;

T h i s problem f r o m p o l a r i z a t i o n w i t h i n t h e acceptor was a l l e v i a t e d by s i m p l y i n c r e a s i n g t h e a i r gap t h i c k n e s s a t t h e acceptor antenna i n t e r - face. Gaps o f 6.35 mm and 12.7 mm were i n v e s t i g a t e d f o r PETN systems. Both gap thicknesses gave unambiguous s i g n a l s , 'and e i t h e r would be acceptable. However, a gap t h i c k n e s s o f 6.35 mm i s p r e f e r r e d and.was used f o r a l l subsequent t e s t i n g , s i n c e measured s i g n a l amplitudes vary i n v e r s e l y w i t h d i s t a n c e between source and d e t e c t o r .

The n e x t o b j e c t i v e s were t o a p p l y t h e method t o HNS and t o r e f i n e t h e technique. Two types o f compacted HNS I 1 MDF were prepared. P e r t i n e n t p r o p e r t i e s a r e g.iven i n Table I. Acceptor p e l l e t s were pressed t o 2.54 mm t h i c k n e s s x 12.7 mm diameter. Up t o t h r e e p e l l e t s were stacked on each s h o t . The HNS I 1 p e l l e t s were made from t h e same two l o t s used f o r m a n u f a c t u r i n g t h e MDF; t h e HNS I p e l l e t s were made from Ensign-Bickford L o t 5737 and Chemtronics L o t 66-48.

I n i t i a l i n t e r e s t was i n d e t e r m i n i n g whether d e t o n a t i o n would t r a n s f e r f r o m t h e MDF t o a p e l l e t pressed from t h e same m a t e r i a l a t approximately t h e same d e n s i t y as i n t h e MDF. The p e l l e t s were pressed from HNS

I 1

t o 1.65 Mg/m3. D e t o n a t i o n d i d n o t t r a n s f e r f o r e i t h e r t h e E-B o r t h e

t h i c k n e s s x 12.7 mm diameter i n f r o n t o f t h e p e l l e t w i t h t h e MDF i n s e r t e d through a h o l e i n t h e c e n t e r of t h e d i s k and c o n t a c t i n g t h e . p e l l e t . The t h i r d was t h e 'placement o f a PBX 9407 b o o s t e r p e l l e t 2.0 mm t h i c k x 5.1 mm diameter a t 1.62 Mg/m3 between t h e MDF 'and p e l l e t . With t h i s m o d i f i - c a t i o n r e a c t i o n occurred i n one o f t h r e e shots.

The e f f o r t was t h e n d i r e c t e d toward more c l o s e l y s i m u l a t i n g t h e con- d i t i o n s e x i s t i n g i n t h e end t i p s f o r t h e C-4 energy t r a n s f e r system. P a r t i a l r e s u l t s o f a p r e s s i n g s t u d y which was b e i n g done a t Pantex i n d i c a t e d t h a t HNS I when pressed a t 220 MPa ( t h e pressure a t which t h e end t i p s a r e f i l l e d ) y i e l d s a d e n s i t y o f approximately 1.55 Mg/m3(3). Therefore, p e l l e t s were pressed from b o t h Ensign-Bickford and Chemtronics HNS

I

a t 1.55 Mg/m3. Shots were b u i l t t o a s c e r t a i n whether t r a n s f e r would occur from E-B MDF t o an E-B p e l l e t , from E-B MDF t o a Chemtronics p e l l e t , f r o m Chemtronics MDF t o a Chemtronics p e l l e t , and from Chemtronics MDF t o an E-B p e l l e t . A t y p i c a l r e c o r d i s shown i n F i g . 6. R e s u l t s a r e g i v e n i n Table 11. Both t r a n s f e r and n o n t r a n s f e r o f d e t o n a t i o n t o t h e a c c e p t o r p e l l e t was observed. The c a l c u l a t e d excess t r a n s i t times f o r t h e acceptor p e l l e t s a r e based upon a d e t o n a t i o n v e l o c i t y o f 6.75 km/s f o r HNS I a t 1.55 Mg/m3, which i s an i n t e r p o l a t i o n from measurements on Chemtronics L o t 66-48 a t d e n s i t i e s o f 1.50 and 1.60 Mg/rn3(4). E v i d e n t l y t h e donor s i z e was near t h e t h r e s h o l d f o r i n i t i a t i o n o f t h e HNS

I

a t 1.55 Mg/m3. A l s o evidence from t h e s h o t remains, e.g. pieces of t h e p e l l e t s t i l l i n t a c t and l e s s d e s t r u c t i o n than expected, i n d i c a t e d t h a t t h e e n t i r e p e l l e t d i d n o t detonate i n many o f t h e shots.

For comparison w i t h a i r gap excess t r a n s i t times i n PETN systems, those f o r HNS were determined. HNS MDF segment l e n g t h s were 6.35 mm and 12.7 mm and a l l a i r gaps were 25 pm. Excess t r a n s i t times due t o a i r gap

e f f e c t s were c a l c u l a t e d by two methods:.

Excess T t = 2 Tt (6.35 mm l e n g t h segment)

-

T t (12.7 mm l e n g t h segment) and

Len t h o f Se ment Excess Tt = T t ( f o r a segment l e n g t h )

-

Detznation

V ~ l o ~ t y The d e t o n a t i o n v e l o c i t y used i n t h e second f o r m u l a i s t h a t g i v e n i n Table I. Average excess t r a n s i t times c a l c u l a t e d by each formula f o r E-B MDF were 12 and 11 ns, r e s p e c t i v e l y ; f o r Chemtronics MDF they were 13 and 12 ns. A f t e r s u b t r a c t i n g these excess t r a n s i t times from t h e t o t a l segment t r a n s i t times, t h e c a l c u l a t e d average v e l o c i t y o f each MDF agreed w i t h t h a t i n Table I w i t h i n 0.1%. For PETN MDF excess times f o r a 2.5 pm a i r gap was 9 t o 10 ns. T h i s decreased t i m e i n t e r v a l r e l a t i v e

t o HNS systems i s p r o b a b l y i n d i c a t i v e o f m a t e r i a l s e n s i t i v i t y .

had a l l been l a i d d i r e c t l y upon t h e s t e e l pad and t h e s i g n a l - t o - n o i s e r a t i o was v e r y good. However, when t h e shots were placed upon a wooden s t a n d about 0.6 m above t h e pad, an o r d e r of magnitude i n c r e a s e i n e l e c t r i c a l n o i s e r e s u l t e d . Records a r e shown i n Fig. 7 f o r a comparison o f n o i s e p i c k u p under i d e n t i c a l circumstances except f o r s h o t placement.

C O N C L U S I O N S . .

Donor

>

Detonator

. .

20 4 0 60 80 100 120 Gap Thickness (pm)

a d

thdrd

domr

s e g w ~ ~ t s

A i r

gap

bWam1~l

%hYN

%mJ

f@v%A

&mr

s m . n t s

fitr

gap

be%wwn

faup& anel

QOFtYl

&nap

sqp-ren.ts

A i r

gap betmiwn

f t f t h

and

sixth

donor

segments

A i r gap

between

s W h

and seventh

donor

segments

A f r

gap

ktwrrew

seventh

and

eight donor

segments

Air gap

between

acceptor and antenna

Fig. 4, Transi' '

PETN PEllet Thickness (mn)

Camnent

_- S t a r t

o f current flow i n bridgewire

B r i dgewi

r e burst

A i r gap

between

detonator and f i r s t donor segment

A i r

gap

between f i r s t and second

donor

segments

A i r

gap between second

and

t h i r d donor segments

A i r

gap

between

t h i r d and fourth donor segments

A i r

gap between acceptor and antenna

r

Final

Donor

Segment-Acceptor

Pellet

Interface

0

Sweep i s f i r s t Part

o f A

Sweep

Expanded

Shot Above Pad

Shot

On

Pad

Fig.

7.

Comparison o f CDU

Induced NoSse

as a FunctSon

Tab1 e I . P e r t i nent Properties of HNS MDF

~nsi~n- irkf ford

Chemtroni cs

Property HUS 5737-IIB HNS 6647-IIA

MDF Inner Diameter (mm)

MDF

Outer Diameter (rnm)

MDF Load Size (g/m) 0.364 0.386 :

HNS F i nal Densi t y (Flg/m3) 1.69 1.67

MDF

able

11. Results of HNS Work f o r an Acceptor

P e l l e t Density of 1.55 Mg/m3

~ n s i ~ n - ~ i c k f o r d ~ Ens i gn-Bi ckford

Acceptor Pel 1 e t Acceptor Excess Trans i

t

Time (nsec) d Ensign-Bickford Chemtroni cs 4

2

Ensign-Bi ckford Chemtronics b Chemtroni cs Chemtronics , Chemtroni cs Chemtroni cs

4

1 Ensign-Bickford 43 Ensign-Bi ckford Chemtroni cs

.

Chemtronics a P r o p e r t i e s given i n Table I. b ~ r o p e r t i e s given i n Table I. c

1 2 . 7 nun diameter peZZet pressed from HNS-IB, Lot No. 5737.

d12. 7 mm diameter p e l l e t pressed from HNS-IA, Lot No. 66-48.

. . . . . . . .. . . _{. .} .. REFERE,NCES' . . . . .

Bernard 'Hayes, "The D e t o n a t i o n . E l e c t r i c E f f e c t ,I1 J o u r n a l d f Appl i e d Physics, Vol

.

38, No. 2.. (February 1967). . .

" P r o p e r t i e s of Chemical Explosives 'and E x p l o s i v e Simulants

,"

Compi l e d and. E d i t e d . by, D. M,. Dobraty; UCRL-51319, Rev.

1

( J u l y 31, 1974).

J. A. ~ r u t c h ~ e r ,."HNS ~ r e ' s s ~ b i . . . 1 i ty Study," MHSMP-75-27 (June 1975). . .

R. J . Slape, " ~ e t o n c i t i o n ~ r e s s h r e o f HElS I and 1 1 MHSMP-75-23, June 1975.

R. B. L i n v i 1 l e y 'Signal Enhancement f o r t h e D e t o n a t i o n E l e c t r i c E f f e c t , " PXD-13-75 (June'1975)., ' . . '

. ,