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DEVELOPPllENT DIVISION APRIL - JUNE 1975 FINAL REPORT. Normal Process Development Endeavor No. 231

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DEVELOPPllENT

DIVISION

APRIL

-

JUNE

1 9 7 5

FINAL

REPORT

Normal Process Development

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DISCLAIMER

(3)

DISCLAIMER

(4)

NOTICE

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C . E . Canada '1.

D.

tianu

DEVELOPMENT. D I V I S I O N

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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 diameter unconfined acceptor 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 of 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 technique 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 assembl i e s

.

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

transmitta1.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 . 1 ength o f small diameter .MDF, whi.ch i s . terminated w i t h a much 1 a r g e r diameter booster s e c t i o n : f o r a c t i v a t i o n o f downstream components. Propagation 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 a n d . m a t e r i a 1 dependent waves generated at 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 ' . a s a f u n c t i o n of 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 o f 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 RESU'LTS

The experimental technique i s i l l u s 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 lengths, 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 electromagnetic 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

(water, P l e x i g l a s , Krylon, and a i r ) t h e a i r gap produced b o t h t h e f a s t e s t r i s e and h i g h e s t amp1 i tude 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 circumference. 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. O f 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 g a p - t h i c k n e s s e s 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 these shims between t h e segments o f t h e donor w i t h proper a l i g n - ment o f t h e h o l e s .

a

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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 o f donor. One method used was t o v a r y t h e l e n g t h s of 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 of 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 times 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 thicknesses. 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 a 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 n o t e d 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 f r o m t h e curves o f Fig. 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 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, a1 though i n t e r e s t i n g , was n o t pursued here s i n c e a knowledge o 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 n e d 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 i c a l r e c o r d f o 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 segment 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 c o n t a c t 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

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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 n o t 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 data 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.ig. 4 a r e least-squares f i t s assuming a s l o p e o f 7.482. ,These l i m i t e d da'ta t h u s 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 ) o f 40 ns and 130 ns, r e s p e c t i v e l y , f o r t h e 2.1 g/m and 0.21 g/m donor systems.

Tests u s i n g an RDX/Sylgard 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 record. 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 d i a m e t e r by 6.35 mm e x t r u s i o n 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, and 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 l 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 and 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 ~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 and 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 - f a c e . 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 a c c e p t a b l e . 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 i v e n 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

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t h i c k n e s s x 12.7 mm diameter i n f r o n t of 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 o f 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 of approximately 1.55 Mg/m3(3). Therefore, p e l l e t s were pressed f r o m 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 , from 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/m3(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 f r o m t h e shot 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 t h a n 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 of 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 = Tt ( f o r a segment l e n g t h )

-

Detznation

Y ~ l o c i ty

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 formula i s t h a t g i v e n i n Table I . Averdye excess t r a n s i t t S m e S 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 t h e y 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 probably i n d i c a t i v e of m a t e r i a l s e n s i t i v i t y .

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had all been laid directly upon the.stee1. pad and the signal-to-noise

.

ratio was very, good. However, when the-

shots. were.

placed upon a wooden

- .

stand about 0.6 m above the pad, an order of magnitude increase in

electrical noise resulted; Records aye shown in Fig.

7

for a comparison

:

of noise pickup under identical cir.cumstances except for shot placement.

C O N C L U S I O N S

An experimental technique sui tab1 e for determining excess transit times

as a function of donor-acceptor configurations has been establ

i

shed.

Assemblies described herein all had coaxial geometries with small dia-

meter confined donors in direct contact with larger diameter, unconfined

acceptors. However, the technique is compatible with investigations of

other interface geometries more closely simulating those found in actual

explosive components.

F U T U R E W O R K

HNS systems which have both optical as we1

1

as electrical coverage will

be tested in order to better correlate acceptor detonation.with electrical

signal s produced.

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(12)

Gap Thickness {pm) .

(13)

S t a r t

o f

current

flow

i n bridgewire

Bridgewire

burst

Air

gap

bhmn

PBX

9401

p a l l e t

and

f i r s t

donor

segment

AQr

gap

betwen

f9rst

and

second

donor

segments

A i r

gap

between

seoond

and

t h i r d

donor

segments

A i r

gap

between

t h i r d

and

fouith

donor

segments

Atr

gap

between

fourth

and

f i f t h

donor

segments

A i r

gap

between

f i f t h and

sixth

donor

segments

Air

gap

b e w e n sixth

and

seventh

donor

segments

A i r gap

between

seventh

and

eight

donor

segments

Air

gap

between

acceptor

and

antenna

: M g .

3. Typi-cal Record f o r

a PETR

Ezploslve

System

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(15)

Comment I n

Start

o f current

flow

I n bridgewire

Bpi d w i

re

Burst

A S 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

Air

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

Air

gap

between

acceptor and antenna

(16)

1

A i r

Gap

signals

Final

Donor

%gent-Accepar

Pellet

Interface

Pellet

Output

Surface

B T

fs

Fimt

Part

of

A

S-P

p a d

A

-P

B

Sweep

(17)
(18)
(19)

Table 11. ~esulis of

HNS

Work for an Acceptor Pel let Density of 1.55 ~ g / m ~

MDF

~ n s i gn-~ickforda Ensi

gn-Bi

ckford Ensi gn-Bickford Ensign-Bickford Chemtronics b Chemtronics Chemtronics Chemtronics . .. Acceptor Excess Transit Acceptor ' . Time ,Pellet (ns)

Ensign-Bi

ckford NO GO Chemtronics d 42 Chemtronics

4

1 Ensign-Bickford 43 ~nsi~n-~ickford 3

4

Chemtronics NO GO Chemtronics 4 1

a Properties given in Table I.

bProperties given in Table I. C

12. 7 nun diameter pellet pressed from HNS-IB, Lot No. 5737.

d12. 7 nun diameter pellet pressed from HNS-IA, Lot No. 66-48.

e

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1. Bernard Hayes, "The Detonation E l e c t r i c E f f e c t , " Journal o f A p p l i e d Physics, Vol

.

38, No. 2 (February 1967).

2. " P r o p e r t i e s o f Chemical Explosives and Explosive Simul ants,

"

Compiled and E d i t e d by D.

M.

Dobraty, UCRL-51319, Rev. 1 ( J u l y 31, 1974).

3. J. A. Crutchmer, "HNS Pressabi 1 i t y Study," MHSMP-75-27 (June 1975). 4. R. J. Slape, "Detonation Pressure o f MNS I and 11," MHSMP-75-23,

June 1975.

References

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