A mechanism of explosive bonding
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F. KOWALICK
AND
D. ROBERT
HAY
An aero-hydrodynamic analogy is used to construct a description of the formation of wavy interfaces during explosive bonding. Avon Karman vortex street in the wake of the reentrant jet formed at the collision point of the parent and flyer plates yields the required interface structure. The reentrant jet is considered as a transverse obstacle behind which the main flyer and parent streams join and form a periodic wake. The fluid flow analogy is amenable to description in terms of Reynolds numbers. A cylindrical parent plate technique is employed to obtain a spectrum of interface configurations as a function of collision point velocity. The results establish a characteristic range of values of the Reynolds number for the onset of wave formation and the range over which wave formation occurs (2 -< NRe --< I0). Grain deformation adjacent to the direct bond are interpreted in terms of a laminar flow model.
DURING
the last decade, explosive bonding has experienced growth in the number of applications and metal combinations joined as well as in fundamental understanding of the process. Analysis of the bonding process is conveniently divided into two parts. The f i r s t c o n s i d e r s the t r a n s f e r of e n e r g y f r o m the e x p l o sive, upon detonation, to the f l y e r plate. E m p i r i c a l r e l a t i o n s h i p s for this phase of the p r o c e s s have been d e v e l o p e d 1,2 as well as t h e o r e t i c a l a n a l y s e s . 3'4 A s e c ond g e n e r a l c o n s i d e r a t i o n is the t r a n s f o r m a t i o n of f l y e r plate kinetic e n e r g y into d e f o r m a t i o n s at the int e r f a c e and the actual bonding m e c h a n i s m . The l a t t e r is c o n s i d e r e d in this p a p e r and r e c a s t s c u r r e n t theor i e s so that v a l u e s of p a r a m e t e r s c h a r a c t e r i s t i c of the a p p e a r a n c e of the bond may be evaluated. Fig. 1 i l l u s t r a t e s s c h e m a t i c a l l y the p a r a l l e l and inclined plate cladding g e o m e t r i e s and defines a n u m b e r of r e l e v a n t t e r m s . C o l l a p s e of the f l y e r plate and its c o l l i s i o n with the p a r e n t plate c o r r e s p o n d s to the i m p i n g e m e n t of a s t a t i o n a r y fluid s t r e a m on a m o v i n g p a r e n t plate. P l a t e v e l o c i t i e s used in e x p l o s i v e bonding a r e in the r a n g e f r o m 30 to about 1000 m p e r s e c which, for m o s t m e t a l s , c o r r e s p o n d s to a shock wave p r e s s u r e of up to 5 m i l l i o n psi in the s u r f a c e l a y e r s at the c o l l i s i o n point. As this is c o n s i d e r a b l y in e x c e s s of the yield s t r e n g t h s of m e t a l s , h y d r o d y n a m i c t h e o r y has p r o v e n an e f f e c t i v e context for a d i s c u s s i o n of the d y n a m i c s and the r e s u l t i n g m i c r o s t r u c t u r e . A continuous s p e c t r u m of i n t e r r a c i a l c o n f i g u r a t i o n s has been o b s e r v e d f r o m the d
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