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OFHC copper e x p l o s i v e l y d e f o r m e d at p r e s s u r e s between 75 and 435 k b a r s is c h a r a c t e r i z e d by high r e s i d u a l s t r e s s e s , c o m p r e s s i v e n e a r the s u r f a c e and t e n s i l e f u r t h e r in. A n n e a l i n g a f t e r this d e f o r m a t i o n t a k e s place in t h r e e somewhat o v e r l a p p i n g s t a g e s . P r o p e r t y changes a s s o c i ated with these s t a g e s and p o s s i b l e i n t e r p r e t a t i o n of the effects a r e d i s c u s s e d in detail. Cont r a r y to the a n n e a l i n g b e h a v i o r of c o n v e n t i o n a l l y d e f o r m e d m e t a l s , the f i r s t stage of a n n e a l i n g i s a c c o m p a n i e d by a decrease in d e n s i t y and an increase in e l e c t r i c a l r e s i s t i v i t y . It is postulated that these changes a r e due to s t r e s s r e l i e f and m i c r o c r a c k growth. Also, unlike m o s t c o n v e n t i o n a l l y d e f o r m e d m a t e r i a l s , the m a j o r softening stage is found to have r e c o v e r y r a t h e r than r e c r y s t a l l i z a t i o n c h a r a c t e r i s t i c s . The data in this stage a r e q u a n t i t a t i v e l y c o n s i s t e n t with a m e c h a n i s m involving d i s l o c a t i o n a n n i h i l a t i o n . T H E study of p r o p e r t y changes d u r i n g the a n n e a l i n g of c o l d - w o r k e d m a t e r i a l s has long been a m a j o r a r e a of m e t a l l u r g i c a l r e s e a r c h . In the case of m e t a l s that have undergone explosive loading, h o w e v e r , r e s e a r c h effort has until r e c e n t l y 1 c o n c e n t r a t e d on d e v e l o p m e n t of the t e c h n i q u e s of explosive loading and on the r e s u l t ing p r o p e r t y changes r a t h e r than on e v a l u a t i o n of the r e s p o n s e to s u b s e q u e n t a n n e a l i n g . P r e l i m i n a r y s t u d i e s of the a n n e a l i n g of e x p l o s i v e l y loaded copper by Iyer and Gordon 2 i n d i c a t e d that in c o n t r a s t to c o n v e n t i o n a l l y d e f o r m e d c o p p e r the s t o r e d e n e r g y of d e f o r m a t i o n was r e l e a s e d d u r i n g a n n e a l i n g l a r g e l y p r i o r to the onset of r e c r y s t a l l i z a t i o n . The l a t e r work of Klein and Rough 3 on t u n g s t e n and c o l u m b i u m s i m i l a r l y r e v e a l e d an a c c e n t u a t i o n of r e c o v e r y type p r o c e s s e s as c o m p a r e d with a n n e a l i n g of c o n v e n tionally deformed materials. The p r e s e n t study was u n d e r t a k e n in o r d e r to p r e s e n t a c o m p r e h e n s i v e d e s c r i p t i o n of the a n n e a l i n g of copper in the e x p l o s i v e l y loaded condition and to d e l i n e a t e the d i f f e r e n c e s b e t w e e n the a n n e a l i n g r e s p o n s e of such m a t e r i a l and that which has b e e n c o n v e n t i o n a l l y deformed. The study involved the use of six different e x p e r i m e n t a l m e a s u r e m e n t t e c