Stage II fatigue crack growth in copper in nitrogen and in air
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Stage II Fatigue Crack Growth in Copper in Nitrogen and in Air R . Y E S K E AND J . W E E R T M A N It h a s b e e n e s t a b l i s h e d t h a t the r a t e of f a t i g u e c r a c k g r o w t h in s e v e r a l m e t a l s is i n c r e a s e d upon e x p o s u r e to a i r , c o m p a r e d w i t h that found in i n e r t a t m o s p h e r e s . ~ H o w e v e r , l i t t l e is k n o w n r e g a r d i n g the c o m p a r a t i v e r a t e s of S t a g e II f a t i g u e c r a c k g r o w t h in c o p p e r in a i r and ine r t a t m o s p h e r e s . T h e r e i s s o m e e a r l y w o r k in w h i c h t h e l i f e t i m e s f o r c o p p e r f a t i g u e d in a i r and in i n e r t a t m o s p h e r e s w e r e c o m p a r e d . C o m p a r e d to l i f e t i m e s in v a c u u m , G o u g h and S o p w i t h 2 found a f i v e - f o l d r e d u c t i o n in f a t i g u e l i f e for c o p p e r t e s t e d in c o m b i n e d o x y g e n and w a t e r v a p o r , a l t h o u g h n e i t h e r of t h e s e c o m p o n e n t s r e d u c e d l i f e t i m e s a c t i n g a l o n e . W a d s w o r t h and H u t c h i n g s 3 p e r f o r m e d s i m i l a r t e s t s on c o p p e r u s i n g s e v e r a l i n e r t g a s e s and a b e t t e r v a c u u m and t h e y c o n c l u d e d t h a t o x y gen g a s a l o n e d o e s h a v e a d e l e t e r i o u s e f f e c t on f a t i g u e l i f e . T h e f a t i g u e l i f e is f u r t h e r s h o r t e n e d by the a d d i t i o n a l p r e s e n c e of w a t e r v a p o r . A f t e r e x a m i n i n g the s u r f a c e s of t h e i r r e v e r s e d b e n d i n g t e s t s a m p l e s , t h e y c o n c l u d e d t h a t c r a c k n u c l e a t i o n in a p e r s i s t e n t s l i p band o c c u r r e d at the s a m e r a t e in v a c u u m and in o x y g e n e n v i r o n m e n t s , but t h a t s u b s e q u e n t g r o w t h of the m i c r o c r a c k is f a s t e r in the p r e s e n c e of o x y g e n . S i n c e the c r a c k s w h i c h t h e y e x a m i n e d w e r e s u r f a c e c r a c k s a few m i c r o n s d e e p , it w a s t h e S t a g e I p o r t i o n of c r a c k g r o w t h , in c u r r e n t t e r m i n o l o g y , w h i c h w a s b e i n g a d v e r s e l y affected. Because they were doing plane be
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