Synchrotron radiation microradiography of cracks in aluminum alloys
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A r e l i a b l e technique to i m a g e c r a c k s and c r a c k tip p l a s t i c zones in r e a s o n a b l y thick s p e c i m e n s can be v a l u a b l e in a n s w e r i n g m a n y b a s i c q u e s t i o n s on the f r a c t u r e of m e t a l s and a l l o y s . We b e l i e v e that the i n tense X-radiation available from synchrotron sources could be developed to s e r v e this p u r p o s e . In p a r t i c u l a r , s y n c h r o t r o n r a d i a t i o n m i c r o r a d i o g r a p h y in c o n j u n c t i o n with s y n c h r o t r o n white r a d i a t i o n topography can be used to i m a g e c r a c k s and c r a c k tip p l a s t i c zones in r e a s o n a b l y thick (~ 200 p m ) m e t a l l i c s p e c i m e n s . The e x t r e m e l y high d e g r e e of c o l l i m a t i o n and high level of photon fluxes c h a r a c t e r i s t i c of s y n c h r o t r o n s o u r c e s 1'2 as c o m p a r e d to c o n v e n t i o n a l X - r a y s o u r c e s can p o t e n t i a l l y allow for high r e s o l u t i o n i m a g i n g of c r a c k s as well as p l a s t i c z o n e s within s h o r t e x p o s u r e t i m e s . As a f i r s t step t o w a r d s d e veloping s y n c h r o t r o n m i c r o r a d i o g r a p h y and p l a s t i c zone topography, we have p e r f o r m e d p r e l i m i n a r y e x p e r i m e n t s at the Stanford S y n c h r o t r o n R a d i a t i o n L a b o r a t o r y (SSRL) to v e r i f y the f e a s i b i l i t y of using s y n c h r o t r o n m i c r o r a d i o g r a p h y to i m a g e c r a c k s and notches which were i n t r o d u c e d , a p r i o r i , in s p e c i m e n s of a l u m i n u m and a l u m i n u m b a s e a l l o y s . The r e s u l t s of these e x p e r i m e n t s will be d e s c r i b e d in this note. The f e a s i b i l i t y s t u d i e s on s y n c h r o t r o n white r a d i a t i o n topography of c r a c k tip p l a s t i c zones a r e b e i n g p e r f o r m e d and the r e s u l t s will be d i s c u s s e d in a s u b s e quent p a p e r .
to o b t a i n e n h a n c e d a b s o r p t i o n c o n t r a s t in m i c r o r a d i o g r a p h y without having to c o n t e n d with the l i m i t a t i o n s of lower photon flux l e v e l s and long e x p o s u r e t i m e s . A l s o , s i n c e the d i v e r g e n c e of the s y n c h r o t r o n X - r a d i a tion is only 20 s of a r c as a g a i n s t d i v e r g e n c e s of up to 10 deg in the c a s e of c o n v e n t i o n a l X - r a y s o u r c e s , b e t t e r g e o m e t r i c a l r e s o l u t i o n in m i c r o r a d i o g r a p h y can also be a c h i e v e d . 3-5 A l u m i n u m and a l u m i n u m - b a s e a l l o y s w e r e c h o s e n for the f e a s i b i l i t y s t u d i e s s i n c e t h e i r low a b s o r p t i o n for X - r a y s allows the use of f a i r l y thick s p e c i m e n s to be r a d i o g r a p h e d within s h o r t e x p o s u r e t i m e s e v e n at the lower flux l e v e l s c o r r e s p o n d i n g to the lower e l e c t r o n e n e r g y (clo
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