Ultrasonic testing of microstructure with surface waves
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Ultrasonic Testing of Microstructure With Surface Waves W. D. RODDY AND N. F. FI O RE
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s t r u c t u r e - s e n s i t i v i t y , the a t t e n u a tion and v e l o c i t y of sonic and u l t r a s o n i c a c o u s t i c r a d i a tion a r e u s e d a s g a g e s of m i c r o s t r u c t u r a l f e a t u r e s such a s g r a i n s i z e 1 and s e c o n d - p h a s e s i z e and shape, z The n o n d e s t r u c t i v e t e s t i n g of m i c r o s t r u c t u r e in the s oni c r a n g e i s c a r r i e d out e i t h e r by m e a s u r e m e n t of d a m p i n g and r e s o n a n c e f r e q u e n c y (dynamic m o d u l u s ) of a t e s t p i e c e d r i v e n at s t e a d y s t a t e r e s o n a n c e o r by m e a s u r e m e n t of t h e s e q u a n t i t i e s in a p i e c e which h as b e e n " r u n g " , with t h e v i b r a t i o n s f r e e l y d e c a y i n g f r o m t h e i r i n i t i a l l y high a m p l i t u d e s . Two d i s a d v a n t a g e s of the so n i c t e s t m e t h o d a r e that the e n t i r e t e s t p i e c e m u s t be b r o u g h t to r e s o n a n c e , a difficult a c c o m p l i s h m e n t f o r l a r g e t e s t p i e c e s , and that c l o s e c o n t r o l o v e r the d i m e n s i o n s of the e n t i r e p i e c e m u s t be m a i n t a i n e d s i n c e r e s o n a n c e f r e q u e n c y is d e t e r m i n e d by g e o m e t r y a s w e l l a s the m i c r o s t r u c t u r e . In the u l t r a s o n i c r e g i o n , t e s t i n g i s c a r r i e d out by the t h r o u g h - t r a n s m i s s i o n m e t h o d , in which the a t t e n u at i o n and v e l o c i t y of an u l t r a s o n i c p u l s e a r e d e t e r m i n e d as the p u l s e r e v e r b e r a t e s b e t w e e n two flat and p a r a l l e l s u r f a c e s . An obvious d i s a d v a n t a g e of t h e t h r o u g h - t r a n s m i s s i o n m e t h o d is that the flat, p a r a l l e l s u r f a c e s m u s t be p r o d u c e d on the p i e c e , u s u a l l y at s i g n i f i c a n t a d d i t i o n a l co st . T h i s note d e s c r i b e s a t e c h n i q u e f o r m i c r o s t r u c t u r e t e s t i n g with u l t r a s o n i c s u r f a c e w a v e s . Kolsky 3 ha s p r o v i d e d a m a t h e m a t i c a l d e s c r i p t i o n of s u r f a c e o r R a y l e i g h w a v e s , and t h e i r g e n e r a l a p p l i c a t i o n in nond e s t r u c t i v e
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