An acoustic surface wave method for rapid, nondestructive texture evaluation
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Communications
F
FLEXUREWAVE
An Acoustic Surface Wave Method for Rapid, Nondestructive Texture Evaluation
TRANSVERSE DIRECTION
B. R. TITTMANN AND G. A. ALERS T H E u s e of r o l l i n g t e x t u r e to obtain e n h a n c e m e n t of d e s i r e d p r o p e r t i e s is an i m p o r t a n t technique in m a t e r i a l s d e s i g n . ~'2 D u r i n g the d e v e l o p m e n t of the alloys and the r o l l i n g p r o c e d u r e s for t e x t u r e i m p r o v e d sheet, as well as for quality a s s u r a n c e of the m a n u f a c t u r e d product, a r a p i d m e a s u r e m e n t of the type and d e g r e e of t e x t u r e in the e n v i r o n m e n t of a r o l l i n g m i l l would be v e r y helpful. This communication describes a simple, rapid method for the n o n d e s t r u c t i v e e v a l u a t i o n of t e x t u r e in m e t a l s h e e t and plate p r o d u c t s of a r b i t r a r y t h i c k n e s s . The method u s e s a r e c e n t l y developed i m p u l s e t e c h nique 3 to g e n e r a t e and r e c e i v e Rayleigh waves on thick p l a t e s or L a m b waves on thin m a t e r i a l s . The t e c h nique u t i l i z e s the e a s e of r e p o s i t i o n i n g a g e n e r a t o r and r e c e i v e r to m e a s u r e the o r i e n t a t i o n dependence of the velocity of sound p r o p a g a t i o n r e l a t i v e to the s p e c i m e n c o o r d i n a t e s . The technique is applied to t i t a n i u m alloy s h e e t and plate m a t e r i a l s whose t e x t u r e was i n t r o d u c e d by the r o l l i n g p r o c e s s . We have u t i l i z e d the method in the study of t e x t u r e in t i t a n i u m alloys w h e r e a i r c r a f t s t r u c t u r a l p a r t s d e m a n d the o p t i m u m in s t i f f n e s s - t o - w e i g h t r a t i o . The r e l a t i o n s h i p b e t w e e n the m e a s u r e d sound v e l o c i t y , the e l a s t i c s t i f f n e s s , and the c r y s t a l l o g r a p h i c o r i e n t a t i o n s d e t e r m i n e d by X - r a y t e c h n i q u e s have a l r e a d y b e e n studied e x t e n s i v e l y 4,5 so that a good t h e o r e t i c a l foundation for the m e a s u r e m e n t is a v a i l a b l e . The technique u s e s two s m a l l c e r a m i c p i e z o e l e c t r i c t r a n s d u c e r s placed on top of the s a m p l e , one acting as t r a n s m i t t e r and the other as r e c e i v e r . 3 A s h a r p dc voltage spike applied to the t r a n s m i t t e r c e r a m i c g e n e r a t e s an u l t r a s o n i c wave t r a i n c o n s i s t i n g of a few c y c l e s at a p p r o x i m a t e l y 1 MHz in f r e q u e n c y and r a d i ating outward in all d i r e c t i o n s . The r e c e i v e r t r a n s d u c e r , a few c e n t i m e t e r s away, m e a s u r e s the v e r t i c a l c o m p o n e n t of s u r f a c e p a r t i c l e velocity as a function of t i m e , e n a b l i n g one to d i s t i n g u i s h c l e a r l y between v a r i o u s types of a c o u s t i c wave m o d e s , e.g. R a y l e i g h wave, pseudo s u
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