Measurements of cavitation activity in liquids

T h e b o o k t h a t has resulted is m o d e s t in scope a n d by no m e a n s fully correlated, as the work is still in progress. H o w e v e r , the results are t h o u g h t to be important enough and consistent e n o u g h to justify their p u b l i c a t i o n . T h e f o u r basic e x p e r i m e n t a l i n s t a l l a t i o n s used by the a u t h o r h a v e p r o v e d sufficiently c o n s i s t e n t a n d reliable a n d can already be used in practice. He has placed great e m p h a s i s on d e s c r i b i n g the actual e q u i p m e n t a n d the e x p e r i m e n t a l p r o c e d u r e a n d c o n t r a s t s t h e m with c o n v e n t i o n a l testing installations. M a n y new m a t e r i a l s are r e q u i r e d to work at u p to 2,000"C a n d testing at these t e m p e r a t u r e s has been given special

attention, particularly the various m e t h o d s of c o u p l i n g : in s o m e instances air c o u p l i n g is sufficient. T h e e r r o r s a n d c o r r e c t i o n s of the different m e t h o d s are fully discussed a n d t r e a t e d m a t h e matically. In C h a p t e r I the a u t h o r derives the basic e q u a t i o n s of p r o p a g a t i o n for longitudinal, torsional and flexural waves, discusses t h e i r r e s o n a n c e cond i t i o n s at length, analyses mathematically the construction of the m e a s u r i n g a p p a r a t u s a n d the factors influencing the accuracy of various systems. This c h a p t e r can t h e r e f o r e be c o n s i d e r e d a reference c h a p t e r to the r e m a i n d e r of the b o o k . T h e following

c h a p t e r s describe the e q u i p m e n t a n d p r o c e d u r e in detail, classify the various m e t h o d s of d e t e r m i n i n g elastic moduli in elastic materials a n d m a t e r i a l s not o b e y i n g the H o o k e ' s law a n d c o n s i d e r the t e m p e r a t u r e a n d energy s c a t t e r i n g effects. Stress/strain hysteresis curves, the effects o f high f l e q u e n c y l o a d i n g o n fatigue a n d s i m u l t a n e o u s m e a s u r e m e n t s of Y o u n g ' s m o d u l u s a n d bulk m o d u l u s are i l l u s t r a t e d by specific examples. T h e last c h a p t e r deals with fatigue testing at sonic a n d u l t r a s o n i c frequencies, which is p r o b a b l y the least k n o w n subject in the book a n d s h o u l d s t i m u l a t e great interest in the near future. I.

"&'O I.()SI I Y N

LETTERS TO THE EDITOR MEASUREMENTS OF C A V I T A T I O N A C T I V I T Y IN L I Q U I D S From Dr. 6. Bradheld I u n d e r s t a n d that, of the total value of u l t r a s o n i c devices m a d e in this c o u n t r y , the part c o n c e r n e d with ultrasonic c l e a n i n g f o r m s m u c h the greater proportion. S o m e years ago, at these laboratories, we m a d e c o n t r i b u t i o n s in this field a n d as users of u l t r a s o n i c c l e a n i n g as well as r e p r e s e n t a t i v e s on the British Scientific Instrument Manufacturers" Association sub-committee ol; u l t r a s o n i c c l e a n i n g we still m a i n t a i n o u r interest. T h e review p a p e r in y o u r J a n u a r y M a r c h 1965 issue by N e p p i r a s 1 is an excellent c o n t r i b u t i o n to the subject of m e t r o l o g y of u l t r a s o n i c activity in liquids. T h e m a t t e r falls into three c a t e g o r i e s : (a) m e a s u r e l n e n t s below c a v i t a t i o n level, which present no real difficulties but w h o s e results are little related to the n o r m a l c o n d i t i o n s used a n d are of value mostly to define a n d assess causes o f inefficiency in t r a n s ducers; (h) m e a s u r e m e n t s a b o v e cavitat i o n ; these are realistic c o n d i t i o n s but the p o w e r m e a s u r e m e n t s a m o u n t a l m o s t entirely to c a l o r i m e t r y t h o u g h with care they can p r o v i d e a little design i n f o r m a tion s u p p l e m e n t a r y to (a); (c) m e a s u r e m e n t s at c a v i t a t i o n levels but in t e r m s of n o n - t h e r m a l effects, i.e. noise producing, s o n o l u m i n e s c e n t , s o n o c h e m i c a l , e r o s i o n , emulsification a n d cleaning. O f these effects we infer t h a t w h a t N e p p i r a s has said m e a n s t h a t n o n e c a n be accurately relied u p o n to m e a s u r e another. Let us c o n c e n t r a t e o n the most i m p o r t a n t a p p l i c a t i o n : cleaning. Even this h a s s u b - s e c t i o n s w h e r e the effects differ in m a g n i t u d e a c c o r d i n g to the precise task. T h a t of r e m o v i n g oxide

100

ULTRASONI('s/ApriI-June 1965

scale from metals (the first task, incidentally, \~hich we tackled 16 years ago) by b r e a k i n g of b o n d s is nlore difficult t h a n the remoxal of ball-pen m a r k s from t r a c i n g plastic a n d this, in turn, is m u c h m o r e difficult t h a n the renloxal of pencil marks. The cleaning ability of a tank for the first a n d third of these tasks might be difficult to assess with m u c h accuracy from a n l e a s u r e n l e n t if its cleaning capability when tested by the soil-filnl-plus-dye m e t h o d . Nevertheless, the recent investigation carried out Oll the latter will p r o v e v a l u a b l e if a really r e p r o d u c i b l e t e c h n i q u e emerges. T h e A m e r i c a n s seem likely to c h o o s e a different c o m p r o m i s e using the c h l o r i n e liberation n l e t h o d . P e r h a p s the erosion m e t h o d , a f o r m of which was described by Crawford,'-' a n d which we believe f r o m o u r e x p e r i m e n t s can be m a d e nluch m o r e linear a n d r e p r o d u c i b l e using, e.g. etched lead tape, say 0-06 in wide a n d 0.0025 in thick, a n d a resistance c h a n g e t e c h n i q u e , s h o u l d not i m m e d i a t e l y be ruled out. F o r this is just the sort of test which c o u l d give v a l u a b l e g u i d a n c e as to the risk which exists of d a m a g e to delicate parts f l o m t o o high an ultrasonic intensity. T h e user of ultrasonic c l e a n i n g o u g h t to be in a position to test f r o m place to place in his o w n t a n k u n d e r his o w n c o n d i t i o n s a n d also to m o n i t o r its overall efficiency a p p r o x i m a t e l y in some extremely simple way to s u p p l e m e n t the c h o s e n m o r e q u a n t i t a t i v e test. One likely way to d o this is to p r e p a r e n a r r o w (say 1/4 in) thin m a t t e d t r a n s p a r e n t plastic tape c o a t e d o n o n e side with a thin u n i f o r m coat of dried a q u a d a g . Such a material c o u l d s t a n d a r d i z e d a n d supplied in reels for these check tests. This subject is o n e of such i m p o r t a n c e t h a t a f u r t h e r i n t e r c h a n g e of views a n d

experience through y o u r c o r r e s p o n d e n c e c o l u m n s x~ould be welcome a n d would assist progress t o w a r d s a practical s o l u t i o n of this m e a s u r c m e l l t p r o b l e m . (.~, B R A I ) I If{I I)

[. 2.

N a t i o n a l PI13sical L a b o r a t o r 3 , lcddinglon, England NI:PPIRAS, E. /\., lilt'tlXOIlil~, 3, 9 ( [ 9 6 5 ) CRAN~Ft )RI), A . ~., ( ¢llrawulic~, 2. 120 { 1964).

EEG, SEG OR S O N A R From Dr. D. M. Makow Tile t e r m e c h c - e n c e p h a l o g r a p h y (echo brain p h o t o g r a p h y ) was i n t r o d u c e d b3 Leksell in 19555 It describes a m e t h o d which permits finding the l o c a t i o n of internal b r a i n s t r u c t u r e s with respect to the skull, by m e a s u r i n g echo p o s i t i o n s of an u l t r a s o n i c pulse b e a m e d into the head. In a recent paper (I rossnlan e expresses his dissatisfaction with this t e r m a n d p r o p o s e s the n a m e s o n o e n c e p h a l o g r a p h y or S E G . His most c o n v i n c i n g a r g u m e n t is thai of a b b r e v i a tion, since e c h o - e n c e p h a l o g r a p h y a n d e l e c t r o - e n c e p h a l o g r a p h y have b o t h the s a m e s h o r t f o r m of E E G . T h i s is a cause of c o n f u s i o n as b o t h m e t h o d s are used often by the s a m e people. G r o s s n l a n also p r o p o s e s to use the prefix "'sono'" a n d the suffix "'graphy'" t o g e t h e r with the n a m e of the o r g a n u n d e r investigation, for e x a m p l e "'sonoc a r d i o g r a p h y " to describe the p r o c e d t u e of heart e x a m i n a t i o n , a n d the n a m e s o n o g r a m for the u l t r a s o n i c r e c o r d or graph. In d i s c u s s i o n s on this p o i n t with colleagues in the field, o t h e r v i e w p o i n t s have been expressed. T h i e s s e n of this division feels t h a t the prefix "'sono'" is t o o general as it covers the w h o l e sonic field. F o r example, a recently r e p o r t e d