ULTRASONIC ATTENUATION NONDESTRUCTIVE MATERIALS CHARACTERIZATION

HAL Id: jpa-00225395

https://hal.archives-ouvertes.fr/jpa-00225395

Submitted on 1 Jan 1985

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

ULTRASONIC ATTENUATION NONDESTRUCTIVE

MATERIALS CHARACTERIZATION

R. Green, Jr.

To cite this version:

R. Green, Jr..

ULTRASONIC ATTENUATION NONDESTRUCTIVE MATERIALS

CHAR-ACTERIZATION. Journal de Physique Colloques,

1985,

46 (C10),

pp.C10-827-C10-834.

ULTRASONIC ATTENUATION NONDESTRUCTIVE MATERIALS CHARACTERIZATION

R.E. GREEN, Jr.

Center for Nondestructive Evaluation, The Johns Hopkins University, Baltimore,MD 21218, U.S.A.

-

Nous pre'sentons une revue de l ' e t a t a c t u e l de l ' u t i l i s a t i o n de l t a t t e n u a t i o n des u l t r a s o n s comma technique non-destructive pour l a c a r a c t 4 r i s a t i o n . d e 3ateriaux. Des examples vont &re pr&entes pour i l l u s t r e r comment l e choix approprie d e s parametres experimentaux permet l ~ u t i l i s a t i o n des mesures d'attenuation d'ultrasons pour l ( 6 t u d e des grosseur de g r a i n s , deformation plastique, e t concentration

d'impurete$. Nous a l l o n s cormenter l e s nouvelles techniques u t i l i s a n t l a generation e t l a ddtection de faisceaux de l a s e r q u i permettent l'emploi des mesures

dvattenuation d'ultrasona

dI

de c a s non-accessibles aux mbthodes plus conventionelles e t e l a r g i s s a n 5 par consequent l f u t i l i t e ' pratique des mesures d'attenuation

ultrasonique a l a c a r a c t e r i s a t i o n non-destructive des matgriaux.

Abstract

-

The present paper w i l l present an overview of t h e c u r r e n t state-of-the-art of t h e use of u l t r a s o n i c a t t e n u a t i o n a s a nondestructive technique f o r m a t e r i a l s characterization. Examples w i l l be given a s t o how proper ohoice of experimental parameters permit u l t r a s o n i c a t t e n u a t i o n measurements t o be used t o study g r a i n s i z e , p l a s t i c deformation, and impurity concentration. Some comments w i l l be made a s t o new techniques using l a s e r beam generation and d e t e c t i o n which afford t h e p o s s i b i l i t y of making u l t r a s o n i c a t t e n u a t i o n measurements not possible by more conventional means and thereby expanding t h e p r a c t i c a l usefulness of u l t r a s o n i c a t t e n u a t i o n non-

d e s t r u c t i v e m a t e r i a l s characterization.

The use of u l t r a s o n i c waves a s nondestructive probes has a s a p r e r e q u i s i t e t h e c a r e f u l documentation of t h e propagational c h a r a c t e r i s t i c s o f t h e u l t r a s o n i c waves themselves / I / . Since i n nondestructive evaluation a p p l i c a t i o n s i t is not d e s i r a b l e f o r t h e u l t r a s o n i c waves t o alter t h e m a t e r i a l through which they pass, it is necessary t o work with very low amplitude waves, which a r e normally regarded t o obey

linear e l a s t i c i t y theory. The u l t r a s o n i c waves generated experimentally behave a s l i n e a r e l a s t i c waves i n many of t h e i r propagational c h a r a c t e r i s t i o s , but i n o t h e r c h a r a a t e r i s t i c s associated with wave i n t e r a c t i o n s , d i s t o r t i o n , harmonic generation, and energy l o s s mechanisms, t h e i r behavior i s nonlinear and i n some r e s p e c t s even nonelastic. Although most p r a c t i c a l uses of u l t r a s o n i c s a r e applied t o s o l i d

m a t e r i a l s which a r e p o l y c r y s t a l l i n e aggregates and t h e r e f o r e assumed t o be i s o t r o p i c , with real c r y s t a l l i n e s o l i d s t h e condition of i d e a l isotropy is extremely d i f f i c u l t

i f not impossible t o a t t a i n . Therefore, most r e a l p o l y c ~ y s t a l l i n e aggregates possess a atexturem which strongly inf'luenoes t h e mechanical p r o p e r t i e s of t h e a n i s o t r o p i c m a t e r i a l including u l t r a s o n i c wave propagation.

Although many i n v e s t i g a t o r s draw a c l o s e analogy between electromagnetic wave propagation and e l a s t i c wave propagation i n s o l i d m a t e r i a l s , g r e a t caution should be exercised i n doing so. The behavior of anisotropic m a t e r i a l s with respect t o propagation of e l a s t i c waves is much more complicated than is t h e case f o r propagation of electromagnetic waves, s i n c e t h e m a t e r i a l c o n s t i t u t i v e equations required t o properly describe e l a s t i c waves are of higher order tensor rank than those required t o d e s w i b e electromagnetic waves /2/.

JOURNAL

DE

PHYSIQUE

For a l l real s o l i d s , t h e assumption of pure e l a s t i c k t y is only an approximation, s i n c e a l l real. u l t r a s o n i c waves a r e attenuated a s they propagate. Ultrasonic a t t e n u a t i o n measurements serve a s a very s e n s i t i v e i n d i c a t o r of i n t e r n a l l o s s mechanisms caused by microstructures and microstructural a l t e r a t i o n s i n t h e m a t e r i a l /3/. Figure 1 shows t h e experimental r e s u l t s of Klinman and Stephenson /4/, who measured l o n g i t u d i n a l u l t r a s o n i c wave a t t e n u a t i o n a s a function of g r a i n s i z e f o r both laboratory and commercially produced p l a t e s of p l a i n carbon-manganese

f e r r i t e - p e a r l i t e s t e e l . I n order t o obtain t h e data shown i n Fig. 1 measurements were made a t both 5 and 10 HHz. It i s evident t h a t f o r t h i s material t h e higher frequency established a much more d e f i n i t i v e r e l a t i o n s h i p between a t t e n u a t i o n and metallographically measured g r a i n s i z e . The usefulness of such measurements f o r i n d u s t r i a l q u a l i t y c o n t r o l ia self-evident.

h b a u m and Green /5/ measured u l t r a s o n i c a t t e n u a t i o n a s a function of l o c a t i o n along t h i c k s e c t i o n weldments of titanium alloys. Not only was a dramatic decrease i n a t t e n u a t i o n observed a s t h e transducer crossed t h e weld region, but marked inoreaseb in a t t e n u a t i o n were observed on each s i d e of t h e weld c l e a r l y d e l i n e a t i n g t h e h e a t a f f e c t e d zones. In companion work, t h e u l t r a s o n i c a t t e n u a t i o n of 2.25 MIlz

longitudinal waves was measured &s a function of oxygen content i n titanium specimens possessing oxygen l e v e l s of 0.07, 0.14, 0.20. 0.24 abd 0.29 percent by weight.

Figure 2 shows t h e r e s u l t s , proving t h a t such measurements provide a simple technique f o r monitoring t h e oxygen content i n t h e s e materials.

Sachse and Green /6/ conducted experiments which i l l u s t r a t e t h e extreme s e n s i t i v i t y of u l t r a s o n i c a t t e n u a t i o n measurements t o d i s l o c a t i o n motion and dislocation-point d e f e c t i n t e r a c t i o n s . Figure 3 shows t h e r e s u l t s of an experiment i n which an aluminum c r y s t a l , which had previously been loaded t o a p l a s t i c load of 180 kg, was reloaded t o 60 kg and maintained a t t h i s load f o r one minute, unloaded t o 45 kg and maintained f o r one minute, unloaded t o 30 kg and maintained f o r one minute, unloaded t o 15 kg and maintained f o r one minute, and then unloaded completely. Upon

subsequent reloading t o 70 kg and unloading, t h e u l t r a s o n i c a t t e n u a t i o n displayed d i p s a t those load values which had been maintained f o r a . s h o r t time during t h e previous cycle. Note t h a t even though t h e a t t e n u a t i o n "remembered* t h e discontinuous n a t u r e of t h e first load-unload cycle, t h e load-unload curve ( o r equivalently t h e a t r e s s - s t r a i n curve) gave no i n d i c a t i o n of it. The observed r e s u l t s were a t t r i b u t e d t o t h e pinning of d i s l o c a t i o n loops by point d e f e c t s which were p r e f e r e n t i a l l y looated a t the p o s i t i o n they ocoupied when t h e load was maintained constant f o r t h e one minute i n t e r v a l s . Upon reloading, these point d e f e c t s pinned t h e d i s l o c a t i o n loops again when t h e d i s l o c a t i o n s a r r i v e d a t t h e l o c a t i o n of t h e d e f e c t s thus causing t h e d i p s i n attenuation. T h e s e - r e s u l t s show t h a t u l t r a s o n i c a t t e n u a t i o n measurements a r e s e n s i t i v e t o migration of point d e f e c t s and t h e i r i n t e r a c t i o n with dislocations. I n t h e event t h a t t h e wave amplitude is increased t o s u f f i c i e n t l y l a r g e values e f f e o t s may a r i s e , which can manifest themselves both a s nonlinear e l a s t i c behavior /1/ o r more d r a s t i c a l l y a s p l a s t i c deformation of t h e insonated material. Mignogna and Green /7/ developed a multipararaeter experimental system which, f o r t h e first t h e , permitted simultaneous measurement of s u f f i c i e n t q u a n t i t i t e s t o test a l l of t h e proposed mechanisms f o r t h e influence of high-power ultrasound on t h e mechanical p r o p e r t i e s of metal specimens. Figure 4 shows a s e t of t y p i c a l d a t a obtained frcrm an aluminum s i n g l e c r y s t a l speclmen subjected t o high-power insonation a t 20 kEz. The insonation was applied a t a constant power l e v e l f o r d i f f e r e n t time periods: I = 0.03 s e c , I1

=

0.63 s e c , I11

=

1.23 s e c , IV

=

1.83 s e e , V = 2.43 see, and V I

=

3.63 sec. Depicted a r e change i n specimen length, r e l a t i v e change i n low-power

m a t e r i a l s by t r a n s i e n t s u r f a c e h e a t i n g and r e s e a r c h h a s continued i n t h i s a r e a up t o t h e p r e s e n t time /9 - I T / . Although t h r e e d i f f e r e n t mechanisms have been proposed t o account f o r t h e g e n e r a t i o n o f u l t r a s o n i c waves by t h e impact of pulsed l a s e r beams, namely r a d i a t i o n pressure, a b l a t i o n , and t h e r m o e l a s t i c i t y , t h e thermoelastic process is t h e only process which is t r u l y nondestructive and still capable of g e n e r a t i n g a n u l t r a s o n i c wave of s u f f i c i e n t amplitude f o r nondestructive e v a l u a t i o n purposes. Figure 5 , taken from t h e work o f Rosen / l 7 / shows a schematic i l l u s t r a t i o n of a l a s e r beam generation and d u a l l a s e r beam i n t e r f e r o m e t r i c d e t e c t i o n system used t o make non-contact measurements of u l t r a s o n i c waves i n s u r f a c e l a y e r s o f m e t a l l i c specimens which had been m i c r o s t r u c t u r a l l y modified by e l e c t r o n beam o r high-power l a s e r i r r a d i a t i o n t o e i t h e r form a n amorphous l a y e r o n t h e c r y s t a l l i n e bulk, t o produce d i f f e r e n t l a y e r s o f transformed phases, o r t o induce c a s e hardening of s t e e l oomponents.

Although a number of i n v e s t i g a t o r s have r e p o r t e d both g e n e r a t i o n and d e t e c t i o n of u l t r a s o n i c waves i n s o l i d m a t e r i a l s using l a s e r beams, only two i n v e s t i g a t i o n s have been conducted using low-power l a s e r beams. This i s e s p e c i a l l y important f o r many non-contact nondestructive e v a l u a t i o n a p p l i c a t i o n s where p o r t a b i l i t y and power l i m i t a t i o n s a r e a necessity. I n 1983, Dewhurst /13/ constructed a hand-held l a s e r g e n e r a t o r of u l t r a s o n i c p u l s e s based o n components t a k e n from a l a s e r range f i n d i n g device. The o p t i c a l o u t p u t was s u f f i c i e n t t o g e n e r a t e both s u r f a c e and bulk u l t r a s o n i c waves with a n aluminum speoimen. Most r e c e n t l y , Bourkoff and Palmer /16/ have succeeded i n generating u l t r a s o n i c p u l s e s i n metals and composite m a t e r i a l s using a low-energy tunable dye l a s e r . The u l t r a s o n i c waveforms were deteoted o p t i c a l l y with a l a s e r i n t e r f e r o m e t e r having improved signal-to-noise r a t i o and a n e l e c t r o n i c o o n t r o l system, which enables i t t o be operated near common low frequency n o i s e sources. The o v e r a l l s e n s i t i v i t y is about 50 pm over a 10 MHz bandwidth. This work has shown t h a t i t i s e n t i r e l y f e a s i b l e t o u s e a p o r t a b l e l a s e r g e n e r a t i o n l a s e r d e t e c t i o n system f o r non-contact c h a r a c t e r i z a t i o n o f m a t e r i a l s .

Another technique of i n c r e a s i n g importance f o r nondestructive e v a l u a t i o n of m a t e r i a l s i s thermal wave imaging. A s i n i t i a l l y developed t h i s technique was c a l l e d

photoacoustic spectroscopy and c o n s i s t s o f l a s e r beam scanning o f a t e s t o b j e c t placed i n a closed g a s - f i l l e d container. This scanning c a u s e s ohanges i n t h e g a s p r e s s u r e i n d i r e c t proportion t o thermal property changes i n t h e s u r f a c e l a y e r s of t h e t e s t o b j e c t . Recording o f t h e p r e s s u r e changes a s a f u n c t i o n o f p o s i t i o n o f t h e l a s e r pump beam permits imaging o f s u r f a c e and sub-surface m i c r o a t r u c t u r a l f e a t u r e s and d e f e c t s i n t h e t e s t object. More r e c e n t developuents have permitted e l i m i n a t i o n of t h e g a s - f i l l e d c o n t a i n e r by use of a second probe l a s e r beam, which e i t h e r d e t e c t s s u r f a c e displacements o f t h e t e s t o b j e c t due t o l o c a l i z e d thermal expansion o r changes i n t h e r e f r a c t i v e index o f t h e a i r j u s t above t h e sample surface. F i g u r e 6 i l l u s t r a t e s t h e way t h i s nmirage e f f e c t n caused by t h e pump l a s e r beam i n t e r a c t i n g with t h e t e s t o b j e c t causes d e f l e c t i o n s o f t h e probe l a s e r beam t r a n s v g r s i n g t h e index of r e f r a c t i o n a l t e r e d region.

Another modification o f t h i s technique u s e s a chopped e l e c t r o n beam in a soanning e l e c t r o n microsoope t o e x c i t e e l a s t i c and thermal waves a t t h e t o p s u r f a c e of t h e t e s t speoimen. The propagation of t h e s e waves through t h e t e s t speoimen is modified by t h e mechanioal and thermal c h a r a c t e r i s t i c s o f t h e m a t e r i a l inhomogeneities through which they pass. These modified waves a r e d e t e c t e d by a p i e z o e l e o t r i c c r y s t a l

coupled t o t h e bottom s u r f a c e of t h e t e s t specimen. By d i s p l a y i n g and r e c o r d i n g t h e o u t p u t of t h e p i e z o e l e c t r i c o r y s t a l as a f u n c t i o n o f p o s i t i o n o f t h e scanning e l e o t r o n beam an 'electron-aaousticn image of t h e t e s t speoimen oan be obtained. A l t e r a t i o n o f t h e energy of t h e e l e c t r o n beam and chopping frequency permits d i f f e r e n t l a y e r s i n t h e t e s t specimen t o be imaged a s desired. F i g u r e

7

oompares a standard soanning e l e o t r o n image of an unetched s h e e t o f polyorystallfzie aluminm with an e l e c t r o n - a c o u s t i c image of t h e same r e g i o n o f t h e test specimen. As oan be

JOURNAL DE PHYSIQUE

I V

-

CONCLUSIONS

I n o r d e r t o properly use u l t r a s o n i c a t t e n u a t i o n f o r nondestructive m a t e r i a l s c h a r a c t e r i z a t i o n i t is extremely important t o c a r e f u l l y document and understand t h e propagational c h a r a c t e r i s t i c s o f t h e u l t r a s o n i c waves themselves i n t h e s p e c i f i c m a t e r i a l s t o be examined. Once t h i s is done, proper choice of experimental

parameters permits u l t r a s o n i c a t t e n u a t i o n measurements t o be used t o study a g r e a t v a r i e t y o f m a t e r i a l m i c r o s t r u c t u r e s and a s s o c i a t e d mechanical p r o p e r t i e s . New techniques using l a s e r beam g e n e r a t i o n and d e t e c t i o n o f ultrasound a f f o r d t h e p o s s i b i l i t y of making u l t r a s o n i c a t t e n u a t i o n measurements n o t p o s s i b l e by more conventional means and thereby expanding t h e p r a c t i c a l u s e f u l n e s s o f u l t r a s o n i c a t t e n u a t i o n nondestructive m k t e r i a l s c h a r a c t e r i z a t i o n .

REFERENCES

/1/ Green, R.E., Jr., U l t r a s o n i c I n v e s t i g a t i o n o f Mechanical Properties. Vol. I11

tise on M a t e r i a l s Science and Technology, Academic Press, New York (1973).

/2/ Henneke, E.G., I1 and Green, R.E., Jr., Light-Wave/Elastic-Wave Analogies i n C r y s t a l s , J. Acoust. Soc. Amer.

a,

1367-1373 (1969).

/3/ Green, R.E. Jr., E f f e c t o f M e t a l l i c Microstructure on U l t r a s o n i c Attenuation, in &-g&.&rutive E v w t i o n : M i c r o s t r u c t u r a l Ch-ation and Rel-

S t r a t e a m , 0. Buck and S.M. Wolf ( e d s . ) , The M e t a l l u r g i c a l Society of AIME, Warrendale, PA, (1981) pp. 115-132.

/4/ Klinman, R. and Stephenson, E., Relation Between Mechanical P r o p e r t i e s , Grain Size, and U l t r a s o n i c Attenuation i n P l a i n Carbon S t e e l , Research Department, Homer Research Laboratory, Bethlehem S t e e l Corporation, Bethlehem, PA ( 1980).

/5/ Buxbaum, S.R. and Green, R.E., Jr., U l t r a s o n i c C h a r a c t e r i z a t i o n of Titanium 6211 Weldments, i n m e s t r u c t i v e Methods f o r Material P r o ~ e r t v D e t e r n a t i o n , C.L. Ruud and R.E. Green, Jr. (eds. )

,

Plenum Press, NY ( 1984).

/6/ Sachse, W. and Green, R.E. Jr., Experimental Study of t h e O r i e n t a t i o n Dependence of D i s l o c a t i o n Damping i n Aluminum C r y s t a l s , Trans. M e t a l l u r g i c a l Soc. AIME IqZ, 2185-2190 (1968).

/7/ Mignogna, R.B. and Green, R.E., Jr., Multiparameter System f o r I n v e s t i g a t i o n o f t h e E f f e c t s of High-Power Ultrasound o n Metals, Rev. Sci. Instrum.

a,

1274-1277 (1979).

/8/ White, R.M., Generation o f E l a s t i c Waves by Transient Surface Heating, J. Appl. PhyS. W, 3559-3567 ( 1963).

/9/ Bondarenko, A.N., Drobat, Yu. B., and Kruglov, S.V., Optical E x c i t a t i o n

and Detection of Nanosecond Acoustic P u l s e s i n Nondestructive Testing, Soviet J. NDT 12, 655-658 ( 1976).

/lo/ Ledbetter, H.M. and Moulder, J.C., Laser-Induced Rayleigh Waves i n Aluminum, J. Acoust. Soc. Amer.

a,

840-842 (1979).

/1 I / Calder, C.A. and WFlcox, W. W., Non-Contact Material Testing Using Laser Energy Deposition and I n t e r f e r o m e t r y , Mater. Eval.

a,

86-91 (1980).

/12/ Wellman, R.L., Laser System f o r . t h e Detection of Flaws i n S o l i d s , Harry Diamond Laboratories, Report No. HDL-TR-1902 (1980).

/15/ Aindow, A.M., Dewhurst, R . J . , Palmer, S.B., and Scruby, C.B.,

Laser-Based Non-Destructive Testing Techniques f o r t h e U l t r a s o n i c C h a r a c t e r i z a t i o n o f Subsurface Flaws, NDT I n t e r n a t i o n a l

11,

329-335 (1984).

/16/ Bourkof f , E. and Palmer, C.H.

,

Low-Energy Optical Generation and Detection of Acoustic P u l s e s i n Metals and Nonmetals, Appl. Phys. L e t t .

&,

143-145 (1985). /IT/ Rosen, M., A n a l y t i c a l U l t r a s o n i c s f o r C h a r a c t e r i z a t i o n o f M e t a l l u r g i c a l Microstructures and Transformations, t o be published i n t h e &.- o f t h e

Arm

u

U t o Testinn Conferenc

,

NASA Lewis

Research Center, Cleveland, OH (November 1984).

/18/ Aamodt, L.C. and Murphy, J.C., Thermal E f f e c t s i n Photothermal Spectroscopy and Photothermal Imaging, J. Appl. Phys.

a,

581-591 (1953).

/ 19/ Maclachlan, J. W.

,

Murphy, J. C.

,

Givens, R.B. and Aamodt

,

L. D.

,

M i c r o s t r u c t u r e C h a r a c t e r i z a t i o n by Thermal Wave Imaging, t o be published i n Procee-

-

o e o t t v e

,

ASM Metals

Congress, D e t r o i t , Michigan (1984), American S o c i e t y f o r Metals, Metals Park, OH

(1985).

GRAIN SIZE d , Mrn

2.25 MHz lronsducer x o v e r a g e

I=

I std. dev.

Oxygen Content (olomic percent)

Fig. 2

-

Ultrasonic attenuation a s a function of oxygen content for a titanium alloy

C51.

-

2 - 7

0 2 4 6

T I M E ( m i n )

Fig. 4

-

Data obtained from an aluminum s i n g l e c r y s t a l subjected t o high-power u l t r a s o n i c insonation a t a aonstant power l e v e l f o r d i f f e r e n t time periods 171.

A 1 = change i n speoimen length

Av/v= r e l a t i v e ohange i n u l t r a s o n i c velocity

A a

=

change i n ultrasonic attenuation

v

2 Channel Fast Processor

(Frequency Analysis)

I

U Dual Interferometer "0" Switched' Laser Raylelgh Sample "Bulk" Waves

Focused excitation

source

Fig. 6

-

Schematic o f thermal wave imaging technique uaing the %irage effectn C181.

SECONDARY ELECTRON IMAGE _{ACOUSftC MAGNITUDE IMAGE}