Study of Wave Motion on Tubulars Using Broad-Band Laser Ultrasound

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    S t u d y o f W a v e M o tio n o n T u b u la r s U s in g B r o a d - b a n dLaser U l t rasoundby M.E. B al tazar -Lrp ez, C.P. Burger , R. Ch ona an d S. SuhA B S T R A C T - - W e i n v e s ti g a t e t h e t r a n s it io n c h a r a c t e r i s ti c so f l a s e r - g e n e r a t e d u l t r a s o n i c w a v e s p r o p a g a t i n g a l o n g t h eax ia l and c i r c um fe ren t i a l d i r ec t i ons i n t ubu la r s . The the rm o-a c o u s t o - p h o t o n i c n o n - d e s t r u c t i v e e v a l u a t i o n t e c h n i q u e i se m p l o y e d t o i n i t i a t e b r o a d - b a n d s u r f a c e a n d g u i d e d w a v e sin tubu la r s o f s ev era l d i f f e ren t ou te r d iam ete rs and wa l l t h i c k -n e s s e s . A n o n - c o n t a c t b r o a d - b a n d o p t i ca l s e n s o r k n o w n a sf i b e r- t ip i n t e r fe r o m e t r y i s u s e d f o r w a v e a c q u i s it io n . W a v e d i s -pe rs ion as a func t i on o f t h i c k nes s to m ean rad ius ra t i o i sr e s o l v e d u s i n g a G a b o r w a v e l e t t r a n s f o r m b a s e d a l g o r i t h m .T h e a l g o r i t h m e n a b l e s d i s p e r s i o n t o b e e s t a b l i s h e d t h r o u g ht h e d e p l o y m e n t o f j u s t o n e s e n s i n g i n t e r fe r o m e t e r . T h is i s i nc o n t r a s t to t e c h n i q u e s w h i c h r e q u i r e m u l ti p le d e t e c t i o n l o c a -t i o n s f o r t h e d e t e r m i n a t i o n o f w a v e d i s p e r s i o n .K E Y W O R D S - - L a s e r u l t ra s o u n d , c y li n d r ic a l s t r u ct u r e , Gaborw a v e l e t t r a n s f o rmI n t r o d u c t i o nWave mot ions in cy l ind r i ca l s t ruc tu re s have been wide lys tud ied and we l l documen ted . T heore t i c a l s tud ie s inc lud ingt h e f o r m u l a t i o n o f t h e o ry a n d c o m p a r i s o n o f a p p r o x i m a t i o n sto exa c t s o lu t ions a re p len ty . 1 -5 Ar me nak as e t a l . 5 p rov ide as e l f - c o n ta i n e d t r e a t m e n t o n p r o p a g a t i o n o f p l a n e h a r m o n i cwav es in c i rcu la r cy l inde rs , a ll w i th in the f ram ew ork o f th ree -d im ens iona l theo ry o f e la s t i ci ty , Us ing the s e theo r i e s , i t ispos s ib le to s tudy the f i rs t mo des o f p rop aga t ion a s func t ionso f the ra t io o f she l l t h i cknes s to mean rad ius . O the rs have fo -c u s e d t h e i r w o r k o n t h e e x p e r i m e n t a l w a v e m o t i o n s i n c y l i n -d e r s. F o r e x a m p l e , G o l d s m i t h e t a l . 6 o b s e r v e d t h e p r o p a g a t i o no f p u l s e s o n t h in a n d m e d i u m - t h i c k w a l l h o l l o w c y l i n d e r s i nwhich s t ee l s phe re s s t ruck the s pec imens and y ie lded pu l s ed u r a t io n s o f 2 0 - 4 0 I t s t h a t c o r r e s p o n d t o a f re q u e n c y c o n t e n to f u p t o 5 0 k H z . A s i m i l a r a p p r o a c h w a s c a r d e d o u t b y Y ina n d Y ue , 7 w h o u s e d d y n a m i c l o a d s o n t h e e n d s o f a m u l t i l a y -e red c i rcu la r cy l inde r to s tudy t rans ien t r e s pons es . T he re havebeen s tud ie s tha t have looked s pec i f i c a l ly w i th in the u l t r a -s o n i c r a n g e. O n e e x a m p l e i s t h e w o r k b y C a w l e y e t a l. 8 w h ou s e d e l e c t r o m a g n e t i c s e n s o r s t o g e n e r a t e c y l i n d ri c a l g u i d e d

    M.E. Baltazar-lx~pez (SEM member; [email protected]) is a Professor Researcher, Departamento de lngenieria Mecdnica, Centro Nacionalde lnvestigacirn y Desarrollo Tecnolrgico (CENIDET), Int. del lnternadoPalmira S/N, Cuernavaca. Morelos 62490, Mexico. C.P Burger (SEM mereber) is Professor Emeritus, R. Chona (SEM member) is an Associate Pro-fessor, and S. Suh (SEM member) is an Associate Professor, Departmentof Mechanical Eagineering, Texas A&M Universit); College Station, Texas77843, USA.Original manuscript submitted: September 15, 2004.Final manuscript received: May 31, 2005.DO I: 10.1177/0014485105056899

    wav es in tubu la r s. R os e 9 rev iewed exp e r ime n ta l t e chn iquesava i l ab le up to 2002 and d i s cus s ed the fu tu re d i rec t ions fo rp ipe in s pec t ion .B e c a u s e o f t h e v a r io u s p r o b l e m s a s s o c ia t e d w i t h t h e u s e o fcon tac t t r ans duce rs on cy l ind r i ca l geom e t ry , u l t r a s on ic wavemo t ions in cy l ind r i ca l s t ruc tu re s have been d i f f i cu lt t o s tudyexpe r im en ta l ly . T h e l a ck o f re s o lu t ion , t he invas ive na tu re o ft rans duce rs w i th re s pec t to the p ropaga t ing waves , t he s o -ph i s t i c a t ion a s s oc ia t ed w i th tubu la r cu rva tu re and re f l ec tedw a v e f o r m s , a n d p o o r a c c e s s i b i l i t y a r e a m o n g t h e d i f f i c u l -t i e s . By us ing a non-con tac t u l t r a s on ic gene ra t ion and de -t e c t i o n t e c h n i q u e k n o w n a s t h e r m o - a c o u s t i c - p h o t o n i c n o n -d e s t r u c ti v e e v a l u a t i o n ( T A P - N D E ) , B u r g e r e t a l . ] ~ d e m o n -s t ra t ed tha t mos t o f the d i f f i cu l t i e s cou ld be ove rcome . Incon junc t ion w i th an appropr i a t e fea tu re ex t rac t ion te chn ique ,t h e y s h o w e d t h a t T A P - N D E w a s i d e a l f o r c e r t a i n p r o b l e m si n v o l v in g c o m p l e x o r i r r eg u l a r g e o m e t r y .L iu and Qu " t p re s en ted a num er ica l s o lu t ion fo r c i rcum -fe ren t i a l waves tha t a re independen t o f the exc i t ing s ou rce .I n t h e i r w o r k , e i g e n f u n c t i o n e x p a n s i o n w a s e m p l o y e d t oana lyze the in i t i a t ed mul t imoda l , d i s pe rs ive gu ided waves ,A n o t h e r f e a t u r e e x t r a c t i o n t e c h n i q u e w i d e l y u s e d f o r a n a l y s i so f m u l t i m o d e , d i s p e r s i v e g u i d e d w a v e s i s F o u r i e r t r an s f o r m .Such a t e chn ique requ i re s mu l t ip l e de tec t ion po in t s in o r -d e r t o e x t r a c t f e a tu r e i n f o r m a t i o n a b o u t t h e s p e c i m e n b e i n gin te r roga ted . 12 As repor t ed in Z u pan and He m ker 13 whe ret w o d e t e c t i o n p o i n t s w e r e e m p l o y e d f o r m e a s u r i n g i n - p l an es u r f a ce d e f o r m a t i o n s , w a v e f o r m s o b t ai n e d f r o m l a s e r - b a se ds e n s i n g s y s t e m s w e r e s u c c e s s f u l l y p r o c e s s e d u s i n g F o u r i e r -b a s e d t e c h n i qu e s . H o w e v e r , w h e n d e a l i n g w i t h o u t - o f - p l a n ed i s p lacem en t s , s eve ra l s ens ing loca t ions a re neces s a ry fo r thet w o - d i m e n s i o n a l f a s t F o u r i e r t r a n s f o r m ( F F F ) t e c hn i q u e . O n ea p p r o a c h f o r a l l e v i a ti n g t h e d e m a n d o n r e s o l v i n g d i s p e r s iv ewave s us ing Four i e r me tho ds wa s d i s cus s ed in Gao e t a l . 14whe re l inea r s pa t i a l cond i t ion ing a l lowing fo r d i rec t iona l lye n h a n c e d s u r f a c e a c o u s t i c w a v e p r o p a g a t i o n w a s u t i l i z e d ,T h e u s e o f o t h e r p r o c e s s i n g t e c h n iq u e s s u c h a s th e W i g n e r -Vil le d is t r ibut ion was a lso rep orted. 15, ] 6 T h i s p a p e r p r e s e n t s aw a v e l e t - b a s e d m e t h o d t h a t a ll o w s f e a t u r e i n f o r m a t i o n b e e x -t r a c te d t h r o u g h t h e d e p l o y m e n t o f o n l y o n e d e t e c ti o n p o i n t .T h e o b j e c t i v e o f t h e s t u d y i s t o i n t eg r a t e T A P - N D E w i t hG a b o r w a v e l e t tr a n s f o r m s f o r t h e g e n e r a t i o n a n d d e t e c ti o nof gu ided wa ves in cy l ind r i ca l t ub ing . By us ing wa ve le tt r ans fo rm fo r p roces s ing d i s pe rs ive waves , a r i ch s e t o f in -f o r m a t i o n a b o u t t h e w a v e s c a n b e r e a d i l y r e s o l v e d i n t h et i m e - f r e q u e n c y d o m a i n u s i n g o n e w a v e a c q u i s it i o n s e n s o r. 17T h i s i s i n c o n t r a s t t o t h e t w o - d i m e n s i o n a l F F F m e t h o d i nwhich mul t ip l e s ens ing loca t ions a re requ i red . A compar i s on

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    0 . 2 ~

    0 , 1 5

    N!~- 0,~'

    $1

    Ot J0 0,01 0.02 00 3 0,04 OC ~ 0.01~ 0.07t ( m s e c )

    F ig . 1 - - M- H d ispers ion p lo t ted as t ime versus f requency fo ra th in cyl indr ical shel l of m = h/R = 1/30, f lexural mode, n = 1.$1 = f irst ( lowest) f lexura l mode, $2 f irst ( lowest) torsion almode, and $3 = second f lexural mode

    made wi th regard to the two signal processing techniques 18indicates the effect iveness of wavele t t ransf orm as a preferredtool for damage detect ion and heal th moni tor ing.Theory

    Dispe rs ion curves have been comm only used fo r t he ana l-ysis of wave mot ions in cyl indrica l s t ructures. Mirsky andHerr mann 3,19,20 developed a theory ( M -H theory) that de-scr ibed longi tudinal and c i rcumferent ia l wave mot ions incyl inders. Using the theory, dispersion curves were obta inedfor cyl inders of a wide range of thickness to diameter ra t ios.The inc lus ion o f a more gene ra l T imoshenko- type theory toaddress non-ax ia lly sym met r i c mot ions enab led a r i ch se t o fwave ph eno men a to be studied than could c lassica l shel l the-or ie s , which cons ide red o n ly memb rane and bend ing e f fec ts .The dispersion curves presen ted in thei r work s were obta inedby numerical ly solving a character ist ic wave equat ion. Fiveroo t s were found a s a r e su l t and each roo t cor re sponded toa dispersion curve . These curves were plot ted in terms of anon-d imens iona l wave ve loc i ty ( s ) and a non-d imens iona lwav enum ber (~) for a given cyl inder of thickness, h , andmean radius, R.Wave d i spe r s ion i s commonly repre sen ted a s e i t he rwavenu mber ve r sus f requency , f r equency ve rsus phase ve loc -i ty , o r non-d imens iona l w avenum ber ve r sus non-d imens iona lwave veloci ty. In the fol lowing, dispersion informat ion ispresented in terms of t ime and frequency, a representa t iontha t r e su l t s f rom app ly ing wave t r ansform to expe r imenta lwave fo rm process ing. T he d i spe r s ion in forma t ion p re sen tedin Fig. 1 of a wave acq uired in a stee l specimen shows the f i rstthree modes $1, $2, and $3, where each mode is associa tedwith a par t icular type of mot ion. Fo r example , m ode Sl i s thelowest f lexural mode. The non-dispersive $2 mode is asso-c i a ted wi th t he pure ly t o r s iona l mot ion k nown as t he l owertorsional mode, or the f i rst Lobar mode. $3 corresponds tothe second f lexural mode.The p rocess o f ob t a in ing the d i spe r s ion curves i s basedon e l a s t i c wave mot ion and ene rgy me thods . Cons ide r t hedifferent ia l e leme nt depic ted in the reference system in Fig. 2 .

    Fig. 2--Reference system and stress element in a hol lowcy l inder

    The d i sp l acement component s i n t he cy l indr i ca l coord ina t esys tem are des igna ted as 17x, t70, and ~z, whose dependenceson the z-coordinate normal to the middle surface are givenb y

    ux(x, O, Z, t) = u(x, O, t) q- Zq)x(X, O, t)(tO(X, O, Z, t) = v( x, O, t) d- Z~oO(x, O, t)(tz(X, O, Z, t) = w( x, O, t)

    (1 )

    where t i s t ime, u , v , and w are the displaceme nt comp onen tsof a particle o n the m iddl e su rface, z = 0, and 99.~ and ~00 are

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    the angles of rota t ion of the normal to the middle surface inth e x - z and x-O planes, respectively. Note that in eq (1) ~0xand ~00 represent the axia l and c i rcumferent ia l shear effec ts .Integra t ion of the st rain energy densi ty express ion across theshell thickness would then lead to the shell stress equationsof mot ion.

    Consider the solutions for wave propaga t ion in the fol low-ing formu ( x , O, t) = U e i(mt-(xx) cos n0~Ox(X, O, t) = qJ e i(mt-ax) c o s n 0v ( x , 0, t ) = V e i (mt-ax) cos n0r O, t) = qb el(~176 co sn 0w ( x , 0, t) = W e i(mt-c~x) co sn 0

    (2)

    where n = 0, 1, 2 . . . i s an integer indicat ing the num ber ofwaves traveling circumferentially, m is the circular frequency,and c~ is the wave num ber defined as

    m 2rtCp L

    Substituting eqs (1) and (2) into in the equations of motion(not shown), a homogen eous system of l inear equat ions canbe found in the form of the f requency-equ at ion determinant :

    IF] = O. (3)The experime nta l dispersion cu rves are plot ted as t ime versusfrequency a t a single detection point . Figure 3 shows the com-parison betw een theoret ica l dispersion curves and those plot -ted using experimental data. It can be seen that, for relativelow frequencies, the experimenta l G abor wavele t plots corre-spond wel l in t rend and shape to the theoret ica l values. In theexperimenta l case , the addit ional bands are not ext ra modes,but ra ther they are the resul t of using a high value of thet ime- f requency re so lu t ion pa rame te r i n t he Gabor wave le tfunct ion in order to be consistent wi th the zero-mean valuecharacter of the wavele t i t se l f. There i s a lso a discrepancy inthe arr ival t ime of the experimenta l plot compared wi th thetheory. This could be the result of imprecise mea surem ent ofthe propagat ion path. As shown in Fig. 4 , the discrepancy ismore evident when both plots are superimposed.

    Before ca lcula t ing the roots of the character ist ic eq (3) ,a change of var iables i s needed. The change is performedto have the dispersion be displayed as funct ion of t ime, t ,and frequency, m. In the following, wave velocity, s, andwavenumber, ~ , are expressed in t ime and frequency as

    mh . / 2p (1 + v) ~oths = ~ S V E a n d 8 - - ( 4)2~xswith s being the t ravel distance of the propagat in g w ave fromthe excitation poin t to the detection point. D etails of the pro-cess of t ransforming dispersion curves and obta ining disper-sion informat ion from experimenta l data using Gabor wavele tt ransform can be found in Bal tazar e t a l . 21

    Once the theoret ica l dispersion curves are t ransformed,i t is possible to com pare them direct ly to the wav ele t coeff i-c ients resul ted from processing experimenta l wave form. Notethat Gabor wavele t t ransform resolves a t ime waveform into

    Fig. 3--Co mpa rison of theory (top) to experimental data(bottom)

    Fig. 4~C omp aris on of theory (lines) to experimental data(bands)

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    i t s jo int t ime- freq uen cy dom ains. The charac ter is t ic eq (3)is obta ined by ca lcula t ing the de terminant of the f reque ncyequat ion. Ther e are f ive roots , thus f ive possible m odes ex-is t for each case . The wave mot io n correspon ding to n = 0i s one o f ax i symmet ry and a ssumes no w aves p ropaga t ingci rcumferent ia l ly . When n = 1 , the case i s one of f lexura lmot ion w i thou t c i r cumfe ren t ia l l y p ropaga t ing waves .

    One o f the abi l it ies of the M- H theory i s tha t it can beappl ied to a wide rang e of hol low cyl inders . Tubulars as th inas m < 1/10 and as thick as m > 7/1 0 were consideredby M irsky and He rrmann. 3,19,20 Addi t ional ly , the M -H the-ory can inc lude the specia l l imi t cases when m = 0 and wh enm --+ cx~. The form er case cor respond s to a f la t p la te in whic hthe theory reduces to the c lassica l p la te theory discussed byMind lin. 22 The latter l imit case wh en m --+ cx~ corr esp ond sto a so l id cyl indr ica l bar .Experimental Setup

    A typ i ca l TAP-N DE was employe d fo r the s tudy . As show nin the schemat ics in Fig. 5 , the main com pon ents of the sys-t em inc lude a gene ra t ion subs ys t em cons i s t i ng o f an Nd:YAGlaser and focusin g opt ics , a fiber-t ip interferometer (F TI) de-t ec t i on subsys t em powered by an HeNe l a se r , a pho tode -tec tor , an osc i l loscope , and a PC-based signal acquisi t ion-p rocess ing subsys t em.

    The physica l se tup in Fig. 6 shows tha t i t i s possible tohave a dual -FTI se tup. The addi t ional FTI seen in the f ig-ure served as a redundancy for va l ida t ion purpose . 1 i s thefocal lens, 2 are the posi t ioning stages, 3 and 4 are FTI 1and FTI 2 , respect ive ly , and 5 i s a s tee l test specimen. Twofiber-opt ic cables, labeled 6 , a re connec ted to the i r respect iveFBT couplers (not shown), which in turn are a t tached to thephotodetec tors . Acquired waveforms are registered as in ter-ferometr ic beams by the photodetec tors and then output tothe da ta acquisi t ion-processing uni t for fea ture ext rac t ion.

    Four spec imens w i th di f ferent th ickness to mean radius ra-t ios were tested. Th e distance f r om exci ta t ion point to de tec-t ion point was 10 mm for a ll cases. For other parameters andconf igura tiona l details, refer to Balta zar et al .21. As als o notedin Bal tazar e t a l . , 21'23 the ini t ia ted ul t rasonic waves propagat -ing on a tubular surface can be surface waves i f the specim enis re la t ive ly thick, or pla te (guided) w aves i f the specim en isre la t ive ly thin . When analyzing stee l p ipes of severa l th ick-nesses, some genera ted ul t rasonic waves display behaviorstha t a re charac ter is t ic o f both su rface and guid ed wav es in di f -ferent ranges o f f requencies. Thus , of cer ta in cyl indr ica l con-f igura t ion , waves p ropaga t ing i n ho l lowed spec imens cou ldhave t ransi t ion charac ter is t ics tha t a re par t ia l ly dispersive andpar t ia l ly n on-dispersive .Results

    After va l ida t ing the procedures for t ransforming theore t i -ca l d i spe rs ion cu rves t h rough a compar i son wi th t he wave l e tt ime-frequency plots , i t was possible to establ ish a corre la-t ion be tween theory and exper imenta l resul ts . In conjunct ionwi th i n fo rma t ion ava i lab l e f rom pas t expe r imen t s i n w h ichpipes of di f ferent curvatures w ere considered, i t was po ssibleto establ ish a guidel ine for performing test ing on specimensof di f ferent th ickness to mean radius (m) ra t ios. The fourspecime ns considered here in have va lues of m = 0.1575,0.1811, 0 .1871, and 0.2177, respect ive ly .

    Fig. 5--Sche matic diagram of a typical TAP-NDE system

    Fig. 6--Actu al experimental setup with dual FTI

    Experimenta l resul ts a re presented as dispersion in te rmsof t ime versus f req uency f or each case . I t can be seen in Fig. 7tha t , as m is increased, wave dispersion t ransi t ion i s f rom apla te wave charac ter is t ic tha t i s of low-frequency content totha t o f a su r face wave rep re sen t ed by h ighe r - f r equency con-tent. Th e t ransi t ion effec t , noted as a band o f f requencies inwhich t he d i spe rs ion i s no l onge r o f pu re p l a te w ave o r su r -face wave charac ter is t ics , i s observed in each stage . I t shouldbe no ted tha t the s l ight inconsisten cy in the t ime o f a rriva l a taround 3 ~ts i s due to the measurement errors for l i f t ing thepropagat ion length.

    For the specimen wi th m = 0.1575, the dispersion dem on-st rates a guide d wav e a t t r ibute a t re la t ive low freq uencies a t0 .4 MHz. From Fig. 7(a) , a t ransi t ion cover ing ini t ia l ly af requency spec t rum a t 0 .4 -0 .6 M Hz i s seen t o p rogre ss ive ly

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    F ig. 7 - -D i spe rs i on spec t rum fo r f ou r cases o f t h i c kness t o med ium rad ius ra ti o (m = h/R): (a) m = 0.1575, (b) m = 0.1811, (c)m = 0 .1871, and (d ) m = 0 .2177

    change to a more prominent surface wave characteristic pat-tern at 0.6-1.0 MHz. There are also other frequency compo-nents that arrive later in time. These are cons idered noise andare not taken into account for the transition effect. The disper-sion associated with the second specimen with m = 0.1811shows a plate wave attribute at relative low frequencies atapproximately 0.62 MHz. A transition covering frequenciesbetween 0.55 and 0.8 MHz is seen to progressively changeto a surface wave characteristic at 0.8-l.75 MHz. Similarobservations can also be made with the third and fourth spec-imens. A summary of results is shown in Table 1. Dispersioncontours of the four cases displayed in Fig. 8 show that thetransition characteristics fall below the 1 MHz range.Conclusions

    The experimental investigation was carried out using theTAP-NDE system for the non-contact and non-invasive gen-eration and detection of ultrasonic waves in tubular con-figurations of several different thicknesses to mean radiusratios. By using a Gabor wavelet transform based featureinformation extraction scheme, it was possible to establishwave dispersion with the deployment of only one FTI sen-sor. Features characteristic of both surface and plate waves,thus referred to as the transition waves, were studied usingtime-frequency dispersion curves for pipes o f four differentratios of thickness-to-mean radius. It has been demonstrated

    F ig. 8 - - V ie w o f tr ans i t ion ranges f o r f ou r cases

    that time-frequency dispersion better represents the transi-tion effect. Although transition effects were observed in allpipe specimens considered in the study, it is concluded thattransition become non-negligibly prominent when the tubularthickness-to-mean radius ratio is close to 0.18.

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    T A B L E 1 - - F R E Q U E N C Y CHARACTER IST ICS ( M H z /S p e c i m e n M = h /R P l a t e w a v e T r a n s it io n S u r f a c e w a v e

    1 0 . 1 5 7 5 B e l o w 0 . 42 0 . 1 8 1 1 B e l o w 0 . 6 23 0 . 1 8 7 1 B e l o w 0 . 5 54 0 . 2 1 7 7 B e l o w 0 . 6 5

    0 . 4 - 0 . 6 0 . 6 - 10 . 6 2 - 0 . 8 0 . 8 - 1 . 7 50 . 5 5 - 0 . 8 0 . 8 - 1 . 9 50 . 6 5 - 0 . 9 0 . 9 a n d a b o v e

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    terizat ion Using Guide d Circumferent ial Waves," Journal of the Acoust icalSociety of America, 110(3) , 1 282-12 90 (2001) .13. Zupan, M. and Hemker, K.J., "Application of Fourier Ana lysis to theLase r Based Interferometric Strain~Displacement Gage," EXP ERIME NTALMECHANICS, 42 , 214- 2 20 ( 2002).14. Gao, W , Glorieux, C., and Thoen, J., " Stud y of CircumferentialWaves and The ir Interact ion wi th Defec ts on Cyl indrical Shel ls Using Line-source Laser Ultrasonics," Journa l of Appl ied Physics, 91(9), 6 114 -611 9(2002).15. Niethammer, M, Jabobs, L.J., Q u, J., and Jarzynski, J., "Tim e-f requency R epresen ta tions o f L am b W aves," Journa l o f t he A coas t i ca l Soc i e tyof America, 109(5), 1 841-1 847 (2001) .16. Prosser, WH ., Seale, M. D, and Smith, B .T. , " l~me - frequency Anal-ysis o f the Dispersion of Lamb M odes," Journal of the Acous t ical Society ofAmerica, 105(5), 2669 -267 6 (1999) .17. Wooh, S .C. an d Veroy, K., "Spectrotemporal Analysis of Guided-wave Pulse-echo Signals: Pa rt 1 . Dispersive Systems," EX PERIM ENTA LMECHANICS, 41 , 224-331 (2001) .18. Kim, H. and Melhem, H., "Fourier and W avelet Analyses for Fa-t igue Assessm ent of Concrete Beams," EXP ERIME NTAL MECHANICS, 43 ,131-1 40 (2003).19. Herrmann, G. and Mirsky, I., "Three-dimensional and Shell-theoryA na lys i s o f A x ia ll y Symm et r i c M ot ions o f Cy l inders ," Journa l o f A pp l i edMechanics, 23, 563 -568 (1956) .20. Mirsk~, 1. and Herrmann, G. "A-riaI ty Symm etric Motions of ThickCyl indrical Shel ls ," Journal of Appl ied M echanics, 25 , 97-102 (1958) .21. Baltazar, M.E., Chona, R., Suh, C .S., and Burger, C.P, "Stud y onLaser-generated Ultrasonic Waves on Cylindrical Surfaces," N ove l App li-cat ions of Experimental Metho ds in Mechanics, Proceeding s of the SEMA nnua l Con ference and E xpos i t ion o f E xper imen ta l and A pp l i ed M echan-ic.v, June 2-4 , Charlotte, NC, 1 63 -16 7 (2003).22. Mindl in , R .D., "Influence of Rotatory Inert ia and Shear on Flexu -ral Motions o f l sotropic Elast ic Plates," Journal o f Appl ie d Mechanics, 73 ,31-38 (1951) .23. Baltazar, M.E., Suh, C. S, Chona, R., and Burger, C.P, "Applica-t ions of TAP-NDE Technique to No n-contact Ul trasonic Pipe Inspect ion,"Proceedings of the ASN T 2000 Fal l Conference an d Qual i ty Test ing Show,Nove mber 14-17 , Indianapol is, IN, 161-1 66 (2000).

    4 3 2 9 VoL 45, No. 5, O c t o b e r 2 0 0 5 9 2 0 0 5 S o c i e t y fo r E x p e r i m e n t a l M e c h a n i c s