SELECTION OF PIEZOCERAMIC SENSOR PARAMETERS FOR DAMAGE DETECTION AND LOCALIZATION SYSTEM

Transcription

1 DIAGNOSTYKA 4(56)/2 KLEPKA, AMBROZISKI, Slction of pizocramic snsor paramtrs for amag tction 7 SELECTION OF PIEZOCERAMIC SENSOR PARAMETERS FOR DAMAGE DETECTION AND LOCALIZATION SYSTEM Anrzj KLEPKA, ukasz AMBROZISKI Dpartmnt of Robotics an Mchatronics AGH - Univrsity of Scinc an Tchnology, Al. Mickiwicza 3, 3-59 Kraków, tl anrzj.klpka@agh.u.pl,lukasz.ambrozinski@agh.u.pl Summary Damag tction mtho bas on Lamb wavs propagation phnomna ar incrasingly us as a tool for Structural Halth Monitoring (SHM) an Nonstructiv Tsting an Evaluation (NDT/E). Phnomna connct with wav propagation an intraction with amags ar vry complx an complicat. In many cass pns on snsors/actuators location, lctronic systm sign, snsor shap, frquncy rang of xcitation or snsors proprtis. Actuator/snsor slction bas only on spcification sht can b insufficint, so tim an frquncy analysis hav to b appli to signals acquir whn an xamin transucr was attach to a plat. In this papr snsor stuy on th transucr us for Lamb wavs gnration an acquisition has bn prsnt. Robustnss of th array consisting of chosn transucrs has bn vrifi with th scanning vibromtr. Kywors: lamb wavs, amag tction, pizocramics transucrs, phas array tchniqu. DOBÓR PARAMETRÓW PRZETWORNIKÓW PIEZOCERAMICZNYCH DO SYSTEMU DETEKCJI I LOKALIZACJI USZKODZE Strszczni Mtoy tkcji uszkoz opart o zjawiska propagacji fal Lamba s coraz czcij uywan w systmach SHM oraz o niniszczcych mto baa i ocny stanu konstrukcji. Zjawiska zwizan z propagacj fali oraz jj intrakcji z uszkozniami s zoon i skomplikowan. W wilu przypakach zalz o rozmiszcznia naajników/obiorników, ukau lktroniczngo i jgo paramtrów lktrycznych, ksztatu lmntu pizocramiczngo, zakrsu czstotliwoci wymusznia czy waciwoci samgo prztwornika pizocramiczngo (PZT). Wybór lmntów PZT tylko na postawi anych zawartych w spcyfikacji ni zawsz jst wystarczajcy. Koniczn jst przprowazni analiz ukau skaajcgo si z baanj struktury oraz prztwornika. W artykul przstawiono analiz czujników wykorzystywanych o wymuszania struktury oraz o akwizycji sygnaów opowizi. Poprawno przprowazonych tstów zostaa zwryfikowana z wykorzystanim wibromtru lasrowgo. Sowa kluczow: fal lamba, tkcja uszkoz, prztworniki pizocramiczn, tchnika phas array.. INTRODUCTION A varity of mans can b us as Lamb wavs actuators an snsors such as ultrasonic probs, lasrs, pizolctric lmnt, intrigital transucrs, optical fibrs. Brif scription of transucrs can b foun in [2]. A slction of th transucr us in a systm pns on many factors lik a siz an a shap of a monitor lmnt, its matrial proprtis an signal procssing appli to a amag tction algorithm. In this papr a SHM systm bas on pizolctric transucrs us to th amag tction mtho bas on th phas array tchniqu was prsnt. Giurgiutiu in [] show that pizolctric activ wafrs can b us in this mtho with goo rsults. Lamb wavs ar isprsiv an multimo many mos can xist at on frquncy. It mans, that Lamb wavs xcit by PZT contains multipl mos. Howvr whn xcitation frquncy is limit blow so call cut-off frquncy only two: A an S mos xist. Morovr it is possibl to nhanc on mo an ruc th othr by mo tuning tchniqu bas on a transucr siz an an xcitation frquncy slction [3]. Phas array tchniqu is vry oftn us as a non-structiv amag tction mtho bas on ultrasoun wavs. Main ia of that mtho is to str of wavfront shap, gnrat by a matrix of

2 8 DIAGNOSTYKA 4(56)/2 KLEPKA, AMBROZISKI, Slction of pizocramic snsor paramtrs for amag tction pizolctric transucrs [5,6,2]. Th slction of transucr siz, an th xcitation frquncy is ssntial for th phas array tchniqu. Tim lays calculation for ach transucr is bas on th phas vlocity an transucrs spacing so xact matrial proprtis of xamin structur ar ncssary to calculat th phas an th group vlocity. Th xcit wavlngth shoul b at last twic as long as transmittrs spacing, in anothr cas th si lobs an aitional fals ghost amags coul b isclos. Th siz of a PZT trminats th lowst wavlngth an th highst xcitation frquncy. 2. HARDWARE In all xprimnts Phas Array Non Dstructiv Tsting Systm (PAS-8)(fig. ) was us. Th systm nabl sinusoial signal gnration with frquncis btwn 4 5kHz. Aitionally many typs of winows can b appli (squar, triangl or Hanning). 8 channls wav us for signal sning with simultanous phas shifting gnration btwn gnrat signals. Data acquisition was prform by PAQ-6D at 2.5 MHz sampling frquncy. Fig.. PAS-8 an PAQ-6 us in xprimnts. 3. SENSOR STUDY 3.. Tim an frquncy omain tst As mntion abov many factors affct th wav propagation so transucrs attach to th aluminum plat wr tst rathr than unboun ons. Thr typs of multilayr Noliac PZTs transucrs wr xamin: a ring actuator CMAR3 of th iamtr 2 mm an two plat actuators: CMAP7 an CMAP2 of th siz 5x5x2 an 2x2x2 rspctivly. All transucrs wr ma of matrial NCE57 with frquncy constant 95 m/s, so rsonanc frquncis corrsponing to th largst transucr imnsion was calculat as 66 khz, 39 khz an 975 khz for CMAR3, CMAP7 an CMAP2 rspctivly. Examin transucrs wr plac on th 2 mm thick plat in a pitch-catch stup (Fig. ). Fig. 2. Thr typs of Noliac PZTs transucrs: Wax was us as a coupling agnt. Th actuatorsnsor istanc was 5 mm. In th first stp transucrs wr xcit with a broaban squar puls. Frquncy rsponss prsnt in th Fig. 3. rval rsonanc frquncis calculat abov. c) B ] [ itu m agn B ] [ itu m agn B ] [ itu m agn frquncy [khz] frquncy [khz] frquncy [khz] Fig. 3. Frquncy rsponss of transucrs xcit with a broaban squar signal CMAR 3 CMAP7 c) CMAP2. In th scon stp transucrs wr xcit with a ton-burst signal 4 cycls of sinusoi with th cntr frquncy khz, moulat with Hanning winow. Comparisons of th xcitation puls to th tim rsponss, prsnt in th 4, rvals that th bst rprsntation of th xcit signal can b foun in th signal acquir with th CMAP 2. Th CMAP 7 rspons istinctly contain high frquncy componnts, for th CMAR3 it was impossibl to isolat th xcit puls. In th nxt

3 DIAGNOSTYKA 4(56)/2 KLEPKA, AMBROZISKI, Slction of pizocramic snsor paramtrs for amag tction 9 xprimnts only CMAP 7 an CMAP 2 hav bn us. CMAP2 A (Fig. 5b.)mo is vn mor ominant for whol frquncy rang tim [s] x -5 [] p l itu m a c) tim [s] x -4 ) [] p l itu m a [] p l itu m a tim [s] x tim [s] x -4 Fig. 4. Tim rsponss acquir at khz narrowban puls xcitation xcitation signal CMAR 3 c) CMAP7) CMAP Disprsion curvs valiation In th phas array tchniqu tim lays calculation bas on th phas vlocity of xcit mo. To valiat th analytically calculat curvs by comparing thm with th xprimntal ons an to assss th snsitivity of th transucr to th particular Lamb mo, th 2D Fourir transform mtho for th masurmnt of propagating multimo signals was us [4]. In Fig. 5a. can b sn that th S mo is harly rcognizabl for signals acquir by CMAP7 at lowr wavnumbr-frquncy rang. In th rspons from Fig. 5. Thortical an masur wavnumbr vs. frquncy plot obtain for signals acquir by CMAP7, CMAP2. Whn a mo with iffrnt wavnumbr is gnrat with a PZT lmnt an aitional bam is form in th unintntional irction. Gnrat signal contains multipl frquncy componnts with significant amplitu. It may affct mor unwant bams. Th last of th tst transucrs (CMAP2) allows for narrowban xcitation without high frquncy componnts, morovr in th tst plat it gnrat nhanc A with ruc S mo Exprimntal rsults for Damag imaging tchniqu Damag localization algorithm is bas on tim omain rsponss analysis of th structur. Th rsponss ar acquir from th istribut actuators snsors gri, plac on th structur. First stp in this mtho is stimation of th group vlocity for givn plat gomtry. It can b on in two ways: solving isprsion quation or masur th group vlocity xprimntally. Position in tim omain of th incint wav an scattrs from gs can b stimat using tim of flight paramtr[3]. Damag localisation procss consist in rprsnting invstigat ara as an imag, whr

4 2 DIAGNOSTYKA 4(56)/2 KLEPKA, AMBROZISKI, Slction of pizocramic snsor paramtrs for amag tction valus of th pixl quation [3]: ar calculat using () whr valu of th givn pixl, is th istanc from amag to actuator an snsor rspctivly, nvlop of th rcor signal, group vlocity of th wav, is winowing function. Typical structur rspons signal is prsnt in figur 6. Fig. 7. Comparison of amag intification procss with us iffrnt typs of PZT: CMAP 7, CMAP 2 Fig. 6. Exampl of structur rspons signal with amag. For ach actuator snsor path on imag can b obtain. Th final rsult is achiv by summing imags from all paths. Comparison of rsults obtain with us CMAP 7 an CMAP 2 transucrs ar prsnt in figur 7. As can b notic that in cas of us CMAP 2 transucrs amag ara is show corrctly. In cas CMAP 7 transucr, rsults ar not clar Exprimntal rsults for phas array Th scon mtho is bas on th phas array tchniqu. This tchniqu crats th possibility of forming an string th front wav gnrat from a st of transucrs. Th bam forming is raliz by lay gnration uring xcitation of particular transucrs, using quation [6,,]. (2) whr l x is th istanc btwn transucrs, c is phas vlocity, is th angl btwn th actuator lin an wav front. Th acquisition procss is prform with th sam lay as uring xcitation of th structur. Du to th complxity of th phnomna apparing uring th intraction btwn wavs an th amag, som mthos of signal procssing hav bn propos, such as wavlt filtration an nvlop stimation. Main paramtrs of th phas array tchniqu ar istanc btwn transucrs an angl rsolution (with of th main lo. If th som rstriction connct with wav lngth, snsor or actuators placmnt or frquncy componnt of th xcitation signals ar not fulfill, th rsult of th intification algorithm which bas on th rspons signal procssing can b incorrct. In cas whn si lobs hav ominant influnc, th ffcts lik ghost amags or fals amag can appar (Fig.8) Eight CMAP2 plat actuators of th siz 2x2x2 mm wr us to built an linar array. Th istanc btwn PZTs cntrs was qual to 5 mm. Th array was st in th cntr of an aluminum plat with siz xx2 mm. As a coupling agnt a wax was us. Disavantags of this coupling mtho is irrgular wax layr for all transucrs. In th n th amplitus of th signal sning to th plat can b iffrnt for particular lmnts. Bfor th xprimnt a calibration procur was prform. Each actuator on by on gnrat signals captur by on PZT lmnt. Output amplitu gains for all channls wr ajust so th linar an Hamming aprturs was achiv. This problm is not invstigat in th

5 DIAGNOSTYKA 4(56)/2 KLEPKA, AMBROZISKI, Slction of pizocramic snsor paramtrs for amag tction 2 currnt papr but tail information about apoization an ffctiv aprtur can b foun in[7 9,2]. Tim lays calculation was bas on thortical isprsion curvs prsnt in Fig. 5. thortical calculation. A slight iffrnc of string angl is caus by a small rror in th thortical isprs curvs stimation. Th array us in xprimnts was linar so an aitional, symmtric bam is xpct at irction 24 grs..3 ] [m Y.2. Fig. 8. Fals amag ffct X [m] ] [m Y X [m] Fig. 9. Exprimntal stup for phas array tsting. During xprimnt assum xcitation frquncy qual to khz. It is corrspon wavlngth qual 3.57mm. This paramtrs provi half wavlngth conition fulfill (half of th wavlngth shoul b gratr thn transucr spacing). Th string irction was 2 grs. To valiat th prformanc of string th wavfront a scanning lasr vibromtr POLYTEC PSV 4 was us (Fig. 9). Th signals gnrat by th array wr captur by th vibromtr. Th vic nabl noncontact masurmnt of th out of plan prturbation vlocity. Examin points wr istribut in a circl shap so istancs btwn th masurmnt points an th sourc of th wav wr qual. Tim signals wr acquir in th arc shap gri points, th maximum valu of th first arrival wav packt has bn us to crat th bam pattrns. Two mthos of an apoisation hav bn us uring th xprimnt. Th rsults of th xprimnt can b sn abov. Th highst vibration amplitu was appar in th sir irction. Fig. a,b prsnts masur bam pattrn in polar plot. It rprsnts th normaliz maximum amplitu in all irctions for a spcifi array configuration. A thortical bam pattrn was a to Fig c,. It show goo agrmnt with a masur signal an c) ) 5 masur thortical masur thortical Fig.. Masurmnt points an amplitu valus- linar apoization Hamming apoization. Thortical an xprimntal normaliz rsults of wav amplitus in masur irction. - c) linar apoization ) Hamming apoization

6 22 DIAGNOSTYKA 4(56)/2 KLEPKA, AMBROZISKI, Slction of pizocramic snsor paramtrs for amag tction 4. CONCLUSIONS Prform tst show that shap an imnsions of transucr can hav significant impact of amag tction algorithm rsults. Th smallst transucrs hav bttr proprtis but thir powr somtims can b unsatisfactory. Th gomtrical rsonant frquncy can b trmin, but thir influnc on rsults uring narrowban xcitation can b significant. Rsonant frquncy of th PZT lmnts can hav influnc on rsults in spit of frquncy of xcitation is slct finitly outsi th rsonanc. Slction of propr transucrs an thir paramtrs is ky for Phas Array tchniqu an apply togthr with apoization tchniqu allow to cras of silobs, nabl bttr irctionality an prvnt fals amag an ghost amag ffcts. ACKNOWLEDGMENTS Rsarch funing from th Polish rsarch projct MONIT (No. POIG /8-) is acknowlg by th authors. BIBLOGRAPHY []. Giurgiutiu V. Structural Halth Monitoring with pizolctric wafr activ snsors Elsvir Inc. 28. [2]. Zhongqing Su, Lin Y, YLu. Gui Lamb wavs for intiþcation of amag in composit structurs: A rviw Journal of Soun an Vibration 295 (26) [3]. Giurgiutiu V (25), Tun Lamb wav xcitation an tction with pizolctric wafr activ snsors for structural halth monitoring. Journal of Intllignt Matrial Systms an Structurs 6, [4]. Allyn D. an P. Cawly (99), "A twoimnsional Fourir transform mtho for th masurmnt of propagating multimo signals" Journal of th Acoustical Socity of Amrica 89(3) pp [5]. M. Vit C. T. Ng S. Hams an T. Wattingr "Imaging Laminar Damag in Plats using Lamb Wav Bamforming" Avanc Matrials Rsarch Vols (28) pp [6]. T. Stpinski, P. Wu, E. Martinz, Ultrasonic inspction of coppr canistrs using phas arrays NDTnt 998 March, Vol.3 No.3. [7]. L. Morau B. Drinkwatr P. Wilcox Ultrasonic Imaging Algorithms With Limit Transmission Cycls for Rapi Nonstructiv Evaluation Transactions on Ultrasonics, Frrolctrics, an Frquncy Control, vol. 56, no. 9, Sptmbr 29 [8]. M. Nikolov V. Bhar Analysis an Optimization of Mical Ultrasoun Imaging Using th Effctiv Aprtur Approach Cybrntics an information tchnologis Volum 5, No 2, Sofia 25 [9]. L. Mažika R. Kažys A. Maciulviius Optimization of transucr arrays paramtrs for fficint xcitation of Lamb wavs ISSN Ultragarsas (ultrasoun), Vol.62, No.4, 27. []. Su Z. an L. Y (29): Intification of Damag Using Lamb Wavs From Funamntals to Applications Springr- Vrlag Brlin Hilbrg, pp. 65. []. Z. Su, L. Y, Intification of Damag Using Lamb Wavs Lctur Nots in Appli an Computational Mchanics, Vol. 48, 346 p. 29 [ ]. [2]. S. C. Wooh, Y. Shi Optimum bam string of linar phas arrays Wav Motion 29 (999) [3]. Q. Wang, S. Yuan Baslin-fr amag imaging mtho for lamb wav bas structural halth monitoring IV ECCOMAS Thmatic Confrnc on Smart Structurs an Matrials. Anrzj KLEPKA Ph.D. is an assistant proffssor at th Dpartmnt of Robotics an Mchatronics of AGH Univrsity of Scinc an Tchmnology. His scintific intrsts focus on signal procssing, nonlinar systms an Structural Salth Monitoring ukasz AMBROZISKI M.Sc. is PhD stunt at th Dpartmnt of Robotics an Mchatronics of AGH Univrsity of Scinc an Tchmnology. His works ar connct with amag tction an localisation an Structural Halth Monitoring.