Research on ultrasonic non-destructive examination in water immersion of a composite material

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1 Reserch on ultrsonic non-destructive exmintion in wter immersion of composite mteril AMZA GHEORGHE, VINTILĂ (MIHAIL) SIMONA, ACHIM VERONICA, OANA ELENA AMZA, MIRCEA DOBRE Mteril nd Welding Technology, University POLITEHNICA from Buchrest, Spliul Independentei no. 313, Buchrest, Romni Abstrct: Nondestructive Evlution is importnt in prticulrly for the control of composite prts. Criticl prts re required more nd more to be tested during the mnufcturing process by more efficient nd ccurcy nondestructive evlution methods (NDE). One of the most suitble method to be utomted is the ultrsonic exm. Inspections with this technique over composite prts introduces dditionl difficulties to the stndrd inspection, becuse the coustic coupling it cn t be done correctly. In this pper, we present method of exmintion with ultrsound, for composite prt. Key words: ultrsound, immersion, probe, higher resolution, defect 1 Introduction Ultrsounds re widely used in helth cre for noninvsive dignostics nd in industry for nondestructive testing [1], [2], [3]. In the humn body, it genertes visul imges from inside the test medium: the fetus, mlignnt tissue, stones, etc. In industril pplictions, besides defect detection, ultrsounds re lso useful for determining significnt mteril chrcteristics such s density, thickness, mechnicl properties, nd level sensing. Knowledge of ultrsoniclly nlyzed informtion is importnt for humn helth s well s for cost-effective production of qulity industril mterils. 1.1 Ultrsonic exmintion in wter immersion The ultrsonic exmintion in wter immersion is wonderful suitble for utomtion. Such exmintion method, under column of wter, void the direct coupling problems - uncertin in mny cses. Also the reproducibility of results obtined by this method re excellent [4], [5], [6]. 1.2 Advntges nd disdvntge of ultrsonic exmintion in wter immersion The ultrsonic exmintion in wter immersion presents number of dvntges nd disdvntges compred with other nondestructive exmintion methods. Among the dvntges we my include: - high sensitivity, llowing detection of crcks with n opening of few microns; - the high penetrtion power, modern flw detectors cn be used to control prts with thickness of m; - brod control posibilities, the sme device cn be used to control the depth of defects of surfce crcks, mteril structure, but lso the determintion nd mesurement of thickness; - the exmintion does not require complicted nd costly preprtory phses nd cn be done quickly nd effectively even in the technologicl production flow. The min disdvntge is the high sensitivity of the method, sometimes leding to n uncertin interprettion of results, therefore, to increse sfety in the interprettion of results, this method is supplemented sometimes with other methods [1], [12]. 1.3 The principl of ultrsonic exmintion in wter immersion The ultrsonic exmintion in immersion is control method in which the test object nd the trnsducer re submerged in liquid (usully wter) tht cts s the coupling medium. Usully, the probe ISSN: ISBN:

2 is not in contct with the test specimen (fig 1). The tnk is device in which the test procedure is crried out, usully consisting of multi xis control. The immersion probes re utomted with motors nd encoders for reding the ctul probe position (fig 2). Immersion tnk Trnsducer where: T is the trnsmission coefficient in the propgtion medium Z 1 is the coustic impednce of the ultrsound crrier medium (for exmple, wter for the NCU mode) nd Z 2 is the coustic impednce of the test medium. The trnsmission coefficient is derived s the rtio of trnsmitted cousticl energy V nd the input energy V 0 of plne wve when refrcted t 0 incidence on the interfce between the two medi: (2) Testing Probe Flw This reltionship cn lso be described by decibel scle: (3) Fig. 1 The principle scheme of ultrsonic exmintion in wter immersion Energy trnsferred in the propgtive medium = (4) For more detils nd the significnce of plne wve trnsmission nd reflection t number of interfces in terms of cousticl pressure nd intensity [4], [12], [13]. Ultrsound in noncontct trnsmission must propgte from wter into the test mteril nd then gin into wter so tht the trnsmitted wve cn be detected by receiving trnsducer (Fig. 3). Interfce corresponds to wter mteril (from coustic impednce Z to Z m ) trnsmission. Interfce b corresponds to mteril wter (from coustic impednce Z m to Z b ) trnsmission. Trnsmitting trnsducer Fig. 2 Experimentl stnd of ultrsonic exmintion in wter immersion UTwin The frction of ultrsound trnsmission nd energy trnsferred t the wter-mteril interfce is given by (1) Z Z b Z m Receiving trnsducer Mteril de testre mteril Interfce, Mteril- Interfce, b Fig 3. Interfces to be crossed by ultrsound (shown by rrow) in the immersion mode to propgte ultrsound through test mteril. ISSN: ISBN:

3 The efficiency of n ultrsonic trnsducer depends on the coupling coefficients nd other electromechnicl properties of the piezoelectric mteril. It lso depends on the mechnism by which ultrsound is trnsferred from the piezoelectric mteril to the medium in which ultrsound needs to be propgted. In the immersion mode, this medium is wter [8], [9], [10]. mm up to 25 mm in dimeter nd operte mostly over frequency rnge of 1 25 MHz. The bem from the probe cn be focused to point using sphericl lens nd to line by mens of cylindricl lens [3], [4], [5]. Tble 1 provides the trnsmission coefficients nd energy losses in selected test mterils in the ultrsonic exmintion in wter immersion clculted by using Eqs. (1) nd (4). Tble 1 Trnsmission Coefficients nd Energy Trnsfer in Selected Mterils t Vrious Interfces in the Ultrsonic Exmintion in Immersion Z(wter); 1,5 Mryl; 1 Ryl = 1 kg/m 2 s Mteril Zm Mryl Steel 51,0 Aluminium 17,0 crylic 3,5 Silicone Rubber 1,0 Interfce (Fig 1) -Steel, Steel-, b luminium, Aluminium - wter, b wtercrylic, Acrylicwter, b wterrubber, Rubberwter, b Trnsmission Coefficient eq (1) Energ Trnsfer eq (4) (db) Totl Energy Loss t Interfces +b (db) 0, , , ,3-10 0,84-1,5 3 0,84-1,5 0,96-0,35 <1 0,96-0,35 Fig. 4 Principle design of ultrsonic immersion probe 3. The technology of ultrsonic exmintion in wter immersion An ultrsonic pulse is trnsmitted through the specimen perpendiculr to the surfce using seprte trnsmitter nd receiver trnsducers opposite to ech other. The signl obtined from the receiver trnsducer is mesure of the totl ultrsonic dmping in the mteril [6], [7], [8]. 2. Ultrsonic trnsducers for immersion exmintion mode The trnsducers used for noncontct scnning methods using wter s contct medium, re pplied in immersion tnks, so they must be wterproof. Mny other scnning techniques use them s well, e.g., gp scnning, probe fixtures cting with wter column or wter jet. The trnsducers, which re invribly of the compression-wve type, re mostly in rnge of 6 The ultrsonic dmping is influenced by the existing of defects in the mteril such s high level of porosity or delmintions. Pores will cuse the ultrsound to be reflected due to the high difference between coustic impednce in the mteril nd in ir. The porosity re normlly much smller tht the focl dimeter nd cnnot be detected one by one. However, the sum of lrge number of pores results in higher totl dmping nd thus smller trnsmitted signl. The ultrsonic equipment ISSN: ISBN:

4 is cpble of mesuring the pek mplitude of the trnsmitted signl. The scns re performed in rectngulr rster pttern. In ech point the mplitude of the trnsmitted ultrsonic signl is mesured. The result of the scnning is presented in color or grey-tone plot where the color scle is in db, which gives high dynmic rnge. In order to locte the depths of the defects immersion pulse-echo hs been used s supplementry technique. Only one trnsducers tht works s both s sender nd receiver re used in this technique [8], [9], [10]. In order to inspect the whole section the ultrsonic signl hs to trvel twice through the specimen down to the bckside of the specimen nd bck to the upper surfce. If there re defects (i.e. pores or delmintions) present somewhere in the trnsversl section the ultrsonic wve will be reflected by the defects nd will be mesured by the trnsducer. For the thick lmintes (50 mm) it is difficult to exmine the whole trnsversl section becuse smll echo is received from the bck surfce. The pplictions shll be mde on experimentl stnd UTwin, in the lbortory of IMST fculty. 3.1 Some of the grphics cpbilities of the UTwin equipment - Exceptionl 2D nd 3D grphing cpbilities; - Disply multiple grphs on screen, limited only by the resolution of the screen itself (fig. 5); - Grphs re individully sizble on screen, mking for very flexible rrngement; - Set up one or more lrge grphs for visuliztion with multiple supporting smll grphs longside or round the min grph; - Arrnge multiple grphs on screen. Set up multiple screens nd ccess ech by selecting userlbeled tb (fig. 6); - Set up themes for screen lyout (e. g. A-Scn, feture monitoring B-Scn, rel-time C-Scn, reply nlysis, themes, etc.). Fig. 6 Disply ny combintion of A, B nd C- Scns. 4. Experimentl results Textolite plte ws used, which were given 6 holes of different sizes nd depths. Textolite pltes re used minly to mnufcture prts in pplictions tht require mechnicl nd electricl insulting properties, such s switching mechnisms. Textolite is lso used in pplictions such s gers nd wheels of friction or friction surfces. Becuse of fine fbric which hs composition, this mteril is recommended nd mnufcturing of smll prts. These mterils re observed by good mchinbility, high wer resistnce nd good resistnce to wter, oils nd lubricnts. Textolite pltes re mnufctured in thicknesses from 0.13 to 300 mm of 2000 x 1000 mm formts [11], [12], [13], [14]. Tble 2 Textolite Plte Fig. 5 Scnning exmple who define seprte pges for multiple chnnel pplictions. ISSN: ISBN:

5 Thickness 8 mm Dimensions bord 150 x 125 Density kg/m³ Working temperture -40ºC +105ºC Bending effort from destruction, not less thn 150 Mp The effort to brek the tension of prllel lyers, not less thn 160 Mp bsorption Mx. 0.7% Tensile strength not less thn On bse On the bottom 49 Mp ph 6 9 Tensile strength (20±5)ºC Specific volumetric electricl resistnce 90 Mp 2 5kW/mm 1.10¹º 1.10¹² Ohm*m Fig. 8 Ultrsonic exmintion in wter immersion of the textolite plte The textolite plte is controlled by immersion (Fig. 8), presents reflections of disc. Exmintion results show reflections defects. By mesuring the propgtion time we determined the depth of defects, s we see occurring in the imge obtined by scnning C. Fig. 7 Geometry of the multilyered composite lminte If there re no interfce delmintions or other discontinuities within the lminte, then the trction nd displcement components must be continuous cross the interfces prllel to the x 1 -x 2 plne, i.e.:,, (4) Fig. 9 Ultrsonic exmintion in wter immersion of the textolite plte, reflector disk type, 9.5 mm dimeter nd 6 mm deep ISSN: ISBN:

6 Fig. 10 Ultrsonic exmintion in wter immersion of the textolite plte, reflector disk type, 7 mm dimeter nd 3 mm deep Fig. 11 Ultrsonic exmintion in wter immersion of the textolite plte, reflector disk type, 7 mm dimeter nd 3 mm deep, TOF 4. CONCLUSIONS The method of exmintion by ultrsonic immersion is the only nondestructive control method which does not require direct contct between the trnsducer nd the test object; The method of exmintion by ultrsonic immersion hs better resolution due to higher frequency nd lower focl point of the immersion trnsducers; The method llows the exmintion of multilyered composite lminte References: [1] Amz, Gheorghe s.. - Ultrsunete plicńii ctive, Editur AGIR, Bucuresti, 2006; [2] Amz, Gheorghe ş. Sisteme ultrcustice, Ed. Tehnică, Bucureşti, 1989; [3] W. Hillger, "Inspection of CFRP components by ultrsonic imging with ir coupling", 8 th Europen Conference on Nondestructive Testing, Brcelon 2002, Conference Proc. on CD-ROM. [4] W. Hillger, "Ultrsonic Testing of Composites - From lbortory Reserch to In-field Inspections", 15 th World Conference on Nondestructive Testing, Rom, October 2000, Conference proc. On CD-ROM. [5] R.E. Green, in Mterils Anlysis by Ultrsonics, A. Vry, Ed. Noyes Dt, NJ, 1987, [6] J.A. Brunk, C.J. Vlenz, nd M.C. Bhrdwj, in Acousto-Ultrsonics, Theory nd Applictions, J.C. Duke, Jr., Ed. Plenum Press, NY, 1988 [7] G.A. Allers, in Intelligent Processing of Mterils nd Advnced Sensors, H.N.G. Wdley, P.A. Prish, B.B. Rth, nd S.M. Wolf, eds., Metllurgicl Society, PA, 1986, [8] M.C. Bhrdwj, I. Neeson, M.E. Lngron, nd V. Vndervlk, 24th Annu. Conf. Composites Adv. Cerm. Mter. Struct. The Americn Cermic Society, Westerville, OH (2000). [9] D.W. Schindel, D.A. Hutchins, L. Zou, nd M. Syer, IEEE Trns. Ultrsonics Ferroelectic Frequency Control [10] Ultrsonic signl processing methods for detection of defects in composite mterils - D.Pgodins [11] Yew, C. H., Chen, K. G., ndwng, D. L., An experimentl study of interction between surfce wves nd surfce breking crck, [12] Qi, Q., Subsonic leky Ryleigh wves t liquid-solid interfces, J. Acoust. Soc. Am., 95: , [13] Prk, C. B., Miller, R. D., Xi, J., Ivnov, J., Sonnichsen, G. V., Hunter, J. A., Good, R., Burns, R., nd Christin, H., Underwter msw to evlute stiffness of wterbottom sediments, The Leding Edge. [14] Cho, C., Surfce wves in n elstic hlf spce, J. App. Mech., 28: , ISSN: ISBN: