LOW-VELOCITY IMPACT LOCALIZATION OF THE COMPOSITE TUBE USING A NORMALIZED CROSS-CORRELATION METHOD

Transcription

1 21 s Inernaional Conference on Composie Maerials Xi an, h Augus 2017 LOW-VELOCITY IMPACT LOCALIZATION OF THE COMPOSITE TUBE USING A NORMALIZED CROSS-CORRELATION METHOD Hyunseok Kwon 1, Yurim Park 1, Praik Shresha 1 and Chun-Gon Kim 1* 1 Deparmen of Aerospace Engineering, Korea Advanced Insiue of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea * cgkim@kais.edu, web page: hp:/ Keywords: Composie ube, Srucural healh monioring, Impac localizaion, Fiber Bragg graing sensor ABSTRACT This sudy presens an experimenal sudy on he low-velociy impac localizaion of cylindrical srucures. A composie ube srucure was used o represen cylindrical srucures such as aircraf fuselage and ail boom. Three FBG sensors were used o acquire he impac signals, and he normalized cross correlaion mehod was employed as he algorihm for localizing he random impac source. A oal of 18 random impacs were applied o he composie ube using an impac hammer, and i was posprocessed using he employed algorihm and reference daabase which was consruced in advance. When hree sensors were used, he localizaion resuls were successfully esimaed wih he average error of 1.89cm and maximum error of 4.97cm. However, when wo sensors were used, he resuls were negaively affeced by he minimal disance beween he sensors, so he resuls for he case using wo sensors locaed farher apar showed lower average and maximum errors. Therefore, i shows ha performance of he impac localizaion for he cylindrical composie srucure is influenced by he number of sensors and he disance or configuraion beween he sensors. 1 INTRODUCTION Since composie maerials have high-specific srengh and siffness, i is being widely used in a variey of indusrial fields, especially in he aerospace indusry. Recenly, he superioriy of composie maerial was proved by he new Boeing 787 Dreamliner which is composed of more han 50% of composie maerials. However, since composie maerials have differen damage ypes wih regard o exising convenional meallic maerials, Srucural Healh Monioring (SHM) o check he sae of composie srucure during operaion is essenial for ensuring he safey and reliabiliy. Among he damage ypes of composie maerials, barely visible impac damage (BVID) caused by he low velociy impac such as ool drop, bird-srike could degrade he mechanical properies of a composie srucure and finally lead o faal accidens wihou perceiving beforehand. Therefore, o preven he poenial BVID, Various sudies for low velociy impac localizaion have been conduced. However, he applicabiliy of he previous sudies is low because mos of hem adoped muliple elecric sensors which offer several problems such as elecro-magneic inerference (EMI) and wiring problems [2-4]. Since he fiber Bragg graing (FBG) sensor have excellen characerisics of small size, muiplexabiliy and EMI immuniy, so i is being widely used in SHM research on composie srucures o overcome he disadvanages of convenional elecric sensors. Especially, since FBG sensor can easily be embedded ino he composie maerials wih barely affecing mechanical properies of he composie maerials, i is suiable for SHM of composie srucure. In addiion, he argeed srucures of previous sudies were concenraed o he wing box and he siffened panel which canno describe cylindrical srucures such as he fuselage or ail boom [1, 4-5]. Lee e al [6] performed he impac localizaion on a aluminum pipe, bu i needs o be applied o he cylindrical composie srucures. In his research, impac localizaion for composie ube based on FBG sensor using normalized crosscorrelaion was conduced. The composie ube which describe he cylindrical srucure was argeed for impac localizaion, and a FBG sensor which have excellen characerisics was seleced.

2 Firs A. Auhor, Second B. Auhor and Third C. Auhor 2 EXPERIMENTAL SETUP As a arge srucure, a composie ube which describes he cylindrical srucures of an aircraf such as ail boom and fuselage was seleced. The composie ube was fabricaed using a carbon/epoxy Prepreg (CU125NS, SK Chemical Co., Republic of Korea). The sacking sequence of he composie ube is [0/±45/90] s, and he composie ube has a diameer of 100mm and a lengh of 300mm. Figure 1 shows he fabricaed composie ube. Figure 1: Fabricaed composie ube. One end of he composie ube srucure was clamped o a fixure, as shown in figure 2. The es secion for he impac localizaion was 150 (longiudinal direcion) 200 (circumferenial direcion), and i was 90mm away from he clamped boundary. The es secion consiss of 63 grid poins, and he disance beween parallel or perpendicular grid poins was 25mm. FBG sensors (FBG KOREA, Inc., Rep. of Korea) which have a cener wavelengh of nm, nm, nm and a gauge lengh of 10mm were chosen. The FBG sensors were aached o he surface of he specimen using he same procedure of a srain gauge. The inervals of each FBG sensor were 50mm in he circumference direcion, and i was aached a an angle of 45 degrees o he cenerline. The aached FBG sensors were conneced o a commercial high-speed inerrogaor (Fiberpro, Inc., Rep. of Korea). The impac signals were acquired wih a sampling frequency of 100kHz, he daa lengh of he signals was Figure 2 shows he experimenal seup. Figure 2: Experimenal seup.

3 21 s Inernaional Conference on Composie Maerials Xi an, h Augus 2017 Impac poin x y As shown in figure 3, a oal of 18 random impacs were applied using he impac hammer. 3 IMPACT LOCALIZATION ALGORITHM Figure 3: locaions of 20 impac poins. Figure 3 shows he flow char of he employed algorihm proposed by Kim [1]. The employed algorihm is divided ino wo secions. The firs par is o exrac he proper signal form from he acquired signals for proper comparison beween differen signals. In his process, he obained signals is adjused o he baseline and signal is cu off using arrival ime of he signal. The second par is o esimae he acual impac locaion using normalized cross-correlaion mehod. The normalized cross-correlaion mehod is based on cross-correlaion mehod. The cross-correlaion mehod is used o calculae and compare he similariy beween wo differen signals. When he similariy beween wo signals is high, i shows a high value and in he opposie case i shows a low value. Therefore, he acual impac locaions is esimaed using he reference signal a each grid poin ha is consruced in advance. The crosscorrelaion beween wo signals is as shown below. (f g)(τ) = f()g( + τ)d In equaion (1), * is he cross-correlaion operaor, and τ is he ime-lag beween he wo differen signals f and g. The normalized cross-correlaion modified he exising cross-correlaion using by adding he normalizaion procedure. The employed normalized cross-correlaion is shown below. ( f F g G ) (τ) = 1 F(kF) (f kf)(τ) = 1 F 2 (f f)(τ) (2) In equaion (2), F and G are he normalizing consan, and k is a consan beween he wo impac signals for an ideal case. I has been proved ha he performance of he normalized cross correlaion is beer han cross correlaion mehod by Kim [1]. The similariy beween he random impac signal and he reference signals a each grid poin is calculaed using he normalized cross correlaion, and for all grid poins exceeding a correlaion value of 90% of maximum, he cenroid among hem is prediced o be he acual impac locaion. (1)

4 Firs A. Auhor, Second B. Auhor and Third C. Auhor Reference daabase 0_0 1_ 0 I 0 0_1 0J I J < Combined correlaion values > IJ (1) Signal exracion ( n ) IJ () S IJ S ( ) Baseline conversion Normalizaion ( n ) () ( n Calculaion of correlaion beween S andarㅐ ) ddd () R ( n ) () R Obained impac signals Sensor 1 Sensor 2 Sensor 3 Sensor n ( n ) Time (msec) IJ () < Esimaion of impac locaion > (2) Impac locaion deerminaion Consrucion of combined correlaion, orr_skumx,xdd corr _ sum IJ ( ) Exracion of maximum combined correlaion values, dcorr_sum corr _ for all raining poins IJ Cenroid beween seleced raining poins : Seleced raining poin : Ac. impac locaion : Es. impac locaion 4 RESULTS Esimaed impac locaion Figure 4: Flow char for he impac localizaion algorihm by Kim [1]. Figure 5 shows he impac localizaion resuls based on hree FBG sensors using he employed normalized cross-correlaion algorihm. The average error was 1.89mm wih a sandard deviaion of 1.16mm, and he maximum error was 4.97mm. The average error and sandard deviaion were similar o he resuls of impac localizaion for aluminum pipe srucure based on he FBG sensor using roo means squired value-based algorihm by Lee [6]. However, if less han 3 sensors were used, he resuls were differen. Figure 5: Esimaed impac locaions using hree FBG sensors. Esimaed poin x y

5 21 s Inernaional Conference on Composie Maerials Xi an, h Augus Average error Maxmum error Error (cm) Single #1 Single #2 Single #3 Two #1, #2 Two #1, #3 The number of used sensors Two Three #2, #3 #1, #2, #3 Figure 6: The error of he esimaed impac locaions according o he number of FBG sensors. Figure 6 shows he impac localizaion resuls according o he number of FBG sensors. In he case of using a single FBG sensor, average error of more han 6cm and maximum error of more han 12cm were shown. If wo sensors were used, he resuls were differen depending on wheher or no hey included FBG # 2 sensors insalled in he cener line of he es secion. When he wo FBG sensors including FBG # 2 sensor were used, i showed an average error of more han 4.5cm wih high sandard deviaion and a maximum error of approximaely 9cm. However, when FBG # 2 sensor was no used, he average error was approximaely 3 cm wih less sandard deviaion and maximum error was less han 7 cm. This is a resul of a 36% reducion in he average error compared o he resuls using #2 FBG sensor. The FBG # 2 sensor was insalled in he cener line, bu i is expeced o be no a because i was insalled a an angle of 45 degrees o avoid symmerical signal acquisiion in he upper and lower areas wih respec o he cener line. Figure 7 shows he comparison of he acquired impac signals a he difference poins which are symmerically locaed wih regard o cenerline a he es secion. The acquired signals a he symmerical poins shows he low similariy, so i can be confirmed ha FBG #2 sensor don have any signal similariy wih regard o he cener line. Figure 7: The comparison of acquired impac signals a symmerical grid poins. The reason for reducion of error migh be because he inerval beween he sensors is wider. Hence, he cross-correlaion value can be compensaed wih each oher as compared wih he case where he inervals beween he sensors are close o each oher. In he case of previous research, he disance beween he sensors were 50mm and 100mm. However, since he diameer of he pipe was 60.7mm, he relaive disance beween he sensors was wider han his experimen and hus shows beer resuls.

6 Firs A. Auhor, Second B. Auhor and Third C. Auhor Therefore, i migh be beer o use many sensors o improve he impac localizaion performance of a cylindrical srucure, or o no insall he sensor in close proximiy o anoher sensor. 5 CONCLUSIONS In his sudy, low-speed impac localizaion was conduced on he composie ube which represen cylindrical srucures. Three FBG sensors were used o acquire he impac signals, and a normalized cross correlaion mehod was employed as he algorihm for localizing he random impac source. A oal of 18 random impacs was applied o he composie ube using he impac hammer, and i was posprocessed using he employed algorihm. When hree sensors were used, he average error and he sandard deviaion were similar o hose of he impac localizaion for aluminum pipe srucure by previous research. However, if less han 3 sensors were used, he resuls were negaively affeced by he nominal disance beween sensors. Especially, he accuracy was decreased when he sensors locaed close o each oher were used. Since he configuraion of FBG sensors in he sudy by previous research was relaively wider compared o diameer of he aluminum pipe, he resuls can be conribued o he close arrangemen of sensors. Therefore, i would be beer o use many sensors o improve he impac localizaion performance of he cylindrical srucure, or o no insall he sensor in close proximiy. Furhermore, furher work for various sensor locaion is needed o deermine he effecive locaion for sensors in he cylindrical srucures because he sensors used in his sudy were concenraed on he upper surface. ACKNOWLEDGEMENTS This research was suppored by he Technology Innovaion Program funded by he Minisry of Trade, Indusry & Energy (MI, Korea) ( , Developmen of aircraf healh monioring inegraed measuremen sysem for composie. REFERENCES [1] J.-H. Kim, Y.-Y. Kim, Y Park and C.-G. Kim, Low-velociy impac localizaion in a siffened composie panel using a normalized cross-correlaion mehod, Smar Maerials and Srucures, 24(4), 2015, pp (doi: / /24/4/045036). [2] R.K. Ing, N. Quieffin, S. Caheline and M. Fink, In solid localizaion of finger impacs using acousic ime-reversal process, Applied Physics Leer, 87(20), 2005, pp (doi: / ). [3] F. Ciampa and M. Meo, Impac localizaion on a composie ail roor blade using an inverse filering approach, Journal of Inelligen Maerial Sysems and Srucures, 25(10), 2014, pp (doi: / X ). [4] B. Park, H. Sohn, S.E. Olson, M.P. DeSimo, K.S. Brown and M.M. Derriso, Impac localizaion in complex srucures using laser-based ime reversal, Srucural Heal Monioring, 11(5), 2012, pp (doi: / ). [5] B.-W. Jang, Y.-G. Lee, J.H. Kim, Y.Y. Kim, C.-G. Kim, Real-ime impac idenificaion algorihm for composie srucures using fiber Bragg graing sensors, Srucural Conrol and Healh Monioring, 19, 2012, pp (doi: /sc.1492). [6] Y.-G. Lee and C.-G. Kim, Impac source idenificaion for pipe srucure based on a onedimensional fiber Bragg graing sensor array, Journal of Inelligen Maerial Sysems and STrucures, 69, 2016, pp (doi: / X ).