In-plane and Out-of-plane Displacement of Lamb Waves Test with Laser Vibrometer

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1 JOURNAL OF MECHANICAL ENGINEERING Vol.48 No.8 Apr. 1 DOI1.391/JME * ( 114) (Electromagnetic acoustic transduceremat) EMAT 15 1 khz S 515 khz A S 3D TG5 TB553 In-plane and Out-of-plane Displacement of Lamb Waves Test with Laser Vibrometer HE Cunfu ZHENG Yang ZHOU Jinjie WU Bin (College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing 114) AbstractExcited modes and frequency response are two key parameters of ultrasonic guided wave transducers evaluating. However, traditional transducers such as piezoelectric transducer and electromagnetic acoustic transducer (EMAT) can t measure these two parameters efficiently because of the limit of frequency bandwidth and mode selection of themselves. Laser vibrometer can be employed to measure the raw in-plane and out-of-plane displacement of elastic waves in the structure without the limit of bandwidth. Thus it could be one of the ideal methods to identity the excited modes and measure the frequency response curve. A kind of omnidirectional lamb wave EMAT is been inspected by this method. The results show that the transducer can produce purity S mode in 15 khz and both A and S mode in 515 khz. It can be predicted that the method using laser vibrometer to detect the in-plane and out-of-plane displacement is an efficient method of evaluating the transducer and receiving Lamb waves, and can be widely used in no-contact measurement, high temperature testing and 3D visualization of elastic waves propagation. Key wordslaser vibrometer Lamb wave Out-of-plane displacement In-plane displacement Electromagnetic acoustic transducer (EMAT) * [1] [] [3] [4] (19714) [5] STASZEWSKI [6] A 3D

1 4 7 [7] DUROUX [8] (Electromagnetic acoustic transducer EMAT) [4] EMAT 3D 1 1.

2 1 4 7 [7] DUROUX [8] (Electromagnetic acoustic transducer EMAT) [4] EMAT 3D EMAT π ux U x exp ikx t x e (1) uz U zexpikx te z () uux u z x, t (3) U x U z e x e z x z (1)() π / u x u z =(3) 3 mm khz 1 1a A 1b S 1 3 mm khz 1. EMAT EMAT [9] VII 1 mm 8 mm [9] EMAT EMAT EMAT EMAT EMAT EMAT EMAT EMAT EMAT da RddR df rr ( RR ) ddr

8 48 8 rr ( R) =1 N/m ( ) EMAT (d, ) (4) r ( d Rcos ) ( Rsin ) Rsin (4) arctan d Rcos r EMAT d R(4) r d Rcos [911] uz( r ) u rr ( ) ik

H ( kr) H [ k( d Rcos )] exp(i kd )exp( i kr cos ) (6) πkdi mi U i P mi Ui / P P [1] * v σ P pnds n ds (7) S S v σ EMAT u z( x) u x(

1 Handyscope HS3 (Tie Pie Engineering, 5 MS/s)(Polytec OFV-55 Single point vibrometer sensor head) (Polytec OFV 7 Ultrasonics

3 rr ( R) =1 N/m ( ) EMAT (d, ) (4) r ( d Rcos ) ( Rsin ) Rsin (4) arctan d Rcos r EMAT d R(4) r d Rcos [911] uz( r ) u rr ( ) ik (1) uzr ( ) Fr mxmzcos( ) H ( kr)exp( i t) 8 (5) ik (1) urr ( ) Fr mxmxcos( ) H ( kr)exp( i t) 8 u i( j) i j k H (1) Hankel r (1) (1) H ( kr) H [ k( d Rcos )] exp(i kd )exp( i kr cos ) (6) πkdi mi U i P mi Ui / P P [1] * v σ P pnds n ds (7) S S v σ EMAT u z( x) u x( x) uz( x) A kmxmziexp[i( kxt)] (8) ux( x) A kmxmxiexp[i( kxt)] A A1/8 i/πd D D1 (9) I R cosexp( ikrcos )ddr D 1 D EMAT.1 Handyscope HS3 (Tie Pie Engineering, 5 MS/s)(Polytec OFV-55 Single point vibrometer sensor head) (Polytec OFV 7 Ultrasonics Vibrometer Controller)(Amplifier Research, Model 75A5)(3 mm mm) EMAT 3 HS3 5 EMAT 3 mm USB HS3 438 mm( )EMAT 5 mm 3a 34 mm( ) EMAT 3 mm 3b (b) 3 EMAT ( )

4 1 4 9 Polytec OFV-55 5 nm/v A 3 mm S 3 mm 5 mm. 1 SR () t SR ( ) G( ) H ( ) H( ) S ( ) ( ) ( ) exp c T G ST c c c 3 (Inverse fast Fourier transformifft) 4 EMAT 3 mm khz 5 khz 3 khz 1 khz 4 SRF () t ( S A ) 4c SRF ( ) SRF () t ST () t ST ( ) 5 4 4c S 5 c1 khz 4 SRF ( ) FR lg ST ( ) 5 c 1 khz khz 5 EMAT

5 EMAT 6 6 6a 3 mm 5 mm S 5 khz 3 khz db (8) 1/ d 1/d d 4b khz 3 mm 1 mv Polytec OFV-55 5 nm/v.5 nm 6b 3 mm 1/d d 4b S A S A EMAT 15 1 khz S 6b 8 khz A A S 1 db S EMAT 19 khz S db A 4 db S 4 6 EMAT (1) () EMAT EMAT S EMAT [1] CHO H, MATSUO T, TAKETNOTO M. Long range inspection of wall reduction of tank utilizing zero-th

6 order symmetric mode lamb wave Performance demonstration of the method proposed[j]. Materials Transactions, 7, 48(6) [] BINGHAM J, HINDERS M, FRIEDMAN A. Lamb wave detection of limpet mines on ship hulls[j]. Ultrasonics, 9, 49(8)76-7. [3] DIAMANTI K, SOUTIS C. Structural health monitoring techniques for aircraft composite structures[j]. Progress in Aerospace Sciences, 1, 46(8) [4] LEE J R, SHIN H J, CHIA C C. Long distance laser ultrasonic propagation imaging system for damage visualization[j]. Optics and Lasers in Engineering, 11, 49(1) [5] DEWHURST R J, SHAN Q. Optical remote measurement of ultrasound[j]. Measurement Science & Technology, 1999, 1(11) [6] STASZEWSKI W J, LEE B C, MALLET L, et al. Structural health monitoring using scanning laser vibrometryi. Lamb wave sensing[j]. Smart Materials & Structures, 4, 13()51-6. [7] STASZEWSKI W J, LEE B C, TRAYNOR R, et al. Crack detection in metallic structures with Lamb waves and 3D laser vibrometry[j]. Measurement Science & Technology, 7, 18(3) [8] DUROUX A, SABRA K G, AYERS J, et al. Using cross-correlations of elastic diffuse fields for attenuation tomography of structural damage [J]. Journal of the Acoustical Society of America, 1, 17(6) [9] WILCOX P D, LOWE M J S, CAWLEY P. The excitation and detection of lamb waves with planar coil electromagnetic acoustic transducers[j]. IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 5, 5(1) [1] AULD B A. Acoustic field and waves in solids[m]. FloridaKrieger Publishing Company, 199. [11] WILCOX P. Modeling the excitation of Lamb and SH waves by point and line sources[c]// Quantitative Nondestructive Evaluation, July 7-Aug. 1, 3, Green Bay, Wisconsin, 3, hecunfu@bjut.edu.cn ()1984 EMAT zysnow@ s.bjut.edu.cn

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