Measurement of local elastic modulus with CLUE

Transcription

1 Measurement of local elastic modulus with CLUE Alexander A.Karabutov 1, Alexander A.Karabutov (Jr.) 2, Elena V.Savateeva 3 1 International Laser Center of Moscow State University aak@ilc.edu.ru 2 Deptm.of Physics of Moscow State University, akarabutov@gmail.com 3 Institute for laser information technology RAS evsav73@mail.ru

2 Abstracts The problem of local elastic properties measurement at part of construction is of great importance for estimation of active stresses and life service, especially for composites. Contact Laser-Ultrasonic Evaluation (CLUE) makes it possible to measure acoustic wave velocity with high precision at short path. Comparison with theoretical model of the stiffness matrix enables one to measure the complete set of elastic modulus. We measure the elastic modulus of isotropic solids and 1-D carbon fiber reinforced composite. For isotropic medium the velocity of longitudinal and shear wave was measured simultaneously. For the samples with the thickness greater, then 2 mm the accuracy was as high as (0.1-1)%. The resolution in lateral direction was ~3mm. For orthotropic 1-D CFRC opto-acoustic transducers of different schemes were explored to measure the ultrasonic wave velocity, propagating at different angles to the fibers. The accuracy of 1% was provided for the measurements. The applications of elastic modulus measurement with CLUE are discussed.

3 Ultrasonic measurement of elastic modulus Modulus of elasticity E c 2 s 3c 4c 2 2 L s c c 2 2 L s Shear modulus G c 2 s Poisson ratio c 2c 2 2 L s 2 2 2( cl cs)

4 Precise time-resolved measurement of ultrasonic wave velocity Amplitude of signals, Volts 1.0 3t t Time-delay between echo signals can be measured with high accuracy 0.2 t = 2h/c , m

5 sample Contact Laser Ultrasound Evaluation. Optical fiber Laser DPSS Q-switched laser pulse is absorbed in optoacoustic generator/ Laser Irradiation exited wideband probe ultrasonic pulse propagates to a sample under investigation/ Data acquisition system Optoacoustic generator probe pulse is scattered at the sample structures/ wideband piezotransducer detects backscattered ultrasound waves/ Backscattered signals deliver the information about the sample, namely, on the acoustic properties of different structures of the sample.

6 Comparison of Laser and Piezo UT 1 0, s 0.58 s 0-0,5-1 z piezo >(6-7)z CLUE Laser UT Piezo UT 0 0,5 1 1,5 2 2,5 3 3,5 4 Time, s In-depth resolution of UT is determined by probe pulse duration. CLUE pulse duration is 6-7 times shorter then that for traditional UT at the same central frequency.

7 Advantages of CLUE Short duration of a probe ultrasonic pulse enhanced in-depth resolution for limited frequency band Smooth temporal shape of a probe ultrasonic pulse no deadzone, discrimination of soft and rigid impurities Small diameter of a probe ultrasonic beam enhanced sensitivity of small defect detection

8 Sensitivity, V/bar LASER-ULTRASONIC DEFECTOSCOPE UDL-2M Specific features Short UT pulses are excited in a course of laser pulse absorption in a Laser-Ultrasonic transducer. Back-scattered UT signals are detected with ultra wide-band piezo-receiver. It makes it possible to enhance spatial resolution and to reduce dead-zone. Probe Ultrasonic pulse Spectral sensitivity of detection ,8 50 0,6 0 0,4-50 0,2 4,2 4,4 4,6 4,8 5 5,2 5,4 Время (мкс) Time, s Частота (МГц) Frequency, MHz

9 Measurement of elastic modulus in echo-regime with CLUE Probe pulse Ultrasonic trace Time H/C S +H/C L 2H/C L 2H/C L OA-Generator L L L L S Sample

10 Measurement of Elastic Modulus with UDL-2M Longitudinal Pulses Sample thickness (1-20) mm, Beam diameter 2 mm, Relative error of C L 0.1% Relative error of C S 1% Scatter of C L 0.02% Sear Pulse

11 Ultrasonic wave velocity in stressed medium Stress-free medium Calculation of stresses Acousto-elastic effect ) ( ) 2 ( 2 yy xx zz z B A V ) 2 ( 2 0 V z z z z z zz yy z z z xz xx V V V B V V V A

12 Ultrasonic Velocity in Stressed Al y Width z x Base , dv 5 1 V velocity 0.8*10 d MPa 0,08 0, , deformation 0, Stress xx, MPa

13 Residual stress distribution in weld Stainless steel 250 MPa

14 Laser-Ultrasonic Tomography of Mechanical Modulus To measure the complete set of elastic modulus of anisotropic solid it s necessary to determine the velocity of all types of acoustic wave quasi-longitudinal, quasi-shear propagating in various directions. The optoacoustic transducer discussed above provides the excitation of longitudinal wave normal to the surface. So, it s necessary to design the transducers provided measurement of the velocity of acoustic wave of another types and directions of propagation. They are discussed below.

15 Rayleigh wave velocity measurement with CLUE Opto - electronic unit Laptop fiber signal cable power cable ОА- Transducer Specific features Short SAW pulse is excited in a course of laser pulse absorption at a metal surface under testing. SAW pulse is detected with point-like piezo-receiver. Laser excitation and piezo-detection of SAW pulse is combined in a Optoacoustic Transducer. Optical fiber fiber adapter preamplifier Optoacoustic transducer

16 Ultrasonic Trace detected by LUIT 6 4 U, mv Shear wave signal Rayleigh wave signal Time, s The base of measurement 15 mm, ultrasonic beam width 2 mm, relative error of SAW velocity measurement ~ 1%, scatter %

17 SAW Velocity in Stressed Metal Stainless steel 12X18H10T 0,025 y = -5,0768e ,019e-05x R= 0, ,02 0,015 0,01 velocity variation 0, Stress, MPa

18 z y x Width CLUE of Residual Stress in Al Base Sample #07 (Al-ST) Al7050 6,28 2,84 6,275 2,835 6,27 2,83 6,265 2,825 6,26 CLZ, mm/us CRX, mm/us X, mm 2,82 Homogeneous sample Sample with residual stress Distribution of C LZ and C RX along the sample.

19 Measurement of longitudinal wave velocity with inclined probe ultrasonic beam Base 30 mm Beam width 3 mm Relative error of C L 1% Scheme of optoacoustic transducer PLU-6H-02.

20 Stressed state of rail

21 CONCLUSIONS Contact Laser-Ultrasonic Evaluation (CLUE) makes it possible a measurement of elastic modulus locally. The accuracy is better then 1%. Investigation of stressed state of solid can be realized effectively with CLUE. 3-D distribution of stress with Laser-Ultrasonic Tomography is discussed.