Poisson s Ratio. Dimensionless parameter. Poisson s ratio (μ) = - transverse strain/axial strain. Large μ ~ softer material

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2 Poisson s Ratio Poisson s ratio (μ) = - transverse strain/axial strain Large μ ~ softer material However, rarely used because: Narrow range of value Long. trans. wave velocities must be measured Dimensionless parameter

3 Correlations Poisson s ratio decreases with increase in ultrasonic velocities. Micro-structural variation or temperature has an effect on ultrasonic velocities. (A. Kumar et al., Acta Materialia, 2003)

4 Poisson s ratio and microstructure Negative poisson s ratio.

5 How to measure Poisson s ratio Destructive testing Tensile test Nondestructive testing Contact method Noncontact method

6 Dry couple Nondestructive contact method Dry coupling Measured wave velocities using longitudinal and transverse transducers. (Don J. Roth et al, NASA Technical Paper, 1993)

7 PVDF film PVDF(polyvinylidene fluoride) piezoelectric NDT High frequency : thickness mode vib. (long.) Low frequency : radial mode vib. (trans.) Fig. 2. PVDF transducer oscillation modes (a) transversal, (b) longitudinal. (private communication) Fig. 4. Signals obtained from one of the nylon test cylinder at different frequencies. The two top graphs correspond to shear mode of the emitter transducer and the two bottom graphs to the longitudinal mode.

8 Mode conversion S R L-wave T-wave

9 Mode conversion of normal beam 1 Normal beam contact transducer. Observation of mode converted transverse signals. (Kim et al., J Korean Phys Soc, 2003)

10 Mode conversion of normal beam 2 Good agreement with theoretical prediction. (Kim et al, J Korean Phys Soc, 2003)

11 Mode conversion using immersion UT 1 Wave speeds were measured using immersion UT. (Shin et al., JKSNT, 2008)

12 Mode conversion using immersion UT 2 Poisson s ratio was obtained from the wave speed values. (Shin et al., JKSNT, 2008)

13 Nondestructive measurement : ratio of transverse and longitudinal wave speeds

14 Poisson s ratio scanning using immersion UT Velocity ratio can be obtained without the knowledge of specimen thickness. Mu-scan was proposed. Aluminum (Oh et al., JKSNT, 2008) Steel

15 What is good about Immersion UT Simultaneous measurement of two wave velocities from mode converted signals. Uses single transducer. Having no couplants makes free scan. Fast scan over large surface area. Velocity ratio can be obtained without prior information of specimen thickness.

16 Work scope Feasible study for field application of mu-scan. Poisson s ratio reflects microstructure of materials. Mu scan applied to material characterization. Specimen was welded zone.

17 Equipments Transducer Motion controller System controller Pulsar Receiver Step motors

18 Welded specimen Double-V-grooved Carbon-steel. Water jet cutting (in order to avoid thermal change of microstructure) natural stain Unknown welding condition.

19 Typical wave form 3P1S is clearer than 1P1S f r o n t 2 P 4 P 6 P 8 P Amplitude (Arb. Units) 1 P 1 S 3 P 1 S 2 P 2 S T i m e ( µ s )

20 Peak search algorithm Gaussian filter ( identify each echo) Threshold (large/small echo) Classify normal and abnormal signals Nullification for abnormal signals 90,60 50,60 Amplitude (Arb.Units) Amplitude (Arb. Units) Time (µs) normal Time(µs) abnormal

21 Mu-scan of weldment 1 90,60 Amplitude (Arb.Units) Time (µs) 50,60 Range 0.26~0.32 about 20% variation Amplitude (Arb. Units) Time(µs)

22 Mu-scan of weldment 2 Similar pattern Welded zone can be distinguished from the base metal.

23 Mu-scan of weldment 3 BASE META L HAZ WM HAZ BASE META L

24 Conclusions 3P1S signal offers clearer information than 1P1S signal. Welded zone is well distinguished from base metal. Mu-scan shows high potential to characterize materials.

25 Future works Comparison of mu-scan with microstructure and microhardness test Why 3P1S? theoretical analysis Relationship between mu-scan and test conditions, such as, thickness of specimen, frequency, diameter of the transducer. Application to other materials Sintered ceramics uniformity testing.

26 References 1. Young H. Kim et al., 'Transverse-Wave Modes in the Pulse-Echo Signal of a Normal- Beam Longitudinal-Wave Mode Transducer', Journal of the Korean Physical Society, Vol. 42, No. 1. January Yosub Shin, Yeo Ho Yoon and Young H. Kim, Measurement of Longitudinal and Transverse Wave Speed in Solid Materials Using Immersion Ultrasonic Testing, Journal of the Korean Society for Nondestructive Testing Vol. 28, No. 1. February SeoYoung Oh, Young H. Kim, Yosub Shin and Hyun Joon Cho, Poisson s Ratio Scanning Using Immersion Ultrasonic Testing, Journal of the Korean Society for Nondestructive Testing Vol. 28, No. 6. December Kuhn, G. J. and Lutsch, A., Elastic wave mode conversion at a solid boundary with transverse slip. J. Acoust. Soc. Am J.Krautkramer, H.Krautkramer, Ultrasonic Testing of Materials, 4 th edition, Springer Pollard, Sound Waves in Solids, Pion Ltd, London, pp Kumar, Jayakumar, Raj and Ray, Correlation between ultrasonic shear wave velocity and Poisson s ratio for isotropic solid materials, Acta Materialia 51, pp , Don J. Roth et al., Quantitative Mapping of Pore Fraction Variations in Silicon Nitride Using an Ultrasonic Contact Scan Technique, NASA technical paper 3377, S. Matsuoka et al., Young's Modulus and Poisson's Ratio on Low-Cycle Fatigue, Trans. Japan Soc. Mech. Eng. 488, Jeffery T. Fong et al., Basic Questions in Fatigue, American Soc. for Testing and Materials, pp.84-87, 1988

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