AAE552-Session24

AAE552-Session24 - AAE 552 Spring 2009 A. F. Grandt AAE...

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AAE 552 Spring 2009 – A. F. Grandt 1 1 AAE 552: Nondestructive Evaluation of Structures and Materials A. F. Grandt, Jr. Professor of Aeronautics and Astronautics Purdue University W. Lafayette, IN 47907 Session 24 – 9 March 2009 2 Contact Information Alten F. (Skip) Grandt, Jr. Email: aae552@ecn.purdue.edu Telephone: Office: 765-494-5141 Home: 765-463-4276 FAX: 765-494-0307 Course webpage accessed at: http://www.itap.purdue.edu/tlt/blackboard 3 AAE 552 Session 24 9 March 2009 Last Time: Ultrasonics Boundary interactions Attenuation Today: Ultrasonic inspection strategies Ultrasound generation/detection 4 Assignment Please read Textbook : Chapter 12 – Ultrasonics Webpage powerpoint references “Ultrasonic Testing, ” collaboration for NDT education Exam #1 – Session 29 (Friday, 27 March 2009) Boundary Interactions 5 6 Reflection/Refraction with Mode Change Incident compression wave in material A results in reflected and refracted compression and shear waves in materials A and B V SA V SB V CB V A > V B B V CA V CA i A r s r c R c R s Eq. 12.9 Fig. 12.7 CB C SB S CA C SA s CA V R sin V R sin V r sin V r sin V i sin = = = =
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AAE 552 Spring 2009 – A. F. Grandt 2 7 Incident Shear Wave (Fig. 12.8) Incident shear wave in material A results in reflected and refracted compression and shear waves in materials A and B V CA V SB V CB V B > V A V SA V SA B A r s = i i R c r c i R s Eq. 12.10 SB S CB C CA C SA V R V R V r V i sin sin sin sin = = = 8 First Critical Angle (Fig. 12.9) Incident compression wave at first critical angle i 1 results in compression wave along interface in material B and transmitted shear wave R c = 90 o A B V B > V A V CA V SA V SB V CA V CB i 1 R c = 90 o CB CA 1 V V i sin = Eq. 12.11 9 Second Critical Angle (Fig. 12.10) Only a shear wave is transmitted along interface at second critical angle i 2 A B V CA V SA V SB V CA i 2 V B > V A R s = 90 o Eq. 12.12 SB CA 2 V V i sin = 10 Table 12.3 Critical Angles for Compression Waves Material Interface First Critical Angle α 1 Second Critical Angle 2 water/steel 14.6 o 27.5 o water/aluminum 13.7 o 28.7 o plexiglass/steel 26.9 o 55.8 o plexiglass/aluminum 25.1 o 59.5 o 11 1 2 compression shear Corner Interactions (Fig. 12.13) Corners result in complex wave reflections and refractions and loss in energy “poor” reflections for 30 o and 60 o angles Ultrasound Attenuation 12
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AAE 552 Spring 2009 – A. F. Grandt 3 13 Ultrasonic Attenuation (Section 12.4) Sound waves lose energy as they propagate through system Beam spreading over larger area intensity ~ (1/distance) 2 loss ~ (distance) 2 Absorption Mechanical energy heat loss More significant loss for shear waves Loss increases with frequency Scattering – materials not homogeneous Minimal if grain boundaries < λ /100 Significant if gb > λ/10 λ/10 loss ~ (g.b.) 3 Loss could indicate unacceptable grain size 14 Ultrasonic Attenuation (cont)
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AAE552-Session24 - AAE 552 Spring 2009 A. F. Grandt AAE...

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