Applications of Lamb waves for material characterization : a laser based study /
The research described involves implementing digital signal
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=743267291&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The research described involves implementing digital signal processing techniques to calculate phase velocities from transient, multi-mode Lamb waves. A laser based non destructive testing system is used to generate and subsequently record transient waves in homogenous and composite plates. Digital Finite Impulse Response (FIR) filters are shown to be effective tools for isolating individual Lamb modes from the multi-mode waveform time histories. Phase information from Fast Fourier Transforms (FFTS) is used to calculate the isolated Lamb modes' phase velocities. For an appropriate FIR bandpass filter, it is shown that time domain windowing variations had a minimal effect on the calculated phase and hence phase velocity. A non-linear error minimization technique is developed from the governing transcendental Lamb equations to estimate the thickness of homogeneous plates from the phase velocity data. The processing procedures and algorithms are shown to work effectively on both thin and thick plates. Analysis is presented for Copper plates ranging in thickness from 100 gm to 2.4 mm. The laser based system is also used to generate and detect transient Lamb waves in a unidirectional composite plate. Phase velocities of the zeroth order, antisymmetric Lamb modes are found for three directions'of propagation within the composite plate. The results are found to be in good agreement with an exact theory for Lamb waves propagating in an equivalent homogeneous, anisotropic material. |
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| Item Description: | Vita. "Major Subject: Mechanical Engineering". "May, 1996". |
| Physical Description: | xviii, 202 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 168-175. |