http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Applications of Lamb waves for material characterization
xviii, 202 leaves : illustrations ; 28 cm.
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
"Major Subject: Mechanical Engineering".
Issued also on microfiche from University Microfilms Inc.
Includes bibliographical references: pages 168-175.