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TECHNICAL UNIVERSITY OF CLUJ-NAPOCA
ACTA TECHNICA NAPOCENSIS
Series: Applied Mathematics and Mechanics
53, 2010
EXPERIMENTAL VALIDATION OF GUIDES WAVES USE FOR
COATED PLATES INSPECTION
Cristian Cătălin PETRE 1), Mihai Valentin PREDOI2), Marian SOARE3)
1) Politehnica University of Bucharest, Department of Strength of Materials, Splaiul Independenţei 313,
060042, Bucharest, Romania
2) Politehnica University of Bucharest, Department of Mechanics, Splaiul Independenţei 313, 060042,
Bucharest, Romania
3) S.C. Nuclear NDT Research & Services, Şoseaua Berceni, Nr.104, Sector 4, Bucharest , Romania.
Corresponding author: predoi@cat.mec.pub.ro
1. Introduction
Nondestructive testing (NDT) of paint coated thick
plates represent a challenge for the periodic
inspection of cargo vessels, railroad or road tank
cars, fixed tankers, etc. Ultrasonic testing using
longitudinal waves in the pulse-echo method are
commonly used, together with other NDT
methods. The main inconvenient of this method is
the necessity to cover large areas by repeatedly
positioning the ultrasonic transducer. In the recent
decades, guided waves became more interesting
for researchers in this field [1], due to their
capability to propagate along relatively long
distances. The presence of paint coatings poses
supplementary difficulties on this technique. The
main difficulty in implementing on a large scale
this technique is the wave attenuation due to the
material viscosity. This aspect has been treated in
another paper [2]. A companion paper presents the
selection of the most appropriate mode for the
plate inspection. The present work is focused on
testing the guided waves at the plate edge
reflection and developing new experimental
techniques for the detection of the lack of paint
coating.
a 180 μm of acrylic paint is considered in the
following. The most effective modes in inspecting
surface flaws are the fundamental antisymmetric
A0 and the symmetric S0 modes, at least for the
uncoated plate. The symmetry/antisymmetry
characteristic of these modes is lost in the presence
of the thin paint layer (Fig.1). The modal
displacement is confined to the free steel surface,
corresponding to the position -3mm on this figure.
The larger amplitude corresponds to displacements
which are normal to the surface. On the opposite
side, the paint layer almost completely cancels any
movement, and this result is obtained in the
absence of any structural dissipation in the model.
Fig. 1: Dispersion curves for the steel plate
2. Guided modes features
The dispersion curves relating the wavenumbers to
the frequency have been obtained in the
companion paper, using a computer code based on
[3]. A 6mm thick steel plate, coated on one side by
3. Experimental Validation
Fig. 2 presents the experimental setup used to
test the sensitivity of the guided modes to the
reflection from the plate edge.
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Several configurations have been tested in order
to reduce the direct signal between the transducers.
In the best configuration, the signal from Fig. 5 has
been recorded at 80dB amplification. The guided
mode presented in the companion paper has been
used, corresponding to a 40° wedge angle.
Fig. 2: Experimental setup for edge reflection with
one wedge transducer
The plate edge is at 300mm distance from the
transducer front. The Krautkramer-Branson USIP
12 is used as pulser-receiver.
Fig. 5: Signal obtained with two wedge transducers
4. Conclusions
Fig. 3: Reflected signal from plate edge
On Fig.3 is presented the reflected signal at 55°
wedge angle, with the wave front at 7.7 ms, and
amplitude of 50% for 78 dB amplification. This
signal corresponds to the mode presented on Fig.1,
which is attenuated by the paint layer. Even in
these conditions, the surface wave can inspect the
plate and detect possible large flaws.
The second experiment concerns the possibility
to detect the interruption of the paint coating. On
Fig.4 is presented the setup using two wedge
transducers. One is sending the guided mode
towards the paint layer boundary and the other one
is tuned to receive the same mode, or its angle is
modified to receive converted modes.
Fig. 4: Two wedges configuration for paint edge
detection
The experiments with one and two transducers
have proven that selected guided waves can be
used for NDT of paint coated thick steel plates,
opening the perspective for more detailed
parametric studies.
5. Acknowledgements
This work was supported by the EC-funded
project under 7th framework programme SCP7GA-2008-218637, Cost Effective Corrosion and
Fatigue Monitoring for Transport Products
(CORFAT).
6. References
[1] Achenbach, J.D.,”The Evaluation of Materials
and Structures by Quantitative Ultrasonics”,
Springer Verlag, 1993.
[2] Predoi M.V., Predoi D., Soare M.,
Experiments and numerical simulation of
ultrasound propagation in coated plates, 10th
International Conference, RASD 2010, 12-14
July 2010, (accepted for presentation).
[3] COMSOL Multiphysics, User Manual,
http://www.comsol.com/, 2009.