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A Simulation Study for Mode Selection by Means of MultipleElement Ultrasonic Transducers Acting from

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Context: guided wave (GW) testing and mode selection ... SUMMARY PRESENT WORK. Summary: - Two methods of mode selection using multiple-element transducers ... – PowerPoint PPT presentation

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Title: A Simulation Study for Mode Selection by Means of MultipleElement Ultrasonic Transducers Acting from


1
A Simulation Study for Mode Selection by Means of
Multiple-Element Ultrasonic Transducers Acting
from the Section of a Waveguide
  • by Karim Jezzine and Alain Lhémery
  • French Atomic Energy Commission
  • CEA - Saclay

2
  • Context guided wave (GW) testing and mode
    selection
  • Simulation of GW generation by a transducer
    mounted on the section
  • Mode selection principle and simulation results

3
GUIDED WAVE TESTING
4
MODE SELECTION
How to select a single mode in this configuration?
5
  • Context guided wave (GW) testing and mode
    selection
  • Simulation of GW generation by a transducer
    mounted on the section
  • Mode selection principle and simulation results

6
SIMULATION TOOLS FOR GW
All these terms can be obtained thanks to
calculations based on the Semi-Analytical Finite
Element Method (guide of arbitrary section
normal crack).
7
VALIDATION OF THE MODEL
8
  • Context guided wave (GW) testing and mode
    selection
  • Simulation of GW generation by a transducer
    mounted on the section
  • Mode selection principle and simulation results

9
MODE SELECTION
Theoretical observation If both the normal and
tangential stress of the selected mode could be
imposed on the section, only this mode would be
generated.
In practiceThe transducer is modelled as a
source of normal stress with zero tangential
stress imposed (piezo transducer with viscous
fluid coupling)
10
MODE SELECTION PRINCIPLE
  • (1) Find modes showing frequencies at which the
    tangential stress is zero or negligible with
    respect to normal stress.
  • (2) Use a multiple-element ultrasonic transducer
    to reproduce the normal stress profile of the
    mode at these frequencies.
  • Waveguide geometries investigated
  • cylindrical (rod, tube) Pochhammer modes
  • plate Lamb modes
  • rectangular
  • Two frequencies have been identified as
    favourable to mode selection
  • (1) So-called universal frequency strictly
    zero tangential stress
  • Lamé modes in a plate (Lamb 1917)
  • Axisymmetric modes in a cylinder or tube (Hudson
    1943)
  • Identified for several modes in a rectangular
    waveguide (Jezzines PhD 2006)
  • (2) Frequency close to a maximum of group
    velocity negligible tangential stress
  • Symmetric and antisymmetric modes in a plate
  • Axisymmetric modes in a cylinder or tube
  • Identified for several modes in a rectangular
    waveguide

11
UNIVERSAL FREQUENCIES IN A CYLINDER
Identification of universal frequencies for
axisymmetric modes in a steel cylinder of radius
10 mm
Phase velocity Vjw/bn
Group velocity Vgdw/dbn
(km/s)
(km/s)
6
4
2
(MHz)
2
1
(MHz)
12
DISCRETISATION OF THE SOURCE
Mode chosen L(0,5) fu51.09 MHz
z
Distribution of normal stress szz(r)
L(0,5) discretised with 5 elements
Imposed normal stress (zero crossing respected)
Multiple-element transducer
(mm)
13
SIMULATION RESULTS
z
ExcitationToneburst centered on fu5 with 10
relative bandwidth
d20 mm
Emitter
Cylindrical guide
Receiver
Imposed normal stress at z0
(µs)
14
FREQUENCY OF MAX GROUP VELOCITY
Identification of the maxima of group velocity
for axisymmetric modes in a steel cylinder of
radius 10 mm
Minimisation of tangential stress
15
DISCRETISATION OF THE SOURCE
Mode chosen L(0,5) fMaxVg50.77 MHz
z
Distribution of normal stress szz(r)
L(0,5) discretised with 6 elements
Multiple-element transducer
16
SIMULATION RESULTS
z
ExcitationToneburst centered on fMaxVg5 with
10 relative bandwidth
d20 mm
Emitter
Cylindrical guide
Receiver
Imposed normal stress at z0
(µs)
17
ACCOUNT OF A NORMAL CRACK
Axisymmetric normal crack
(A) fc900 kHz
(B) fc1140 kHz
(C) fc771 kHz
0
d/2
0
d/2
0
d/2
(a) Full crack (pa)
(b) Partial crack (p3a/4)
(c) Partial crack (pa/2)
(µs)
18
SUMMARY PRESENT WORK
Summary - Two methods of mode selection
using multiple-element transducers mounted on
the section of an elastic waveguide proposed.
- Their performances have been assessed thanks
to simulations based on the semi-analytical
finite element method.
  • Present work
  • - Industrial transfer - Manufacturing of the
    transducer
  • - Experimental validation

19
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20
VALIDATION OF THE MODEL
21
COMPARISON OF BOTH METHODS
Universal frequency or frequency of Vg Max ?
22
Phase velocity Vfw/bn
(km/s)
EMAT, Comb probe, interdigital transducer, rings
of transducers for pipe inspection Constant
wavelength imposed
Variable angle beam probe Constant phase
velocity imposed
(MHz)
23
z 500mm
z 250mm
0
d/2
Standard Exc.
0
d/2
Ideal Exc.
0
d/2
5 rings
24
z 500 mm
z 250 mm
Standard Exc.
Ideal Exc
6 rings
25
(No Transcript)
26
E/R
p
z 0.5 m
27
SOURCE OF NORMAL STRESS
z
guide axis
28
z zl
z 0
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