investigation on feature guided wavesinvestigation on feature guided waves david fan, mike lowe...
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Investigation on Feature Guided Waves
David Fan, Mike Lowe
Non-Destructive Testing Group
David Fan, Mike Lowe
Department of Mechanical Engineering
Imperial College London
SW7 2AZ
United Kingdom
1/18Feature Guided Wave NDT Laboratory
Motivation
• Large area inspection by guided wave
2/18Feature Guided Wave NDT Laboratory
Discovery of feature guiding
• Inspection of plate with weld
Weld guided waveWeld guided wave
J S t (BAE t ) 2006
3/18Feature Guided Wave NDT Laboratory
J.Sargent (BAE systems), 2006
Finite element modelling
Semi-Analytical Finite Element (SAFE) method:
3x2x 12 mm
1x
Ab bi iAb bi i S l PlSt l Pl t W ld
2 mm
6 mm
Absorbing regionAbsorbing region Steel PlateSteel Plate Weld
400 mm800 mm 800 mm
4/18Feature Guided Wave NDT Laboratory
SAFE results – compression mode
6000Phase velocity 150 kHz
m/s Weld guided mode
6mm plate S0
10 l t S0
loci
ty in
m
SH0 in a steel plate
Weld guided mode10mm plate S0200 kHz
Phas
e ve
l
Leaky Non-300 kHLeaky
leaky 300 kHz
50 150 250 350 4500
Frequency in kHz
5/18Feature Guided Wave NDT Laboratory
Discovery of a new mode – shear mode
3500Phase velocity
100 kHz3500
m/s
100 kHz
ocity
in m
SH0 in a steel plate 150 kHz
Phas
e ve
lo
Weld guided mode
P
250 kHz
50 100 150 200 2503000
Frequency in kHzFan & Lowe
Proc. R. Soc. A, 2009
6/18Feature Guided Wave NDT Laboratory
,
Why the waves are trapped?
3x2x
1x
Weld Pl t
1
Weld Plate
SAFE method Analytical method
7/18Feature Guided Wave NDT Laboratory
Why the waves are trapped?
L dPh l it
• Condition 1: Similar mode shape Weld cap Plate
S0 dL mode6000
Phase velocity
Longitudinal mode
S0 mode
F mode 1in m
/s
SH0 mode
velo
city
i
Flexural mode 1
Torsional modeSH0 mode
Phas
e
Flexural mode 2F mode 2 A0 mode
250500
F i kH
8/18Feature Guided Wave NDT Laboratory
25050 Frequency in kHz
Why the waves are trapped?
• Condition 2: Lower velocity in the weld
plate(faster) weld
(slower)
9/18Feature Guided Wave NDT Laboratory
Why the waves are trapped?
• Condition 2: Lower velocity in the weldT d d
6000Phase velocity
S0 L mode
Trapped modes:
S0 mode
n m
/s
Longitudinal mode
velo
city
in
F mode 1
Torsional mode SH0
F mode 1 SH0 mode
Phas
e v F mode 1
F mode 2
A0
0 Exciting mode for inspection
10/18Feature Guided Wave NDT Laboratory
25050 Frequency in kHzc t g ode o spect o
Typical results from FE (crack parallel to the weld)( p )
Absorbing regionMonitor 1
Monitor 2
11/18Feature Guided Wave NDT Laboratory
Defect scattering study
Laser interferometer
Monitor
Shear transducer
12/18Feature Guided Wave NDT Laboratory
Typical results from Experiment
30mm slot parallel to the weld
0.14
30mm slot parallel to the weld
0.1
0.12
oeffi
cien
t
0.06
0.08
ectio
n C
o40 50 60 70 80 90 100 110 120 130 1400.02
0.04Ref
l40 50 60 70 80 90 100 110 120 130
Frequency (kHz)
13/18Feature Guided Wave NDT Laboratory
Discussion - crack parallel to the weld
Different length of the crack:
ent
30 mm24 mm16 mm
0.12
0.14SH0 wave interaction with axial crack on a plate
n C
oeffi
cie
0.08
0.1
Ref
lect
io
0 04
0.06
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.30.02
0.04
Length of crack to wavelength ratio
14/18Feature Guided Wave NDT Laboratory
Discussion - crack parallel to the weld
FE results Experimental results
0.12
0.14
cien
t 0.12
0.1430 mm24 mm16 mm
0.08
0.1
ion
Coe
ffic
0.08
0.1
0.04
0.06
Ref
lect
i
0.04
0.06
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.30.02
0.04
L h f k l h i
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.30.02
0.04
L h f k l h iLength of crack to wavelength ratio Length of crack to wavelength ratio
Possible reason: difference between the milled slot (experiment) and the FE crack
15/18Feature Guided Wave NDT Laboratory
milled slot (experiment) and the FE crack
Discussion - crack normal to the weld
E i l l
0.24
0.26
t 0 35
0.4FE results Experimental results
0 18
0.2
0.2240 mm
Coe
ffici
ent
30 mm0.3
0.35
40 mm
0.14
0.16
0.18
20 mm
Ref
lect
ion
C
0 2
0.25
20 mm
70 80 90 100 110 120 130 1400.1
0.12
R
70 80 90 100 110 120 130 140
0.2 20 mm
Frequency (kHz) Frequency (kHz)
Possible reason: un-uniform of the weld geometry
16/18Feature Guided Wave NDT Laboratory
the weld geometry
Discussion: Flat-bottom hole
Different depth of the hole:
0.2
0 12
0.14100%
FE results Experimental results
0.16
coef
ficie
nt
0.1
0.12
84 %
0 08
0.12
Ref
lect
ion
c
0.06
0.08
49 %
65 %
0.04
0.08R
0.02
0.04
17 %
33 %
0.3 0.40.2
Length of diameter to wavelength ratio0.2 0.25 0.3 0.35 0.4
0
Length of diameter to wavelength ratio
17/18Feature Guided Wave NDT Laboratory
Summary
The feature guided wave has been studied by the SAFE h d B h h i d d hSAFE method. Both the compression mode and the shear mode have been investigated and compared.
The reason for the trapping effect has been di d d i ddiscussed and summarized.
Experiments have been taken to validate the existence of the trapping mode and its sensitivity to certain defects
18/18Feature Guided Wave NDT Laboratory