ULTRASONIC BACKSCATTERING PROFILES ON PERIODICALLY
ROUGH INTERFACE
Sung D. Kwon1, Seok S. Yoon1
Department of Physics , Andong National University, 388 Songchundong, Andong 760-749
Korea
ABSTRACT. The angular dependence(profile) of backscattered ultrasound was measured for steel
specimens with periodical surface roughness (l-71um). Backward radiations showed more linear
dependency than normal profile. Direct amplitude increased and averaging amplitude decreased with
surface roughness. Painting treatment improved the linearity in direct backward radiation below
roughness of 0.03X. Scholte and Rayleigh-like waves were observed in the spectrum of averaging
backward radiation on periodically rough surface.
INTRODUCTION
When an incident broadband pulse at an arbitrary angle of incidence will be
reflected, if there is the phase matching between the incident beam and surface wave modes
is satisfied, the Rayleigh wave is generated which will propagate with a given velocity
along the surface[l]. When a pulse-echo method at an arbitrary angle is used on the
liquid/solid boundary, the received signal is called the ultrasonic backscattering. Angular
dependence of the ultrasonic backscattering involves the coherent backward radiation
returning along the incident direction from backward propagating surface waves so that
ultrasonic backscattering profiles involve normal profile by interface roughness and
backward radiation profiles by backward propagating leaky SAW, etc[2]. During the past
few years, many problems, which include the determination of the grain size and shape in
metal poly crystals, and cold work in steel have been studied[3]. Recently, it was found that
periodic surface roughness, as influenced by machining, can have a significant influence on
the experimental measurements of attenuation and backscattering, which play a great role
on these materials characterization procedures[4]. Since these surface roughness effects
also have a significant influence on flaw detection, they are of considerable generic interest.
Hence, these surface roughness effect should be studied in advance to evaluate the
microstructural properties. In this study, roughness dependency of backscattering profiles,
painting effect on rough interface for the purpose of evaluation of hidden roughness will be
discussed and observation of interfacial modes by backward radiation will be reported.
CP657, Review of Quantitative Nondestructive Evaluation Vol. 22, ed. by D. O. Thompson and D. E. Chimenti
© 2003 American Institute of Physics 0-7354-0117-9/03/$20.00
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Direct method
method
Direct
Averagingmethod
method
Averaging
FIGURE
1. Direct
Direct and
and averaging
averagingbackward
backwardradiation
radiationmethods.
methods.
FIGURE 1.
FIGURE 2. Surface roughness profiles measured by Sufcoder 1700 of Kosaka Lab. Ltd.
FIGURE 2. Surface roughness profiles measured by Sufcoder 1700 of Kosaka Lab. Ltd.
EXPERIMENTS
EXPERIMENTS
A broadband ultrasonic transducer was used to interrogate the specimen at different
transducer
was used
interrogate
the specimen
at different
anglesAofbroadband
incidence.ultrasonic
Incident angle
was changed
bytomoving
continuously
the probe
with
angles
of
incidence.
Incident
angle
was
changed
by
moving
continuously
the
with
constant angular speed. The principal frequency of used transducer was 4.7 MHz.probe
Normal
constant
angular
speed.
The
principal
frequency
of
used
transducer
was
4.7
MHz.
Normal
profile was obtained around normal incidence angle and direct and averaging method were
profile
obtainedbackward
around normal
incidence
direct and
averaging
method
were
appliedwas
to measure
radiation
profile angle
aroundand
Rayleigh
angle
as shown
in Fig.l.
applied
to
measure
backward
radiation
profile
around
Rayleigh
angle
as
shown
in
Fig.1.
Various roughness was induced by changing the movement velocity of bite. The measured
Various
roughness and
was periodicity
induced byranged
changing
movement
velocity
of bite.
surface roughness
fromthe1.52
to 70.74jam
and from
132The
to measured
520jiim?
surface
roughness
and
periodicity
ranged
1.52 to
70.74µmspecimens
and fromwere
132 shown
to 520µm,
respectively.
Surface
roughness
profiles
for from
4 different
roughness
in
respectively.
roughness
for 4 to
different
roughness
werepainting
shown in
Fig.2. All theSurface
specimen
surface profiles
was painted
cover the
surface specimens
roughness and
Fig.2.
All was
the about
specimen
surface was painted to cover the surface roughness and painting
thickness
60-80|im.
thickness was about 60-80µm.
BACKSCATTERING PROFILES AND PAINTING EFFECT
BACKSCATTERING PROFILES AND PAINTING EFFECT
The ultrasonic reflectivity and the angular dependence of backscattering have been
usefulThe
and ultrasonic
classical technique
to assess
surfacedependence
roughness. Fig.3
is the normalhave
profiles
reflectivity
and thetheangular
of backscattering
been
of (a) unpainted
and technique
(b) paintedtosteel
specimens.
As shown
in Fig.3(a),
reflectivity(peak
useful
and classical
assess
the surface
roughness.
Fig.3 the
is the
normal profiles
intensity
of normal
decreased
with roughness
and the
profile width
became wider
of
(a) unpainted
and profile)
(b) painted
steel specimens.
As shown
in Fig.3(a),
the reflectivity(peak
as the roughness
increased
the linearity
not good.
When
rough surface
was painted
intensity
of normal
profile)but
decreased
withwas
roughness
and
the profile
width became
wider
and
normal
profile but
failed
distinguish
roughness
and wesurface
can't use
as
thehidden,
roughness
increased
thetolinearity
wassurface
not good.
When rough
wasnormal
painted
profile
in evaluating
hiddenfailed
roughness
since the profiles
nearly
pattern.
and
hidden,
normal profile
to distinguish
surface showed
roughness
andsame
we can’t
use normal
profile in evaluating hidden roughness since the profiles showed nearly same pattern.
1266
(a)
(a)
(b)
(b)
FIGURE 3. Normal profiles of unpainted and painted steel specimens: (a) unpainted (b) painted.
FIGURE 3. Normal profiles of unpainted and painted steel specimens: (a) unpainted (b) painted.
BACKSCATTERED
INTENSITY (dB)
Fig.4
of direct
direct backward
backward radiation
radiation intensity(peak
intensity(peak
Fig.4 shows
shows the
the roughness
roughness dependence
dependence of
intensity
of
profile).
These
intensities
of
not
only
the
unpainted
and
but
also
the painted
painted
intensity of profile). These intensities of not only the unpainted and but also the
specimens
increased
with
roughness.
Specially,
painting
treatment
in
direct
method
specimens increased with roughness. Specially, painting treatment in direct method
improved
roughness range
range than
than 0.03
0.03 wavelength
wavelength of
of SAW
SAW as
as shown
shown
improved the
the linearity
linearity in
in smaller
smaller roughness
in
Fig.4.
Painting
equalized
the
generation
efficiency
of
SAW
and
made
the
surface
in Fig.4. Painting equalized the generation efficiency of SAW and made the surface
roughness
painting layer.
layer. Therefore
Therefore the
the unique
unique factor
factor
roughness the
the subsurface
subsurface periodic
periodic fatigue
fatigue under
under painting
affecting
roughness scattering
scattering of
of SAW
SAW so
affecting the
the direct
direct radiation
radiation intensity
intensity became
became the
the roughness
so that
that the
the
roughness
linearity than
than the
the unpainted.
unpainted.
roughness dependence
dependence showed
showed better
better linearity
Averaging
related to
to the
the SAW
SAW generation
generation and
and the
the
Averaging backward
backward radiation
radiation intensity
intensity is
is related
attenuation
of
SAW
during
propagation
from
and
to
corner.
As
the
surface
roughness
attenuation of SAW during propagation from and to corner. As the surface roughness
increased,
increased, the
the generation
generation of
of SAW
SAW decreased
decreased and
and SAW
SAW attenuated
attenuated by
by the
the roughness
roughness
scattering
and
the
energy
leakage
during
propagation
so
that
the
averaging
radiation
scattering and the energy leakage during propagation so that the averaging radiation
intensity
decreased
with
roughness
as
shown
in
Fig.5.
Since
the
generation
efficiency
is
intensity decreased with roughness as shown in Fig.5. Since the generation efficiency is
more
important
factor
affecting
the
averaging
intensity
in
the
roughness
range
used
in
this
more important factor affecting the averaging intensity in the roughness range used in this
experiment,
better linearity
linearity than
than the
the painted.
painted.
experiment, the
the unpainted
unpainted specimen
specimen showed
showed better
£u
PQ
-25
25
After
After
Painting
Painting
-35
35
-45
45
-55
55
-25
-25
-35
-35
-45
-45
00
55
10
10
-55
-55
15
15
0
0
ROUGHNESS,
ROUGHNESS,Ra(µm)
Ra(jim)
5
5
10
10
ROUGHNESS,
ROUGHNESS, Ra(µm)
Ra(um)
FIGURE
FIGURE4.4.Roughness
Roughnessdependence
dependenceofofdirect
directbackward
backwardradiation
radiationintensity.
intensity.
1267
15
15
BACKSCATTERED
INTENSITY (dB)
-20
-20
-20
After
After
Painting
Painting
-30
-30
-40
-40
-50
-50
-30
-40
-50
0
0
20
20
40
40
60
60
0
80
20
0
80
ROUGHNESS, Ra(µm)
ROUGHNESS, Raftim)
20
40
40
60
60
80
80
ROUGHNESS, Ra(µm)
ROUGHNESS, Raftim)
FIGURE 5. Roughness dependence of averaging backward radiation intensity.
FIGURE 5. Roughness dependence of averaging backward radiation intensity.
OBSERVATION OF
0F INTERFACIAL
INTERFACIAL MODES
MODES
OBSERVATION
Fig.6(a) is
is the
the averaging
averaging backward
backward radiation
radiation spectrum
spectrum on
on 520jim
520µm periodically
periodically rough
Fig.6(a)
rough
interface
when
the
incidence
position
was
3cm
apart
from
corner
and
interface when the incidence position was 3cm apart from corner and involves
involves three
three
frequency peaks
peaks of
of 0.92,
0.92, 2.54
5.24MHz. The
The appearance
appearance of
of these
these three
three peaks
peaks can
frequency
2.54 and
and 5.24MHz.
can be
be
explained as
as followed:
followed: Some
of the
the incident
incident energy
energy at
at Rayleigh
Rayleigh angle
angle is
transformed to
explained
Some of
is transformed
to
Scholte wave
wave and
and Rayleigh-like
Rayleigh-like wave
propagate along
the interface.
interface. Some
Scholte
wave propagate
along the
Some of
of this
this energy
energy
will reradiate
reradiate along
along the
the Rayleigh
Rayleigh angle
water as
as the
the these
these waves
waves scatter
will
angle into
into water
scatter and
and converted
converted
to
backward
propagating
waves
from
subsequent
groove
and
troughs.
The
to backward propagating waves from subsequent groove and troughs. The leaky
leaky energy
energy
from backward
backward propagating
propagating Rayleigh
Rayleigh waves
waves have
have three
three frequency
frequency components
components of
of
from
(1)
0.92MHz: Originally
(1)
0.92MHz:
Originally induced
induced Rayleigh
Rayleigh wave,
wave, of
of which
which intensity
intensity and
and peak
peak
frequency
decrease
as
propagating
distance
increases
frequency decrease as propagating distance increases
(2)
2.54MHz:
(2)
2.54MHz: Rayleigh
Rayleigh wave
wave converted
converted from
from Scholte
Scholte waves
waves by
by scattering
scattering from
from
subsequent
grooves
and
troughs,
of
which
peak
frequency
corresponds
subsequent grooves and troughs, of which peak frequency corresponds to
to
the resonant
resonant frequency
frequency determined
by grating
grating theory[5]
theory[5]
the
determined by
(3)
5.24MHz:
(3)
5.24MHz: Rayleigh-like
Rayleigh-like wave,
wave, of
of which
which the
the velocity
velocity is
is same
same with
with Rayleigh
Rayleigh
wave
and
the
peak
frequency
in
spectrum
corresponds
to
wave and the peak frequency in spectrum corresponds to the
the resonant
resonant
frequency
by grating
theory[5]
frequency determined
determined by
grating theory
[5]
.
(b)
(a)
FIGURE 6. Spectra of (a) averaging backward radiated and (b) normally reflected signals at 3cm.
FIGURE 6. Spectra of (a) averaging backward radiated and (b) normally reflected signals at 3cm.
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At initial stage of propagation after corner reflection in averaging method, because
originally induced Rayleigh wave has so relatively great intensity and wide spectrum with
central frequency 4.7MHz, Scholte and Rayleigh-like components are veiled so that we
can't observe the resonant frequencies in the averaging backward radiation spectrum. But
as the propagation distance increases, the intensity of originally induced Rayleigh wave
decreases and the peak frequency and width in the spectrum decrease, consequently
showing the 0.92MHz peak frequency at 6 cm propagation distance. Then three frequency
components are not overlapped anymore and their intensities are comparable so that we can
distinguish three separated modes as shown in Fig.6(a). Wood anomalies[6] shown in
Fig.6(b) are another evidence of the existence of two interface waves. Missing of 2.62MHz
and 5.43MHz components in the spectrum of normally reflected ultrasound are by the
generation of Scholte wave and Rayleigh-like wave, respectively.
CONCLUSION
1. The peak intensities of backward radiation profiles by direct method and averaging
method increased and decreased with surface roughness, respectively.
2. Painting treatment greatly improved the linearity in smaller roughness range than 0.03
wavelength of SAW in direct method.
3. Frequency components by Scholte wave and Rayleigh-like wave were observed in the
spectrum of backward radiated ultrasound corresponding to missing components in Wood
anomalies of grating diffraction effect.
ACKNOWLEDGMENTS
This work was supported by grant No. R05-000-00086-0 from the Basic Research
Program of the Korea Science & Engineering Foundation.
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2.
3.
4.
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(2000).
Kirn, H.C., Lee, J.K., Kirn, S.Y., and Kwon, S.D., Jpn.JAppl.Phys., 38, 1 260-267
(1999).
Guo, Y., Margetan, F.J., and Thompson, R.B., in Review of Progress in QNDE, 20B,
edited by D.O. Thompson and D.E. Chimenti, Plenum, New York, 2001, pp!3061313.
Rayleigh, Lord, Proc. Roy. London Ser. A 79, 399 (1907).
Wood, R.W., Philos. Mag. 4, 396 (1902).
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