Transcript Defektoskopia ultradźwiękowa

Defektoskopia ultradźwiękowa
bezkontaktowa
Bolesław AUGUSTYNIAK
Metody bezkontaktowe badania
Wzbudzanie drgań –
klasyczny nadajnik poprzez powietrze
wiązka laserowa
siła Lorentza (EMAT)
Detekcja drgań –
klasyczny odbiornik poprzez powietrze
wiązka laserowa (interferometr)
elektromagnetyczna (EMAT)
Badanie odkształceń – za pomocą wiązki laserowej
shearography
UT wzbudzanie i detekcja drgań ze sprzężeniem przez powietrze
This technique uses a high sound pressure
to compensate losses and low frequencies
(50kHz to some 100 kHz).
A double shell structure with foam core
inside is investigated by impact tests.
The stringer debonding is clearly visible
in the C-scan.
http://www.ndt.net/article/cdcm2006/papers/schnars.pdf
Laserowe wzbudzanie i detekcja drgań
Sketch of the principle
of laser-ultrasonics or
of a “laser-ultrasonic
transducer”.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Laserowe wzbudzanie i detekcja drgań 2
http://www.ndt.net/article/ecndt2006/doc/P223.pdf
Laserowe wzbudzanie i detekcja drgań 3
http://www.ndt.net/article/cdcm2006/papers/schnars.pdf
Laserowe wzbudzanie drgań
There are essentially two kinds of mechanisms for generating
ultrasound:
the first one is perfectly nondestructive and is based on a
thermoelastic mechanism
the second one is invasive and is based on the ablation of
the sample or on the vaporization of some surface layer.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Laserowe wzbudzanie drgań
efekt termoelastyczny
The principle of thermoelastic generation is the following: laser
light is absorbed to some depth inside the material releasing heat
locally; the heated region then expands producing a strain and a
corresponding stress that is the source of waves propagating in
the material or at its surface. When light penetration is small and
the excitation spot much less than an acoustic wavelength, a
complex emission pattern is observed in the far field with inclined
lobes (from 30 to 60°) for the longitudinal and shear waves. There
is in particular no longitudinal emission along the normal to the
surface.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
efekt termoelastyczny cd
Surface waves and plate waves can also be generated efficiently and in
a very versatile manner. When the laser beam is focused to a small
circular spot, a surface wave with a cylindrical symmetry is emitted from
this spot. Good directivity is obtained by focusing the beam with a
cylindrical lens to get a line source.
More complicated patterns can even be used, such as an array of lines,
giving narrower band emission but having the advantage to distribute
the laser energy over a broader area so surface damage can be
avoided.
A converging circular Rayleigh surface wave giving very strong
displacement at the center of convergence can be readily obtained by
using, in addition to the conventional spherical lens, an axicon (conical
lens). Enhancement techniques have been developed by sweeping the
line or line array source with a proper velocity.
.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
efekt plastyczny
If one increases the energy density, particularly for small light
penetration (metals), one reaches the threshold where the surface starts
to melt and then to get vaporized. At this point, matter is ejected from
the surface and through various physical processes this vapor and the
surrounding air is ionized, thus producing a plasma plume that expands
away from the laser spot on the surface. Generation of ultrasound
originates from the initial recoil produced by the material ablation and
from the plasma pressure. A similar vaporization effect occurs also when
the material is covered by a thin absorbing layer, which is blown off,
leaving the substrate underneath substantially unaffected if the energy
density is below some threshold. In the strong plasma regime on the
other hand, a crater mark is left on the surface. .
.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Laserowa detekcja drgań
To detect ultrasound, the surface
is illuminated by a laser beam,
continuous or of pulse duration
sufficiently long to capture all the
ultrasonic signal of interest.
Scattered or reflected light is
then collected by an optical
receiver, which is in the case of
most industrial applications an
interferometer
Principle of optical detection of ultrasound with an interferometer
(here sketched as a confocal Fabry-Perot): the interfrometer converts the phase or
frequency modulation produced by the surface motion in an intensity modulation.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Intereferometr Febry- Perot
A practical interferometer, which is by now widely used, is the confocal FabryPerot. This is a simple system made of two concave identical mirrors separated
by a distance equal to their radius of curvature. In excellent approximation each
ray retraces its path after multiple reflections in the resonator, which gives to
the system a high collection efficiency (etendue or throughput). It can be used
in transmission or in reflection. In transmission the responsivity peaks at a
frequency equal to about a resonance width. The reflection scheme has on the
other hand nearly flat frequency response above this frequency, except for
periodic drops at integer of the free spectral range. It should be noted that the
responsivity is practically zero at very low frequencies, which means that this
system is intrinsically insensitive to vibrations, a key advantage for use in
industrial environments. The main weakness of Fabry-Perot demodulators is
their lack of sensitivity at low ultrasonic frequencies (below 2 MHz), which is
circumvented by devices based on two-wave mixing in photorefractive
materials.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Laserowa detekcja drgań – układ dwuwiązkowy
A signal beam which acquires phase shift and speckle after reflection on a
surface in ultrasonic motion, is mixed in a photorefractive crystal with a pump
plane wave to produce a speckle adapted reference wave that propagates in the
same direction as the transmitted signal wave and interferes with it.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Laserowa detekcja drgań – układ dwuwiązkowy cd
One important advantage of the photorefractive demodulator with respect to the
confocal Fabry-Perot is its better sensitivity at low ultrasonic frequencies (below
1 MHz), thus allowing probing more easily materials with strong ultrasonic
attenuation. The system has also the advantage to be easily combined with a
differential or balanced scheme (two detectors giving responses to phase
modulation of opposite sign), so the noise coming from the laser intensity
fluctuations can be eliminated to a large extent.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Laserowa detekcja drgań - cechy lasera
One key element of the detection scheme is the detection laser. It should be
high power, since sensitivity increases with power, and should not contribute to
any noise in addition to the fundamental photon or shot noise. High power is
particularly needed when the surface is absorbing and detection is at a large
distance giving a small collection solid angle. The pulse duration should be
sufficiently long to capture all the signal of interest, which means for many
applications a duration between 10 and 100µs. Nd-YAG technology at 1.06
µm, which is known to provide high amplification gain, is particularly suited for
realizing such a laser by amplifying a small and very stable Nd-YAG laser
oscillator. A suitable oscillator is commercially available with power from 100
mW to about 2 W and is based on a small monolithic cavity pumped by a laser
diode. Depending upon the repetition rate, the amplifier could be flashlamp
pumped (up to 100 Hz) or diode pumped (above 100 Hz). Peak powers of 1
kW and more are typically obtained with pulse duration of the order of 50 µs.
More recently, since such a master oscillator-pulsed amplifier system is
complex and costly, IMI/NRC has been working on the development of a
pulsed oscillator without seeding giving directly about 100 W
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Laserowa detekcja drgań – obróbka obrazu
Regarding imaging, a numerical imaging approach such as the one based on
the Synthetic Aperture Focusing Technique (SAFT) can be combined with
laser-ultrasonics to obtain high quality images.
Processing can be done in the time domain but since this is can be very
computation intensive and fairly long, methods that operate in Fourier space
and make use of Fast Fourier Transform algorithms have been developed.
These methods, significantly different from the conventional time SAFT,
although sometimes called F-SAFT, are based on a plane wave decomposition
of the acoustic field for each frequency combined with a back-propagation
algorithm.
This processing technique has been applied in particular to the imaging of
stress corrosion cracks in steel.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Przykład obrazu – pęknięcia korozyjne
Comparison of crack opening images obtained by liquid penetrants (left) and
laser-ultrasonic F-SAFT processing using shear waves and an annular
aperture (right). The horizontal lines observed at right are artifacts originating
from the small size of the test sample.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Przykład zastosowań – 1
Effect of optical scaning occurs
as if a conventional
piezoelectric transducer was
moved over the surface
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Przykład zastosowań – lotnictwo
Laser-ultrasonic C-scan image of part of the horizontal stabilizer of a CF18 airplane in undismantled and ready for take-off conditions. One will
notice that, unlike conventional water jet ultrasonics, laser-ultrasonic
allows scanning to the very edge of the part.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/722_monchalin.pdf
Przykład zastosowań – lotnictwo 2
The inspected surface is at the corner..
http://www.ndt.net/article/wcndt2004/pdf/noncontact_ultrasonics/722_monchalin.pdfh
ttp://www.ndt.net/article/cdcm2006/papers/schnars.pdf
Przykład zastosowań – beton
Specimen with artificial voids: Thin Styrofoam plates (150 x 150 x 10 mm) were
embedded at different depths in concrete
http://www.ndt.net/article/ecndt2006/doc/P223.pdf
Przykład zastosowań – beton cd
Comparison of
waveforms
between with
and without
defects
Velocity dispersion curve without defect
Velocity dispersion curve with defect (defect-A)
http://www.ndt.net/article/ecndt2006/doc/P223.pdf
Metoda mieszana :
laser wzbudza – detekcja poprzez
powietrze
The Nd:YAG oscillator is coupled to a 1 mm diameter multimode optical fiber (ended with an
SMA connector), and a variable optical attenuator is used to adjust the maximum power level
that can be delivered onto the sample without damage. In order to concentrate as much as
possible the ultrasound energy in the direction of the air coupled transducer, a focusing
probe was developed to focus the laser beam into a line. In this way sufficient energy can be
deposited without raising the power density so high as to cause ablation, and the wave
propagation direction is restricted to be perpendicular to the line. The focusing arrangement
is made of a plano-convex lens to collimate the laser beam emerging from the fiber, and a
cylindrical lens to focus the beam into the line (about 10 mm x 0.5 mm) at the top surface of
the sample. The optical assembly is placed into a stackable lens tube. Rayleigh waves
propagating in the direction perpendicular to the laser line are detected with the
air-coupled transducer placed at few millimeters in front of the optic probe. .
http://www.ndt.net/article/wcndt2004/pdf/laser_ultrasonics/276_guillorit.pdf
Metoda
mieszana :
cd
This scanner moves the probe holder above the sample and keeps a constant gap between
the transducer/optic probe block and the sample. The ultrasonic signal is amplified with a 25
dB LECOEUR Electronique preamplifier, and filtered with a WIDERANGE Decade Filter
module. A digital AGILENT 54622A oscilloscope displays the ultrasonic waveforms, and the
data are transferred and stored into a PC using an AGILENT E8408A VXI mainframe. A
software was developed on HP VEE to control the generation laser, the XY scanner and the
VXI board. Finally, the signal processing and the plot of the C-scan are performed with a
dedicated PV WAVE software.
http://www.ndt.net/article/wcndt2004/pdf/laser_ultrasonics/276_guillorit.pdf
Metoda
mieszana :
cd 2
(a): Portable head C-scan of a 4.6 mm thick CFRP composite sample with Teflon
foils, and (b): detail drawing of the sample
http://www.ndt.net/article/wcndt2004/pdf/laser_ultrasonics/276_guillorit.pdf
Metoda mieszana : cd 3
C-scan of a composite honeycomb sandwich sample with structural inserts.
(a): Portable head equipment, (b): Through transmission air-coupled equipment
http://www.ndt.net/article/wcndt2004/pdf/laser_ultrasonics/276_guillorit.pdf
Shearography
laserowe
badanie
odkształceń
powierzchni
.
Typical
shearographic setup in which the modified Michelson interferometer is
used as a shearing device. The modified Michelson interferometer brings the light
waves from two points: P1 and P2, on the object surface into one point: P, on the
image plane by tilting the mirror 1 a very small angle. The intensity of the
interferogram is then registered by a CCD camera and saved in the computer
http://www.ndt.net/article/wcndt2004/pdf/optical_techniques/534_yang.pdf
Shearography laserowe badanie – zasada
działania
Digital shearography is a laser measuring technique based on digital data
processing, phase-shifting techniques and interferometry. According to
the common sense of interferometry, two beams with an identical
wavelength are required for a purpose of interference. Usually, an
identical wavelength for the two beams can be obtained from one laser
by using a beam splitter, such as the object beam and the reference
beam used in the setups of holography and electronic speckle pattern
interferometry (ESPI)7.
A distinguishing feature of shearography is the use of a self-reference
interference system. Instead of using a reference beam, shearography
utilizes
a shearing device to bring the light waves from two points on the
.
object surface into one point on the image plane, which results in an
interference phenomenon, i.e. so-called speckle interferogram, without
using an additional reference beam.
http://www.ndt.net/article/wcndt2004/pdf/optical_techniques/534_yang.pdf
Shearography – a holografia
.
Holography detects a flaw by
looking for displacement
anomalies induced by the
defect which look like a circular
fringe patterns, whereas,
shearography detects a flaw by
looking for strain anomalies
induced by the defect which
look like a butterfly pattern in
fringe pattern. Compared with
holography which measures
full-field displacement,
shearography directly
measures strain information
and thus it is more direct and
simple for detection of strain
concentrations which are
usually created at the positions
of defects that decrease the
strength of the structure.
http://www.ndt.net/article/wcndt2004/pdf/optical_techniques/534_yang.pdf
Shearography – przykłady
Left: holographic NDT, in which circular anomalous fringe patterns appear at the
debond positions, right: Shearographic NDT, in which butterfly patterns appear at the
debond positions.
.
http://www.ndt.net/article/wcndt2004/pdf/optical_techniques/534_yang.pdf
Shearography – przykład 2
.
NDT of a GFRP rotor vane about 5 meters in length by internal pressure (about .p =
0.01 MPa); (a) view of the rotor vane, (b) showing the passage of lamination, (c)
showing a delamination, and (d) displaying a micro crack.
http://www.ndt.net/article/wcndt2004/pdf/optical_techniques/534_yang.pdf
EMAT electromagnetic acoustic transducer
The EMAT consists of a
magnet that produces a bias
magnetic field and a sensor
coil that produces a dynamic
magnetic field. The driving
force uses a high frequency
vibration of magnetostriction
generated in the direction of
the compound’s magnetic
field by combining the
dynamic magnetic field
generated by a high
frequency electric current in
the sensor coil and the static
field by the electromagnet.
http://www.ndt.net/article/wcndt2004/pdf/petrochemical_industry/67_murayama.pdf
EMAT sondy
Construction details of an EMAT. (a) Simplified structure to show the essential
parts – a wire to induce eddy currents in a conducting surface and a static
magnetic field. (b) A meander line coil under a large permanent magnet pole. (c) A
periodic array of magnets that apply alternating magnetic fields to an eddy current
sheet flowing in a race-track pattern.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/691_alers.pdf
EMAT głowice dla fal poprzecznych
The RF-coil is placed
very close 0.5 mm) to
the materials surface
underneath a periodic
arrangement of
permanent magnets of
alternating polarity
Głowice z
magnesami
Głowice meandrowe bez
magnesu
http://www.ndt.net/article/wcndt2004/pdf/noncontact_ultrasonics/599_salzburger.pdf
EMAT
zastosowania spoiny
The probe (T/R-type with a focus in a distance of 65 mm) is placed on one of the surfaces of
the thinner sheet and radiates the ultrasonic pulse into the weld. Back reflected signals
(echoes) from weld defects such as pores, holes, incomplete through-welding… are digitized;
the maxima of the echo-amplitudes are displayed versus the probe position as AmplitudeLocus Curves (Scan). Fig. 7a shows such a scan with the indication of an internal lack of
fusion between the weld and the base metal of the thicker blank.
http://www.ndt.net/article/wcndt2004/pdf/noncontact_ultrasonics/599_salzburger.pdf
EMAT automatyczne badanie spoiny 2
The combined evaluation of the pulse-echo- and pulse transmission inspection
using the dispersive SH-mode propagating in circumferential direction of the pipe
wall. The inspection frequency is 0.8 MHz. The echo- and roundtrip signals are
gated out electronically. Their maximum is displayed on-line as scan (see fig. 11).
Fig. 10 shows in the foreground the tube; the weld is in the 12 o’clock position. At
the backside the probe holder is located; the probe is (hidden by the tube) fixed in
the central part of the holder. The tube is moving along the probe in a fixed
distance of 0.2 mm (assured by the holder rollers) with a speed of up to 1m/s
http://www.ndt.net/article/wcndt2004/pdf/noncontact_ultrasonics/599_salzburger.pdf
EMAT automatyczne
badanie spoiny 3
The US-scans of a 16 m long weld. The curves represent the echo maxima of a well
scraped weld (up) and of a very badly scraped weld (down). The well scraped weld
shows a very low amplitude level along the whole 16 m; whereas the scan of the
badly scraped weld has a much higher amplitude level. The oscillations in the first
7 meters show a periodic change of the quality of the scraping. In the second half of
the scan the decreasing level indicates a slow increasing of the scraping quality.
http://www.ndt.net/article/wcndt2004/pdf/noncontact_ultrasonics/599_salzburger.pdf
EMAT badanie grubości
ścianek
In case of external defects the wall
(upper) thickness can be calculated
using the time-offlight of the
ultrasonic backwall echo signal. The
shape of the artificial defects and the
measured wall thickness fit very well.
As expected, the EC technique does
not show any indication.
Figure (bottom) shows the results
when the defects are located at the
internal side. In the defect areas the
EMAT signal breaks down, and the
ultrasonic thickness measurement is
no longer possible. However, the EC
technique now detects the inside
defects.
http://www.ndt.net/article/wcndt2004/pdf/noncontact_ultrasonics/599_salzburger.pdf
EMAT badanie rur
Example of an E-scan of a 14” diameter x 0.25” wall pipe containing
simulated corrosion pits in the form of 1” diameter. hemispherical
depressions with depths of 0.050” (20%), 0.102” (40%), 0.145” (60%)
and 0.194” (80 %).
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/569_alters.pdf
EMAT badanie rur cd
Three E-scan presentations of a field of general corrosion and pits near a
circumferential weld in a 30” diameter pipe.
http://www.ndt.net/article/wcndt2004/pdf/non-contact_ultrasonics/569_alters.pdf
Podsumowanie
Zalety technik bezkontaktowych
- ‘szybkie’ badanie dużych powierzchni i w
wysokich temperaturach
- automatyzacja badań
Wady
- ograniczona ‘rozdzielczość’
- znaczące koszty aparatury
- konieczne specjalne szkolenie personelu