Abstract: Wavelet analysis and bispectrum was applied to Acoustic Emission (AE) signals from
scratch tests on corroded hot-dip galvanized samples in order to achieve the detection of corrosion
products in pieces non reachable by visual inspection. AE signals were correlated with the fracture
mechanisms occurring during scratch tests, while the contact force increased. Results were
corroborated by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy
(EDX) and X-Ray Diffraction (XRD).
Abstract: This paper proposes a method for both the out-of-plane and in-plane displacement
sensitivity calibration of an acoustic emission (AE) sensor. In the method, a laser homodyne
interferometer is used to measure the out-of-plane and in-plane displacement of the surface of a
large test block excited by a repeatable source transducer. The out-of-plane displacement is
measured by aligning the laser beam perpendicular to the surface with time gating of the receive
waveform used to isolate only the direct arrival of the longitudinal wave produced by the piston
source transducer. For the in-plane displacement measurement, the laser beam is aligned parallel to
the surface to intersect a small optically reflective step with the time waveform being gated to
measure only the direct shear arrival produced using a normal incidence shear wave source
transducer. In each case, the interferometer measurement is followed by coupling the sensor under
test to the measurement surface, which is then exposed to the same acoustic field and the sensor
output signal measured. This substitution method allows the sensor sensitivity to be obtained in
terms of volts per unit displacement for both the out-of-plane and in-plane surface displacement.
The method allows a comprehensive description of an AE sensor response to different planes of
displacement and offers the potential for a traceable sensor calibration to units of length.
Abstract: A novel fibre optic sensor system has been developed for detection of acoustic emission.
The sensor design was based on a 2×2 fused tapered optical fibre coupler configuration. Given the
intended use of this sensor for the detection of acoustic emission in smart materials and structures,
its lightweight, compatibility with composite material and immunity from electromagnetic
interference are great advantages. Apart from the performance specification and reliability, the
overall cost of the sensor system is a major factor in their adoption by end-users. The manufacturing
of this sensor is low-cost and the signal output from the sensor system developed can be directly fed
to the commercial AE acquisition system. The demonstration of acoustic emission detection was
conducted using fibre coupler-based AE sensors in different materials and structures. The AE
sources are various and depend on the different applications. In the current paper, we report on the
use of the fibre optic AE sensor system for concrete damage monitoring. An experiment on damage
detection on a composite plate with this fibre optical AE sensor is also reported in the paper.
Abstract: Development of modern society is converging to a status where many human actions can
be performed by machines. To achieve production without human intervention, machines require
artificial receptors. Data gathering for processing and analysis of signals, together with
determination of feedback reactions can be achieved by a suitable decision maker unit. A sensed
value suited to this so-called intelligent sensing process would be the acoustic emission signal. In
the case of intelligent cutting tools this would require miniature highly sensitive sensors integrated
into the cutting tool body. Part I of this paper deals with the possibility of practical usage of the
piezoelectric properties of copolymer foils for the acoustic emission sensor as a transducer of a
mechanical surface wave into electrical signal. Part II of the paper deals with the most fundamental
requirement for monitoring of cutting conditions during machining, i.e. excellent processing of
measured data. Data obtained from machining process obtained by means of acoustic emission
sensors, as discussed in the first part of this article, have high-frequency and continuous character of
a white noise. These data are very difficult to process. New apparatus for transformation of acoustic
emission into audible sound in the workplace is presented. The first stage of processing is by
listening to transformed data it is subjectively possible to recognize differences in audible spectrum,
corresponding to different states of the cutting tool. The second step is visualization of the
differences via the fast Fourier transform (FFT) in the spectrum graphic chart.
Abstract: Aluminum nitride (AlN) is a promising Acoustic Emission (AE) sensor element for
high-temperature environments such as gas turbines and other plants because AlN maintains its
piezoelectricity up to 1200°C. Highly c-axis-oriented AlN thin-film sensor elements were prepared
on silicon single crystals by rf magnetron sputtering. Both ordinary-temperature AE sensors and
high-temperature AE sensors have been developed using these elements. In this paper, to study effects
of d33 and thickness of AlN elements on sensor sensitivity, AlN elements with d33 from 2 to 7 pm/V
and thickness from 3 to 9 /m were prepared. It is confirmed that the AE sensor sensitivity increased
with d33 and thickness of AlN elements. The sensitivity of the high-temperature AE sensor was also
improved by a design of the sensor structure. The sensor characteristics were evaluated at elevated
temperatures from 200 to 600°C. It was confirmed that the AE sensor works well at 600°C and does
Abstract: An acoustic emission test was simulated using a three point bend specimen and an
artificial AE source. Waveform data was recorded as the sample was cyclically loaded in three
point bending, and the cross correlation coefficient of the waveforms was used to measure the
repeatability of the test. Results were twofold: the stress state of a specimen affects the ultrasonic
propagation therein; and the coupling condition of a transducer may not remain constant during a
Abstract: Acoustic emission testing (AT) is in Europe an already well established non-destructive
testing (NDT) method. Qualification requirements as well as certification of testing personnel are
laid down in European standard EN 473. A widespread application of AT deals with testing of
unfired pressure vessels for re-qualification after a certain period of service (repetition test). The
advantages of applying AT compared to the traditional procedure of hydrostatic test plus visual
inside inspection are numerous. Just to name the most important: reduction of downtime, omitting
of residual humidity and no risk of product contamination with water. It is a fact that AT provides
much more useful information concerning the condition of the pressure vessel under test than a
simple ‘passed’ or ‘not passed’ obtained usually by a hydrostatic test. This contribution gives two
examples of practical experience, where severe corrosion defects have been detected by AT. The
defects have been found in both cases on the vessel’s shell under the thermal insulation, where they
have been hidden undetected for years. It can be assumed that even the vessel with the most severe
damage (loss of more than 50% of the nominal wall thickness) would have passed the traditional
repetition test procedure and that failure within the following service period would have occurred.
In contrary to this scenario, AT enabled the vessel operator to perform appropriate repair in time.
Abstract: The main obstacle which prevents the rapid spread of Acoustic Emission (AE) testing on
refinery structures in Russia is the complexity of this NDT tool. The lack of well- defined methods
of data analysis and the huge amount of AE data collected within each test are the major problems.
The possibility of mistakes in a period of testing and data analysis leading to erroneous conclusions
related to the condition of the structure sometimes negatively affects the image of the AE method.
However, the correct application of AE can bring unique opportunities in the inspection of
structures in the industry. Some examples of successful applications and the unique possibilities of
AE testing are presented in this paper.
Abstract: Contribution contains an application of acoustic emission method during instability and
growth of fatigue crack in reactor pressure vessel specimen loaded by means of bending.
Material of specimen was typical material of pressure water reactor vessel covered by austenitic
cladding as a protection layer against corrosion. Specimen had shape of prism with defect in the
middle where fatigue crack was created very close to austenitic cladding.
Loading of specimen was done in special loading machine with defined speed of loading resp.
Investigation of instability and propagation of inertial crack was observed by acoustic emission
technique, potential drop method, by using of straingauges and by high-speed camera.
Acoustic emission sensors were located from both sides of specimen.
By this experimental technique was possible to observe "pop-in" of crack during loading.
Different types of specimen with different mode of aging were investigated.
Results of acoustic emission activity are described graphical curves in relation to individual
stages of loading.
Abstract: It is known that the basic mechanism of fatigue crack growth in ductile pressure vessel
steels, which is repetitive blunting and re-sharpening of the crack tip, is a weak acoustic emission
(AE) source. On the other hand, a large number of AE events occur during cyclic crack growth.
Most AE events are caused by repetitive friction at the fracture surfaces, but these AE events show
relatively weak correlation with the crack growth velocity. In the paper it is shown, based on
examples – fatigue crack growth starting from an artificial weld defect, cycling of a natural crack
defect, crack initiation and growth in gas cylinders - which information can be gained by relatively
simple analyses of the AE data from cyclic pressure tests.