EMAT, which is based on magnetostrictive effects, was employed to detect flaws in a sample with surface oxide scale. Chromium molybdenum steel (SCM415) was annealed at 600C to 900C from two to eight hours and subjected to EMAT to survey its signal properties. Oxide scales has ferromagnetism. The data from these samples were compared to an actually used samples. The EMAT signal derived from the actual sample was found to be too noisy due to Barkhausen effect to identify reflections from internal flaws and to reconstruct flaw images in a computer. This study proposes spectrum analysis and statistical methods based on noise probability to decrease this noise.
A lack of safety and the reliability of the existing metallic structure can threaten people's lives today. It is
getting stronger to demand to ensure reliable safety in society. Non Destructive Testing(NDT) can support to
public safety with finding damaged structure. Eddy Current Testing (ECT) is a one of NDT for metallic or
conductive materials. It already plays an important role in very wide field such as airline and power plants
for maintenance, ironworks for production. Though ECT is considered as a finished testing method,it has the
unwanted property that flaw blur in ECT signal.This defect partly comes from the essential principle of ECT.
In order to obtain fine image of flaw, the authors proposed a method with signal processing to reconstruct more
finer image of flaw from ECT signal. The method is based on simple relationship that signal are expressed as
a convolution of response function and flaw shape. Many obtained results, more fine images of points flaw and
both short and long line flaw than images of those ECT signal were reconstructed, show validity of the method
for those flaws. Nevertheless its aim was fundamental survey on validation of the method so that tested flaws
were limited in shape.In this paper,beyond that limitation, the authors wish to report the results of applications
to complex shape flaws that are likely to be found in actual inspection site. The obtained reconstructed images
show notable results indicate that the validity is kept even for complex flaw.
An eddy current testing (ECT) and an electromagnetic acoustic testing (EMAT) employ electromagnetic methods
to induce an eddy current and to detect flaws on or within a sample without directly contacting it. ECT produces
Lissajous curves, and EMAT gives us a time series of signal data, both of which can be directly displayed on
nondestructive testing (NDT) equipment screens. Since the interpretation of such output is difficult for untrained
persons, images need to be properly reconstructed and visualized. This could be carried out by single-probe
2/3D scanners with imaging capabilities or with array probes, but such equipment is often too large or heavy
for ordinary on-site use. In this study, we introduce a flexible scanning tablet for on-site NDT and imaging of
detected flaws. The flexible scanning tablet consists of a thin film or a paper with a digitally encoded coordinate
system, applicable to flat and curved surfaces, that enables probe positions to be tracked by a specialized optical
reader. We also discuss how ECT and EMAT probe coordinates and measurement data could be simultaneously
derived and used for further image reconstruction and visualization.
Eddy Current Testing(ECT) has been used in wide field such as airline and power plants for maintenance, ironworks for production.
However original flaw shape blur in image by signal of ECT.
In our previous work an image reconstruction method from signal had been proposed.
The method is based on
that simple relationship between signal and source are described by a convolution of response function and flaw shape.
The method was able to show more fine image of points flaw, short line flaw, long line flaw
than images of those original signal.
One difficulty in the method was to determine empirical parameter by trial and error.
In this paper, we propose a concept of modified response function and signal that
enable to make empirical parameter unnecessary.
Those modification process is fully programmable and is carried out automatically.
Validity of introducing those modification are considered from mathematical view point.
Numerical results shows the method with this concept
reconstructed image as same as empirical parameter method.
An image by Eddy Current Testing(ECT) is a blurred image to original flaw shape. In order to reconstruct fine
flaw image, a new image reconstruction method has been proposed. This method is based on an assumption that
a very simple relationship between measured data and source were described by a convolution of response function
and flaw shape. This assumption leads to a simple inverse analysis method with deconvolution.In this method,
Point Spread Function (PSF) and Line Spread Function(LSF) play a key role in deconvolution processing. This
study proposes a simple data processing to determine PSF and LSF from ECT data of machined hole and line
flaw. In order to verify its validity, ECT data for SUS316 plate(200x200x10mm) with artificial machined hole
and notch flaw had been acquired by differential coil type sensors(produced by ZETEC Inc). Those data were
analyzed by the proposed method. The proposed method restored sharp discrete multiple hole image from
interfered data by multiple holes. Also the estimated width of line flaw has been much improved compared with
original experimental data. Although proposed inverse analysis strategy is simple and easy to implement, its
validity to holes and line flaw have been shown by many results that much finer image than original image have
been reconstructed.
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