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Innovative Metrology 2017

Rückblick: Innovation Messtechnik 2015

22nd IMEKO TC2 Symposium on Photonics in Measurement 2017

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Development of a measurement system for detecting subcutaneous inclusions in steel sheet

On a proposal of the appraisal committee the president of the “Austrian Company for Measurement and Automation Technics” has awarded Dipl.-Ing. Dr. Johannes Atzlesberger with the OGMA-PRIZE 2013 for his Dissertation “Development of a measurement system for detecting subcutaneous inclusions in steel sheet”.
May 22, 2014

Dipl.-Ing. Dr. Johannes Atzlesberger

Dipl.-Ing. Dr. Johannes Atzlesberger

Supervisory committee:

Univ.-Prof. Dipl.-Ing. Dr. Bernhard Zagar
a.Univ.-Prof. Dipl.-Ing. Dr.techn. Kurt Preis

Final exam:

February 12, 2013

In recent years magnetic imaging technologies has become a great concern in non-destructive testing (NDT). Due to the advent of highly sensitive magnetic field sensors based on the GMR-effect (Giant Magneto Resistance) the flux leakage (which depends on magnetic inhomogeneities inside the inspected material) can be measured precisely. During the work on this thesis a testing device was developed (see Figure 1) which is able to detect magnetic flux density variations from mT (millitesla) down to only some nT (nanotesla). Thus defects, corrosion, non-metallic inclusions, surface defects, cracks, specimen thickness variations and even residual stresses can be detected.

Figure 1: Developed testing device ready for operation in a testing plant for detecting magnetic inhomogeneities in ferromagnetic material. The device can operate using GMR--magnetometers and GMR--gradiometers exhibiting different sensitivities.

In Figure 2 the schematic test set-up of the magnetic flux leakage (MFL) method is shown which was already applied - of course in a highly simplified way - in the 19th century for detecting flaws in gun barrels and railway tracks. An electro magnet magnetizes the ferromagnetic specimen and the specimen's surface is scanned with the developed testing device. In Figure 3 an exemplary 2-dimensional magnetic image of a steel sheet containing artificial inhomogeneities is shown.

Figure 2: Schematic test set-up of the magnetic flux leakage (MFL) method using an electro magnet for the magnetic excitation. Any magnetic inhomogeneity inside the specimen between the two pole shoes produces a variation of the magnetic flux density near the surface of the specimen and can be measured using appropriate magnetic field sensors.

Figure 3: Two-dimensional field image of a ferromagnetic specimen. The magnetic field strength increases in regions containing inhomogeneities.

Keywords: Magnetic Flux Leakage (MFL), Giant Magneto Resistance (GMR), Non-Destructive Testing (NDT).

The circulation of the project work is restricted from January 28th, 2013, for a period of 5 years.