Imaging of Cracks and Weak Spots in Steel and Aluminium Plate Rolls

Because of several - sometimes extreme - complications caused by cracks and weak spots in a metal industry roll, it is of great importance to detect these defects in time. Measurements on rolls with artificial- and natural defects have been performed. An imaging operator is introduced, which uses the measurement data to depict the correct locations of the scatterers in the roll. Even when almost 95% of the original measurement data is discarded, the defects in the roll can still be detected. This thesis shows how these imperfections cause deviations in the eddy current measurement setup and presents how the deviations can be used to locate these defects in the steel. The roll is modeled as a conductive half space after which the inhomogeneous Helmholtz equation will be solved to find the electromagnetic fields inside the steel. Defects are modeled as small spheroids with respect to the wavelength, which makes it possible to find the fields inside these scatterers. Furthermore, an equation is found which relates deviations in receiver signals to the electric- and magnetic fields and contrasts in the roll. The quasi-static approach is used to simplify this equation, after which results are shown for different defects and antenna configurations. Similar outcomes are obtained when the measurement data is compared to the theory.

Subject

cracks
imaging
electromagnetic
helmholtz
roll

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http://resolver.tudelft.nl/uuid:e06abee4-e41a-44f7-b603-779d1dbe9f9d

Embargo date

2013-08-11

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Student theses

Document type

master thesis

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MScThesisJHFvanGemert.pdf

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