A Numerical Study of the Inclusion Problem in Electromagnetic Testing

Marc Kreutzbruck; Hans-Martin Thomas; Roland Sickert; Ralf Casperson; Rainer Boehm; Kai Allweins; Gertrud Lemke

doi:10.3139/120.110098

Article

A Numerical Study of the Inclusion Problem in Electromagnetic Testing

Marc Kreutzbruck , Hans-Martin Thomas , Roland Sickert , Ralf Casperson , Rainer Boehm , Kai Allweins and Gertrud Lemke

Published/Copyright: May 28, 2013

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From the journal Materials Testing Volume 51 Issue 11-12

Abstract

The determination of magnetic distortion fields caused by inclusions hidden in a conductive matrix using homogeneous current flow needs to be addressed in multiple tasks of electromagnetic non-destructive testing and materials science. This includes a series of testing problems such as the detection of tantalum inclusions hidden in niobium plates, metal inclusion in a nonmetallic base material or porosity in aluminum laser welds. Unfortunately, easy tools for an estimation of the defect response fields above the sample using pertinent detection concepts are still missing. In this study the Finite Element Method (FEM) was used for modeling spherically shaped defects, and an analytical expression was developed for the strength of the response field including the conductivity of the defect and matrix, the sensor-to-inclusion separation, and the defect size. Finally, the results were adapted to Eddy Current Testing problems, in which the skin effect was taken into consideration for an appropriate estimation of the signal strength.

Kurzfassung

Die Bestimmung magnetischer Feldverzerrungen durch verdeckte Einschlüsse in einer leitenden Matrix mit homogenem Stromfluss erfordert Beachtung in vielfältigen Aufgaben der zerstörungsfreien elektromagnetischen Prüfung und der Materialforschung. Das schließt eine Reihe von Prüfproblemen ein, wie die Detektion von verdeckten Tantal-Einschlüssen in Niob-Blechen, metallischen Einschlüssen in nichtmetallischem Basismaterial oder die Porosität in Aluminium-Laserschweißungen. Leider mangelt es für die Abschätzung der Defektantwort der Felder an der Probenoberfläche noch immer an einfachen Prozeduren mittels geeigneter Detektionskonzepte. Hier wird die Finite-Elemente-Methode (FEM) für die Modellierung von sphärischen Defekten eingesetzt und ein analytischer Ausdruck für die modifizierte Feldstärke entwickelt, der sowohl die Leitfähigkeit von Defekt und Matrix berücksichtigt als auch den Sensor-Defekt-Abstand und die Defektgröße. Schließlich werden die Ergebnisse auf Probleme der Wirbelstromprüfung übertragen, wobei der Skin-Effekt für die richtige Abschätzung der Signalstärke berücksichtigt wird.

Dr. rer. nat. habil. Marc Kreutzbruck received his PhD in 1998. After habilitation in 2005 he was a lecturer at the University of Gießen. Since 2007 he is head of Division VIII.4 at the Federal Institute for Material Research and Testing (BAM) focussed on acoustic and electro magnetic non-destructive testing. The activities include modern methods of ultrasound, eddy current, and thermography.

Dr. Hans-Martin Thomas, born in 1951, studied electrical engineering at the Technical University of Berlin, where he received his PhD in 1986. Since 1978 he is engaged at BAM where he is head of the laboratory for Electrical and Magnetic Methods. He has received the Adolf Martens Award.

Dr. Roland Sickert, born in 1954, studied electrical engineering at the Technical University of Ilmenau. After receiving his Dr. of engineering in 1986 he was worked at the Academy of Science of the GDR on surface acoustic waves. Since 1989 he is engaged at the BAM where his activities include non-destructive materials testing by ultrasound, electrical and magnetic methods.

Dipl.-Ing. Ralf Casperson, born in 1966, studied electrical engineering at the Technical University of Berlin. Since 1993 he is engaged at the BAM with the working group for eddy current techniques.

Dipl.-Phys. Rainer Boehm, born in 1955, studied physics at the Technical University (TUB) of Berlin. In 1984 he worked at BAM in the laboratory for electrical and magnetic testing, and from 1985 at the Optical Institute of the TUB. Since 1990 he is engaged at BAM VIII.42 in modeling methods for nondestructive testing.

Dr. rer. nat. Kai Allweins is currently employed as a research associate at the Institute of Applied Physics. His work areas include non-destructive material testing using sensitive magnetometers, and (finite element) simulations of eddy current testing. Currently his work is focused on pulse-tube coolers at low temperatures.

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Published Online: 2013-05-28

Published in Print: 2009-11-01

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https://doi.org/10.3139/120.110098