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Magnetic NDT technology for characterizing materials - a state of the art survey

: Dobmann, G.

Fulltext urn:nbn:de:0011-n-502180 (535 KByte PDF)
MD5 Fingerprint: fc3453057d5cb4f84dc1a129cfb0f6ff
Created on: 11.7.2008

Indian Society for Non-Destructive Testing:
NDE 2006. Seminar on Non-Destructive Testing & International Exhibition. CD-ROM : NDE in Knowledge Society, Hitex Exhibition Center, Hyderabad, India, December 7-9, 2006
Hyderabad: Indian Society for Non-Destructive Testing, 2006
pp.TP 41
Seminar on Non-Destructive Testing (NDE) <2006, Hyderabad>
Conference Paper, Electronic Publication
Fraunhofer IZFP ()
magnetic testing; magnetic probe; material characterization; process control; mechanical property determination; ageing phenomena

Per definition, magnetic NDT can be applied at ferromagnetic material only. However, most of the materials we use today still are iron-based steels with bcc lattice and therefore magnetic. The magnetic properties of these materials can be utilized in NDT for defect detection and sizing as well as for materials characterization in terms of mechanical properties determination, also in on-line process-controlled systems.
MT is old and one of the most applied NDT techniques in the world for detecting surface-breaking cracks by using magnetic particles. Nowadays the technique can be mechanized and the interpretation of powder indications as findings is performed by intelligent pattern recognition software, i.e. the drawback to be working with a high human factor influence can be eliminated. However, in complex shaped geometries, for instance pusher beams of steering gears in car industry, the existence of pseudoindications prevent the application of MPI. Based on new magnetic sensors, i.e. GMR, an automatic detection with high sensitivity became possible.
Manufacturers in automotive industry after validation of the new technology ask for a replacement of MPI.
There are many similarities between mechanical and magnetic properties of magnetic materials. Microstructure characteristics like vacancies, dissolved atoms, dislocations, precipitates, and grain and phase boundaries influence the dislocation movement under mechanical loads similar as they hinder the Bloch wall movement under magnetic loads. Therefore micro-magnetic techniques are suitable to characterize properties like hardness, yield and tensile strength but also toughness properties like Charpy energy or ductile - brittle transition temperature. The contribution introduces into recently developed industrial applications in steel industry to non-destructively and on-line characterize mechanical properties in the manufacturing process as well as to approaches to describe the ageing state of steels in power plant applications performing an in-service inspection.