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Open AccessArticle

The Role of Surface Topography on Deformation-Induced Magnetization under Inhomogeneous Elastic-Plastic Deformation

1
Bundesanstalt für Materialforschung und -prüfung (BAM), Department 5: Materials Engineering, Unter den Eichen 87, 12205 Berlin, Germany
2
Bundesanstalt für Materialforschung und -prüfung (BAM), Department 8: Non-Destructive Testing, Unter den Eichen 87, 12205 Berlin, Germany
3
University of Stuttgart, IKT, Pfaffenwaldring 32, 70569 Stuttgart, Germany
*
Author to whom correspondence should be addressed.
Materials 2018, 11(9), 1518; https://doi.org/10.3390/ma11091518
Received: 3 August 2018 / Revised: 17 August 2018 / Accepted: 22 August 2018 / Published: 23 August 2018
(This article belongs to the Section Structure Analysis and Characterization)
It is widely accepted that the magnetic state of a ferromagnetic material may be irreversibly altered by mechanical loading due to magnetoelastic effects. A novel standardized nondestructive testing (NDT) technique uses weak magnetic stray fields, which are assumed to arise from inhomogeneous deformation, for structural health monitoring (i.e., for detection and assessment of damage). However, the mechanical and microstructural complexity of damage has hitherto only been insufficiently considered. The aim of this study is to discuss the phenomenon of inhomogeneous “self-magnetization” of a polycrystalline ferromagnetic material under inhomogeneous deformation experimentally and with stronger material-mechanical focus. To this end, notched specimens were elastically and plastically deformed. Surface magnetic states were measured by a three-axis giant magnetoresistant (GMR) sensor and were compared with strain field (digital image correlation) and optical topography measurements. It is demonstrated that the stray fields do not solely form due to magnetoelastic effects. Instead, inhomogeneous plastic deformation causes topography, which is one of the main origins for the magnetic stray field formation. Additionally, if not considered, topography may falsify the magnetic signals due to variable lift-off values. The correlation of magnetic vector components with mechanical tensors, particularly for multiaxial stress/strain states and inhomogeneous elastic-plastic deformations remains an issue. View Full-Text
Keywords: magnetic stray fields; magnetomechanical effect; damage; topography; multiaxial deformation; notch; plastic deformation; metal magnetic memory; digital image correlation; structural steel magnetic stray fields; magnetomechanical effect; damage; topography; multiaxial deformation; notch; plastic deformation; metal magnetic memory; digital image correlation; structural steel
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Sonntag, N.; Skrotzki, B.; Stegemann, R.; Löwe, P.; Kreutzbruck, M. The Role of Surface Topography on Deformation-Induced Magnetization under Inhomogeneous Elastic-Plastic Deformation. Materials 2018, 11, 1518.

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