Sonntag Nadja, Skrotzki Birgit, Stegemann Robert, Löwe Peter, Kreutzbruck Marc
Bundesanstalt für Materialforschung und -prüfung (BAM), Department 5: Materials Engineering, Unter den Eichen 87, 12205 Berlin, Germany.
Bundesanstalt für Materialforschung und -prüfung (BAM), Department 8: Non-Destructive Testing, Unter den Eichen 87, 12205 Berlin, Germany.
Materials (Basel). 2018 Aug 23;11(9):1518. doi: 10.3390/ma11091518.
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.
人们普遍认为，由于磁弹性效应，铁磁材料的磁状态可能会因机械加载而发生不可逆的改变。一种新型的标准化无损检测（NDT）技术利用了弱磁杂散场，这些杂散场被认为是由不均匀变形产生的，用于结构健康监测（即用于损伤的检测和评估）。然而，损伤的力学和微观结构复杂性迄今尚未得到充分考虑。本研究的目的是通过实验并从更强的材料力学角度，探讨多晶铁磁材料在不均匀变形下不均匀“自磁化”的现象。为此，对带缺口的试样进行了弹性和塑性变形。用三轴巨磁阻（GMR）传感器测量表面磁状态，并与应变场（数字图像相关）和光学形貌测量结果进行比较。结果表明，杂散场并非仅由磁弹性效应形成。相反，不均匀塑性变形会导致形貌变化，这是磁杂散场形成的主要原因之一。此外，如果不考虑形貌，由于提离值的变化，形貌可能会使磁信号失真。磁矢量分量与机械张量的相关性，特别是对于多轴应力/应变状态和不均匀弹塑性变形，仍然是一个问题。
