Abstract
Measurement of spontaneous magnetic stray field signals has been reported to be a promising tool for capturing macro-scale information of deformation states, defects and stress concentration zones in a material structure. This paper offers a new method for self-magnetic leakage field detection using a magneto-optical (MO) hand-held microscope. Its sensor has a dynamic field range between ±0.05 and ±2 kA/m and a lateral optical resolution of approx. 10 μm. We examined flat tensile test specimens of metastable austenitic steel AISI 304. Static tensile tests were repeatedly interrupted at various predetermined states of strain and the magnetic information was measured by the MO system. Comparative measurements using a high-precision magnetic field GMR-sensor, verify the outstanding capability of the MO microscope regarding spatial resolution of magnetic fields.
Highlights
The self-magnetic-leakage field (SMLF) detection is based on the assumption of “naturally” emerging magnetic fields in the presence of so-called stress concentration zones [1]
This paper offers a new method for self-magnetic leakage field detection using a magneto-optical (MO) handheld microscope
We examined flat tensile test specimens of metastable austenitic steel AISI 304
Summary
The self-magnetic-leakage field (SMLF) detection is based on the assumption of “naturally” emerging magnetic fields in the presence of so-called stress concentration zones [1]. In contrast to traditional magnetic flux leakages testing, the samples are not intentionally magnetized by an external magnetic field [2]. It is assumed, that the distribution of the SMLF highlights areas of potentially pre-cracked and fatigued material zones. The SMLF detection could be a convenient method for evaluating areas of potential crack initiation. The influence of martensitic phase transformation on the SMLF is the reference for comparison of a magneto-optical (MO) and a giant magneto resistance (GMR) high resolution measurement technique
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