Abstract
Uniaxial fatigue testing of micro-mechanical metallic specimens can provide valuable insight into damage formation. Magnetic and piezomagnetic testing are commonly used for qualitative characterization of damage in ferromagnetic specimens. Sensitive and accurate measurements with magnetic sensors is a key part of such a characterization. This work presents an experimental setup to induce structural defects in a micro-mechanical fatigue test. Simultaneously, the resulting piezomagnetic signals are measured during the complete lifetime of the tested specimen. The key component is a highly sensitive optically pumped magnetometer (OPM) used to measure the piezomagnetic hysteresis of a small specimen whose structural defects can be analyzed on a small scale by other metallographic characterization methods as well. This setup aims to quantify the magnetic signatures of damage during the fatigue process, which could enable non-destructive mechanical testing of materials. This paper reports the initial results obtained from this novel micro-magneto-mechanical test setup for a ferritic steel specimen.
Highlights
Featured Application: Piezomagnetic fatigue testing of ferromagnetic specimens with highly sensitive optically pumped magnetometers as a method for early damage formation detection
Several different types of optically pumped magnetometer (OPM) are commercially available and they can be sorted into two main classes: √
Several different types of OPMs are commercially available and they can be sorted into two main classes: zero-field OPMs and total-field OPMs
Summary
Several different types of OPMs are commercially available and they can be sorted into two main classes: √. Electron backscatter diffraction image of a cross-section of this ferritic steel conveys an impression of the texture, which features grain sizes of 10–15 μm For this setup, we redesigned a micro-mechanical tensile testing device in such a way thatFor the this. The 2 subsets with a size of 51 × 51 pixel, i.e., the inner green squares, measure integral strain This is analogous to a mechanical extensometer placed at the beginning of the dovetails of the SUT at a distance of 469 pixels (1.3 mm). (3) Mechanical loading of the specimen by exerting a tension and compression force on (4) Measuring a change in the magnetic field B in the vicinity of the specimen using the the specimen; readout of the OPM. The lateral specimen holder alignment was confirmed using dedicated alignment markers in the holders while the vertical alignment was approximated by focusing on the support area of both holders
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