Citation: Koss, P.A.; Durmaz, A.R.;
Blug, A.; Laskin, G.; Pawar, O.S.;
Thiemann, K.; Bertz, A.; Straub, T.;
Elsässer, C. Optically Pumped
Magnetometer Measuring
Fatigue-Induced Damage in Steel.
Appl. Sci. 2022, 12, 1329. https://
doi.org/10.3390/app12031329
Academic Editors:
Alberto Campagnolo and
Alberto Sapora
Received: 3 December 2021
Accepted: 25 January 2022
Published: 26 January 2022
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Article
Optically Pumped Magnetometer Measuring Fatigue-Induced
Damage in Steel
Peter A. Koss
1,
* , Ali Riza Durmaz
2,
* , Andreas Blug
1
, Gennadii Laskin
1
, Omkar Satish Pawar
2
,
Kerstin Thiemann
1
, Alexander Bertz
1
, Thomas Straub
2
and Christian Elsässer
2
1
Fraunhofer Institute for Physical Measurement Techniques IPM, 79110 Freiburg, Germany;
andreas.blug@ipm.fraunhofer.de (A.B.); gennadii.laskin@ipm.fraunhofer.de (G.L.);
kerstin.Thiemann@ipm.fraunhofer.de (K.T.); alexander.bertz@ipm.fraunhofer.de (A.B.)
2
Fraunhofer Institute for Mechanics of Materials IWM, 79108 Freiburg, Germany;
omkar.pawar@iwm.fraunhofer.de (O.S.P.); thomas.straub@iwm.fraunhofer.de (T.S.);
christian.elsaesser@iwm.fraunhofer.de (C.E.)
* Correspondence: peter.koss@ipm.fraunhofer.de (P.A.K.); ali.riza.durmaz@iwm.fraunhofer.de (A.R.D.);
Tel.: +49-761-8857-243 (P.A.K.); +49-761-5142-195 (A.R.D.)
Featured Application: Piezomagnetic fatigue testing of ferromagnetic specimens with highly sen-
sitive optically pumped magnetometers as a method for early damage formation detection.
Abstract:
Uniaxial fatigue testing of micro-mechanical metallic specimens can provide valuable in-
sight 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 piezomag-
netic 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.
Keywords:
magnetic material testing; cyclic mechanical loading; fatigue damage; hysteresis;
optically pumped magnetometers (OPM); quantum sensing; ferritic steel; mesoscale specimen;
magnetomechanical effects
1. Introduction
Magnetic material testing methods are well-established for non-destructive testing
(NDT) of materials or devices composed of steel, cast iron, or other ferromagnetic mate-
rials [
1
]. The fundamental principle involves an outer field
H
applied to a ferromagnetic
material to measure the response of the specimen to the exciting field
H
. This concept
is utilized by some of the most frequently applied NDT techniques, such as magnetic
flux leakage (MFL), magnetic Barkhausen noise (MBN), and more recently, metal mag-
netic memory (MMM) [
2
]. Using either one of these techniques as a kind of “magnetic
microscope”, one can investigate the microstructure of ferromagnetic materials [
3
]. Addi-
tionally, these NDT techniques can routinely be applied to industrial in-line monitoring of
manufacturing processes.
Alternatively, testing is possible based on the phenomenon of mechanical stresses
altering the intrinsic magnetization state of ferromagnetic materials. This effect is the
so-called magneto-mechanical Villari effect, which is also known as the magnetoelastic
Appl. Sci. 2022, 12, 1329. https://doi.org/10.3390/app12031329 https://www.mdpi.com/journal/applsci
