TY - CONF A1 - Sonntag, Nadja A1 - Stegemann, Robert A1 - Skrotzki, Birgit A1 - Kreutzbruck, Marc ED - Grellmann, W. ED - Frenz, H. T1 - Verformungsinduzierte Magnetisierung ferromagnetischer Stähle am Beispiel eines unlegierten Baustahls T1 - Deformation-induced magnetization of ferromagnetic steels exemplified by an unalloyed structural Steel N2 - Die zerstörungsfreie Detektion potenzieller Rissinitiierungsorte in unlegierten Baustählen und Pipelinestählen mit der Metal Magnetic Memory (MMM) Methode basiert auf der Messung schwacher magnetischer Streufelder, die sich im Zuge statischer oder zyklischer Belastung durch irreversible Änderungen der initialen magnetischen Mikrostruktur (Weiß’sche Bezirke) ausbilden. Spannungskonzentrationsstellen und höchst beanspruchte Werkstoffbereiche kleiner Dimensionen im ferromagnetischen Material können daher mit magnetischen Methoden detektiert werden. In einem klassischen Baustahl (S 235) werden mittels hochauflösender GMR-Sensorik Veränderungen der natürlichen Magnetfeldverteilung durch statische Zugbelastungen visualisiert. Ergänzende profilometrische Messungen veranschaulichen die prinzipielle Beteiligung geometrischer und topografischer Effekte an der Entstehung der sich unter plastischer Verformung ausbildenden Magnetisierungszustände des ferromagnetischen Materials. N2 - pipeline steels by the Metal Magnetic Memory (MMM) method is based on the measurement of weak magnetic stray fields, which are formed during static or cyclic loading by irreversible changes of the initial magnetic structure (magnetic domains). Therefore, stress concentration sites and highly stressed areas in small dimensions of ferromagnetic materials may be detected by magnetic methods. The changes of the distribution of the natural magnetic field by static tensile loading are detected by high resolution GMR sensors in conventional constructional Steel (S 235). In addition, profilometric measurements Show the general contribution of geometric and topographical effects to the development of the magnetic States formed during plastic deformation of a ferromagnetic material T2 - Tagung Werkstoffprüfung 2014 - Fortschritte in der Werkstoffprüfung für Forschung und Praxis - Werkstoffeinsatz, Qualitätssicherung und Schadensanalyse CY - Berlin, Germany DA - 04.12.2014 KW - MMM KW - 3D-GMR-Magnetometer KW - Topografie KW - Verformungsinduzierte Magnetisierung KW - Baustahl KW - 3D-GMR magnetometer KW - Topography KW - Deformation-induced magnetization KW - Construction steel PY - 2014 SN - 978-3-9814516-8-9 SN - 1861-8154 SP - 355 EP - 360 AN - OPUS4-32222 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sonntag, Nadja A1 - Cabeza, S. A1 - Kuntner, M. A1 - Mishurova, Tatiana A1 - Klaus, M. A1 - Kling e Silva, L. A1 - Skrotzki, Birgit A1 - Genzel, Ch. A1 - Bruno, Giovanni T1 - Visualisation of deformation gradients in structural steel by macroscopic magnetic domain distribution imaging (Bitter technique) N2 - Abstract While classically used to visualise the magnetic microstructure of functional materials (e.g., for magnetic applications), in this study, the Bitter technique was applied for the first time to visualise macroscopic deformation gradients in a polycrystalline low-carbon steel. Spherical indentation was chosen to produce a multiaxial elastic–plastic deformation state. After removing the residual imprint, the Bitter technique was applied, and macroscopic contrast differences were captured in optical microscopy. To verify this novel characterisation technique, characteristic “hemispherical” deformation zones evolving during indentation were identified using an analytical model from the field of contact mechanics. In addition, near-surface residual stresses were determined experimentally using synchrotron radiation diffraction. It is established that the magnetic domain distribution contrast provides deformation-related information: regions of different domain wall densities correspond to different “hemispherical” deformation zones (i.e., to hydrostatic core, plastic zone and elastic zone, respectively). Moreover, the transitions between these three zones correlate with characteristic features of the residual stress profiles (sign changes in the radial and local extrema in the hoop stress). These results indicate the potential of magnetic domain distribution imaging: visualising macroscopic deformation gradients in fine-grained ferromagnetic material with a significantly improved spatial resolution as compared to integral, mean value-based measurement methods. KW - Bitter technique KW - Deformation KW - Expanding cavity model KW - Indentation KW - Magnetic domain distribution KW - Residual stress PY - 2018 DO - https://doi.org/10.1111/str.12296 SN - 1475-1305 VL - 54 IS - 6 SP - e12296, 1 EP - 15 PB - Wiley AN - OPUS4-46569 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Sonntag, Nadja T1 - Dwell-Fatigue and Cyclic Softening of Grade P92 Steel under LCF and TMF Conditions N2 - Tempered martensite-ferritic steels, such as the grade P92 steel studied in this contribution, exhibit pronounced macroscopic cyclic softening under isothermal low-cycle fatigue (LCF) and non-isothermal thermomechanical fatigue (TMF) conditions, which is considered to be the predominant degradation mechanism in high-temperature fatigue in this and other material groups. However, such softening processes are highly complex since microscopic (e.g., recovery) and macroscopic (e.g., crack initiation and growth), as well as global and local effects superimpose, especially under creep-fatigue conditions. In this contribution, we discuss the cyclic deformation and softening behavior of P92 in strain-controlled LCF, in-phase (IP) TMF, and out-of-phase (OP) TMF tests with and without dwell times in the temperature range from 300 °C to 620°C. EBSD-based dislocation analysis on various fatigued material states confirms the continuous redistribution and annihilation of geometrically necessary dislocations in all studied states, which can be quantitatively correlated with macroscopic softening despite different damage mechanisms for different test types. Deviations from this correlation are observed for OP TMF and LCF with dwell times, i.e., for conditions where optical microscopy reveals pronounced crack-oxidation interactions at the specimen surfaces. T2 - LCF9 - Ninth International Conference on Low Cycle Fatigue CY - Berlin, Germany DA - 21.06.2022 KW - LCF KW - TMF KW - EBSD PY - 2022 DO - https://doi.org/10.48447/LCF9-2022-111 AN - OPUS4-55128 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -