Entropy as a material response to fatigue in metals and related thermographic assessment

The dissertation comprehensively proposes multi non-destructive testing methods investigation in mechanical degradation of metallic materials. First, high cycle fatigue of an unalloyed medium carbon steel SAE1045 is quantified investigated through thermographic measurement; a short-term evaluation procedure is proposed based on the intrinsic thermal dissipation model to determine the S-N curves by performing two constant amplitude tests and one load increase test. Second, a unified approach is developed by evaluating the evolution of intrinsic dissipation and microplasticity. This plasticity is derived from temperature and is correlated to the fatigue process and related to fatigue life. Furthermore, a modified fracture fatigue entropy (FFE) method is modeled to evaluate the fatigue damage. It is shown that the FFE can be better used as an index to trace the fatigue damage as an irreversible degradation of a metallic material of its non-linearity. Finally, the mechanical and magnetic behavior of an ultrafine-grained medium manganese transformation-induced plasticity steel is investigated in its plastic instability. Lüders bands are characterized by digital image correlation and magnetic Barkhausen noise (MBN), and the final results show that MBN can be used as a potential means for the non-destructive evaluation for the strengthening of this steel.In der Dissertation werden mehrere zerstörungsfreie Prüfverfahren zur Untersuchung der mechanischen Degradation metallischer Werkstoffe vorgeschlagen. Erstens wird das Ermüdungsverhalten in dem Zeitfestigkeitsbereich (engl. high cycle fatigue) eines unlegierten Kohlenstoffstahls (SAE1045/C45E) durch thermografische Messungen quantifiziert ermittelt, wobei ein Kurzzeitverfahren zur Lebensdauerberechnung abgeleitet wird, das auf dem Modell der intrinsischen Wärmedissipation basiert, sodass die Bestimmung der Wöhlerkurven mit zwei Einstufenversuchen und einem Laststeigerungsversuch ermöglicht wird. Darüber hinaus wird ein einheitlicher Ansatz entwickelt, indem die Entwicklung der intrinsischen Dissipation und der Mikroplastizität bewertet wird. Diese Plastizität wird hierbei von der Temperatur abgeleitet, mit dem Ermüdungsprozess korreliert und auf die Ermüdungslebensdauer bezogen. Zudem wird eine modifizierte Fracture Fatigue Entropy-Methode (FFE) modelliert, um die Ermüdungsschädigung zu evaluieren. Schließlich wird das mechanische und magnetische Verhalten in der plastischen Instabilität eines ultrafeinkörnigen TRIP-Stahls mit mittlerem Mangangehalt untersucht. Lüders-Bänder werden durch digitale Bildkorrelation (DIC) und magnetisches Barkhausenrauschen (MBN) charakterisiert. Die Ergebnisse zeigen, dass MBN als potenzielles Mittel für die zerstörungsfreie Bewertung der Festigkeit dieses Stahls verwendet werden kann

Thermodynamic entropy as a marker of high‐cycle fatigue damage accumulation: Example for normalized SAE 1045 steel

A nondestructive thermographic methodology is utilized to determine the fracture fatigue entropy for evaluating the fatigue damage in metals within the high‐cycle fatigue regime. Thermodynamic entropy is shown to play an important role in the fatigue process to trace the fatigue damage as an irreversible degradation of a metallic material being subjected to cyclic elastic‐plastic loading. This paper presents a method to evaluate fatigue damage in the normalized SAE 1045 steel being based on the concept of thermodynamic entropy and its nonlinearities. The procedure looks to be applicable to constant and load increase tests proven by experiments

Characterization and Analysis of Plastic Instability in an Ultrafine‐Grained Medium Mn TRIP Steel

Herein, the mechanical and magnetic behavior of an ultrafine-grained (UFG) medium manganese (Mn) transformation-induced plasticity (TRIP) steel is focused on in its plastic instability. The in situ methods of digital image correlation (DIC) and magnetic Barkhausen noise (MBN) are used to macroscopically characterize the propagation of the Lüders band (stretcher–strain marks) and the evolution of MBN activities during quasistatic tensile deformation. The evolution of microstructure during the plastic instability is investigated ex situ using X-Ray diffraction (XRD) and transmission electron microscopy (TEM) for selected plastic strain states. It is showed in the results that the plastic instability of this steel is associated with an increase of hardness and enrichment of dislocation density, which can also amplify the MBN signal, while the derived coercivity behaves reversely on an overall trend due to work hardening. The different stress response of the medium Mn steel is closely related to the kinetic martensite microstructure, which in turn modifies the domain–structure response. Thus, the MBN can be used as a potential means for nondestructive evaluation (NDE) for the strengthening of the UFG medium Mn TRIP steel

Data on prevalence of atrial fibrillation and its association with stroke in low-, middle-, and high-income regions of China

Data presented in this article are supplementary material to our research article entitled " Prevalence of Atrial Fibrillation in Different Socioeconomic Regions of China and Its Association with Stroke: Results from a National Stroke Screening Survey" (Wang et al., 2018) [1]. This data article summarizes previous studies of Atrial Fibrillation (AF) prevalence in China, and estimates the association between AF and stroke in different socioeconomic regions of China through a national survey

Data on prevalence of atrial fibrillation and its association with stroke in low-, middle-, and high-income regions of China

Data presented in this article are supplementary material to our research article entitled " Prevalence of Atrial Fibrillation in Different Socioeconomic Regions of China and Its Association with Stroke: Results from a National Stroke Screening Survey" (Wang et al., 2018) [1]. This data article summarizes previous studies of Atrial Fibrillation (AF) prevalence in China, and estimates the association between AF and stroke in different socioeconomic regions of China through a national survey

Prevalence of atrial fibrillation in different socioeconomic regions of China and its association with stroke: Results from a national stroke screening survey

Background: Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice. This study aimed to estimate the prevalence of AF in different socioeconomic regions of China and identify its association with stroke, through a national survey. Methods: The study included 726,451 adults aged ≥40 years who were participants of the China National Stroke Screening and Prevention Project, a nationally representative cross-sectional study. Stepwise logistic regression analyses were conducted to investigate the association between AF and stroke. Results: The overall standardized prevalence rate of AF was 2.31%. The prevalence of AF was highest in high-income regions (2.54%), followed by middle-income regions (2.33%), and lowest in low-income regions (1.98%). Women had a higher prevalence of AF than men in all regions (low-income regions, 2.30% vs 1.65%; middle-income regions, 2.78% vs 1.89%; and high-income regions, 2.96% vs 2.12%). Compared with urban residents, the prevalence of AF among rural residents was higher in low- (2.03% vs 1.91%) and middle-income regions (2.69% vs 1.90%), but lower in high-income regions (2.44% vs 2.58%). Participants with AF were more likely to have a stroke than those without AF (9.48% vs 2.26%). After adjusting for age, sex, location, overweight or obese, smoking, drinking, physical inactivity, hypertension, diabetes, dyslipidemia, and a family history of stroke, results showed that AF was significantly associated with stroke. Conclusions: The prevalence of AF has increased in recent years, and it was positively correlated with socioeconomic status, sex (women), location (rural areas), and stroke

Friction Force Microscopy as a tool to investigate (electro)catalytic processes at surfaces

Friction Force Microscopy as a tool to investigate (electro)catalyticprocesses at surfacesM.Maksumov1,2, A. Kaus2,3, Z. Teng4, K. Kleiner4, F. Gunkel3, F. Hausen1,21Forschungszentrum Jülich, IEK-9, 52428 Jülich, Germany2RWTH Aachen University, IPC, Landoltweg 2, 52065 Aachen, Germany3Forschungszentrum Jülich, PGI-7, 52428 Jülich, Germany4University of Münster, MEET, Correnstraße 46, 48149 Münster, [email protected]@fz-juelich.deA thorough understanding of (electro)catalytic surface transformations under dynamic reaction conditions is of utmost importance for a knowledge-based catalyst design. Friction Force Microscopy (FFM) as an atomic force microscopy based technique is capable to obtain materials specific information in addition to electrical and structural properties of catalysts in liquid media and under electrochemical conditions. This is especially relevant as surface transitions at early catalytic activity are subtle and might be easily overseen by pure topography mapping.It is the objective of this work to demonstrate the capabilities of FFM for investigating (electro)catalysts. It has been shown earlier that the frictional behavior of a bare metal differs significantly from its oxy/hydroxy-terminated surface under electrochemical conditions.The new results on combined electrochemical and frictional experiments on well-defined epitaxial perovskite oxide structures in aqueous liquids are illustrated. This approach represents the first application of these technique with respect to (electro)catalysis. Simultaneously recorded cyclic voltammograms and lateral forces, so-called frictograms, allow to correlate subtle and local surface transformations and the applied potential precisely.In conclusion, FFM represents a versatile new operando technique to investigate (electro)catalytic reactions under dynamic conditions on a local scale with high sensitivity to materials and structural changes

Friction Force Microscopy as a tool to investigate (electro)catalytic activities at surfaces

Production of green hydrogen energy based on water electrolysis, currently, have become one of the crucial topics in the framework of energy transition towards green energy technologies. In water splitting electrolysis catalysis or electrocatalysts play a critical role, where the development of active, stable and low-cost electrocatalysts is always on the agenda of the research works. [1] Designing of electrocatalysts with fundamental understanding of their surface transformations under dynamic reaction conditions still remains very challenging. This requires a fundamental understanding of all the processes involved on the atomic level, which is the main focus of my research work and part of the common goals of DFG Priority Programme 2080. The slow reaction kinetics at oxygen evolution reaction (OER) due to high overpotentials keep electrolysis from being of practical use and perovskites, as catalysts, could be used to minimize the overpotentials. However, perovskite electrocatalysts suffer from irreversible degradation reactions such as undesired surface transformations and morphology changes at grain boundaries and surfaces. [2-3] A comprehensive understanding of perovskite surface transformations under dynamic OER conditions at atomic level could be achieved by implementation of different electrochemical scanning probe microscopy techniques. Mainly, to investigate fundamental processes at the solid/liquid interface in electrocatalysis advanced atomic force microscopy (AFM) and scanning tunneling microscopy (STM) are employed in liquid environment under applied voltage bias. AFM enables the collection of data regarding the nanomechanical, electrical, and structural properties of sample in addition to the standard topography map that is captured. This is highly valuable considering sole topography mapping likely to miss the expected surface changes at the beginning of the OER. Previously, F. Hausen et al [4] applying a common tribology method based on AFM, operando electrochemical friction force microscopy (EC-AFM), reported that friction differences between a bare metal and and oxy/hydroxy-terminated surface in liquid environment clearly indicates direct fingerprint of chemical surface transformation. In our work, we investigate exclusively epitaxially grown perovskite oxide catalysts based on La1-xSrxCoO3 in alkali environment before and after electrocatalysis under dynamic and steady state operation conditions (as illustrated in Fig.1). Figure 1 clearly illustrates the difference of surface between as-grown perovskite oxide with the higher average friction of 18-20 nN than the post-catalaysis perovskite oxide with the average friction of 10-12 nN. The relevance of this research work and necessity to exchange the ideas with researchers around the world working on hydrogen energy technologies is highly encouraged from SPP2080 project as well as well aligned within the scope of H2Educate program from National Energy Education Development (NEED Project, US), which was designed to promote young researchers with educational materials, training and exchange programs. Figure 1. Friction maps of as-grown and post-catalysis of LaxSr1-xCoO3 in air, a and b respectively.1. Wang S., Lu A., Zhong CJ. Hydrogen production from water electrolysis: role of catalysts. Nano Convergence 8, 4 (2021). 2. Grimaud, A. et al. Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution. Nat. Commun. 4, 2439 (2013).3. Wan, G. et al. Amorphization mechanism of SrIO3 electrocatalyst: How oxygen redox initiates ionic diffusion and structural reorganization. 4. Hausen, F. et al. Anion adsorption and atomic friction on Au (111). Electrochimica Acta. 56, 28, 10694-10700 (2011)