Mechanism-based modelling and simulation of the VHCF deformation behaviour of austenitic stainless steels

In der vorliegenden Arbeit wird ein Modell zur Beschreibung des VHCF-Wechselverformungsverhaltens eines metastabilen und eines stabilen austenitischen Edelstahls vorgestellt und mit Hilfe einer erweiterten numerischen Randelementemethode gelöst. Aufbauend auf experimentellen Untersuchungen des Ermüdungsverhaltens beider Werkstoffe bis hin zu sehr hohen Zyklenzahlen (engl. very high cycle fatigue, VHCF) werden in dem Modell charakteristische Mechanismen für die plastische Verformung in Gleitbändern und die deformationsinduzierte Phasenumwandlung von Austenit zu α‘-Martensit abgebildet. Als numerische Methode dient eine zweidimensionale Randelementemethode, die hinsichtlich der Beschreibung elastisch anisotroper Eigenschaften und der räumlichen Verformungsbeschreibung erweitert wird. Die Lösung des Modells mit der numerischen Methode erlaubt die Simulation der zyklischen plastischen Verformung in zweidimensionalen Gefügestrukturen. In erweiterten Studien gehen ebenfalls der Einfluss eines vorverformten Zustandes und einer moderaten Temperaturerhöhung mit ein. Die Simulationsergebnisse werden einerseits direkt mit der beobachteten Verformungsentwicklung auf realen Probenoberflächen verglichen und andererseits auf Basis des Resonanzverhaltens der Ermüdungsproben und der modellierten Gefüge einander gegenübergestellt. Gute Übereinstimmungen der Ergebnisse bestätigen die Modellannahmen, wodurch ein Beitrag für ein tiefergehendes Verständnis des VHCF-Wechselverformungsverhaltens der beiden austenitischen Edelstähle geleistet werden kann.In this work, a model describing the VHCF deformation behaviour of a metastable and a stable austenitic stainless steel is presented and solved by means of a boundary element method. Based on the experimental examination of the fatigue behaviour of both alloys until very high number of loading cycles (very high cycle fatigue, VHCF) characteristic mechanisms of plastic deformation in shear bands and of deformation-induced phase transformation from the austenite to the α‘-martensite are described. A 2-D boundary element method is extended regarding the description of elastic anisotropic properties and the calculation of spatial deformation. Solving the model by using the boundary element method allows simulating the cyclic plastic deformation within two-dimensional microstructures. In extended studies, the effect of a predeformed condition and of a moderate increase of temperature is also considered. Simulation results are directly compared to the observed deformation evolution on real fatigue specimen surfaces and, in addition, a comparison is carried out on the basis of the resonant behaviour of fatigue specimens and of modelled microstructures. Good accordance of results confirms the model assumptions and thereby provides a more profound understanding of the VHCF deformation behaviour of both austenitic stainless steels

Bronchopulmonary dysplasia - an overview about pathophysiologic concepts

Neonatal chronic lung disease in the preterm infant, i.e. bronchopulmonary dysplasia (BPD) is characterized by impaired pulmonary development with its effects persisting into adulthood. Triggered in the immature lung by infectious complications, oxygen toxicity and the impact of mechanical ventilation, a sustained inflammatory response, extensive remodeling of the extracellular matrix, increased apoptosis as well as altered growth factor signaling characterize the disease. The current review focuses on selected pathophysiologic processes and their interplay in disease development. Furthermore, the potential of both, acute and long-term changes to the pulmonary scaffold and the cellular interface in concert with dysregulated growth factor signaling to affect aging and repair processes in the adult lung is discussed

Composite spheres made of bioengineered spider silk and iron oxide nanoparticles for theranostics applications

Bioengineered spider silk is a biomaterial that has exquisite mechanical properties, biocompatibility, and biodegradability. Iron oxide nanoparticles can be applied for the detection and analysis of biomolecules, target drug delivery, as MRI contrast agents and as therapeutic agents for hyperthermia-based cancer treatments. In this study, we investigated three bioengineered silks, MS1, MS2 and EMS2, and their potential to form a composite material with magnetic iron oxide nanoparticles (IONPs). The presence of IONPs did not impede the self-assembly properties of MS1, MS2, and EMS2 silks, and spheres formed. The EMS2 spheres had the highest content of IONPs, and the presence of magnetite IONPs in these carriers was confirmed by several methods such as SEM, EDXS, SQUID, MIP-OES and zeta potential measurement. The interaction of EMS2 and IONPs did not modify the superparamagnetic properties of the IONPs, but it influenced the secondary structure of the spheres. The composite particles exhibited a more than two-fold higher loading efficiency for doxorubicin than the plain EMS2 spheres. For both the EMS2 and EMS2/IONP spheres, the drug revealed a pH-dependent release profile with advantageous kinetics for carriers made of the composite material. The composite spheres can be potentially applied for a combined cancer treatment via hyperthermia and drug delivery