Chemomechanische Modellierung der Wärmebehandlung von Stählen mit der Phasenfeldmethode

Die Entwicklung hochfester Stähle kann mithilfe numerischer Verfahren beschleunigt werden. Insbesondere die Phasenfeldmethode hat sich als mächtiges Werkzeug etabliert, um die Mikrostrukturentwicklung auf mesoskopischer Längenskala zu beschreiben. In der vorliegenden Arbeit werden Multiphasenfeldmodelle vorgestellt, um die Gefügeentwicklung während der Wärmebehandlung von Stahl numerisch abzubilden, was im weiteren Verlauf Rückschlüsse auf das Materialverhalten unter mechanischer Belastung ermöglicht. Dabei stehen die Phasenumwandlungen im Fokus, bei denen elastische treibende Kräfte maßgeblich zur Mikrostrukturentwicklung beitragen. Als ein wesentlicher Teil dessen wird ein neues Multiphasenfelmodell zu Simulation der martensitischen Umwandlung entwickelt, das elastische treibende Kräfte verwendet, die auf den mechanischen Sprungbedingungen basieren. Die beim Abschrecken einer ferritischen-austenitischen Mikrostruktur auftretende martensitische Umwandlung wird mithilfe elastischer und elastoplastischer Simulationen untersucht und der resultierende Materialzustand analysiert. Es werden Methoden vorgestellt, um die Energielandschaft zu quantifizieren, die sich nach dem Wachstum einer bainitischen Untereinheit ausbildet, um Aussagen über das Nukleationsverhalten nachfolgender Untereinheiten zu treffen. Zudem wird ein Modell für das Wachstum von Widmanstätten-Ferrit vorgestellt, bei dem die nadelartige Struktur ein Resultat anisotroper Eigendehnungen darstellt. Es wird festgestellt, dass zwei Widmanstätten-Nadeln, die in einem gewissen Abstand zueinander wachsen, über das Spannungsfeld interagieren, wodurch die Morphologie beeinflusst wird. Darüber hinaus wird am Beispiel der Wärmebehandlung von Dualphasenstahl eine digitale Prozesskette aufgebaut, die es ermöglicht, die Auswirkungen einzelner Prozessparameter auf nachfolgende Prozessschritte zu berücksichtigen

Influence of stress-free transformation strain on the autocatalytic growth of bainite: A multiphase-field analysis

Analytical treatments, formulated to predict the rate of the bainite transformation, define autocatalysis as the growth of the subunits at the bainite-austenite interface. Furthermore, the role of the stress-free transformation strain is often translated to a thermodynamic criterion that needs to be fulfilled for the growth of the subunits. In the present work, an elastic phase-field model, which elegantly recovers the sharp-interface relations, is employed to comprehensively explicate the effect of the elastic energy on the evolution of the subunits. The primary finding of the current analysis is that the role of eigenstrains in the bainite transformation is apparently complicated to be directly quantified as the thermodynamic constraint. It is realized that the inhomogeneous stress state, induced by the growth of the primary subunit, renders a spatially dependent ill- and well-favored condition for the growth of the secondary subunits. A favorability contour, which encloses the sections that facilitate the elastically preferred growth, is postulated based on the elastic interaction. Through the numerical analyses, the enhanced growth of the subunits within the favorability-contour is verified. Current investigations show that the morphology and size of the elastically preferred region respectively changes and increases with the progressive growth of the subunits

Phase-Field Model for the Simulation of Brittle-Anisotropic and Ductile Crack Propagation in Composite Materials

In this work, a small-strain phase-field model is presented, which is able to predict crack propagation in systems with anisotropic brittle and ductile constituents. To model the anisotropic brittle crack propagation, an anisotropic critical energy release rate is used. The brittle constituents behave linear-elastically in a transversely isotropic manner. Ductile crack growth is realised by a special crack degradation function, depending on the accumulated plastic strain, which is calculated by following the J2-plasticity theory. The mechanical jump conditions are applied in solid-solid phase transition regions. The influence of the relevant model parameters on a crack propagating through a planar brittle-ductile interface, and furthermore a crack developing in a domain with a single anisotropic brittle ellipsoid, embedded in a ductile matrix, is investigated. We demonstrate that important properties concerning the mechanical behaviour of grey cast iron, such as the favoured growth of cracks along the graphite lamellae and the tension–compression load asymmetry of the stress–strain response, are covered by the model. The behaviour is analysed on the basis of a simulation domain consisting of three differently oriented elliptical inclusions, embedded in a ductile matrix, which is subjected to tensile and compressive load. The material parameters used correspond to graphite lamellae and pearlite

KadiStudio: FAIR Modelling of Scientific Research Processes

FAIR handling of scientific data plays a significant role in current efforts towards a more sustainable research culture and serves as a prerequisite for the fourth scientific paradigm, that is, data-driven research. To enforce the FAIR principles by ensuring the reproducibility of scientific data and tracking their provenance comprehensibly, the FAIR modelling of research processes in form of automatable workflows is necessary. By providing reusable procedures containing expert knowledge, such workflows contribute decisively to the quality and the acceleration of scientific research. In this work, the requirements for a system to be capable of modelling FAIR workflows are defined and a generic concept for modelling research processes as workflows is developed. For this, research processes are iteratively divided into impartible subprocesses at different detail levels using the input-process-output model. The concrete software implementation of the identified, universally applicable concept is finally presented in form of the workflow editor KadiStudio of the Karlsruhe Data Infrastructure for Materials Science (Kadi4Mat)

Managing FAIR Tribological Data Using Kadi4Mat

The ever-increasing amount of data generated from experiments and simulations in engineering sciences is relying more and more on data science applications to generate new knowledge. Comprehensive metadata descriptions and a suitable research data infrastructure are essential prerequisites for these tasks. Experimental tribology, in particular, presents some unique challenges in this regard due to the interdisciplinary nature of the field and the lack of existing standards. In this work, we demonstrate the versatility of the open source research data infrastructure Kadi4Mat by managing and producing FAIR tribological data. As a showcase example, a tribological experiment is conducted by an experimental group with a focus on comprehensiveness. The result is a FAIR data package containing all produced data as well as machine- and user-readable metadata. The close collaboration between tribologists and software developers shows a practical bottom-up approach and how such infrastructures are an essential part of our FAIR digital future

Kadi4Mat : A Research Data Infrastructure for Materials Science

The concepts and current developments of a research data infrastructure for materials science are presented, extending and combining the features of an electronic lab notebook and a repository. The objective of this infrastructure is to incorporate the possibility of structured data storage and data exchange with documented and reproducible data analysis and visualization, which finally leads to the publication of the data. This way, researchers can be supported throughout the entire research process. The software is being developed as a web-based and desktop-based system, offering both a graphical user interface and a programmatic interface. The focus of the development is on the integration of technologies and systems based on both established as well as new concepts. Due to the heterogeneous nature of materials science data, the current features are kept mostly generic, and the structuring of the data is largely left to the users. As a result, an extension of the research data infrastructure to other disciplines is possible in the future. The source code of the project is publicly available under a permissive Apache 2.0 license