Modellierung der Gefüge-Eigenschafts-Korrelation bei Dualphasenstahl

Dualphasenstahl zeichnet sich durch eine für Strukturwerkstoffe wünschenswerte Kombination aus hoher Dehnbarkeit bei gleichzeitig hoher Festigkeit aus. Die Ursache der Eigenschaften liegt in seinem Gefüge bzw. seiner Mikrostruktur, bestehend aus weichem Ferrit und hartem Martensit, begründet. Die vorliegende Arbeit befasst sich mit der Modellierung dieser Gefüge-Eigenschafts-Korrelation durch numerische Simulationen auf Basis dreidimensionaler Mikrostrukturen. Die Betrachtung umfasst alle zur Modellierung relevanten Schritte, von der experimentellen Untersuchung der Materialeigenschaften über die numerische Umsetzung der Materialtheorie bis hin zur Simulation der mechanischen Eigenschaften. Ein Verfahren zur Bestimmung der Größe des repräsentativen Volumenelements wird dazu ebenso entwickelt wie eine praktikable Methode zur Steigerung der numerischen Effizienz. Die Erzeugung virtueller Dualphasenstahl-Mikrostrukturen ist ein zusätzlicher Schwerpunkt der Arbeit. Zu diesem Zweck wird ein Modell zur numerischen Erstellung virtueller Mikrostrukturen entsprechend vorgegebener Geometrieparameter entwickelt und validiert. Ziel des Vorgehens ist, nicht nur bekannte Stähle in der Simulation zu untersuchen, sondern auch die Möglichkeit zur Evaluation neuer Mikrostrukturen zu schaffen.Dual-phase steel is characterized by a combination of high ductility and high strength that is preferable for structural materials. This is due to its microstructure consisting of soft ferrite and hard martensite. The present work deals with the modelling of microstructure-property correlation by numerical simulations on the basis of three-dimensional microstructures. The analysis includes all steps relevant for modelling, from the experimental investigation of material properties and the numerical implementation of the material theory up to the simulation of the mechanical properties. A method for the determination of the size of the representative volume element will be developed as well as a straightforward method to increase numerical efficiency. The generation of virtual dual-phase steel microstructures is a further focus of the work. For this purpose a model for the numerical construction of virtual microstructures according to given geometry parameters is developed and validated. The aim of the procedure is to not only investigate known steels in the simulation, but also to create the possibility of evaluating new microstructures

Numerical simulation of dual-phase steel based on real and virtual three-dimensional microstructures

Dual-phase steel shows a strong connection between its microstructure and its mechanical properties. This structure–property correlation is caused by the composition of the microstructure of a soft ferritic matrix with embedded hard martensite areas, leading to a simultaneous increase in strength and ductility. As a result, dual-phase steels are widely used especially for strength-relevant and energy-absorbing sheet metal structures. However, their use as heavy plate steel is also desirable. Therefore, a better understanding of the structure–property correlation is of great interest. Microstructure-based simulation is essential for a realistic simulation of the mechanical properties of dual-phase steel. This paper describes the entire process route of such a simulation, from the extraction of the microstructure by 3D tomography and the determination of the properties of the individual phases by nanoindentation, to the implementation of a simulation model and its validation by experiments. In addition to simulations based on real microstructures, simulations based on virtual microstructures are also of great importance. Thus, a model for the generation of virtual microstructures is presented, allowing for the same statistical properties as real microstructures. With the help of these structures and the aforementioned simulation model, it is then possible to predict the mechanical properties of a dual-phase steel, whose three-dimensional (3D) microstructure is not yet known with high accuracy. This will enable future investigations of new dual-phase steel microstructures within a virtual laboratory even before their production

RVE-size Estimation and Efficient Microstructure-based Simulation of Dual-Phase Steel

Dual-phase steel shows a pronounced structure-property correlation, caused by its internal structure consisting of asoft ferrite matrix and embedded hard martensite regions. Due to its high strength combined with high ductility, dual-phasesteel is particularly suitable for energy-absorbing and strength-relevant sheet metal applications, but its use as heavy plate isalso desirable. Due to the complex microstructure, microstructure-based simulation is essential for a realistic simulation of themechanical properties of dual-phase steel. This paper describes two important points for the microstructure-based simulation ofdual-phase steel. First a method for the straightforward experimental estimation of the RVE size based on hardness measurementsprior to tomography preparation is presented and evaluated. Secondly, a method for the efficient meshing of these microstructures,based on material definition at the integration points of a finite element model, is developed