3 dagen geleden - Universiteit Utrecht (UU) - Utrecht
Utrecht University's Faculty of Science is looking for a 38 PhD candidates in the field of sustainable energy conversion . Are you interested? Then please read…
2 PhD Student positions Micromechanical modelling and experimental analysis of
advanced high strength steels (AHHS).
Two PhD vacancies are available in the Mechanics of Materials group led by Prof. Marc Geers (www.tue.nl/mechmat ...
Digitally Enhanced New Steel Product Development (DENS) program
Significant progress has been made in the past decades in the development of advanced models that describe the behavior of steel during processing and subsequent applications. However, the quantitative application of through process models in new steel product development still lacks predictivity and therefore faces a number of scientific challenges. In modern steel grades, parameters of the steel production process have a significant influence on the final material properties. Furthermore, the trend towards complex multi-phase microstructures requires very sophisticated models to describe their mechanical properties in a predictive manner. Accordingly, a through process model (from process to engineering properties) relies on a series of models at different scales that strongly interact with each other. The main scientific challenge addressed in this program is to integrate state-of-the-art models in a single through process model framework that can be applied in practice for new steel product development. To this aim, a Digitally Enhanced New Steel Product Development (DENS) program has been initiated as a collaboration between Tata Steel Europe, Materials innovation institute (M2i), Max Planck Institute for Iron Research and academic partners TU Delft, UTwente and TU Eindhoven. In order to enhance this collaboration and ensure the maximum efficiency in knowledge transfer, parts of the projects will be executed at the main industrial partner (Tata Steel).
PhD project 1: Microstructural aspects of damage and fracture for edge ductility
A key engineering problem that is not fully resolved nor understood is the poor edge ductility of advanced high strength steels (AHSS). Edge ductility refers to the amount of deformation a cut (e.g. sheared, punched) edge can endure before fracturing. On the one hand, an improved measure characterising this behaviour is required, applicable by customers in their process simulations in order to prevent problems in the process design stage. On the other hand, there is a need for improving the edge ductility performance itself. This project mainly aims to address the latter need by developing a statistical representative volume element (RVE) simulation based methodology to systematically study the damage behaviour of AHSS microstructures - in particular near edges which may contain defects and processing-induced gradients in the microstructure - in order to be able to predict key elements governing the fracture behaviour. The starting point will be an RVE model with a planar free surface (cut edge) and a two-phase microstructure (cf. dual phase steel). This baseline cut-edge model will then be extended along two paths, (i) a systematic study of the role of the phase distribution, phase contrast, microstructural gradients, and surface defects on the nucleation and propagation of damage from the (proximity of the) cut edge, and (ii) application of the methodology to realistic microstructures that are obtained from detailed experimental metallurgical characterization. Based on the understanding gained in these case studies, macroscopic damage criteria will also be formulated, which will be validated against in-situ SEM hole expansion tests.
PhD project 2: Multi-phase interfacial models for multi-phase steels
Interfaces are key ingredients for the engineering properties of AHSS, and in particular for formability, strength and edge ductility. Interfaces in AHSS are generally complex, multi-phase in nature, with a great intrinsic variability. Interfaces either separate different phases, grains or other units of the same phase (e.g. martensite blocks). These interfaces are formed throughout the whole material processing chain, whereby specific processing routes define specific physical, chemical and morphological features of the interfaces, e.g. distribution of carbon and alloying elements at and in the vicinity of the interface, possibly presenting non-negligible gradients, precipitates of various chemical compositions, sizes and shapes etc. These features will determine the strength and deformation mechanisms of the interfaces as well as of the surrounding phases. Interfacial properties therefore govern to a large extent the engineering properties of AHSS, in particular all deformation-driven properties (formability limits) and fracture (strength) and damage. A realistic through process modelling approach would therefore be incomplete without the incorporation of physically based models properly describing the mechanical behaviour of interfaces at the scale of the multi-phase microstructure of the AHSS.
The goal of this project consists in the development and numerical implementation of a generic class of physically based interface models, based on a two-scale representation of the multi-phase interfacial morphology and geometry, which enables the characterization of interfaces in AHSS. The generic model should incorporate fine scale chemical, physical and morphological features of the interfaces and the resulting elementary deformation mechanisms through an appropriate homogenization technique. The fine-scale parameters of the model need to be identified experimentally. To this end, a dedicated fine scale experimental program should be setup and executed within the project.
Research group Mechanics of Materials
The scientific research activities in the Mechanics of Materials group (www.tue.nl/mechmat) concentrate on the experimental analysis, theoretical understanding and predictive modelling of a range of phenomena in engineering materials at different length scales, which emerge from the physics and the mechanics of the underlying multi-phase microstructure. The main challenge is the accurate prediction of the mechanical properties of materials with complex microstructures. This focus is closely related to intrinsic material properties (multi-scale plasticity in advanced steels, interfacial properties in laminates, thermo-mechanical fatigue in cylinder heads, etc.), the application of materials in microsystems (i.e. multi-phase functional materials, MEMS, stretchable electronics, etc.) and various systems and processes involving mechanically complex interfaces (e.g. in Systems in Package, flexible displays, electronic textiles). The aim is a substantial increase of the predictive power of state-of-the-art models, thereby enabling the optimization of critical, high-tech products and manufacturing processes in direct relation to the complex loading history of the underlying materials and joining interfaces. A systematic and integrated numerical-experimental approach is generally adopted for this purpose.
The group has a unique research infrastructure, both from an experimental and computational perspective. The Multi-Scale Lab allows for quantitative in-situ microscopic measurements during deformation and mechanical characterization within the range of 10-9-10-2 m. In terms of computer facilities, several multiprocessor-multi-core computer clusters are available, as well as a broad spectrum of in-house and commercial software.
Talented, enthusiastic candidates with excellent analytical and communication skills and high grades are encouraged to apply. A MSc degree (or equivalent) in Mechanical Engineering, Applied Mathematics, Physics or a related discipline is required, as well as a strong background in continuum mechanics and computational methods. Experience in micromechanics, non-linear material modelling, finite element techniques and experimental microstructural material characterization are of benefit.