Papers by Thomas Hochrainer
Konstruktion
ABSTRACT Moderne Stahlsorten erreichen heute hohe Festigkeiten und zum Teil überragende Duktilitä... more ABSTRACT Moderne Stahlsorten erreichen heute hohe Festigkeiten und zum Teil überragende Duktilitäten, die in dieser Kombination noch vor wenigen Jahrzehnten kaum vorstellbar waren. Diese höher- und höchstfesten Stähle bieten zum Beispiel im Automobilbau enormes Leichtbaupotential, da sie mit deutlich weniger Material die gleiche Funktionalität für die Karosseriestabilität und die Energieaufnahme im Crashfall bieten.
Scripta Materialia, 2006
We outline a method for representing the dynamics of interacting curved dislocations in a continu... more We outline a method for representing the dynamics of interacting curved dislocations in a continuum framework. Starting from a pseudo-continuum representation of the kinematics of discrete lines, we demonstrate how this can be used to derive a set of coupled equations for the densities of screw and edge components. We discuss how long- and short-range dislocation interactions can be treated within this framework, and apply the resulting equations to a simple model of channel slip.
Steel Research International, 2008
The high work hardening rate and ductility of high manganese austenitic steels is mainly attribut... more The high work hardening rate and ductility of high manganese austenitic steels is mainly attributed to the strong twinning induced plasticity (TWIP) effect found in the material. With a low stacking fault energy, mechanical twinning acts as a competitive mechanism to the more common dislocation glide. In order to understand the micromechanical behaviour of such steels, especially with respect to texture and anisotropy, constitutive models for twinning which account for the TWIP effect both in orientation changes and plastic behaviour are required. Using a self-consistent texture model, we evaluate two twin modelling approaches in view of prediction of crystallographic texture. Tension experiments were carried out on a rolled TWIP sheet and the textures compared with the simulated results. The evolution of twin volume fractions from the two models is also evaluated.
Journal of Materials Research, 2011
Miniaturization of components and devices calls for an increased effort on physically motivated c... more Miniaturization of components and devices calls for an increased effort on physically motivated continuum theories, which can predict size-dependent plasticity by accounting for length scales associated with the dislocation microstructure. An important recent development has been the formulation of a Continuum Dislocation Dynamics theory (CDD) that provides a kinematically consistent continuum description of the dynamics of curved dislocation systems [T. Hochrainer, et al., Philos. Mag. 87, 1261]. In this work, we present a brief overview of dislocation-based continuum plasticity models. We illustrate the implementation of CDD by a numerical example, bending of a thin film, and compare with results obtained by three-dimensional discrete dislocation dynamics (DDD) simulation.
Machining Science and Technology, 2007
... DOI: 10.1080/10910340701697086 M. Weber a * , T. Hochrainer a , P. Gumbsch a , H. Autenrieth ... more ... DOI: 10.1080/10910340701697086 M. Weber a * , T. Hochrainer a , P. Gumbsch a , H. Autenrieth b , L ... The thermal part of the yield stress at zero Kelvin is denoted as σ 0 , the free activation enthalpy necessary to overcome the decisive obstacles is ΔG 0 . The critical strain rate is ...
Current Opinion in Solid State and Materials Science, 2014
We present an assessment of the diffuse interface models of void growth in irradiated materials. ... more We present an assessment of the diffuse interface models of void growth in irradiated materials. Since the void surface is inherently sharp, diffuse interface models for void growth must be constructed in a way to make them consistent with the sharp-interface description of the problem. Therefore, we first present the sharp-interface description of the void growth problem and deduce the equation of motion for the void surface. We also compare two existing phase field models to determine which one corresponds to the sharp-interface analysis. It was shown that a phase field model of type C, which couples Cahn-Hilliard and Allen-Cahn equations, is the most adequate since this type of model can take into account the reaction of point defects at the void surface via an Allen-Cahn equation. Fixing the model parameters in the diffuse interface model is discussed from the points of view of asymptotic matching. Sample results for void growth in a single component metal based on sharp and diffuse interface models are presented. Finally, a perspective on the use of atomistic modeling in both constitutive and nucleation modeling within the phase field approach for void formation in irradiated materials is presented.
Computational Materials Science, 2014
ABSTRACT We perform asymptotic analysis and uncertainty quantification of a phase field model for... more ABSTRACT We perform asymptotic analysis and uncertainty quantification of a phase field model for void formation and evolution in materials subject to irradiation. The parameters of the phase field model are obtained in terms of the underlying material specific quantities by matching the sharp interface limit of the phase field model with the corresponding sharp interface theory for void growth. To evaluate the sensitivity of phase field simulations to uncertainties in input parameters we quantify the predictions using the stochastic collocation method. Uncertainties arising from material parameters are investigated based on available experimental and atomic scale data. The results of our analysis suggest that the uncertainty in the formation and migration energies of vacancies are found to have a strong influence on the void volume fraction (or porosity). In contrast, the uncertainty resulting from the void surface energy has minimal affect. The analysis also shows that the model is consistent in the sense that its predictions do not drastically change as a result of small variations of the model input parameters.
Numerical studies of dislocation pair correlations have played a central role in deriving a conti... more Numerical studies of dislocation pair correlations have played a central role in deriving a continuum theory from the equations of motion of 2D dislocation systems in a mathematically rigorous way. As part of an effort to extend this theory into the full 3D dislocation problem, 3D dislocation pair correlations were studied with discrete dislocation dynamics simulation. As a first approximation, dislocations were modeled as uncharged curves in space (their Burgers vectors were disregarded). An inverse square decay with distance was found to describe the numerically obtained pair correlations of the studied curve system.
In the context of recent proposals to use statistical mechanics methods for building a continuum ... more In the context of recent proposals to use statistical mechanics methods for building a continuum theory of dislocation lines, mathematical modelling has to answer three essential questions: (i) What is the mathematical object representing the single dislocation as basic "particle"? (ii) What is the law of motion of this object? (iii) What is the mathematical nature of a dislocation density built of such objects? If a mathematically rigorous answer to these questions can be given, one may expect to derive the kinetic evolution equation for such a density solely from its definition and a conservation law. We present a method for deriving classical and non-classical dislocation density measures as well as their evolution equations from the properties of single dislocations, using the close connection between differential forms and geometrical objects such as dislocation lines. Several dislocation density measures are compared in view of their ability to represent vital aspects of the statics and dynamics of discrete dislocation configurations. A dislocation density measure which considers line directions and curvatures is defined as differential form, and it is shown that its evolution correctly represents the essential features of dislocation motion.
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Papers by Thomas Hochrainer