[Zurück]


Dissertationen (eigene und begutachtete):

R. Traxl:
"Continuum Micromechanics-Based Determination of Effective Properties of Elastoplastic Matrix-Inclusion Materials: Application within the Finite Element Analysis of Indentation and Impact Problems";
Betreuer/in(nen), Begutachter/in(nen): R. Lackner, H. J. Böhm; Institut für Konstruktion und Materialwissenschaften, Universität Innsbruck, 2016; Rigorosum: 15.09.2016.



Kurzfassung englisch:
Material inhomogeneities such as pores and particles are common constituents of natural materials (e.g., wood, bone, soil, etc.) as well as engineering materials (e.g., concrete, foam materials, different kinds of composites, etc.). In case of the latter, material inhomogeneities may be either provoked on purpose or aimed to be prevented in the production process in order to influence the effective material properties. In this context, knowledge of the potential effects of inhomogeneities is of crucial importance. Substantial experimental studies dedicated to this matter are indispensable - though, sometimes not sufficient for a purposeful development process of materials, as theoretical and computational
methods may provide useful additional information.

This thesis shall contribute to the state of knowledge on the influence of material inhomogeneities on the effective mechanical material properties using the method of continuum micromechanics on the one hand and numerical simulations (finite element method) on the other hand. The main focus is on the nonlinear behavior of material
constituents described in the framework of elastoplasticity. Accordingly, this thesis provides approaches for the advancement of continuum micromechanics in the context of nonlinear behavior. Respective numerical simulations of the loading of material samples (representative elementary volumes) serve as validation of the presented models and give additional insights. The subjects treated in specific are the following:
* First, a homogenization approach for the determination of an effective yield surface of a matrix-inclusion material is presented. It allows the consideration of empty pores, fluid-filled pores and rigid particles as inclusions and matrix materials whose domains of admissible stress states are defined by second-order yield surfaces comprising, e.g., Mises, Mises-Schleicher, Drucker-Prager and ellipsoidal yield surfaces.
* Subsequently, the influence of the inclusion shape is addressed. After presenting a semi-analytical methodology allowing the incorporation of arbitrary inclusion shapes into the framework of the aforementioned homogenization scheme, the effect of some selected morphologies is regarded more closely (spheroids, and tetrahedra
and octahedra with curved surfaces).
* In the third part, the post-yield behavior of elastoplastic matrix-inclusion materials is treated, including the effective flow rule as well as the effective hardening behavior. Three models addressing different problems are proposed: (i) for obtaining the effective post-yield behavior in case of strain-hardening matrix materials, (ii) for estimating the contribution of compaction to the effective hardening behavior (geometric hardening), and (iii) the post-yield behavior in case of quasi-brittle matrix material behavior.

The developments presented in the aforelisted three parts are then applied within the numerical analysis of indentation experiments and of porous materials subjected to impact loading. In both cases the significance of the involved material parameters is discussed.

Erstellt aus der Publikationsdatenbank der Technischen Universität Wien.