TY  - THES
A1  - Kurukuri, Srihari
T1  - Homogenization of Damaged Concrete Mesostructures using Representative Volume Elements - Implementation and Application to SLang
N2  - This master thesis explores an important and under-researched topic on the so-called bridging of length scales (from >meso< to >macro<), with the concept of homogenization in which the careful characterization of mechanical response requires that the developed material model >bridge< the representations of events that occur at two different scales. The underlying objective here is to efficiently incorporate material length scales in the classical continuum plasticity/damage theories through the concept of homogenization theory. The present thesis is devoted to computational modeling of heterogeneous materials, primarily to matrix-inclusion type of materials. Considerations are focused predominantly on the elastic and damage behavior as a response to quasistatic mechanical loading. Mainly this thesis focuses to elaborate a sound numerical homogenization model which accounts for the prediction of overall properties with the application of different types of boundary conditions namely: periodic, homogeneous and mixed type of boundary conditions over two-dimensional periodic and non-periodic RVEs and three-dimensional non-periodic RVEs. Identification of the governing mechanisms and assessing their effect on the material behavior leads one step further. Bringing together this knowledge with service requirements allows for functional oriented materials design. First, this thesis gives attention on providing the theoretical basic mechanisms involved in homogenization techniques and a survey will be made on existing analytical methods available in literature. Second, the proposed frameworks are implemented in the well known finite element software programs ANSYS and SLang. Simple and efficient algorithms in FORTRAN are developed for automated microstructure generation using RSA algorithm in order to perform a systematic numerical testing of microstructures of composites. Algorithms are developed to generate constraint equations in periodic boundary conditions and different displacements applied spatially over the boundaries of the RVE in homogeneous boundary conditions. Finally, nonlinear simulations are performed at mesolevel, by considering continuum scalar damage behavior of matrix material with the linear elastic behavior of aggregates with the assumption of rigid bond between constituents.
KW  - Schadensmechanik
KW  - Finite-Elemente-Methode
KW  - Beton
KW  - Homogenisierung
KW  - Repräsentative Volumen Elemente
KW  - Mesoskala
KW  - Homogenization
KW  - Representative Volume Elements
KW  - Mesoscale
Y1  - 2005
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20111215-6670
N1  - Der Volltext-Zugang wurde im Zusammenhang mit der Klärung urheberrechtlicher Fragen mit sofortiger Wirkung gesperrt.
ER  - 
TY  - THES
A1  - Almasi, Ashkan
T1  - Stochastic Analysis of Interfacial Effects on the Polymeric Nanocomposites
N2  - The polymeric clay nanocomposites are a new class of materials of which recently have become the centre of attention due to their superior mechanical and physical properties. Several studies have been performed on the mechanical characterisation of these nanocomposites; however most of those studies have neglected the effect of the interfacial region between the clays and the matrix despite of its significant influence on the mechanical performance of the nanocomposites.

There are different analytical methods to calculate the overall elastic material properties of the composites. In this study we use the Mori-Tanaka method to determine the overall stiffness of the composites for simple inclusion geometries of cylinder and sphere. Furthermore, the effect of interphase layer on the overall properties of composites is calculated. Here, we intend to get ounds for the effective mechanical properties to compare with the analytical results. Hence, we use linear displacement boundary conditions (LD) and uniform traction boundary conditions (UT) accordingly. Finally, the analytical results are compared with numerical results and they are in a good agreement.

The next focus of this dissertation is a computational approach with a hierarchical multiscale method on the mesoscopic level. In other words, in this study we use the stochastic analysis and computational homogenization method to analyse the effect of thickness and stiffness of the interfacial region on the overall elastic properties of the clay/epoxy nanocomposites. The results show that the increase in interphase thickness, reduces the stiffness of the clay/epoxy naocomposites and this decrease becomes significant in higher clay contents. The results of the sensitivity analysis prove that the stiffness of the interphase layer has more significant effect on the final stiffness of nanocomposites. We also validate the results with the available experimental results from the literature which show good agreement.
KW  - Homogenization
KW  - Multiscale modeling
KW  - Nanocomposite materials
KW  - Stochastic analysis
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20150709-24339
ER  -