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J.L. Vázquez Lopez:
"Study of Microfields in the Reinforcement Phase of Two-Phase Composites";
Betreuer/in(nen): H. J. Böhm; Institut für Leichtbau und Struktur-Biomechanik, TU Wien; Universidade de Vigo, 2012.

Over the last years, the interest in fiber reinforced composites by engineers and researches has been growing due to their applications in many industry fields. Many studies have been carried out on the macroscopic behavior of these composites, but, the microscopic behavior is a recent field of study. Hence, there are few reference data for it and it is necessary to use the macroscopic behavior for checking the results.

Statistical volume element (SVE) were used in order to study the behavior of these composites. These volume elements should be statistically random for extrapolating the results to the real material. A periodic approach was used to solve the problem. Under these assumptions, the analytical and numerical methods of continuum micromechanics can be brought to bear on the problem, the emphasis being put on Finite-Element-based unit cell methods in the present case.

An automatic process was created to generate arrangements of fibers embedded in the matrix and study the stress and strain microfields in the reinforcing phase. Using random arrangements of fibers, the method creates the mesh of the unit cell, analyses it and postprocesses the results for studying the microfields obtained. Four different software were used within this work: Arigen, Hypermesh, ABAQUS and Matlab.

The predictions of the FEM-based periodic study show that the microscopic behavior is strongly influenced by the position of the fibers in the arrangements. Hence, probably the volume elements used are not statistically homogeneous or the number of fibers covered is not sufficient.

However, good agreement with the analytical three-point estimates was achieved in the macroscopic behavior. Thus, the modeling work is verified. In summary, it can be concluded that reasonable macroscopic description does not imply adequate resolution in terms of microfields.