ABSTRACT of the Habilitation Thesis
The present contribution describes a series of micromechanical studies of the thermomechanical behavior of unidirectional metal matrix composites (MMCs). Two-dimensional unit cell models are used, on the one hand, to compute the effective macroscopic properties of the composites from the material behavior of fibers and matrix, and, on the other hand, to describe the microscale stress and strain distributions within the MMC. The unit cells are analyzed via the Finite Element Method.
The focus of the work lies on describing the thermoelastoplastic behavior of a composite that consists of unidirectional boron fibers embedded in a matrix of aluminium 6061-0. Axial, transverse and thermal loads are considered. Of special interest are the influence of microscale residual stresses that are generated both during the production process of the MMC and upon surpassing the yield limit during loading as well as shakedown in the matrix under thermomechanical loading.
The influences of different fiber arrangements on the effective material properties of the MMC and on the microscale stresses and strains are studied via appropriate unit cells at a given fiber volume fraction. A marked influence of the microgeometry on the macroscopic behavior under transverse mechanical loading and on the microfields under thermal and transverse loading are found. The consequences of such phase arrangement effects with respect to failure relevant parameters in the matrix and to microstresses in the fiber-matrix interface are discussed.
The final part of the work studies the thermomechanical properties of a composite consisting of pure aluminium and ceramic fibers. It is shown that the effective axial thermal expansion of continuously reinforced unidirectional composites is dominated by the fibers once the matrix is fully yielded. On this basis, a combination of experiments and of micromechanical simulations is used for determining the coefficient of thermal expansion of the fibers, which is difficult to measure, in dependence on temperature.