Anisotropic Creep Behavior of a Unidirectional All-Oxide CMC

Abstract

This paper is intended to give an overview of the creep behavior of unidirectional porous all-oxide CMC including experimental results as well as numerical simulations. The creep behavior was investigated by means of creep tests proving a tension- compression asymmetry. For compression creep, stress and temperature dependencies were determined and described by power-law creep equations. Activation energy was similar for all fiber orientations whereas the stress exponent differed with respect to the loading direction. Thus, for modeling the creep behavior of CMC lamina anisotropic creep must be taken into account. Within commercial finite element software implemented anisotropic creep laws are rare. The anisotropic approach according to Hill was tested for compression creep with regard to the applicability and limitations for CMCs. Since the Hill-approach did not capture the experimental results sufficiently, compression creep was further investigated by simulations on a microscopic scale via unit cells. Thereby the effect of different creep parameters for fibers and matrix and the resulting lamina’s deformation rate could be investigated. It became apparent that additionally compaction of the porous matrix has to be included in the numerical description.