In-plane mechanical properties of an all-oxide ceramic composite

The present article examines the in-plane tensile properties of a two-dimensional (2D) all-oxide ceramic composite. The distinguishing characteristics of the material include fine-scale porosity within the matrix: and the absence of a fiber coating. The anisotropy in the elastic-plastic properties has been studied through tension tests in the axial (fiber) direction and at 45 degrees to the fiber axes, both in the presence and the absence of holes or notches. The notch sensitivity in the axial direction is comparable to that of conventional dense-matrix, weak-interface composites, demonstrating the effectiveness of the porous matrix in enabling crack deflection and damage tolerance. Furthermore, the notch sensitivity is rationalized using models that account for the effects of inelastic straining on the local stress distributions around notches and holes, coupled with a scale-dependent failure criterion. In the off-axis orientation, the tensile strength is dictated by a plastic instability, analogous to necking in metals. Following instability, deformation continues within a diffuse localized band, with a length comparable to the specimen width. Similar deformation and fracture characteristics are obtained both with and without holes. The off-axis properties are discussed in terms of the comminution and rearrangement of matrix particles during straining.