fiber regions, resulting in oxidation in oxidizing atmospheres, weakening the material. Increasing temperature, applied stress, and defect densities lead to greater creep deformation and earlier failure. A rule of mixtures may be applied to find the strain rate of the composite given the strain rates of the constituents. For particulates, a simple sum of the product of the cross-sectional area fraction and creep response of each constituent can determine the composite’s total creep response. For fibers, a sum of the constituents’ creep response divided by the cross-sectional area fraction determines the total creep response. Particulates: Fibers: where is the creep response and is the constituent cross sectional area fraction. Other mechanical properties In many CMC components the fibers are arranged as 2-dimensional (2D) stacked plain or satin weave fabrics. Thus the resulting material is anisotropic or, more specifically, orthotropic. A crack between the layers is not bridged by fibers. Therefore, the interlaminar shear strength (ILS) and the strength perpendicular to the 2D fiber orientation are low for these materials. Delamination can occur easily under certain mechanical loads. Three-dimensional fiber structures can improve this situation (see micrograph above). The compressive strengths shown in the table are lower than those of conventional ceramics, where values above 2000 MPa are common; this is a result of porosity. The composite structure allows high dynamical loads. In the so-called low-cycle-fatigue (LCF) or high-cycle-fatigue (HCF) tests the material experiences cyclic loads under tensile and compressive (LCF) or only tensile (HCF) load. The higher the initial stress the shorter the lifetime and the smaller the number of cycles to rupture. With an initial load of 80% of the strength, a SiC/SiC sample survived about 8 million cycles (see figure). The Poisson's ratio shows an anomaly when measured perpendicular to the plane of the fabric because interlaminar cracks increase the sample thickness. Thermal and electrical properties The thermal and electrical properties of the composite are a result of its constituents, namely fibers, matrix, and pores as well as their composition. The orientation of the fibers yields anisotropic data. Oxide CMCs are very good electrical insulators, and because of their high porosity, their thermal insulation is much better than that of conventional oxide ceramics. The use of carbon fibers increases the electrical conductivity, provided the fibers contact each other and the voltage source. The silicon carbide matrix is a good thermal conductor. Electrically, it is a semiconductor, and its