Ceramic composites: Experimental and analytical study of silicon carbide/silicon nitride composites.

The mechanical behavior of fiber-reinforced SiC/Si$\sb3$N$\sb4$ ceramic matrix composites has been analytically and experimentally studied. Experimental approaches for the mechanical testing of ceramics composite materials is discussed. Approaches used for the gripping of single fibers were also investigated; this investigation included the influence of misalignment on fiber strength. Both aligned and misaligned single fiber testing was conducted. Also the stiffness properties of the fiber was measured and the bending strength of the fiber was determined. It was shown that the bending strength of the fiber is extremely high compared to the tensile strength. The monotonic tensile testing of SiC/Si$\sb3$N$\sb4$ composite results a discontinues stress/strain behavior. The tensile fatigue testing which was conducted at 10 Hz cyclic loading showed a gradual failure of the composite. Also the hysteresis and the ratcheting were observed. The hysteresis behavior which was observed during the cyclic loading of SiC/Si$\sb3$N$\sb4$ composites was analytically modeled. It was shown that the interfacial friction forces which are produced along a debonded fiber/matrix interface give rise to stress-strain hysterises. The influence of the axial and radial residual stresses to the interfacial on debonding was explored. A new model for interfacial failure in fiber-reinforced ceramic composites was developed. This model was used to analyze experimental approaches for determining interfacial shear, such as fiber pushout and pullout specimens produces a stress singularity in the fiber/matrix interface; under this residual loading, debonding can propagate along the interface. For a brittle material, the fiber/matrix interface can easily fail during the pullout test due to this stress singularity. It was shown that the debonded fiber may separate from matrix under tensile loading which results complete debonding. Because the fracture of the interface may produce a rough surface which gives a rise to a false bonding effect.PhDApplied SciencesMaterials scienceMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128753/2/9135626.pd