Thermal and mechanical properties of the ceramic matrix composites

Typically fiber reinforced ceramic matrix composite (CMCs) are widely used as thermal structural materials in aeronautic and astronautic fields. Thermal and mechanical properties are of significance for high temperature used ceramic matrix composites. Thermal stress induced in a body when some or all of its parts are not free to expand or contract in response to changes in temperature. Thermal stress produced in a body as a result of a nonuniform distribution of temperature in different parts of the body and some restriction on the possibility of thermal expansion or contraction imposed by adjacent parts of the body or by other bodies surrounding the body in question. An example of thermal stresses is the tensile stresses produced in a wire stretched between fixed supports as the wire is cooled. Thermal stresses can cause the failure of aircraft components, buildings, and structural members. Expansion joints and other means, including gaps between successive lengths of rails, gaps between the blocks of a dam, and rollers on bridge supports, are used to prevent such failures. The motivation to investigate thermal and mechanical properties was to understand the scientific and engineering problems associated with thermal stress and strain of high temperature materials in possible applications. In the servicing environment, CMCs are usually subjected to thermal cycling in the load or displacement constraints, heat treatment in the ultrahigh temperatures, and oxidation in the harsh atmosphere. Therefore, thermal cycling behaviors in the constraints, heat treatment properties, mechanical hysteresis behaviors, strengthening and toughening behaviors, and high temperature oxidation behaviors of the ceramic matrix composites will be discussed and the associated mechanisms will be analyzed in this chapter.