Ultra-High Temperature Properties of Advanced Carbon/Carbon Composites
(Development of Testing Equipment and the Influence of Thermal Shock on the Properties)

Advanced carbon fiber reinforced carbon (C/C) composites are one of the candidate materials for realizing a space plane in the 21st century. Research on C/C composites goes back almost two decades, but the influence of neither temperature nor heating/cooling rates on material properties has been fully made clear yet. In this paper, a developed material testing equipment is presented first. The main advantage of this equipment is the capability of quite fast heating and cooling rates by using high-frequency induction method. After verifying the temperature distribution of a specimen, experimental studies are performed for two types of non-oxidation-protected plain woven C/C composites whose heat treatment temperatures are 1600 and 3000 �� respectively. Obtained results are summarized as follows: (1) Serial data are obtained about the temperature dependence of the spectral emissivity, the coefficient of thermal expansion, the tensile modulus, the tensile strength and the fracture strength of notched specimens. The tensile strength and the fracture strength increase with increasing temperature, which is a characteristic feature of C/C composites. (2) After the thermal shock treatment, the tensile strength of the unnotched specimens decreases, but the fracture strength of the notched specimens increases. From a SEM observation and thermo-elastic consideration, it can be inferred that the increase in fracture strength is owing to the release of a thermal residual stress by microcracking in matrix carbon. The decrease in tensile strength may be the result of a delamination which was observed only in the unnotched specimens.