Development of ultra-high temperature testing equipment and some mechanical and thermal properties of advanced carbon/carbon composites

Advanced carbon fiber reinforced carbon (C/C) composites are one of candidate materials for leading success of a space plane program in the 21st century. Though ultra-high temperature experimental studies for C/C composites have been performed, the effect of neither temperature nor heating/cooling speed on material properties have been fully made clear yet. In this paper, highfrequency induction heating material testing system developed by us is presented first; the main advantage of this system is the capability of quite fast heating and cooling speed. After verifying the temperature distribution of the specimen, some experimental studies are performed for two types of non-oxidation-protected C/C composites whose heat treatment temperatures are 1600 and 3000° C. Obtained results are summarized as follows; (1) Only tensile strength tends to decrease when cooling speed becomes fast although heating speed does not have an influence upon both thermal and mechanical properties of C/C composites. This phenomenon may be the effect of microcracks in the matrix of C/C composites. Therefore, it is important to investigate the effect of cooling speed and the number of heat cycles on material properties for the practical use of C/C composites. (2) Serial data are obtained about the dependence of temperature on tensile modulus, tensile strength and coefficient of thermal expansion. Especially, a characteristic feature of C/C composites which is so called 'inverse temperature dependence of the strength' is made clear, i.e., the strength increases gradually with elevating temperature. Furthermore, the mechanism of this phenomenon is discussed from the viewpoint of the release of residual stress.