Carbon fiber composite material at 2400 DEG C to phase transition from turbostratic structure to 3D ordered structure, the composites of carbon / carbon composites by CVD resin, carbon fiber, carbon carbon three carbon, so in the phase interaction is inevitable, CVD carbon free graphite, and the remaining two species non graphitized carbon, but the degree of graphitization is 60%-80% in the temperature of above 2700 DEG C, the reason is considered to have high temperature carbon carbon fiber resin shrinkage, swelling stress between the two promote the transformation of resin carbon carbon composites, improve / graphitization of carbon composite materials.

After graphitization, the main problems of the products are cracks and stratification. The longitudinal strength of the layered main felt is low, and it is a natural deficiency, and the cause of longitudinal cracking is more complicated. There are three reasons for it to be summed up.

1, in the CVD process, because of the density difference caused by the internal thermal gradient method, the stress is induced in the thermal environment. The stress is released in graphitization, and its value exceeds the strength value, causing cracks.

2. During the process of rise and fall of graphitization, the internal and external temperature difference is large, which causes large enough thermal stress to lead to cracks.

3, the original defects in carbon felt matrix, such as slag and coking, become the source of crack. However, the fiber discontinuities of felt can not effectively prevent the development of cracks and cause cracking.

Of course, the size effect is also large, more than φ 400 of the products, the ratio of cracking is higher than that of φ less than 400. This can be explained in the thermal stress formula.

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