Abstract: As a high performance thermal-resistant composites, carbon/carbon composites have the highest mechanical strength in the temperature more than 1600℃,
but the brittleness of C/C is the main shortcoming limitting its usage. Delamination constitutes the principal threat to structure strength of two dimensional carbon/carbon
composites. There are three kinds of crack extension modes in general. In this paper, two kinds of modes, that is, mode Ⅰ and Ⅱ were discussed. On the basis
of failure evolution features in composites, the delamination crack extension energy G_ⅠC 、G_ⅡC, the extension patterns and the influencing factors were researched. It is revealed that the
critical interlaminar crack extension energy of 2D carbon/carbon increases as the material density goes up, therefore, the ability to resist fracture evolution
improves. The experimental results show that the extension energy G_ⅡC rises with the increase of fiber volume fractions.
Also, it is observed that the G_ⅡC increases greatly after filling the matrix with powdered pyrolytic carbon and graphite.

Key words: carbon/carbon composites, delamination, crack extension energy