Strength and fracture behavior of two-, three- and four-dimensionally reinforced carbon/carbon composites

A comparative study has been carried out on mechanical behavior of two dimensionally (2D), three dimensionally (3D) and four dimensionally (4D) reinforced carbon/carbon composites (C/Cs) having 50, 48 and 37 vol.% carbon fibers, respectively. The tensile and flexural strengths of 2D- and 3D-C/Cs, found as ∼25% higher than that of 4D-C/C, appear related to fiber volume fraction. The load-displacement plots obtained from three-point bend tests on single edge notch bend specimens appear non-linear, suggesting graceful failure. Scanning electron microscopy studies of crack paths have shown high tortuousity due to crack deflection, branching as well as fiber debonding and breakage. The results indicate that total fracture energy release rate (Jc) and displacement (δ0.6) at 60% of peak load are suitable parameters for evaluation of fracture resistance and damage tolerance, respectively of multi-directionally reinforced C/Cs. The values of Jc and δ0.6 have been found as maximum for 2D- and 4D-C/C, respectively.