Progressive fracture testing of Carbon-Carbon composites

Carbon-Carbon (C/C) composites can retain their mechanical properties at extreme temperatures of up to 3000 degrees C. This study quantifies damage resistance in cross-ply C/C composites by means of compact tension tests at room temperature adapted from typical tests on carbon fibre reinforced polymers. The analysis of different specimen sizes reveals that baseline (dimensions: 70 mm x 90 mm) and large scaled-up samples yield consistent fracture energy values of 15-30 kJ/m2 while the scaled-down version shows unwanted failure around the loading pins. A microscopic cross-sectional analysis explains the relatively low fracture energy values of carbon/carbon composites compared to carbon fibre reinforced polymers. It is found that only 20%- 40% of the carbon fibres in loading direction fail in C/C composites which leads to reduced energy absorption during the progressive fracture test.