Effect of silicon infiltration on the bend and tensile strength of 2D cross-ply carbon-carbon composites are studied. It is observed that bend strength higher than tensile strength in both types of composite is due to the different mode of fracture and loading direction. After silicon infiltrations bend and tensile strength suddenly decreases of carbon-carbon composites. This is due to the fact that, after silicon infiltration, silicon in the immediate vicinity of carbon forms the strong bond between carbon and silicon by formation silicon carbide and un-reacted silicon as free silicon. Therefore, these composites consist of three components carbon, silicon carbide and silicon. Due to mismatch between these three components secondary cracks developed and these cracks propagate from 90˚ oriented plies to 0˚ oriented plies by damaging the fibers (i.e., in-situ fiber damages). Hence, secondary cracks and in-situ fiber damages are responsible for degradation of mechanical properties of carbon-carbon composites after silicon infiltration which is revealed by microstructure investigation study by scanning electron microscope.

• S.R. Dhakate(Advanced Composites Evaluation Technology Center, Japan Aerospace Exploration Agency, Carbon Technology Unit, Engineering Materials Division, National Physical Laboratory)
• T. Aoki(Advanced Composites Evaluation Technology Center, Japan Aerospace Exploration Agency)
• T. Ogasawara(Advanced Composites Evaluation Technology Center, Japan Aerospace Exploration Agency)