Impact and Flexural Strengths of Carbon-Carbon Composites Prepared by Preformed Yarn Method
Anilas K1, AO Surendranathan2*, Sunil Kumar BV3, J Gururaja Rao4
1PG scholar, 2Professor, Department of Metallurgical and Materials Engineering, National Institute of Technology Karnataka, Surathkal, India.
3Assistant Professor, Department of Mechanical Engineering, Canara Engineering College, Mangalore, VTU, Karnataka, India.
4Scientist ‘E’, High Temperature Composite Centre, Advanced Systems Laboratory, DRDO, Hyderabad, India.
Carbon-carbon composites, due to their unique properties like high specific strength, stiffness and in plane toughness as well as refractory properties like retention of mechanical properties at extremely high temperatures of the order of 3000oC, find application as structural materials in space vehicles, heat shields, rocket nozzles and aircraft brakes. Properties like biocompatibility and chemical inertness have led to new applications in medicine industry. Advanced fabrication techniques like Preformed Yarn (PY) method showed exceptional values for specific strength and fracture toughness than conventional methods already available. The present study centres on the PY method where a PY (Preformed Yarn) machine is the backbone, to synthesize preformed yarns (PYs). PYs were synthesised from carbon fibre filaments, used as reinforcement, and coke and pitch, used as matrix. Upon fabrication of PYs of sufficient quantity, hot pressing, pitch impregnation and heat treatment (carbonization and graphitization) were done at sufficiently higher temperatures to get the final CCC. Characterization by XRD (X-Ray diffraction) and SEM (scanning electron microscope) was done. Impact strength and flexural strength were tested and studied with reference to the previous work in this field. The CCC fabricated by PY method was found to have superior properties than other fabrication techniques, however, optimization of the method is still possible. Increasing the fibre content and attaining the maximum possible level of graphitization are the key points to be noted for the fabrication of best CCC.
Key words: Carbon fibre, Coke, Pitch impregnation, Graphitization, Carbon-Carbon Composites.