Compressive mechanical behavior of carbon/carbon composites under dynamic loading

Both quasi-static and dynamic compressive properties of 2-D carbon/carbon (C/C) composites in their thickness direction were determined using a universal test machine and Split Hopkinson Pressure Bar with pulse shapers. The compressive failure of the composite was photographed to demonstrate the failure mode at different strain rates, and the effects of strain rate on fracture mode are discussed. Results show that the compressive stiffness and strength of the C/C composites increase with strain rate. The compressive stiffness and strength of the C/C composites under dynamic loading with a strain rate of 5×10²/s are increased by about 66% and 55% respectively compared with quasi-static results with a strain rate of 10^-4/s. Under quasi-static conditions, the samples failed by shear with a shear fracture angle of approximately 40o, and carbon fiber bundles were sheared and crushed. Under dynamic conditions, the samples were broken into many fragments with different sizes, and carbon fiber bundles were fractured by splitting. The different failure modes may be related to the strain rate sensitivity of the carbon matrix and the interface strength.