| We used micro- and nanoindentation, macroscopic strain gage methods and FE studies to correlate the indentation modulus and the macroscopic in- and out-of-plane Young's moduli of transversely isotropic pyrolytic carbon. The out-of-plane indentation modulus of bulk PyroC was comparable with predicted values and more than a factor of two higher than the out-of-plane Young's modulus. The in-plane indentation modulus was significantly lower than predicted values which we attribute to nanobuckling of graphite-like planes. Polarized light microscopy studies on carbon-carbon composite samples infiltrated at 10, 20, 30 kPa demonstrated that the increase in pressure leads to lower texture of the PyroC and higher in-plane indentation modulus due to a decreased tendency toward nanobuckling for more isotropic structures. We observed damage of PyroC layers at critical loads when indenting normal to the plane of isotropy and attribute the damage to a combination of crack propagation and delamination types of deformation mechanisms. |
