MECHANICAL-PROPERTIES IN COMPRESSION OF LOW-DENSITY CARBON/CARBON COMPOSITES

Low density, two-dimensional planar-random carbon/carbon composites with densities in the range 0.17-0.40 Mg m(-3) were tested in compression and the strength, modulus and strain-rate sensitivity evaluated. The specimen geometry was found to affect greatly the compressive property values and hence a constant geometry was used for all tests. The compressive strength and modulus increased with increasing density, with in-layer values being greater than the respective out-of-layer values. Within the range of strain rate investigated, a greater strain rate was not found to give a significantly stiffer or stronger material. The stress/strain curves of samples tested out-of-layer try-plane perpendicular to compressive axis) exhibited up to three distinct moduli before the maximum stress was reached. At the lower densities the in-layer samples failed through an interfacial mechanism whereas higher density samples failed through kinking. The compressive modulus anisotropy decreased with increasing density as had been expected, although the compressive strength anisotropy remained approximately constant with increasing density. The results are explained using a previously developed microstructural model of the composite.