Solid particle erosion of highly porous carbon-carbon composites

Abstract

The solid particle erosion behaviour of highly porous two-dimensional planar random carbon-carbon composites, with densities in the range 0.12–0.38 Mg m^-3, was characterised. The effects of angle of incidence, erodent particle size, orientation of the anisotropic composite relative to the erosion surface, and substitution of recycled fibrous material for virgin fibres in production of the composite, were evaluated. The erosion rate of the composite that contained no recycled fibrous material increased as the angle of incidence increased and reached a maximum when the erodent stream was perpendicular to the erosion surface; this behaviour is typical of brittle materials. The erosion rate was found to be independent of composite orientation relative to the erosion surface at a fixed angle of incidence, which may be because the scale of the impact site is significantly greater than the size of the fibres. The erosion rate increased with particle size according to a power law relationship. The values of the size exponents were larger than typically found for brittle materials but decreased as the proportion of recycled fibrous material increased, which was accompanied by an increase in density. The large size exponents were related to erodent particle penetration into the porous composite which resulted in a reduction in the efficiency of material removal, especially for the smaller erodent. The relationship between the erosion rate and the proportion of recycled fibrous material was found to be dependent on the erodent particle size. For the 370 and 230 μm particles, the erosion rate increased to a maximum at 25 and 45% recycled material content respectively and then decreased, whereas, for the 160 μm particles a continuous increase in the erosion rate was found as the proportion of recycled material increased. The relationships between the erosion rate and the percentage of recycled material were explained in terms of the effects of the recycled material constituents, i.e. short fibres, denser agglomerates, and the reduction in the erosion efficiency because of the penetrated erodent particles. The extent of erodent particle retention in the porous composite is greater for the smaller erodent particles and for the lower density samples.