Effect of fibre direction on surface roughness measurements of machined graphite/epoxy composite

Abstract Machined graphite/epoxy composite surfaces were studied using surface profilometry and scanning electron microscopy to determine suitable surface-describing parameter(s) for machined fibrous composite surfaces. It was found that the microgeometrical variations in terms of roughness parameters Ry and Rz are better descriptors of the machined surface than the commonly used roughness parameters Ra and Rq. The surface roughness and profile are found to be highly dependent on the fibre orientation and the measurement direction. The power spectral density function is shown to be capable of identifying the wavelength distribution of the machining damage that corresponds to the spatial distribution of the valleys in the profiles. Surface profiles of machined unidirectional composite laminates are found to be Gaussian and periodic in the direction of machining, and Gaussian and random perpendicular to the cutting direction. While edge-trimmed cross-ply laminate surfaces are Gaussian and random for profiles measured along the tool movement direction, they are periodic and non-Gaussian in the direction perpendicular to the tool movement.