A new approach for surface profile roughness characterization in the laminated composite ply plane

Based on observations, current surface profile roughness parameters have some limitations to characterization a surface texture. The classical roughness parameters, such as the average deviation Ra, the root mean square... [ view full abstract ]

Based on observations, current surface profile roughness parameters have some limitations to characterization a surface texture. The classical roughness parameters, such as the average deviation Ra, the root mean square deviation Rq, the skewness or asymmetry Rsk, the kurtosis or flatness Rku, the total height Rt, the maximum height Rz, may give similar results for visually different roughness profiles. Indubitably, the possible misdescription of roughness surfaces may cause problem during the assembly process e.g. diverse adhesiveness of composite parts. Even though roughness parameters are within the tolerance requirements, the surface adhesiveness range may be wider than expected and even might be outside tolerance requirements.
Besides observed limitations of the actual roughness parameters, characterizing the surface texture of a machined laminated composite is more complex due to its anisotropic and heterogeneous nature at a micrometer scale. In addition to different types of surface roughness profiles depending on the ply orientation and the milling type, the tool wear impacts the composite machining leading to rougher or smoother surfaces depending on conditions.
In this study, novel roughness parameters are proposed to describe the surface texture of a composite. Those parameters are based on the fractal analysis and the chaos theory allowing to describe the complexity, the regularity and the auto scale dependency of the profile. The used fractal analysis, which is the regularization analysis, is adapted to the surface texture definition of the profile method. Besides the roughness profile itself, this adapted fractal analysis is only configured with the profile sampling length.
To depict these parameters and their estimation method, experiments of carbon fibre reinforced polymer (CFRP) trimming were conducted and roughness profiles were measured using a contact profilometer. Both up and down milling faces were inspected in the feed direction also within ply stacking. Four profile measurements were performed on each ply orientation (0°, 90° and ±45°) and on each milling face type. This measurement serie was executed for different tool wear and three cutting parameter sets on a 24-ply laminated CFRP.