The acting of composite materials roughness measuring method on surface estimation
Andrzej Posmyk, Ireneusz Piotr Chmielik
Quarterly No. 3, 2010 pages 229-234
DOI:
keywords: composite, roughness, measuring methods, measuring errors
abstract The influence of roughness measuring on surface structural inhomogeneous materials has been presented in this paper. Inhomogeneous materials are composite with Al, Mg alloys or polymer matrix, including reinforcing phase having significantly higher than matrix hardness, e.g. SiC and Al2O3. Analogous problems with composites can be observed by roughness measuring on composite nickel or chromium covering, including soft PTFE particles. There are two groups of measuring methods, i.e. mechanical method using diamond stylus and an optical, interference method, using light beam (non-contact). The results delivered from the instruments according to both measuring methods are not comparable. Another problem can be observed by surface roughness measuring of composite materials with aluminium alloy matrix and alumina as reinforcing phase. The surface topography of matrix alloy EN-AW 6061 having hardness (39 HB, T0) and the alloy reinforced with 22% of alumina particles (59 HB, T0) has been investigated. The samples have been specially prepared by metallographic polishing on Struers equipment. Two profilometers, i.e. mechanical Taylor Hobson Talysurf and optical FRT have been used during the investigation. The measurement using the mechanical profilometer has been conducted with an adjusted load on the diamond stylus of 1 mN. The diamond stylus during the measurement process contacts the measured material and scratches along the surface. It has been stated that the stylus leaves ploughing traces on the surface if the hardness is to low. On the matrix material the traces were continuous on the sampling length. On the composite material the traces were none continuous, i.e. doted. Roughness parameter Sa of matrix material measured by the contact method (0.073 m) was about 2.63 times lower than parameter of composite material (0.20 m), parameter Sp was about 2.7 times and Sv about 2.9 times lower than parameter of composite material. The reason for such differences is the dihedral surface of composites. The first plane (lower) creates a surface of matrix material and the second plane (upper) create polished peaks of alumina particles. Between both planes the measured distance is up to 2 m. Roughness parameters of matrix material measured by non-contact method were higher (5.9x - Sa; 12.8x - Sp; 26x - Sv) than measured by contact method. The reason for such significant differences is the ability of aluminium to oxidize. A thin oxide film absorbs part of the light beam and gives the wrong results.