Aerospace Engineering Guide
Aerospace Engineering Guide21Latest information available at April 2008Surface Finish (Measurement Methods)Ra- Arithmetic Average RoughnessRoughness averages are the most commonly usedparameters because they provide a simple value foraccept/reject decisions. Arithmetic average roughness , orRa, is the arithmetic average height ofroughness-component irregularities (peak heights andvalleys) from the mean line, measured within the samplinglength, L. See figure measurements are taken as the fine point of the styluson a profilometer which traverses the sampling length onthe surface being = individual measured peak heightLValleyPeakMean lineRa=1LqL0|y(x)|dxRq=1LqL0Yz(x)dx nX Figure 29 Surface Finish - RaVersus RqRq- Geometric Average RoughnessRqis the current term for what was formerly calledroot-mean-square or RMS.
Aerospace Engineering Guide 21 Latest information available at www.tss.trelleborg.com Edition April 2008 Surface Finish (Measurement Methods) Ra - Arithmetic Average Roughness Roughness averages are the most commonly used
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