CRITERIA
3PP
M3PP-0.5
M3PP-1
M3PP-2
M3PP-5
M3PP-10
Peak threshold value
0% Rq
µm
0.5% Rq
µm
1% Rq
µm
2% Rq
µm
5% Rq
µm
10% Rq
µm
Roughness 1
Rq = 0.004 µm
0
2.0·10-5
4.1·10-5
8.2·10-5
2.0·10-4
4.1·10-4
Roughness 2
Rq = 0.041 µm
0
2.0·10-4
4.1·10-4
8.2·10-4
2.0·10-3
4.1·10-3
Roughness 3
Rq = 0.094 µm
0
4.7·10-4
9.4·10-4
1.9·10-3
4.7·10-3
9.4·10-3
Roughness 4
Rq = 0.249 µm
0
1.2·10-3
2.4·10-3
5.0·10-3
1.2·10-2
2.4·10-2
Roughness 5
Rq = 0.843 µm
0
4.2·10-3
8.4·10-3
1.7·10-2
4.2·10-2
8.4·10-2
After the elimination of the profile tilt and the calculations of the peak-threshold values, the profiles were further analysed with in-house-developed software. The surface profiles for a selected surface roughness are imported into the software and the asperity peaks are identified according to all the different asperity-peak criteria (Table 3). The asperity-peak radii and heights were also calculated for these profiles. After all the profiles were analysed, the average number of asperity peaks, the average height and the average radii were calculated for a selected surface roughness. The procedure is then repeated for all the selected surface roughnesses.
In order to also introduce the effect of the Δx data resolution on the asperity-peak properties, the surface profiles from our measurements were modified in such a way that the different Δx distances were considered for the existing profiles. Thus a different data resolution was obtained by using only every 2nd, 4th, 6th or 10th profile data point. These modified profiles were taken into consideration and used in the asperity-peak-properties analysis - in exactly the same way as explained above. The complete set of Δx resolutions analysed is presented in Table 4. This variation was employed only for the 3PP criterion.
Table 4: Variation of Δx resolutions.
''Original'' Δx
resolution, µm
Variation of Δx resolution, µm
Δx
2·Δx
4·Δx
6·Δx
10·Δx
0.1875
0.375
0.750
1.125
1.875
3. Results
3.1 Effect of neighbouring points (asperity-peak width) on the asperity-peak properties
Number of asperity peaks per profile
Figure 5 shows the number of asperity peaks for the 3PP, 5PP and 7PP criteria. For the 3PP criteria, the number of asperity peaks decreases with the increasing surface roughness, from 1400 asperity peaks for the smoothest surface to 650 asperity peaks for the roughest surface. It seems that the number of asperity peaks levels out for the rougher surfaces. However, the 5PP and 7PP criteria have almost no effect on the number of asperity peaks. The number of asperity peaks for the 5PP is almost constant throughout the whole roughness range at a value of 260 asperity peaks, while the values are around 200 for the 7PP criteria, but again almost constant for all roughnesses (except for the smoothest surface, where the number of asperity peaks is even lower).
Figure 5: Number of asperity peaks in relation to the roughness parameter Ra for 3PP, 5PP and 7PP criteria (Δx = 0.1875 µm).
Asperity-peak radii
The asperity-peak radii decrease with the increasing surface roughness for all three criteria (see Figure 6). The values are around 3.6 µm for the 3PP at the smoothest surface and decrease to a value of 2.3 µm for the roughest surface. For the 5PP and 7PP, the radii for the smoothest surface are about 6.9 µm, and they again decrease towards the highest surface roughness to values similar to the 3PP, i.e., about 2.3 µm. There is only a small difference in the radii calculated with the 5PP and 7PP, but the 5PP always has the higher radii values. The difference between the 3PP and the other two criteria is almost two-fold for the smoothest surface, but this decreases with an increasing surface roughness.
Figure 6: Asperity-peak radii in relation to the roughness parameter Ra for the 3PP, 5PP and 7PP criteria (Δx = 0.1875 µm).
