Civil Engineering Reference
In-Depth Information
9.1.1 Specimen Preparation (Surface Ground)
Specimens were prepared in two different ways. Stainless Steel 304 specimens
were cut from 6.35-mm- and 4.76-mm-diameter rods. Then, the overall lengths of
the specimens were sized using different surface grinding wheels for different spec-
imens to create specimens with specific surface roughnesses on their contact faces.
The grinding wheels used were 320, 600, and 800 grit. A Zygo New View 7200 was
used to quantify the different surface roughnesses produced by the grinding wheels.
To accomplish this, roughnesses were measured on both sides of each specimen,
and two locations were measured on each side. Further, at each location one hori-
zontal and two diagonal measurements were taken to remove any directional bias
from the measurements. Figure
9.1
shows an example of this measurement strategy.
Table
9.1
displays the different roughness profiles which were determined.
Magnified pictures of the surface ground specimens from the profilometer can
be seen in Fig.
9.2
. Additionally, surface roughness profiles of the same specimens
are shown in Fig.
9.3
.
9.1.2 Specimen Preparation (Enhanced Asperities)
In addition to using the different surface grinding wheels to produce different sur-
face roughness, it was quickly determined that the difference in the surface rough-
ness was not large enough to show any trends in the experimental thermal data.
0measurement
°
45measurement
°
135 measurement
°
Fig. 9.1
Surface roughness measurement strategy [
6
]. Measurements were taken at two loca-
tions on each side of the specimen. At each location, several roughness profiles were determined
along imaginary lines drawn at various angles (0°, 45°, and 135°)
Table 9.1
Wheel grit versus surface roughness relationship [
6
]
Size
−
x
(mm)
Size
−
y
(mm)
Wheel Grit
Avg Ra (µm)
Avg RMS (µm)
320
0.668
0.909
2.83
2.12
0.539
0.729
2.83
2.12
600
0.217
0.288
2.83
2.12
800
As a higher grit grinding wheel is used, average roughness value is decreases (i.e., the surface
becomes smoother)
