Biomedical Engineering Reference
In-Depth Information
0.5
0.4
0.3
0.2
0.1
0.0
-10
-5
0
5
10
15
Specific (acid-base) free energy (kJ/mol)
Figure 4.5
Specific acid-base free energy distributions of studied
HA powder as observed for selected wetting probes. Square:
acetone; diamond: acetonitrile; triangle: ethanol
The results of the powder flow measurements are summarised in
Figure 4.6
, which shows the results of yield loci and Mohr´s circles
at defined consolidation stresses for the studied HA sample. The
relevant consolidation stress s
1
is equal to the major principal stress
of the Mohr stress circle which is tangential to the yield locus and
intersects at the point of steady flow. It was found to be 16.4 kPa.
The latter stress circle represents the stresses in the sample at the
end of the consolidation procedure (stress at steady-state flow).
It corresponds to the stress circle at the end of consolidation at the
uniaxial compression test. The unconfined yield strength s
c
was
found to be 5.08 kPa which results from the stress circle which is
tangential to the yield locus and which runs through the origin (minor
principal stress s
2
= 0). Because the largest Mohr stress circle indicates
a state of steady-state flow, the internal friction angle (31.9°) can be
regarded as a measure of the internal friction at steady-state flow.
For the samples studied, the effective angle of internal friction was
observed to be 40.75°. It can be stated that materials with higher
friction angles seem to have easy flow properties.
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