| dc.description |
An apparatus has been developed for determining the high
temperature creep and recovery characteristics of graphite by applying
torsional stresses to thin-walled tubes. This method has the advantages
of a simple stress system, constant stress for constant load, easy
rapid removal of load and the independence of the strain measurement
from thermal expansion. Torsional, stress-strain curves show a decreasing
modulus with increasing temperature from 2000 - 2850°C. The rate of
creep in this range is increased by increasing temperature and stress.
Recovery rate is not so sensitive to increasing temperature. Using a
method developed for metals, where recovery can be subtracted from
forward creep, a secondary creep rate is deduced. This rate, when
plotted according to the Arrhenius' equation, yields an activation energy
for secondary creep of 154 kcals over the temperature range 2100 - 2700°C.
These results are critically examined and the future extension of the
work discussed. |
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