CHARACTERISTICS OF THE HIGH TEMPERATURE MECHANISMS OF CREEP AND RECOVERY IN GRAPHITE.
Final technical sheet no. 1, 1 Aug 62-31 June 63.
COLLEGE OF AERONAUTICS CRANFIELD (ENGLAND)
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An apparatus was 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 stressstrain 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. Author