ABSTRACT
Geothermal power energy is prospective energy resource in Japan because it is inexhaustible and clean. Utilization of geothermal energy requires to dig geothermal wells near the magma located about 3,000m below the surface of the earth. An excavator for digging geothermal wells is called downhole motor (DHM). Polymeric elastomers such as natural rubber have been used as sealing materials and stators of DHM. The life time of DHM is very short because these materials are exposed to severe geothermal environment. Therefore the development of polymeric composites with heat resistance and long-term durability has been demanded to dig geothermal wells efficiently. In the present study, long-term durability was evaluated on a Carbon/polytetrafluoroethylene (CF/PTFE) composite material which is one of the prospective materials used for DHM. We experimentally fabricated a testing machine to simulate geothermal environment. Using the testing machine creep tests with mixed-mode loading of compression and torsion were performed for 100 hours at room and elevated temperatures. The master curves to predict the lifetime of the material were obtained.
