Abstract
Many guide parts of Al2O3 ceramics are used as mechanical components in the hot environment of textile machines. Some guide parts are occasionally fractured via fatigue failure due to thermal stress in service. The analysis of thermal stress requires knowledge of the heat transfer coefficients between a ceramic guide and cold airflow, as well as of the hot environment in service, because a continuous string running at a high speed of 10m/s carries cold room-temperature air to the ditch bottom of guide parts in the hot environment. However, for the heat transfer coefficients in such a situation, there has been no example of practical direct measurement in the past. Therefore, the heat transfer coefficients were estimated using an inverse analysis method, in which suitable heat transfer coefficients were estimated through trial and error, considering the correspondence of the fracture mode and strength between analytical fracture and actual fracture in service. From the analytical results for the thermal stress using the estimated heat transfer coefficients, the cause of fracture of some ceramic guides was clarified through fracture mechanics of a surface crack in a thermal stress field. The lifetime of ceramic guides was estimated probabilistically also from the viewpoint of fracture lives in long-term service.
