ソフトガスケットを用いた単一ボルト締結体の高温長期軸力緩和挙動の評価

抄録

PTFE (Polytetrafluoroethylene) gasket is recently widely used as a substitute of compressed asbestos sheet gasket. Even though the PTFE gasket has excellent seal performance, heat resistance, and chemical resistance, a large reduction of axial bolt force under high temperature condition is a serious problem for a bolted connection with PTFE gasket. What is a dominant factor for bolt force reduction in the connection is not clear because of complex high temperature performance of such soft gasket. In this study, finite element simulations to investigate axial bolt force reduction of single bolt connection with soft gasket are performed under some temperature conditions, where temperature and time dependent gasket material properties, such as stress-strain relation, thermal expansion factor and creep performance, are measured and employed. As a result, we can confirm the validity of the finite element simulation by comparing numerical and experimental results of time changes of axial bolt force. Furthermore, to specify the dominant factor of gasket performance for bolt force reduction, the finite element simulations are conducted. It is concluded that temperature dependent stress-strain relationship and creep performance of gasket are the most dominant factors for bolt force reduction at unsteady and steady state conditions, respectively.