Mechanical Behaviors of Bolted Joints Considering Visco-Elastic-Plastic Properties of Gasket

In Case of Using PTFE Gasket

Abstract

The mechanical behaviors of bolted joints with PTFE gasket have been evaluated by taking visco-elastic-plastic properties of the gasket into account. The strain-time equation of the gasket under multi-step unloading has been proposed by conducting the compression tests with loading and unloading, creep tests and creep-relaxation tests. By applying the equation, the analytical model which can calculate the variations in axial bolt loads for a joint tightened by single bolt has been also developed. The bolt load relaxation tests under some different gasket contact stresses have been performed for the single bolted joint. As a result, it has been observed that the developed analytical model could reproduce the bolt load variations within accuracy of 10%. Furthermore, the finite element model using the strain-time equation of the gasket has been proposed to simulate the bolt load relaxation and time variation of gasket contact stress of a pipe flange connection. By comparing to experimental results, it has been confirmed that the developed FE model can simulate the bolt loads relaxation with accuracy enough for practically. The gasket contact stresses have been evaluated numerically, and it has been concluded that the examination including the gasket viscous properties are very important.