A method for determining equi-biaxial fatigue in elastomers

The development of an axi-symmetric bubble inflation fatigue test rig is described. The rig allows the determination of real time stress/strain data for thin elastomeric sheets subjected to cyclic loading. It is intended that this data will be used to produce accurate mathematical models for finite element analysis (FEA) of hyperelastic and viscoelastic material behaviour during fatigue loading leading to failure. This work involves the development of a real time surface measurement system for the bubble profile in conjunction with a fully integrated hydraulic pressure control system. The systems provide a method of continuously monitoring bubble profile dimensions, inflation pressures, and associated stress–strain data during repeated inflations and deflations leading to failure. Recent publications have highlighted the dependency of the fatigue life of non strain-crystallising elastomers, subjected to uniaxial deformation, on both mean stress and stress amplitude. The bubble inflation tests will establish if a similar dependency exists for bi-axial deformation.