Towards a rational approach for multi-axial experimental campaigns for rubberlike material

This work takes up the developments around the logarithmic strain tensor and uses the invariants of this tensor to propose a new approach to multi-axiality of fatigue experiments for elastomers. This study leads to the introduction of a new notion, modality, which is intended as the microscopic counterpart of uni- and multi-axiality. This notion is quantified by the $K_3$ invariant (mode of deformation) of the logarithmic strain tensor, and is used to rationalize tension–torsion experimental campaigns. It is illustrated using two examples: the perfect cylinder and the AE2 “diabolo” sample. We then propose a methodology for building a test campaign based on this new definition.