In-situ coupled mechanical/electrical investigations of EPDM/CB composite materials: The electrical signature of the mechanical Mullins effect

In-situ coupled mechanical/electrical investigations on EPDM-based composite materials prepared using CB fillers of different (low and high) structure and at different concentrations have been carried-out by cyclic and continuous loading, with simultaneous measurements of stress, strain and electrical conductivity. By investigations in dependence on the strain amplitude and unloading rate, the relationship linking the evolution of the electrical conductivity during mechanical deformation to the mechanical Mullins effect is demonstrated. A characteristic electrical signature accompanying the mechanical Mullins effect is revealed, originating from a kinetic reorganisation of the CB fillers by competing mechanisms of de-percolation and re-percolation. Notable differences between the electrical and the mechanical Mullins effect are also found, in particular, in relation to the kinetics of the stabilization of properties after the first mechanical deformation cycle. Our study brings new light into understanding the coupled evolution of mechanical and electrical properties of elastomeric composite materials, with possible applications in monitoring the material properties under mechanical deformation by in-situ electrical measurements.