Impact of pre-softening on rubber adhesion

The effect of stress softening, namely the Mullins effect, on elastomers’ mechanical properties such as fatigue, strength, or toughness is widely studied, but mainly on bulk materials. The present contribution presents experimental evidence that applying a pre-softening load may significantly alter the critical strain energy release rate (SERR), which controls the interface adhesion between a soft solid and a rigid substrate. Here, we focus on the adhesion of a natural rubber matrix to a single metal wire, characterized using the Rubber Cord Adhesion Inflation Test. This protocol allows for the observation of a stable steady-state crack propagation under an axisymmetric configuration. An experimental protocol is proposed that utilizes a pre-load sequence to achieve a controlled softening of the rubber sheath surrounding the wire. Quantification is carried out through numerical simulations and subsequent material characterization. The adhesion results indicate that the pre-loading sequence reduces the specimen’s overall resistance to decohesion. A more detailed analysis reveals that the critical SERR value is also lower. These findings provide new insights into the role of energy dissipation, both within the bulk material and at the interface level, in influencing the interface failure between an elastomer matrix and a rigid reinforcement.