Stretch-induced softening in filled elastomers: A review on Mullins effect related anisotropy and thermally induced recovery

Abstract

The Mullins effect of filled elastomers, corresponding to their softening under stretching, has been widely explored and several models have been proposed to reproduce it. However, the observed anisotropy in the material mechanical response induced by a stretch and the thermally induced recovery of the pristine material behaviour are two aspects of the phenomenon that are difficult to model. In this review, an update collection of the main results from literature experimental works about these topics is reported, with the aim to provide a support for the improvement of existing models or the formulation and validation of new ones. A part of the review details testing methods used to investigate the anisotropic mechanical response induced by differently pre-stretching the materials. Another part, focused on studies highlighting the recovery of the original behavior after a thermal treatment of the stretch-softened material, is aimed at approaching a more comprehensive understanding of the phenomena. The results of literature studies are summarized emphasizing the type of rubber and filler, the filler content as well the applied stretching conditions. An overview of physical interpretations of stretch-induced anisotropy and thermal recovery is provided, which could be useful for the development of the physically based models.