Finite strains explain the non-monotonic change of contact area in soft rubber contacts loaded in torsion?

In unidirectional sliding of rubber contacts on smooth hard surface it has been found that contact shrinks largely in longitudinal directions, and generally much less in the transverse direction, and two explanations have been suggested to explain this: one is the effect of mixed mode fracture mechanics in the presence of adhesion (with mode II reducing adhesion and mode III less clear), and another uniquely based on finite strain effects even for a simple material model as neo-Hookean hyperelastic material. To shed some light an interesting recent paper (Zhang et al 2024 Tribology Letters, 72(4), 132) has studied the case of torsional contact, which leads to a pure mode III condition, and also unidirectional loading, but both with a higher normal load than so far (which would suggest adhesion is reduced and finite strain effects are increased). A small increase at low torsional loads, and more significant decrease of contact area was found at large loads. In this short comment, we discuss the problem and also obtain qualitative indication that with simple models only decrease of contact area can be understood. However, it is remarked that it requires very sophisticated Finite Element investigations to predict these second order effects, which may depend also on details of boundary conditions, material models, conditions at the interface, and this raises the question on what can really be the impact of a change of few percent of contact area variation on engineering applications, for which Hertz theory after almost 150 years works surprisingly well.

For more details, please see https://www.researchgate.net/publication/386013870

Regards

Mike