[SY-O1] Soft Matter Mechanics: numerical and experimental methodologies for dry and lubricated tribological problems
Assessing the mechanics of soft matter is a crucial point in modern research, involving, at the same time, engineering, physics and material science. Indeed, modelling soft materials is particularly challenging given the strongly time-dependent and usually nonlinear constitutive stress-strain relations that govern their response. Further complexity is embedded in the modelling analysis when soft solids are into contact and the problem is exacerbated by the geometry of the intimately mating surfaces. In this work, we focus specifically on the contact mechanics of linear viscoelastic materials and we present a variety of Boundary elements methods developed to determine the mechanical solution in terms of stresses, strains and, ultimately, friction. In particular, we describe the main features of viscoelastic contact mechanics under different contact conditions, involving steady-state, reciprocating and generalized motion laws. Each configuration is different since the solution is dramatically influenced by the relaxation of the different regions into contact. In all these analyses, a fundamental role is played by the surface roughness, which introduces a huge number of space and, consequently, time scales. Such a scenario is furtherly complicated when the presence of a fluid is considered at the contact interface: indeed, the fluid viscosity, coupled with the material viscoelasticity, determines tremendous variations in comparison with the classical elasto-hydrodynamic theory. In detail, the pressure and the film thickness distributions show strongly non-symmetrical trends at the contact inlet and outlet. All this entails a friction curve strongly different from the Stribeck curve, usually predicted for elastic solids, and demonstrates the necessity of ad hoc developed modelling strategies for soft materials.