Sphere and cylinder contact mechanics during slip

Abstract

Using molecular dynamics (MD) we study the dependency of the contact mechanics on the sliding speed when an elastic block (cylinder) with a cos(q0x) surface height profile is sliding in adhesive contact on a rigid flat substrate. The atoms on the block interact with the substrate atoms by Lennard-Jones (LJ) potentials, and we consider both commensurate and (nearly) incommensurate contacts. For the incommensurate system the friction force fluctuates between positive and negative values, with an amplitude proportional to the sliding speed, but with the average close to zero. For the commensurate system the (time-averaged) friction force is much larger and nearly velocity independent. For both type of systems the width of the contact region is velocity independent even when, for the commensurate case, the frictional shear stress increases from zero (before sliding) to ≈ 0.1 MPa during sliding. This frictional shear stress, and the elastic modulus used, are typical for Polydimethylsiloxan (PDMS) rubber sliding on a glass surface, and we conclude that the reduction in the contact area observed in some experiments when increasing the tangential force must be due to effects not included in our model study, such as viscoelasticity or elastic nonlinearity.

Macroscopic Modeling of Fingerpad Friction Under Electroadhesion: Possibilities and Limitations

“…As already stressed in the previous section, we believe that adhesion is not the decisive factor for the area reduction. It is known from experiments that the measured macroscopic adhesion for the contact of skin and dry glass is negligibly small (Wang et al, 2020) and cannot explain the significant reduction without any influence of electroadhesive forces. Delhaye et al (2014) make the non-linear elastic properties of skin responsible for the area reduction.…”

“…However, we believe that the large deformation of the finger and the complex layered structure contribute to the observed effect as well. Without further investigation, this assumption was already expressed by Wang et al (2020).…”

Cylinder–flat-surface contact mechanics during sliding

“…The elastic block is treated using the smart-block description (with 13 layers with the same spacing as for the first layer plus four layers on top of it, where at every step we double the lattice spacing in the x and z directions) discussed in Ref. [11], where the bending and elongation spring FIG. 1.…”

“…For stationary contact with F x = 0, where F x is the applied tangential force, the adhesive interaction is well described by the Johnson-Kendall-Roberts (JKR) theory [5,6] which has been tested in great detail. However, when the tangential force F x is nonzero, the problem becomes much more complex and not fully understood [7][8][9][10][11][12].…”

“…In Refs. [11,12] we studied the opposite situation of an elastic block with a flat surface in contact with a rigid solid with the height profile z = h 0 cos(q 0 x). We will refer to this system as flat curved.…”