“…This yields the behavior of a non-linear spring which, depending on the principal curvatures of the two surfaces at the points of maximum penetration 2 , generates a restoring force which opposes the penetration of the undeformed object geometries. There are numerous extensions of this model where both dissipative effects due to local material deformation [40,41,42,43,44,45,46] 3 and forces due to friction [49,50,51,52,53] are added. All these approaches require the common normal and the maximum penetration depth to determine the interaction forces.…”