Ciavarella, MicheleMicheleCiavarellaPapangelo, AntonioAntonioPapangelo2019-04-262019-04-262018-01-28Journal of Adhesion 2 (94): 155-165 (2018-01-28)http://hdl.handle.net/11420/2542Recent numerical investigation on self-affine Gaussian surfaces by Pastewka and Robbins (PR) has led to a criterion for “stickiness” based on when the slope of the (repulsive) area–load relationship appears to become vertical in numerical simulations at a ratio of contact area to nominal one (rather arbitrarily) fixed to 1%. Since pull-off and slope of the area–load are two faces of the same medal, a simple check of the results in terms of pull-off shows that PR have many more data which fail their criterion than the ones that satisfy it, and this is evident even in their own figures. As a small improvement, a proposal to modify the criterion to better fit their own data is put forward. However, the pull-off decay seems rather exponential so that it is unclear if their slope criterion really corresponds to a “thermodynamic” limit, and consequently their conclusion that stickiness should depend only on slopes and curvature may be an artifact of their assumption of defining a secant at 1% contact area ratio and of using truncated potentials, rather than a true important property of rough contact. Both the PR criterion and the present modified one imply that for fractal dimension D < 2.4, stickiness should increase with resolution, so the problem of truncation of the spectrum seems ill-defined: in fact, PR define rigid self-affine surfaces with rather smooth and well-defined slopes, and not a realistic atomic roughness as first studied by Luan and Robbins.en0021-846420182155165Journal Article10.1080/00218464.2017.1292139Journal Article