In between stress and strain, which one is the more fundamental physical quantity? Or is it the case that each is defined independent of the other and so nothing can be said about their order? Is this the case?
A recent string of papers originated from Persson's paper in the physics literature contain a number of interesting new ideas, but compare, of the many theories for randomly rough surfaces, only Persson's and Bush et al, BGT. These papers often assume the original Greenwood and Williamson (GW) theory [1] to be inaccurate, but unfortunately do not test it, assuming BGT to be its better version. The original GW however is, I will show below, still the best paper and method today (not surprisingly, as not many papers have the level of 1300 citations), containing generally less assumptions than any other model, including the constitutive equation which does not need to be elastic! I just submitted this Letter to the Editor: On "Contact mechanics of real vs. randomly rough surfaces: A Green's function molecular dynamics study" by C. Campaña and M. H. Müser, EPL, 77 (2007) 38005. C. Campaña and M. H. Müser also make several questionable statements, including a dubious interpretation of their own results, and do not even cite the original GW paper; hence, we find useful to make some comments.
It was recently pointed out that much of the technical literature is inaccessible to the English speaking world, having been published in other languages such as Russian or Chinese. At the moment iMechanica is primarily an English-language website and we are therefore potentially limiting the discussion based on language.
A sponge is an elastic solid with connected pores. When immersed in water, the sponge absorbs water. When a saturated sponge is squeezed, water will come out. More generally, the subject is known as diffusion in elastic solids, or elasticity of fluid-infiltrated porous solids, or poroelasticity. The theory has been applied to diverse phenomena. Here are a few examples.
It is well known that the algebra associated with edge dislocations can be forbidding. As Prof. Frank (of the Frank-Read source fame) noted once,
You can receive posts and comments by email. They are faster than uploading webpages. They come into folders other than your regular emails, so you don't need to look at the posts if you have no time.
I use Thunderbird. Other email applications might have the similar feature. (If your email applications do not have this feature, you can always set up a feed reader.)
We report the direct molecular dynamics simulations for molecular ball bearings composed of fullerene molecules (C60 and C20) and multi-walled carbon nanotubes. The comparison of friction levels indicates that fullerene ball bearings have extremely low friction (with minimal frictional forces of 5.283×10-7 nN/atom and 6.768×10-7 nN/atom for C60 and C20 bearings) and energy dissipation (lowest dissipation per cycle of 0.013 meV/atom and 0.016 meV/atom for C60 and C20 bearings). A single fullerene inside the ball bearings exhibits various motion statuses of mixed translation and rotation. The influences of the shaft's distortion on the long-ranged potential energy and normal force are discussed. The phonic dissipation mechanism leads to a non-monotonic function between the friction and the load rate for the molecular bearings.
The discovery of a new material type, graphene and extremely thin platelets of graphite, was discussed in several articles from my research group published in 1999:
Lu XK, Huang H, Nemchuk N, and Ruoff RS, Patterning of highly oriented pyrolytic graphite by oxygen plasma etching, APPLIED PHYSICS LETTERS, 75, 193-195 (1999).
In the very beginning of 2007 I have four papers published or accepted (one is independent research and others are collaborated). All of them are the work done in my doctoral period. The topic is focusing on the enhancement of creep resistance of polymers by incorporating of nanofillers including particles and CNTs.
