  We present to the community a surface-definition problem, whose solution we
consider to be critical for the proper description of contacts between
nominally flat surfaces [1,2]. In 2015, M\"user and Dapp issued the Contact
Mechanics Challenge, which provided complete topography data for a fictional
surface and asked theorists and modelers to compute the expected contact
parameters for such a surface. This effort was a success, but exposed one
glaring flaw in the community's understanding of the nature of contact: these
models require as input a complete description of surface topography, which is
rarely or never available for real-world surfaces [3-6]. The present challenge
is to experimentalists: we will send you samples of two materials (one smoother
and one rougher); you determine the surface topography of these materials. We
call on you to measure such surfaces however you wish, using contact-based
techniques, light scattering, microscopy, or other techniques. Examples of
quantities of interest are: root-mean-square (RMS) parameters; the power
spectral density (PSD); or the autocorrelation function (ACF). For the
material, we have chosen chromium nitride, a wear- and corrosion-resistant
coating used in industrial applications including automotive components,
cutting tools, and die-casting. To participate, simply go to:
https://contact.engineering/challenge to provide your shipping address and
other information, then samples will be shipped out to you. The only
requirement of participation is that your raw topography measurements are
deposited on the free contact.engineering web app to facilitate data sharing.
The purpose of this challenge is for our community to move towards: (a) better
agreement on how to describe the multi-scale topography of experimental
surfaces; and (b) better understanding of how to apply the well-developed
models and theories to real-world surfaces.
