  True contact between randomly rough solids consists of myriad individual
micro-junctions. While their total area controls the adhesive friction force of
the interface, other macroscopic features, including viscoelastic friction,
wear, stiffness and electric resistance, also strongly depend on the size and
shape of individual micro-junctions. Here we show that, in rough elastomer
contacts, the shape of micro-junctions significantly varies as a function of
the shear force applied to the interface. This process leads to a growth of
anisotropy of the overall contact interface, which saturates in macroscopic
sliding regime. We show that smooth sphere/plane contacts have the same
shear-induced anisotropic behaviour as individual micro-junctions, with a
common scaling law over four orders of magnitude in initial area. We discuss
the physical origin of the observations in the light of a fracture-based
adhesive contact mechanics model, described in the companion article, which
captures the smooth sphere/plane measurements. Our results shed light on a
generic, overlooked source of anisotropy in rough elastic contacts, not taken
into account in current rough contact mechanics models.
