  The classical Hertzian contact model establishes a monotonic correlation
between contact force and area. Here, we showed that the interplay between
local friction and structural instability can deliberately lead to
unconventional contact behavior when a soft elastic shell comes into contact
with a flat surface. The deviation from Hertzian contact first arises from
bending within the contact area, followed by the second transition induced by
buckling, resulting in a notable decrease in the contact area despite increased
contact force. Friction delays both transitions and introduces hysteresis
during unloading. However, a high amount of friction suppresses both buckling
and dissipation. Different contact regimes are discussed in terms of rolling
and sliding mechanisms, providing insights for tailoring contact behaviors in
soft shells.
