  Elastomeric materials when sliding on clean and rough surfaces generate
wrinkles at the interface due to tangential stress gradients. These interfacial
folds travel along the bottom of elastomer as surface detachment waves to
facilitate the apparent sliding motion of elastomer. At very low sliding speed
compared to elastic surface waves, the process is dominated by surface adhesion
and relaxation effects, and the phenomenon is historically referred to as
Schallamach waves. We report in this letter the observation of fast-traveling
intersonic detachment waves exceeding the Rayleigh and shear wave velocities of
the soft material in contact. The spatio-temporal analysis revealed the
accelerating nature of the detachment wave, and the scaling of wave speed with
the elastic modului of the material suggests that this process is governed by
elasticity and inertia. Multiple wave signatures on the plot were connected to
different stages of surface wrinkles, as they exhibited distinctive slopes
(from which velocities were derived) in the generation, propagation and rebound
phases. We also characterized the frequencies of wrinkle generation in addition
to the speeds and found a consistent scaling law of these two wave
characteristics as the stiffness of elastomer increased. Physical implications
of this new finding may further promote our understanding of elastomer noise
generation mechanisms, as at macroscopic sliding velocity, the frequency of
elastomer instability readily enters human audible ranges and interacts with
other vibratory frequencies to cooperatively create harsh and detrimental
noises in disc braking, wiper blade and shoe squeaking among many other
elastomer applications.

Soft Condensed Matter;Materials Science;Applied Physics