Water entry with ultraelastic floating films

We study water entry of steel spheres in the presence of an ultrasoft, ultraelastic membrane of thickness of a few hundred microns floating on a free surface. The presence of a thin elastic layer of negligible inertia establishes an air-water interface that can sustain a strain-dependent surface tension. As the sphere impacts the free surface, we observe the formation of a dynamically elongating and propagating deformation front surrounding the impacting body, which elastically stores the energy in the membrane material. During the first stage of impact and elongation, an outer zone beyond the deformation front of the membrane is unperturbed by the impact and penetration of the sphere. Remarkably, a nonstretchable membrane is unable to produce this effect, suggesting an optimal range of elastic modulus (expressed dimensionless) necessary to absorb the impact energy of the projectile. By simultaneously tracking the projectile trajectory (particle tracking), the membrane's elastic deformations (using DIC) and the flow field (using PIV), we identify a "turbo-elastic" dissipation mechanism at play by which the projectile is efficiently retarted and brought to a complete stop, with its impact energy rapidly dissipated in the fluid through turbulent motion.