The interaction of a coated target and an impinging waterdrop

The work deals with the evolution of the stresses and the damage in targets with thin protective layers due to perpendicular high-velocity waterdrop impacts. The analysis involves a modeling of the impact in the liquid and the solid, and exploration of possible damage mechanisms in the coating and the substrate. We identify three state of stresses that can produce damage, radial tensile stresses that propagate on the surface of the coating, subsurface shear stresses that develop at the coating-substrate interface, and bending stresses near the inner face of the coating. The patterns of these stresses and the locations where they develop are in good agreement with experimental findings. The intensities and the impulses of the stresses are related to the impact velocity by a power-law rule reminiscent of the one used in experimentally motivated damage criteria. We find that the peak of the tensile stresses propagates on the surface of the coating at the speed of the Rayleigh wave in the substrate. The possible role of the subsurface shear stresses in the evolution of damage in coated targets is also discussed.