Subsurface microtunneling in ductile material caused by multiple droplet impingement at subsonic speeds

This article deals with the analysis of the subsurface deformation effects of materials due to the periodic action of liquid droplets, each with a constant volume of approximately 36 mm(3) distributed with a spatial frequency of 20,000 i/mm. Sample grooves were analyzed within standoff distances where the prevailing mechanism is acceleration culmination depletion using the stair trajectory to avoid a possible Doppler effect. Using X-ray mu-CT, a network of cavities corresponding to a fractal shape was identified below the surface. It is apparent that the ability to erode does not end with the formation of a groove but continues into the core of the material in the form of microjetting, tunneling, or piercing. From that perspective, two types of these cavities have been identified, blind and transient, with diameters of a few micrometers. The topological changes in the subsurface region of the sample were analyzed using X-ray tt-CT progressive sectioning. The anticipated subsurface deformation was further explored and analyzed using SEM analysis. The integrity of the material around the cavities was assessed according to microhardness to explain the microjetting, tunneling, and piercing propagation. The results suggest that the effect of the lateral jetting after droplet collapsing causes extensive hydrodynamic tunneling in the material that is much higher during the intense periodic action of water droplets, even at subsonic speeds.

Automated summary

This article analyzes the subsurface deformation effects of materials caused by the periodic action of liquid droplets. X-ray micro-CT and SEM analysis were used to study the subsurface deformation and the formation of cavities. The results suggest that lateral jetting after droplet collapsing leads to the formation of hydrodynamic tunnels in the material.