Machine Vision System for Measuring Subsurface Damage

The dimpling technique is widely used to measure subsurface damage SSD. The ground surface is first acid etched to open up the fractures. A dimple is polished into the surface by a sphere of a known diameter, and the diameters of the circular zones with and without visible subsurface fractures are measured to determined the damage depth. The measuring system consists of a microscope with a reticule and a linear translation stage. The diameters of the various zones are visually interpreted and measured. The dimpling technique provides a direct measurement of SSD, as opposed to other techniques where the SSD is implied from other properties such as scattering. The manual measurements associated with this technique are tedious and requires a trained operator to identify the deepest fracture.