Rapid assessment of surface topography via non-destructive acoustic testing

An impact between two solid bodies generates an acoustic output, the characteristics of which depend on the geometry of the bodies, the material properties, and the nature of the contact. Parameters including density, modulus, and surface topography influence the properties of the sound generated, and therefore the acoustic output produced from an impact can in principle be used for the evaluation of material and surface properties. This work reports on the recent development of a non-destructive method for assessing the surface topography of engineered materials. The protocol involves delivering a low kinetic energy impact to a sample, allowing correlation between the specimen surface topography and the acoustic output from the impact event. The sound generated from the impact of a nylon sphere onto a series of aluminium plates was recorded. The plates were polished to different grades and exhibited surface roughnesses in the range 500 – 3,000 nm. Analysis of the sound generated revealed that surface topography was discernible from this rapid test, which took only a few seconds to perform; post-processing required only a few seconds of computation. The prospects for using this methodology for identifying changes in surface topography will be discussed, along with the opportunities for automated data acquisition and processing. It is envisaged that this method could be suitable for in situ monitoring of the extent of wear progression.