Surface periodicity index (SPI): A measure of periodicity of surface topography

The periodicity of surface features generated by various manufacturing processes plays a vital role in the functionality of the parts. Quantifying the periodicity of such surfaces is essential, which is not effectively captured by the existing surface topography characterization parameter. In this work, a new characterization parameter called surface periodicity index, SPI, is defined to identify and quantify the periodicity of a surface. It also indicates the significance of a periodic feature shrouded by a broad range of aperiodic features on a surface. SPI, established using the power spectral density, measures the energy of the periodic features in the context of the surface. Simulated periodic and aperiodic surfaces are used to demonstrate SPI. Finally, the utility of SPI is demonstrated with a case study of pulsed laser micro polishing. It will be shown that the parameter can also be used to distinguish different process regimes and for process design.