On the characterisation of periodic patterns in tessellated surfaces

Tessellated surfaces are a class of structured surfaces where texture has been engineered to reproduce a periodic pattern, specifically designed to meet a functional requirement. Despite having gained considerable acceptance in industrial production, tessellated surfaces still pose considerable challenges in terms of their metrological verification. The small scale of the dominant texture features requires the application of instruments typical of surface metrology; however, the computation of conventional surface texture parameters generally is not sufficient to capture the geometric properties and regularity aspects, which are fundamental for a complete characterisation of the pattern. In the work reported here, the characterisation of a periodic texture pattern is approached as a dimensional metrology problem, where the aim is the determination of target dimensional and geometric properties directly mapped to the design specifications. To illustrate the approach presented in this paper a specific test case, involving laser textured dimpled patterns designed to reduce friction in bearing applications, has been selected. This test case is used to highlight the many issues and critical aspects involved in the characterisation of tessellated surfaces