Modeling the topographic evolution of a rough metallic surface resulting from impact of water droplets

Waterjet peening (WP) is usually used to roughen metallic surfaces in order to improve cell adhesion on biomedical implants. Hence, surface roughness control using WP is of prime importance for such applications. A random finite element model of WP was developed, aimed at characterizing the surface coverage (the ratio of jet-affected area over total contact area) and surface roughness (in particular, the heights distribution). One perfectly flat and three rough metallic surfaces with different initial Sa (area arithmetic mean height) were generated, impacted and compared with each other. Numerical results show that a rougher initial surface necessitates more impingements than a smooth one to attain full surface coverage. The mechanisms influencing surface topography evolution, namely plastic deformation-induced roughening, peak clipping, valley deepening and valley filling are discussed. By modeling the roughness evolution resulting from WP, it appears that the process can be applied not only to roughen but also to polish rough initial surfaces in the investigated range. The present approach allows for systematic tuning of the system parameters in order to control the surface roughness.