Roughness Influence on Human Blood Drop Spreading and Splashing.

Bloodstain pattern analysis (BPA) is used on a daily basis as evidence in crime scene reconstruction. However, though the impact behavior of complex fluid droplets have been extensively studied, important questions still remain. We investigate the influence of surface roughness and wettability on the splashing limit of droplets of blood, a non-Newtonian colloidal fluid. Droplets of blood perpendicularly impacting different surfaces at different velocities were recorded with a high-speed camera. The recordings were analyzed as well as the surfaces characteristics in order to find an empirical solution because we found that roughness plays a major role in the threshold of the splashing/nonsplashing behavior of blood compared to the wettability. Moreover, it appears that roughness alters the deformation of the drip stains. These observations are key to characterizing features of drip stains with the impacting conditions, yielding a more complete forensic analysis in certain cases.