Modelling ballistic cranial injury and backspatter using smoothed particle hydrodynamics

ABSTRACT Forensic investigation has the primary challenge of assessing cause from limited evidence. The use of computational modelling can play a role in assessing potential ballistic pathways in a crime investigation by analysing; (a) the entry wound and blood spatter patterns; (b) the influence of target materials; and (c) the cranial geometry, to inform the investigation process. In particular, the retrograde ejection of blood and tissue from the entry wound following projectile impact, called ‘backspatter’, and can help inform the proximity of the shooter and potentially differentiate between suicide and homicide, while providing other important forensic information. However, the ‘backspatter’ phenomenon is not well understood due to the lack of viable surrogate models and the difficulties of analysing the high-speed, extreme-force impact. This study presents (i) the development of an anatomically based model of cranial ballistic injury using the Smoothed Particle Hydrodynamics (SPH) method; (ii) the simulation of the tail splashing and temporary cavitation mechanisms and the effect of different cranial skin and cranium simulants on backspatter generation; (iii) an evaluation of anatomical geometry simulation results such as stress and strain and velocity of the particles ejected as backspatter; and (iv) a parametric study of the effect of bullet calibre and speed on the ballistic response of the anatomical geometry computational model.