AbstractBallistic impact is one of the major causes for traumatic brain injury (TBI) and ballistic helmets are designed to provide protection from TBI. In real life, it is impossible to use real human subjects for experiments. Therefore, simulation based-methods are convenient to assess the rear effect to ballistic helmet impact and can provide crucial insights to injury. Rear effect happens when the interior of helmet is deformed and contacts with the human head. This paper proposes a simulation-based method to study the rear effect by using Head Injury Criterion (HIC) when the ballistic helmeted headform is impacted by a bullet with different impact angles and at various impact positions. Commercial software package LS-DYNA is employed to simulate the impact. A high fidelity headform model including detailed skull and brain has been used for the simulation purpose. Helmet and bullet are modeled according to the real shapes. The results show that, with a larger impact angle, the HIC score is smaller and ...