Behaviour of helmets during head impact in real accident cases of motorcyclists

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Abstract
A motorcyclist is a vulnerable road user and the most often injured body segment is the head. The present study deals with motorcyclist's head protection and is focused on the behaviour of the helmet during simulated head impact in real accident cases. The analysis of real-world motorcyclist head trauma can be divided into three steps, i.e. accidentology to collect several real accident cases, kinematics reconstruction to obtain the initial conditions of the head just before the impact and helmeted head impact simulation to evaluate the behaviour of the helmet during impact and to assess the head injury risk. For each accident case, body kinematics has been simulated using MADYMO software. The initial condition, in terms of velocity and impact location, of the head just before the impact was then extracted and implemented in the finite element model of the human head coupled with a validated finite element model of a helmet in order to reconstruct the head impact. This impact analysis on the helmeted head allowed us to highlight the injury mechanisms specific to motorcyclists especially in terms of helmet and head loading. In this study, the relative velocities between head and impacted structure vary from 25 to 60 km/h with significant tangential components. The deformations of the constituting helmet's material vary from 17% to 90% for this rather low-energy impacts, demonstrating that improvement in material behaviour is needed in order to increase survival chances in the case of impact speeds above 30 km/h.