Experimental and numerical considerations of helmet evaluation under oblique impact

Abstract

Based on real-world bicycle accident reconstructions and virtual accident simulations, the present study proposes realistic head-impact conditions in terms of oblique impact velocities. Thus, an existing bicycle helmet has been impacted frontally and laterally under oblique impacts with a Hybrid III dummy head fully instrumented for a 6D motion recording. The head acceleration curves were implemented in the Strasbourg University Finite Elements Head Model to assess the brain-injury risk in terms of intracerebral Von-Mises stress. Results of the experimental respectively numerical head response are expressed in terms of maximum linear and rotational accelerations, HIC, and brain-injury risk. Results show maximum linear acceleration of about 152g leading to HIC of 700. The maximum rotational head accelerations ranged from 5 to 12 krad/s², according to the rotation axis. The numerical head-injury risk assessment conducted to a risk of moderate DAI (Diffuse Axonal Injury) in the 27% to 70% range. These results demonstrated that the direction and time evolution of linear and rotational accelerations need to be taken account via the use of model-based head-injury criteria. This study is therefore a demonstrator for novel helmet test method as well as a step for advanced bicycle helmet design.