Plusieurs études ont montré que dans les accidents réels, la vitesse d’impact de la tête n’est que rarement normale à la surface et présente une composante tangentielle non négligeable. Aucune norme, à l’heure actuelle ne propose de choc oblique avec enregistrement de l’accélération en translation et en rotation de la fausse tête. Un aspect essentiel de cette recherche a été d’aborder les descriptions d’accidents réels impliquant un motocycliste et un véhicule afin d’évaluer les conditions aux limites de la tête juste avant impact, en termes de vecteur vitesse et de localisation d’impact. Cette étude a permis d’établir le vecteur vitesse possible et de l’angle d’impact de la tête du motocycliste en situation. Une méthode de test pour évaluer le casque a été proposée. Les tests d'impact obliques, sont effectués avec une vitesse d’impact de 8.5 m/s sur une enclume inclinée de 45° permettant la rotation autour de l’axe Y X et Z. Les accélérations 6-D sont implémentés dans le modèle SUFEHM afin d’extraire la déformation axonal maximale et le risque lésionnel. Cette fusion de la méthode expérimentale et numérique donne un avantage par rapport aux normes conventionnelles, tant en termes de conditions d’impact qu’en termes de critère de blessure de la tête. / It is well know that in case of accident the head does not only impact perpendicularly to the impacted structure but presents an oblique impact condition. However none of the today helmet standards do integrate oblique impacts with the recording of the dummy head rotational acceleration. An essential aspect of the present research is to simulate real world accident and to compute the victim’s kinematic in order to extract the head impact conditions. In collaboration with University Florence (Italy) 19 cases were considered and it was shown that the head impact velocity vector presents a significative angle. A novel helmet test method has been proposed. Helmeted headfoml is impacting a 45° inclined anvil at a speed of 8.5 m/s and the 6D acceleration versus time curves are introduced into an existing head FEM in order to compute the axon strains and to derive the brain injury risk.

Les piétons comptent parmi les usagers de la route les plus vulnérables dans la mesure où ils ne bénéficient d'aucune protection en cas d'impact avec un véhicule automobile. Plus de 1,17 millions de personnes sont tués sur la route de part le monde dont environ 65% ce piétons. Les blessures de la tête, souvent fatales, concernent environ 30 % des blessures enregistrées. Ces blessures conduisent à des incapacités de longue durée avec un coût sociétal et économique immense. Il est par conséquent essentiel de comprendre aussi bien les mécanismes d'accidents que les mécanismes de blessure de la tête afin d'intervenir sur la conception de la face avant des véhicules automobile. Dans ce contexte l'objet de la présente thèse est d'analyser la répons dynamique du piton en cas d'accident et ce contribuer au développement de critères de blessure de la tête. Dans le but d'étudier l'influence de la position du piéton, de la géométrie de la face avant du véhicule et de sa vitesse initiale sur la cinématique du piéton et les conditions d'impact de la tête, une simulation multi-corps a été mise en place. Les résultats de ces simulations donnent la vitesse et l'angle d'impact de la tête et la position de l'impact sur le véhicule. Cette analyse paramètrique a été conduite sur cinq types de véhicules et pour un modèle humain adulte et enfant de 6 ans et a permis de consolider les connaissances sur la conditions d'impact de la tête en comparaison avec les tests normatifs en vigueur.[...] / Pedestrians are regarded as an extremely vulnerable and high-risk group of road users since they are unprotected in vehicle impacts. More than 1.17 million people throughout the world are killed in road traffic accidents each year. Where, about 65% of deaths involve pedestrians. The head injuries in vehicle-pedestrian collisions accounted for about 30% of all reported injuries on different body regions, which often resulted in a fatal consequence. Such injuries can result in disabilities and long-term sequence, which lead to significant social costs. It is therefore important to study the characteristics of pedestrian accidents and understand the head injury mechanism of the pedestrian so as to improve vehicle design for pedestrian protection. The aim of this study is to investigate pedestrian dynamic response and develop head injury risk functions.In order to investigate the effect of pedestrian gait, vehicle front geometry and impact velocity on the dynamic responses of the head, the multi-body dynamic (MBD) models were used to simulate the head responses in vehicle to pedestrian collisions with different vehicle types in terms of head impact point measured with Wrap Around Distance (WAD), head relative velocity and impact angle. A simulation matrix is established using five vehicle types, and two mathematical models of the pedestrians represented a 50th male adult and a 6 year old child as well as seven pedestrian gaits based on typical postures in pedestrian accidents. In order to simulate a large range of impact conditions, four vehicle velocities (30 km/h, 40 km/h, 50 km/h and 60 km/h) are considered for each pedestrian position and vehicle type.A total of 43 passenger car versus pedestrian accidents were selected from In-depth Investigation of Vehicle Accidents in Changsha, China (IVAC) and German In-Depth Accident Study (GIDAS) database for simulation study. According to real-world accident investigation, accident reconstructions were conducted using multi-body system (MBS) pedestrian and car models under MADYMO simulation environment to calculate head impact conditions, in terms of head impact velocity, head position and head orientation. In order to study kinematics of adult pedestrian, relationship curves: head impact time, throw distance, head impact velocity and vehicle impact velocity, were computed and logistic regression models: head impact velocity, resultant angular velocity, HIC value, head contact force and head injuries, were developed based on the results from accident reconstructions.The automobile windshield, with which pedestrians come into frequent contact, has been identified as one of the main contact sources for pedestrian head injuries. In order to investigate the mechanical behavior of windshield laminated glass in the caseof pedestrian head impact, windshield FE models were set up using different combination for the modeling of glass and PVB, with various connection types and two mesh sizes (5 mm and 10 mm). Each windshield model was impacted with a standard adult headform impactor in an LS-DYNA simulation environment, and the results were compared with the experimental data reported in the literatures.In order to assess head injury risks of adult pedestrians, accident reconstructions were carried out by using Hybrid III head model based on the real-world pedestrian accidents. The impact conditions were obtained from the MBS simulation, including head impact velocity, head position and head orientation. They were used to set the initial conditions in a simulation of a Hybrid III FE head model striking a windshield FE model. Logistic regression models, Skull Fracture Correlate (SFC), head linear acceleration, Head Impact Power (HIP), HIC value, resultant angular acceleration and head injuries, were developed to study brain injury risk.{...]