Geometrical and material parameters to assess the macroscopic mechanical behaviour of fresh cranial bone samples.

The present study aims at providing quantitative data for the personalisation of geometrical and mechanical characteristics of the adult cranial bone to be applied to head FE models. A set of 351 cranial bone samples, harvested from 21 human skulls, were submitted to three-point bending tests at 10 mm/min. For each of them, an apparent elastic modulus was calculated using the beam's theory and a density-dependant beam inertia. Thicknesses, apparent densities and percentage of ash weight were also measured. Distributions of characteristics among the different skull bones show their symmetry and their significant differences between skull areas. A data analysis was performed to analyse potential relationship between thicknesses, densities and the apparent elastic modulus. A specific regression was pointed out to estimate apparent elastic modulus from the product of thickness by apparent density. These results offer quantitative tools in view of personalising head FE models and thus improve definition of local injury criteria for this body part.

Kinematics and dynamics of the pelvis in the process of submarining using PMHS sled tests.

This study focused on a better understanding and characterization of the submarining phenomenon that occurs in frontal crashes when the lap belt slides over the anterior superi or iliac spine. Submarining is the consequence of the pelvis kinematics relative to the lap belt, driven by the equilibrium of forces and moments applied to the pelvis. The study had two primary purposes; the first was to provide new PMHS data in submarining test configurations, the second was to investigate the Hybrid II and Hybrid III dummies biofidelity regarding submarining. Several Post Mortem Human Subject (PMHS) studies have been published on this subject. However, the lack of information about the occupant initial positioning and the use of car seats make it difficult to reconstruct these tests. Furthermore, the two dummies are rarely compared to PMHS in submarining test configurations. A fifteen frontal sled test campaign was carried out on two Anthropomorphic Test Devices (ATDs) and nine PMHS. The test environment was designed to be reproducible. It consisted of a rigid seat, a 2-poi nts shoulder belt and a 2-points lap belt instrumented to record their 3D forces at anchorage. The subjects were instrumented with angular sensors at the sacrum, T1 and T12 levels to record their initial angles. Kinematics was measured at these three levels by means of three accelerometers and angular velocity sensors. A PMHS positioning procedure was developed to ensure repeatability. A pre-test was performed on each subject to characterize its lumbar spine static behavior. All the subjects were CT-scanned from head to toe prior to the test. The campaign was divided into three test configurations leading to different surrogates' interaction with the environment and different kinematics. This resulted in a wider range of behaviors for the dummies evaluation. The deceleration pulse, initial lap belt angle, lap belt slack, seat pan angle and footrest position varied. The Hybrid II and Hybrid III dummies and three PMHS were tested in each configuration. Forces and kinematics time history corridors based on the PMHS responses are provided for each configuration. The dummies' responses are evaluated against these targets. For the first configuration (40 km/h), the peak lap belt tension for both sides was between 3,000 N and 6,385 N for the three PMHS while it was around 4,700 N and 6,200 N in average for Hybrid II and Hybrid III respectively. The maximum pelvic rotation ranged from 41° to 80° for the PMHS and reached approximately 45° for the two dummies. For the other two configurations (50 km/h), the peak lap belt tension varied from 3,660 N to 7,180 N for the PMHS and was between 5,400 N and 6,100 N for Hybrid II and between 7,145 N and 7,900 N for Hybrid III. The maximum pelvic rotation ranged from 43° to 73° for the PMHS, while it reached approximately 54° and 46° for Hybrid II and Hybrid III respectively.

Determination of pre-impact occupant postures and analysis of consequences on injury outcome--part II: biomechanical study.

This paper considers pre-impact vehicle maneuvers and analyzes the resulting driver motion from their comfort seating position. Part I of this work consisted of analyzing the driver behavior during a simulated crash in a car driving simulator. The configuration of the virtual accident led to an unavoidable frontal crash with a truck. The typical response to this type of emergency event was to brace rearward into the seat and to straighten the arms against the steering wheel, or, to swerve to attempt to avoid the impacting vehicle. In a turn crossover maneuvers, the forearm is directly positioned on the airbag module at time of crash. This position represents a potential injurious situation and is investigated in this Part II. Static airbag-deployment tests were realized in collaboration with Zodiac using conventional airbag (sewn cushion, pyrotechnical system and open event) and a Hybrid III 50th Male Dummy seated with the left arm positioned in the path of the deploying airbag. These experiments were numerically reproduced with Madymo and the ellipsoid Hybrid III dummy model. The dummy arm interaction with airbag was correlated with experiments. Then, a numerical simulation of a frontal collision at 56 km/h was realized. The results of the computational runs put forward injurious situations when the driver's arm was in front of the steering wheel. Indeed, in this case, the arm could hit the head under airbag deployment and induced serious neck bending and violent head launching. To mitigate head and neck trauma in this out-of-position situation, an airbag prototype (bonded cushion, two pure helium cold gas generators allowing mono- or multi-stage inflating, patented silicone membrane) was proposed by Zodiac. The results of static airbag-deployment tests with conventional and prototype airbags showed a significant reduction of the maximum linear head acceleration and neck bending with airbag prototype when a dual stage inflating was ignited, due to a reduced 'flinging' of the arm.

Traumatic rupture of thoracic aorta in real-world motor vehicle crashes.

OBJECTIVE: Traumatic rupture of thoracic aorta (TRA) was reported in the literature to be a major cause of death in motor vehicle crashes. This study aims at evaluating the most relevant risk factors of TRA. It also aims at analyzing the types of TRA as a function of car crash conditions and rib cage fractures. METHODS: In-depth crash data collected from 1998 to 2006 as part of the Co-operative Crash Injury Study (CCIS) were retrospectively investigated to assess frontal, near-side, and far-side injury risks. This database includes 15,074 occupants with individual detailed autopsy reports. Multivariate statistical analyses were performed. The influence of the following variables on TRA occurrence was studied: gender and age of the involved occupant, ETS, compartment intrusion, and restraint system. Features of TRA and rib cage fractures were described thanks to autopsy data. RESULTS: Although TRA occurred in only 1.2% of all occupants, TRA victims accounted for 21.4% of all fatalities. The incidence of TRA was found twice higher in side impacts (2.4%) than in frontal ones (1.1%). TRA injury risk increased with ETS, intrusion, and age and decreased with the absence of intrusion regardless of the impact direction. It also decreased for belted occupants in frontal impacts. Except for the site of injury, the TRA features were similar whatever the crash conditions. The multiple ribs fractures were the most common injuries associated with TRA (79.1%) and TRA victims with uninjured or slightly injured (AIS 1) rib cage were significantly younger (p < 0.0001) than other TRA victims. Whatever the impact type, the TRA victims sustained mostly bilateral rib fractures (68%). Results also emphasized a close relationship between the principal direction of force and the body side with more fractured ribs. However, whatever the impact type, the aortic injury site or the side of the thorax, fractures concerned mainly the 2nd up to the 7th ribs of TRA victims. CONCLUSIONS: This study emphasized four main variables influencing the TRA occurrence: ETS, compartment intrusion, age, and seat belt use. The results suggested that the injury site may be different depending on the occupant or the impact type. However, the typical TRA, i.e., a partial or complete aorta transection within the peri-isthmic region, affected any occupant independently of age and impact type. The high frequency of bilateral rib cage fractures observed in TRA victims and the significant influence of intrusion on TRA occurrence emphasized that the aortic injury mechanism mainly involves a severe direct chest impact or compression.