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.

Response of the human torso to lateral and oblique constant-velocity impacts.

The objective of this study was to provide new biomechanical response data for the thorax with lateral and oblique loading, so as to support the development of safety systems for side impact protection that would offer the level of protection that has been achieved in frontal impact. Three male human cadavers were successively impacted by an impactor system delivering a constant velocity impact from the left and the right sides at three levels (shoulder, upper chest and mid-chest). Different impact directions were also chosen for each side: lateral, +15° posterolateral, -15° anterolateral. One subject was impacted at 1, 3 and 6 m/s whereas the other two subjects were impacted at 3 m/s only. A total of nineteen tests was performed. The impact force and the chest lateral deflection were measured using respectively a standard data acquisition system and also an optoelectronic stereophotogrammetric system (OSS). After each test, attempts were made to detect rib fractures by palpation, and a necropsy of the torso was performed after the tests series to document the injuries produced by all the tests. Overall, the peak impact force increased from the lowest impact level (mid-chest) to the highest (shoulder) and was found to be rate-sensitive. The force-deflection relationship was non linear for the shoulder impacts (stiffness increased with increasing deflection) whereas stiffness was nearly constant for the mid- and upper-chest impacts. The anterolateral impacts to the mid- and upper-chest generated more rib fractures than the other impact directions.

Biomechanical properties of the costovertebral joint.

Proper modeling of the human trunk requires a quantitative assessment of the stiffness of the costovertebral joints. Twelve samples (adjacent thoracic vertebrae and one rib segment) were harvested from three subjects. The ribs were loaded in the cranial-caudal direction, the ventral-dorsal direction and in torsion around the cervical rib axis. The force applied to and the displacement of the loading point on the rib were measured and used to determine the moment-angle responses. Characteristic average curves and boundary curves containing the dataset were developed. The torsion response presented a range of motion--defined as the change in the angle for an applied moment varying from -0.1 to 0.1 Nm--of 16.9+/-6.8 degrees which is more than three times the range in cranial-caudal flexion and five times the range in ventral-dorsal flexion. Statistical tests showed a significant difference between these ranges of motion. Significant inter-subject variability was observed for the cranial-caudal flexion (p<0.05) while no intra-subject variability appeared. The characteristic moment-angle responses of the joints were well represented by third order polynomials (R(2)>0.9). This study expands and supplements the limited data available in the literature. Furthermore, it provides biomechanical data (closed-form moment-angle functions) that can be directly integrated into spine-ribcage models.

Impact response of restrained PMHS in frontal sled tests: skeletal deformation patterns under seat belt loading.

This study evaluated the response of restrained post-mortem human subjects (PMHS) in 40 km/h frontal sled tests. Eight male PMHS were restrained on a rigid planar seat by a custom 3-point shoulder and lap belt. A video motion tracking system measured three-dimensional trajectories of multiple skeletal sites on the torso allowing quantification of ribcage deformation. Anterior and superior displacement of the lower ribcage may have contributed to sternal fractures occurring early in the event, at displacement levels below those typically considered injurious, suggesting that fracture risk is not fully described by traditional definitions of chest deformation. The methodology presented here produced novel kinematic data that will be useful in developing biofidelic human models. Additional analysis of the data produced by the reported tests as well as additional tests with a variety of loading conditions are required to fully characterize torso response including ribcage fracture tolerance.

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.

Investigations on the belt-to-pelvis interaction in case of submarining.

This study focuses on the phenomenon of lap belt slip on the iliac spines of the pelvis, commonly named "submarining". The first objective was to compare the interaction between the pelvis and the lap belt for both dummies and Post Mortem Human Subjects (PMHS). The second objective was to identify parameters influencing the lap belt hooking by the pelvis. For that purpose, a hydraulic test device was developed in order to impose the tension and kinematics of the lap belt such that they mimic what occurs in frontal car crashes. The pelvis was firmly fixed on the frame of this sub-system test-rig, while the belt anchorages were mobile. Fourteen tests on four Post-Mortem Human Subjects (PMHS) and fifteen tests on the THOR NT, Hybrid III 50th and Hybrid III 95th percentile dummies were carried out. The belt tension was kept constant while a dynamic rotation was imposed on the belt anchorages. The test results show that, in the tests where submarining occurred, the belt angle relative to the pelvis was systematically greater for the pelves of dummies than for those of PMHS. An increase in the belt tension resulted in a greater submarining angle for both dummies and PMHS. The pelvis and abdomen stiffnesses were observed to be similar for the PMHS and the THOR NT dummy while significantly lower for the Hybrid III dummies.