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Airbag induced injuries to front seated infants and children have resulted in US government recommendations that suggest, among other things, the placement of children into the rear seat area of motor vehicles. During a rear impact, however, most conventional automotive front seats occupied by adults will collapse into the rear seat area. This exposes the rear-seated children to other risks of injuries. Rearward load strength tests run on a wide variety of commercially available automotive front seat systems, such as the single or dual sided recliner types and the stronger belt integrated types, demonstrate a wide range of occupant load resistance. Digital human simulation offers a cost effective, efficient, and accurate means for predicting occupant response and interactions influenced by various types of non-linear deforming seat systems, as well as various types of restraints, and vehicle interior structures.

Static and dynamic studies were conducted with conventional and belt integrated vehicular seats. Most conventional seat backs failed with a static FMVSS 207 rearward torque of approximately 700 to 800 Newton meters (Nm) while integrated seats sustain a comparably measured torque of up to approximately 3,500 to 4,000 Nm. Correspondingly greater rearward changes in speed can be sustained by integrated seats with less likelihood of injury to front and rear seated occupants. The dynamic tests demonstrate the importance of testing within the full vehicle interior structure to insure that floor strength is compatible with seat strength to attain optimum occupant protection in stronger seat designs and to assess injury risk to occupants in collapsing seat designs.

Current transportation safety interests involving the use of restraints in school buses, coupled with litigation claims arising from injuries to unrestrained occupants of school buses involved in rollovers, resulted in a study aimed at: understanding the biomechanical response and injury causing factors associated with unrestrained students involved in an actual school bus roll-over accident; and, comparing the unrestrained response condition to the hypothetical response if the students were lap belt restrained in the same rollover. A numerical occupant simulation computer code was used to input vehicle rollover motion to both belted and unbelted occupants. The unrestrained case theoretically duplicated the injury producing conditions that led to serious head and neck injury in certain students.

This study examines in some detail 23 actual rear-impact cases dealing with front seat collapse and compares the findings with similar results from 23 Canadian cases. In addition, seat tests and car-to-car crash tests are utilized to examine the potential hazards and/or benefits of collapsing versus non-collapsing seat systems. Evaluation of the above 46 cases indicates that an extremely high rate of rearward ejection occurs to restrained front-seat occupants subjected to rear impact. The majority of those ejected experienced serious to fatal injuries, either from contact in the rear or outside of the vehicle, when seated in collapsing seats. These results are contrary to some earlier published data and, as such, recommendations are made which could help improve data collection methods so as to better evaluate the issues associated with rear-impact seat strength.

An experimental design strategy is presented for the purpose of obtaining efficient and statistically reliable data for the evaluation of multi-variable parameter effects on crash-impact and passive occupant protection materials. Two methods in particular, the factorial and the box-Behnken, are presented and applied to a variety of energy-absorbing materials including: Ethafoam, Ensolite, Sorbothane, and expanded bead polystyrene. Results of the study suggest that Sorbothane could be used to effectively reduce injury potential in vehicle areas which are size constrained from using lighter but thicker energy-absorbing padding materials. The factorial method is also used to demonstrate qualitative evaluation of data obtained from the National Highway Transportation Safety Administration Thoracic Side Impact Protection Research Program. The results of this phase of the paper indicate the high level of importance associated with side-impact occupant protection materials.

The basic physical mechanisms underlying recent experimentally observed anomalous behavior in the impact performance of safety helmets evaluated with soft (human-like) and hard (magnesium alloy) headform surrogates are qualitatively and quantitatively explained in this paper. The principal and physical mechanisms brought to light in the headform surrogate investigation are directly applicable to the utilization of other forms of surrogates (head -neck, thorax, whole body). In particular the results raise a serious question as to the validity of using non-human responding surrogates, with human generated injury tolerance data, for the purpose of assessing safety system performance. The implications of the results are that good crash-impact protective devices (helmets, restraints, etc.) could be penalized and, equally important, less safe crash-impact protective system designs could result from improper assessment of safety system performance.

An interactive hybrid technique has been investigated as a feasible method for allowing the designer a means to predict failure modes and general crashworthiness response of complex multi-degree of freedom structural systems, such as the automotive vehicle, without the necessity of innumerable, costly destructive tests. The technique employs average internal energy of deformable elements and internal reaction load density spectrums, with a simplified yield and buckling criterion, as the mechanism for predicting collapse modes of the shock excited system containing large arbitrary shaped rigid bodies which are linked by structural elements, composed of nonlinear, rate-sensitive, materials. Incremental finite element approximations account for the system nonlinearities in critical regions, identified by the predicted collapse mode, so as to allow judicious modeling of the system.