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This study explores the dynamics of head and cervical spine impact with the specific goals of determining the effects of head inertia and impact surface on injury risk. Head impact experiments were performed using unembalmed head and neck specimens from 22 cadavers. These included impacts onto compliant and a rigid surfaces with the surface oriented to produce both flexion and extension attitudes. Tests were conducted using a drop track system to produce impact velocities on the order of 3.2 m/s. Multiaxis transduction recorded the head impact forces, head accelerations, and the reactions at T1. The tests were also imaged at 1000 frames/sec. Injuries occurred 2 to 30 msec following head impact and prior to significant head motion. Head motions were not found to correlate with injury classification. Decoupling was observed between the head and T1, resulting in a lag in the force histories.

Basilar skull fractures comprise a broad category of injuries that have been attributed to a variety of causal mechanisms including mandibular impacts. The objective of this work is to develop an understanding of the biomechanical mechanisms that result in basilar skull fractures when the head is subject to a mandibular impact. In the characterization of the injury mechanism, two experimental studies have been performed. The first study evaluated the tolerance of the mandible subject to midsymphysis loading on the mental protuberance (chin). Five dynamic impacts using a vertical drop track and one quasi-static test in a servo-hydraulic test frame have been performed. Impact surfaces were varied to assess the influence of loading rate. The mean mandibular fracture tolerance among the six tests was 5270 ± 930 N and appears insensitive to loading rate. In each test, clinically relevant mandibular fractures were produced. No basilar skull fractures were observed.

The passive combined flexion and axial loading responses of the unembalmed human cervical spine were measured in a dynamic test environment. The influence of end condition (the degree of constraint imposed on the head by the contact surface) was varied to determine its effect on observed column stiffness and on failure modes of the cervical spine. Multi-axis load cells were used to completely describe the forces and moments developed in the specimen. Twenty three specimens were studied. The Hybrid III neckform performance was assessed to determine its suitability as a mechanical simulator of the neck during head impact. Changes in end condition produced significant changes in axial stiffness in both the Hybrid III neckform and the cadaver neck. The mode of injury also varied as a function of end condition in a repeatable fashion. Separation of injuries based upon imposed end condition identified groups with significantly different axial load to failure.

The passive torsional responses of the human cervical spine were investigated using unembalmed cervical spines in a dynamic test environment. Kinematic constraints were designed to simulate in vivo conditions. A physiologic axis of twist was determined based on a minimum energy hypothesis. Six-axis load cells completely described the resultant forces. Results include viscoelastic responses, moment-angle curves, and piece-wise linear stiffness. The Hybrid III ATD neckform was also tested, and its responses compared with the human. The Hybrid III neckform was stiffer than the human, was more rate sensitive than the human, and unlike the human, was relatively insensitive to the axis of twist. A rotational element to improve the biofidelity of the Hybrid III neckform in rotation was developed, and the results presented.

The lateral, anterior and posterior passive bending responses of the human cervical spine were investigated using unembalmed cervical spinal elements obtained from cadavers. Bending stiffness was measured in six modes ranging from tension-extension through compression-flexion. Viscoelastic responses studied included relaxation, cyclic conditioning and constant velocity deformation. A five-axis load cell was used to measure the applied forces. Results include moment-angle curves, relaxation moduli and the effect of cyclic conditioning on bending stiffness. The Hybrid III ATD neckform was also tested and its responses are compared with the human. It was observed that the Hybrid III neckform was more rate sensitive than the human, that mechanical conditioning changed the stiffness of the human specimens significantly, and that changing the end condition from pinned-pinned to fixed-pinned increased the stiffness by a large factor.

Time-varying compressive loading was applied to unembalmed human cervical spines using an MTS closed-loop hydraulic testing machine. Load programs included relaxation, cyclic loading, variable rate constant velocity loading (0.13-64 cm/sec), and constant velocity loading to failure. The failures produced were similar to those observed clinically. A generalized quasi-linear viscoelastic Maxwell-Weichert model incorporating a continuous relaxation spectrum was developed to predict the relaxation and constant velocity test responses. The fit was adequate considering the complexity of the structure involved.

A new crash test device has been developed, called “Repeatable Pete.” It is a repeatable, durable anthropomorphic dummy with humanlike dynamic performance. This paper describes the device and gives details of its design and performance during testing in automotive situations. The head, neck, and chest match the latest biomechanical information on the dynamic responses of unembalmed cadavers. The head c.g. accelerations adequately match the skull acceleration, so that head injury criteria based upon cadaver skull acceleration may be used.

This paper describes the development of an improved neck simulation that can be adapted to current anthropometric dummies. The primary goal of the neck design is to provide a reasonable simulation of human motion during impact while maintaining a simple, rugged structure. A synthesis of the current literature on cervical spine mechanics was incorporated with the results of x-ray studies of cervical spine mobility in human volunteers and with the analysis of head-neck motions in human volunteer sled tests to provide a background for the design and evaluation of neck models. Development tests on neck simulations were carried out using a small impact sled. Tests on the final prototype simulation were also performed with a dummy on a large impact sled. Both accelerometers and high-speed movies were used for performance evaluation.

This paper discusses the development of adequate criteria and evaluation methods for seat belt restraint design. These criteria should include the effect of seat belts in abdominal injury as well as head injury. It is concluded that belt load limiters and energy-absorbing devices should limit head-to-vehicle contact, ensure that the lap belt maintains proper contact with the bony pelvic girdle, and limit the belt loads. Studies are made of pulse shape and belt fabrics. Currently available mathematical models are used for the studies included in the paper.

In a previous study, an extensive study of the dynamic performance of child seating systems indicated that little protection was provided under circumstances other than panic braking. This study was performed with impact test conditions of 30 mph frontal and 20 mph lateral and rear barrier impacts with seating systems meeting the requirements of FMVSS 213. Additionally, the performance of prototype seats developed under contract with the Department of Transportation under similar test conditions will be presented to compare the protective qualities available with seats of current design and those that could become available in the future. The performance of the child seats will be evaluated using two criteria, motion limits and acceleration limits. It is believed that the performance of child seats can be determined without the extensive test equipment and facilities required for adult seating and restraint systems.

A study of the biomechanical factors concerned with the design of side structures and doors for crashworthiness has been made. Questions regarding optimum stiffness, location of reinforcing members, effect of armrests, and padding have been answered within the framework of injury criteria models. Results of animal studies, cadaver studies, and anthropometric dummies have been combined to produce injury criteria for lateral impacts to the head, thorax, and abdomen. Impacts were applied utilizing a specially designed “air gun” in a laboratory environment emphasizing reproducibility and control. Full-scale crash simulations were performed on an impact sled to verify the results of the more specialized tests and analyses. Scaled models of current production doors were used in the animal series. Scaling relationships for various species of animals have been developed and extrapolated to man. Significant differences in right and left side tolerances to impact were noted and detailed.