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This paper describes the development of a hybrid-computer simulation of a recreational snowmobile. The vehicle has been mathematically represented by a displacement-driven, damped nonlinear spring-mass system with two degrees of freedom. The analog circuit and the logic level control system of the analog/hybrid computer is discussed. The use of a hybrid system using Hytran Operational Interpreter to perform OFF-LINE and ON-LINE checks is also discussed. Finally, a method to display a visual representation of the vehicle on an oscilloscope screen is presented. The simulation permits vehicle designers to vary at will the various design parameters and to observe immediately the effect of so doing.

Recently, several cases of mild traumatic brain injury to American professional football players have been reconstructed using instrumented Hybrid III anthropomorphic test dummies ATDs. The translational and rotational acceleration responses of injured and uninjured players'' heads have been documented. The acceleration data have been processed according to all current head injury assessment functions including the GSI, HIC and GAMBIT among others. A new hypothesis is propounded that the threshold for head injury will be exceeded if the rate of change of kinetic energy of the head exceeds some limiting value. A functional relation is proposed, which includes all six degrees of motion and directional sensitivity characteristics, relating the rate of change of kinetic energy to the probability of head injury. The maximum value that the function achieves during impact is the maximum power input to the head and serves as an index by which the probability of head injury can be assessed.

A new form of head and neck protection for racing car drivers is examined. The concept is one whereby the helmet portion of the system is attached, by way of a quick release clamp, to a collar-like platform which is supported on the driver's shoulders. The collar, which encircles the back and sides of the driver's neck, is held in place by way of the on-board restraint belts. The interior of the helmet portion of the assembly is large enough to provide adequate volitional head motion. The overall objective of the design is to remove the helmet from the wearer's head and thereby to mitigate the deleterious features of helmet wearing such as neck fatigue, poor ventilation and aerodynamic buffeting. Just as importantly, by transferring the weight of the helmet and all attendant reaction forces associated with inertial and impact loads to the shoulder complex (instead of to the neck), reduced head and neck injury probability should be achievable.

This paper discusses an attempt to relate measured loading at the head neck junction of arestrained six year old ATD during a frontal crash, to the mechanism of upper cervical fracture dislocation in young children. Lap belt, lap shoulder belt anda four point restraint system are considered. The basis for the reconstructions is the fatal injury to lap-belt restrained young children seated in the rear seat of contemporary minivans. The study concludes that simple forces and bending moments measured on such an ATD may not provide a sufficient basis for judging the likelihood of such an injury. Suggestions for a more comprehensive injury analysis are made.

This paper describes the efforts of one group to improve the biomechanical fidelity of ATD headforms used in automotive crash testing. On the basis of recent cadaver head impact studies and on the literature dealing with facial bone tolerances, several refinements have been made to the Hybrid III head-form. These include a slight modification of effective skull stiffness, the addition of a frangible faceform sub-assembly and the introduction of a compliant mandible. The purpose of these modifications is to improve both the response characteristics to impact as well as to provide a direct means to monitor for facial bone injury.

The braking characteristics of three typical recreational snowmobiles have been studied. Of particular interest was the sensitivity of the machines to different applied braking loads. The data were collected using a variable-load braking apparatus and stop-action high-speed photography. The results have been described with an empirical equation. It was determined further that the most effective braking was achieved when the track was locked and this particular behavior has also been characterized by an empirical expression.

Abdominal injury to automobile occupants can be caused by the lap portion of the belt restraint if it is not well deployed below the wearer's iliac spines. A new test device, capable of providing a quantitative measure of lap belt fit is described. Based on the standard 3 dimensional “H-point machine”, the device has been validated with a large number of occupants seated in a wide variety of contemporary passenger cars. Procedures for employing the device are presented.

The origin and development of the Head Injury Criterion (HIC) has been reviewed. The concept of correlating internal head injury with measured kinematics has also been re-examined. It is concluded that since no general kinematic correlation can be developed, the HIC concept is invalid. Recent attempts to develop relationships between head injury AIS and HIC, are shown to substantiate this view. Alternatives to HIC are reviewed and other approaches to head injury assessment are proposed.

The validity and appropriateness of the application of the Head Injury Criterion (HICm) concept to motorcycle helmet testing has been examined. Its derivation has been reviewed and its logic assessed. It is shown to be an inconsistent and unreliable criterion for helmet performance evaluation. This inconsistency stems primarily from its poor correlation with experimental data and from the basic assumption that the seriousness of a head impact can be ascertained by considering only a portion of the test headform acceleration pulse. Several alternative criteria which all are physically sound and mathematically consistent and which are more amenable to protective headgear design and testing are proposed. These criteria include force and loading time minimization; load distribution; minimization of loading rate and maximization of energy dissipation.

Impact performance criteria employed in the evaluation of protective headgear often consider the temporal characteristics of the translational acceleration induced in the helmeted headform during impact. These implicit criteria may appear as limits on the time during which the test headform acceleration is allowed to exceed certain values, or may be inherent in the pass/fail criterion itself. The present study examines the significance of time as a parameter in the prediction of head injury likelihood or severity. It is shown that since the temporal characteristic of the acceleration waveform is simply a reflection of the mechanical characteristics of the headform/helmet assembly it bears only a trivial relation to the input forcing function and thus is generally uncorrelatable to head injury severity.

A high-speed motion picture analysis of a typical snowmobile suspension system has been conducted. The bogie wheel system at the vehicle track and the leaf springs at the skis have both been examined as the vehicle traversed a prescribed ground profile. The technique has proven to be quite useful in determining the effectiveness of the suspension system. Several tentative recommendations for improving vehicle stability have been made as a result of this study.