Claude Tarriere

Development of a Finite Element Model of the Neck

Head neck responses from volunteer experiments, as obtained in various loading directions by the Naval Biodynamics Laboratory (NBDL), represent a unique set of data in the biomechanical research field. From this a set of volunteer thoracic (TI) and head responses were selected as a reference for this study. The objective of the study is to develop a finite element model (FEM) of the human neck in frontal and lateral directions. The number of elements in the model were kept low in order to reduce the processing time for simulation and to minimize damping problems. The structure of the model is as follows: the vertebrae and the head were considered as rigid bodies. The interface between vertebrae such as discs and different ligaments are modelled by brick and spring elements. The passive action of the muscles are taken into account when determining the stiffness characteristics of the ligaments. Satisfactory results were obtained in terms of kinematic responses of the head (comparison with NBDL data) in frontal and lateral directions. Further investigations are needed for modelling the muscles to allow for injury prediction. The paper describes the characteristics of this model, the rationale behind the definition of model elements, and the performance compared with the volunteer reference. For the covering abstract of the conference see IRRD 879189.

Correlation between thoracic lesions and force values measured at the shoulder of 92 belted occupants involved in real accidents

The 3-point static belts that are installed in Renault and Peugeot vehicles are equipped with a force limiter near the upper anchorage. This system is made up of several bands of textiles that tear successively for the increasing levels of force exerted by the occupant. One can thus associate, for each person in the accident, the degree of the thoracic AIS and the value of the support force, expressed in daN. This relationship is established for 92 belted occupants who were involved in frontal impacts. In addition it is indicated which are the distributions of impact violence parameters incurred and which are the distributions of ages in order to determine the statistical meaning of the required results. The levels of tolerance observed in this sample are compared to thoracic injuries observed on belted cadavers exposed to equivalent violent impacts.

VALIDATION STUDY OF A 3D FINITE ELEMENT HEAD MODEL AGAINST EXPERIMENTAL DATA

The basis of assumptions involved in the development of a 3D human head model by comparing its global response with cadaver tests is evaluated. Finite element model development is based on idealizations concerning the geometry, the material properties, the boundary conditions of each represented part and the interfaces between the different parts. The relevance of the model idealizations specially related to the skull and subarchnoid space modelling is assessed.

Comparison of Experimental Car-Pedestrian Collisions Performed with Various Modified Side-Impact Dummies and Cadavers

Experimental car-pedestrian collisions were performed with a modified PART 572 dummy and cadavers; they involved some reconstructions of real accidents. These collisions brought to light the differences between the kinematics and the impact responses when dummy and human subject are compared under identical and realistic test conditions to simulate a pedestrian struck sideways. These differences are mainly due to the overall relative stiffness of the PART 572 dummy when compared to cadavers. Same-type collisions were therefore carried out again with other dummies which were designed so as to simulate human response in lateral impact better; thus they were also assumed to display better kinematics as pedestrians. APROD and ONSER dummies were used; when compared to PART 572, their flexibility and deformation capabilities are greater, in particular as regards their thoraxes and shoulders.

CONDITIONS REQUIRED TO AVOID BEING KILLED IN CARS IN SIDE IMPACT

A study was made of the conditions in which occurred side impacts having led to death of 369 car occupants. This sample is representative of the population of fatal collisions having occurred on French roads, in 1980. 28% of killed were victims of collisions against another private car, 34% struck a fixed obstacle, 21% underwent a collision against a truck. The other types of collisions account for 17%. The performances to be reached in order to spare an important number of victims are of a high level. This is measured as a function of the distribution of impact violences and occupants ages. The description given in this report of fatal side-impact collisions yields insight into the level of requirements that must be satisfied in order to protect a significant proportion of victims. It enables us to measure the challenge represented by protection against the risk of the occurrence of death in this kind of accident.

OCCUPANT VELOCITY CHANGE IN SIDE IMPACT METHOD OF CALCULATION--APPLICATION TO A SAMPLE OF REAL-WORLD CRASHES

A method is presented for calculating the change in velocity (deltaV) of the occupant on the near side of impact in a car-to-car collision. The method can be applied to real-world accidents under the following conditions: presence of an occupant in a line with the impacted structure, impacted vehicles longitudinal velocity not exceeding 20% of the impacting vehicles velocity, and angle of collision 90 degrees plus/minus 30 degrees. Preliminary validation of the method via a series of experimental collisions is described, and application to 60 real-world accidents is discussed. A high correlation was found between occupant deltaV and pelvis and thorax injury severity (Abbreviated Injury Scale). The correspondence between injury severity and either car deltaV or impact velocity was not as great. For given occupant deltaV values, relationships are established between Hybrid II dummy acceleration levels and the severity of injuries sustained by cadaver subjects and by persons involved in crashes.

Reconstruction of actual car-pedestrian collisions with dummy and cadavers

Car-pedestrian accidents were selected with reference to criteria like relevance in terms of injury severities, representativity and reproducibility, aiming for as accurate as possible reconstructions by dummy and cadaver tests. Parameters necessary for performance of these reconstructions were evaluated from the data of accident investigation teams. Preliminary tests were performed by research departments of automobile manufacturers to check the estimated conditions of these accidents before performing their reconstructions. A particular aim was to obtain insights into the mechanisms leading to injuries in pedestrian accidents; more generally, reconstructing actual accidents is a privileged approach to determine human tolerance limits and the corresponding protection criteria on dummies; the injuries resulting from the actual accidents are consequently compared with the data measured on dummies and cadavers in the reconstruction experiments. Conclusions are also related to the methodology of such reconstructions.

FROM THREE-YEARS-OLD TO ADULT SIZE--HOW TO ENSURE CHILD PROTECTION IN AUTOMOBILE ACCIDENTS

Safety of children as car occupants raises a specific problem: it is necessary to take into account two factors which are particular to them: their very fast growth and their behavior, which corresponds to a need for movement. An analysis of statistical and accidentological data points to the fact that whereas traffic accidents account for 25% of adult deaths, they account for nearly 50% of deaths for children (all kinds of road-users). Measures were adopted in France; such as the obligation for children of less than 10-years-old to travel on rear seats of cars and the definition of an homologation procedure for children restraint devices, with the aim of limiting the consequences of these accidents. The most common restraint devices look like little individual seats and are designed to protect young children (less than 3-years-old). Recently, new restraint devices, called cushions, were developed. They are designed for children of over 3 and they can be used almost up to small adult sizes. They enable some improvements in the location of the adult belt on the childs body; thus, improving safety. Several cushions were submitted to simulated frontal collisions, by using them in a car body fixed to a sled; the impact severity was similar to that encountered in some European restraint system certification tests. These runs brought to light the dynamic response obtained with these cushions and their efficiency, as regards the restraint of child dummies. From these results and with the help of an anthropometric survey concerning the heights of children between 3 and 10 years old, cushion shapes were defined, to be used simultaneously with a 3-pt-belt. This cushion was tested with the 3-year and 6-year child dummies and proved to be very efficient as regards safety; it also appears suitable from the standpoint of comfort.

INFLUENCE OF THE TYPE OF THORACIC PROTECTION CRITERIA USED IN SIDE IMPACTS ON THE CHOICE OF THORAX MODEL AND INTERIOR FITTINGS

Protection criteria aside from deflection are defined on the basis of measurement functions taken at various but unique points on the thorax (rib, spinal column); these functions may also use two points (two ribs, for example) which results in deflection intervening as a criterion. The conditions imposed by these criteria result in different requirements for vehicle wall conditions and thorax model construction. Mathematical modeling of the vehicle wall-thorax collision is performed in order to compare possible criteria on this basis. Concurrently, a statistical analysis performed on a sampling of side impacts occurring with human subjects permits injury severity to be expressed by means of several functions whose predictive qualities are unequal. These functions include deflection, and their literal expression takes into account the state of the subjects bone structure. The criteria produced by these predictive functions are used in the preceding mathematical model. The possibility of optionally using different criteria is discussed.