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Trim covers made of impact resistant polymers on vehicle interior sheet metal can contribute to reduction of HIC(d) (Head Injury Criterion, dummy) during headform impact. Air-gap between trim and interior sheet metal can also induce deceleration of striking headform before it forces trim to contact sheet metal surface. As evidenced from laboratory component testing, situations may arise where additional protective measures may need to be incorporated between trim and sheet metal in order to attain acceptable levels of HIC(d). Two such alternatives in the form of energy-absorbing foam, and trim with molded collapsible stiffeners are discussed in this paper. The effectiveness of these countermeasures is evaluated through nonlinear finite element analysis, and favorable comparison with laboratory results is reported.

This paper examines the theoretical worst case of normal headform impact on an infinitely rigid surface with the help of a dynamic spring-mass model. It is pointed out that the current approach is not an actual representation of any vehicle upper interior but is useful in gaining insight into the headform impact phenomenon and determining how to further enhance design. After considering force-deflection characteristics of a variety of commonly used headform impact protection countermeasures, a mathematical model is set up with spring properties that approximate those of physical countermeasures. Closed-form solutions are derived for various dynamic elasto-plastic phases including elastic unloading and contact. A parametric study is then carried out with HIC(d) as the dependent variable, and spring stiffness, yield force and spring length (representing countermeasure crush space) as the design variables.

Vehicle side impact performance is potentially affected by a large number of parameters which may be related to body stiffness and energy absorption characteristics, and packaging dimensions. An understanding of the principal variables controlling TTI (Thoracic Trauma Index) is fundamental to the achievement of high LINCAP (Lateral Impact New Car Assessment Program) rating especially for sedans. In the present study, the effects on TTI of the following are considered: response-related parameters such as velocity and intrusion (which are in turn related to body structure), countermeasures such as side airbag, and dummy to structure clearance dimensions. With the help of test data gathered from side impact tests carried out on cars and trucks at Ford, a new “best subset” regression model is developed and is shown to be able to predict TTI for a number of LINCAP tests which were not part of the suite used in the derivation of the model.