Compatibility of vehicles of different mass and stiffness in head-on collisions was studied in earlier paper(13). It was concluded that mass ratio was the most important parameter in the mechanics of head-on collision. To improve compatibility, it was also suggested that stiffness might be reduced with longer crumple zone for heavier vehicles. This paper continues the study by considering the impact of changing stiffness of a vehicle on the level of protection the vehicle provides to its own occupants when colliding with similar vehicle. Such study is prompted by the fact that there is a strong link between aggressivity of a vehicle to the partner vehicle’s occupants and the level of protection the vehicle provides to its own occupants. In other words safer vehicles are usually more aggressive. A compromise between the level of protection and aggressivity of the vehicle design need to be investigated using basic laws of mechanics of head-on collisions. An eight-degrees of freedom, two-dimensional lumped-mass simulation model was used for this purpose.

Three injury risk criteria have been considered in this study; delta V or change in velocity of vehicle after impact, maximum acceleration sustained by the passenger compartment throughout impact, and length of deformation sustained by the car front Both mass and stiffness are crucial for the occupants safety. Higher mass provides protection to its occupant as well as aggressivity to occupants of the partner vehicle. Higher stiffness provides little protection to its occupants in terms of the intrusion injury criterion but more aggressive to its own occupants as well as occupants of the partner vehicle in terms of other injury criteria. A slightly softer and longer crumple zone is proposed for heavier vehicles to achieve better protection for occupants of both colliding vehicles.

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