Sharing of collision energy between cars in frontal impacts

It has been generally accepted that car mass is an important factor in two vehicle collisions, with the occupants of the lighter vehicle experiencing more frequent and more severe injuries. The apparent dominance of mass in relative injury risk has been shown in the numerous statistical studies of real life frontal collisions between dissimilar cars. These studies have shown that Relative Injury Risk is proportional to Mr n ; the exponent n increases from n=1 to n=2.8/3.7 as injury severity increases from minor (AIS 1) injuries to fatalities. Extensive research has been carried out into the compatibility of dissimilar cars in frontal collisions (1-7), and into the possible methods of reducing the size and mass effect. Wood & Simms (8) proposed a theoretical model for the apparent mass effect for frontal collisions between dissimilar cars. The central tenet of this theory is that the apportionment of collision energy between the colliding pair is a function of the structural collapse forces at maximum dynamic crush. (Up to the instant of maximum dynamic crush, the interface forces between the two vehicles are a combination of structural collapse and inertial forces, with the consequence that the structural force balance only becomes valid at maximum dynamic crush, when the vehicles have no relative velocity, i.e. the inertial forces at the interface are zero.) This theory, which was used in combination with a generalized characterization of the energy absorption characteristics of the car population with Monte Carlo simulation, predicted Relative Injury Risk versus Mass Ratio characteristics which were similar to the real life data over the collision speed range, up to EES values of 25m/s.