Multivariate head injury threshold measures for various sized children seated behind vehicle seats in rear impacts.

Government recommendations to place children into the rear areas of motor vehicles to avoid airbag induced injuries have been complicated by the fact that most adult occupied front seats will collapse into the rear area during rear-impacts, and thus pose another potentially serious injury hazard to rear-seated children. Many variables affect whether or not a front seat occupant will collapse into the rear child, and whether that interaction could be injurious to the child. For instance, the severity of rear impact, coupled with front and rear occupant sizes (mass and stature), and the level of front seat strength, all interrelate to influence whether or not a rear seated child is likely to be impacted and possibly injured. The most common types of child injuries in these instances are head and chest injuries. In this study, a "high-low" experimental method was employed with a multi-level "factorial analysis" technique to study "multivariate" biomechanics of child head injury potential determined from rear-seated 3 and 6 year-old child surrogates in different types of vehicle bodies mounted to a sled system. The sled-buck systems were towed rearward into crushable barriers that matched the crash pulses of the vehicle types being tested. Various sizes of adult surrogates (i.e. 50 kg up to 110 kg), seated in both the "typical" low strength "single recliner" collapsing type front seat (i.e. 3.2 kN) and a much stronger "belt-integrated" seat design (i.e. up to 14.5 kN), were tested in the two different "sled body-buck" set-ups at various impact levels (i.e. 22.5 to 50 kph). One set-up used a popular minivan vehicle body with "built-in booster" seats for the 3 year-old. The other used a 4-door family sedan vehicle body with the 6 year-old in a standard rear bench seat. The parameters of the tests enabled the experimental data to be combined into polynomial "head injury" functions of the independent variables so the "likelihood" of rear child head-injury potential could be "mapped" over ranges of the key parameters. Accident cases were compared with predictions to verify the methodology.

Biomechanical analysis of motor vehicle seat belt buckles.

Various studies have reported that inertially sensitive buckles are susceptible to impact unlatching. The present work synthesizes the results from various experimental studies conducted over the years to study the mechanical behavior of buckles and subsequent injuries to occupants. First, the side press button seat buckle due to impact a lateral impact from an adjacent child restraint seat component indicated that the side button RCF-67 buckle released at a speed of 2.2 m/sec with a force range of 264 to 440 N and acceleration range of 100 to 175 G. In contrast, the top button Autoliv Lockarm buckles did not release up to 1300 vertical G's. Second, side release RCF-67 buckles when loaded with the webbing required approximately three times more force to open than top press buckles. Inverted occupants in a three-point belt could not release the RCF-67 buckle. Third, a side sled impact on the drivers side of a production vehicle buck with a three-point belt and a RCF-67 buckle was done at 7 m/s to 8 m/s. A convertible child seat with a dummy in the passenger seat moved inboard toward the buckle and unlatched it. Fourth, an intact vehicle drop study at 0.3 m showed that the accelerations on a JDC buckle on a metal stalk are large compared to acceleration of the floor pan. The present study provides comprehensive data to evaluate the mechanical behavior of seat buckles under various motor vehicle crash conditions.