Effect of seat belt pretensioners on human abdomen and thorax

Abstract

A better coupling of the occupant to the car seat in the early phase of a frontal or far side impacts using pretensioner systems may reduce the likelihood of the submarining effect or increases the likelihood of seat belt engaging the shoulder, respectively. However, the high belt forces may also increase the risk of upper body injuries to the vehicle occupant (especially in abdominal region). It was hypothesized that human body characteristics, such as body mass index (BMI) influence the biomechanical response and injury outcome to the abdominal regions during static pretensioning deployment tests. Four postmortem human specimens (PMHS), in a BMI range from 15.6 to 31.2, were positioned in production seats in a normal passenger position and were restrained using a standard three-point belt system. The pretension forces in the belts were generated at two points (retractor and right anchorage) or at all three locations (retractor, left anchorage, and right anchorage). An optical motion capture system and acceleration cubes mounted to the lumbar spine were used to measure the abdomen deformation during testing. The normalized deflections of the thorax recorded at the level of fourth rib were under 10% (noninjury level). Two different patterns were observed in the time histories of abdominal penetration rate in the four PMHSs associated with lower and higher BMI. Abdominal injuries (spleen lacerations) were observed only in the two PMHS with highest BMI. Based on data from this study and similar data from the literature, belt velocity and FmaxCmax were shown to be the best injury predictors for injury risk analysis for Abbreviated Injury Scale 2+ and for Abbreviated Injury Scale 3+ injuries, respectively.