Evaluation of lap belt-pelvis load transfer in frontal impact simulations using finite element occupant models

The goal of this study was to examine the relationship between lap belt tension and force measured at the iliac wing and the effects of model type and torso posture on this relationship. From this analysis, preliminary transfer functions were developed to predict loads applied to the iliac wing as a function of lap belt tension at magnitudes typically measured in sled and vehicle crash tests.

A DOE study was conducted to provide a robust assessment of the lap belt-pelvis load relationship under various conditions. The GHBMC, THUMS, and THOR FE models were positioned in upright and reclined postures with several other intrinsic and extrinsic parameters varied for a total of 360 simulations. For the HBMs, instrumentation was developed to measure ASIS load at each iliac wing. Simulations that resulted in submarining were identified and removed from the subsequent development of lap belt-ASIS force transfer functions.

The GHBMC exhibited submarining more frequently than the THUMS and THOR models. In addition to submarining, there were several cases in which the lap belt remained below the ASIS instrumentation or roped during the model's forward excursion. These phenomena, particularly prevalent in the THUMS model, also influenced how the lap belt engaged the ASIS instrumentation and were thus eliminated from the transfer function development. Transfer functions relating peak lap belt tension and corresponding ASIS force magnitudes were developed for the GHBMC and THOR models in upright and reclined postures. In the upright posture, the THOR showed a higher level of ASIS load measured for a given level of lap belt tension than the GHBMC; however, in recline the lap belt-pelvis load relationship was similar between the two models.

The lap belt-pelvis load relationship was found to be affected by model type, posture, the area in which the ASIS instrumentation was defined, and occupant kinematics. This study showed it was possible to minimize the ASIS force by having the lap belt engage low on the pelvis and upper thighs, though further study is needed to determine if this loading mechanism is truly protective from an injury standpoint or an artifact of bypassing the ASIS instrumentation. The transfer function that showed the highest ASIS force measured for a given level of lap belt tension is recommended for future use.