To achieve overall good ratings in frontal impacts according to US and Euro NCAP, low chest deflection values have to be obtained. Concerning belt induced chest deflection, belt forces as well as the geometry of the belt system have to be optimized. Hence, the objective of this study was to analyse the influence of the buckle position and motion during crash on chest deflection.

Theoretical investigations as well as simulations (software MADYMO / Facet - Q-dummy) were used to study the influence of the buckle position and motion on chest deflection. Sled tests, where the environment represents a middle class vehicle, were conducted to verify the findings. In order to obtain detailed insight regarding the deformation of the HIII 50% dummy’s thorax and the load distribution, rib eye sensors were used showing the deformation of each individual rib during the crash.

As an outcome, the rib eye sensors show an unbalanced thorax deformation. Relevant differences in rib deformation are observed between left and right ribs of the thorax. Smaller differences are seen between upper and lower ribs. Concerning chest deflection, simulation and test results show an important influence of the buckle motion on chest deflection and on the energy absorption of the dummy. Significant differences in load distribution are detectable by the usage of rib eye sensors.

The retention of a Hybrid III 50% dummy with a 3-point belt leads to an unbalanced deformation of the thorax ribcage. To achieve low chest deflection values, the upper and lower diagonal belt force as well as the belt geometry have to be tuned. In fact, the belt geometry significantly influences the deflection of the ribcage. The buckle position and buckle motion during forward displacement of the dummy can be identified as significant tuning parameters.