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Abstract
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27th International Technical Conference on the Enhanced Safety of Vehicles (ESV)
https://www-esv.nhtsa.dot.gov/Proceedings/27/27ESV-000271.pdf
The THOR-50M dummy is instrumented with acetabulum force sensors which is a novelty when compared to previous dummies like the Hybrid III. It has been proposed to use the acetabulum resultant force to predict hip injuries. Injury Risk Curves (IRCs) for cadavers have previously been developed, however it is not clearly estab- lished if the cadaver IRCs can directly be applied to the THOR measurements or if a transfer function is needed. As femur and acetabulum forces are located on the same load path, it is also questionable if it is necessary to use two different injury criteria to predict knee-thigh-hip injuries.
To investigate these questions, a simulation study was performed using a THOR model and two human body models (HBMs). Load cases included impactor tests derived from published cadaver testing as well as sled simu- lations in belted and unbelted configurations with a validated environment. The knee, femur and acetabulum forces measured in the different models were compared and the ratios between these forces were also analyzed. Additionally, based on the measurements from the THOR and HBMs simulations and published Injury Risk Curves for cadavers and the THOR, the risks of hip and knee/femur injuries were calculated for each load case.
Results show that the relationship between the forces measured in the THOR model and in the HBMs could depend on the loading conditions. The forces measured in the unbelted sled simulations are similar between the three models, however the acetabulum forces measured for the HBMs in the belted sled configuration are signif- icantly lower than that of the THOR. For impactor configurations, the risk calculated at the hip for the THOR overestimates the likelihood of cadaveric injuries. For sled configurations, no cadaver test result was available, findings are based on simulations only and comparison with field data. For all simulations, the risk of hip injury predicted for the THOR was significantly higher than the risk predicted for both HBMs. The risk of hip injuries for the THOR was also, for all simulated load cases, higher than the risk of knee/femur injuries which is contrary to the injury frequencies observed in the field for belted occupants.
Overall, the risks calculated for the THOR from the acetabulum forces seem overestimated which is likely caused by the transfer coefficient used to calculate the THOR risks based on the human IRCs. An adjustment of the transfer coefficient is necessary and might require a different value for belted and unbelted cases.
This study has limitations. Firstly, the ability of the human body models to measure accurately the acetabulum force in sled configurations is not established due to the lack of relevant cadaver data. Secondly, parameter studies and real car simulations would be needed to generalize the results.
To conclude, it is necessary to define a transfer function for the acetabulum force to predict hip injury risks properly. This transfer function might be load case dependent. |