Chest injury criterion: an update of the equivalent deflection (DEQ)

The rodpot chest deflection measured on the HIII dummy does not discriminate the contributions of the belt and the airbag in crashes. The risks associated to the deflection being different for these two kinds of devices, the assessment of the risk with the rodpot deflection is erroneous for combined restraining systems. Combined restraints known to be efficient in protecting the thorax are consequently penalized. In 2003, the equivalent deflection (Deq) criterion based on the HIII rodpot deflection and the shoulder belt force and applicable to belt, airbag as well as combined restraints was proposed. It has since been evaluated and reviewed by users providing some requests for improvements such as the sensitivity to changes in the pelvic restraint. The objective of this study was to update the Deq criterion to address as much as possible the feedback from the users and better predict chest injuries. New data from HIII 50th percentile tests performed under conditions more representative of the loading encountered with current restraints were collected from the literature. It allowed to better define the relationship between the shoulder load and the deflection caused by the belt. The Deq formulation was updated in order to increase its sensitivity, particularly to airbag loading. Additional paired dummy and PMHS (Post-Mortem Human Subject) tests allowed increasing the size of the sample used to validate the principle of the Deq criterion. The validation of the new formulation was also conducted through simulations with human and HIII models. Then, the biomechanical data were reprocessed with currently recommended statistical methods (based on survival analysis) to build a thoracic injury risk curve for the HIII 50th dummy. Finally, a thoracic injury risk curve was provided for the HIII 5th female. This paper provides the set of data (dummy, PMHS and numerical simulations) used to define and validate the criterion, as well as the equations of the thoracic injury risk curves as a function of the Deq resulting from their processing. The feedback from the users as well as the related improvements of the criterion are presented. The effect of the rodpot deflection and the upper shoulder belt force on the Deq is described. The aim of the Deq criterion is to improve the thoracic protection in frontal crash in the short term, therefore using the currently used HIII dummy. As such, this criterion enhances the prediction of the risk associated with combined restraints compared to the HIII rodpot deflection. However, it does not fully compensate the error introduced by the use of the rodpot deflection.