Estimating infant head injury criteria and impact response using crash reconstruction and finite element modeling

A combination of finite element modeling and sled test reconstruction of real-world infant head injury scenarios has been used to investigate infant head impact response and tolerance to skull fracture. Studying the role of cranial sutures on infant skull response was of particular interest. The specific injury scenarios selected for reconstruction involved infants in rear-facing child restraint systems (CRS) who sustained skull fractures and brain injuries from deploying passenger-side frontal airbags. Approximations of the loading conditions for three injury cases, as well as estimates of loading conditions not expected to result in head injury, were produced in the laboratory. A finite element model (FEM) of a six-month-old infant head was developed using available material properties and humanlike geometry. The infant head FEM was used to simulate different injury and no-injury loading conditions based on CRS response data from the reconstruction tests. Acceleration results and stress distributions are consistent with the level of injury in the different real-world cases. Cranial sutures have a negligible effect on stress distribution in the infant skull. Logistic regression analysis was used to estimate threshold stresses associated with skull fracture. The acceleration responses of the infant head FEM and the CRABI ATD were compared for the no-injury and injury-producing conditions. Results suggest that the biofidelic loading range of the CRABI ATD may be limited to impacts at or below injury-producing loading severities. Provisional injury assessment reference values corresponding to the threshold for minor skull fracture over a limited loading range were estimated for the current CRABI ATD, and recommended improvements for the CRABI ATD head are presented.