Estimating infant head injury tolerance and impact response.

Abstract

A unique mechanism of infant death in motor-vehicle crashes has developed in the past decade. In relatively minor frontal impacts, infants have sustained serious head injuries while restrained in rear-facing child restraint systems (CRS) that were loaded by deploying passenger-side airbags. This study combines finite element modeling (FEM) and physical reconstructions of infant head injury scenarios to investigate infant head impact response and skull fracture tolerance. FEM supplemented the results from reconstruction testing to examine the role of cranial sutures on infant skull response and to estimate stresses associated with infant skull fracture. A secondary goal was to assess the ability of the current CRABI anthropomorphic test device (ATD) to evaluate safety countermeasures for infants. The specific injury scenarios selected for laboratory reconstruction involved infants in rear-facing CRS who sustained skull fractures from deploying passenger-side 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. Concurrently, a FEM of a 6-month-old infant was developed, and a parameter study was performed to evaluate the effect of different material properties. A method was developed to use the CRS acceleration data measured in the reconstruction tests to load the infant head FEM. The infant head FEM was used to simulate different loading conditions estimated in the reconstruction tests. The parameter study showed that skull modulus and brain incompressibility had the greatest effect on head impact response, while cranial suture modulus had a negligible effect. Infant head FEM acceleration results and stress distributions are consistent with the level of injury for each case. Estimates of threshold stresses associated with skull fracture were made through logistic regression analysis. 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 those below injury-producing loading severities. Injury assessment reference values corresponding to the threshold for minor skull fracture were estimated for the current CRABI ATD, in addition to recommended improvements for the CRABI ATD head.