Countermeasures to mitigate head and neck injuries to toddlers in frontal and lateral vehicle crash conditions

Abstract

This study focuses on methods to reduce injuries, specifically in the head and neck region, sustained by children seated in forward-facing child safety seats during a vehicle crash. A fully deformable finite element model (FEM) of a child restraint seat incorporating a Hybrid III 3-year-old dummy has previously been developed which has been validated for frontal impacts under CMVSS 208 and FMVSS 213 testing conditions, and near-side impacts under ANPRM (FMVSS 213) norms. Observations from this previous work have illustrated higher values of neck forces and moments sustained by the dummy's neck. The main objective of this research was to develop a head and neck restraining device in order to limit the forward and lateral head movement/rotation of the child. The head and neck safety device comprised two parts, namely the collar and the tether. The collar was restrained to the dummy's torso with the seatbelt and the tether was constrained to the dummy's head. In addition, the effect of using a cross-shaped rigid ISOFIX system was also investigated. Three numerical models were developed incorporating a Hybrid III 3-year-old dummy, Q3/Q3s child dummies and a child FEM. Numerical simulations were completed in frontal, near-side and a 45° impact situation in accordance with the FMVSS 213 norms in the absence and presence of the head and neck safety device, for both the flexible LATCH and the cross-shaped rigid ISOFIX system. Evaluation of injury criteria based on the quantitative analysis of the simulations yielded that the head and neck device in conjunction with the rigid ISOFIX system was effective in reducing the resultant upper neck forces by approximately 40 to 75% for all the child models under different impact conditions. In addition, the head injury criterion was observed to be reduced by approximately 45 to 65% for all the impact conditions. Presence of the head and neck device effectively reduced the head excursions for all the impact conditions. In addition, the cross-shaped rigid ISOFIX further decreased the CRS displacement in both the forward and lateral directions. The forward and lateral displacement of the centre of mass of the head was observed to be reduced by approximately 30 to 50% for different impact conditions. Greater amount of bending in both the lateral and forward directions was observed for the Q3/Q3s dummies and the child FE model. This can be attributed to lower degree of stiffness and geometrical differences in the Q3/Q3s dummy's neck, which make the neck more flexible.