Load Limiting Behavior in CRS Tether Anchors as a Method to Mitigate Head and Neck Injuries Sustained by Children in Frontal Crash

OBJECTIVE: This study focuses on methods to reduce injuries, specifically in the head and neck region, sustained by children seated in forward-facing child restraint system during a frontal vehicle crash. The main objective of this research was to implement load-limiting behavior into the upper tether and lower LATCH anchors of the CRS in order to reduce the neck injury criteria by increasing forward head excursion. METHODS: Federal Motor Vehicle Safety Standard 213 outlines that the maximum limit for head excursion of the child dummy should be 720 mm, and the neck injury criteria should be less than 0.33 beyond the first 30 ms of the impact. Working within these limits, a fully deformable finite element model of a child restraint seat incorporating a Hybrid III 3-year-old dummy has been previously developed that has been validated for frontal impacts under CMVSS 208 and FMVSS 213 testing conditions. Observations from this previous work have illustrated that despite the head excursion being significantly less than the proposed limit of 720 mm, values of the neck injury criteria exceeded the protection reference values. Values of the load limits for both upper tether and lower LATCH anchors were calculated based on two approaches, initially based upon neck injury criteria and then an energy-based approach. Three numerical models were developed incorporating a Hybrid III 3-year-old dummy, Q3 child dummy, and a child finite element model. Numerical simulations, utilizing the identical 213 testing conditions, were completed incorporating load-limiting capabilities of the upper tether and lower LATCH anchors. RESULTS: Evaluation of injury criteria based on the quantitative analysis of the simulations yielded that the implementation of load-limiting behavior in the upper tether and lower LATCH anchors was effective in reducing the head injury criteria by approximately 60 to 70%. CONCLUSION: Implementation of load-limiting behavior in the upper tether and lower LATCH anchors of the child restraint system effectively reduces the head and neck injuries sustained by toddlers in a frontal vehicle crash while controlling forward head excursion within the limits as defined by NHTSA.