THOR Neck Moment Calculation at Atlanto-Occipital Joint 2019-01-1037
In biomechanics research of human neck injuries, the moment for the upper neck was calculated to the Atlanta Occipital (AO) joint. The measurement in anthropometry test device (ATD) design needs to be converted to the AO joint for comparison to evaluate the ATD biofidelity or determine the injury risks. Typically, the ATD load cell’s neutral axis, which is the measurement location, can not be designed to align with the human anatomical AO joint exactly. For Hybrid III dummies, the upper neck load cell was designed and located above the AO joint. Because the ATD head and neck have a single connection at the AO joint, moment at AO joint can be calculated by a simple rigid body load shift with the distance between load cell neutral axis and the AO joint. For Test Device For Occupant Restraint (THOR) ATD design, the neck load cell was designed and located below the AO joint. In addition, there are two cables in the neck design that were intended to simulate the neck muscle functions. With the introduction of the two neck cables at front and rear of the neck, the calculation of the neck moment to the AO joint becomes much more complicated because the head and neck are connected not only at the AO joint, but also by the two cables. In this paper, it presented a mathematical method to calculate the moment at AO for both THOR 50th male and THOR 5th female ATDs for both frontal and lateral bending directions. Detailed formula was derived according to the mechanical design and how parts functions in the ATD. The constant parameters for both THOR 50th and 5th were provided for the calculation. One case for each ATD, THOR 50th and THOR 5th, calculation was presented in this paper to illustrate the results.