Biomechanical neck injury predictor (NIJ)
Biomechanical neck injury predictor (NIJ)
The biomechanical neck injury predictor is a measure of the injury due to the load transferred through the occipital condyles. Its calculation combines the neck axial force and the flexion/extension moment about the occipital condyles.
It is used in association with the USSID dummy for standard American frontal impact tests.
The shear force (Fx), axial force (Fz) and bending moment (My) are measured by the dummy upper neck load cell for the duration of the crash, using force and moment definitions consistent with SAE J221/1. T/HIS will calculate the bending moment using the equation:
My = My' - e Fx
Where e is the e distance specified in the input window, Fx is the shear force.
Shear force, axial force and bending moment must be filtered using an SAE Channel Frequency Class 600 filter (C600) for the purposes of calculation.
During the collision, the Axial Force (Fz) can be in either tension or compression whilst the occipital condyle bending moment (Mocy) can be in either flexion or extension. This results in 4 possible loading conditions corresponding to the 4 curves output by T/HIS; tension-extension (Nte), tension-flexion (Ntf), compression-extension (Nce), and compression-flexion (Ncf). At each point in time only one of these 4 conditions can be met, hence the NIJ value is calculated for that condition and the value for the other 3 conditions is considered a value of zero..
The expression for calculating each NIJ loading condition is given by:
NIJ = (Fz/Fzc) + (Mocy/Myc)
where Fz and Mocy are as defined above, Fzc and Myc refer to the axial force and Bending moment critical values, given below:
The values of Fzc and Myc vary depending on the occupant, the occupants position and the sign of Fz and Mocy
For the dummy to pass the test, the following conditions must be met:
(i) None of the 4 NIJ values may exceed 1.0 at any time during the event
(ii) Peak Tension Force (Fz), measured at the upper neck load cell, may not exceed the specific dummy's limit (e.g. 2070N for the Hybrid III small female) at any time
(iii) Peak Compression Force (Fz), measured at the upper neck load cell, may not exceed the specific dummy's limit (e.g. 2520N for the Hybrid III small female) at any time
For more information on the use and calculation of NIJ, refer to the FMVSS 208 document