Kinematics Validation of Age-Specific Restrained 50
Percentile Occupant FE Model in Frontal Impact
Recently, the global increase of elderly vehicle users has become an issue to be considered in the effort of enhancing safety performance of vehicle restraint system. It is thought that an evaluation tool for the system representing properties of age-specific human body will play a major role for that. In previous research, the authors had developed age-specific component finite element (FE) models for the lower limb, lumbar spine, and thorax representing the adult and elderly occupants. However, the models have not been validated in terms of full body kinematics. It is essential for such models to be validated in terms of full body kinematics in order to ensure validity of the results of the assessment of the safety performance of restraint systems.
In the present research, the adult and elderly occupant full body FE models were developed by incorporating the lower limb, lumbar spine and thorax of the adult and elderly FE models established in previous research. To represent the kinematics of the shoulder of the adult occupant model, the shoulder girdle muscles were modeled and incorporated into the models. The full body kinematics of the adult occupant model were validated against published frontal sled test results using post-mortem human subjects (PMHS). The seating position of the model was determined according to the average seating position in the PMHS tests. The frontal impact sled buck model consisted of the seat, knee bolster, footrest and pelvis block. These components were modeled with shell elements and treated as rigid bodies. The occupant restraint system consisted of the shoulder and lap belts, modeled with bar and membrane elements. The trajectories were compared between the model and the average PMHS test results by using the coordinates of the head, the first and eighth thoracic vertebrae, the second and fourth lumbar vertebrae and the pelvis. A published ranking system for the biofidelity was applied to them in order to quantitatively evaluate the appropriateness of the full body kinematics of the adult occupant FE model.
Model results include peak displacements of the head, the first and eighth thoracic vertebrae in the X direction of 362 mm at 112 ms, 267mm at 121 ms and 207 mm at 115ms, respectively. The peak displacements of the corresponding body regions in the X direction from the average PMHS test results were 354 mm at 113 ms, 257 mm at 115 ms and 216 mm at 113 ms, respectively. The error was less than 5 % compared with the average PMHS test results. The kinematics of the other points selected from the head to the pelvis on the spine of the model showed agreement with the average PMHS test results as well. In addition, the results of the biofidelity rating obtained by applying the rating system also supported good agreement of most of the kinematic parameters.
For the elderly model, the kinematics and the predicted rib fracture were compared with those of the adult model. Little difference was found in the whole body kinematics, while larger deflection was found at the thorax as well as a significant increase in rib fractures, which were assumed to be caused by the lowered body stiffness and tolerance by aging.