Research on Cervical Spine Impact Injury and Protection of Rail Vehicle Driver in Collision Accident

Abstract

Human neck injury is an important factor leading to occupant casualties in rail traffic accidents, which leads to fractures of the vertebral body, paraplegia, and death. During the collision accident, the driver has a secondary collision with the vehicle interior structure. The inertial difference between the head/neck and the torso is likely to cause neck whiplash injury. Compared with automobile collision accidents, train accidents have obvious peculiarities with large collision energy, large inertia, diverse damage forms and destabilization patterns, and no restraint system protection, which increases the incidence of neck injuries. In this thesis, the dangerous neck kinematic posture is identified based on the driver impact dynamic model. A human body model with neck active muscle is developed. The effects of muscle activation on driver neck impact injuries are analyzed. A hybrid framework for safety design of driver-rail vehicle multilevel system is established to reduce the driver impact injury. The main research contents are as follows:

First, the most dangerous driver’s neck posture and the influence of workspace layout during train collision are explored. The driver flipping over behavior results in a small value of the head rotation angle relative to the upper torso (β+γ), while the submarining posture generates a large (β+γ) value. The chest-first impact postures generate higher normalized neck injury criterion (N_ij) values and are more dangerous than the knee-first impact postures. The injury posture category with the larger (β+γ) value leads to more severe neck responses. The varying trend of neck responses and (β+γ) values are generally positively correlated with the distance between the console and seat (L₁), the distance between the console edge and knee bolster (L₂), and the console plate thickness (T). The neck responses and (β+γ) values generally decrease with increasing pedal height from the floor level (H₁) and seat height from the floor level (H₂). L₂ is the most crucial parameter influencing the neck response, and H₁ and L₁ follow L₂ according to their importance. L₂ is related to the first contact point of the driver and then determines the neck kinematic posture. These dimensional parameters should be prioritized to design a much safer cab workspace.

Second, the human body biomechanics model with neural feedback control of active neck muscle is developed based on the intelligent optimization and decision-making method. A PID controller is used to represent the neuromuscular reflex control mechanism of the human vestibular system for balancing the head-neck position. An integrated optimization method combining multi-objective optimization and multiple criteria decision-making to select the Pareto optimum of the PID controller is proposed. The contradictory optimization objectives between the head longitudinal and vertical kinematic responses are balanced. The head-neck kinematics of the active human body model are in better agreement with the volunteer experimental responses. A global coordinate system with X forward, Y to the left, and Z upward is utilized. Compared with the passive human body model, the active model improves the head kinematics agreement with volunteer data for head linear resultant acceleration, head Y-angular displacement, and head Z-linear displacement by 23.83%, 52.39%, and 8.60%, respectively. Although the head X-linear displacement is decreased by 4.05%, it is still located on the “excellent” rating scale. This finding implies that the developed active human body model is effective.

Third, the effects of neck muscle activation on driver neck impact injuries are analyzed. The active human body model can restrict excessive flexion motion of the cervical spine. The driver head displacements, cervical segmental flexion angles, von Mises stresses of cervical vertebral bones, facet joint displacements, cervical vertebral artery elongations, and variation of intervertebral foramen space are decreased in the active human body model. The driver head and cervical segmental displacements, vertebral stresses, anterior shear motion of both regions and compression of the anterior-most region for the facet joint are increased, and the posterior shear motion is decreased with increasing train collision velocity. The train velocity has an obvious effect on cervical vertebral artery elongation. The driver head vertical and rotational displacements, cervical segmental flexion angles, anterior shear motion of both facet joint regions in the lower cervical spine, and cervical vertebral artery elongations are decreased and the head horizontal displacement is increased with increasing main energy-absorbing structural force. The driver head rotational movement, cervical segmental flexion angles, vertebral stresses, anterior shear motion of both regions and compression of the anterior-most region for the facet joint increase with increasing distance between the console edge and knee bolsters.

Fourth, the driver-rail vehicle crash safety protection method is established based on stochastic analysis and a hybrid optimization strategy. The stochastic approach evaluates the statistical characteristics of system responses and quantifies the contribution ranking of uncertain parameters to response variations. The hybrid optimization strategy addresses hesitant linguistic evaluations for the Pareto front and selects the final optimal solution. The optimization results show that the human AIS 3+ joint injury probability is reduced from 67.08% to 14.17%. The driver’s head angular displacement is decreased by 57%. The cervical segmental angular displacement is reduced by 45.17%. The von Mises stresses of cervical trabecular and cortical bones are decreased by 14.41% and 27.77%, respectively. The anterior-posterior and superior-inferior displacements of the facet joint are reduced by 40.66% and 46.12%, respectively. The vertebral artery elongation is decreased by approximately 2.8 mm. The results prove that the proposed safety protection method is effective in reducing human impact injuries.

In summary, this thesis establishes a framework for driver neck injury and protection research based on neck collision dynamic responses, active human body models, soft tissue injuries, and vehicle optimization design, which effectively improves driver crash safety.

Date of Award	25 Sept 2023
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yong Peng (External Supervisor) & Dong SUN (Supervisor)