Research On The Stratrgy Of Muscle Recruitment And Its Influence On The Cevical Injury In Crash Scenario

With the development of passive safety system,an active human body model(HBM)which can resemble the reactions in a vehicle impact has become an important research field.The instinctive reaction of the occupant before the occurrence of a collision will change the occupant’s posture and load distribution,and finally affect the degree of an injury.The inclusion of muscular activity in HBM makes it able to perform a humanlike movement.The study is designed to provide a view on the biomechanics of human movement for cervical muscles and its influence on the degree of injury in a vehicle impact.The state-of-the-art modeling techniques of muscle control in HBM were classified on the basis of the biomechanics of human movement.Firstly,a strategy of goal directed movement has been studied in a driver-aware frontal impact.The driver,with advance awareness of the coming crash,will take protective action such as muscle contraction instinctually,which can affect the kinematics and in turn the degree of physical injury of the driver.A crash scenario,in which 10 volunteers were employed to drive the simulator at 20km/h,50km/h,80km/h and 100km/h,was developed on the vehicle driving simulator.Electromyography(EMG)was recorded from the right sternocleidomastoideus(SCM),splenius cervicis(SPL),and trapezium(TRP)muscles by a data acquisition system,and the level of muscle activation was calculated.The results show that,as part of the driver’ protective action,cervical muscles are activated.The EMG of cervical muscles are higher than that during the normal driving.The EMG of SCM grows by 13% as compared with that in the normal situation,while the TRP grows by 23%.The EMG grows with the increase in the car speed,the SCM and TRP goes up dramatically,while the SPL does not see a significant growth.Then,a numerical study has been conducted to analyze the effect of muscle force on the cervical injury.The purpose of the chapter is to investigate the response and effect of drivers’ cervical muscles in a frontal impact.According to the anatomical structure,the neck muscles consist of deep and superficial muscles,and the activations of deep muscle are obtained by optimization,while the activation of superficial muscle is calculated according to the anatomical structure and function.The kinematics and load of the driver are influenced by muscle activation.Before the collision,the head of an active human model stretched backward,while the passive model kept the head upright.In low speed impact,the torque and shear of the cervical muscle in the active model were much lower than those in the passive model,while the tension of the cervical muscle was higher in the active model compared with the passive model.The results indicate that the incidence of cervical injury in high speed impact is complex.And the posterior muscle represented by the trapezius might be injured by eccentric-contraction.The neck muscle activation triggered by the impact force is obtained from lower-speed volunteer test.Through simulation,it is found that the muscle activation caused by the impact had a greater influence on the movement and injury of the occupant in a low-speed collision.Furthermore,the effect of muscle recruitment on the rear impact has been studied.Startle response explains the activation in the neck muscles during an unexpected rear-end impact.Muscle activation is described by two dynamical processes: neural excitation and active state dynamics.The normalized neural excitation is described by the first-order system.The static optimization was used again to resemble the muscle activation during the normal driving.The simulation shows that the active muscle force reduces the cervical injury.In a low-speed rear-end impact,the occupant’s neck is not injured due to low acceleration,while the neck muscle strength has a greater impact on the occupant’s trajectory.In order to test the parameters known to affect the whiplash injury risk,rear-end impact simulations were performed with the active human model in conditions where occupants stay in a forward position,with head yaw and pitch.Compared with normal position,head turning to the right will reduce the injury index,and forward position will increase the neck injury.Finally,the strategy of postural control task has been introduced in automated brake scenario.This chapter describes the development of numerical model of human neck,which is able to perform stabilization task as a result of muscle activation controlled by a PID-based controller.The task was defined by functions of specified angle and length for the cervical spine.PID controller was implemented to control the rotation of the head by regulating the activation of superficial cervical muscles.All the superficial muscles were governed by the controller for the all freedom.And the activities of deep cervical muscles were determined by static optimization.The simulation results show that due to the effect of automatic emergency braking,the active and the passive model are different in the movement,resulting in different boundary conditions before impact.And,active model is more vulnerable compared to the passive model.