The Effect Of Automatic Brake System On The Response Of The Lower Limbs Based On Muscle Active Force

Along with the popularization of automobiles,the incidence of road traffic accidents has also increased greatly.The frontal collision is the highest proportion of accidents with the highest number of casualties.The lower extremities are the most vulnerable parts,and it,though not fatal,brings great distress to the families and personal lives of the victims.The active safety technology dedicated to occupant protection has been developing rapidly in recent years,especially the Automatic brake system has been widely applied in the production of automobiles.Although the Automatic brake system can effectively reduce the casualty rate,the impact on the injury of lower limb remains unknown.Understanding the influence of braking process on the response of lower limb can help design and optimize the parameter of the Automatic brake system.The aim of the present work was to study the effect of Automatic brake system on the injury of lower limb by developing a finite element model of the lower extremities with active muscle force.The basic model was from Pedestrian Lower Limb finite element model of Hunan University.The Improvements included mesh reclassification,replacement of old material parameters,increas ing of articular capsule,articular ligament,articular cartilage and so on.The Hill constitutive model was developeded to simulate the muscle active force,and the physiological parameters of muscle were set up.A fully validated low-limb model with the muscle active force was combined with the Hybrid III dummy finite element model to create a50th percentile mixed dummy model.This paper selected Camry as a crash test vehicle,developed and validated the driver restraint system,and extracted the acceleration curve of the vehicle as the input condition of the human body's lower limb injury simulation subsystem.Then,28 simulations of finite element model were carried out to study the effects of braking duration and muscle activity on the responses of the lower extremity in this paper,the design variables included collision speed(40km/h and 50km/h),braking duration,braking deceleration(5m/s~2,8m/s~2 and10m/s~2),the muscle activated or not.The results showed that the braking process had a positive effect on the X acceleration of the dummy's head.For the injury of the lower limb,the braking process would reduce the injury of thigh with the collision speed of 50km/h,while an opposite phenomenon occurred at 40km/h.At both collision speeds,the braking process aggravated the damage of lower limb below the knee,and there was a tendency to increase with the time of braking.Under the action of muscle force,the femoral axial force and tibia index of the lower extremity increased,while the stress decreased in biomechanical response.The above result laid a theoretical foundation for the protect devices design of lower limb.