Research and Application of Dynamic Equation for Full Frontal Impact

Full frontal impact theory needs researching and exploring to satisfy the primary safety design of occupant restraint system,avoiding the increasingly "engineering"trend in order to develop and design safety vehicle. After occupant restraint system is simulated by using linear elastic stiffness k,the occupant-vehicle frontal rigid barrier impact model is established. Dynamic equation of dummy chest coupling vehicle is built for full frontal impact based on ordinary vehicle deceleration by Hooke law,and the equation is solved by comparing coefficient and satisfying boundary qualifications. While relative vehicle characteristic parameters are kept unchanging,the actual vehicle deceleration is fitted to the simplified equivalent square wave( ESW),tipped equivalent square wave( TESW) and equivalent dual trapezoids wave( EDTW). Phase angle  and amplitude A of dynamic equations based on ESW,TESW and EDTW are calculated and deduced. The results show that: the dynamic equation of dummy chest coupling vehicle can be well utilized to instruct the primary safety design of full frontal impact for objective vehicle to satisfy chest deceleration demands and the equation based on TESW is best for this design.

Viscosity Transient Phenomenon in Drop Impact Testing of Soft Material

The authors carried out drop impact tests for several soft materials under a flat frontal impact condition in which a drop hammer with a flat bottom surface strikes a plate-like soft material in the normal direction. The experimental results indicated that the impact force waveforms of soft materials consisted of a thorn-shaped waveform and a subsequent mountain-shaped waveform. The thorn-shaped waveform was strongly affected by the strain rate. In the present study, the occurrence mechanism of this distinctive waveform was discussed from the viewpoint of the viscosity transient phenomenon. A standard linear solid (SLS) model in which the viscosity transient phenomenon was considered was applied to the simulation. Some features of the impact force waveform of soft materials could be explained by the SLS model. Furthermore, the thorn-shape waveform could also be observed in the impact force waveforms of human skin and free-falling hollow balls.

Lumbar and neck injuries of occupants in different reclining postures

Purpose:With the increasing level of automation in automobiles,the advent of autonomous vehicles hasreduced the tendency of drivers and passengers to focus on the task of driving.The increasing automation in automobiles reduced the drivers'and passengers'focus on driving,which allowed occupants tochoose a more relaxed and comfortable sitting position.Meanwhile,the occupant's sitting position wentfrom a frontal,upright position to a more relaxed and reclined one,which resulted in the existing restraint systems cannot to keep occupants safe and secure.This study aimed to determine the effects ofdifferent reclining states on occupants'lumbar and neck injuries.Methods:This is an original research on the field of automotive safety engineering.Occupants indifferent initial sitting positions(25°,35°,45°,and 55°)were adapted to changes in seat back angle andrestraint systems and placed in the same frontal impact environment.Neck injury indexes,lumbar axialcompression force and acceleration,as well as occupant dynamic response during the impact,werecompared in different sitting positions.The injury response and kinematic characteristics of occupants indifferent reclining positions were analyzed by the control variable method.Results:As the sitting angle increased,the occupant's head acceleration decreased,and the forward-leanangle decreased.Occupants in the standard sitting position had the greatest neck injury,with an Nij of0.95,and were susceptible to abbreviated injury scale 2+cervical medullary injuries.As the seatbackangle increased,the geometric position of the lumbar spine tended to be horizontal,and the impact loadtransmitted greater forces to the lumbar spine.The occupant's lumbar injury was greatest in the lyingposition,with a peak axial compression force on the lumbar region of 5.5 KN,which was 2.3 KN greaterthan in the standard sitting position.Conclusion:The study of occupant lumbar and neck injuries based on different recline states can providea theoretical basis for optimizing lumbar evaluation indexes,which is conducive to the understanding ofthe lumbar injury mechanism and the comprehensive consideration of occupant safety protection.

Experimental and Numerical Study of Cervical Muscle Contraction in Frontal Impact

In a crash situation,drivers typically make evasive maneuvers before an upcoming impact,which can affect the kinematics and injury during impact.The purpose of the current study was to investigate the response and effect of drivers’cervical muscles in a frontal impact.A crash scenario was developed using a vehicle driving simulator,and 10 volunteers were employed to drive the simulator at 20 km/h,50 km/h,80 km/h and 100 km/h.Electromyography(EMG)was recorded from the sternocleidomastoideus(SCM),splenius cervicis(SPL)and trapezium(TRP)muscles using a data acquisition system,and the level of muscle activation was calculated.A numerical study was conducted using data collected in the experiment.The results revealed that the cervical muscles were activated during drivers’protective action.EMG activity of cervical muscles before impact was greater than that during normal driving.EMG activity increased with driving speed,with the SCM and TRP exhibiting larger increases than the SPL.The kinematics and load of the driver were influenced by muscle activation.Before the collision,the head of an active 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 indicated that the incidence of cervical injury in high-speed impact is complex.