Research On Key Technologies Of Vehicle Occupant-restraint System Under Explosion Impact

Under the current international situation,regional armed conflicts occur frequently.Severe challenges are still exisiting in national defense.In military conflicts or peacekeeping operations,the explosive is one of the main factors that threats the mobility of vehicles,safety of the crew and the combat capability of troops.In recent years,the safety problem of special vehicles has become increasingly prominent,and higher requirements have been put forward for the anti-explosion protection capability of vehicles.Occupant-restraint system is the last barrier for protective vehicles to save lives under explosive impact load.It can reduce the impact load transmitted from the vehicle to passengers via several buffer devices.Meanwhile,the occupant-restraint system limits the relative displacement of passengers to avoid the collision between human body and the internal structure of vehicle.This paper studies the protection mechanism and development method of the occupant restraint system via the finite element method,multi-body dynamics model,explosion experiment and its equivalent experiments,and multi-objective optimization method.The main research work of this paper is as follows:(1)The numerical simulation method of the ‘vehicle-occupant-restraint system’ when subjected to an explosion impact is studied.The TNT explosive and sand are defined by PBM(Particle blast method)and DEM(Discrete element method)particles respectively.An efficient and high-precision finite element model of vehicle anti-explosion impact is constructed.Taking the living space,occupant injury and seat strength as evaluation indexes,the protection evaluation process of vehicle occupant restraint system is proposed.Combined with experiment and simulation,the protection ability of restraint system is systematically evaluated.The influence law of restraint system on human body injury response is studied,and the deficiency of ‘buffer’ and ‘restraint’ ability of current occupant restraint system is pointed out.(2)A ‘seat-occupant-safety belt’ multibody dynamic model which is suitable for vertical impact condition is developed.Based on the Error Assessment of Response Time Histories(EARTH)metric and the data of measured by Hybrid III dummy under impact load,parameters of the model are optimized.After parameter identification,the model can accurately reflect the motion of human body under impact load.Also,it can effectively predict the injuries of various parts of the passenger.(3)The equivalent experimental method for simulating explosion impact is studied.Based on the human body model,the influence of different impact loads on the injuries of various parts of body is studied.The results show that: for the impact load with small pulse width(≤20ms),the damage response is not sensitive to the change of waveform.For the impact load with similar waveform,when the pulse width is constant,the damage response of human body can be effectively reduced by reducing the velocity change(? ).In different impact experiments,the core of the equivalent explosion experiment is effectively controlling the velocity variation characteristics of the structure near the occupant.The variables that have a great influence on the pulse characteristics in the lower limb impact experiment and the drop experiment are selected and analyzed.Based on it,the ‘equivalent experimental parameter identification process’ is proposed.Through the equivalent experiment,approximate injury responses are obtained,and the simulation of explosion condition is realized.(4)Protection mechanisms of buffer devices of the occupant-restraint system are studied.Firstly,the lower-limb impact experiment and finite element simulation are carried out for expanded polypropylene(EPP)materials.The influence law of EPP materials on the lowerlimb injury is studied.Secondly,based on the bending theory and the assumption of elastic linear work-hardening material,the deformation energy of the metal plate is calculated theoretically.The static tension test,impact test and simulation are systematically conducted to study the load controlling process of the seat suspension.The buffer devices above are optimized and a vehicle anti-explosion experiment is carried out according to the optimization results.The results show that the optimal solution reduces the WIC by 47.3%,and significantly improves the protective ability of the occupant restraint system.(5)In order to improve the restraint ability of the restraint system under explosion condition,the ‘pre-tightening force-limiting’ seatbelt is introduced.The correlation analysis between the parameters of seatbelt and injuries is carried out.It is found that the seatbelt can reduce the wearing clearance,limit the vertical displacement of passengers in the vehicle and avoid(or reduce)the collision between human body and cabin structure.However,it cannot reduce the inertia damage of human body caused by explosion impact.Based on the 6σrobustness design method,optimizations have been carried out.The results show that injuries of body are more robust under the influence of the fluctuation of wear gap.The vertical displacement of head is greatly reduced by 88.4% and the living space is improved.The restraint system can effectively play the role of ‘buffer’ and ‘restraint’,which is of great significance for the research and development of all kinds of compact protective vehicles.