汽车碰撞安全基础 (26).pdf
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1、INTRODUCTIONIn the current pedestrian impact safety assessment testmethods,the upper legform impactor is used to represent thehuman femur and pelvis.For vehicles with high front ends,e.g.SUVs,the bonnet and its leading edge are most frequentsources of injury 1.The aim of the upper legform to bonnetl
2、eading edge test is to evaluate the aggressiveness of thebonnet leading edge in causing femur/pelvis fractures 2.Responses of the human body FE model and upper legformwhen impacted with a vehicle have been compared since2001 3-4.It is revealed that the upper legform to bonnetleading edge impact test
3、 method has low biofidelity.Nevertheless,widely accepted conclusion has not beenobtained yet 5-6.Compared to the pedestrian head impactprotection and lower leg impact protection,there have beenmuch fewer vehicle models that have received good scores inthe Euro NCAP assessment test of the upper legfo
4、rm tobonnet leading edge 3.Some research show that properspatial arrangement and structure design of the partsunderneath the bonnet lead may benefit the upper legformimpact response 7.Though some concept design could beexamined using simulations of upper legform impactingvehicle front-end 8,guidance
5、 for vehicle front-end designfor upper legform protection is seldom proposed in recentyears.Pedestrian upper leg impact protection is still a quitechallenging requirement.The upper legform impactor consists of rigid front andrear members and has a foam padding covering the contactside.Such an upper
6、legform structure can represent thecharacteristics in the human femur and pelvis impact withreal vehicles 9,10,11.In upper legform tests,the initialkinetic energy,the initial velocity and impact angle aredetermined by the bonnet leading edge height(BLEH)andthe bumper lead(BL)of the target vehicle.Th
7、e sum of theimpact forces and the peak bending moment measured in themain legform member are the injury indexes.The EuroNCAP test prescribes threshold values to the injury indexesfor their assessment rating.Some research shows that theforce to moment ratio on upper legform can be taken as aconstant
8、12.In general,when the summed force is belowthe threshold,the peak bending moment can always meet therequirement.For this reason,in this study,the impact forces2012-01-0272Published 04/16/2012Copyright 2012 SAE Internationaldoi:10.4271/2012-01-0272saepcmech.saejournals.orgInfluencing Factors of Cont
9、act Force Distribution in PedestrianUpper Legform Impact with Vehicle Front-EndBingbing Nie,Jun Huang,Yong Xia and Qing ZhouTsinghua UniversityABSTRACTPedestrian upper leg impact protection is a challenging requirement in the Euro NCAP assessment.In upper legform tobonnet leading edge tests,the legf
10、orm impact force,the legform intrusion and the injury parameters(impact force andbending moment measured on the upper legform)are highly related to design of vehicle front-end styling and structure,aswell as clearance underneath bonnet leading edge.In the course of impact,the contact area variation
11、has significantinfluence on the stress distribution and consequently the force and the bending moment on the upper legform.Using finiteelement simulations of upper legform impact with a typical sedan,the deformation of the legform and the vehicle structure,and the variation of the contact force dist
12、ribution are characterized and analyzed.Based on the study,a method forcalculating the contact force is put forward by assuming a shape of the contact zone on the upper legform and a stressdistribution function within the contact zone.The calculation method is verified using a simplified model of ve
13、hicle front-end structure developed in a previous study.Then a parametric study is conducted using the simplified vehicle front-endmodel to study influence of key design variables.The results of the parametric study,to some extent,have revealedrelationship among vehicle front-end design parameters s
14、uch as styling,geometry and stiffness,contact characteristicssuch as the maximum stress on outer foam,and the injury parameters(mainly the impact force).CITATION:Nie,B.,Huang,J.,Xia,Y.and Zhou,Q.,Influencing Factors of Contact Force Distribution in PedestrianUpper Legform Impact with Vehicle Front-E
15、nd,SAE Int.J.Passeng.Cars-Mech.Syst.5(1):2012,doi:10.4271/2012-01-0272._Gratis copy for Bingbing NieCopyright 2012 SAE InternationalE-mailing,copying and internet posting are prohibitedDownloaded Thursday,March 15,2012 10:05:05 AMare taken as the study object while the peak bending momentis only mon
16、itored.A substantial portion of the initial legformkinetic energy will be absorbed by the deformation of thevehicle body components around the impact area.Propervehicle front-end styling,structure design or spatialarrangement of the parts underneath the bonnet lead willbenefit the upper legform impa
17、ct response 13,14,15,16.In upper legform tests with bonnet leading edge,theimpactor is launched with a specified velocity and its motionis constrained by a guiding system.Thus the upper legformcan only move in the straight direction of the guiding whencontacting with the target vehicle.The first con
18、tact point isaround the mid-point on the upper legform,and,as the outerflesh foam of the legform and the affected vehicle structureare compressed,the contact area spreads out in the course ofthe impact.The contact area variation has significantinfluence on the stress distribution and consequently th
19、e forceon the upper legform.And the size and shape of the contactzone and their variation in the impact are determined by thevehicle styling parameters and stiffness parameters aroundthe bonnet leading edgeTo obtain a good understanding to this problem,finiteelement(FE)simulations of upper legform i
20、mpact with atypical sedan are conducted.The impact pulse,characterizedby the impact force vs.legform impactor intrusion measuredon the upper legform,is studied.The shape and size of thecontact zone on the upper legform is analyzed.A calculationmethod for the contact force estimation is put forward b
21、yassuming a shape of the contact zone on the upper legformand a stress distribution function within the contact zone.Thecalculation method is verified using a simplified model ofvehicle front-end structure developed in a previous study.Using this simplified model,a parametric study is conductedto st
22、udy influence of key design variables related to vehiclegeometry and stiffness characteristics of the local area aroundthe bonnet leading edge.The results of the parametric studyhave revealed relationship among vehicle front-end designparameters such as stiffness,styling and geometry,contactcharacte
23、ristics such as the maximum stress on the mostoutside layer in the outer foam,impact energy absorbed bythe outer foam and the injury parameters.TYPICAL RESPONSE OF UPPERLEGFORM IMPACT TESTSUPPER LEGFORM IMPACT PULSEFigure 1 shows typical simulation results of upperlegform impact on a sedan model in
24、the middle position.Theimpact force is the summation of the two individual forcesmeasured at each end of the upper legform impactor frontmember,as specified in the test methods.In this simulation,the mass of the legform is 14.60 kg and the initial impactvelocity is 8.75 m/s.The upper legform impact
25、force response is caused by thecontact of vehicle front-end and usually exhibits multi-peakcharacteristics.The first peak is in accordance with the firstcontact of the upper legform on the bonnet lead area withhigher relative velocity.During this period the bonnet leadingedge usually receives suppor
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