NHTSA's Recent Test Program On Vehicle Compatibility Sanjay Patel .

The forces on the ORB easily exceeded 100 kNin 400 mm displacement. However, forces intwo of the five ORB exceeded the load cellscapacity as shown in Figure 9 plot of individualORB load cells. The results of this test beyond400 mm displacement are of questionablequality.Figure 12.The pre-test picture of thealignment of the ORB and the SEASFigure 10. The energy absorbed by SEASTotal crash Energy 143,838 J% absorbed by SEAS in 400 mm 27.5 %VTV crash test into the 2002 Ford Focus wasconducted with the Ridgeline SEAS only, sinceSEAS can not be removed for this vehicle. Theinjury measures in this test were much higher.These high injury values suggest that theRidgeline SEAS structure was stiff. This resultcalls for further research to evaluate SEASstructure and especially redesign the ORB tomeasure its strength.Figure 13. The post-test picture showing thedeformed PEAS and SEAS2007 Chevrolet Silverado ResultsThe Silverado has brackets attached to PEAS asshown in Figure 11-12. These brackets areintended to bend the PEAS downwards in afrontal crash.Figure 11. Silverado SEAS design8, Patel

COMPUTER SIMULATION RESULTSThe structural interaction between passenger carsand Option 2 LTVs in frontal crashes wasinvestigated using computer simulations. TheNCAC/GWU has developed a fleet of virtualvehicles which were used to evaluate theeffectiveness of static geometric alignment onstructural interaction.The vehicle modelschosen for this study as shown in Figure 16,were based on the 1996 Dodge Neon, 2006 FordF-250 and the 2007 Chevrolet Silverado. All ofthese FE models were validated to full .edu/vml/models.html].Figure 14.Chevrolet Silverado forcesrecorded by the ORB load cells (ForceDeformation plot)The SEAS for this vehicle met the TWG criteriaof 100 kN in 400 mm displacement and observedthat forces were not exceeded the load cellscapacity.Figure 16. Finite Element Models of Neon,F-250 and SilveradoFrontal impacts between the following vehicle’spairs were analyzed in this study:1996 Dodge Neon–2006 Ford F-250 (Option 2LTV, cross-member type SEAS)1996 Dodge Neon–2007 Chevy Silverado(Option 2 LTV, PEAS Extension)Figure 15. The energy absorbed by SEASTotal crash Energy 160,276 J% absorbed by SEAS in 400 mm 8.9 %VTV crash test into the 2002 Ford Focus wasconducted with the Silverado SEAS only. SEASfor this vehicle can not be removed. VTV testcould be conducted with the SEAS bracketsremoved by cutting off the brackets at theattachment point with the PEAS. However, sucha test has not been conducted. The results fromthe VTV test (with SEAS) with the Ford Focushad high injury assessment values for the Focusoccupants.The Force-Deformation (F-D) characteristic forthe Neon, F-250 and Silverado in a full frontalfixed barrier impact is shown in Figure 17. Fromthe F-D curves, it is evident that the frontalstructure of the F-250 and the Silverado aremuch stronger than that of the Neon. TrueAHOF400 (average height of force delivered bya vehicle in the first 400 mm of crush), and theKw400 (measure of stiffness based on crushenergy absorbed by a vehicle in the first 400 mmof crush) [Mohan, 2008] were calculated foreach of the vehicles. Table 1 summarizes thedifference in mass, geometry and stiffnessbetween the target vehicle (Neon) and the twobullet vehicles (F-250 and Silverado). Thesimulations were conducted such that the targetvehicle (neon) experienced an impact severitysimilar to that of the frontal NCAP testcondition.9, Patel

Consequently, the energy required to crush 400mm of the front end of the F-250 and theSilverado is much higher than the Neon, asreflected by their respective Kw400 measures.VTV full frontal simulations were conductedbetween Neon-F-250 and Neon-Silverado. Theclosing speed was chosen to match the impactseverity of an NCAP test for the Neon.Figure 18. Geometric Alignment, Neon-F250Figure 17. Force Deformation Comparison ofNeon, F-250 and SilveradoTable 1. Mass, AHOF400 and Kw400 forNeon, F-250 and SilveradoMassTarget Veh.NeonBullet 1F-250Bullet 2Silveradokg1335299826222.251.96mm448Mass RatioTrue AHOF400AHOF RatioKw400N/mm1251Kw400 RatioApproach Velocit mphClosing Speed 2.80The front-end structural alignment between theNeon-F-250 and the Neon-Silverado is shown inFigure 18 and Figure 19. There is a significantvertical geometric mismatch between the PEASof the Neon and F-250. The SEAS positionedbelow the PEAS of the F-250 overlaps 50% ofthe Neon PEAS as required by the Alliancevoluntary commitment to improve compatibilityin frontal impacts for Option 2 LTVs. Due to thepresence of SEAS, the Silverado is classified asan Option 2 LTV in this study. Geometrically,the vertical mismatch of the PEAS is much lowerbetween Neon-Silverado when compared toNeon-F-250.Figure 19.SilveradoGeometric Alignment, Neon-F-250-Neon Simulation ResultsFull frontal simulations between the Neon andF-250 were conducted with and without the F250 SEAS to evaluate the influence of SEAS onstructural interaction between the two vehicles.The interaction between the PEAS of the Neonand the F-250 is illustrated in Figure 20 (withSEAS) and Figure 21 (without SEAS). TheSEAS on the F-250 prevents the Neon fromcompletely under riding the F-250. The front ofthe Neon PEAS interacts with the F-250 SEASand crushes axially in the beginning, but as theSEAS starts to fail the Neon PEAS starts to bendtowards the ground. Without the SEAS on theF-250, the structural interaction between thefrontal structures is significantly reducedresulting in notable underriding of the Neonfront end.10, Patel

Figure 20. Structural Interaction betweenNeon and F-250 (with SEAS)Figure 21. Structural Interaction betweenNeon and F-250 (without SEAS)The change in structural interaction wasprimarily investigated based on the amount ofcrash energy absorbed by the vehicles involvedin the crash. The amount of structural intrusioninto the occupant compartment of the vulnerablevehicle was also compared.The crash energy absorbed by the vulnerablevehicle (compact car, Neon in this study) isfurther divided into two groups:Front engine compartment energyOccupant compartment energyThe front engine compartment energy is theenergy absorbed by the components that aredesigned to absorb the crash energy. Theoccupant compartment energy is the energyabsorbed by the occupant compartment, which isprimarily designed to prevent any structuralcollapse into the occupant compartment.Figure 22. Energy Distribution (Neon-F-250)The benchmark for energy comparison is a fullfrontal simulation between identical Neon’s atthe same impact severity.The mass, theAHOF400 and the Kw400 are all equal. Theenergy distribution for the Neon front enginecompartment and occupant compartment for fullfrontal impact between Neon-F-250 (withSEAS), Neon-F-250 (without SEAS) and NeonNeon is shown in Figure 22. Due to significantmismatch between the Neon PEAS and theF-250 PEAS, the Neon frontal structures do notdeform ideally (as design optimized for frontalimpact into fixed barrier). Consequently, theenergy absorbed by the Neon front enginecompartment is lower compared to thebenchmark simulation between identical Neon’s.11, Patel

The presence of SEAS shows that the occupantcompartment energy initially follows thebenchmark simulation, but due to the taller,stiffer and heavier F-250, the Neon occupantcompartment continues to crush and absorb moreenergy to satisfy the conservation of energyprinciple. On the other hand, without the SEAS,there is significant underride of the Neon frontalstructures and the energy absorbed by the Neonoccupant compartment converges to thebenchmark simulation. Based on past crashtesting, NHTSA has found that structuralmismatch may reduce compartment accelerationon the partner vehicle; however, it is neverdesired.The energy comparison would not be conclusivewithout evaluating the resulting intrusions intothe occupant compartment of the vulnerablevehicle. The intrusion into the Neon occupantcompartment in full frontal impact with F-250(with and without SEAS) and Neon is shown inFigure 23. The structural underride between theNeon and F-250 without SEAS resulted in lowertoe pan intrusions compared to the impactbetween Neon and F-250 with SEAS. This isexpected as the lower load path is not utilizeddue to the geometrical mismatch of the structureswithout the SEAS on the F-250. The toe panintrusions in the case of the Neon to F-250 withSEAS are very similar to the benchmark impactbetween identical Neons. However, in bothcases (Neon to F-250 with SEAS and withoutSEAS) the driver side A-pillar intrusions arenearly twice (160mm) that of the benchmarkimpact between identical Neons. This intrusionis highly undesirable as the dash, steeringcolumn and the air bag modules are movingrearward and are compromising the survivalspace of the occupant. This may also result inlowering the effectiveness of the driver air bag inreducing risk of serious injuries.Figure 23. Neon Intrusions (Neon-F-250)Silverado-Neon Simulation ResultsThe structural interaction between the PEAS ofthe Neon and the Silverado is illustrated inFigure 24 (with SEAS) and Figure 25 (withoutSEAS). The presence or absence of SEAS onthe Silverado has negligible effect in the overallcrush kinematics of the Neon frontal structures.Figure 24. Structural Interaction betweenNeon and Silverado (with SEAS)Figure 25. Structural Interaction betweenNeon and Silverado (without SEAS)The energy distribution between the front enginecompartment and occupant compartment of the12, Patel

Neon for full frontal impact between NeonSilverado (with SEAS), Neon-Silverado (withoutSEAS) and Neon-Neon is shown in Figure 26.The energy absorbed by the Neon frontalstructures in a frontal impact between NeonSilverado is similar to the benchmark simulationbetween identical Neons. The Neon frontalstructures deform ideally (as design optimizedfor frontal impact into fixed barrier) absorbingthe crash energy. However, the energy absorbedby the occupant compartment is significantlyhigher when compared to the benchmarksimulation. Since, the Silverado is much heavierand stiffer than the Neon; the Neon structure hasto absorb the remainder of the crash energy tosatisfy the conservation of energy principle.One interesting observation is that both the frontengine compartment and occupant compartmentenergies of the Neon are marginally lower whenimpacted by the Silverado without the SEAS.The design and placement of the SEAS makesthe Silverado PEAS stiffer and reduces itscontribution to energy absorption in a frontalimpact with the Neon. When the SEAS isremoved, there is slightly higher energyabsorption by the Silverado PEAS which lowersthe amount of energy to be absorbed by the Neonfrontal structure.The resulting Neon compartment intrusionscomplement the observation above on energydistribution. The resulting toe pan and A-pillarintrusions are notably higher for the NeonSilverado (with and without SEAS) simulationcompared to the benchmark simulation Figure27. Without the SEAS, the intrusions at the toepan are slightly lower as some of the crashenergy is absorbed by the Silverado PEAS.Figure 27. Neon Intrusions (Neon-Silverado)SUMMARY OF COMPUTER SIMULATIONSFigure 26.Silverado)EnergyDistribution(Neon-The observations from the Neon-F-250simulations demonstrate that the cross-membertype SEAS design helps prevent underriding ofthe Neon frontal structures. However, the SEASin the Silverado was a non-contributing factor inthe overall crush kinematics of the Neon frontalstructures, mainly because of the vertical overlapof the PEAS structures of the Neon andSilverado. In fact, the Silverado without SEASshowed slight improvement in both intrusionsand energy absorption of the Neon.Improvement in geometric compatibility isessentially a step in the right direction. Further13, Patel

improvement in structural interaction is possibleby lowering the aggressiveness of the LTV’s.This preliminary analysis was limited tounderstanding the structural interaction in fullfrontal impacts. Other frontal and obliqueimpact conditions and impact locations and theireffect on structural interaction were notconsidered in this preliminary analysis.CONCLUSIONSThe industry voluntary test for the SEAS is aquasi-static push test that requires the SEASstructure to withstand a minimum of 100 kN offorce before 400 mm deflection from the front ofthe primary structure (e.g., the rails on which it ismounted).Such a test may guarantee aminimum strength, but it does not prohibit thestructure from being designed too strong forgood car compatibility. An energy absorptionevaluation could optimize the SEAS forcompatibility.The ORB dynamic tests showed that the vehiclestested meet the proposed SEAS performancecriteria suggested by the Alliance’s TWG.The full frontal simulations between a compactpassenger car (Neon) and the Ford F-250 withoutthe SEAS showed reduced intrusions in the Neontoepan area. However, there was significantunderride of the Neon which resulted inincreased intrusions near the driver side A-pillar.In the case of F-250 with SEAS, there wasincreased structural interaction between theSEAS and the Neon PEAS which preventsfrontal structures from underriding each other.As a consequence there is more intrusion into theoccupant compartment when compared to thefrontal impact without the SEAS. Thisobservation was based on the simulation resultswith FE model of the 1996 model year Neon. Inrecent years, the structural design and selfprotection levels of compact passenger cars havesignificantly improved (based on frontal NCAPand IIHS front offset test results) and theobservation may be different in frontal impactsbetween these newer compact cars and the FordF-250 with and without the SEAS. The presenceor absence of SEAS on the Chevrolt Silveradohad negligible effect in the overall crushkinematics of the Neon frontal structures. Thisis primarily attributed to the SEAS design and itslocation.Further study is needed to determine theeffective performance requirements for SEAS.This study was limited to the three SEAS designsthat were available in production vehicles at thetime of testing. Other SEAS designs and theirperformance may need to be considered beforean appropriate ORB test procedure is identified.The difference in the design of the PEASconfounds the study of the effects of SEAS inVTV tests. In the case of the Ford F-250, wherethe SEAS could be removed, the VTV tests showa benefit from SEAS. However, the SEAS onthe F-250 had the lowest strength. Additionalcriteria for the SEAS, like energy absorbed, maybe considered in the future.Like most programs using crash tests, this studyis subject to limitations in the number of vehiclesstudied. Additional SEAS designs will need tobe studied, along with their effect in mitigatinginjuries in the partner vehicle, before anyconclusions can be made about the effectivenessof the proposed TWG performance criteria.Option 2 LTV’s reward the added SEAS toreduce override of passenger cars.Thesestructures will require a new test procedure forevaluation. This paper shares the designs of theORB, and results from tests of Option 2 vehiclesequipped with and without SEAS.ReferenceBarbat S. (2005). “Status of Enhanced Vehicleto-Vehicle Crash compatibility Technicalworking Group Research and Commitments; 19thESV Conference, Washington, D.C., Paper No.05-463.Alliance of Automotive Manufacturers,letter to Acting Administrator, NHTSA, May 10,2006, (Docket # NHTSA-2003-14623-24).Patel S., Smith D., Prasad A., (NHTSA) &Mohan P. (The George Washington University),“NHTSA’s recent vehicle crash test program oncompatibility in front-to-front impacts”, 20thESV Conference, Paper No. 07-0231.Baker, B., Nolan, J., O’Neill, B., Genotes, A.,(2007). “Crash Compatibility between Cars andLight Trucks: Benefits of Lowering Front-EndEnergy-Absorbing Structure in SUVs andPickups”, Insurance Institute for HighwaySafety, Arlington, VA, 2007.Alliance of Automotive Manufacturers, letter toRonald C. Medford, NHTSA, July 30, 2007,(Docket # NHTSA-2003-14623-63).14, Patel

d 134&cat oluntarycommitment to enhance vehicle to vehicle crashcompatibility", December 2003.http://www.access.gpo.gov/nara/cfr/waisidx 99/49cfr581 99.htmlMohan, P., "Development of Objective Metricsto Improve Compatibility in Frontal Collisions",Doctoral Dissertation, The National CrashAnalysis Center, The George WashingtonUniversity, Washington DC, August 2008.15, Patel

characteristics of SEAS. The performance of SEAS in VTV tests was expected to show a benefit from using SEAS. Updated ORB design The initial full frontal tests and ORB design as shown in Figure 1 were described but the results were not included in ESV paper 07-0231 because the results were not completely analyzed at the time of writing that paper.