Technical Note on the EuroSID-2 with Rib Extensions (ES-2re)

Transcription

1 Technical Note on the EuroSID-2 with Rib Extensions (ES-2re) WG12 report October 2006

2 Technical Note on the EUROSID-2 with Rib Extensions (ES-2re) WG12 Biomechanics March 13 th 2006 SUMMARY The ES-2re dummy is a variant of the ES-2 dummy proposed by NHTSA for the new FMVSS 214 standard. This variant has been developed to entirely delete the back plate seat interference that still may exist with the standard ES-2. Working Group 12 has reviewed the design and existing test data available in Europe. TRL performed lateral/ oblique impactor and Heidelberg sled tests with ES-2 and ES-2re. In these tests, the biofidelity of ES-2re was unchanged in sled test (thorax, pelvis) with respect to the standard ES-2, but larger rib deflections and V*C were observed. Also, larger rib accelerations were found due to added mass to the ribs. Finally, angular impactor tests confirmed a higher sensitivity of the ES-2re, in particular in rear oblique loading. Other test data reviewed were produced by MIRA on the MSIS sled under the SIBER project. These tests confirm that the ES-2re generally shows higher rib deflections and lower back plate loads compared to ES-2 in perpendicular and oblique loading conditions. Based on these test results, and with the notion that EuroNCAP has a firm penalty system on high ES-2 back plate loads in place, the working group does not see the value added of recommending the ES-2re for use in ECE R95. The group acknowledges that if there is a benefit, it must come from full harmonization with the US. A re-calibration of the (thoracic) injury tolerance values used with the ES-2re would be recommended in that case. 1. Background In August 2001, WG12 issued the report Development and evaluation of the ES-2 Dummy [1]. The report provides the rationale for the improvement of the regulatory test dummy EUROSID-1 used in Regulation ECE R95. Furthermore, it describes the design upgrades implemented in the ES-2 dummy that include a new thorax assembly and back plate design to reduce the flattopping effect and dummy-seat interference. Following an EEVC recommendation in 2002, the ES-2 dummy was adopted by EuroNCAP in 2003 and, as alternative test device to the EUROSID-1, in ECE R95 in 2004 [2]. The purpose of the ES-2 development was to address a number of known deficiencies of the EUROSID-1 dummy, hence making the dummy acceptable for use in the proposed updated FMVSS 214 standard in the US [3]. The harmonization challenge was to implement the required technical changes yet to stay close to the original EUROSID-1 performance in order to respect the wide use of this dummy by the industry outside of the US. While Europe and Japan recently have successfully made the transition from the EUROSID-1 to ES-2, NHTSA has experienced few occurrences of notable dummy-seat interaction in crabbed barrier testing, causing the agency to revisit the ES-2 design. The ES-2re (for Rib Extensions) is an ES-2 dummy with proposed modification to the rib unit, closing the space between the ribs and the spine. The design change is intended to effectively eliminate any grabbing of the dummy back plate into the seat structure. The NPRM on the update of FMVSS 214 recommends the use of the ES-2RE dummy, alongside with the small female SID-IIs dummy, in the barrier and the Page 1 of 8

3 new oblique pole tests. Once turned into final rule, the ES-2 will be used globally; however, different versions have prevented full harmonization at this point. The question rises whether the technical specification of the ES-2 dummy in ECE should be updated to line up with NHTSA s proposal. Preempting such discussions at the GRSP, EEVC WG12 has studied the ES-2re design and available data in order to support an official EEVC position on this subject. 2. What is ES-2re? One of the original problems observed with the EUROSID-1 is that the seat frame could catch the dummy back plate during the initial phases of the impact, mitigating the rib deflections measured at the dummy (Figure 1). For ES-2 the back plate was re-designed, bringing it back inside the anthropometric shape of the human back and making it narrower and rounded to reduce the likelihood of grabbing [1]. In addition, a back plate load cell was developed that could measure forces and moments generated in the event. EuroNCAP applies a penalty for high back plate loads, by which it effectively ensures that no significant load path is introduced through the back plate, intentionally or not [4]. For the European market in which cars are now developed against EuroNCAP criteria, this has largely resolved the back plate grabbing issue. In the US, a different situation exists however. In two occasions, NHTSA has observed extreme back plate loads generated by the seat frames of cars tested with ES-2 [5]. It was recognized that the improved design did not fully resolve problem, and lacking a penalty system, NHTSA asked for a resolution. Steel rib extensions were developed that would allow the seat frame to load the ribs, and not back plate. The steel rib extensions are bolted between a slider and the existing rib, while the ribs rest on roller bearings in the new back plate (Figure 2). With this proposed new configuration, back plate loads can still be measured. In repeated tests, NHTSA appeared satisfied with design back plate as the Fy loads were minimal and rib deflections not mitigated. Rib Figure 1: Seat frame caught by back plate Rib extension slides on backplate New backpla Figure 2: ES-2re new rib unit layout 3. Performance of ES-2re At the time of writing of this document about 30 ES-2re dummies are available in Europe and Japan. Despite this amount, only relatively little information about the ES-2re performance Page 2 of 8

4 compared to the standard ES-2 is available in the public domain. Asked about ES-2re earlier this year, only three out of twelve members of WG12 admitted to have experience with the dummy. Two important and relevant sources of information were reviewed by WG12: Biofidelity evaluation of the modified ES-2 back plate and rib extensions, a study carried out by the Transport Research Laboratory (TRL) in the UK in 2003 on behalf of the Department for Transport [6]; Sensitivity to crash parameters of WorldSID, ES-2 and ES-2re dummies, a study performed as part of the EC sponsored SIBER project by MIRA in the UK [7]. 3.1 TRL Study The deformation of the door in a side impact is often such that the loads applied to the dummy are not purely from a lateral direction, but contain oblique components. Therefore, in this study the ES-2 and Es-2re thorax were subjected to pendulum impactor tests performed at different impact directions; oblique rear, lateral and oblique frontal impacts. The objective of the tests was to establish whether the sensitivity of the ES-2 thorax to oblique impacts was affected by the addition of the revised back-plate with rib extensions. Changes to the sensitivity of the ribs in localised oblique impacts were noted: the accelerations in rearward of lateral impacts were particularly affected, with the ES-2 when fitted with the modified back-plate and rib extensions recording a greater acceleration (Figure 3). This could have implications and cause problems in vehicle testing, particularly in procedures that were based on using TTI as an injury parameter. Part of this was attributed to the increase in rib mass with the rib extensions and part to the lack of foam (representing the flesh) covering the rib extensions. It was recommended that a production version of the dummy should have Confor foam covering on the rib extensions as well as the rest of the rib Peak acceleration (g) Previous tests Original back plate Modified back plate degrees +10 degrees purely lateral -10 degrees -20 degrees Impact angle Figure 3: Comparison of the mean peak rib acceleration for each impact angle of ES-2 (original back plate) and ES-2re (modified back plate) [6]. Page 3 of 8

5 Furthermore, the biofidelity of the thorax and pelvis of the ES-2 dummy, when fitted with the original and modified back-plate, was evaluated by replicating the original Heidelberg lateral sled tests. Heidelberg sled tests are based on PMHS tests carried out in at the University of Heidelberg in collaboration with the US National Highway Traffic Safety Administration (Figure 4). From these data, EEVC WG9 derived target corridors for dummy biofidelity for the thorax and pelvis and peak value targets for lateral pelvis acceleration. It was found that the biofidelity of the dummy is unchanged with either dummy configuration. The rib and thorax accelerations in the Heidelberg sled tests were also similar for both dummy configurations. However, top rib deflection, which is the largest deflection in this test configuration, was 2 mm greater with the rib extensions fitted. The V*C increased by up to 36 % and TTI(d) decreased by up to 15 % when the modified back-plate with rib extensions was fitted, as assessed in the Heidelberg sled tests. Figure 4: Configuration of the Heidelberg sled test bench, set-up for a rigid wall test. 20 Normalised thorax force (kn) Upper EEVC thorax target Lower EEVC thorax target Original back plate, test 1 Original back plate, test 2 Original back plate, test 3 Modified back plate, test 1 Modified back plate, test 2 Modified back plate, test Time (ms) Figure 5: Sled test results: Normalised thorax plate force, low speed (7.6 m.s -1 ), rigid wall Page 4 of 8

6 20 Normalised pelvis force (kn) Upper EEVC pelvis target Lower EEVC pelvis target Original back plate, test 1 Original back plate, test 2 Original back plate, test 3 Modified back plate, test 1 Modified back plate, test 2 Modified back plate, test Time (ms) Figure 6: Sled test results: Normalised pelvis plate force, low speed (7.6 m.s -1 ), rigid wall The results of the TRL tests series demonstrate that the biofidelity of the ES-2 was not greatly affected by the modifications proposed by NHTSA. However, it should be noted that the assessment of thorax and pelvis biofidelity in this case is based on wall force-time data only, and does not incorporate an assessment of V*C nor deflection. These parameters, used in regulations, have shown to increase for ES-2re compared to ES-2 under identical loading conditions. Based on the increased acceleration levels, it is not recommended using TTI (or any other rib acceleration based criterion) as an injury parameter with the ES-2re dummy. Page 5 of 8

7 3.2 SIBER Study The effect of angled impacts on ES-2, ES-2re and WorldSID was investigated by MIRA on a side impact simulator (M-SIS) on a HyGe acceleration sled facility [7]. The dummy was seated in a simulated car interior, with current production car components, and subjected to impacts of an intruding door at realistic impact velocities. The velocity profiles were derived from those measured in full-scale tests. The dummy seating position (in particular the angle with respect to the door) was changed to study changes in response for ES-2, ES-2re and WorldSID. In the lateral tests, 90, all three dummies had similar overall impact kinematics. In terms of the rib deflections, the ES-2 and ES-2re had identical rise characteristics and peak deflections over the three ribs, but the ES-2re had consistently higher deflections at peak loading, see Table 1. On angling the door to 20 (rear oblique), it was observed that both the ES-2 and ES-2re rotate into the door during acceleration so that they are perpendicular to the door by peak rib deflection, while the WorldSID remain angled to the door. This rotation of the ES-2 and ES-2re dummies is a result of the box shaped thorax and restricted lateral motion of the ribs. Although the overall rib rise characteristics were not affected, the peak rib deflections were reduced in angled loading. The ES-2 produced significantly lower rib deflections, see Table 1, due back plate interaction, as was confirmed by high back plate loads (Figure 7). With the rib extensions, the back plate interaction has been significantly reduced as the majority of the loading is transferred through the ribs resulting in an only small reduction in deflection. The results of this test series show that, although ES-2 and ES-2re share similar kinematics, the dummies predict different risk at thoracic injury in identical loading situations. This is particularly the case in oblique loading conditions, such as might occur during full-scale crash tests. Table 1: ES-2 and ES-2re rib deflections measured in the SIBER MIRA M-SIS sled tests. Dummy Impact Rib Deflections msecs) Angle Thorax rib 1 Thorax rib 2 Thorax rib 3 ES ES ES-2re ES-2re Figure 7: Back plate moment Mz in perpendicular ( ) and angled ( ) impacts, for ES-2 (blue) and ES-2re (red) from the MIRA M-SIS sled tests performed in the EC SIBER project. 20 Page 6 of 8

8 4. Conclusions The test results reviewed in this document suggest that the design change introduced in ES-2re is effective in eliminating any back plate interference without significantly changing the dummy s overall biofidelity as assessed in the Heidelberg lateral sled tests. There is clear evidence that the internal dummy measurements, rib deflections, V*C and rib accelerations, are affected by the new designed back plate and rib extensions. The increase observed in these values is found most pronouncedly in an oblique loading condition, which is not uncommon in vehicle side impact crash tests. Furthermore, the sensitivity of the dummy rib deflection and particular rib acceleration to small changes in impact direction has increased. It has been noted that in Europe vehicles are designed to EuroNCAP. EuroNCAP has a firm penalty system on high ES-2 back plate loads in place that effectively has reduced the ES-2 back plate load issue. Taking this into account, the working group does not see the value added of using the ES-2re in ECE R95 or EuroNCAP. The group acknowledges the economical benefit of having a harmonized dummy between ECE and the US. If ES-2re was proposed as such, we would recommend that an additional investigation would be performed into the (thoracic) injury tolerance values to be used with the ES-2re. March 13, 2006 Members Participating in EEVC WG12 J.S.H.M. Wismans (TNO, NL), F. Bermond (INRETS, secretary, FR), D. Hynd (TRL, UK), C. Pastor (BAST, GE), J. Davidsson (Chalmers University, S), G. Gertosio (FIAT, I), L. Martinez (INSIA, E), K de Jager (TNO, NL). Industry advisors are: K. Bortenschlager (PDB, G), H. Öhrn (Volvo, S), P. Petit (LAB, FR) and M. van Ratingen (FTSS, NL). References 1. M. van Ratingen, C. Waagmeester, D. Twisk, M. Philippens, A. Roberts, D. Hynd, T. Kreuzinger, S. Compigne, Development and Evaluation of the ES-2 Dummy, WG12 report, Addendum 94: Regulation No. 95 Amendment 4, Supplement 1 to the 02 series of amendments - Date of entry into force: 12 August 2004, Uniform Provisions Concerning The Approval Of Vehicles With Regard To The Protection Of The Occupants In The Event Of A Lateral Collision, DoT, National Highway Traffic Safety Administration, 49 CFR Parts 571 and 598 Docket No. NHTSA , RIN AJ10, FMVSS; Side Impact Protection; Side Impact Phase-In Reporting Requirements, EuroNCAP Side Protocol and Assessment Protocol and Biomechanical Limits v4.1, Page 7 of 8

9 5. R. Radwan Samaha, ES-2 Crash Test Performance, 2002 SAE Government/Industry Meeting, Biofidelity evaluation of the modified ES-2 back plate and rib extensions, Unpublished report PR/SE/842/2003, J.A. Carroll, D. Hynd, TRL, SIBER, Side Impact dummy Biomechanics and Experimental Research, Contract N : G3RD-CT , Project N : GRD , Page 8 of 8