Mr. Takahashi also presented the document on the biofidelity issues. He concluded that, compared to the EEVC LFI, biofidelity has improved significantly. First, the risk of bone fracture is evaluated over the entire length of the tibia. As the peak stress of the bone is generally located below the impact point, the injury risk could not be addressed using the EEVC LFI accordingly. Second, an elongation of the cruciate ligaments is caused by both shear and valgus bending which is addressed accordingly by the FlexPLI while the EEVC LFI is using two separate thresholds for the knee shear displacement and the knee bending angle.
For the tibia fracture prediction, Mr. Takahashi had presented results for three different vehicle front ends (passenger car, SUV with low lower bumper reference line and SUV with high lower bumper reference line) in their original state as well as in a modified state. Mr. Zander wondered why for vehicles A and B the performance with the EEVC LFI was worse while it improved for vehicle C. Mr. Takahashi explained that vehicles A and B had relatively soft front ends and were modified to be stiffer while vehicle C already had a stiff front end and was modified to become softer. This explains the different results.
Also, Mr. Zander asked which simulation models were used. Mr. Takahashi stated that the human model was developed jointly by Honda and JARI. Detailed information on the human model is available in the references listed in the document GTR9-1-05. The vehicle models are simplified vehicle models and the derivation is described in detail in the reference paper (see list of references at the end of document GTR9-1-05) of Konosu et al. from the IRCOBI 2009 conference.
Mr. Bilkhu added that the EEVC LFI had been developed to address knee injuries. So, one should not be surprised that the performance regarding tibia injuries is limited. However, also with the FlexPLI the correlation of the knee response with the human model is not yet perfect compared to that of the tibia. Mr. Takahashi replied that they are aware of this and plan to study this in more detail in the future. On request he confirmed that this should not affect the design of the current impactor.
Besides, Mr. Bilkhu stated that both impactors do not seem to be very good for knee injury prediction (r value below .8) Mr. Takahashi answered this being one of the limitations of the legform only representing the isolated human leg. He stated that JARI is currently working on a study to incorporate the upper body mass effect. However, the study is at a too early stage for conclusions.
Ms. Versailles added that the US also had shown in their document GTR9-1-12 that the performance had been improved. Mr. Kinsky stated that however the presentation of the US may cover a mistake in its conclusions: due to the fact that the FlexPLI has an overload protection device (the steel cables along the long bones) and the EEVC LFI does not have such a device it is not possible to compare test results well above the limits. This was confirmed by Mr. Been (Humanetics).
Mr. Takahashi promised to also provide an updated version of this presentation that will include some slight corrections (see doc. GTR9-1-05r1).
Mr. Takahashi (JASIC) presented document GTR9-2-07 in a version that had been already revised (see document GTR9-2-07r1). He mentioned that some of the information had already been presented during the 1st meeting of the IG GTR9-PH2.
Mr. Takahashi explained that the biofidelity of the FlexPLI has improved significantly. Mr. Bilkhu felt that the presentation here is not fully correct: Data are mainly based on simulation data and it seems impossible with this to prove that the biofidelity has really improved. All models may have different correlations. Dr. Otubushin (OICA) suggested to clearly state that the performance of the two impactors’ FE models was compared with the human body model which should address the concerns of the Alliance. Dr. Konosu stated that those FE models are validated by comparing with actual impactor responses or PMHS responses. No concerns regarding validity therefore exist with those FE models. Mr. Takahashi wondered whether he needs then to change the former presentation since the slides under discussion were just copied from the other document. Also, he pointed out that the time where the earlier presentation had been shown no comments on this had been made. Finally it was suggested to modify the presentation accordingly but to go through the presentation here to assure that the information is shared.
During the ongoing presentation, Ms. Chaka (OICA) explained that the data from the U.S. may need to be processed in another way. Classification of injury severities from accident data (AIS coding) refers to vehicle occupants but not to pedestrians. In addition, data are not nationwide. Finally, it should be defined how the terms fatal, severe and minor were used for the injuries.
Mr. Bilkhu added that legform injuries usually are not fatally (max. AIS 3) and that therefore the approach for establishing the costs may be misleading and needs to be changed. The Alliance sees some difficulties in agreeing on the way JASIC performed the analyses. After some intense discussion on this it was finally clarified by the chair that the information represents the approach of JASIC. The chair therefore suggested that the Alliance may hand in their comments and concerns via OICA. A constructive document proposing alternative methods would be very much appreciated.
Afterwards, Mr. Takahashi presented again document GTR9-1-05r1 of the 1st meeting since the Alliance questions referred to this. The presentation explains in detail the methodology of JASIC to prove the biofidelity of the FlexPLI. Mr. Bilkhu again mentioned that some of the slides need to clearly state that the impactors are compared with a human body model. Mr. Takahashi replied that the presentation reflects JASIC’s findings and that the Alliance should hand in their comments for discussion.
Mr. Frost (U.K. DfT) wondered whether the knee stiffness is acceptable. The EEVC LFI clearly has its limitations but seems to good represent the knee injuries. In contradiction, the presentation of Mr. Takahashi shows that knee injuries are underrepresented. Dr. Konosu (JARI) replied that the FlexPLI covers both, knee as well as tibia injuries. Due to this, compromises had to be found and main priority was given to tibia fractures based on the relevance according to accident studies. However, Mr. Frost stated that he is concerned with the decreasing ability to assess knee injuries. Dr. Konosu therefore explained that knee injuries are rare in accident statistics. He wondered whether more statistics on this are available from the United Kingdom or EEVC. Mr. Frost promised to check this.
Dr. Otubushin asked the group to not only consider the detailed scientific comparisons between the EEVC legform impactor and the FlexPLI: It may be the case that also differences in the operational area of testing are relevant. For example, in slide 16 of the JASIC presentation, at the level of 340 Nm the difference in displacement between FlexPLI and EEVC LFI is only approximately 10 mm whereas consideration of the whole range of responses including the rebound phase as presented in this slide would lead to drastically different conclusions. The group should therefore always ask themselves if the differences between the impactors in the operational area specified in the GTR are relevant in the real world.
Mr. Hardy (TRL) asked why the bending moment at the knee is zero at the knee joint since the joint itself also can withstand certain loads. Mr. Takahashi explained that he does not know the boundary conditions of this study that was done by experts from the Nagoya University. It was agreed that JASIC will come back to this.
On behalf of NHTSA Mr. Nguyen presented details from a research project of NHTSA and Autoliv. Mr. Nguyen apologized that this is preliminary information from this study but promised to deliver the final results at one of the next meetings. Sources of the data used are the Pedestrian Crash Data Study (PCDS) and the German In-Depth Accident Study (GIDAS). The analyses only cover AIS 3-6 injuries, looking at disabling injuries according to the Functional Capacity Index (FCI) based on AIS. According to both studies, bumper-caused injuries represent up to 40% of all pedestrian injuries. Despite there are notable differences between the two sources regarding the number of injuries to the different body regions the number of injuries to lower extremities caused by the bumper is in both cases close to 100% (94% for PCDS and 99% for GIDAS). The presentation also showed the ranking of injured body regions for serious and disabling injuries.
Mr. Edwards (OICA) asked when the final study will be available. Mr. Nguyen responded that he does not have this information right now.
On request of the Mr. Bilkhu Mr. Nguyen clarified that only injuries of people above 18 years were considered. Ms. Chaka wondered how PCDS data were used to represent nationwide data. Mr. Nguyen explained that the PCDS data set was weighted using the data of the General Estimates System (GES) of the National Automotive Sampling System (NASS). However, it was again promised to come back to the details as soon as the study is finally published.
Mr. Takahashi presented document GTR9-2-12 representing a reexamination of the data of document GTR9-2-07r1 and which addresses the concerns raised by Mr. Bilkhu and Ms. Chaka mentioned before. He admitted that indeed the data of the PCDS had counted MAIS1+ injuries as severe injuries in some cases and MAIS2+ injuries as minor injuries. Considering and correcting these mistakes Mr. Takahashi found that the number of severe injuries rises while the number of minor injuries decreases.
It was finally concluded that the discussion on these items is expected to go on during the next meeting.