In Euro NCAP, there is currently a set of test procedures for evaluating the safety performance of cars when they impact pedestrians. The Euro NCAP test procedures comprise three sub-system impact tests to assess a car’s performance. Separate impactors are used to represent the pedestrian in each main phase of impact with respect to the relevant body loadings. The three impactor types are: a FlexPLI for the assessment of pedestrian lower leg and knee injuries; an upper legform impactor representing the thigh and pelvis to record bending moments and forces; and child and adult head impactors to record head accelerations during impact on the vehicle front including the bonnet leading edge. Each impactor is propelled into the car and the output from the impactor instrumentation is used to establish whether the energy absorbing characteristics of the car are acceptable.
Accident data points on head, thorax and lower extremities as the most relevant body regions not only for the average population, but in particular for the elderly. Consequently, SENIORS is also focusing on the improvement and development of impactors representing these body regions and the definition of test and assessment procedures.
Improving kinematics correlation by adding mass
The overall goal within the external road user branch of SENIORS is the enhancement of the safety of older road users. Taking into account the latest accident data analysis, existing pedestrian test tools for the head and lower extremities will be improved. Prior to prototyping of the improved tools and definition of updated test and assessment procedures, a broad variety of human body model and impactor simulations serve as a basis for further development, as shown in Figure 1.
The need to improve the current headform impactor arises during impacts on angled or curved vehicle surfaces when, sometimes, partly high impactor rotations lead to unrealistic results in terms of linear accelerations and calculated values for the Head Injury Criterion (HIC). The purpose of a new Head Neck Impactor (HNI) is to improve the kinematics correlation and the injury assessment by adding a neck mass. The application of an additional neck mass to the impactor is meant to limit the impactor rotation in these cases, bringing the results back into a more realistic range. Simulations with the head neck impactor already showed at an early stage of the programme that the development derived from the APROSYS project is not yet ready for implementation within consumer or regulatory testing.
The FlexPLI updated with a pedestrian torso mass surrogate (UBM – upper body mass) differs from the previous one in that it has an upper body mass which significantly changes the impact response of the lower limb. Through current test tool FlexPLI, the testing of vehicles with high leading edges cannot always be performed in an appropriate way. The starting point for the improvement of the upper body mass for the FlexPLI and the development of a test procedure were comparative simulations with THUMS and the FlexPLI-UBM against generic vehicle frontends. The FlexPLI-UBM shows a much higher correlation with HBM kinematics and time histories as it can be used to address femur injuries and assess higher vehicles, as can be seen in Figure 2.
HBM as well as impactor simulations with added mass were carried out under identical impact conditions against a generic test rig that was developed out of data from more than 160 actual vehicles and that is representing four different vehicle categories (Sedan, SUV, Sport Car, MPV/Van) with three different frontshapes each category.
In the next step, the impactor will be fine-tuned and transfer functions for the injury parameters (knee elongations and femur and tibia bending moments) will be established before validating the final version with simulations against actual vehicles.
Designing new prediction tools
In addition to the legform and headform impactors, a thorax injury prediction tool is being explored in SENIORS. According to the accident data analysis done [article 1], in terms of AIS 3+ pedestrian and cyclists injuries, the thorax is the most relevant body region for the elderlies . For this reason, SENIORS is focusing on the development of a new test tool for the assessment of thoracic injuries of pedestrian and cyclists named Thorax Injury Prediction Tool (TIPT).
The first promising simulation results with TIPT have indicated that the ES-2 torso is applicable for assessing rib injuries to vulnerable road users at speeds representing consumer or regulatory vehicle speeds of 40 km/h and 35 km/h respectively. However, the results were still not that satisfying in terms of correlations that were aimed to be established, but indicated the general possibility for the development of a test tool with good thoracic injury assessment ability. A modification of the TIPT by adding a weight to the neck or to the neck and the pelvis likewise did not improve the overall results in terms of correlations, but could significantly improve correlations for the 4th rib. Figure 3 shows a comparative of the simulations with THUMS and TIPT.
Furthermore, a simplified simulation setup will be considered to eliminate possible scatter of results due to the usage of the SAE buck. If transfer functions can be established in a next step, the original plan to validate the new tool against actual vehicles will be maintained. Prototyping of a first impactor is planned during a subsequent research project.
Additional information can be found in the following papers:
- Zander, O., et al. (2017). “Safety enhanced innovations for older road users (SENIORS): Further development of test assessment procedures towards an improved passive protection of pedestrians and cyclists”. ESV Conference Paper number 17-0268.
- Zander, O., et al. (2017). “EU Project SENIORS: Evaluation of test tools for an improved assessment of pedestrian and cyclist injuries.” Carhs Presentation.
- Burleigh, M. (2017). “EC SENIORS PROJECT (Safety Enhanced Injury for Older Road Users).” BSI committee meeting Presentation.
- Lemmen, P., et al. (2016). “Design specifications for improved pedestrian tools.” Derivable Report D3.1B.
For more information on the SENIORS project check out http://www.seniors-project.eu/
Inquiries: Adrià Ferrer, Innovation Project Manager (Applus+ IDIADA). E-mail: firstname.lastname@example.org