Collision data analysis has revealed that elderly car occupants are at higher risk of chest injury than younger car occupants, particularly in low or moderate impact speed crashes. SENIORS aims at improving the methods to assess thoracic injury risk.
The traditional approach to develop dummy-based injury criteria and risk functions is to perform paired tests with dummies and post mortem human subjects (PMHS). However, the focus of the available PMHS test data is on higher injury levels and might not be completely representative for modern restraint systems. To overcome this limitation in the development of improved thoracic injury risk functions, a new approach has been applied in SENIORS by performing paired simulations with a THOR dummy model and human body models. The results were then compared with PMHS test data with the desired moderate loading conditions.
The results using these methods can only be fully compared if the test conditions are also comparable (within the constraints of each method). To enable this approach a new simplified and generic test rig was developed both as physical prototype and as finite-element model for testing and simulation respectively. For a more detailed description see Eggers et al. (2017). The aim was to create a more representative set-up of contemporary vehicles, ensuring good test repeatability and enabling the comparison of test results. Requirements for the generic test rig were defined from previous projects such as THORAX (Lemmen et al. 2013; Davidsson et al. 2014). It is based on the Gold Standard fixture (Shaw et al. 2009) as it is simple and easy to use in virtual testing. The new test rig is composed of: (i) a cable seat back, (ii) a foot rest, (iii) a modified seat pan design, (iv) a seatbelt system and (v) a pre-inflated driver airbag (Figure1).
Figure 1: Set-up of sled tests with THOR-50M
The seat pan used is a modified rigid seat developed in an earlier project funded by SAFER and is referred to as the SAFER seat. This seat pan aims to limit the x- and y-displacement of the occupant pelvis similar to a real vehicle seat and that is the reason why we have a seat ramp (Figure 2). More details can be found in a publication by Pipkorn et al. (2016). Also, to measure the loads between occupant and seat a 6-axis load cell was used.
Figure 2: The SAFER Seat used in the SENIORS generic test rig
While in the Gold Standard test fixture the pelvis of the occupant is restrained by a knee bolster, in the SENIORS generic test rig this is accomplished by an increased interaction between the pelvis and the SAFER seat.
A three-point belt system was defined with adjustable anchor points to evaluate the influence of different belt geometries on chest deflections and injury risk. At the upper shoulder belt anchor point a steel D-ring without any plastic cover was used (Figure 3), which does not need to be replaced between the tests and reduces manufacturer variability. Also, for further simplification and improved repeatability instead of a production buckle a generic one was used with a uniaxial load cell to measure the sum force of lap and shoulder belt in a reliable way (Figure 4). Moreover, a generic load limiter was integrated into the test rig which was developed by the Centre for Applied Biomechanics at the University of Virginia to achieve representative but still repeatable results (Figure 5).
Figure 3: D-ring
Figure 4: Generic buckle
Figure 5: Generic belt load limiter
GENERIC DRIVER AIRBAG
The introduction of a generic driver airbag in the set-up is one of the main improvements. It consists of a generic statically pre-inflated driver airbag, which was developed to be useable multiple times enabling distributed airbag loading to the occupant but, at the same time, avoiding production components to maximise repeatability. Also, a system to keep the pressure conditions was integrated. Moreover, an external wrap was introduced to achieve the desired shape of a standard airbag, which also kept the oscillation of the bag (Figure 6)under control. Parameters such as initial pressure, venting size or venting trig time are adjustable to simulate different conditions.
Figure 6: Generic airbag
We carried out several physical tests and simulations with the THOR-M dummy in the generic test set-up in different configurations (Figure 7) to adjust the restraint systems with the required parameters in order to achieve the desired loading performance. The aim was to achieve reasonable occupant kinematics and a distributed chest loading which results in a low range of AIS3+ chest injury risk. The tests were performed at:
• Two different deceleration pluses (25 km/h with an acceleration peak of 13 g and 35 km/h with an acceleration peak of 17 g)
• Three different positions of the upper shoulder belt anchor point were investigated: D1, D2 and D3
Figure 7: Physical and simulation tests with the THOR-M dummy
Moreover, these tests enabled the validation of the SENIORS generic sled model where the generic driver airbag model was integrated. Prior to that, a finite-element model of the generic driver airbag was developed and its response correlated by means of linear impactor tests at 7 m/s using an impactor mass of 22 kg (Figure 8).
Figure 8: Impactor test and FE-model simulation
The results observed in the THOR-M dummy tests at different configurations were more representative of the loading regarding a contemporary vehicle than most available PMHS tests. However, the parameter configuration finally proposed still showed a predicted injury risk higher than the desired moderate loading. A possible explanation might be the absence of a pretensioner which is a restraint component available in most contemporary vehicles. To achieve the desired loading with moderate severity chest loading in the future, it might be necessary to develop a generic pretensioner component.
Davidsson, J.; Carroll, J.; Hynd, D.; Lecuyer, E.; Song, E.; Trosseille, X.; Eggers, A.; Sunnevang, C.; Praxl, N.; Martinez, L.; Lemmen P. and Been, B. (2014). Development of injury risk functions for use with the THORAX Demonstrator; an updated THOR. Proceedings of IRCOBI Conference, 2014, Berlin, Germany.
Eggers A, Ott J, Pipkorn B, Bråse D, Mroz K, López Valdés F and Hynd D (2017). A generic sled test set-up for frontal occupant evaluation developed within the EU project SENIORS. Proceedings of the 25th Enhanced Safety of Vehicles (ESV) Conference, 5-8 June, Detroit, USA
Lemmen P.; Been B.; Carroll, J.; Hynd, D.; Davidsson, J.; Martinez, L.; García, A.; Vezin, P.; Eggers, A. (2013). An advanced thorax-shoulder design for the THOR dummy. Proceedings of the 23rd International Technical Conference on the Enhanced Safety of Vehicles, 2013, Seoul, Korea.
Pipkorn, Bengt; Lopez‐Valdes, Francisco J.; Juste‐Lorente, Oscar; Maza, Oscar and Sunnevång, Cecilia (2016) Study of the Kinematics of the THOR dummy in Nearside Oblique Impacts. Proceedings of IRCOBI Conference, 2016, Malaga, Spain.
Shaw, G.; Parent, D.; Purtsezov, S.; Lessley, D.; Crandall, J.; Kent, R.; Guillemot, H.; Ridella, S. A.; Takhounts, E; and Martin, P. (2009). Impact response of restrained PMHS in frontal sled tests: skeletal deformation patterns under seat belt loading. Stapp Car Crash Journal, vol. 53 (November 2009), pp. 1-48