Development of an advanced head/neck system for 5th percentile female anthropomorphic test dummies (2002)

This paper presents the development of an advanced dummy head/neck system which can be used with 5 percentile female crash test dummy. The system will become part of the 5 percentile female Thor dummy, currently under development. It can also be retrofitted to the standard 5 percentile female Hybrid III. An overview of the new head/neck system design is described in the paper. The biomechanical requirements for the neck response for the 5 percentile female have been scaled from the 50 percentile male response and these requirements are reviewed. The design methodology, which includes mechanical design, simulation, and component tests, is presented. Finally, results from preliminary quasi-static and dynamic testing of the new design are discussed and compared to the response of the 5 percentile female Hybrid III neck. INTRODUCTION cording to the NASS data, over 22% of female occupants involved in tow away accidents are 1.58 meters (62 inches) in stature or less, and over 2.5% of these suffer serious or fatal injuries (Backaitis, 2003). The 5th percentile female size is thus representative of a significant proportion of occupants who suffer serious injuries. Furthermore, this point has been reemphasized recently by the studies revealing that a number of deaths and serious injuries have occurred to small statured women because of deploying airbags in out-of-position environments. Head and neck injuries are among the injuries with severe consequences. An anthropomorphic test dummy (ATD) is often used as a tool to investigate and reduce this kind of injures. The limitations of the head/neck system of currently available dummies identify a need to develop a more biofidelic head/neck system for the current 5 percentile female ATD. A Injury Biomechanics Research 64 Over the years, different 50 percentile male neck designs have been developed with various degrees of success. For example, a neck developed by General Motors (Foster et al., 1977) is used in the current Hybrid III dummy. By using scaling techniques (Schneider et. al, 1983; Mertz 1984; Eppinger et. al, 1984), the researchers developed the female neck based on its male counterpart. and its 5 percentile female Hybrid III (Mertz, 1989; NHTSA, 1998) is developed based on these techniques. This female neck meets the scaled Mertz corridors, which correlate the moments around the occipital condyle joint with head angle relative to T1 (Mertz et al., 1973; Patrick and Chou, 1976). However, this neck did not have good agreement with respect to head kinematics when compared to results from volunteers tests conducted at the Naval Biodynamics Laboratory (NBDL) (Ewing et al., 1975). An advanced 50 percentile male head/neck system , with improved biofidelity, was developed, and is part of the NHTSA frontal dummy known as THOR (White et al., 1996). The current version of THOR is known as THORAlpha. One of its main improvements was to use a spring/cable assembly exterior to the neck to simulate human neck muscular contribution during impact. The spring/cable design was meant to simulate proper excursions and lag which were seen in the NBDL volunteer experiments. The male THOR neck was evaluated by several research institutes such as TNO and JARI (Hoofman et al., 1998) and the results indicated that the neck substantially satisfied the frontal and lateral flexion requirements. However, additional improvement of the neck was still needed. For example, new experiments on volunteers have been conducted by several researchers in recent years (Davidsson et al., 1998; Ono et. al, 1999) and newly updated corridors were developed according to these data. Another area was in improving the anthropometry of the THOR-Alpha neck. In the THOR-Alpha neck, the location of the C7/T1 joint is not clearly delineated and it was thought that a properly defined T1 would help in the definition of any injury assessment using THOR. In addition, there appeared to be a need to retrofit the conventional Hybrid III dummy with the head/neck assembly from THOR. A similar retrofit has been done for the Hybrid III lower extremity by using the newly designed Thor-Lx and Thor-FLx (Shams et al.1999; Shams et al. 2002). In order to meet these new design criteria, a new THOR-Beta neck was developed and the basic properties of this neck design have been presented in the 2001 Workshop. A 5 percentile female version of the THOR-Beta neck has now been developed as well, by scaling the male version. In this paper, the development of this 5 percentile female head/neck system is discussed. DESIGN REQUIREMENTS The design requirements for the new 5 female percentile head/neck system are similar to the 50 percentile male THOR-Beta head/neck. The basic design requirements are matching human anthropometry, matching human neck responses in kinematics and dynamics, and meet the geometry constraints for retrofitting to the HIII ATD. First, the new neck needs to generally match the anthropomorphic landmarks for AATD (Schneider et. al., 1983) such as the occipital condyle (O.C.) joint and T1. The second important criterion is to match the dynamic and kinematic responses of this mechanical neck to the human responses. The current corridors of human head/neck responses in kinematics (Wismans and Spenny, 1983 Thunnisen et. al, 1995; Davidsson et al. 1998; Ono et. al, 1999; Ono et. al, 2001) are for the male. Therefore, scaling procedures (Mertz 1984; Eppinger et. al, 1984) have to be applied to obtain the corridors from these male versions. Two of these 5 percentile female corridors in kinematics are shown in Figures 1 and 2 (flexion and lateral flexion). In addition, the scaled Mertz corridors (Mertz et al., 1973; Patrick and Chou, 1976) have been utilized as secondary requirements as well. Finally, as this neck is expected to retrofit into the Hybrid III, the current constraints in the Hybrid III head/neck complex have to be considered. These constraints include the neck length, a large horizontal offset from the neck base to the occipital condyle joint, and the location of the pitch change relative to the thoracic spine. Development of an Advanced Head/Neck System for 5 Percentile Female Anthropomorphic Test Dummies 65 Figure 1: Kinematic corridors for 5 female neck in 15g flexion. Figure 2: Kinematic corridors for 5% female neck in 7g lateral flexion. DESIGN OVERVIEW The new 5 percentile female head/neck system, called THOR-Beta, is based on its 50 percentile male counterpart. By using the requirements described in the previous section and standard scaling techniques, the new neck was designed and fabricated (see Figure 3). Figure 3: 5 percentile female Thor-Beta neck The principal design features of the new female Beta neck (similar to the features in the male Beta neck) are: 4 Pucks and Offset Geometry The 4-puck neck agrees with the OC-T1 length derived from NBDL tests and the T1 is located at a well-defined rigid position. In addition, the new neck has to satisfy the design -20 0 20 40 60 80 100