Durability Over Time of Skin Used for JAMA–JARI Pedestrian Headform Impactor Measured by Biofidelity Certification Testing

Head injuries are the most common cause of pedestrian deaths in car–pedestrian accidents. To reduce the severity of such injuries, the ISO, IHRA and Japan MLIT proposed subsystem tests in which a headform impactor is impacted upon a car bonnet top. JAMA and JARI have developed the headform impactors in compliance with the ISO standard, the IHRA recommendation and the Japan MLIT safety regulation. The impactor consists of the core and skin. Since the skin is made of nonferrous material, the stiffness of the skin would be changed due to time elapse. The stiffness of the skin was confirmed by assessing the peak resultant acceleration of the gravity center measured in the biofidelity certification test, the so-called drop certification test. The ISO, IHRA and Japan MLIT specified the corridor of the peak acceleration impact must range from 245 to 300 G for a child headform impactor. In the present study, the newly developed skin durability over time at 0 month, 13, 16, 19, 22, 25, 28 and 31 months after manufacture was investigated in a room either with or without control of temperature and humidity. The results indicated that the peak acceleration impact using the two skins immediately after manufacture was 270 G. The peak acceleration of 287 G using the skin kept in a room with control of temperature and humidity increased 17G at 31 months after manufacture. The peak acceleration impact of 288 G using the skin kept in a room without control of temperature and humidity increased 18 G at 31 months after manufacture. The respective increases of 17 G and 18 G correspond to 31% and 33% of the range of certification test corridor (55 G), respectively. These results indicate that if the acceleration is close to the middle of the drop certification corridor (272.5 G) immediately after purchase by a testing facility, the skin is available for pedestrian impact test use with a storage period of at least 31 months. The results also suggest that if the acceleration is close to the upper limit of the drop certification corridor (300 G), the skin expiration time may be drawing very near. The findings also indicated temperature and humidity did not significantly affect the skin durability over time. INTRODUCTION Head injuries are the most common cause of pedestrian deaths in car-pedestrian accidents, and countermeasures against them are of the highest priority in traffic safety strategy [1]. The key element in this strategy is improvement of the safety performance of the car front. To reduce the severity of pedestrian head injuries in bonnet top contacts, the International Organization for Standardization (ISO) [2][3] and International Harmonized Research Activities (IHRA) [4] have proposed subsystem tests in which a headform impactor is impacted upon a car bonnet top. The ISO and IHRA have specified the biofidelity requirements for the headforms in terms of the peak value of the resultant centre of gravity (CG) acceleration measured in biofidelity certification tests (hereafter referred to as the drop certification test). In 2004, the Japan Ministry of Land, Infrastructure and Transport (Japan MLIT) officially announced the Japanese safety regulation for the evaluation of car–front safety performance in terms of pedestrian head protection. The Japanese standard requires headform impactors to be in compliance with the IHRA specification. The IHRA required the specification of headform impactor for mass, diameter, moment of inertia, location of center of gravity, seismic mass location of accelerometer, first natural frequency and resultant acceleration in the biofidelity certification test as listed in Table 1. The same table also indicates that any impactor built according to the IHRA proposal [5] fulfills the ISO specifications [2][3]. The Japan Automobile Manufacturers’ Association (JAMA) and the Japan Automobile Research Institute (JARI) have thus far jointly developed headform impactors which are compliant with the ISO/IHRA/Japan MLIT requirements (hereafter referred to as the JAMA–JARI headform impactor) [6]. The JAMA–JARI headform impactor consists of the core (sphere and baseplate) and the skin which is made of polyvinyl chloride (PVC) (Figure 1). Skin stiffness was confirmed by assessing the peak resultant acceleration of the gravity center measured in the drop certification test. Since the skin material is nonferrous, the skin impact durability and