applied sciences Article EffectArticle of Seat Condition on Abdominal Injuries to Effect of Seat Condition on Abdominal Injuries to VehicleVehicle Occupants inin FrontalFrontal ImpactImpact AccidentsAccidents Yasuhiro Matsui 1,* and Shoko Oikawa 2 Yasuhiro Matsui 1,* and Shoko Oikawa 2 1 National Traffic Safety and Environment Laboratory, 7-42-27 Jindaiji Higashi-machi, Chofu, 1 National Traffic Safety and Environment Laboratory, 7-42-27 Jindaiji Higashi-machi, Chofu, Tokyo 1820012, Japan Tokyo 1820012, Japan 2 Faculty of Systems Design, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino-city, Tokyo 1910065, 2 Faculty of Systems Design, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino-city, Tokyo 1910065, Japan; Japan; [email protected] [email protected] * Correspondence: [email protected]; Tel.: +81-422-41-3371 * Correspondence: [email protected]; Tel.: +81-422-41-3371 Received: 21 September 2018; Accepted: 20 October 2018; Published: 25 October 2018 Received: 21 September 2018; Accepted: 20 October 2018; Published: 25 October 2018 Abstract: Vehicle occupants were killed in 33% of all traffic accidents in Japan in 2017. Of the vehiclesAbstract: inVehicle vehicle occupants-to-vehicle were accidents killed in, 54% 33% ofwere all trafficimpacted accidents from in the Japan front. in 2017. In frontal Of the vehiclesimpact accidents,in vehicle-to-vehicle when the lap accidents, belt moves 54% away were from impacted the iliac fromcrests the of the front. pelvis In of frontal a vehicle impact occupant, accidents, the beltwhen moves the lapdirectly belt movesinto the away abdomen. from Here, the iliac we investigated crests of the causes pelvis of of a abdominal vehicle occupant,injuries to thevehicle belt occupantsmoves directly, because into the the abdomen abdomen. is Here,associated we investigated with the highest causes rates of abdominalof severe injury injuries and to fatality. vehicle Theoccupants, purpose because of this study the abdomen was to clarify is associated the correlation with the between highest downward rates of severe movement injury andof the fatality. seat andThe of purpose the lap ofbelt this away study from was the to iliac clarify crests the correlationof a human betweenoccupant downward of a car, in movementthe event of of a thefrontal seat impact.and of theWe lap investigated belt away fromthis phenomenon the iliac crests by of conducting a human occupant simulations of a using car, in an the anthropomorphic event of a frontal 50thimpact. percentile We investigated male (AM50 this) phenomenonhuman model by wearing conducting a three simulations-point seatbelt. using an We anthropomorphic set two deformable 50th spercentileeat conditions: male V (AM50)ertical movement human model and wearinglean forward a three-point movement. seatbelt. Our results We set revealed two deformable that the seatlap beltconditions: came off Vertical from both movement of the iliac and crests lean forwardduring lean movement. forward Ourmovement results but revealed only from that theone lap of beltthe iliaccame crests off from during both vertical of the iliac movement. crests during We concluded lean forward that movement abdominal but injuries only from can onebe caused of the iliac by downwardcrests during movement vertical movement. together with We concludedforward rotation that abdominal in the seat injuries during can vehicle be caused-to-vehicle by downward frontal impacts.movement together with forward rotation in the seat during vehicle-to-vehicle frontal impacts. KKeywords:eywords: humanhuman model; model; abdominal abdominal injury; injury; frontal frontal impact impact accidents; accidents; simulation simulation 1.1. Introduction Introduction VehicleVehicle occupants occupants were were kill killeded in in 33% 33% (1221) (1221) of of all all traffic traffic accidents accidents (3694) (3694) in in Japan Japan in in 2017 2017 [1] [1] ((FigureFigure 11).). Therefore, Therefore, countermeasures countermeasures to to reduce reduce fatal fatal traffic traffic accidents accidents are required. are required. In Japan, In Japan, when roadwhen-users road-users are killed are killedor injured or injured in traffic in traffic accidents, accidents, police police officers officers and medical and medical doctors doctors determine determine the mainthe main body body regions regions associated associated with with severe severe injuries injuries that that led led to to death. death. R Resultsesults of of these these investigations investigations revealreveal serious serious and and fatal fatal injury injury rates rates for for each each main main body body region, region, presented presented in in Table Table 11.. The abdominal regionregion is is associated withwith thethe highesthighest raterate of of severe severe injury injury and and fatality fatality of of vehicle vehicle occupants occupants (Table (Table1)[ 1)1]. [1].The The same same trend trend has has also also been been observed observed in Francein France [2]. [2]. Therefore, Therefore, in in this this study, study, we we focus focus on on causes causes of ofabdominal abdominal injuries injuries to to vehicle vehicle occupants. occupants. 2017年：状態別死亡者 Car Pedestrian 1221 1347 33% 36% 3694 Motor Bicycle cycle 480 448 Moped 13% 12% 184 5% FigureFigure 1 1.. DistributionDistribution of of車 traffic traffic自転車 fatalities fatalities原付 自動二輪 by by crash crash歩行者 type type in in Japan Japan in in 201 2017.7. Appl. Sci. 2018, 8, x; doi: FOR PEER REVIEW www.mdpi.com/journal/applsci Appl. Sci. 2018, 8, 2047; doi:10.3390/app8112047 www.mdpi.com/journal/applsci Appl. Sci. 2018, 8, 2047 2 of 13 Table 1. Severe injury and fatality rates for individual body regions of vehicle occupants involved in traffic accidents in Japan in 2017. Number Rate (%) Main Body Region (a) Minor Injured (b) Serious Injured (c) Fatality Serious Injury Fatality Rate Occupants Occupants Occupants Rate b/(a+b) c/(a+b+c) Head 9047 738 305 8 3 Face 3507 304 14 8 0 Neck 302,051 2325 67 1 0 Chest 12,348 2836 444 19 3 Abdomen 1558 511 147 25 7 Back 3009 141 3 4 0 Hip 22,329 937 36 4 0 Arms 8334 985 5 11 0 Legs 7259 1251 28 15 0 Total 369,442 10,028 1049 - - Fifty-four percent of vehicles struck in vehicle-to-vehicle accidents in Japan were impacted from the front [3]. A US accident investigation database of occupant injuries in the front passenger seat of impacted vehicles showed that 59% of abdominal injuries were directly caused by seatbelts [4]. Two detailed accident case studies revealed that lap belts caused serious abdominal injuries and residual deformation marks were left behind on seat surfaces, which suggests that the seat moved vertically during the frontal impact [4]. Some studies have attempted to evaluate the relationship between lap belt condition and abdominal injury. Zhu et al. performed simulations using a vehicle cabin model with a rigid-seat model to investigate injury risk, considering the abdomen, for the anthropomorphic 50th percentile male (AM50) and obese male models during frontal impact [5]. In addition, Steffan et al. investigated the relationship between lap belt loading and abdominal response using an AM50 dummy and post mortem human subjects (PMHSs), by employing a rigid seat during frontal impact to facilitate the design and development of seat belt tensioning systems [6]. However, only a few studies have focused on the movement of a seat during frontal impact. Kitamura et al. investigated two accidents in which drivers sustained abdominal injuries owing to car-to-car frontal impacts [7]. These authors indicated the possible cause of abdominal injuries may be due to deformation of the seat during impact. Matsui and Oikawa investigated the relationship between seat height vertical movement and lap belt upward movement, in which an anthropomorphic 50th percentile male Hybrid III dummy model (hereafter referred to as an AM50 Hybrid III model) was seated in a passenger seat model [8]. Results revealed that when the AM50 Hybrid III model moved 150 mm vertically downward, the lap belt exhibited significant upward movement from its initial position on the dummy’s waist. This phenomenon resulted in the abdomen being directly compressed, owing to tightening of the lap belt. In the upper body structure of a Hybrid III dummy, there is a space between the thoracic and waist part [9] because the dummy does not have internal organs. Currently, Toyota Motor Corporation and Toyota Central Research and Development Labs. Inc. have jointly developed a finite element model, the total human model for safety (THUMS) version four, which includes an internal organ finite element model [10]. It is possible that dynamic movement of a seatbelt on a Hybrid III dummy may be different from that of a seatbelt worn by a human, i.e., after a lap belt moves away from the iliac crests of the human pelvis it moves deeply into the abdomen. Thus, the purpose of this study is to clarify the correlation between different downward movement conditions of the seat and those of the lap belt from the iliac crests of a human occupant in the front passenger seat of a car in the event of a frontal impact. We investigate this phenomenon by conducting simulations using an AM50 human model. Figure2 shows a photograph of residual deformation of the front passenger car seat after a Japan new car assessment program (JNCAP) full frontal rigid barrier impact test, in which a Hybrid III dummy was seated in the passenger seat during the test. The frontal edge of the seat exhibits residual Appl. Sci. 2018, 8, x FOR PEER REVIEW 3 of 12 Appl. Sci. 2018, 8, x FOR PEER REVIEW 3 of 12 dummyAppl. Sci. 2018 was, 8 seated, 2047 in the passenger seat during the test. The frontal edge of the seat exhibits residual3 of 13 deformationdummy was seatedof 100 inmm, the whichpassenger suggests seat during the seat the movedtest. The downward frontal edge along of the with seat aexhibits small forwardresidual rodeformationtation. Therefore, ofof 100 100 mm, inmm, this which whichstudy, suggests suggestswe select the thetwo seat seat movedconditions: moved downward 150downward mm along vertical along with downward a with small a forward small movement forward rotation.