# Effect of Seat Condition on Abdominal Injuries to Vehicle Occupants in Frontal Impact Accidents
## 2 Materials and Methods  
An AM50 THUMS ver.4 model (hereafter referred to as the AM50 human model) [10] was placed on a seat fixed to a vehicle cabin model (Figure 3). The AM50 human model is composed of finite elements for all body parts. The height and mass of the AM50 human model were 1.78 m and 74 kg respectively. The thorax and whole-body response of the AM50 human model seated in a vehicle impacted from the front were validated through a comparison with responses of post mortem human subjects (PMHSs) [10]. All simulations were performed using the LS-DYNA commercial finite element software [11]. The vehicle cabin model was fixed to the vehicle coordinate system. Normally, a seat belt is the only system that restrains the upper body of an occupant. The AM50 human model wore a three-point seatbelt. The vehicle cabin model and three-point seatbelt (model number 100112_V1.0) were developed by Livemore Software Technology Corporation (LSTC) [12]. In the National Highway Traffic Safety Administration (NHTSA) New Car Assessment Program (NCAP) test report, load limiters for drivers and front-seat passengers were identical at approximately 5 kN [13]. [PERSON] et al. reported that vehicle occupants with a 5 kN load limiter, without an airbag, could experience multiple rib fractures [14]. [PERSON] et al. suggested that a load limiter of 4 kN would provide reasonable safety when used in combination with an airbag [15]. In this study, the upper limit of the force limiter was regulated to 3.3 kN. We excluded the airbag from the current vehicle cabin model in order to investigate potential for abdominal injury under the most severe conditions, where there was a large movement of the hip and lower extremities. The seat-back and floor of the vehicle cabin model were rigid. Figure 3: Anthropomorphic 50 th percentile male total human model for safety ver.4 (AM50 human model) [10] seated in the vehicle cabin model [12]. Figure 2: Photograph of residual deformation of the front passenger seat in a car after a Japan new car assessment program (JNCAP) full frontal rigid barrier impact test. The vehicle cabin model used in our research is shown in Figure 4, together with springs representing seat and knee-panel characteristics. The seat was set to move downwards (z-axis) with an increase in applied forces from the thigh and breech. In this study, the center of the seat was moved downward by a maximum displacement of 150 mm, as previously obtained results indicated that this amount of vertical downward movement resulted in upward movement of the lap belt from its initial position at the waist of the AM50 Hybrid III model [8]. We set two seat movement conditions: (a) vertical movement and (b) lean forward movement. For vertical movement, we assigned one spring in the seat to represent vertical seat movement (Figure 4a). The seat moved vertically downwards according to force-displacement characteristics in one spring model of the seat, as shown in Figure 5a. For lean forward movement, we assigned two springs in the seat to reproduce forward rotation of the seat (Figure 4b). The seat moved downwards together with forward rotation according to force-displacement characteristics in the front spring and back spring models of the seat, as shown in Figure 5b. The knee panel was set to move in the forward direction (x-axis) with an increase in applied forces from the knee through the axial force of the thigh of the AM50 human model. Thus, the knee panel was arranged to move forward, as shown in Figure 6. The initial seat angle and seat-back angle were set to 16\({}^{\circ}\) and 62\({}^{\circ}\) respectively (Figure 4). Figure 4: Vehicle cabin model and modified spring model used in this study: (a) vertical seat movement and (b) lean forward seat movement. Figure 5: Force-displacement characteristics used in the spring models of the seats: (a) vertical seat movement and (b) lean forward seat movement.