**3. Occupant injury analysis for the seating subject to PDOF 360 degree**

An occupant could be injured at a vehicle crash when the external impact forces on his/her body regions exceed the tolerances. The force magnitude related to the vehicle crash severity and the principal direction of force (PDOF) affect the body region


#### **Table 2.**

*The human body region injury risk functions for the 50th%ile male occupant.*

injury patterns and severities. The PDOF could vary for an occupant on a given seating position with different crash scenarios (frontal, oblique, side, or rear impacts to the vehicle), or vary with different seating orientations under one vehicle crash. In the real-world, there are more occurrences of vehicle frontal crashes than other impacts.

Kitagawa et al. [81] analyzed occupant kinematics in simulated frontal collisions with three speeds assumed (56 km/h, 40 km/h and 30 km/h) using the THUMS Version 4 AM50 occupant human model representing the 50th%ile male occupant seated varying seating orientations with every 45-degree increment from 0 degree (forward-facing) to �180 degrees (rear-facing) with respect to the impact direction, and with three angles of the seatback from 24 degrees to 36 degrees for two seating positions. The results showed that the occupant had the largest torso lateral excursion (up to 700 mm at a 56 km/h frontal crash) at �45 degrees and � 90 degrees orientated (side-facing) seating positions.

In this study, we focused on analysis of occupant injury patterns and risks for a mid-size male occupant on a seat with the orientations varying to the PDOF 360 degree under a moderate frontal crash pulse.

#### **3.1 Methods**

We simulated a belted mid-size male occupant on a seat in a conceptual automated vehicle subject to the 40 km/h (25 mph) frontal crash pulse from Shaw PMHS golden test [70] as shown in **Figure 2** (left graph). The 3-point seatbelt restraint was with pretensioner and 3.5 kN load limiter. **Figure 2** (right graph) shows the simulation cases with the GHBMC M50-O v4.5 model representing the male occupant. For each

*Accidental Injury Analysis and Protection for Automated Vehicles DOI: http://dx.doi.org/10.5772/intechopen.105155*

**Figure 2.**

*The 40 kph (25mph) frontal crash pulse (left graph) and the 50th%ile occupant seating positions considered in this study (right graph).*

simulation case, the seat was rotated with every 30-degree increment from 0 degree to 360 degrees respect to the frontal impact. It is noted that each case number is named same as the clock number.

The models of the seat and seatbelt were used the same as what have been validated from the NHTSA's Advanced Adaptive Restraint Program (AARP) [82]. For the seat model, additional validation was made for the rotational stiffness of the seat back against the published body block test data [83], in which the seat back forwardrearward rotation was allowed within +20 degrees.

From the simulations for the twelve cases with the defined different seating orientations, analyses were made on the occupant kinematics, forces on the occupant, and injury patterns and severities for each case.

### **3.2 Results**

#### *3.2.1 Occupant kinematics and external forces*

Respect to the impact direction, the seating orientations could be classified as the frontal/oblique facing (within 0— 60 degree orientations or 10, 11, 12, 01, 02 O'clock (OC)), side facing (within 90— 120 or 03, 04, 08, 09 OC), and rearfacing (within 120–180 degrees or 05, 06, 07 OC). **Figure 3** shows the maximum human body movement of each case varying with seat orientations. Significant kinematics differences of the human occupant among the seat facing classifications were observed.

**Figure 4** (left graph) shows the time-history traces of the head, T1, and pelvis of the frontal/oblique facing seated occupant during the crash. **Figure 4** (right graph) depicts the maximum external forces on the occupant from the seatbelt and the seat back. As the occupant faced more obliquely, the Head/T1 displacements increased while the pelvis displacement sightly decreased. The seatbelt routing obviously affected the kinematics. It was observed that the occupant at 11 & 10 OC had larger displacement than 01 & 02 OC. The seatbelt shoulder forces were all above 5 KN, while the seat back force to the occupant increased as the occupant had more side facing.

**Figure 5** (left graph) shows the time-history traces of the head, T1, and pelvis of the side facing seated occupant during the crash. **Figure 5** (right graph) depicts the external forces on the occupant from the seatbelt and the seat back. The occupant at

**Figure 3.** *The seat facing classifications and the 50th%ile occupant kinematics under the 40 km/h frontal crash pulse.*

**Figure 4.**

*The 50th%ile occupant kinematics (left graph) and maximum forces on the occupant (right graph) at the frontal/ oblique facing seating positions under the 40 km/h frontal crash pulse.*

03 & 04 OC showed twisting head while the torso was restrained by the seat belt and the seat back. The occupant seating at 09 & 08 OC showed shoulder belt slip-off and significantly larger displacement than 03 & 04 OC. In these side facing seat positions, the seatbelt restraint forces were reduced to 2–3 KN, while the seat back forces on the occupant increased to 7.1–8.7 KN.

**Figure 6** (left graph) shows the time-history traces of the head, T1, and pelvis of the rear facing seated occupant during the crash. **Figure 6** (right graph) depicts the maximum seatbelt shoulder forces and the seat back forces on the occupant. No significant difference between 05 OC and far-side 07 OC was shown. In this seat facing group, much larger head and T1 displacement occurred compared to the other two groups. The restraint forces from the seat back increased significantly to 15.5–22.7 KN, while the seatbelt forces were below 1 KN. Hyperextension of the neck was observed.

*Accidental Injury Analysis and Protection for Automated Vehicles DOI: http://dx.doi.org/10.5772/intechopen.105155*

#### **Figure 5.**

*The 50th%ile occupant kinematics (left graph) and maximum forces on the occupant (right graph) at the side facing seating positions under the 40 km/h frontal crash pulse.*

#### **Figure 6.**

*The 50th%ile occupant kinematics (left graph) and maximum forces on the occupant (right graph) at the rear facing seating positions under the 40 km/h frontal crash pulse.*

#### *3.2.2 Occupant injury patterns*

For each case, the body injury measures, HIC, BrIC, Chest Deflection and Femur Load, were calculated. **Figure 7** plots these normalized injury measures varying with the seating orientations. From the HIC and BrIC plots, we see that the more rearward the occupant faced, the larger HIC and BrIC had. The occupant at the front/oblique facing (12–02 OC) showed largest anterior-posterior chest deflection, followed by pure rear facing (06 OC) due to the restraints from the seatbelt or seat back. The occupant at the side facing (04 & 08 OC) showed largest lateral chest deflection, followed by front/oblique facing (11 & 10 OC) because the torso moved laterally to the seat and contacted the seat side structure.

#### *3.2.3 Discussion*

**Figures 3**–**6** show that the occupant had the largest torso excursion laterally in the 90 degrees (or 09 OC side-facing) orientated seating position. The maximum Y-displacement of the T1 kinematics target reached 751 mm. This trend was same as what Kitagawa, Y., et al. found in their study similar to this setup [81].

#### **Figure 7.**

*The 50th%ile occupant body region injury measures at all the seating positions under the 40 km/h frontal crash pulse.*

**Figures 3**–**6** show that the shoulder seatbelt had the largest restraint force on the occupant at the 12 OC seating position under the frontal loading, while the restraint force on the occupant from the seat back reached the maximum at the 06 OC seating position.

From **Figure 7**, the worst cases were identified as

