Effects of Occupant Size, Military Gear, Seatbelt Type, and Advanced Seatbelt Features on Occupant Kinematics in Tactical Vehicles during Frontal Crashes

The objective of this study is to understand the occupant kinematics and injury risks in a light tactical vehicle under frontal crash conditions using a combination of physical tests and computer simulations. A total of 20 sled tests were conducted in a representative environment to understand occupant kinematics, and quantify the effects from occupant body size (5/50/95), military gear (helmet/vest/varying gear configurations), seatbelt type (5point/3point), and advanced seatbelt features (pre-tensioner/load limiter) on occupant kinematics and injury risks in frontal crashes. These tests have been used to validate a set of finite element (FE) models of occupants, gear, and restraints. Kinematics exhibited often included submarining due to the lack of knee bolster and the added weight from the military gear. Body size, seatbelt type, and advanced belt features also showed significant effects on occupant kinematics. INTRODUCTION Advanced restraint technologies, such as seatbelt pretensioners, load limiters, and airbags, have the potential to provide improved occupant protection in crashes, but they are currently not utilized in military vehicles. Optimally implementing these technologies requires a better understanding of the occupant kinematics and injury risks in crash scenarios with military vehicles. The solutions are not necessarily the same as those used in passenger vehicles because of differences in crash involvement, occupant characteristics, vehicle compartment geometry, and occupant seating posture. Military gear may also affect restraint system interaction and injury risk. Experimental data and computational models for quantifying occupant impact responses and injury risks in military vehicles are largely lacking. The limited research available regarding the influence of personal protection equipment is mainly focused on lower extremity protection in landmine blasts (Harris et al. 1999) and head protection in blast-wave situations (Grujicic et al. 2011). Therefore, the impact of military gear on whole body injury during frontal impacts is entirely unknown. Additionally, although the influence of advanced restraint systems on civilian occupant kinematics and injury outcomes has been extensively studied (Forman et al. 2009; Hu et al. 2015; Newberry et al. 2006), the influence of military gear on seatbelt interactions is limited. Therefore, the objective of this study is to understand the occupant kinematics and injury risks in a representative light tactical vehicle environment under frontal crash conditions using a combination of physical tests and computer simulations. METHODS An overview of the methods being used during the entire study is shown in Figure 1, which include two series of sled tests, computational model development and validation, baseline full vehicle crash test, parametric simulations, design optimizations, and final full vehicle crash test. Since this is an on-going project, in this paper we are only presenting the results for sled tests without airbag use, and model development and validation against those sled tests. Proceedings of the 2015 Ground Vehicle Systems Engineering and Technology Symposium (GVSETS) Effects of occupant size, military gear, seatbelt type, and advanced seatbelt features on occupant kinematics in tactical vehicles during frontal crashes, Hu, et al. Page 2 of 8 UNCLASSIFIED: Distribution Statement A. Approved for public release. Figure 1: Method overview for the entire project Sled Tests A total of twenty frontal-impact sled tests were conducted using a custom-built sled buck which was constructed from 3D scans of a Hummer H1 vehicle (Figure 2). The buck was reconfigurable to represent both the driver and passenger compartments. All the tests were performed in a frontal crash configuration with a 30 mph delta-V and a peak acceleration of 25 g (Figure 2). Figure 2: 3D scan of a Hummer H1 (top), custom-built frontal impact test buck (middle), and sled crash pulse (bottom). The tests in this study used the Hybrid III 5 percentile female, 50 percentile male, and 95 percentile male anthropomorphic test devices (ATDs). All ATDs were outfitted with standard issue military combat boots and Advanced Combat Helmet (ACH) for every test. Additional tests were conducted with one of three additional military gear configurations (Figure 3) – Improved Outer Tactical Vest (IOTV) only, IOTV and Squad Automatic Weapon (SAW) Gunner set with a Tactical Assault Panel (TAP), and IOTV and Rifleman set with TAP. ATDs with the SAW Gunner and Rifleman gear sets were tested in the passenger configuration, while ATDs with helmet only and IOTV only were tested in the driver configuration. Two types of seatbelts, 3-point and 5-point seatbelts, with and without pretensioner(s) and load limiter(s), were also used. Pre-tensioners were used on the shoulder and lap belts, and were set to fire at 12ms. In tests using load limiters, a 4.9 kN load limiter was used on the shoulder of the 3-point belt, and 2x2.7 kN load limiters were used on the shoulders of the 5-point belt. Two tests used an Airbelt (inflatable shoulder belt and regular lap belt) in combination with a single pretensioner on the lap belt and one 4.9 shoulder belt load limiter. A complete matrix of the test series is shown in Table 1. Figure 3: Military gear configurations Each ATD was positioned based on UMTRI’s seated solder posture recommendations (Reed and Ebert 2013), which was a volunteer study. The ATD posture was verified using a FaroArm digitizer. Head, neck, chest, and lower-extremity injury measurements from the ATDs, as well as the belt loads, were collected in each test. Multiple high-speed video cameras were also used in each test to record the kinematics of the ATDs. Proceedings of the 2015 Ground Vehicle Systems Engineering and Technology Symposium (GVSETS) Effects of occupant size, military gear, seatbelt type, and advanced seatbelt features on occupant kinematics in tactical vehicles during frontal crashes, Hu, et al. Page 3 of 8 UNCLASSIFIED: Distribution Statement A. Approved for public release. Table 1: Sled test matrix. PT: Pre-tensioner, LL: Load limiter Test ID Side ATD Size IOTV Gear Seat belt Type PT+LL TD1403 Driver 50th N N 5-pt N TD1404 Driver 50th Y N 5-pt N TD1405 Driver 50th N N 3-pt N TD1406 Driver 50th Y N 3-pt N TD1407 Passenger 50th Y SAW Gunner 5-pt N TD1408 Passenger 50th Y SAW Gunner 3-pt N TD1409 Passenger 50th Y SAW Gunner 5-pt Y TD1410 Passenger 50th Y SAW Gunner 3-pt Y TD1411 Passenger 95th Y SAW Gunner 3-pt Y TD1412 Passenger 95th Y SAW Gunner 5-pt Y TD1413 Passenger 95th Y SAW Gunner 3-pt N TD1414 Passenger 95th Y SAW Gunner 5-pt N TD1415 Driver 5th Y N 5-pt N TD1416 Driver 5th Y N 3-pt N TD1417 Driver 50th Y N 3-pt Y TD1418 Driver 50th Y N 5-pt Y TD1419 Passenger 50th Y Rifleman 5-pt Y TD1420 Passenger 50th Y SAW Gunner 3-pt Airbelt Y TD1421 Passenger 50th Y Rifleman 3-pt Y TD1422 Driver 50th Y N 3-pt Airbelt Y The injury outcomes for each test were determined using each respective ATD’s Injury Assessment Reference Values (IARVs) as shown in Table 2. The injury measures examined in the present study include the head injury criterion (HIC), neck tension (NeckT), neck compression (NeckC), neck injury criteria (Nij), chest acceleration (ChestG), chest deflection (ChestC), and left and right femur force (LFF, RFF). The HIC is a measure of the likelihood of head injury resulting from an impact, and is defined as HIC15 = max [ 1 t2 − t1 ∫ a(t)dt t2 t1 ] 2.5 (t2 − t1) [1] where a(t) is head acceleration as a function of time, and t1 and t2 represent a 15-ms time interval over the acceleration pulse. The Nij measures the likelihood of neck injury using measured neck forces and moments normalized to critical injury tolerance levels determined from experimental testing. Nij is defined as Nij = Fz Fint + My Mint [2] where Fz is the axial load on the neck, My is the flexion/extension bending moment of the neck, and Fint and Mint are the corresponding critical intercept values of load and moment, respectively, used for normalization. Nij is computed at all time instances, and the maximum value from all combination of loading modes (tension, compression, flexion, extension) is reported. In this manuscript, the results for each test are reported as a percentage of the ATD’s respective IARVs. Table 2: IARVs (Mertz et al. 2003). Body Region Injury Measure 95M ATD 50M ATD 5F ATD Head HIC-15 700 700 700 Neck Nij Critical Intercept Values Ten and Comp (N) Flexion (Nm) Extension (Nm) 1.00