Injury Risk Functions for the Midsized Male Wrist and Elbow as a Result of Behind Shield Blunt Trauma.

Ballistic shields protect users from a variety of threats, including projectiles. Shield back-face deformation (BFD) is the result of the shield deflecting or absorbing a projectile and deforming toward the user. Back-face deformation can result in localized blunt loading to the upper extremity, where the shield is supported by the user. Two vulnerable locations along the upper extremity were investigated-the wrist and elbow-on eight postmortem human subjects (PMHS) using a pneumatic impacting apparatus for investigating the fracture threshold as a result of behind shield blunt trauma (BSBT). Impacting parameters were established by subjecting an augmented WorldSID anthropomorphic test device (ATD) positioned behind a ballistic shield to ballistic impacts. These data were used to form the impact parameters applied to PMHS, where the wrist most frequently fractured at the distal radius and the elbow most frequently fractured at the radial head. The fracture threshold for the wrist was 5663±1386 N (mean±standard deviation), higher than the elbow at 4765±894 N (though not significantly, p = 0.15). The failure impact velocity for wrist impacts was 17.7±2.1 m/s, while for the elbow, the failure impact velocity was 19.5±0.9 m/s. An approximate 10% risk of fracture threshold was identified on the modified WorldSID ATD (no flesh analogue included) to inform future protective standards.

Injury Risk for the Hand and Forearm Under Loading Representative of Behind Shield Blunt Trauma.

Ballistic shields protect users from a variety of threats, including projectiles. Shield back-face deformation (BFD) is the result of the shield absorbing energy from a projectile and deforming towards the user. Back-face deformation can result in localized blunt loading to the upper extremity, where the shield is supported by the user and may cause injury through behind armour blunt trauma (BABT) mechanisms. Post-mortem human subject (PMHS) responses are critical to identify the injury risk in these high-rate scenarios and are used to quantify the injury tolerance. Two vulnerable locations along the upper extremity were investigated-the hand and forearm-using eight PMHS to identify the fracture threshold resulting from shield BABT loading conditions. Impacts delivered to the hand at 16.4 ± 0.8 m/s resulted in failure loads of 3818 ± 897 N, whilst the forearm impacts delivered at a similar velocity of 16.9 ± 1.9 m/s had lower failure loads at 3011 ± 656 N. The corresponding 10% risk of hand and forearm fractures (as measured on a modified WorldSID Anthropomorphic Test Device) were identified as 11.0 kN and 8.1 kN, respectively, which should be used when evaluating future designs of composite ballistic shields. This study is the first known investigation of the upper extremity to this high loading rate scenario and provides the foundation for future biomechanical research in the area of behind shield blunt trauma.

Behind Shield Blunt Trauma: Characterizing the Back-Face Deformation of Shields with a Focus on Upper Limb Loading.

Shield back-face deformation (BFD) is the result of composite ballistic shields deflecting or absorbing a projectile's energy and deforming towards the user. BFD can result in localized loading to the upper extremity, where the shield is secured to the user. An augmented anthropomorphic test device upper extremity was used to quantify this applied load. Four locations along the upper extremity were tested-the hand, wrist, forearm, and elbow-for investigating differing boundary conditions and their effect on resultant load. Varying stand-off distances, the distance between the back of the shield and the force sensor, were investigated. Digital image correlation was also conducted to measure the dynamic displacement of the shield. The mean peak back-face velocity of the shield was 208.4 ± 38.8 m/s, while the average affected area was 1505 ± 158.3 mm2. Impulse was not significantly affected by anatomical location for the same stand-off distance; however, as stand-off distance decreased, the measured force significantly increased (p < 0.05). Notably, impact duration did not differ significantly for any of the impact scenarios. This is the first step in developing injury criteria for this region resulting from behind shield blunt trauma, and these data will be used for developing injury thresholds in post-mortem human surrogates.