Characterising the Back-face Deformation of Ballistic Shields using an Augmented WorldSID Upper Limb

Shield back-face deformation (BFD) is the result of composite ballistic shields deflecting or absorbing a projectile and deforming towards the user. Back-face deformation can result in localised loading to the upper extremity, where the shield is supported. An anthropomorphic test device upper extremity was modified to quantify applied load due to shield BFD. Four vulnerable locations along the upper extremity were investigated - the hand, wrist, forearm, and elbow - for examining differing boundary conditions and their effect on resultant load. Fifteen shots were conducted on composite shields according to Level III ballistic test standards, with an average bullet velocity of 840.7 ± 5.0 m/s. The mean peak back-face velocity of the shield was 208.9 ± 44.6 m/s. Results showed minimal effect of anatomical location, with only the wrist forces exceeding the elbow (p = 0.004), suggesting a more simplified version of testing may be used for future safety tests. The average duration for all impacts was 0.569 ± 0.233 ms, with no significant differences among locations. This is the first step in developing injury criteria for the upper extremity resulting from behind shield blunt trauma and these data will be used for developing injury thresholds in post-mortem human surrogates.