ICF13A

13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- (a) 0.25 ms (b) 1 ms (c) 4 ms (d) 0.25 ms (e) 1 ms (f) 4 ms Figure 6. Comparison of experimental (a-c, physical model MDF-1) and computational (d-f) results of projectile impact on MDF (d-f: coloured by plastic strain, red=0.5%) 5. Discussion and Conclusions The study has shown that projectile impact causes fragmentation of material at the impact site, whilst transferring momentum to fragmented particles. The particles travel along the path of least resistance, leading to partial material movement in the opposite direction of the projectile motion, which is known as backspatter. The amount of backspatter depends on the strain limit of each material and the closure time of the initial projectile hole. SPH was shown to be an ideal numerical method for handling the high impact fragmenting nature of the materials, and the predictions compared well to the experimental data of medium density fiberboard (MDF). Results were also noted to be highly dependent on the constitutive laws. Specifically, the MDF impact fracture results suggest that energy from the projectile causes material at the impact site to fail in a brittle manner with fracture into small particles. Momentum is transferred from the projectile to the particles with the majority of fragments travelling in the original projectile direction. However, for a proportion of the fragments the entrance site acts as the path of least resistance causing material movement axially backwards. This is similar to the tail-splashing mechanism that is postulated as a mechanism of backspatter from a cranial gunshot [9, 13, 14]. The other potential skull simulant, polycarbonate, has a high failure strain and good impact resistance, compared to a real skull, leading to a lack of backspatter and no significant material fracture. Bullet impact in human bones is known to leave a clear hole and shows radial facture [35] suggesting that polycarbonate is not a suitable simulant for human bone or skull. This is the first study to use SPH to study backspatter in ballistic impacts. The SPH model

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