CATALIN PIRVU, ANDREA ELENA MUSTEATA, GEORGE GHIOCEL OJOC, SIMONA SANDU, LORENA DELEANU A MESO LEVEL FE MODEL FOR THE IMPACT BULLET - YARN This paper presents a study based on simulating the impact between a yarn (or a single fiber with greater dimensions) and a bullet, the impact velocity being 400 m/s. The characteristics of the involved materials are taken from literature. The yarn is considered isotrope, but the values of the characteristics are close to those of aramid fibers and cooper and lead alloys used for manufacturing the bullets. Analysing the yarn failure caused by a bullet, this FE model allows for identfying the stages in the failure process. First, the yarn is pushed by the bullet and the local elongation of the yarn is tacking place. The yarn rupture occurs in the “strangled” zones, caused by the stretch of the yarn directly supporting the impact. The breaking of the yarn in the thinned zone (more pronounced asymmetric breaking) and it is visible that the yarn elastic recoil starts next the bullet. The friction between the yarn and the bullet is only on the conical surface of the bullet in the tapered zone of the bullet. The yarn is detaching from the bullet (the contact zones between the bullet and the yarn in polymeric matrix become smaller, justifying a neglectable influence of the thermal effect). The yarn has no more contact with the bullet. This step is in the favor of the assumption that, in the actual multi-yarn impact, the other layers of yarns maintain the bullet and the first yarns in contact and this is why bunch of fibers (fragments of the failed yarns) are pressed against the bullet and remain on it. The simulation results were qualitatively validated by SEM investigations of fiber failure under the same conditions as the model.
Keywords: FE model, ballistic impact, polymeric yarn