عنوان مقاله [English]
In this paper, the performance of the rigid polyurethane (PU) foams used in composite armors to mitigate the impact pressure and energy of a projectile has been studied numerically through finite element methods. The armors of this study comprise two layers, namely, a metal layer and a PU-foam layer. A sophisticated FE-Model was developed to simulate the dynamic performance of the composite armor under the impact of a projectile using the software package ANSYS-Autodyn. The FE-Model was verified with the results of a previous experimental study in which a projectile impacted a certain two-layer armor comprising a steel front face that was attached on a layer of PU-foam. The main objectives of this research study are to study the effects of design parameters such as the thickness and density of the PU-foam and the impact velocity of the projectile (representing the strain rate) on the performance of a composite armor. To achieve the research objectives, PU-foams of different densities of
80, 160, 288 and 320 kg/m3, at six different thicknesses of 1.25, 2.5, 5, 7.5, 10 and 12.5 mm were modeled. Additionally, the armors were subjected to projectiles with different impact velocities of 400, 450, 509 and 550 m/s. Results of the FE-Analysis runs conducted in this paper indicate that the response mitigation of a composite armor is significantly affected by both the density and thickness of its PU-foam layer. For a given thickness of foam layer, it was observed from the FE-analysis runs that the optimum value for the foam-density that results in the maximum response mitigation is approximately 150 kg/m3. The impact pressure that is dissipated by a composite armor is significantly decreased as the foam-density diverts from its optimal value. For a given foam-density, it was found that the response mitigation of the armor was improved with an increase in the thickness of the foam layer. For the composite armors investigated in this study, the rate of improvement in the response mitigation with increased foam-layer thickness was found to be very slow for the thickness values beyond 5 mm. The impact velocity of the projectile, as an indicator of strain rate, was also investigated in this paper. The dynamic response of foam layers of relatively lower thickness and density was found to be more sensitive to the variations of strain rate.