Termoplastik levhaların darbe davranışının nümerik olarak incelenmesi

In this thesis, dynamic response of exposure to a certain velocity impact of polycarbonate and polymethylemethacrylate plates were investigated depending on increasing thickness of plates and impacts at locations center of the plate, 20 and 40 mm were carried out by a spherical steel projectile using finite element and compare to each target plate behavior. First of all, it was investigated that impact events for polycarbonate and polymethylemethacrylate armor plates. It was conducted that explicit analyses later in this way. Analysis methods for impact problem are searched Lagrangian formulation is chosen for this study. Also, von Mises criteria is used for pc plates in this thesis. PMMA was assumed to obey the Drucker – Prager material model in the present study. Polycarbonate and PMMA materials are shown elastic- plastic behavior. Further, these polymer types are also shown viscoelastic behavior. However, it is realized that at extremely high strain rates, the strength of the material does not increase indefinitely. For these reasons, a reasonable choice was made to preserve the measured ductility while neglecting viscous effects at very high strain rates. That is, it was ignored viscoelastic behavior in this thesis. Thus, polymers like pc and PMMA are only modeled with elasic-plastic properties when it is used analysis program which Abaqus, Autodyn etc. Three different thickness of plate and three different impact locations are taken consideration in this study. Plate thickness was selected as 1.4, 1.9 and 2.4 mm. In addition, the plates were modeled using 90×90 mm. Thin square polycarbonate and PMMA plates was subjected to a spherical projectile impact at a velocity of 140 m/s. Subsequent impacts were made at plate center, 20 and 40 mm of the plate depending on changing plate thickness. The target plate outer edge was constrained for all degrees of freedom. A spherical steel projectile of 6.98 mm diameter was launched against the square plate and also the mass of projectile was calculated as 0.00139 kg. According to this information, kinetic energy of the projectile was computed as 13.693 joule. The distance between target plate and projectile doesn't have any effect on the results, because gravitational force is neglected. When setting the material properties, "Bilinear Kinematic Hardening" model is used from the Ansys Library. Since polycarbonate is a ductile material, it is selected that plastic strain failure criteria for pc. PMMA is shown brittle fracture and ductile deformation at room temperature. Therefore, two failure criteria are combined which tensile failure and ductile failure during numerical modeling. Plastic strain, von Mises stresses, maximum shear stresses, deformation of plate and energy absorption histories were recorded in this study. As increasing plate thickness, energy absorption quantity is increased as predicted for both polycarbonate and PMMA plates. At 1.9 and 2.4 mm thick, there was no fragmentation for pc plates. However, it was observed that perforated event at all plate thickness for PMMA. It is expected that this phenomenon because PMMA has less impact resistance than pc material. Also, all energy absorption values are seen to be higher for pc than PMMA material at all plate thickness. That is, kinetic energy was not completely transformed into internal energy and therefore it was occurred that perforated event during impact loading for PMMA target plate. Furthermore, maximum plastic strain values were decreased while thickness of plate was increased. This situation was expected as well because resistance of plate is increased when the plate thickness is higher. On the other hand, it is occurred that higher stress values at close to fixed edge than other impact locations for both target material since square plate edges are constraint, as expected. It is observed that plastic deformation and fragmentation events with different plate thickness and impact points in this thesis. Furthermore, it was conducted that a validation analysis before thesis study. It can be said that this verification study is similar with thesis thesis. It was used that a circular polycarbonate plate. Once it was accomplished the validation analysis, it was implemented thesis study.