Özet:
This thesis study aims to maximize the bending strength of a sandwich composite plate with an egg-crate shaped core under three-point bending loading. The material is chosen as epoxy-reinforced with non-crimp E-glass fabric and the layup configuration is quasi-isotropic for both core and face sheets. The mechanical response of the composite material is determined by conducting tension tests on specimens with quasi-isotropic [0/45/-45/90]s, cross-ply [0/90]2s, and angle-ply symmetric [45/-45]s layup sequences. Acoustic emission (AE) monitoring is used to detect the damage events, identify the damage mechanisms, and ascertain the load levels at which different laminae fail. By making use of a progressive failure model and the tension test data, the mechanical properties of a ply are determined. A finite element model is developed in ABAQUS environment to simulate the behavior of the composite sandwich plate under three-point bending. The first-ply failure load level is determined based on Tsai-Hill failure criterion using the secant algorithm. The model is validated by comparing its predictions with the results obtained by three-point bending tests. A two-variable shape optimization study is performed using Nelder-Mead method for the core structure to maximize the overall bending strength of the composite sandwich plate. The optimum core structure is manufactured by using a 3D-printed polylactic acid (PLA) mold. The face sheets and the core structure are manufactured using vacuum infusion process (VIP). The comparison between the test results and the finite element model shows that the finite element model sufficiently predicts the first-ply failure load level and the failure region.
