PSI - Issue 61

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Ahmet Çevik et al. / Procedia Structural Integrity 61 (2024) 291–299 Cevik et al. / Structural Integrity Procedia 00 (2019) 000 – 000

The schematic of the specimen geometry is given in Figure 1a. The length of the vertical arm (L VA ) and horizontal arm (L HA ) is 90 mm. The inner radius of the curved region (R i ), thickness (t) and the width (w) of the specimen are 8 mm, 5.04 mm and 25 mm, respectively. A hole is drilled in each arm of the specimen to be able to mount it to the test fixture, and the distance between the center of the hole and the end of the arms (given as L SH1 and L SH2 in Figure 1a) are 15 mm. The curved specimens have a stacking sequence of [(45/0) 7 /45/45/0/45] and 5 Harness Satin weave pattern. The microscopic views of this weave pattern and stacking sequence are shown in Figure 1b. This stacking sequence is chosen as representative of the stacking sequence currently used in commercial airplanes.

(a) (b) Fig. 1. (a) The schematic of fabric curved composite specimen, (b) micrographs showing the weave pattern of the fabric prepreg and stacking sequence of the specimens. 2.2. Test Fixture The curved composite laminates are subjected to axial load, shear load and bending moment in the industry. The main experimental problem is to mimic appropriate boundary conditions required to apply these loadings separately to the curved composite specimens. Pure shear loading case, where the vertical arm of the curved specimen is fixed while the horizontal arm is subjected to pure shear load, is among the most used in the literature and is considered in this paper. For accurate modeling with the finite element model of even the elastic behavior of the curved beam under shear loading, the boundary conditions in the experiments should be correctly specified. However, the comparison of load-displacement plots under shear loading is lacking in the literature. In order to validate the pure shear loading case, a model polycarbonate cut in the shape of a curved beam is used and loaded under fixtures that have been used in the literature in addition to revised fixture designs. The finite element model is generated for a curved beam subjected to pure shear load using the commercial finite element method package ABAQUS®. The load displacement curve obtained from the finite element analysis is taken as reference data for the design process of the experimental loading fixture. The specimens used in the experiment are manufactured from the polycarbonate (MAKROLON®) material. The geometry and boundary conditions for pure shear loading in the finite element model are shown in Figure 2a. In the FEA model, the vertical arm of the curved specimen is free to move in the x-direction, while it is fixed in the y-direction. Displacement loading is applied in the y-direction to the end of the horizontal upper arm using kinematic coupling to a reference point corresponding to the loading point the experiments. In the analysis, 4-noded two-dimensional plane stress elements (CPS4) are used, and Young’s modulus and Poisson’s ratio of polycarbonate material are taken as 2.4 GPa and 0.38, respectively. The load-displacement curve obtained from the finite element analysis is shown in Figure 2b.