▪ Examined the concepts of linear & nonlinear buckling behaviours of stiffened plates (shell structures).▪ Firstly, conventional stiffened plates (riveted stiffened plates) were modelled and analysed by Ansys Static Structural tool.▪ Integrally stiffened plates with lower weight and higher ultimate buckling load were designed by optimizing the height, thickness and number of stiffeners.▪ As a result of the project, when compared with conventional stifened plates, 15.2% weight reduction and 27.7% increase in ultimate buckling load were obtained for integrally stiffened plateproducable by NC Machines.
In Ansys, large deflection module can be enabled to activate geometrical nonlinearity. Nonlinear material properties can be added to the engineering data to activate material nonlinearity. Besides, contact nonlinearity is automatically activated when a nonlinear contact type is used . In our study First, geometric nonlinearity which is included due to the plastic behavior of the material, secondly due to the friction of the connection status, and thirdly, the activation of the large deflection option. In the riveted stiffened plate analysis, contact nonlinearity occurs due to the frictional contact. In the integrated panel, the connection status is bonded since there is no non-linearity. There are only two non-linearities due to material and geometry.
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The definition of the material property is very crucial for materials not to behave as ideally elastic such as aluminium alloys. Aluminium 2024 T3 was used for integrally stiffened plate validation analysis. Aluminium 2014A-T6 was used for riveted stiffened plate validation analysis and other analyses. Therefore, the addition of nonlinear behaviour is important while defining the material properties in Ansys. Multilinear Isotropic Hardening module provides to determine the stress/strain behaviour to Ansys. The RambergOsgood formulation was used to obtain the nonlinear behaviour of aluminium alloy and stress/strain graph shown in figure 4. : True Stress : True Strain E: Young's Modulus = 68000 N/mm2 y: Yield Stress = 340 N/mm2 v: Poisson's ratio = 0.33 fn = 296 N/mm2 m = 17
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Nonlinear buckling analysis was performed using the static structural module of Ansys. In order to confirm the accuracy of the analysis method used, some works on riveted stiffened panel and integrally stiffened panel in the literature were examined.
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How the method, modeled in ANSYS, applied is shown in Fig.6. Structures are modeled in SolidWorks. While using the same method for both analyzes, there are differences in the modeling of rivets. The main differences are the use of the spot weld tool in ANSYS and the area of contact is in different connection situations. Another difference is that the boundary conditions are varying. Boundary conditions are proceeded by selecting the nodes of the edges. According to Wang ., in the riveted model, both (lower and upper) sides are fixed completely except for the positive axial in-plane direction and displacement is given in that direction, and this method was applied in the study. In the integrated model analyzed in the work of A. Murphy et.al. the clamped boundary conditions were applied . The reason for the analysis to be carried out based on displacement is to see the ultimate load of the model in the load-displacement graph. The non-linear analysis was carried out in order to r
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