Perpustakaan Digital ITB

The aft fuselage structure is a critical part of the aircraft fuselage that functions to transfer loads from the horizontal tail plane (HTP) and the vertical tail plane (VTP) to the main fuselage structure. The combined loads from these two components generate compressive and shear stress that may potentially trigger buckling failure. This study aims to explain the application of the Finite Element Method (FEM) in the buckling analysis of the aft fuselage structure, to observe the buckling phenomena that occur, to assess the structural capability in withstanding buckling failure, and to identify the potential for structural weight reduction. The structural model was developed using Abaqus by simplifying the components into shell elements, replacing bolts and rivets with connector features, and defining the loading cases based on previous studies and CASR 23 regulations. The analyses were conducted sequentially through static analysis, Linear Buckling Analysis (LBA), and Non-Linear Buckling Analysis (NLBA) using the arc-length method in the Static/Riks step. The loading conditions consisted of several load cases representing the effects of HTP, VTP, and their combination under the limit load condition of 3.6n/?1.44n. Prior to the main analyses, a mesh convergence test was performed to determine a representative mesh size for critical components, particularly in the angle region at Frame_8, which was identified as the location of maximum stress. The static analysis results show that all maximum stresses remain below the material yield strength of 345 MPa, with the highest stress of 216.9 MPa occurring under the combined 3.6n HTP + VTP load case. Therefore, the structure is considered safe against static failure. The LBA results indicate that several load cases have critical buckling loads below the reference load, necessitating further investigation using NLBA. In the NLBA, the effects of geometric nonlinearity and initial imperfections were introduced based on the first buckling mode obtained from LBA. The imperfection sensitivity study shows that increasing the imperfection scaling factor leads to a decrease in the critical load. A scaling factor of 1% was selected as the most representative value because it produces results close to those of the LBA while still being able to trigger stable post-buckling behavior. The NLBA results demonstrate that the structure is able to exceed the reference load and reach an ultimate collapse load of approximately 29.5 kN for pure HTP load and 29 kN for HTP load coupled with VTP load, indicating that although local instability occurs, the structure remains globally capable of sustaining additional loads. The snap-through buckling phenomenon is also observed as a transition in the buckling shape due to a change in the equilibrium path after the initial instability. The stress distribution evaluation shows that the front frames and the back-bracket assembly experience relatively low stress under all load cases, indicating potential for weight reduction without significantly compromising structural safety. Overall, this study confirms that the FEM-based approach is capable of accurately representing the buckling and post-buckling behavior of the aft fuselage structure and demonstrates that the analyzed structure remains safe against both static and buckling failures under the applied loading conditions, with opportunities for weight optimization in specific regions.