CRACK INFLUENCE ON AEROELASTIC INSTABILITY CHARACTERISTIC OF A UNIDIRECTIONAL COMPOSITE PLATE

• Main Author: Pangihutan Simbolon, Daniel
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/84960
• Institution: Institut Teknologi Bandung

In this work, evaluation on the aeroelastic instability characteristic of a composite plate is conducted. A unidirectional composite with 50% volume fraction is investigated. On the undamaged plate, modal analysis and aeroelastic evaluation are performed to determine the benchmark for the damaged configurations. Static crack is introduced as the damage to the plate. In the present case, no crack propagation is observed; however, various crack lengths and locations are studied. The crack lengths are varied from 20% to 80% of the chord length, and the crack locations are varied on the 20% to 80% of the spanwise length. Computational analyses are done by means of Finite Element Method (FEM) to develop the structural model, and Doublet Lattice Method (DLM) to calculate the aerodynamic loads of aeroelastic evaluation. Modal analysis is conducted to obtain the first few mode shapes, in this case six modes are obtained, i.e., 3 bending modes, 2 torsion modes and 1 swaying mode. The natural frequencies for the undamaged one ranged from around 6 Hz to 320 Hz. By varying the crack location, it is found that the natural frequencies are almost consistent with the undamaged one’s. In contrast, as the crack length becomes longer, up to 80% of the chord length, the natural frequencies of the 1st and 2nd torsion modes also the 1st swaying mode decreases. Meanwhile, the bending modes’ natural frequencies remain consistent with the change in the crack length. Thus, the order of the modes change with the size of the crack, i.e., the 1st swaying mode could appear earlier than the 1st torsion or the 3rd bending mode. Furthermore, with the decrement of the 1st torsion mode’s frequency, both the 2nd bending and the 1st torsion frequencies become closer as the crack length increases. This phenomenon aligned with the results of the aeroelastic analyses. The critical instability boundaries, i.e., flutter speeds, are insignificantly changed with the crack location. However, as the crack size becomes longer, the critical flutter speed decreases, reduced by almost 40% when the crack length is 80% chord. Therefore, this study emphasizes the effect of crack on the aeroelastic composite plate.