Component-wise Analysis of Reinforced Thin-walled Metallic and Composite Structures

Reinforced structures are thin structures reinforced using additional components, which are joined using different technologies, milling, riveting or welding. The technological process used to realize a reinforced structure makes it possible to have structural continuity between elements on which it is realized, such as the plate, stringers, and ribs. In fact, when a reinforced structure is realized using a milling machine, the stringer derives from the same work-piece and inevitably the continuity between plate and stringers is guaranteed. When the classical joints, like welding and rivets, are used the congruence of the displacements is verified only in a portion of the interface; moreover, the joints may have a lower strength of the original material. For these reasons the mathematical model used is crucial because otherwise the results are not representative of the component analyzed. Accurate analyses of reinforced structures require the use of 3D (Solid) FEM (Finite Element Method) models. A large number of degrees of freedoms (DOFs) is needed, and the computational costs could become prohibitive when solid models are used. 2D (Shell) and 1D (beam) models are used instead of 3D models to reduce the CPU in FEM analysis. These simplified mathematical models introduce assumptions, based on geometrical and kinematic approximations, which reduce the DOFs but could largely increase the error. For these reasons contribution direct to introduce efficient and robust reduced models are welcome. Among these, those referenced as "Component-Wise" approaches which are based on FEs based on Carrera Unified Formulation (CUF) have been recently proved to be a reliable framework for further developments which are the object of the present research proposal. Various analysis of simple components, such as plate and curved reinforced panels, are considered to analyze the effect of the stringers in the FE models compared to the 1D-CUF models. The stringer changes the solution locally, in term of stress and displacement field and also regarding the local vibration because indeed the local strength increases. The shape of the stringer is an additional parameter to consider when reinforce structures are modeled using the refined models (beam and shell/plate) in the FE modeling. The one-dimensional CUF formulation is also used to analyze the effect of the reinforced configurations in the case of complex structures In fact, in the case of reinforced cylindrical components or launchers, the reinforced layout must be modeled considering the local and the global effects. Composite materials, non-structural masses, and load-factor are included in the analysis, performing the implications for the dynamic analysis due to the different approaches used in the modeling. Various FE models are used to carry out the results of the FE modeling. In particular, in the 3D FE models, both plate and stringer are modeled using the same solid elements. In the 2D FE models, shell elements are utilized for the plate and also for the stringers. In contrast, the 2D-1D FE models are characterized by the coupling between shell and beam elements, in particular, the shell elements are used for the plate while the beam elements for the stringers. The 3D, 2D, and 2D-1D models are analyzed using the commercial NASTRAN code, where the 3D solution is used as the reference solution. The results show the need for the reduced FE models to adopt appropriate valuations and accurate analysis when reinforced structures are modeled, because the stringer and its shape can influence the static and dynamic analyses. In addition, the results show the capabilities of the present approach to deal with the analysis of conventional complex space structure. The results indicate that the current models can give accurate results with a high reduction in the computational cost with respect traditional approaches.