Structural deformation reconstruction using the hybrid shell-beam inverse Finite Element Method: experimental application on a thin-walled stiffened panel

The continuous developments in the field of Structural Health Monitoring (SHM) and the simultaneous push toward the realization of the digital twin paradigm has generated a strong request for the on-line monitoring of structural responses that are usually difficult to measure through direct sensing. Among these responses, the displacements, and the stresses that can be derived from them, play a crucial role. The indirect computation of the displacement field from easily measurable surface strains, known as shape sensing, has inspired the definition of an inverse formulation of the Finite Element Method, the iFEM. As for the standard FEM, this approach is based on the discretization of the structural domain with finite elements. Therefore, 2D inverse shell elements and 1D inverse beam elements have been separately proposed and tested for the shape sensing of plate and beam-like structures, respectively. However, especially in aerospace applications, thin-walled stiffened panels are often adopted. These structures can be discretized using hybrid shell-beam models. In this work, the iFEM hybrid shell-beam formulation is applied for the first time to the experimental shape sensing of an aluminum stiffened panel instrumented with strain sensing optic fibres. The displacements’ reconstruction is compared to the one obtained with a high-fidelity shell-only inverse model of the same structure. The comparison shows that the hybrid iFEM is capable of the same level of accuracy of the shell-only one, using a more computationally efficient model with less degrees of freedoms. These results prove that the proposed hybrid formulation is a valuable displacements’ monitoring tool for applications where computational efficiency is paramount and the level of detail achieved by low-fidelity hybrid models is sufficient, as it occurs in aeroelastic models.