Study on the equivalent model considering in-plane and out-of-plane mechanical properties for a curved sandwich structure with square honeycomb core

The curved honeycomb sandwich structure has larger surface area, effectively reducing the number of fasteners and parts of civil airplane fuselages, engine cowls, and ship’s hulls. Its equivalent model building can significantly shorten the simulation analysis time and improve the efficiency of optimal design and performance prediction, but the reliability and precision of the model are closely related to the calculation accuracy of equivalent elastic parameters. In the present study, an equivalent model considering the in-plane and out-of-plane mechanical properties of the core is developed for a curved square honeycomb sandwich structure. The in-plane and out-of-plane equivalent elastic parameters of the honeycomb core composed of hollow quadrangular frustum cells with symmetrical rectangular sides (i.e. square cell) are derived by analytical method, equivalent strain energy principle, and equivalent stiffness principle. And then combined with the sandwich panel theory, an equivalent model of the curved sandwich structure is established. The three-dimensional (3D) geometric models of planar honeycomb cores with hollow quadriprism cells are built by SolidWorks software, and the 3D printing is performed using Polylactic Acid (PLA) material. The three-point bending tests are conducted on the planar honeycomb sandwich structures with carbon fiber composite face sheets, and the test data are compared with the numerical results of this structure and its equivalent model. Based on ANSYS Workbench, the static analysis under bending and compression conditions, modal analysis, and harmonic response analysis are implemented on honeycomb sandwich structures with different bending degrees and their equivalent models. The results show that the load-displacement test curves of planar sandwich structures agree well with the finite element results of these structures and their equivalent models, and the equivalent models of curved sandwich structures accurately reflect the bending and vibration characteristics, fully verifying the feasibility of the presented equivalent model. This study provides important references and guidance for establishing the equivalent model of curved honeycomb sandwich structures.