Influence of damage (delamination) on modal responses of sandwich composite panel-numerical and experimental analysis

The current research numerically investigates the influence of delamination on the natural frequencies of intact and delaminated glass fiber–reinforced composite (GFRC) sandwich panels. The sandwich structure synthesized via the hand lay-up method consists of two laminated GFRC face sheets bonded to an isotropic cured epoxy core. The results obtained using the present finite element (FE) model implemented in ABAQUS are compared to previous numerical and current experimental findings, demonstrating that the model functions consistently, with major differences of 10.77% and 14.84% found in a few modes. This validated FE model is used to systematically evaluate the influence of boundary conditions, fiber orientation, aspect ratio, core-to-face thickness ratio, and delamination shape on natural frequencies. Results show that fully clamped plates exhibit the highest frequencies, but are also most sensitive to delamination, with reductions approaching 50% in specific modes. Increasing the core-to-face thickness ratio significantly enhances modal performance, yielding up to 29% improvement in higher modes. The unidirectional fiber ([0°/0°] _S ) configuration with a core-to-face thickness ratio of 3 offers peak modal performance, with Mode 5 frequencies improving by over 29% and 20%, in intact and delaminated states, respectively. Among all shapes, the rectangular delamination produces the highest natural frequencies, while the square shape results in the lowest overall values. Notably, circular delamination leads to a 16.6% drop in Mode 5, demonstrating strong higher-mode sensitivity to delamination geometry. The findings provide design guidelines for optimizing stiffness and vibration resilience in GFRC sandwich structures.