Combined Effect of Stacking Sequence, Mid-Plane Circular Delamination, Fibre Orientation and Boundary Conditions on the Modal Parameters of Four-ply Composite Plate

A three-dimensional finite element (FE) model of a four-ply fiber-reinforced composite plate, with and without delamination, is developed using ABAQUS software to investigate its vibration characteristics. Initially, modal analysis is conducted on the undamaged (healthy) composite plate to examine the influence of stacking sequence, boundary conditions (BCs), and fiber orientation angle on the fundamental natural frequency. Four different stacking sequences are analyzed, comprising two symmetric layups—[ϴ/ϴ/ϴ/ϴ] and [ϴ/-ϴ/-ϴ/ϴ]—and two antisymmetric layups—[ϴ/-ϴ/ϴ/-ϴ] and [ϴ/ϴ/-ϴ/-ϴ]. The boundary conditions considered include Clamped-Free (CF), Clamped-Clamped (CC), Clamped-Simply Supported (CS), and Simply Supported-Simply Supported (SS). The fiber orientation angle (ϴ) is varied from 0° to 90° in 15° increments. The simulation outcomes are validated by comparing them with existing numerical and experimental results from the literature. Subsequently, the developed plate model is employed to investigate the effect of mid-plane circular delamination on the modal natural frequencies of the composite structure. Delaminations of varying diameters—2 cm, 4 cm, and 8 cm—are introduced at the mid-plane to assess their influence under different stacking sequences and fiber orientation angles, consistent with the configurations used in the healthy beam model. However, in this phase, the boundary condition is limited to a single case: one edge clamped and the remaining edges free. The results reveal that delamination size has a pronounced impact on the fundamental frequency, with larger delaminations causing greater reductions. These findings highlight that changes in modal parameters, particularly natural frequency, can serve as effective indicators for detecting delamination in composite plates.