Delamination detection on composite laminates using the modal displacement unevenness coefficient

This paper develops a new detection method taking the power function of the modal displacement curvature difference as a damage index to accurately identify the location and degree of the delamination. The 4-layer Poly Tetra Fluoro Ethylene films of size 0.02 m × 0.11 m are embedded between adjacent carbon fiber prepregs being 0.06 m and 0.115 m away from the left edge, respectively. The force-hammer excitation experiment is carried out on the prepared laminates with fixed supports at both ends, and the frequency response curves of measuring points are processed by the Polylscf algorithm in Dong-Hua Data Analysis System. The finite element model of delaminated laminates is established through adding new layers with film properties, and the modal displacements of nodes are compared with experimental data. The number of measuring points in the experiment is limited, making the precise characterization of surface abrupt characteristics difficult. The numerical results are used to calculate the square of the Gaussian curvature difference between the modal displacements of intact and damaged laminates. Significant improvement of the delamination detection accuracy is achieved in this process, confirming that the developed method constitutes a valuable tool for the Non-Destructive Testing of the laminates.