Wavelet transform-based damage identification in laminated composite beams

Abstract

Laminated composite structures suffers from delamination, the detachment of the layers due to the rupture of the fiber-matrix interface, as their principal mode of failure. Differently from other damages, such as cracks, delaminations are often not visible on the surface causing a late detection and leading to sudden failures. To ensure that laminated composite structures operate flawlessly, precise monitoring methods are required. The present study proposes a damage index to identify delaminations in a laminated composite beam, yet, the development is based on a well-defined methodology. The proposed damage index is composed of a weighted sum of Discrete Wavelet Transform detail coefficients, obtained by applying the transform to the mode shapes of the structure. Numerical models of the beams with a stiffness reduction in limited areas to simulate damage, provided data for tuning the coefficients of the damage index by performing a mixture design analysis and a multiobjective optimization. After substantial results for identifying damage in numerical cases, the damage index efficiency was tested with real carbon fiber-reinforced polymer beams. The experimental specimens were manufactured with delaminations induced by embedding non-sticking films between the layers. Again, substantial results in identifying damaged were achieved. The damage index proved to be efficient to locate damage in almost all positions along the beam. It is important to emphasize that the proposed damage index is a no-baseline method, a method that does not require information of the pristine structure. Finally, this study performs a deep statistical analysis on the effects of damage characteristics, such as position and severity, in a damage identifying technique. The results of the analysis serves as basis for developing more sophisticated and optimized damage identifying methods.