Numerical Study of Ultrasonic Guided Wave in Composite Reinforced Panels with Different Stiffener Shapes

The aim of this work is to propose a numerical methodology based on the finite element (FE) method to study the propagation mechanisms of transmitted, converted, and reflected guided waves in stiffened fiber-reinforced polymeric (FRP) composite structures. The dispersion curves of such modes can help designers to improve the damage detection sensitivity of Lamb waves based structural health monitoring (SHM) systems. Using a FE model, whose accuracy is demonstrated against semi-analytical data in a previous work, the phenomena of scattering and mode conversion in composite panels characterized by a structural discontinuity, such as a stiffener, are investigated. In particular, the behavior of guided waves is analyzed using stiffeners of different shapes, C and Omega shaped. The research activity makes it possible to highlight conversion of modes and reflected waves at stiffeners, providing new observations compared to the state of the art. The morphological complexities of the structure (thickness steps, multiple boundaries, stiffeners) can be used to redirect guided waves and to allow monitoring of a specific area. Wave reflections interacting with stiffeners, therefore, can be analyzed to improve diagnostics or design new detection strategies.