Integrally stiffened plate is widely used in aerospace, marine and other engineering structures. These structures are prone to unavoidably generate minor fatigue and damage during service, which should be paid more attention to for keeping structural safety and reliability. Therefore, structural health monitoring (SHM) plays a critical role in these applications. In recent years, ultrasonic guided wave SHM methods have attracted much attention because guided waves can travel long distance with less energy loss and are sensitive to small damage. However, the dispersion, multi-modal and scattering from structural discontinuities are the main laminations to the engineering application of the method. It is necessary to well understand the wave propagation behavior in complicated structures to further mature the guided wave SHM method.&nbsp;In this paper, the interaction between the fundamental anti-symmetric guided Lamb mode (A0) and T-stiffener in an integrally stiffened thin plate is studied by finite element method. In the FE model, plate and T-stiffener are modeled separately and plane strain condition is assumed. Both the size of the element and the size of time step meet the requirements of mesh convergence, and the four-node bilinear plane strain element is used to discretize the structure. The propagation behavior of A0 mode in stiffened plate is actuated using a piezoelectric wafer active sensor, and piezoelectric mechanical coupling analysis is carried out. The excitation pulse consists of five cycles tone-burst modulated using a standard Hanning window. Absorbing layer technique is used to reduce the effect of boundary reflection. In order to verify the validity of the finite element model, two-dimensional semi-analytical result and numerical result are compared, and the group velocity calculated by these two methods are basically the same. The characteristics of wave propagation caused by the presence of stiffener are analyzed in time domain, frequency domain and wavenumber domain respectively. It can be found that in time domain, the existence of stiffener causes obvious mode conversion of reflected and transmitted waves in the structure. In time-frequency domain, the main frequency components of the receiving signal are mainly distributed near the central excitation frequency, while no other frequency components are generated. In frequency-wavenumber domain, for single A0 mode excitation, only the fundamental S0 and A0 modes which are generated due to mode conversion exist in the receiving signal, still no other higher modes exist. With the change of excitation frequency, the reflection and transmission behaviors of guided waves in A0 and S0 modes change obviously. Because of the anti-symmetric excitation, the amplitude of A0 mode is higher than S0 mode in both reflected and transmitted waves.

Interaction of T-Stiffener on A0 Lamb Mode Wave Propagation Behavior in Thin Plate

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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