This paper proposes a framework of using deep learning-assisted methods for the prediction of interfacial conditions in coated plates using guided wave data. The coating-substrate interface is modeled as a linear spring layer of zero thickness, and the mechanical behavior of this spring layer is characterized by the spring compliance. Both tangential and normal spring compliances are introduced to characterize the bond quality. Numerical simulations are conducted for a wide range of spring compliances to generate the corresponding dispersion curves. A Long Short-Term Memory (LSTM) network is utilized to predict the interfacial conditions. In addition, we consider the delamination cases where the coating layer is completely separated from the substrate over the delaminated region. Finite element simulations are carried out to model guided wave generation, propagation, interaction with delamination, and reception. The time-space images are formed by measuring the time-domain signals by receivers at several locations downstream from the source transducer, which are then fed into the developed Convolutional Neural Network (CNN). Once trained, this Deep-Learning (DL) model enables the accurate prediction of delamination location and size. Results of this paper demonstrate that the proposed methodologies have tremendous potential for characterizing interfacial conditions in practical Nondestructive Evaluation (NDE) and Structural Health Monitoring (SHM) applications.
This paper presents the numerical study of the piezoelectric composite transducers for active sensing of concrete structures. A three-dimensional coupled field finite element model is initially constructed to capture the electro-mechanical impedance features of the piezoelectric composite transducers. The elaborated transducer takes the shape of a cube filled with the piezoelectric material. The spatially interdigitated electrodes are integrated to evenly separate the entire piezoelectric medium, forming the stacked piezoelectric units with opposite poling directions. Subsequently, the proposed transducers are embedded in a concrete beam, serving as the transmitter and the receiver, respectively. The electro mechanical impedance approach enabled by the proposed piezoelectric composite sensor is numerically conducted for crack detection. In addition, a pitch-catch active sensing procedure in concrete structures is realized via the transient analysis, modeling ultrasonic wave generation by the transmitter, propagation inside the concrete beam, interaction with the crack, and reception by the receiver. The developed piezoelectric composite transducer possesses tremendous potential for health monitoring of concrete structures. The paper finishes with discussion, concluding remarks, and suggestions for future work.
This paper presents a graphical user interface (GUI) for modeling ultrasonic guided wave propagation in elastic solids. The software exploits the semi-analytical finite element (SAFE) method for the calculation of wave-propagation characteristics. The interface allows for the modeling of piezoelectric effects in plate-like and arbitrary cross-sectional waveguides. The isotropic and anisotropic materials with damping effects are also considered. For anisotropic composite material cases, directivity plots can be extracted, containing the phase-velocities, group velocities, and slowness curves. The frequency-dependent mode shapes can also be obtained, including displacement, strain, stress, and other electric components for piezoelectric materials. The corresponding mode shapes for arbitrary cross-sectional waveguides are presented in the form of vivid animations, demonstrating the cross-sectional harmonic motions. All the computational outcomes are compared with commercial finite element (FE) codes via the Bloch-Floquet boundary conditions. The paper finishes with discussion, concluding remarks, and suggestions for future work.
This paper presents a Lamb wave virtual time reversal algorithm with transducer transfer function compensation to eliminate the transducer influence for dispersive, multimodal Lamb waves. This virtual time reversal procedure builds upon a complete 2D analytical model for Lamb wave generation, propagation, and reception. The analytical solution shows that, with the transducer transfer function compensation, a perfect reconstruction of the original excitation waveform can be achieved for both symmetric and antisymmetric Lamb wave modes. In addition, the Finite Element Modeling (FEM) and experimental validations are further performed to verify the compensated virtual time reversal procedure. Finally, a time reversal tomography experiment is conducted with a piezoelectric transducer array for structural damage imaging. The Lamb wave virtual time reversal algorithm with transducer transfer function compensation can achieve more accurate and robust damage imaging results. The paper finishes with discussion, concluding remarks, and suggestions for future work.
This paper presents the investigation of nonlinear scattering features of guided waves from fatigue cracks. The fatigue cracks nucleated from a rivet hole are studied as the representative case. A small-size numerical model based on the Local Interaction Simulation Approach (LISA) is introduced, which enables the efficient analysis of the Contact Acoustic Nonlinearity (CAN) of guided waves. Fatigue tests on a thin aluminum plate with a rivet hole is conducted to induce cracks in the specimen. An active sensor array surrounding the crack zone is implemented to generate and receive ultrasonic guided waves in various directions. Several distinctive aspects of the nonlinear scattering phenomenon are discussed: (1) the directivity and mode conversion features, which addresses the scattering direction dependence of fundamental and superharmonic wave mode components; (2) the amplitude effect, which stems from the rough crack surface condition with initial openings and closures; (3) the nonlinear resonance phenomenon, which maximizes the nonlinear response during the wave crack interactions at certain excitation frequency ranges. All these features may provide insights and guidelines for nonlinear guided wave based Structural Health Monitoring (SHM) system design. The numerical studies are compared with experimental data. The paper finishes with discussion, concluding remarks, and suggestions for future work.
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