This paper investigates the effect of axial stress on acoustoelastic guided wave propagation in arbitrary cross-section. Many researchers have investigated the effect of stress on guided wave propagation in arbitrary cross-section. However, the effect of high-order elastic constants in guided waves propagation of such structures is not as well understood. This paper deals with an acoustoelastic theory combined with semi-analytical finite element (AE-SAFE) method for modeling stressed wave propagation. The dispersive solutions are obtained in terms of phase velocities, group velocities and velocity sensitivities to stress variations in complex arbitrary cross-section. These results can be utilized to select the appropriate points and are significant for stress measure in arbitrary cross-section at high frequency region. The AE-SAFE method is applied to three examples, including plates, load bearing stringer and rail track.

This paper presents a new method to separate multi-mode signal of Lamb wave through reconstruction of pure mode basis signals calculated based on phase and group velocity. Individual signal of each mode contained in multi-mode signal can be obtained and analyzed by mode separation. Simultaneously, the hidden damage scattering signal can be extracted after removing the undesired signal. Two simulations are conducted on aluminum plates as examples to demonstrate the procedure of mode separation in detail. The first one models Lamb wave propagating in an aluminum plate without damage to separate each mode step by step. Extraction of damage scattering signal through mode separation is presented with the other simulation conducted on a damaged aluminum plate. Also an experiment is designed to example the applicability of this method. The results of both simulations and experiment verify the validity and accuracy of this method. This mode separation method provides a potential baseline free approach for damage detection using Lamb wave.

To assure the integrity and safety of truss structures, much work has been done for inspection in bars using ultrasonic guided waves methods. Guided waves have been widely used for Non-Destructive Testing (NDT) and Structural Health Monitoring (SHM) because of their long propagation distance and reliable responses. Though good for assessment of guided wave in the regular section structures such as cylinders, pipes and rails, the excitation of guided wave modes in irregular bars lack further research due to the arbitrary cross-section. This paper presents the excitation and propagation of guided waves in arbitrary cross-section structures by coupling the normal mode expansion (NME) method with the semi-analytical finite element (SAFE) method. Then, a Tee-bar example of finite element (FE) simulations is performed to validate the proposed SAFE-NME method. Moreover, the validated method is used to develop a double mode inspection strategy for multi-damages identification, showing the potential for NDT & SHM applications.

Large-scale plate-like structural components have been widely used in various aerospace structures. Subject to complex loading conditions and environmental factors, the integrity of plate-like structures is threatened by the occurrence and accumulation of structural damages, calling for the development of structural health monitoring (SHM) methods and techniques. Guided wave-based SHM methods have been demonstrated with a high sensitivity to small-scale damage. In particular, the probability-based diagnostic imaging (PDI) algorithm is able to achieve enhanced accuracy and efficiency of damage localization. Typically, the PDI defines damage index (DI) in terms of the deviation between the baseline and real-time guided wave signals. However, as the baseline signals are highly sensitive to environmental factors, such as temperature, the DI may exhibit large instability subject to varied environmental factors and lead to inaccurate damage detection results. In this study, a novel damage diagnostic imaging approach free of a baseline signal is presented for nonpenetrating damages. The approach is established based on the modification of conventional baseline-dependent PDI, into which the converted mode extraction (CME) strategy is integrated to give rise to the DI in terms of the energy of the converted modes. As the essential part of the CME-PDI approach, the converted modes caused by nonpenetrating damages as structural thickness variation are extracted from the primitive multimode wave signals according to a recently proposed CME method featured by intrinsic basis mode reconstruction. The effectiveness of the approach is first examined numerically, and then an experiment is carried out by taking into account the temperature effect. Compared with conventional PDI, the CME-PDI approach shows apparently enhanced accuracy and stability in damage localization.

Large-scale plate-like structural components have been widely used in engineering fields. The occurrence and accumulation of structural damage will threaten the integrity of plate-like structures. Guided wave-based structural health monitoring (SHM) technology has been demonstrated as an effective tool to detect small-scale damage at a high sensitivity. Due to the advantages of baseline-free, concentrated sensor arrays and rapid inspection of the full area, Lamb wave-phased array SHM systems have been extensively investigated in recent years. However, the inherent multi-mode characteristic of Lamb waves is well-known to have a significant influence on wave propagation and further development of phased array method. In this study, a single Lamb wave mode extraction method combined with phased array SHM system is proposed based on a concentric piezoelectric active transducer (CPAT). First, a brief review of a Lamb wave-phased array system is presented, including working principle, sensor array, and Lamb wave excitation and sensing. Then, the single mode wave extraction method is performed based on the CPAT. The effectiveness of the single mode wave extraction-based phased array SHM system is first examined numerically. Finally, the proposed phased array system is used to monitor large plate-like structures and the availability and validity of the proposed SHM system is confirmed by an experimental study. This work provides an effective and practical tool to detect damage in large-scale plate-like structures.