Showing papers by "Ye Lu published in 2008"

Quantitative assessment of through-thickness crack size based on Lamb wave scattering in aluminium plates

Abstract: The interaction of Lamb wave modes at varying frequencies with a through-thickness crack of different lengths in aluminium plates was analysed in terms of finite element method and experimental study. For oblique-wave incidence, both numerical and experimental results showed that the wave scattering from a crack leads to complicated transmission, reflection and diffraction accompanied by possible wave-mode conversion. A dual-PZT actuation scheme was therefore applied to generate the fundamental symmetrical mode (S0) with enhanced energy to facilitate the identification of crack-scattered wave components. The relationship between crack length and the reflection/transmission coefficient obtained with the aid of the Hilbert transform was established, through which the crack length was quantitatively evaluated. The effects of wavelength of Lamb waves and wave diffraction on the properties of the reflection and transmission coefficients were analysed.

Damage detection in a large composite panel of five stiffeners using Lamb wave signals

Abstract: The propagation characteristics of Lamb waves activated and collected by an active piezoelectric (PZT) sensor network in a CF/EP composite panel of five stiffeners were investigated. In particular, wave attenuation in terms of propagation distance and wave energy loss induced by reinforced stiffeners were evaluated. The interaction between Lamb wave modes and a through-thickness hole of 11.9 mm diameter was subsequently examined. Given the complexity of the captured wave signals, an inverse algorithm based on correlation between wave signals in the benchmark and damaged structures was developed. Different combinations of actuator-sensor paths were used to estimate the location of damage. The diagnostic results demonstrate that the proposed approach has a good capability for defining location of damage using the probability of occurrence of damage.

Guided Wave Propagation and Interaction with Damage in Tubular Structures

Abstract: A piezoelectric active sensor network is configured to collect the wave scattering from a throughthickness hole on an aluminium rectangular tube. It is found that guided waves are capable of propagating across the tube edges, while keeping the sensitivity to the damage even not on surfaces where the actuator and sensor are located. Signal correlation between the intact and damaged structure is evaluated and the probability distribution of damage is thus achieved on the unfolded tube surface.

Damage Detection in Thick Steel Beam Using Lamb Waves

Abstract: Different from the mostly concerned Lamb wave-based damage detection for thin plates, this paper presents a diagnosis procedure on thick steel beams with thickness of 34 mm. The diagnosis strategy and specimens were first described, and some parameters, such as the frequency and the number of cycles of the diagnostic waveform, were discussed. Based on finite element method (FEM) simulation, the experiment configuration was addressed, results from which show good similarity between the outcomes from the simulations and those from the experiments. Wavelet transform was further used to process the acquired Lamb wave signals for the purpose of damage detection and localization. Meanwhile, the velocity of the Lamb waves was calculated, illustrating that the fundamental anti-symmetric (A0 ) Lamb wave mode was excited in this case. The results demonstrate that Lamb waves can also be applied to some thick structures for the purpose of structural health monitoring.© 2008 ASME