Search

The mode manipulation of Lamb waves plays an important role in damage detection and identification of damage types, location, and size. In this paper, we propose a composite phononic crystal (PC) plate with antisymmetric and symmetric PCs for realizing mode conversion from A0 to S0 mode of Lamb waves. The theoretical analysis, numerical simulations, and experimental validation are introduced and the mode conversion mechanism of the composite PC plate is systematically investigated. The effect of geometrical parameters on band structures of antisymmetric and symmetric PCs is first discussed. Then multi-physics field simulation models are developed and in-plane displacement fields are obtained in numerical simulations, which shows that the mode conversion is enhanced when the period number of the antisymmetric PC decreases and that of symmetric the PC increases. The composite PC plate specimens are fabricated with precision wire cutting technology for experimental measurements and the self-designed polyvinylidene fluoride (PVDF) comb transducer is used to stimulate the Lamb waves. The experimental results are consistent with the numerical simulations, which demonstrate that the proposed composite PC plate can achieve the mode conversion from A0 to S0 mode of Lamb waves. Our proposed structures have applicable values for the mode manipulation of Lamb waves in damage detection. [ABSTRACT FROM AUTHOR]

The dispersion and multimode natures of guided waves bring forth difficulties in signal analysis, limiting the application of traditional transducers. In this paper, we report the design, fabrication and characterisation of transducers composed of a polyvinylidene fluoride (PVDF) film with comb electrodes that can excite selectable single-mode guided waves for high-precision damage diagnosis and localization. The frequency response of the PVDF comb transducers was analysed with respect to the geometric parameters of the comb electrodes, and the sound-field directivity was determined by measuring the in-plane and out-of-plane displacements of the far field around the transducers by means of a double-wave mixed interferometer. In experimental measurements, a surface damage was located using such a PVDF comb transducer to excite single A0 and S2 mode guided waves. In addition, quarter omnidirectional PVDF comb transducers were fabricated and deployed on the corners of a square 7075 aluminium alloy plate for locating multi-type damages. It is found that the proposed quarter omnidirectional PVDF comb transducers are capable of locating multi-type damages with high accuracy. The PVDF comb transducers has the capability of the guided waves mode selection and flexibility, which is expected to achieve high-precision, long-time and online multi-type damages detection and monitoring. [ABSTRACT FROM AUTHOR]