Microcrack localization using a collinear Lamb wave frequency-mixing technique in a thin plate

Abstract

A novel Lamb wave frequency-mixing technique is proposed for locating microcracks in a thin plate, which does not require the resonance condition of Lamb wave mixing and can accurately locate the microcracks through only one-time sensing. Based on the bilinear stress-strain constitutive model, a two-dimensional finite element (FE) model is built to investigate the frequency-mixing response induced by the interaction between two primary Lamb waves and a microcrack. When twoprimary Lamb waves of A0 and S0 modes with different frequencies excited on the same side of the plate simultaneously impinge on the examined microcrack, under the modulation of the contact acoustic nonlinearity, the microcrack itself can be deemed as the secondary sound source and it will radiate the Lamb waves of new combined frequencies. Based on the timeof flight of the generated A0 mode at difference frequency, an indicator named normalized amplitude index (NAI) is defined to directly locate the multi-microcracks in the given plate. It is found that the number and location of the microcracks can be intuitively visualized by using the NAI based frequency-mixing technique. It is also demonstrated that the proposed frequency mixing technique is a promising approach for the microcrack localization.

Defect Localization in Metal Plates Using Vibroacoustic Modulation

“…This article selects a low-frequency (LF) signal as an S 0 -mode continuous signal, which is excited by two piezoelectric sensors placed on both sides of the plate, as shown in Figure 2a. As soon as the LF signal reaches a steady-state condition, an A 0 -mode high frequency (HF) tone burst signal is excited by another pair of piezoelectric sensors attached at both sides of the plate [16,18] (Figure 2a). A double-sided tape of about 0.23 mm in thickness is used for the application of the piezoelectric sensor (thickness of about 2.2 mm) on a 1.2-mm-thick aluminum plate.…”

“…The Lamb wave frequency-mixing method for localizing a crack in a thin plate, using a 2D finite element model (2000 mm × 2 mm), was introduced by Wang et al [16]. An A 0 -mode low-frequency tone burst signal and an S 0 -mode high-frequency tone burst signal were excited by two piezoelectric sensors on the same side of the sample.…”

“…Since the study introduced herein focuses on metal structures, the defect chosen is a single crack. Various parameters are introduced in the literature for use as governing parameters to indicate the existence of defects; among them are the modulation index or damage index [4,10,12,14,15], the harmonics [7][8][9][10][11][12][13][14], and the first sideband [6,7,9,16].…”

“…Conversely, the nonlinear Lamb wave mixing/VAM technique uses two signals of two different frequencies. An evolving defect, such as a crack, causes a modulation by using these two signals, making it a nonlinear modulation [4,[6][7][8][9][10]12,[14][15][16]. In the approach introduced herein, the VAM technique is combined with the delay and sum (DAS) damage imaging method for localizing a defect.…”