Influence of localized microstructure evolution on second harmonic generation of guided waves

Nonlinear guided waves exhibit high sensitivity to material microstructural changes, thus attracting increasing attention for incipient damage monitoring applications. However, conventional nonlinear guided-wave-based methods suffer from two major deficiencies which hinder their applications: 1) mostly relying on the first arrivals of wave signals, they apply to limited inspection areas in simple structures in order to avoid wave reflections from structural discontinuities or boundaries; 2) they are prone to numerous deceptive nonlinear sources in the measurement system which might overwhelm damage-induced signal components. To tackle these challenges, we propose a metamaterial-assisted coda wave interferometry method using second harmonic Lamb waves, applicable to the monitoring of local incipient damage in complex structures. Embracing the metamaterial concept, a so-called meta-screen is designed, whose geometry and layout can be flexibly tailored to target specific inspection zones in a structure. Capitalizing on its customized bandgap features, the proposed meta-screen allows for the passing of fundamental waves while preventing the second harmonic components generated by deceptive nonlinear sources from penetrating into the inspection area. Through numerical analyses on a plate with a rib stiffener, the efficacy of the meta-screen and the influence of occasional disturbance and regular pollution are evaluated. Experimental validations on an adhesive structure also confirm the superior sensitivity of the nonlinear coda waves to incipient damage, which is further enhanced by the deployment of the meta-screen alongside improved robustness against deceptive nonlinear sources outside the inspection area. The proposed metamaterial-assisted coda wave interferometry method with second harmonic Lamb waves holds great promise for local incipient damage monitoring of complex structures.

Section: Enhanced Damage Detection Sensitivitymentioning

confidence: 99%

A metamaterial-assisted coda wave interferometry method with nonlinear guided waves for local incipient damage monitoring in complex structures

Shan,

Liu,

Zhang

et al. 2024

“…Specifically, Set-I represents pure linear aluminum and Set-II the intact aluminum with weak nonlinearity. As the higher order elastic constants are closely related to the material microstructures, the last two sets in the table are used for two aluminum materials containing incipient damage of increasing levels, from Set-Ⅲ to Set-IV, which are taken from literature [34]. In addition, the plate is divided into four zones (A-D) where the material properties are selected from the four sets of material data in different simulations.…”

Section: Fe Investigationsmentioning

confidence: 99%

Mode-mixing-induced second harmonic A0 mode Lamb wave for local incipient damage inspection

Shan

2020

This paper reports the discovery of a special type of second harmonic A0 mode Lamb wave, which is generated through the mixing of primary S0 and A0 mode Lamb waves in a PZT-activated weakly nonlinear plate. Owing to the different propagating velocities of the S0 and A0 waves and the finite duration of their corresponding tone-burst wave packets, wave mixing takes place within a confined area which can be precisely controlled by tuning the wave excitation durations. When local incipient damage falls into the mixing zone, this second harmonic A0 mode wave provides higher damage detectability than the commonly used second harmonic S0 mode wave resulting from the global material nonlinearity. Moreover, through a tactic tuning of the mixing zone size, damage detection can be carried out zone by zone along the transmitter-receiver path to achieve damage localization. Finite element (FE) simulations are first carried out to ascertain the theoretically predicted phenomenon and the underlying generation mechanism of the second harmonic A0 mode Lamb waves. Capitalizing on its mode mixing feature between the primary A0 and S0 mode Lamb waves, a dedicated damage localization strategy alongside the corresponding algorithm is then proposed. Experiments are finally carried out with a dedicatedly designed inspection system with mitigated non-damage-related nonlinear interference. Both FE and experimental results demonstrate the appealing characteristics and the potential of the second harmonic A0 mode Lamb waves for local incipient damage detection and localization.

“…As the normal strain of the host structure is a known variable, the differential equation with respect to the normal strain of the sensor can be obtained by substituting the geometric and constitutive equations of the bonding layer into equation (35) as…”

Section: Wave Sensingmentioning

confidence: 99%

“…where g L bs can be obtained by combining equation (35) and the constitutive equation of the bonding layer. As the SAN shares the same mechanism with AAN, the governing equations for the nonlinear wave sensing problem are identical to those in the nonlinear wave actuating process, with different subscripts used for the corresponding elements.…”

Section: Wave Sensingmentioning

confidence: 99%

See 1 more Smart Citation

Adhesive nonlinearity in Lamb-wave-based structural health monitoring systems

Shan

2016

Structural health monitoring (SHM) techniques with nonlinear Lamb waves have gained wide popularity due to their high sensitivity to microstructural changes for the detection of damage precursors. Despite the significant progress made, various unavoidable nonlinear sources in a practical SHM system, as well as their impact on the detection, have not been fully assessed and understood. For the real-time and online monitoring, transducers are usually permanently bonded on the structure under inspection. In this case, the inherent material nonlinear properties of the bonding layer, referred to as adhesive nonlinearity (AN), may create undesired interference to the SHM system, or even jeopardize the damage diagnosis if they become serious. In this paper, a nonlinear theoretical framework is developed, covering the process of wave generation, propagation and sensing, with the aim of investigating the mechanism and characteristics of ANinduced Lamb waves in plates, which potentially allows for further system optimization to minimize the influence of AN. The model shows that an equivalent nonlinear normal stress is generated in the bonding layer due to its nonlinear material behavior, which, through its coupling with the system, is responsible for the generation of second harmonic Lamb waves in the plate, subsequently resulting in the nonlinear responses in the captured signals. With the aid of the finite element (FE) modeling and a superposition method for nonlinear feature extraction, the theoretical model is validated in terms of generation mechanism of the AN-induced wave components as well as their propagating characteristics. Meanwhile, the influence of the AN is evaluated by comparing the AN-induced nonlinear responses with those caused by the material nonlinearity of the plate, showing that AN should be considered as a non-negligible nonlinear source in a typical nonlinear Lamb-wave-based SHM system. In addition, the theoretical model is also experimentally validated in terms of the frequency tuning characteristics of the ANinduced wave components. A fairly good agreement is found among the theoretical model, FE model and the experiments, thus confirming the theoretically predicted AN-induced wave generation mechanism and their characteristics.