Selective generation of Lamb wave modes and their propagation characteristics in defective composite laminates

Abstract

Techniques for the generation of Lamb waves with purpose of non-destructive inspection (NDI) were brie y reviewed. An active excitation control circuit was designed and instrumented with an online damage diagnosis system, by which the desired fundamental symmetric Lamb mode, shear mode and antisymmetric mode can be selectively stimulated. A signal processing and identi cation algorithm in the timescale domain, using spectrographic analyses based on the wavelet transform technique, was developed to assist the wave signal interpretation. The proposed excitation methodology was applied to the study of the dispersion and propagation characteristics of Lamb waves in quasi-isotropic CF/EP composite laminates with delamination. For validation, numerical simulations were conducted in parallel with experimental investigations.

On the Directivity of Lamb Waves Generated by Wedge PZT Actuator in Thin CFRP Panel

“…2,b demonstrates that the wawelength of A0 Lamb waves mode is 2 -5 time less than wawelength of SS0 horizontally polarized shear wave, i.e. spatial defects resolution of A0 waves can be significantly better that is fully consistent with the results of the papers [11,20,22,30]. 2.…”

“…As the results of this study three eigenfrequencies and natural vibration modes were chosen, at which the actuator supplied the most intensive contact surface displacement amplitude. At these natural frequencies (15,30, and 65 kHz), all subsequent numerical and experimental studies were performed.…”

“…This limitation is an impossibility to controllable change of their directivity. In order to overcome it the following approaches has been developed applying to the problem of controlled directivity of the excited guided waves: the use of the distributed PZT transducers array, which generate selectively the desirable Lamb modes [30]; active fiber composites and macro-fiber composites due to their broad frequency of operation, high reliability and easy installation [6,15]; the interdigital transducers, which able to generate bidirectional waves with relatively low side lobe level [6]. However, SHM of the large composite structures, where the acoustic waves generated by the spatially fixed exciter quickly attenuate and cannot spread over long distance, is difficult.…”

Quantitative Accessibility of Delamination in Composite Using Lamb Wave by Experiments and FEA

“…Additionally, for application in the excitation mechanism of a piezoelectric (PZT) actuator, the S 0 mode always exists in the actuated Lamb waves. To excite the A 0 mode solely at low frequencies, some specific method, such as dual actuators with reverse phase actuation, is required [18]. In this study, PZT actuators were embedded within a composite plate to actuate Lamb waves wherein both S 0 and A 0 modes were generated synchronously.…”

Systematic multiparameter design methodology for an ultrasonic health monitoring system for full‐scale composite aircraft primary structures

“…The performance of PZTs as ultrasonic GW transducers for damage diagnostics depends on several key parameters that must be selected before installing the SHM system, namely, piezoelectric properties, geometry, excitation frequency content, and the network configuration (i.e., the relative position of the transducers within the area to be monitored). Usually, the excitation centre frequency is selected assuming the ideal scenario of pure guided mode excitation or time‐domain discrimination between guided modes, after which a theoretically optimal dimension for the PZT transducer can be found from the wavelength tuning effect . Another criterion for choosing the excitation centre frequency is to match the minimum resolvable distance by a certain pure guided mode with the minimum size of the damage to be detected .…”