W. J. Staszewski

Experimental Study of Impact-Damage Detection in Composite Laminates using a Cross-Modulation Vibro-Acoustic Technique

The paper demonstrates the application of cross-modulation vibro-acoustic technique for impact-damage detection in composite laminates. A composite plate is monitored for damage resulting from a low-velocity impact. The plate is excited simultaneously with two harmonic signals: a slow amplitude-modulated vibration pumping wave and a constant amplitude-probing wave. The frequency of both the excitation signals coincides with the resonances of the plate. An electromagnetic shaker is used to introduce the pumping wave to the plate. Two surface-bonded, low-profile piezoceramic transducers are used for probing-wave excitation and measurement. The wave modulation is transferred from the pumping wave to the probing wave in the presence of impact damage. This effect is exhibited in a power spectrum of the probing wave by a pattern of sidebands around the carrier harmonic. The results show that the amplitude of the sidebands is related to the severity of damage. The study also investigates also the effect of boundary conditions on the results.

Impact damage detection in light composite sandwich panels using piezo-based nonlinear vibro-acoustic modulations

The nonlinear vibro-acoustic modulation technique is used for impact damage detection in light composite sandwich panels. The method utilizes piezo-based low-frequency vibration and high-frequency ultrasonic excitations. The work presented focuses on the analysis of modulation intensity. The results show that the method can be used for impact damage detection reliably separating damage-related from vibro-acoustic modulations from other intrinsic nonlinear modulations.

Peridynamics as an analysis tool for wave propagation in graphene nanoribbons

The work is devoted to the study on elastic wave propagation in graphene nanoribbons, performed with peridynamics. Graphene nanoribbons have recently gained dramatic increase of interest in the fields of nanoelectronics and nanoelectromechanical systems. They can play a key role as either modern metallic or semiconductor materials, depending on the edge structure, with zigzag or armchair layout, respectively. Moreover, graphene opens new perspectives for the millimeter wave-based measurements systems. The authors present a peridynamic model used as alternative approach to analyze the dynamic behavior of a graphene nanoribbon. The model is considered as a periodic structure, i.e. an assembly of fundamental structural elements, with the first Brillouin zone under study, which undergoes propagation of elastic wave. The commonly applied auxiliary atomistic-continuum model for a C-C bond is used to set equivalent elastic properties, which are applied to find reference dispersion relation via FE model to study the behavior of the peridynamic model. The paper discusses its capability of recovering the physical nature of the reactions at the atomic scale present in a graphene applying dispersion characteristics. The peridynamic model of the graphene nanoribbon results from upscaling process carried out for a small-scale atomic model, making use of reference dispersion curve. The material properties are homogenized over studied domain indirectly by tuning the phase velocity for longitudinal in-plane elastic waves. As shown, nonlocal nature of peridynamics allows to preserve the lengthscale effect, local small-scale inhomogeneity and wave dispersion. Hence, the effect of spatial discretization at nano scale, arising from the distribution of atoms of carbon in the structure of graphene, may be represented with a nonlocal peridynamic model effectively.

Fatigue crack detection using nonlinear vibro-acoustic cross-modulations based on the Luxemburg-Gorky effect

This paper investigates the nonlinear cross-modulation vibro-acoustic technique for fatigue crack detection in metallic structures. The method is used in an aluminium plate instrumented with low-profile piezoceramic transducers that are used for excitation. Laser vibrometry is used to acquire vibro-acoustic responses. The results demonstrate the modulation transfer from one excitation signal to the other excitation signal in the presence of crack in the plate. The work presented focuses on the analysis of modulation intensities. The paper demonstrates that the method can be used for fatigue crack detection in metallic structures.

Wideband excitation in nonlinear vibro-acoustic modulation for damage detection

The paper discusses the use of wideband excitation in nonlinear vibro-acoustic modulation technique (VAM) used for damage detection. In its original form, two mono-harmonic signals (low and high frequency) are used for excitation. The low frequency excitation is typically selected based on a modal analysis test and high frequency excitation is selected arbitrarily in the ultrasonic frequency range. This paper presents a different approach with use of wideband excitation signals. The proposed approach gives the possibility to simplify the testing procedure by omitting the modal test used to determine the value of low frequency excitation. Simultaneous use of wideband excitation for high frequency solves the ambiguity related to the selection of the frequency of acoustic wave. Broadband excitation signals require, however, more elaborate signal processing methods to determine the intensity of modulation for a given bandwidth. The paper discusses the proposed approach and the related signal processing procedure. Experimental validation of the proposed technique is performed on a laminated composite plate with a barely visible impact damage that was generated in an impact test. Piezoceramic actuators are used for vibration excitation and a scanning laser vibrometer is used for noncontact data acquisition.

Damage detection in plate-like structures based on mode-conversion sensing with 3D laser vibrometer

Interpretation of Lamb waves signals raises serious difficulties due to their multi-modal nature. Various modes propagating with different velocities can be confused and erroneously treated as damage reflected components. Both S0 and A0 Lamb modes exhibit elliptical polarization, therefore, their in-plane and out-of plane motion components are shifted by ± 90°. Also, the ratios of in-plane and out-of-plane displacements between these components vary and the direction of particle motion is opposite for both modes. Using a 3D scanning laser vibrometer it is possible to capture the in-plane and out-of-plane motion. The modes differ not only in polarization parameters but also in group velocities, therefore, normally they are well separated in time. Two modes can occur simultaneously only close to the wave source or to a defect that leads to mode conversion. Since the in-plane and out-of plane motion components are generally out-of-phase, a comparison of these components permits detection of mode conversion, which leads to superior and reliable damage detection. Here, we present a damage imaging method based on mode-conversion indicator (MCI).