Guang Meng

A correlation filtering-based matching pursuit (CF-MP) for damage identification using Lamb waves

Time of flight (ToF) plays a key role in positioning structural damage, but the exact determination of ToF in complicated Lamb wave signals is somewhat challenging. A signal processing approach, taking advantage of correlation filtering-based matching pursuit (CF-MP), was developed. In this approach, correlation among wave signals captured from the same structure under different damage statuses was calibrated, which served as an indicator for the occurrence and severity of structural damage. The ToF of a damage-scattered Lamb wave was pinpointed with high precision. With it, the approach was then applied to Lamb wave signals acquired from delaminated carbon-fibre/epoxy (CF/EP) composite beams, and the location and size of the delamination were exactly predicted. Experimental validation indicated that such an approach is able to filter boundary-reflected signal components involved in a complex wave signal, making the wave-based damage identification technique practical for small structures.

Dispersion analysis of Lamb waves and damage detection for aluminum structures using ridge in the time-scale domain

In this paper, the dispersion of Lamb waves in aluminum structures was systematically analyzed to differentiate the mode of each package in Lamb wave signals and localize damage. Piezoelectric transducers were bonded on the surfaces of aluminum structures, functioning as actuator and sensor to excite and acquire Lamb waves, respectively. Wavelet transform was applied to the acquired Lamb wave signals, in which the optimal mother wavelet was selected using the concept of Shannon entropy to obtain the most accurate location of each wave package. The ridge and contour of the Lamb wave signals in the time-scale domain were obtained to distinguish the mode of each wave package and pinpoint these packages for estimating the actual group velocities of dispersion curves and localizing damage. The proposed approach could help search the actual dispersion curves in the excitation frequency band by using only one Lamb wave signal. Ridges in the time-scale domain and the actual group velocities were further used to identify damage in the structures. Results demonstrate that the proposed approaches were effective in dispersion analysis, wave mode differentiation and damage localization.

Vibration characteristics of electrorheological elastomer sandwich beams

The vibration characteristics and control capabilities of a cantilever sandwich beam with electrorheological (ER) elastomers subjected to different electric fields are investigated in this study. Considering ER elastomers as viscoelastic damping materials with electrically controllable properties, a finite element model of a sandwich beam with an ER elastomer core is developed to predict the vibration responses of the proposed beam. An experimental analysis was also conducted to illustrate and evaluate the effects of an electric field on the frequency responses and natural frequencies of the sandwich beam. The results show that natural frequencies of the ER elastomer sandwich beam increase and vibration amplitudes at natural frequencies of the ER elastomer beam decrease, as the strength of the applied electric field increases. It is demonstrated that the vibration characteristics of ER elastomer beams are similar to those of ER fluid beams, which could be controlled by changing the strength of the applied electric field. This controllable characteristic of ER elastomer beams is useful for applications in engineering structures where variable performance is desired.

Identification of Dual Notches Based on Time-Reversal Lamb Waves and a Damage Diagnostic Imaging Algorithm

An integration of time-reversal Lamb wave signals from a sensor network and a damage diagnostic imaging algorithm is developed to identify dual notches in an aluminum plate. The time reversibility of Lamb waves for one wave propagation path in an aluminum plate is investigated using dynamic finite element analysis (FEA). A time-reversal-based damage index (DI) is calibrated by correlation of the reconstructed waveform and the original activated tone burst, when the fundamental symmetric (S0) mode alone is reversed or when both the S0 mode and the fundamental antisymmetric (A0) mode are reversed. Simulation results demonstrate that the calibrated DI is almost identical for the time reversal of single or multiple Lamb modes. On the basis of the time reversibility of Lamb waves, dual notches in an aluminum plate are identified using the damage diagnostic imaging algorithm in the experiment. With the availability of time-reversal-based DI for individual sensing paths on the aluminum plate, the probability values for the presence of dual notches are estimated in the inspected area enclosed by the sensor network. Identification results demonstrate that the integrated approach with time-reversal Lamb waves and the damage diagnostic imaging algorithm is independent of additional benchmark signals, and it can be used confidently to locate multiple instances of damage.

Optimal Mother Wavelet Selection for Lamb Wave Analyses

Structural health monitoring (SHM) system, usually consisting of a sensor network for collecting the structural response signal and data analysis algorithms for interpreting the signal, plays a significant role in fatigue life and damage accumulation prognostics. Wavelet transform (WT) has gained popularity as an efficient means of signal processing in SHM, in which an optimal mother wavelet-based WT can carry out feature extraction with high precision. This article is to provide criteria of optimal mother wavelet selection in Lamb wave analysis for SHM, motivation of which is that small error in Lamb wave analysis can result in much larger error in damage localization because of very fast propagating velocities of Lamb waves. A concept, Shannon entropy of wavelet coefficients, was established to calibrate the degree of optimization of the selected mother wavelet. As application, various mother wavelets selected using the proposed criteria were applied to Lamb wave signals acquired from CF/EP composite laminates containing delamination. With the optimum mother wavelet, the essential information of the delamination-generated Lamb waves was achieved with high precision. The results demonstrate the excellent capacity of the approach for selecting the most appropriate mother wavelets for Lamb wave analyses and therefore damage localization.

Damage Identification in Thick Steel Beam Based on Guided Ultrasonic Waves

Most current studies of guided-wave-based damage detection have been con- ducted on thin plate-like structures. This article presents a study of damage identification based on activated ultrasonic waves in a thick steel beam. The diagnosis procedure, with key parameters such as excitation frequency and cycle number of the diagnostic waveform, is elaborated in relation to beam dimension as well as pulse-echo/pitch-catch configurations of PZT active sensors attached to the beam. Finite element simulation was conducted to char- acterize wave propagation in the beam, and the signals of wave propagation were experimen- tally measured; the results show good agreement with outcomes of the simulation. To aid damage identification, the group velocity of the guided wave was calculated using the envelope of the signal, which was obtained by Hilbert transform. The results for damage location and severity assessment demonstrate that the guided-wave-based damage identification approach can also be applied to certain thick structures for the purpose of structural health monitoring.Most current studies of guided-wave-based damage detection have been conducted on thin plate-like structures. This article presents a study of damage identification based on activated ultrasonic waves in a thick steel beam. The diagnosis procedure, with key parameters such as excitation frequency and cycle number of the diagnostic waveform, is elaborated in relation to beam dimension as well as pulse-echo/pitch-catch configurations of PZT active sensors attached to the beam. Finite element simulation was conducted to characterize wave propagation in the beam, and the signals of wave propagation were experimentally measured; the results show good agreement with outcomes of the simulation. To aid damage identification, the group velocity of the guided wave was calculated using the envelope of the signal, which was obtained by Hilbert transform. The results for damage location and severity assessment demonstrate that the guided-wave-based damage identification approach can also be applied to certain thick structures for the purpose of structural health monitoring.

Bearing Fault Detection Using Higher-Order Statistics Based ARMA Model

Impulse response provides important information about flaws in mechanical system. Deconvolution is one system identification technique for fault detection when signals captured from bearings with and without flaw are both available. However effects of measurement systems and noise are obstacles to the technique. In the present study, a model, namely autoregressive-moving average (ARMA), is used to estimate vibration pattern of rolling element bearings for fault detection. The frequently used ARMA estimator cannot characterize non-Gaussian noise completely. Aimed at circumventing the inefficiency of the second-order statistics-based ARMA estimator, higher-order statistics (HOS) was introduced to ARMA estimator, which eliminates the effect of noise greatly and, therefore, offers more accurate estimation of the system. Furthermore, bispectrums of the estimated HOS-based ARMA models were subsequently applied to get clearer information. Impulse responses of signals captured from the test bearings without and with flaws and their bispectra were compared for the purpose of fault detection. The results demonstrated the excellent capability of this method in vibration signal processing and fault detection.

Guided Wave Propagation and Interaction with Damage in Tubular Structures

A piezoelectric active sensor network is configured to collect the wave scattering from a throughthickness hole on an aluminium rectangular tube. It is found that guided waves are capable of propagating across the tube edges, while keeping the sensitivity to the damage even not on surfaces where the actuator and sensor are located. Signal correlation between the intact and damaged structure is evaluated and the probability distribution of damage is thus achieved on the unfolded tube surface.