Guided Lamb waves for identification of damage in composite structures: A review

The paper provides a state of the art review of guided wave based structural health monitoring (SHM). First, the fundamental concepts of guided wave propagation and its implementation for SHM is explained. Following sections present the different modeling schemes adopted, developments in the area of transducers for generation, and sensing of wave, signal processing and imaging technique, statistical and machine learning schemes for feature extraction. Next, a section is presented on the recent advancements in nonlinear guided wave for SHM. This is followed by section on Rayleigh and SH waves. Next is a section on real-life implementation of guided wave for industrial problems. The paper, though briefly talks about the early development for completeness,. is primarily focussed on the recent progress made in the last decade. The paper ends by discussing and highlighting the future directions and open areas of research in guided wave based SHM.

https://iopscience.iop.org/article/10.1088/0964-1726/25/5/053001/pdf

Guided wave based structural health monitoring: A review

This study presents active sensing methods in structural health monitoring, for detecting cracks and debonds in metallic and composite structures, which can be potentially implemented into airframe structures. First, a pitch-catch method using a pair of piezoelectric actuator and sensor is introduced to generate a damage indeX which can be used to characterize damage at a known location. Tests on airbus fuselage panels are conducted to verify the method and damage indeX. The damage indeX relates changes in the energy content of a specific Lamb wave mode selected by group velocity analysis to the eXtent of damage. Second, an imaging method based on multiple pitch-catch information, a network of piezoelectric actuator/sensors, is presented for characterizing damage (location and size) without need for a structural or damage model. The imaging method with an autofocusing feature is applied to aluminum plates and a stiffened composite panel for method verification.

Pitch-catch Active Sensing Methods in Structural Health Monitoring for Aircraft Structures

Permanently attached piezoelectric sensors arranged in a spatially distributed array are under consideration for structural health monitoring systems incorporating active ultrasonic methods. Most damage detection and localization methods that have been proposed are based upon comparing monitored signals to baselines recorded from the structure prior to initiation of damage. To be effective, this comparison process must take into account any conditions other than damage that have changed the ultrasonic signals. Proposed here is a two-step process whereby damage is first detected and is then localized and characterized. The detection strategy considers the long time behavior of the signals in the diffuse-like regime where distinct echoes can no longer be identified. The localization strategy is to generate images of damage based upon the early time regime when discrete echoes from boundary reflections and scattering sites are meaningful. Results are shown for an aluminum plate with artificial damage introduced in combination with temperature variations. The loss of local temporal coherence combined with an optimal baseline selection procedure is shown to be effective for the detection of damage, and a delay-and-sum imaging method applied to the residual signals both localizes the damage and provides characterization information.

http://iopscience.iop.org/article/10.1088/0964-1726/17/3/035035/pdf

Detection, localization and characterization of damage in plates with an in situ array of spatially distributed ultrasonic sensors

http://eig.stanford.edu/publications/hyunwoo_park/jsv_04_park.pdf

Time reversal active sensing for health monitoring of a composite plate

This paper presents an experimental and theoretical investigation of the applicability of the time-reversal concept to guided waves in plate-like structures, where the stress waves are dispersive and of multi-modes. It is shown that temporal and spatial focusing can be achieved through time reversal, although the dispersive behaviour of the flexural waves renders it impossible to exactly reconstruct the waveform of the original excitation. Based on the principle of the time-reversal concept, a digital imaging method suitable for distributed sensor/actuator networks has been developed. This new method, which overcomes the limitation of the conventional phased array method that operates under pulse-echo mode, provides an efficient imaging method for locating and approximate sizing of structural damages. In addition, it has been shown that signal strengths can be considerably enhanced by applying the present synthetic time-reversal method, thus reducing the number of sensors and actuators required to achieve a given signal-to-noise ratio.

https://iopscience.iop.org/article/10.1088/0964-1726/13/2/020/pdf

A synthetic time-reversal imaging method for structural health monitoring

In this paper an experimental and theoretical investigation of the applicability of the time-reversal concept to guided waves in plates, where the waves are dispersive and of multi-modes. It is shown that although temmporal and spatial focusing can be achieved through time reversal, the dispersive behavior of the flexural waves renders it impossible to exactly reconstruct the waveform of the original excitation. Nevertheless, the temporal and spatial focusing allows the development of a synthetic time-reversal array method for a distributed network of sensors and actuators. This new method, which overcomes the limitation of the conventional phased array method that operates under pulse-echo mode, can considerably enhance the signal strength, thus reducing the number of sensors and actuators required to achieve a given signal-to-noise ratio.

James T. Rose

Papers

A synthetic time-reversal imaging method for structural health monitoring

Computerized time-reversal method for structural health monitoring

Design of planar electrodes for multifunctional piezoelectric sensors