Papers by Keyword: Lamb Wave

Abstract: Ultrasonic Lamb waves have gained popularity in non-destructive testing of plate-like structures due to their advantages such as low attenuation, high sensitivity, and wide detection range. This paper presents a novel baseline-free method for inspecting curved plate-like structures based on reciprocity loss. The method combines a modified damage imaging algorithm, a baseline-free detection method based on time reciprocity, and a calculation method for damage index values using the analysis of the focus position of time reciprocity signals. Experimental results demonstrate favorable effectiveness of the baseline-free method in detecting and locating multiple defects in the curved plate made of composite laminate.

Abstract: The present work proposes a vibration study with different surface and layers orientations at 0°, 15°, 30°, 45°, 60°, 75° and 90°using the Abaqus finite element code, the frequencies Stratified laminate composite panels were studied and the comparison between damaged structures and perfect structures we used stiffened panels based on T-shaped reinforced fibers. Lamb waves (LW) were widely proposed for the long-range inspection of Structural Structural Health Monitoring (SHM) oriented composite structures, the obtained results show the angle effects on the natural frequency increase at a peak then decrease in the form of a sinusoidal half-curve and the numerical results found in this work can be compared to those of other authors in the same area of ​​research, A piezoelectric actuator is used to design acoustic waves and a sensor is used for signal acquisition.

Abstract: This work reports on damage detection in a composite plate with an opening. A composite plate with an opening is manufactured and sensorized to investigate the effect of the opening on the wave propagation as well as the reliability of the delay and sum damage detection method in the presence of the opening. The plate was then impacted with a drop mass to cause barely visible impact damage and sensor data are gathered to analyze the diagnosis. The results show that if all the sensors around the opening is used, even though damage can be detected, it cannot be localized accurately. Further investigation shows that by localizing the sensor network to the one close to the damage area (multi-level detection), damage can be both detected and localized reliably. The results of the detection are also compared with the maximum coverage area map to validate the optimal sensor selection strategy.

Abstract: This work focuses on diagnostic methodologies for composite repair patch based on structural health monitoring (SHM) technology. Methodologies based on ultrasonic guided waves (GW) are developed and assessed for monitoring composite scarf repair with piezoelectric transducers. The effectiveness of the RAPID (reconstruction algorithm for probabilistic inspection of defects) algorithm was investigated for adhesively bonded composite patch repair. A composite scarf repair has been weakened by 4-point bending fatigue test and impacted after to generate a Barely Visible Damage (BVID). Both conventional RAPID technique, which requires baseline signals, and the Scaling Subtraction Method (SSM) were applied to detect damage in the bondline. The conventional method showed good performance for defect detection and localization whereas the SSM gives encouraging results for non-linear baseline-free RAPID.

Abstract: Detectability of damage using Lamb waves depends on many factors such as size and severity of damage, attenuation of the wave and distance to the transducers. This paper presents a detectability model for pitch-catch sensors configuration for structural health monitoring (SHM) applications. The proposed model considers the physical properties of lamb wave propagation and is independent of damage detection algorithm, which provides a generic solution for probability of detection. The applicability of the model in different environmental and operational conditions is also discussed.

Abstract: A hybrid piezoelectric (PZT)/fibre optic diagnostic system has been developed for damage detection in built up composite structures. The hybrid system uses PZT transducers to actuate the structure and fibre optic (FO) sensors to capture the propagating wave. The diagnostic system will then have the advantages of both PZT and FO sensors. The applicability of the system is then tested for detecting an artificial damage at a skin/stiffener interface of a thick composite structure. The response of the FO sensors is then compared to PZT sensors and presented.

Abstract: One method that has shown great potential in visualising and characterising the interaction of guided waves with damage in composites is Laser Vibrometry. A Laser Doppler Vibrometer (LDV) can be used to produce 2D wavefield images of guided Lamb waves but a single scan is very time consuming and normally multiple scans are required at various frequencies in order to determine the best input signal. This paper demonstrates the use of a chirp excitation method requiring only a single scan and a post-processing algorithm to obtain results corresponding to any narrowband signal within the frequency range of the chirp signal. The method was used on an artificially delaminated composite panel and showed that the S₀ mode, dominant at higher frequencies, mainly caused mode conversions whilst the A₀ mode, dominant at lower frequencies, mainly caused a change in phase and amplitude across the delaminationOne method that has shown great potential in visualising and characterising the interaction of guided waves with damage in composites is Laser Vibrometry. A Laser Doppler Vibrometer (LDV) can be used to produce 2D wavefield images of guided Lamb waves but a single scan is very time consuming and normally multiple scans are required at various frequencies in order to determine the best input signal. This paper demonstrates the use of a chirp excitation method requiring only a single scan and a post-processing algorithm to obtain results corresponding to any narrowband signal within the frequency range of the chirp signal. The method was used on an artificially delaminated composite panel and showed that the S₀ mode, dominant at higher frequencies, mainly caused mode conversions whilst the A₀ mode, dominant at lower frequencies, mainly caused a change in phase and amplitude across the delamination.

Abstract: Bonded repair of composite structures still remains a major concern for the airworthiness authorities because of the uncertainty about the repair quality. This work, investigates the applicability of conventional Structural Health Monitoring (SHM) techniques for monitoring of bonded repair with ring-shaped low profile sensors. A repaired composite panel has been sensorized with two Ring-Shaped Polyvinylidene fluoride piezopolymer Sensors (RSPS) and a piezoelectric (PZT) transducer. An electromechanical impedance (EMI) and Lamb wave analysis have been carried out to check the sensitivity of these sensors to detect an artificially introduced damage simulating a disbond of the repair. The state of the repair have been successfully monitored and reported by both methods.

Abstract: In this work the optimal configuration of transducers for damage detection and localization has been investigated. A particular interest is given to three optimization methods: mini-max, average Probability of Non Detection (POND) and ray tracing approach, coupled with genetic algorithm. After optimal configurations have been computed for each technique, they are experimentally tested and compared on a composite panel with one or two damages by generating and receiving Lamb waves signals. Damage detection is carried out with the Probability Based Damage Index Method (PBDIM). It was found that, in most cases, the ray tracing method and the average POND technique give better results, with a good detection of damages in comparison to the minimax POND technique, even if the latter seems numerically better.

Abstract: Monitoring of structural integrity of a component is very important, especially for the damage sensitive laminated composite structures. Among the Structural Health Monitoring (SHM) techniques, the Acousto-Ultrasonic (AU) technology is very promising. However, the accurate simulation of Lamb wave propagation is a very demanding task, in terms of computational cost. In the present study, in the frame of Finite Element method, the stacked-shell methodology is proposed for the simulation of Lamb wave propagation in composite laminated panels. The results of the stacked-shell approach are initially evaluated with respect to experimental results; the method is subsequently applied to undamaged and damaged composite laminated panels, in order to assess its efficiency and accuracy in the simulation of Lamb wave-based damage detection techniques.