Papers by Keyword: Lamb Wave

Abstract: Matching layers of acoustic impedance are intensively studied in ultrasonic transducers for the efficiency of wave transmission. Large impedance mismatch between the active element of piezo and parent material in long range ultrasonic is also expected to have the similar affects on the ratio of the transmitted and reflected waves which can cause high reflection at the interface that result acoustic wave ringing and indicate low transmitted energy for inspection over large areas. This simulation study present analysis of Lamb wave propagation through a single matching layer from a piezoelectric transducers. It explains transmitted waves into aluminum plate using different materials of matching plates at thickness of quarter wavelength. Four matching plates with close to the computed value of acoustic impedance had been used in FEM simulations to study effect of the matching layers on the transmitted Lamb wave in aluminum plate. The results indicated slightly different phenomenon of multiple wave reflections from the transmitted S0 and A0 modes at boundary of the matching layer.

Abstract: Complicated Lamb wave propagation in structures can cause a misinterpretation in defect location and sizing during nondestructive inspections. A visualization of Lamb wave interactions with oval defects was carried out in our study to investigate the phenomenon of fundamental Lamb wave interaction around defect by using a reduced model of plate in ABAQUS. The visualized wave propagations with oval shape of through defects in plates demonstrated different patterns of wave interactions for the symmetric and anti-symmetric modes. The results also visualized the mode conversions around defects which converted from the incident waves. The visualized changes on the wave structures due to wave interaction with defects is important to increase our understanding on the guided wave propagation and reduce misinterpretation in nondestructive inspection when using the wave modes during inspection on large structures.

Abstract: In this work a methodology for effective positioning of sensors and actuators for damage detection and characterisation is described. The novelty of the proposed methodology is that the fitness function to be optimised does not contain probability of detection (POD) which needs to be obtained for every possible sensor combination. The proposed fitness function is to provide the maximum coverage of the structure via Lamb waves and reduce the negative effects of boundary reflections. Once the fitness function is defines, genetic algorithm (GA) is used as an optimisation strategy to result in optimal sensor positioning.

Abstract: Structural Health Monitoring (SHM) techniques have gained an increased interest to be utilised alongside NDI techniques for aircraft maintenance. However, to take the SHM methodologies from the laboratory conditions to actual structures under real load conditions requires them to be assessed in terms of reliability and robustness. In this work, a statistical analysis is carried out for an SHM system for damage detection and characterisation in composite structures. The sensitivity of the platform to parameters such as noise, sensor failure, placement tolerances and bonding has been investigated and reported.

Abstract: L shaped braided composites under fatigue load was researched, using piezoelectric sensors and active Lamb wave monitoring technology. HHT transform based signal envelope obtaining method and the damage index method based on signal energy change were used to monitor the damage extending of the braided composites.

Abstract: The implementation of the switch is the stepstone of a fully automated structural health monitoring (SHM) System. This paper attempted to tackle the hardware connectivity issues when dense transducer arrays present in the system with the switch that features the matrix topology. The program that controls the instruments and automates the data acquisition for SHM system was developed in LabVIEW, in which a scanning approach that sensorises the interrogation area and a hybrid programming technique are employed. Through interfacing with a top-level GUI of the program, it is easy to be controlled and employed. The solution showed a significant reduction in testing time comparing that with manual switch operation and a weight-saving solution as a minimum number of shielded cable needed. In addition, because only one channel each from the signal generator and digitiser is required, it is less demanding on the specification of the instruments. The prototype of the current system can be scaled up for testing on a larger structure due to its modular nature in both PXI express system and software design.

Abstract: This paper exploits the implementation of a delay-and-sum imaging method using Lamb wave signals to localise barely visible impact damage (BVID) in quasi-isotropic composite panels. The structural discontinuities, such as opening and stiffener, has also been tested to reflect the common structural features of an aircraft and to examine the feasibility of the proposed detection technique. The prediction results are compared with ultrasonic C-scan images, which indicate location error for three different panels –flat panel, flat panel with an opening and stiffened panel. The accuracy is believed to be improved by increasing the number of transducers. Overall the proposed damage detection technique, with the use of only four transducers, demonstrated sufficient accuracy and efficiency in impact damage detection and can be applied alongside the traditional NDT inspections for providing a priori information of the impact damage location.

Abstract: EMI and the Lamb Wave technology are two kinds of mainstream active detection method in health monitoring , which have a long-term development. Health monitoring based on the combination of the EMI technology and Lamb wave, can be either a single method to conduct monitoring and analysis of specific structure ,or two methods together to conduct more comprehensive damage monitoring.

Abstract: Sensor is the core component of structural health monitoring system, which can collect the data of structural damage. The structural damage state can be gained after further processing. Aircraft serves in rigorous environment, and existing sensors cant meet the demand of its structural damage monitoring for inherent defect. A preparation method of partial poling piezoelectric film sensor was proposed in the paper, which can be used for structural damage monitoring of aircraft in combination with lamb wave.

Abstract: In this study, the marginal spectrum based on instantaneous parameter is applied to the active Lamb wave-based health monitoring of plate structure to investigate the marginal spectrum variation of the signals after being added with damage scattering signal. First,the active Lamb wave monitoring technology is employed to obtain the Lamb wave signals of the plate before and after damage. Then the marginal spectra of the signals before and after damage are obtained using the HHT technology and compared with the spectrum of the signals. The results show that the marginal spectrum can better describe the variation of the signals before and after damage.