Structural damage diagnostics via wavepropagation-based filtering techniques

Damage diagnostics;Lamb waves;Wave propagation;SLDV;Phase gradient;Polarization

Ayers, James Thomas ; Aerospace Engineering

University:Georgia Institute of Technology

Department:Aerospace Engineering

关键词: Damage diagnostics;    Lamb waves;    Wave propagation;    SLDV;    Phase gradient;    Polarization;   

Others  :  https://smartech.gatech.edu/bitstream/1853/34723/1/ayers_james_t_201008_phd.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

Structural health monitoring (SHM) of aerospace components is a rapidly emergingfield due in part to commercial and military transport vehicles remaining in operationbeyond their designed life cycles. Damage detection strategies are soughtthat provide real-time information of the structure's integrity. One approach thathas shown promise to accurately identify and quantify structural defects is based onguided ultrasonic wave (GUW) inspections, where low amplitude attenuation propertiesallow for long range and large specimen evaluation. One drawback to GUWsis that they exhibit a complex multi-modal response, such that each frequency correspondsto at least two excited modes, and thus intelligent signal processing is requiredfor even the simplest of structures. In addition, GUWs are dispersive, whereby thewave velocity is a function of frequency, and the shape of the wave packet changesover the spatial domain, requiring sophisticated detection algorithms. Moreover, existingdamage quantification measures are typically formulated as a comparison of thedamaged to undamaged response, which has proven to be highly sensitive to changesin environment, and therefore often unreliable.As a response to these challenges inherent to GUW inspections, this research developstechniques to locate and estimate the severity of the damage. Specifically, aphase gradient based localization algorithm is introduced to identify the defect positionindependent of excitation frequency and damage size. Mode separation throughthe filtering technique is central in isolating and extracting single mode components,such as reflected, converted, and transmitted modes that may arise from the incidentwave impacting a damage. Spatially-integrated single and multiple component mode coefficients are also formulated with the intent to better characterize wave reflectionsand conversions and to increase the signal to noise ratios. The techniques areapplied to damaged isotropic finite element plate models and experimental data obtainedfrom Scanning Laser Doppler Vibrometry tests. Numerical and experimentalparametric studies are conducted, and the current strengths and weaknesses of theproposed approaches are discussed. In particular, limitations to the damage profilingcharacterization are shown for low ultrasonic frequency regimes, whereas the multiplecomponent mode conversion coefficients provide excellent noise mitigation. Multiplecomponent estimation relies on an experimental technique developed for the estimationof Lamb wave polarization using a 1D Laser Vibrometer. Lastly, suggestions aremade to apply the techniques to more structurally complex geometries.