Date of Award
Open Access Dissertation
Structural Health Monitoring (SHM) and Nondestructive Testing (NDT) techniques are being used as effective tools for investigating variety of civil, mechanical, and aerospace applications. In recent years, these techniques become such incredible tools for continuously monitoring of various structures. The aim of the dissertation work is to develop SHM and NDT methodologies for acoustic emission sources localization, damage detection and quantification in metallic and composite structures using a network of sensors, guided wave and developed imaging methods. This work is implemented through preparing metallic and composite specimens, setting up experiments, designing efficient networks of sensors, modeling guided wave interaction with damages and developing imaging methods. A sparse array of sensors and guided waves in conjunction with imaging methods are powerful tools for quantifying the damage information in metallic and composite structures. The desertion work is organized in three major parts.
In part I, the impact points on metallic plate are localized using efficient a network of sensors, numerical method and developed imaging method. The hyperbola path-based developed imaging method precisely localizes the impact points inside and outside the network area. Two newly imaging methods are used successfully for localizing the impact points on composite plates. The first imaging method is used for localizing the impact points on composite plates with unknown material properties. The second imaging method is used for localizing the impact points on composite plates with known material properties.
In part II, estimation of crack size, shape, and orientation is investigated numerically and experimentally using Lamb wave. A hybrid global-local (HGL) approach is used in conjunction with the imaging methods for the numerical simulation. The HGL approach allowed fast and efficient prediction of scattering wave signals for Lamb wave interaction with crack from various incident directions. The simulation results show the directionality effect of the scattering wave signals and suggested an optimum transmitter- sensor configuration. Two imaging methods are used: one involves synthetic time reversal concept and the other involves Gaussian distribution function. Both imaging methods show very good agreement during simulations. Experiments are designed and conducted based on the simulated results. The directionality effect of incident Lamb waves on the imaging results is studied. The effect of summation, multiplication and combined algorithms for each imaging method is studied. It is found that both methods can successfully predict the crack size and orientation. Attempt is made to use these imaging methods for detecting and sizing smaller sized damage (1-mm to 3-mm diameter hole). The results confirm that these methods can successfully localize the hole.
In part III, four SHM and NDT techniques have been developed and used to localize and quantify the delamination in two composite plates. The effect of delamination size and depths are studied. For the NDT technique, appropriate setting of Rollerform and Omniscan devises is successfully used for localizing and sizing the delamination by extracting C-scan image, S-scan image and A-plot. For SHM technique, new methodologies and efficient networks of sensors (PWAS) are used successfully for accurately imaging the delamination in composite plates. Setting appropriate SLDV experiment helps to study the guided wave interaction with delamination and to study generated trapped waves. A new structural vibration methodology is used for detecting and quantifying delamination in composite plates. This methodology is based on the local vibration under piezoelectric wafer active sensors (PWAS) excitation. The PWAS transducer is used for the high-frequency excitation with a linear sine wave chirp from 1 kHz to 500 kHz and the scanning laser Doppler vibrometer (SLDV) was employed to measure the local vibration response of the composite plates. The local defect resonance frequencies of delamination were determined from SLDV measurements and the operational vibration shapes were extracted and utilized to quantify the delamination. The dissertation finishes with conclusions, and suggestions for future work.
Migot, A. Q.(2019). Structural Health Monitoring and Non-Destructive Inspection of Composite and Metallic Structures. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/5138