Quantitative Structural Diagnosis of Plate-like Structures using Multi-frequency Lamb Wave Diffraction Tomography

Abstract

Quantitative identification and evaluation of damage are of utmost importance for the safety and sustainability of a structure. Identifying early stage damage is also necessary for reducing the maintenance and repair costs of a structure and increasing its service life. Numerous Structural Health Monitoring (SHM) systems have been developed over time to address these issues in various capacities and prevent huge losses to life and economy. Lamb Wave Diffraction Tomography (LWDT) is an advanced SHM process that is used for identifying the location and quantifying the severity of damage. The process consists of interrogating a region of probable damage with Lamb waves and gathering information about the presence and geometry of the damage from the scattered waves. This process can be used in plate-like structures, such as metallic plates and composite laminates. One of the main areas of research in LWDT is investigating the effects of multiple non-central frequency components of data on the image quality and utilizing information from these multiple frequencies to reconstruct the damage. This thesis contains journal papers that 1) study the scattering of Lamb waves at delaminations within a composite laminate, focussing on the mode-conversion effect at the damage boundary 2) study the effects of non-central frequencies on the quality of imaging for damage reconstruction and 3) propose multi-frequency approaches that improve the efficiency of LWDT. The key outcome of this study is that a multi-frequency approach to damage reconstruction greatly improves the resolution of damage in plate-like structures, without increasing the number of transducers. A multi-frequency based reconstruction approach would thus lead to the advancement of LWDT as a feasible technique for the SHM of plate-like structures.