ORCID
0009-0008-5628-4010
Date of Award
2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Civil and Environmental Engineering
First Advisor
Eric M. Hernandez
Abstract
Structural integrity is essential to the long-term success of everything from the foundations of civil infrastructure systems to the performance of aircraft and spacecraft. While structures are designed to withstand extreme loads beyond the levels expected during normal operations, the cyclical and cumulative application of operational loads can induce a failure mode known as fatigue. Fatigue is a significant, complex, and highly uncertain phenomenon occurring in structures and is defined as the degradation of a material, primarily due to the formation and nucleation of cracks resulting from the repeated application of stress cycles. The importance of fatigue is accentuated by past, large-scale, catastrophic failures that resulted in mandatory fatigue inspections for bridges and aircraft at predetermined intervals based on initial analyses predicting the lifespan, durability, and damage tolerance of these structures.
Vibration-based structural health monitoring (SHM) uses periodic or continuous measurements of a structure’s response and/or behaviors to detect, locate, and quantify damage as well as to provide a prognosis of remaining life. Application of SHM techniques for fatigue monitoring have traditionally focused on monitoring changes in natural frequencies as an indicator of damage. More recently, researchers have shifted their attention to using damping as a fatigue damage indicator, however significant challenges still remain due to the epistemic uncertainties regarding physics-based damping models and the aleatoric uncertainties associated with identifying damping from operational vibration measurements. More importantly, there is a missing link between the physics of damping and the identified damping from vibration measurements.
This dissertation presents recent discoveries that aim to clarify the relationship between structural fatigue damage and identified damping from operational acceleration measurements, showing that small changes in damping (inferred from complex eigenvalues) can indicate the onset and location of on-going fatigue damage. Furthermore, this work explores the applicability of sparsity promoting algorithms in inverse analyses to locate the areas of the structure where fatigue damage is taking place.
The proposed method was tested using both small- and large-scale structures. Fatigue testing of 6061-T6 aluminum beams and postprocessing of acceleration data show that identified damping gradually increases as fatigue life progresses, providing a measurable, real-time indicator of fatigue damage. The large-scale test involved identifying changes in complex eigenvalues from an instrumented building in California subject to earthquakes of varying intensity. An algorithm was developed to identify the location of changes in damping using L1 norm minimization and system matrices of the structure’s mass, stiffness, and damping. The results presented in this dissertation indicate opportunities to assess and possibly extend the life of fatigue-critical structures by monitoring their dynamic material properties in real time, using changes in damping to determine not only when damage is present, but also where the damage is located.
Language
en
Number of Pages
171 p.
Recommended Citation
Roberts, Alaina Skye Dickason, "Detection And Localization Of Fatigue Damage In Structures Using Identified Changes In Damping" (2025). Graduate College Dissertations and Theses. 2039.
https://scholarworks.uvm.edu/graddis/2039
