Structural Tailoring for Tomographic Damage Detection, Vibration Control, and Energy Harvesting

This research explores the use of structural tailoring techniques to achieve multiple functionalities, such as, structural damage detection, vibration control, and energy harvesting in thin-walled metallic structures. From a general perspective, structural tailoring techniques provide a viable approach to induce vibration localization, which is an element to enable the above functionalities. In this work, structural tailoring was achieved leveraging the concepts of Frequency Selective Structures (FSS) and Acoustic Black Holes (ABH). The idea of FSS is built around the concept of a periodic structure, that is a structure assembled from a single unit cell that repeats identically in space in order to form the entire (periodic) medium. An interesting property of periodic structures is the occurrence of vibration localization due to disorder or mistuning, that is a local lack of periodicity. Mistuning can either be intentional or it can occur naturally as a result of random imperfections at material or structural level. The ABH is a taper-like feature embedded in the host structure that allows for a smooth reduction of the phase velocity, while minimizing the reflected energy. Although these concepts are general and can be exploited for a variety of applications in mechanical systems, this work explores their use for non-destructive assessment and monitoring of structures, as well as for vibration control, and energy harvesting.

More specifically, for application to structural health monitoring, this thesis explores the role of dynamic tailoring in the context of impediographic sensing. Impediography is a hybrid tomographic method that exploits the fundamental sensing principle of EIT and combines it with localized stress perturbations induced via ultrasonic excitation. This form of hybrid tomography relies on the piezo-resistive coupling between the stress field and the electrostatic response of the host structure. Such coupling allows collecting multiple sets of linearly-independent boundary voltage measurements that result in a remarkable enhancement of the sensitivity and resolution of the reconstructed properties. The FSS-based impediographic technique was explored numerically and the performances were assessed in terms of damage localization and quantification. Overall, results showed that the impediographic approach holds great potential to achieve high damage sensitivity and resolution while concurrently providing a drastic reduction of the size of the sensory network.

In the context of vibration control, this research develops ABH-based thin-walled structural components capable of broadband vibration attenuation characteristics. The performance of ABH structures was numerically and experimentally evaluated under both transient and steady state excitation conditions. Both numerical and experimental results suggested that the proposed approach can enable highly efficient and broadband vibration attenuation performance.

In the context of vibration based energy harvesting, this work presents the idea of ABH-based structural tailoring to enhance vibration-based energy harvesting. Fully coupled electro-mechanical models of an ABH tapered structure with surface mounted piezo-transducers were developed in order to numerically and experimentally explore the response of the system to both steady state and transient excitations. Results showed that the dynamically tailored structural design enables a drastic increase in the harvested energy over a broadband frequency ranges as compared to traditional non-tailored structures.