Date of Award

12-14-2015

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Lingyu Yu

Abstract

Damage detection and health monitoring are critical for ensuring the structural safety in various fields, such as aerospace, civil and nuclear engineering. Structural health monitoring (SHM) performs online nondestructive evaluation (NDE) and can predict the structural remaining life through appropriate diagnosis and prognosis technologies. Among various SHM/NDE technologies, guided ultrasonic waves have shown great potential for fast and large area SHM/NDE, due to their sensitivity to small defects and capability to propagate long distances. Recent advances in guided wave based SHM/NDE technologies have demonstrated the feasibility of detecting damage in simple structures such as metallic plates and pipes. However, there remain many challenging tasks for quantifying damage, especially for damage quantification in complex structures such as laminated composites and honeycomb sandwich structures. Moreover, guided wave propagations in complex structures, and wave interactions with various types of defects such as crack, delamination and debonding damage, need to be investigated. The objective of this dissertation research is to develop guided wave based integrated SHM and NDE methodologies for damage detection and quantification in complex structures. This objective is achieved through guided wave modeling, optimized sensor and sensing system development, and quantitative and visualized damage diagnoses. Moreover, the developed SHM/NDE methodologies are used for various damage detection and health monitoring applications. This dissertation is organized in two major parts. Part I focuses on the development of integrated SHM/NDE damage diagnosis methodologies. A non-contact laser vibrometry sensing system is optimized to acquire high spatial resolution wavefields of guided waves. The guided wavefields in terms of time and space dimensions contain a wealth of information regarding guided wave propagations in structures and wave interactions with structural discontinuities. To extract informative wave signatures from the time-space wavefields and characterize the complex wave propagation and interaction phenomenon, guided wavefield analysis methods, including frequency-wavenumber analysis, wavefield decomposition and space-frequency-wavenumber analysis, are investigated. Using these analysis methods, the multi-modal and dispersive guided waves can be resolved, and the complex wave propagation and interaction can be interpreted and analyzed in time, space, frequency, and wavenumber multi-domains. In Part I, a hierarchical damage diagnosis methodology is also developed for quantitative and visualized damage detection. The hierarchical methodology systematically combines phased array imaging and wavefield based imaging to achieve efficient and precise damage detection and quantification. The generic phased array imaging is developed based on classic delay-and-sum principle and works for both isotropic and anisotropic materials. Using the phased array imaging, an intensity scanning image of the structure is generated to efficiently visualize and locate the damage zone. Then the wavefield based imaging methods such as filter reconstruction imaging and spatial wavenumber imaging are performed to precisely quantify the damage size, shape and depth.

In Part II, the developed methodologies are applied to five different SHM/NDE applications: (1) gas accumulation detection and quantification in water loaded structures, (2) crack damage detection and quantification in isotropic plates, (3) thickness loss evaluation in isotropic plates, (4) delamination damage detection and quantification in composite laminates, (5) debonding detection and quantification in honeycomb sandwich structures. This dissertation research will initiate sensing and diagnosis methodologies that provide rapid noncontact inspection of damage and diagnosis of structural health. In the long run, it contributes to the development of advanced sensor and sensing technologies based on guided waves, and to providing on-demand health information at component or subsystem level for the safety and reliability of the structure.

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