Debonding detection in CFRP-retrofitted reinforced concrete structures using nonlinear Rayleigh wave

This paper proposes the use of nonlinear Rayleigh wave to inspect debonding in carbon fibre reinforced polymer (CFRP) retrofitted reinforced concrete structures. The proposed method requires a network of transducers that are used to scan the CFRP-retrofitted reinforced concrete structures by sequentially actuating and receiving Rayleigh wave. The nonlinear feature used for the debonding detection is second harmonic generation due to the interaction of Rayleigh wave at the debonding between the CFRP and concrete interfaces. A damage image reconstruction algorithm is proposed to provide a graphical representation for detecting and locating the debonding in the CFRP-retrofitted reinforced concrete structures. In this study, experimental case studies are used to demonstrate the performance of the proposed debonding detection technique. A transducer network with four piezoelectric transducers is used to actuate Rayleigh wave and measure the second harmonic in the experiments. The results show that the proposed debonding detection technique is reliable in detecting and locating the debonding in the CFRP-retrofitted reinforced concrete structures.Ching-Tai Ng, Hasan Mohseni, Heung-Fai La

Guided wave mixing for damage detection in structural elements

Thin-walled components are fundamental to numerous civil structures such as bridges, buildings, storage vessels, pipes, and becoming progressively diverse with their use in wind turbines, aircrafts and shipbuilding. Identification and evaluation of damage in such structures plays a significant role in the early stage of the project conception, given that safety, performance and maintenance costs are three fundamental concepts in any engineering design. Structural Health Monitoring (SHM) was originated with collaboration across many disciplines to address a variety of structural issues and prevent dramatic losses. Nonlinear guided waves combines the benefits of nonlinear ultrasound and guided waves. By means of linear parameters such as wave reflection, attenuation and transition, wave velocity, or wave modes, linear guided waves cannot detect microscale damage such as early stage fatigue, corrosion, micro-crack, or microdelamination. In contrast, nonlinear guided wave have resulted promising due to incipient damage detection capabilities and reference-free potential, and leveraged its advantages over linear guided waves. This thesis investigates the use of nonlinear guided waves via a wave-mixing approach, where two ultrasonic frequencies are used, and the spectral content of the response is expected to carry information of the damage. This thesis provides a physical insight into the wave-mixing technique for damage detection in structures. The phenomenon is investigated theoretically, numerically and through laboratory experiments. A number of published and prepared journal papers under the same topic is included in this thesis. In Chapter 1, an overview of the general concepts of Structural Health Monitoring and connected non-destructive testing techniques are introduced along with nonlinear guided wave techniques. A theoretical derivation to correlate the contact effect on a steel bolted joint with the spectral content of a signal response is proposed in Chapter 2. Thorough experiments were carried out and demonstrated the robustness of the technique. Following, in Chapter 3, identification of debonding type of damage in adhesively bonded joints is investigated through three-dimensional finite element simulations and experiments. Numerical and experimental results revealed that guided wave-mixing technique could effectively detect debonding damage. To further extend the advantages of guided wave-mixing for different materials, a composite laminate plate in studied in Chapter 4. In this study, an imaging technique relying of the combined frequency wave is proposed to identify delamination and locate the defect. The proposed approach relies on network of few transducers and does not require reference data from undamaged samples. Lastly, a short study is presented in Chapter 5, where noncollinear pulses of finite time duration and non-planar wave-front are able to generate a resonant wave that is able to measure material nonlinearity, which is subject of study for many early stage fatigue damage detection techniques. Overall, this thesis systematically revealed and capitalized the advantages of nonlinear guided wave-mixing technique for various types of damage in structures across a wide variety of materials.Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental & Mining Engineering, 202

Compressive Sensing and Imaging of Guided Ultrasonic Wavefields

Structural health monitoring (SHM) and Nondestructive Evaluation (NDE) technologies can be used to predict the structural remaining useful life through appropriate diagnosis and prognosis methodologies. The main goal is the detection and characterization of defects that may compromise the integrity and the operability of a structure. The use of Lamb waves, which are ultrasonic guided waves (GW), have shown potential for detecting damage in specimens as a part of SHM or NDT systems. These methods can play a significant role in monitoring and tracking the integrity of structures by estimating the presence, location, severity, and type of damage. One of the advantages of GW is their capacity to propagate over large areas with excellent sensitivity to a variety of damage types while guaranteeing a short wavelength, such that the detectability of large structural damages is guaranteed. The Guided ultrasonic wavefield imaging (GWI) is an advanced technique for Damage localization and identification on a structure. GWI is generally referred to as the analysis of a series of images representing the time evolution of propagating waves and, possibly, their interaction with defects. This technique can provide useful insights into the structural conditions. Nowadays, high-resolution wavefield imaging has been widely studied and applied in damage identification. However, full wavefield imaging techniques have some limitations, including slow data acquisition and lack of accuracy. The objectives of this dissertation are to develop novel and high resolution Guided Wavefield Imaging techniques able to detect defects in metals and composite materials while reducing the acquisition time without losing in detection accuracy

Damage Detection of Submerged Structures Using Linear and Nonlinear Guided Waves

Metallic plates are one of the major components of liquid containment structures and are widely used in petrochemical and civil engineering. In many cases, the metallic plates have one side exposed to liquid and are subjected to different types of loads with varying amplitudes. Corrosion damage and material degradations are the two major concerns. Damage detection of the submerged plate structures plays an important role in maintaining the structural integrity and safety of high-valued infrastructures (e.g. liquid storage tanks and pipes). Guided wave testing is one of the most promising damage detection approaches. Although guided wave based techniques have been extensively studied on different structures in gaseous environments, the design and implementation for the structures immersed in liquid have not been well investigated. This research aims at enhancing the understanding of guided wave propagation and interaction with damage in submerged structures. The focus of this research is on metallic plates that have one side in contact with liquid and the other side exposed to air. The specific objectives of this thesis include the investigation on the propagation characteristics of guided waves in metallic plates with one side exposed to liquid, the development of numerical models to investigate the scattering characteristics of guided waves at corrosion pit damage, the analyses of the influence of the surrounding liquid medium on the linear and nonlinear guided waves features, and the evaluation of the sensitivity of linear and nonlinear guided waves features to different types of damage in the one-side immersed metallic plate. The main body of the thesis consists of four journal articles (Chapters 2-5). Chapter 2 discusses the propagation characteristics and sensitivity to damage of linear guided waves in a metallic plate loaded with water on one side. The targeted damage is local thickness thinning (e.g. corrosion pits) with a size of around a few millimeters. Chapter 3 further investigates and compares the guided wavefields between a plate surrounded by air and the same plate with one side partly exposed to water. The influence of the surrounding liquid medium on the guided wave propagation is demonstrated experimentally and numerically. Chapters 4 and 5 study two different nonlinear guided wave features, which are second harmonic generation and combination harmonic generation, respectively. The nonlinear guided wave features have better sensitivity to microstructural defects that precede the damage in the macroscale. The targeted damage in Chapters 4 and 5 is fatigue degradation in the early stage, where fatigue appears as multiple micro cracks and is distributed in the structural materials. The microstructural defects are too small to be detected by the linear guided wave feature. However, these small defects can distort the guided waves passing through the material, producing new wave components at frequencies other than the excitation frequency of the incident waves. This provides a way for the nonlinear guided wave technique to evaluate the earlystage damage in submerged structures.Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental & Mining Engineering, 202