Guided Wave Based Integrated Structural Health Monitoring and Nondestructive Evaluation

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

Multi-site Delamination Detection and Quantification in Composites through Guided Wave Based Global-local Sensing

Advanced composite materials are contributing to a revolution in aerospace applications. Rapid inspection techniques for detecting and quantifying damage in large composites are critical for ensuring operability and safety of composite structures. Moreover, in the development and manufacturing of next-generation composite materials, rapid inspection techniques are imperative for evaluating and certifying the materials. This paper presents a guided wave based global-local sensing method for rapid detection and quantification of delamination damage in large composite panels. The global-local approach uses a hybrid system consisting of a piezoelectric transducer (PZT) for generating guided waves and a non-contact scanning laser Doppler vibrometer (SLDV) for acquiring guided wave data. The global-local inspection is performed in two steps. First, a phased array configured of a small number of SLDV scan points (for example 10×10 points in a rectangular grid array) performs inspection over the entire plate to detect and locate damage (Figure 1a). Local areas are identified as potential damage regions for the second step. Then high density wavefield measurements are taken over the target damage areas and wavefield analysis is performed to quantitatively evaluate the damage (Figure 1b). For the proof of concept, the global-local approach is demonstrated on a carbon fiber reinforced polymer (CFRP) composite plate with two sites of impact-induced delamination damage. In the first step, the locations of two delamination sites are detected by the phased array method. In the second step, the delamination size and shape are evaluated through the wavefield analysis. The detected delamination location, size and shape agree well with those of ultrasonic C-scan

3D Guided Wave Motion Analysis on Laminated Composites

Ultrasonic guided waves have proved useful for structural health monitoring (SHM) and nondestructive evaluation (NDE) due to their ability to propagate long distances with less energy loss compared to bulk waves and due to their sensitivity to small defects in the structure. Analysis of actively transmitted ultrasonic signals has long been used to detect and assess damage. However, there remain many challenging tasks for guided wave based SHM due to the complexity involved with propagating guided waves, especially in the case of composite materials. The multimodal nature of the ultrasonic guided waves complicates the related damage analysis. This paper presents results from parallel 3D elastodynamic finite integration technique (EFIT) simulations used to acquire 3D wave motion in the subject laminated carbon fiber reinforced polymer composites. The acquired 3D wave motion is then analyzed by frequency-wavenumber analysis to study the wave propagation and interaction in the composite laminate. The frequency-wavenumber analysis enables the study of individual modes and visualization of mode conversion. Delamination damage has been incorporated into the EFIT model to generate "damaged" data. The potential for damage detection in laminated composites is discussed in the end