Ground-penetrating radar (GPR) has been widely used to detect subsurface objects, such as hidden cavities, buried pipes, and manholes, owing to its noncontact sensing, rapid scanning, and deeply penetrating remote-sensing capabilities. Currently, GPR data interpretation depends heavily on the experience of well-trained experts because different types of underground objects often generate similar GPR reflection features. Moreover, reflection visualizations that were obtained from field GPR data for urban roads are often weak and noisy. This study proposes a novel instantaneous phase analysis technique to address these issues. The proposed technique aims to enhance the visibility of underground objects and provide objective criteria for GPR data interpretation so that the objects can be automatically classified without expert intervention. The feasibility of the proposed technique is validated both numerically and experimentally. The field test utilizes rarely available GPR data for urban roads in Seoul, South Korea and demonstrates that the technique allows for successful visualization and classification of three different types of underground objects.

The tensile behavior of Nicalon fiber-reinforced silicon carbide matrix composites (Nicalon/SiC) was investigated with the aid of nondestructive evaluation (NDE) techniques. The NDE techniques include ultrasonic testing (UT), X-ray computed tomography (CT), and infrared (IR) thermography. Before mechanical testing, UT C-scans were developed to investigate defect distributions and to detect variations in the internal flaws. X-ray CT was used to characterize the type of defects and the location of flaws in composites to compare with UT C-scan results. The IR thermography was employed to monitor temperature evolution during tensile testing. This article also investigated the feasibility of using multiple NDE techniques as a means of assessing integrity for Nicalon/SiC composites. Microstructural characterization was performed using scanning electron microscopy (SEM) to investigate failure mechanisms of Nicalon/SiC composites, and the results were compared with NDE data.

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High-cycle fatigue behavior of Nicalon™ fiber-reinforced calcium aluminosilicate (CAS) glass–ceramic matrix composites (Nicalon™/CAS) was investigated with the aid of a nondestructive evaluation (NDE) technique. Infrared (IR) thermography was employed to study two different types of Nicalon™/CAS composites: crossply and unidirectional specimens. During fatigue testing, an IR camera was used for in-situ monitoring of temperature evolution of Nicalon™/CAS samples. Stress versus cycles to failure curves were generated for predicting the lifetime of Nicalon™/CAS composites, and the IR camera measured the temperature changes during high-cycle fatigue testing. Microstructural characterizations using scanning electron microscopy (SEM) were performed to investigate fracture modes and failure mechanisms of Nicalon™/CAS samples. In this study, the NDE technique and SEM characterization were used to facilitate a better understanding of damage evolution and progress of Nicalon™/CAS composites during high-cycle fatigue.

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