Adhesively bonded composites have been widely used in aerospace engineering, renewable energies, and automotive industries. However, the potential weak bonding of the composite structures, which exhibits a low cohesion interface between the adhesive and the composite substrate, greatly threatens the reliability of these structures. The occurrence of weak bonding has yet to be well understood and has posed new challenges for the evaluation of weak bonding in composite structures. Ultrasonic Lamb waves have been shown useful for nondestructive evaluation (NDE) due to their ability to propagate a long distance with less energy loss and their sensitivity to small defects. Among various ultrasonic transducers, air-coupled transducers (ACT) eliminate the need for couplant/adhesive and provide a noncontact actuation method. In this study, a hybrid noncontact system was constructed using an ACT for actuation and a scanning laser Doppler vibrometer (SLDV) for sensing. The ACT provided a narrowband wave actuation, while SLDV provided high-quality wavefield signals for damage detection and evaluation. An adhesively bonded composite structure containing good and weak bond quality areas was manufactured using simulated contamination. Then the composite bond quality inspection was conducted using the ACT-SLDV system. To validate the ACT Lamb wave inspection, a second noncontact inspection by a pulsed laser-SLDV method was carried out.
Nuclear dry cask storage systems are being used for extended periods of time. Structural health monitoring of these casks has grown out of concern that the radioactive waste could jeopardize the casks’ structural health as time progresses. Ultrasonic guided waves offer a potential solution for monitoring the nuclear casks structural health without opening the containers. This paper explores sensing techniques on small-scale mockup and full scale dry cask storage systems. Methods include acoustic emission (AE) as well as active sensing. Results showed accuracies in localizations, differences in sensing techniques, structural responses, and the capabilities of ultrasonic guided waves in dry cask storage systems.
TN32 casks are multi-layer cylindrical structures used for storage of nuclear spent fuel. The National Center for Physical Acoustics at the University of Mississippi has manufactured a scaled down model of the TN32 cask. To identify the most relevant nondestructive evaluation parameters, which will be useful while doing experiments on real TN32 casks, a series of experiments have been conducted on TN32 cask model. This paper discusses the data analysis of the experiments conducted on the cask model and the conclusions based on those experiments. Elastodynamic waves are generated in the cask model by pencil lead break and hammer hit excitation and the waves in the cask at certain locations are sensed using piezoelectric wafer active sensors (PWAS). The waveforms and frequency spectrums of waveforms arriving at PWAS are studied. There are two types of joints on the cask model: structures joined using adhesives and structures joined using press fit. The effects of various joints in the structure on elastodynamic wave propagation are also studied. Pitch catch experiments on the cask was also done using in plane excitation using PWAS. The most sensitive frequency for the cask model was identified from the frequency response spectrum obtained from a wide band chirp excitation. The influence of various joints on the frequency response spectrum is also studied. Analytical modeling of cask geometry for a given excitation is done using Normal Mode Expansion (NME) technique. Prediction of wave propagation through the scaled down model is done based on the theoretical expression derived.
In US, there are over 1482 dry cask storage system (DCSS) in use storing 57,807 fuel assemblies. Monitoring is necessary to determine and predict the degradation state of the systems and structures. Therefore, nondestructive monitoring is in urgent need and must be integrated into the fuel cycle to quantify the “state of health” for the safe operation of nuclear power plants (NPP) and radioactive waste storage systems (RWSS). Innovative approaches are desired to evaluate the degradation and damage of used fuel containers under extended storage. Structural health monitoring (SHM) is an emerging technology that uses in-situ sensory system to perform rapid nondestructive detection of structural damage as well as long-term integrity monitoring. It has been extensively studied in aerospace engineering over the past two decades. This paper presents the development of a SHM and damage detection methodology based on piezoelectric sensors technologies for steel canisters in nuclear dry cask storage system. Durability and survivability of piezoelectric sensors under temperature influence are first investigated in this work by evaluating sensor capacitance and electromechanical admittance. Toward damage detection, the PES are configured in pitch catch setup to transmit and receive guided waves in plate-like structures. When the inspected structure has damage such as a surface defect, the incident guided waves will be reflected or scattered resulting in changes in the wave measurements. Sparse array algorithm is developed and implemented using multiple sensors to image the structure. The sparse array algorithm is also evaluated at elevated temperature.
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