Reconstruction of Laser Ultrasonic Wavefield Images from Reduced Sparse Measurements Using Compressed Sensing Aided Super-resolution

Laser ultrasonic imaging is attractive for damage visualization because of its noncontact nature, sensitiveness to local damages, and high spatial resolution . However, its field application is limited as the scanning with high spatial resolution demands a long scanning time. Recently, compressed sensing (CS) and super-resolution are gaining popularity in the image recovery field. CS estimates unmeasured pixels from measured parts, and SR recovers high spatial frequency information from low resolution images. Inspired by these techniques, a laser ultrasonic wavefield reconstruction technique is developed so that damage can be located and visualized with reduced number of ultrasonic measurements. First, a low spatial resolution ultrasonic wavefield image for a given inspection region is reconstructed from reduced number of ultrasonic measurements using CS. Here, the ultrasonic waves are generated using a pulsed laser, and measured at a fixed sensing point using a laser Doppler vibrometer (LDV). Then, a high spatial resolution ultrasonic wave image is recovered from the reconstructed low spatial resolution image using SR. The number of measurement points required for ultrasonic wavefield imaging is dramatically reduced. The performance of the proposed technique is evaluated through a numerical simulation and an experiment performed on a cracked aluminum plate

Reconstruction of Laser Ultrasonic Wavefield Images from Reduced Sparse Measurements Using Compressed Sensing Aided Super-resolution

Laser ultrasonic imaging is attractive for damage visualization because of its noncontact nature, sensitiveness to local damages, and high spatial resolution . However, its field application is limited as the scanning with high spatial resolution demands a long scanning time. Recently, compressed sensing (CS) and super-resolution are gaining popularity in the image recovery field. CS estimates unmeasured pixels from measured parts, and SR recovers high spatial frequency information from low resolution images. Inspired by these techniques, a laser ultrasonic wavefield reconstruction technique is developed so that damage can be located and visualized with reduced number of ultrasonic measurements. First, a low spatial resolution ultrasonic wavefield image for a given inspection region is reconstructed from reduced number of ultrasonic measurements using CS. Here, the ultrasonic waves are generated using a pulsed laser, and measured at a fixed sensing point using a laser Doppler vibrometer (LDV). Then, a high spatial resolution ultrasonic wave image is recovered from the reconstructed low spatial resolution image using SR. The number of measurement points required for ultrasonic wavefield imaging is dramatically reduced. The performance of the proposed technique is evaluated through a numerical simulation and an experiment performed on a cracked aluminum plate.</p

Instantaneous Damage Identification and Localization through Sparse Laser Ultrasonic Scanning

International audienceThis study proposes an instantaneous damage identification and localization technique through sparse laser ultrasonic scanning. First, an inspection path is selected from an intended inspection region of a target structure. Then, ultrasonic waves are generated at one endpoint A of the path with a pulse laser and the corresponding ultrasonic responses are obtained at the other endpoint B with a laser Doppler vibrometer (LDV). Second, ultrasonic waves generated at point B are measured at point A reciprocally. Once two reciprocal ultrasonic signals are obtained, a damage index (DI) representing the violation of the linear reciprocity on the path is computed by comparing the reciprocal signals. DI will increase when the path passes through damage as this generates nonlinearity to the path. Third, the aforementioned steps are repeated for all predetermined inspection paths within the inspection region by scanning both pulse laser and LDV. Finally, the paths associated with high DI values are identified as damage regions. The effectiveness of the proposed sparse scanning technique is validated using an aluminium plate with a fatigue crack and a composite plate with an impact induced delamination

Damage Detection in Composites by Noncontact Laser Ultrasonic

International audienceThis study proposes an instantaneous damage localization technique for composite structures using noncontact laser ultrasonics. First, a velocity profile of the target composite structure is obtained by measuring wave velocities on paths with various directions. Second, laser ultrasonic responses from two excitation-sensing pairs, called inspection pairs, are obtained. Then possible damage locations are estimated through time-of-flight triangulation of damage reflected waves. Once possible damage locations are estimated, ultrasonic response collection is repeated near the estimated locations for precise damage localization. The proposed technique has following advantages over existing technique: (1) It does not require any sensor installation, (2) Wave velocity profile, which has been mandatory information for time-of-flight triangulation, can be easily experimentally constructed, and (3) It can localize damage with a high precision with its scanning capability. The feasibility of the proposed technique is examined by localizing a delamination in a real 10 kW wind turbine blade

Underground Object Classification for Urban Roads Using Instantaneous Phase Analysis of Ground-Penetrating Radar (GPR) Data

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

EphA2 Interacts with Tim-4 through Association between Its FN3 Domain and the IgV Domain of Tim-4

Tim-4 promotes the engulfment of apoptotic cells or exogenous particles by securing them on phagocytes. It is unable to transduce signals by itself but helps other engulfment receptors sense and internalize them. However, the identity of the engulfment receptors collaborating with Tim-4 is still incompletely understood. In this study, we searched for a candidate transmembrane protein with a FN3 domain, important for interaction with Tim-4, in silico and investigated whether it indeed interacts with Tim-4 and is involved in Tim-4-mediated phagocytosis. We found that EphA2 containing a FN3 domain in the extracellular region interacted with Tim-4, which was mediated by the IgV domain of Tim-4 and the FN3 domain of EphA2. Nevertheless, we found that EphA2 expression failed to alter Tim-4-mediated phagocytosis of apoptotic cells or polystyrene beads. Taken together, our findings suggest that EphA2, a new Tim-4 interacting protein, may intervene in a Tim-4-mediated cellular event even if it is not phagocytosis of endogenous or exogenous particles and vice versa

A Reference-Free and Non-Contact Method for Detecting and Imaging Damage in Adhesive-Bonded Structures Using Air-Coupled Ultrasonic Transducers

Adhesive bonded structures have been widely used in aerospace, automobile, and marine industries. Due to the complex nature of the failure mechanisms of bonded structures, cost-effective and reliable damage detection is crucial for these industries. Most of the common damage detection methods are not adequately sensitive to the presence of weakened bonding. This paper presents an experimental and analytical method for the in-situ detection of damage in adhesive-bonded structures. The method is fully non-contact, using air-coupled ultrasonic transducers (ACT) for ultrasonic wave generation and sensing. The uniqueness of the proposed method relies on accurate detection and localization of weakened bonding in complex adhesive bonded structures. The specimens tested in this study are parts of real-world structures with critical and complex damage types, provided by Hyundai Heavy Industries® and IKTS Fraunhofer®. Various transmitter and receiver configurations, including through transmission, pitch-catch scanning, and probe holder angles, were attempted, and the obtained results were analyzed. The method examines the time-of-flight of the ultrasonic waves over a target inspection area, and the spatial variation of the time-of-flight information was examined to visualize and locate damage. The proposed method works without relying on reference data obtained from the pristine condition of the target specimen. Aluminum bonded plates and triplex adhesive layers with debonding and weakened bonding were used to examine the effectiveness of the method

Dispersion Mechanism and Mechanical Properties of SiC Reinforcement in Aluminum Matrix Composite through Stir- and Die-Casting Processes

In this study, different volume fractions of silicon-carbide-reinforced AA2024 matrix composites were successfully fabricated using stir-casting (SC) and die-casting (DC) processes. The microstructural difference and physical properties of the composites during the manufacturing process were investigated in detail. The microstructural analysis found that the composite produced by the SC process had some reinforcement clusters and pores; however, defects and clusters significantly decreased after the DC process. In particular, the degree of reinforcement dispersion was quantitatively analyzed and compared before and after the DC process using the dispersion-analysis method. As a result of quantitative evaluation, the degree of dispersion was improved 2.5, 4.6, and 4.0 times with 3 vol.%, 6 vol.%, and 9 vol.% SiC-reinforced composite after the DC process, respectively. The electron backscatter diffraction (EBSD) analysis showed that the grain size of the 9 vol.% SiC-reinforced DC composite (17.67 &mu;m) was 75% smaller than that of the SC composite (68.06 &mu;m). The average tensile strength and hardness of the 9 vol.% SiC-reinforced DC composite were 2 times higher than those of the AA2024 matrix. The superior mechanical properties of the DC-processed composite can be attributed to the increase in dispersivity of the SiC particles and to decreases in defects and grain size during the DC process

Mechanical Properties and Epoxy Resin Infiltration Behavior of Carbon-Nanotube-Fiber-Based Single-Fiber Composites

Carbon nanotube fiber (CNTF), prepared by the direct-spinning method, has several nanopores, and the infiltration behavior of resins into these nanopores could influence the mechanical properties of CNTF-based composites. In this work, we investigated the infiltration behavior of resin into the nanopores of the CNTFs and mechanical properties of the CNTF-based single-fiber composites using six epoxy resins with varying viscosities. Epoxy resins can be easily infiltrated into the nanopores of the CNTF; however, pores appear when a resin with significantly high or low viscosity is used in the preparation process of the composites. All the composite fibers exhibit lower load-at-break value compared to as-densified CNTF, which is an unexpected phenomenon. It is speculated that the bundle structure of the CNTF can undergo changes due to the high affinity between the epoxy and CNTF. As composite fibers containing pores exhibit an even lower load-at-break value, the removal of pores by the defoaming process is essential to enhance the mechanical properties of the composite fibers

Mechanical and Thermal Neutron Absorbing Properties of B4C/Aluminum Alloy Composites Fabricated by Stir Casting and Hot Rolling Process

In this study, to fabricate neutron shielding material, boron carbide (B4C)-reinforced aluminum (Al) alloy composites were successfully fabricated by stir casting followed by a hot rolling process. Microstructural analysis of B4C/Al6061 composites with different volume fractions (5, 10, 20, 25, and 30%) revealed that the composites had volume ratios similar to the target volume ratios of B4C. Furthermore, B4C reinforcements were uniformly dispersed in the Al matrix, forming multi-interfacial layers of Al4C3/(Ti,Cr)B2. The interfacial layer generated during stir casting maintained its own structure after the hot rolling process, indicating strong interfacial bonding strength. The tensile strengths of the B4C/Al6061 composites increased to 20 vol.% and stayed above the value for Al6061, even reaching 30 vol.%. The measured thermal neutron shielding rate increased with increasing B4C content, and the highest thermal neutron shielding rate was observed at 30 vol.% composite, which corresponds to 95.6% neutron shielding at 0.158-cm thickness