Different Kinds Of Defects Research Articles

Studying the applicability of non-destructive techniques in diagnosing defects of soil-cement columns

This article studies the applicability of the Non-Destructive Techniques (NDT) into semi-rigid structures, particularly in soil-cement columns. A numerical model for the semi-rigid soil-cement column is first created. Different kinds of defects are intentionally allocated in the model, including necking, bulging, and degraded stiffness. The assumption is that by using an excitation as an impact load at the structure head and then letting the structure vibrating freely, studying the wave characteristics inside the structure, i.e., responsive velocity and displacement at various points along the column shaft, the impedance could be determined. If there is any variation in the mechanical impedance Z, which is defined to be the product of mass density, area of the cross-section, and the wave velocity, the defects are confirmed. The shape of the impedance curves with respect to combined defects is analyzed, and spectral response curves are plotted. The process of analysis in the time domain and frequency domain for the soil-cement column is conducted using Fast Fourier Transformation. The theoretical and computed impedance of the structure from the numerical model will be compared with each other, in the shape of the responsive curves, and the distinguished issues; some discussions on the propagation of waves through semi-rigid structures are summarized. There is no distinguishing feature in the characteristics of the impedance of the structure revealed. It comes to the conclusion that the applicability of the vibration test is not clearly recognized. There is quite a difficulty in evaluating the performance of the semi-rigid structures like soil-cement columns by using vibration or impact load test. This outcome suggests that the column is not the same as the pile, and another alternative and/or approach is recommended to apply in quality assurance/control QA/QC for such embedded semi-rigid structures.

ZnO Nanoparticles with Controllable Ce Content for Efficient Photocatalytic Degradation of MB Synthesized by the Polyol Method

This paper reports on the synthesis of Ce-doped ZnO (CZO) nanoparticles (NPs) by an alternative polyol method at low temperature. The method, facile and rapid, uses acetate-based precursors, ethylene glycol as solvent, and polyvinylpyrrolidone as capping agent. The effects of the Ce-doping concentration (ranging from 0 to 8.24 atomic%) on the structural, morphological, compositional, optical, luminescence, and photocatalytic properties of the NPs were investigated by several techniques. The structural findings confirmed that the CZO NPs have a typical hexagonal wurtzite-type structure with a preferred orientation along the (101) plane. The results obtained by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) revealed that the NPs size decreased (from ~30 to ~16 nm) with an increase in the Ce-doping concentration. Energy Dispersive X-Ray Spectroscopy (EDS) and High Resolution Transmission Microscopy (HRTEM) results confirmed the incorporation of Ce ions into the ZnO lattice. Ce-doping influences the photoluminescence (PL) emission compared to that of pure ZnO. The PL emission is related to the presence of different kinds of defects, which could take part in charge transfer and/or trapping mechanisms, hence playing an essential role in the photocatalytic activity (PCA). In fact, in this work we report an enhancement of PCA as a consequence of Ce-doping. In this sense, the best results were obtained for samples doped with 3.24 atomic%, that exhibited a photocatalytic degradation efficiency close to 99% after 60 min ultraviolet (UV) illumination, thus confirming the viability of Ce-doping for environmental applications.

Inspection of Defects in Weld Using Differential Array ECT Probe and Deep Learning Algorithm

Inspection of defects in weld has both safety and economic significance in industries. However, it is still a challenging problem to be studied due to the interference of the uneven surface of the weld and nonuniformity of the material. This article proposes a new flexible eddy current testing (ECT) probe with differential multimodes for weld inspection. The probe is constructed based on a flexible printed circuit board (PCB). Consequently, it can be bended according to the uneven surface of a weld sample. The differences of pairs of coils are recoded as the outputs of the probe, in which the common mode noises and background signals are canceled. Considering the different orientations of the differential pair coils, the probe has four modes. Different modes complement each other in terms of sensitivity to different kinds of defects. The effect of the excitation frequency has been studied, and 1 MHz is chosen as the operating frequency of the probe. An image preprocessing algorithm called spatial domain filtering and gradient feature edge extraction (SDF-GFEE) is proposed for suppressing the noise of the experimental images. A target detection algorithm based on deep neural network named mask region convolution neutral network (Mask-RCNN) is utilized to identify defects from the images. Experimental results demonstrate that this method is capable of identifying the groove defect with dimensions 3 mm (length) ×0.1 mm (width) ×0.5 mm (depth) and flat bottom hole with dimensions Φ0.8 mm ×0.5 mm in a weld sample.

Failure Mode Analysis of Carbon Fiber Composite Laminates by Acoustic Emission Signals

Composite laminates have complex failure modes. In order to investigate the evolution of failure in the composite laminates, this paper performed an experimental study on four laminates with different layups using acoustic emission (AE) technique. Two different kinds of defects are imposed on the laminates, including a hole and a crack in the center. Tensile and bending tests are performed on the defective laminates and real‐time AE signals are collected. By analyzing the spectrograms of the obtained AE signals and integrating with the dispersion curves, the evolution of failure modes for different laminates can be observed. The tests show that the defects cause multiple failure modes, which change gradually during the experiments. It is also revealed that laminates with different layups have different failure modes. More specifically, the stacking order of different plies has a greater impact on the occurrence of delamination and fiber fracture than matrix crack. The tentative research shows that there is great potential for improving the performance of the composite laminates by careful selection of ply layups.

Effect of Cracks on the Natural Frequency of Cylindrical Shell Structures

Shell structures are liable to different kinds of defects and damage like cracking and corrosion which may destroy their structural safety and affect the service life. The cracks' effects are significant considerations in the design of cylindrical shell structures as they influence the vibration characteristics and safety. This present work is an experimental study on the free vibration analysis of a cylindrical shell involving circumferential surface crack. The influence of the ratio of shell’s radius to a shell’s thickness (R/h)of the shell structure, crack length in the shell, crack depth in the shell, crack location of the shell, and crack orientation in the shell are investigated under a clamped - clamped and simply supported boundary conditions at each end in the shell. Results showed that the minimum impact of the crack is at the angle of crack 75, and the circumferential fissure has more effect than a longitudinal fissure, In addition to this, under SS-SS, C-C the natural frequency will decrease if the fissure is located in the middle of the shell is greater than other locations. but when crack animated across in the ends of the limits the decrease in the natural frequency under C-C only. Results were compared with the literature there was a close agreement.

A visual attention system based anisotropic diffusion method for an effective textile defect detection

Recently, saliency maps are widely used as an image feature to improve results of segmentation or classification of defects. In this paper we tackle the problem of defect detection in fabric images. We propose a defect extraction method in textile images based on a modified anisotropic diffusion filter combined with a saliency image feature. The classical anisotropic diffusion models consider only the image gradient information of a diffused pixel. Consequently, they cannot identify defect edges confused with background texture. Since the defects in the neighborhood of the image generally have larger saliency intensity value than the background, the proposed diffusion model incorporates both local gradient magnitude and a modified saliency map. The aim is to preserve defect edges while effectively removing the textured background. Moreover a new diffusion function is proposed that permits to carry on adaptively a smoothing in faultless regions and a sharpening process at defect boundaries. To confirm the effectiveness of our algorithm, we compare tests and results with different methods on textile images including different kinds of defects and fabrics. Results show that our method outperforms the other considered algorithms and can accurately extracts defects.

Defect-Mediated Piezoelectricity in Boron Nitride Nanotube

Introduction A zigzag boron nitride nanotube (ZBNNT) has a large intrinsic polarized dipole and a piezoelectric tunability with crystal chirality, nanotube diameter, and point defect. The piezoelectric coefficients (e33) of 8-ZBNNT with the VIA-group defects of SN and SeN are estimated to be 18.7×10-2 C/m2 and 14.9×10-2 C/m2, respectively. The coefficients of defect-mediated 8-ZBNNT are 97% and 57% bigger than that of pristine 8-ZBNNT. The elastic modulus of 8-ZBNNT is decreased due to the VIA-group defects, but is increased for the larger number of unit cells along zigzag rolling direction. The electronic band gap of 8-ZBNNT is reduced due to the VIA-group defects. The large piezoelectricity enhancement of 8-ZBNNT with VIA-group defect is attributable to the enhanced piezoelectricity from ionic contribution. Therefore, the unprecedented defect-mediated 8-ZBNNT provides a new material platform of mechanoelectronic devices for nanoscale sensors and energy conversions. Modeling and methodology Figure 1 shows the schematic of a single wall 8-ZBNNT with an atomic defect. The supercell is in a simple orthorhombic box with periodic boundary condition in 30 Å × 30 Å × Lc where Lc is the lattice parameter along the transport direction. The green atom “A” indicates the defect of a single substitution atom per a supercell. The average bond length is defined as the average length of atomic bond between the defect doping atom and the neighboring boron atoms. The first principle calculations were carried out by using the Virtual Nanolab Atomistix ToolKit (ATK) package with the density functional theory (DFT). The localized density approximation (LDA) exchange correlation with a double zeta polarized (DZP) basis was used with a mesh cut-off energy of 150 Ry. All atomic positions and lattice parameters were optimized by using the generalized gradient approximations (GGA) with the maximum Hellmann Feynman forces of 0.05 eV/Å, which was sufficient to obtain relaxed structures. The maximum number of fully self-consistent field (SCF) iteration steps was set to 100. Defect-mediated piezoelectricity The table I includes the piezoelectric coefficient (e33) and average bond length (a0) of 10- and 8-ZBNNT with different kinds of defects including SW deformation, IVA-group, and VIA-group defects within one supercell. Among the defects in ZBNNT, a single nitrogen vacancy or SW defect diminishes the piezoelectric coefficient (e33) of 10- and 8-ZBNNT. However, the atomic defects of IVA- and VIA-group elements in a nitrogen site enhance the piezoelectric coefficient. The piezoelectric coefficient of VIA-group defect is higher than that of IVA-group defect. The piezoelectric coefficient e33 of chalcogen defect SN and SeN in 8-ZBNNT is enhanced 97% and 57% from 9.49×10-2 C/m2 to 18.7×10-2 C/m2 and 14.9×10-2 C/m2, respectively, compared to that of pristine 8-ZBNNT. The table I includes the elastic modulus of pristine10-ZBNNT and 8-ZBNNT and the ZBNNT with defects. The elastic modulus of 10- and 8-ZBNNT with defects is smaller than that of pristine 10- and 8-ZBNNT. The elastic modulus of SW defects in ZBNNT is increased compared to that of pristine 10- and 8-ZBNNT. The structure with smaller elastic modulus has the larger strain response to the constant external stress. Therefore, the ZBNNT with IVA- and VIA-group atomic defects has an efficient response to the external stress for piezoelectric applications. 8-ZBNNT of SN and SeN with the smaller elastic modulus have the larger e33 compared to the structure with ON. Defect-mediated electronic band structure Figure 2 shows the electronic band structure of 8-ZBNNT with (a) pristine structure and (b) defects of ON, SN and SeN. The group VIA-group defects in 8-ZBNNT are n-type doping because the Fermi level is located in the conduction band while the VIA-group defects in 8-ZBNNT are p-type doping. The bandgap in 8-ZBNNT is also reduced from 3.37 eV to 3.16 eV, 3.12 eV and 3.20 eV for the VIA-group defect of ON, SN and SeN, respectively. However, the band gaps of 8-ZBNNT with the IVA-group defects of CN, SiN and GeN is slightly widened to 3.38 eV, 3.49 eV and 3.50 eV compared to the band gap 3.37 eV of pristine 8-ZBNNT, respectively. Conclusions The piezoelectricity of ZBNNT is significantly enhanced by atomic defects. The piezoelectric coefficients (e33) 8-ZBNNT with SN and SeN defects are increased up to 97% and 57%, respectively. The electronic band gap of 8-ZBNNT with defects is reduced. The large piezoelectricity enhancement of 8-ZBNNT with VIA-group defect is attributable to the enhanced piezoelectricity from ionic contribution. Therefore, the unprecedented defect-mediated 8-ZBNNT provides a new material platform of mechanoelectronic devices for nanoscale sensors and energy conversions. Acknowledges This work is supported by ARO W911NF-15-1-0535, NSF HRD-1137747, and NASA NNX15AQ03A. Figure 1

Laser ultrasonic imaging of wavefield spatial gradients for damage detection

This article describes a new damage visualization method to investigate and analyze propagating guided Lamb waves using analyses of wavefield spatial gradients. A laser ultrasonic interrogation system was used to create full-field ultrasonic data measurements for ultrasonic wavefield imaging. The laser scanning process was performed based on both a raster scan and a circle scan. From the high-resolution wavefield data, a spatial gradient–based image processing technique was developed using gradient vectors to extract features sensitive to defects. Local impedance changes at the damaged area would result in a local distortion of the waveform which was captured and quantified by the variation of the gradient vectors in the scanning area as time evolves. Such variation was accumulated over time with a statistical threshold filter to generate a gradient-orientation map for damage visualization. The proposed algorithm was capable of producing distinctive damage patterns when tested experimentally on a 3-mm aluminum plate with multiple simultaneous simulated defects. Compared to conventional techniques like local wavenumber estimation, the generation of the accumulated orientation map involves no filtering process in the frequency or wavenumber domain, at the expense of more accurate shaping of the defect. A spatial covariance analysis was adopted to locate damage from the results as well as to evaluate the correlation between different kinds of defects. Combining the proposed approach with conventional laser ultrasonic imaging techniques enables a fast and robust damage identification and characterization process which requires lower computational burden and practical operation.

Defect originated photoluminescence tuning of silica nanoparticles prepared by electron beam irradiation and their applications

Considering the imminent importance of Silica (SiO2) nanoparticles (NPs), a highly rapid and one-pot scalable approach is being reported for their preparation. Electron-beam was used to derive the formation of SiO2 NPs, while in situ functionalization was carried out by α-Cyclodextrin (α-CD). XRD pattern of as prepared α-CD functionalized SiO2 NPs (i.e., α-CD@SiO2 NPs) revealed their amorphous nature, while imaging studies showed self-assembling of NPs into a porous structure. UV–visible absorption spectra showed multiple peaks at 233, 323, 390 and 455 nm, which signifies the presence of different kind of defects in the as prepared NPs. An interesting aspect of this work is tuning of the photoluminescent properties of NPs from blue to green by simply varying the absorbed dose. This could be attributed to the formation of a particular kind of ‘defects’ at a proportionate absorbed dose. These ‘defects’ act as emission centers (ECs) and were analysed through steady state and time-resolved emission studies. Notably, α-CD played significant role in influencing the composition of the NPs, whilst enhancing their colloidal stability and quantum yield. The prospective applications of α-CD@SiO2 NPs were explored in latent fingerprinting and thermosensing.

A theoretical scenario for the mechanical failure of boron carbide nanotubes

Although the volume of research on carbon nanotubes (CNTs) has increased over a short period, less attention has been paid to other types of carbon-based nano-objects such as boron carbide (BC3) nanotubes (BC3NTs). In the present article, we modeled BC3NTs using molecular dynamics (MD) simulation to investigate the effects of chirality, wall number, diameter and temperature on the mechanical failure of BC3NTs, BC3 nanobuds and BC3NTs with different kinds of defects. In addition, we modeled the corresponding CNTs to validate the results and understand how the replacement of a quarter of the carbon atoms in the CNT by boron atoms affects the properties of the newly formed nanotube. The results showed that the variation of mechanical properties as a function of diameter and temperature was rather limited, regardless of chirality. The Young’s modulus, failure stress and failure strain of the zigzag single-walled BC3NTs (SWBC3NTs) were lower than the armchair ones, and were lower than those of the corresponding CNTs too. Furthermore, adding a second and third wall to the SWBC3NTs significantly improved their mechanical properties. Finally, we modeled BC3 nanobuds with 1 to 4 C60 attached to the surface of SWBC3NTs and observed that the properties decreased as the number of fullerenes increased. Moreover, considering defective SWBC3NTs revealed that two-atom vacancies and Stone-Wales defects resulted in the highest and lowest reduction of mechanical properties, respectively.

Vibration mechanism analysis for cylindrical roller bearings with single/multi defects and compound faults

The generation of defects has a great influence on the vibration characteristic of roller bearings. Thus, it is very important to analyze the vibration mechanism of bearings with different kinds of defects by dynamic models which can make systematic descriptions of truly dynamic behavior. In this paper, dynamic models are developed based on the model proposed by Gupta to investigate the vibration mechanism of cylindrical roller bearings with localized defects. The inner raceway and rollers have five degrees of freedom (DOFs) in the model to better describe the complex dynamic behavior of bearings. Gyroscopic moment, centrifugal force and lubrication traction/slip between roller/raceway, roller/cage, cage/raceway are completely included. Moreover, modeling methods of single defect, multi-defects and compound faults are introduced with the consideration of additional deflection and the change of contact force direction caused by defects. The differential equations used to describe the motions of bearing components are solved by the fourth order Runge-Kutta-Fehlberg scheme with step-changing criterion. Vibration responses of bearings with single defect, multi-defects and compound faults are simulated by the models and analyzed in both time domain and frequency domain. Experiments have been carried out on bearing test rig. The validity of models built in the paper is proved by comparing the simulation results with experiments. In addition, fruitful vibration responses are discovered and proposed, which will provide strong theoretical supports for fault diagnosis of cylindrical roller bearings.

Intrinsic anisotropy and pinning anisotropy in nanostructured YBa2Cu3O7−δ from microwave measurements

Anisotropy is an intrinsic factor that dictates the magnetic properties of YBa2Cu3O7−δ and therefore has a great impact on many applications. Artificial pinning centres are often introduced in an attempt to mitigate its effect, resulting in less anisotropic electrical and magnetic properties. However, the nanoengineering of superconductors makes the quantification of the anisotropy itself uncertain: the intrinsic anisotropy due to the layered structure, quantified by the anisotropy factor γ, mixes with the additional anisotropy due to pinning. As a consequence, there is no consensus on the experimental anisotropy factor γ that can result in YBa2Cu3O7−δ when directional (twin planes, nanorods) or isotropic defects are present. We present measurements of the magnetic field and angular dependent surface impedance in very different nanostructured YBa2Cu3O7−δ films, grown by a chemical route and by pulsed laser deposition with different kind of defects (nanorods, twin planes, nanoparticles). We show that the surface impedance measurements are able to disentangle the intrinsic anisotropy from the directional pinning anisotropy, thanks to the possibility of extracting the true anisotropic flux–flow resistivity and by correctly exploiting the angular scaling. We find in all films that the intrinsic anisotropy γ = 5.3 ± 0.7. By contrast, the pinning anisotropy determines a much more complex, feature–rich and nonuniversal, sample–dependent angular landscape.

Luminescence and dosimetric characteristics of nanocrystalline Al2O3:C synthesized by thermal plasma reactor

Nanocrystalline Al2O3:C has been synthesized by thermal plasma method. The sample was annealed at 1300 °C in air and vacuum. XRD studies show phase change from γ-Al2O3:C to α-Al2O3:C. Average particle sizes estimated from XRD peaks and TEM images show increase in the particle size from ~30 nm to ~ 67 nm. The UV–visible spectrum of the as-synthesized Al2O3:C shows absorption peaks at 209 and 255 nm confirming the formation of F and F+ centers. XPS analysis reveals that the concentration of carbon impurity remains intact in Al2O3 lattice. The TL glow curves were fitted by CGCD method. The glow curve of as-synthesized Al2O3:C found to have six peaks and that of annealed sample have four peaks. The changes in the glow curve structures of the as-synthesized and annealed phosphor may be attributed to the phase change of the crystal structure and/or different kinds of defects formed on annealing in air/vacuum.

Recording and interpreting enamel hypoplasia in samples from archaeological and palaeoanthropological contexts

Enamel hypoplasia is often split into several macroscopic categories, including pit, localised, linear and plane-form defects. All types have been considered a sign of ‘non-specific stress’ during dental development in archaeological, as well as palaeoanthropological and other samples. There is growing evidence suggesting many defects may not be caused by illness or malnutrition during childhood, instead relating to trauma to the developing tooth, genetic conditions or specific environmental factors, i.e., may not be associated with ‘stress’ to the individual. In this study all types of macroscopic enamel hypoplasia were recorded, including pitting, linear, plane and localised type defects, in two extant great ape species and three fossil hominin species. The aim is to compare the characteristics and prevalence of different types of enamel hypoplasia among species and discuss potential differences in aetiology. The results show that samples have diverse prevalence's of different kinds of defects, and pitting, linear and localised defects likely have different aetiologies. Additionally, dental characteristics (e.g., tooth morphology, developmental timing/speed and enamel structure) heavily influence the likelihood of specific types of enamel hypoplasia forming. In sum, studies that include only one type of enamel hypoplasia, or focus on one tooth type, to generate a ‘stress’ rating for a sample may miss relevant information when comparing groups. Instead, it may be beneficial to record different types of defects separately, for all teeth, and then consider how genetic, environmental and tooth property factors may influence sample differences.

Novel array ECT probe with three-phase excitation for steam generator tube inspection

Eddy current testing (ECT) is commonly used in steam generator tube inspection. Among multiple probes applied in this area, array probe shows the merit of the capability of obtaining a C-scan image in a simple linear scan. In this work, a novel array ECT probe with three-phase excitation is proposed. The probe consists of two rows of excitation coils and a row of pickup coils. The induced eddy current shifts electrically in the testing sample so that the necessity of multiplexer is eliminated, resulting in advantages of lower cost, less noise and faster inspection speed. Theoretical analysis indicates that the background signal of the array sensor would be small. A 3D finite element method (FEM) model is developed to study the operating principle and to predict the inspection performance of the probe. A prototype probe has been developed and tested, by which a steam generator tube sample with different kinds of defects was inspected. The experiment results validate the simulation model and further demonstrate the feasibility of the sensor.

A New System for Steam Boiler Tubes Using Artificial Neural Network

A major inspection challenge facing the boiler industries is to satisfy the welds in tubing and plate during the manufacturing, erection and commissioning stages. During commercial operation the plant boiler tubes that leaks due to downtime. As the main part of the boiler, the water wall tube which runs on dangerous environment may lead to serious boiler accidents, causing of the tubes failure. For this reason, inspecting the defects on the steam boiler tube comprehensively is extremely required. However, single traditional NDT inspection method is limited .In terms of the ability of identifying different kinds of defects. In order to meet the requirement of fullscale inspection, in this paper, a new system foe steam boiler tubes are experimented. After experiment, the new system can effectively measure the remaining wall thickness and identify different kinds of defects including pinholes and circumferential cracks with the sensor being moved outside the tubes using artificial neural networks.

Dislocation Damping and Defect Friction Damping in Magnesium: Molecular Dynamics Study

In this study, the molecular dynamics method was used to study the damping mechanism in Mg alloys at the atomic scale. The energy dissipated by the nucleation and motion of dislocations and by defects friction, and the effect of defects, such as vacancies, cracks, and grain boundaries, on them were studied. The study shows that different kinds of defect have different effects on the dislocation damping and defect friction damping. And then, the effect of strain amplitude and temperature on damping capacity of Mg was studied. The result shows that the amplitude independent damping is caused by defect friction and the amplitude dependent damping is mainly caused by the nucleation and motion of dislocation; the damping of Mg increased exponentially with the temperature, and the damping peck appeared at 440 K is attributed to the appearance of dislocations at the grain boundaries which may be caused by boundaries self-diffusion.

Monitoring of properties of epoxy molding compounds used in electronics for protection and hermetic sealing of microcircuits

It is known that epoxy molding compounds have a significant impact on productivity, service life and reliability of electronic microcircuit components. Wrong choice of a molding mixture can lead to mechanical stresses, deformation, cracking or lamination of the protective packaging followed by microcircuit breakage. The study summarizes information on composition, main operating characteristics and application methods of epoxy molding compounds as well as their impact on microcircuit shape distortion. Main methods for control of physical and mechanical properties of epoxy molding compounds with the most significant impact on microcircuit hermetic sealing and on formation of different kinds of defects in the protective packing.

Progress on the ultrasonic testing and laser thermography techniques for NDT of tokamak plasma-facing components

ABSTRACT During manufacturing and operation, different kinds of defects, e.g., delamination or surface cracks, may be generated in the plasma-facing components (PFCs) of a Tokamak device. To ensure the safety of the PFCs, various kinds of nondestructive testing (NDT) techniques are needed for different defect and failure mode. This paper gives a review of the recently developed ultrasonic testing (UT) and laser thermography methods for inspection of the delamination and surface cracks in PFCs. For monoblock W/Cu PFCs of divertor, the bonding quality at both W-Cu and Cu-CuCrZr interfaces was qualified by using UT with a focus probe during manufacturing. A noncontact, coupling-free and flexible ultrasonic scanning testing system with use of an electromagnetic acoustic transducer and a robotic inspection manipulator was introduced then for the in-vessel inspection of delamination defect in first wall (FW). A laser infrared thermography testing method is highlighted for the on-line inspection of delamination defect in FW through the vacuum vessel window of the Tokamak reactor. Finally, a new laser spot thermography method using laser spot array source was described for the online inspection of the surface cracks in FW.

Molecular dynamics simulation on the buckling of single-layer MoS2 sheet with defects under uniaxial compression

The buckling behavior of a single layer MoS2 (SLMoS2) sheet with defects under uniaxial compression is investigated with molecular simulation in the present paper. Five typical defects are introduced to estimate the instability characteristics of defective MoS2 sheet. The buckling responses, including the critical strain and geometric morphology, influenced by defect type, stain rate, defect density and so on, are comprehensively explored. It is found that different type of defects results in reduction of the bending modulus to some different extent. Compared with the other three post-buckling morphologies, the first typical geometric morphology show the biggest difference between the defect-free and defective SLMoS2 sheets. It seems possible to realize our desired morphology in flexible electronics by proper preparing different kinds of defects. The finding in the present paper should be useful for the promising design of flexible optoelectronic devices and soft bioelectronics.