Gap Defect Research Articles

Axial loading mechanism analyses and evaluation methods of CCFT short columns with gap defects

The gap defect has proved to be a common quality issue in concrete-filled tubular (CFT) structures, which offers distinct unfavourable effects on their mechanics properties. To determine out the guidelines of gap defect affecting the axial loading performance of circular CFT (CCFT) short columns, this paper develops an array of refined numerical models of the axially-compressed CCFT short columns with spherical-cap gaps (CCFT-SG) and circumferential gaps (CCFT-CG), whose accuracy is verified by existing experiments. The typical axial force versus longitudinal displacement (N-Δ) curves, the contact stress, the longitudinal stress distribution and the failure modes are respectively given focus to reveal the intrinsic axial loading mechanism of the CCFT short columns, taking the existence of the gap defect into consideration. Based on these analyses, various design methods using confinement regionalization and circumferential expansion thoughts are proposed and adopted to evaluate the load bearing capacities of the axially-compressed CCFT-SG and CCFT-CG short columns. The results declare that the appearance of the gap defects dramatically weakens or delays the contact behaviour between the infilled concrete and the hollow tube, which accelerates the local bulging of the tube, reduces the longitudinal stress of the core concrete, and therefore the axial resistance of the CCFT short column is distinctly influenced. The design approaches delivered in this paper can assess the axial resistances of the CCFT short columns with gap defects accurately according to the test validation. The research may provide a theoretical basis and a reliable way for evaluating and treating the actual CFT structures with gap defects.

Thermal evaporation–deposited hexagonal CdS buffer layer with improved quality, enlarged band gap, and reduced band gap offset to boost performance of Sb2(S,Se)3 solar cells

Chemical bath–deposited cadmium sulfide (CBD-CdS) is the most widely used buffer layer material for antimony selenosulfide (Sb2(S,Se)3) photovoltaic devices, but its medium band gap, large band gap offset with transparent conducting oxides, and surface defects must be addressed to improve its applicability. Hexagonal CdS films (60 nm thick) prepared using the thermal evaporation method were used as the buffer layers of Sb2(S,Se)3 photovoltaic devices. Compared with CBD-CdS (60 nm thick), thermal evaporation–deposited CdS (TED-CdS) films have a larger band gap and fewer surface defects. The Sb2(S,Se)3 film deposited on TED-CdS is more compact, and its 1D ribbons are stacked more vertically to the substrate. The band gap offset between CdS and fluorine-doped tin oxide glass decreases from 0.76 eV (CBD-CdS) to 0.60 eV (TED-CdS). Therefore, suppressed electron trap density and charge recombination, as well as improved light harvesting, are achieved. By replacing CBD-CdS with TED-CdS, the best device efficiency increases from 6.14 % to 7.16 %, with the open circuit voltage, short-circuit current density, and fill factor increasing from 0.660 V, 15.96 mA/cm2, and 58.37 % to 0.664 V, 17.39 mA/cm2, and 62.85 %, respectively. The device stability and reproducibility are also improved.

Solidification Dynamics of Silicone Oil and Electric Field Distribution Within Outdoor Cable Terminations Subjected to Cold Environments

Outdoor oil-filled cable terminations play an important role in power transmission and distribution networks, but their frequent explosions and disintegration accidents in cold environments pose great risks to the stable operation of power systems. In this study, an electric field-temperature multi-physical field simulation model was built based on 220 kV oil-filled cable termination. The dynamic solidification process of the insulating silicone oil was analyzed. It is found that the solidification of silicone oil is a temporal and spatial evolutionary process, which is closely related to the load current and the external environment. The solidification of filled and coated silicone oil will induce air gap defects, which will lead to different electric field distortion at different interfaces, especially at the stress cone/cable insulation interface. So the effects of different states of coated silicone oil on partial discharge at the interface are tested. Compared with the non-coating condition, solidification of coated silicone oil will aggravate partial discharge in cold environments, which is irreversible. The related results indicate the fault mechanism of oil-filled cable terminations subjected to cold environments and provide references for the selection of insulation materials and other measures to improve the reliability of cable terminations considering extreme environments.

Analysis of Electric Field Distribution of Insulators YD-JZ 10 kV Oil-Immersed Transformers

The electric field distribution of the YD-JZ 10 kV oil-immersed transformer insulator is analyzed by COMSOL simulation, calculation, and actual measurement methods. The result shows that the first shed of the insulator accounts for 18% of the voltage drop. After that, the voltage of each umbrella skirt decreased gradually, and the proportion of voltage drop of the last two umbrella skirts increased again. The electric field of the insulator tip burr is 1.16 × 106 V/m; spherical burr is 2.84 × 105 V/m. The simulation result shows that the maximum electric field of spherical air gap defect in an insulator is 1.38 × 105 V/m; conical air gap defect is 1.61 × 105 V/m ; metal particle defect is 1.49 × 105 V/m. The simulated insulator umbrella skirt is covered with water. When the whole insulator umbrella skirt is short-circuited, there may be ground discharge. The measured results and simulation results show that the insulator can work normally if the umbrella skirt is not completely short-circuited.

Experimental investigation and theoretical analysis of axially-loaded concrete-filled elliptical tubes with circumferential gaps

This paper herein conducts an experimental investigation on the axial compression behaviour of the concrete-filled elliptical steel tubular (CFEST) short columns offering circumferential gaps (CFEST-CG) and explores the influence of gap ratio and steel strength on their failure modes, axial compression resistance, initial stiffness and ductility, etc. Moreover, a finite element (FE) model is built and validated by the test observations. A systemic parametric investigation is presented to explore the impact of geometric and material parameters on the axial compression properties of CFEST-CG short columns. The influencing mechanisms of the circumferential gap on the typical load–displacement curve, the stress response and the contact stress are figured out. Two simplified calculation approaches for estimating the axial compression strength of CFEST-CG short columns are proposed in accordance with the unified theory and the simple superposition principle. The research results indicate that the existence of circumferential gap defects may result in failure patterns, such as the brittle cracking of the concrete, the inward and outward bulges in steel tube, due to the weakened steel confining effect and concrete supporting action. And the significant decrease in the axial compressive strength, initial stiffness and ductility of the columns is obtained as well. The accuracy of the design methods is verified by experiments and FE parameter analysis, which would provide a reference for theoretical research and design of CFEST-CG short columns.

Relaxation of externally strained halide perovskite thin layers with neutral ligands

<h2>Summary</h2> The preferred orientation (PO) and non-uniform strain of the perovskite layer coated on the substrate can cause unwanted blue shifts in the band gap and several defects inside and on the grain boundaries. Therefore, suppressing the anisotropic preferred growth of halide perovskite crystals while satisfying the trap passivation of grain boundaries is important to the fabrication of efficient and stable perovskite solar cells (PSCs). In this study, the properties of spin-coated perovskite thin films were investigated by adding an appropriate amount of trioctylphosphine (TOP) as a neutral ligand to a formamidinium lead triiodide (FAPbI₃) precursor solution. The TOP in the FAPbI₃ precursor solution containing MACl significantly alleviated the PO by MACl and further induced a redshift of the band gap through the reduction of microstrain. Furthermore, TOP contributed to the passivation of defects via the surface termination of grain boundaries. PSCs based on these perovskite thin films exhibited an efficiency close to 25%.

Enhancing the Fluorescence Activity of Graphitic Carbon Nitride Nanosheets by Eliminating the Active Defect States: Implications for Fluorescent Sensing and Biological Imaging

The fluorescence (FL) activity of graphitic carbon nitride nanosheets (CNNSs) is dependent on both their band gap and surface defect states. It is known that the band gap of CNNSs is difficult to tune; however, studies on the regulation of the FL activity of CNNSs by surface defect states are still few. Herein a facile strategy to enhance the FL activity of CNNSs is developed by alkali-mediated passivation of the active defect states (dangling bonds) on CNNSs. With alkali treatment, the active defect states of CNNSs are eliminated and replaced with the passivated −NH2 groups, leading to significant enhancement of the FL quantum yields. We believe that this work will promote an understanding of the structure–FL properties of CNNSs, advancing an understanding of the luminous mechanisms and the application of CNNSs in FL sensing as well as biological imaging.

Characterization and repair of core gap manufacturing defects for wind turbine blades

Various wind turbine blade components, such as shear webs and skins, commonly use fiber-reinforced composite sandwich structures with a core material like balsa or foam. During manufacturing, core gap defects may result from the misalignment of adjacent foam or balsa core sheets in the blade mold. It is important to understand the influence that core gaps have on the structural integrity of wind turbine blades and how to mitigate their influence. This research characterized the effects of core gap defects at the manufacturing and mechanical levels for both epoxy and next-generation thermoplastic composites. Common repair methods were assessed and compared. Multiple defect sizes were compared using temperature data gathered with thermocouples embedded during manufacturing to core gap defect characteristics obtained using image-mapping techniques, optical microscopy, and mechanical characterization by long beam flexure. Results showed that peak exothermic temperatures during curing were closely related to core gap size. The long beam flexure tests determined that transverse core gaps under pure bending loads can have a substantial effect on the ultimate facesheet strength of both epoxy and thermoplastic composite sandwich structures (up to 25% strength reduction), although the size of the defect itself had less of an influence on the magnitude of the strength reduction. The supporting image-mapping techniques indicated that the distortion of the composite facesheets by the core gaps contributed to the premature failures. The repair methods used in this study did very little to improve the ultimate strength of the sandwich panels that previously had core gap defects. The repair of the thermoplastic panel resulted in a further loss in ultimate facesheet strength. This research demonstrated that there is a vital need for the development of a compatible thermoplastic polymer repair resin system and appropriate resin specific repair procedures for the next generation of recyclable thermoplastic wind blades.

Eccentric compression behaviour and assessment of CFET short columns offering spherical-cap gaps

This paper designs and tests a total of 14 specimens to explore the effect of load eccentricity and spherical-cap gap on the compressive strength, ductility, failure modes, and strain distribution of the concrete-filled elliptical steel tubular (CFET) short columns with spherical-cap gaps. A finite element (FE) model of the eccentrically-pressured CFET short column is established by taking the characteristics of spherical-cap gap and elliptical cross-section into consideration. Extensively parametric studies on the impact of various geometric and material variables are further developed via FE analytical models. Intensive mechanical responses, such as the contact pressure between concrete core and hollow steel section (HSS) and the compressive stress at the mid-height cross-section, are presented as well. Based on the comparison between the test results and the predicted data obtained from the design provisions in specifications EN 1994–1-1, AISC 360–16, and GB 50936–2014, proper design formulae for evaluating the eccentric compressive strength of the CFET-SG short columns are proposed. The research results show that the existence of the spherical-cap gap significantly weakened the interaction between the HSS and the concrete core, leading to a reduction in the eccentric compressive strength and ductility behaviour. The concrete around the gap region appeared brittle collapse due to the shrinking confining effect of the HSS, and the HSS exhibited inward and outward local buckling because of the lack of concrete supporting action. The observations of this paper may furnish a scientific reference for the performance evaluation and prevention measures of CFET short columns with spherical-cap gap defects.

Study of the clinical features of Downs’s syndrome and relation between dermatoglyphics and congenital heart disease if any

Introduction: Down syndrome is one of the most common cause of congenital malformation with mental retardation seen with an estimated prevalence of 1/600 – 1/800 births. A wide range of abnormalities are seen, some of which are characteristic of Downs syndrome. Objectives and Aim: The present study was aimed at studying the various clinical features including dermatologlyphic patterns in Down syndrome and to find any correlation with congenital heart disease. Materials and Methods: 34 children £18 years with features of down syndromes were assessed for various clinical presentation and dermatoglyphic patterns analyzed. Those with congenial heart disease were also noted to check for any correlation with dermatoglyphic patterns in Downs syndrome.3 ml blood was drawn and thyroid function were recorded. Results: The majority of clinical features observed include slanted palpebral fissure, icrocephaly, epicanthal fold, macroglossia, hypotonia, flat facies, brachycephaly, high arched palate. Dermatoglyphic patterns show increased prevalence of simian crease clinodactly ulnal loops on the finger tips and atd angle &gt;45 in the children. Statistically significant correlation was found when clinodactly of the left hand, left third inter digital space pattern, open field defect and sandal gap of the toes was compared with down syndrome children with CHD.

ANALISIS CACAT PADA PEMASANGAN GASKET DI LINI ASSEMBLY DENGAN PENDEKATAN DMAIC SIX SIGMA

In the production process, defects or defects are difficult to avoid. The same thing happens in the process of installing gaskets on the refrigerator door. The gasket itself serves as an insulator and also as a door adhesive with the refrigerator cabinet. Inside the gasket is a magnetic metal plate. The defect that occurs is the gap between the door and the refrigerator cabinet. In other words, the gasket does not sit properly in the refrigerator cabinet, causing a gap called a defect gap. This defect gap greatly affects the performance of the refrigerator, because cold air from the refrigerator will come out through the gap between the gasket and the refrigerator cabinet which can cause the cooling process of the refrigerator to be disrupted. To reduce these defects, further analysis is needed to find the causes and at the same time alternative improvements. The method used in this study is the DMAIC six sigma approach

Evaluation of the penetration of intracoronal bleaching agents into the cervical region using different intraorifice barriers

BackgroundThe present study aimed to make a comparison between the effects of 35% hydrogen peroxide gel (HP) and sodium perborate with distilled water (SP) bleaching agents on the sealing characteristics of glass ionomer cement (GIC), TheraBase, ProRoot MTA and Biodentine intraorifice barriers.MethodsOne hundred and twelve single-rooted mandibular human premolar teeth extracted from young patients (14–25 years) were chosen. Root cement and cementoenamel junction (CEJ) of teeth were examined under a stereomicroscope at 10 × magnification to ensure there was no cement defect or dentin gap in CEJ. After the endodontic access cavities were opened on the occlusal surfaces of the teeth, the working length was determined. Instrumentation of each root canal was performed with a ProTaper Gold rotary system in the determined working length and filled with gutta-percha + AH Plus with a single cone technique using. Root fillings were removed 3 mm short of the CEJ and sealed with one of the following intraorifice barrier materials (n = 30/group): 1. GIC; 2. TheraBase; 3. ProProot-MTA; 4. Biodentine. In each of the sub-groups, either HP or SP was used to perform intracoronal bleaching on days 1, 4, and 7. All outer surfaces of the specimens except the 3 mm cervical region were covered with nail polish and modeling wax layers. Specimens were immersed in a 5 ml Eppendorf tube that contained 2 mL of distilled water. The penetration of peroxide release was measured using the colorimetric ferric thiocyanate method. Statistical analysis of the data was performed with Three-way ANOVA and Tukey’s test (P = 0.05).ResultsIn the HP groups, GIC showed the greatest peroxide release when compared with other tested groups on day 1 (P < 0.05). Biodentine and ProRoot MTA displayed a significantly lower peroxide leakage when compared to GIC and TheraBase on days 1 and 4 (P < 0.05). While GIC and TheraBase were used, HP observed higher peroxide penetration when compared with SP on days 1 and 4 (P < 0.05).ConclusionsPeroxide diffusion was significantly influenced by the kind of intracoronal bleaching agents and intraorifice barrier materials used.

Research on Improving the Partial Discharge Initial Voltage of SiC/EP Composites by Utilizing Filler Surface Modification and Nanointerface Interaction.

SiC/EP composites are promising insulating materials due to their high thermal conductivity, stable chemical properties, and nonlinear electrical conductivity. However, the compatibility of micron-sized SiC particles with the organic polymer matrix is poor, and defects such as air gaps may be introduced at the interface, which reduces the partial discharge resistance of the composite materials. In order to improve the partial discharge initial voltage (PDIV) of SiC/EP composites, in this paper, SiC/EP composites with different proportions were prepared by surface modification of filler and compound of micro/nano particles. Firstly, a method of secondary modification of SiC particles was proposed, which was first modified by alkali washing and then silane coupling agent KH560, and the effectiveness of the modification was verified. Therefore, the interface bonding ability between the filler and the matrix was improved, the air gap defects at the interface were reduced, and the PDIV of the composite material was improved. When the filling ratio is 10 wt%, the PDIV was enhanced by 13.75%, and when the filling ratio was further increased, the improvement was reduced. In contrast, the introduction of nanoparticles into the composites can effectively improve the PDIV of composite materials. In this study, nanoparticles were used to form a shell-core structure in epoxy resins to exert their huge specific surface area and active surface properties, thereby changing the overall crosslinking properties of the composites. Through experimental research, the optimal micro-nano particle compounding ratio was explored. Under the optimal mixing ratio, the PDIV of the composite material can be increased by more than 90%.

Investigation of effects of manufacturing defects on bursting behavior of composite pressure vessels with various stress ratios

This paper focuses on investigation of effects of defects, which may occur during manufacturing process, on bursting behavior of filament wound composite pressure vessels. A comprehensive experimental study was carried out to understand how manufacturing defects affect bursting behavior of pressure vessels with various stress ratios. Firstly, effect of stress ratio on bursting behavior was studied with the pressure vessels with no defect. Safe and unsafe failure modes were determined for pressure vessels with different stress ratios. Then, delamination and gap defects were deliberately embedded to pressure vessels with safe and unsafe failure modes. Thus, effects of manufacturing defects on bursting behavior for pressure vessels with both safe and unsafe failure modes were studied successfully. Strain gage measurement and high-speed camera were utilized to interpret bursting behavior in detail.

Numerical simulation of the interfacial stress between epoxy resin and metal conductor of power equipment during epoxy curing

There are many metal and epoxy resin interfacial structures in power equipments, which can generate interfacial stress concentrations and may induce accidents due to epoxy curing. In this paper, through simplifying interface structure into a coaxial cylindrical model, the formation mechanism of interfacial stress concentration of this interface structure was studied during epoxy resin curing process. The strain and temperature at the interface were measured by the strain and temperature measurement system. Then a model for calculating the interface stress distribution was established, including the heat conduction module, curing dynamics module and curing deformation module. The validity of the model was verified by comparing the calculated results with the measured results. In addition, the air gap defects at the interface, appearing after the curing process, were simulated. The results show that, after the curing process, the first principal stress at the centre of the interface gradually increases from the centre to the edge, reaching 41.06 and 40.20 MPa at the upper and lower edges respectively. The existence of air gap leads to partial discharge at low voltage. The calculation model can be extended to the stress prediction between the metal and epoxy resin in other power equipments.

Charge-Transfer Resonance and Surface Defect-Dominated WO3 Hollow Microspheres as SERS Substrates for the miRNA 155 Assay.

Chemical enhancement with charge transfer (CT) between the adsorbed Raman molecule and the semiconductor mainly contributed to semiconductor surface-enhanced Raman scattering (SERS). In this work, a three-dimensional (3D) WO3 hollow microsphere is first developed as a SERS-active substrate. This 3D WO3 has a smaller band gap and rich surface defects compared with flake WO3. Interestingly, these properties in the WO3 hollow microspheres lead to an increase in charge transfer, which causes a strong CT interaction between the substrate-Raman molecule interfaces, resulting in a large SERS enhancement. The 3D WO3 showed an excellent SERS performance with an enhancement factor (EF) of 1.6 × 106. Finally, a SERS biosensor is constructed based on the above-mentioned semiconductor materials, which can be used for the sensitive detection of miRNA 155 with a limit of detection (LOD) of 0.18 fM by employing a catalytic hairpin assembly (CHA) strategy. This work provides important guidance for semiconductor topography design to improve the SERS performance, supplying a new strategy for biomolecular analysis and disease diagnosis.

Numerical analysis of temperature characterization of air gap discharge in solid insulation under power frequency voltage

Air gap defects in solid insulation of power equipment can cause partial discharge. Temperature, as an important characterization of partial discharge, can be used as a criterion for the deterioration degree of air gap defects to some extent. In this paper, the temperature characterization of air gap discharge is studied. A plasma-kinetics-based dielectric barrier discharge model is constructed. The calculation method of air gap discharge heat source under power frequency voltage is presented. Moreover, the influence of voltage amplitude and gap thickness on temperature is studied. Obtained results indicate that under the power frequency voltage, Joule (Ohmic) heat contributes 90% to the heat source, and O4+ and O2+ and electron e are the main contributors to Joule (Ohmic) heat. O4+ is also the dominant ion in the mixed gas. As the discharge progressed, O4+ almost all clustered near the instantaneous cathode. The O2+ density generally depends on the electron density, but compared with the electron, the spatial distribution of O2+ density is slightly shifted to the instantaneous cathode. The discharge heat source is positively correlated with the air gap thickness and the voltage amplitude. With the increase in air gap thickness, the rising rate of heat sources will also increase. However, when the voltage is 10 kV, the heat source increases first and then decreases with the increase in the air gap thickness. The discharge does not occur when the air gap thickness reaches above 4 mm. This study provides theoretical support for identifying the deterioration degree of air gap defects from the view of temperature.

Elucidation of intermetallic compounds and mechanical properties of dissimilar friction stir lap welded 5052 Al alloy and DP590 steel

The friction stir lap welding (FSLW) was employed to join the dissimilar 5052 Al alloy and DP590 steel. The intermetallic compound (IMC) formation area and thickness increased linearly with increasing rotation speeds at 300 mm/min welding speed. Microvoid and gap defects existed on low-rotational-speed-produced lap interfaces, disappearing with increasing rotation speeds. However, cavities defects neighbouring the large-sized steel fragment appeared in the stir zone of the Al matrix with rotation speeds higher than 750 rpm. The negative influences from the Al-rich IMCs layer exceeding 1.5 µm thick and the aggravating internal cavities defects significantly reduced the joint strength. Correspondingly, the fracture mode of the friction stir lap welded 5052 alloy and DP590 steel was converted from the semi-brittle fracture into the full-brittle fracture. The maximum tensile shear force of 4.52 kN reached 75.2% of the Al 5052 base metal, obtained at the rotation speed of 750 rpm. However, from the combined perspective of integral bearing load capacity and local shear strength, the rotation speed of 500 rpm was recommended to achieve sound FSLW joints of Al5052/DP590.

Fundamental Frequency Optimization of Variable Angle Tow Laminates with Embedded Gap Defects

Variable stiffness composite laminates can improve the structural performance of composite structures by expanding the design space. This work explores the application of variable stiffness laminated composite structures to maximize the fundamental frequency by optimizing the tow angle. To this end, an optimization framework is developed to design the fiber angle for each layer based on the maximization of the fundamental frequency. It is assumed that the design process includes the manufacturing constraints encountered in the automated fiber placement process and a linear fiber angle variation. The current study improves existing results by considering embedded gap defects within the optimization framework. The plates are assumed symmetric, with clamped and simply supported boundary conditions. The optimal results and a comparison between the non-steered and steered plates with and without gaps are presented. Results show that, although gaps deteriorate the structural performance, fiber steering can still lead to an increase in the fundamental frequency depending on the plate’s geometry and boundary conditions.

Cu-Doped Layered Double Hydroxide Constructs the Performance-Enhanced Supercapacitor Via Band Gap Reduction and Defect Triggering

Cu-Doped Layered Double Hydroxide Constructs the Performance-Enhanced Supercapacitor Via Band Gap Reduction and Defect Triggering