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This investigation aims to make clear the relationships among geometric features, macrostructures, microstructures, and mechanical performances of the weld bead in the gas metal arc welding (GMAW) process for ASTM A606 type IV weathering steel. The results indicate that with the increase of welding heat input, the geometry of the top reinforcement and penetration increases proportionally until reaching the peak value, and then declines with the further increase of welding heat input; while the values of bottom reinforcement increase continuously with the increase of welding heat input. The average ultimate tensile strength (F), maximum displacement (L), and failure energy (E) of the welded joint produced by the moderate welding heat input are 10.27 kN, 1.88 mm, and 13.55 J, respectively, which are obviously larger than those obtained by the insufficient welding heat input (F: 8.33 kN, L: 1.20 mm, and E: 7.10 J). Although the mechanical properties of the welds achieved by the overlarge welding heat inputs present comparable levels (F: 9.73 kN, L: 1.86 mm, and E: 13.51 J), their standard deviation is much higher. Acicular ferrite, grain boundary ferrite, side plate ferrite, Widmanstatten ferrite, and pearlite are noticed in the fusion zone (FZ), while the coarse grain heat-affected zone (CGHAZ) is composed of upper and lower bainite, grain boundary ferrite, Widmanstӓtten ferrite, polygonal ferrite, and pearlite. As the welding heat input increases, the pre-austenite grain width in the FZ and CGHAZ decreases. The descending order of the microhardness distributed in the welded joints is fusion line, CGHAZ, FZ, fine grain heat-affected zone (FGHAZ), and base metal. In addition, the microhardness values of FZ and CGHAZ decline with the rise of the welding heat input. Nonetheless, no apparent links are found between the microhardness levels of the FGHAZ and welding heat input.

Photocatalytic CO2 reduction is a sustainable and inexpensive method to solve the energy crisis and the greenhouse effect. However, the major stumbling blocks such as poor product selectivity, low yield of the multi-carbon products, and serious recombination of electron-hole pairs hinder practical application of photocatalysts. Herein, a high-performance Bi@Bi2 MoO6 photocatalyst, Bi nanoparticles grown on the surface of Bi2 MoO6 nanosheets with oxygen vacancies, was fabricated via a simple solvothermal approach. Benefiting from the abundant active sites and effective separation of photogenerated carriers of Bi2 MoO6 nanosheets, and the localized surface plasmon resonance effect of Bi nanoparticles, the Bi@Bi2 MoO6 sample exhibited great photocatalytic CO2 reduction activity. Furthermore, adding NaHCO3 into the system not only significantly increased the C2 H5 OH generation rate but also enhanced the product selectivity. In the photocatalytic measurement (0.17 mol L-1 CO2 -saturated NaHCO3 solution), the highest formation rates of CO, CH3 OH, and C2 H5 OH were reached at 0.85, 0.59, and 17.93 μmol g-1 h-1 (≈92 % selectivity), respectively.

In this investigation, the regression analysis together with the desirability function approach was involved to optimize the resistance welding parameters for the high-strength steel HSLA 420. The Box-Behnken experimental design (BBD) was employed for the control factors of welding time, welding current, and electrode pressure. The values of nugget diameter, ultimate peak load, maximum displacement, and absorption energy were identified and processed using the approach of multiple-objective optimization based on ratio analysis (MOORA). The weight loss of the base metal before and after welding was measured and computed to estimate the welding expulsion magnitude. The calculated statistical parameters displayed that the welding current had the most momentous influence on the welding quality and welding expulsion. The welding joints free of expulsion with sufficient mechanical properties can be achieved at the welding current of 8.4 kA, electrode pressure of 0.5 MPa, and welding time of 13 cycles.

A couple of models were established to investigate the effects of welding parameters (voltage, wire feed speed, and welding speed) on the resultant mechanical properties of welding bead and welding heat input on the basis of a Box-Behnken experimental design (BBD). The three key mechanical parameters, that is, maximum displacement, peak load, and energy absorption, were processed via the technique in order of preference by similarity to ideal solution (TOPSIS) and Shannon entropy technique. After that, the correlations among the mechanical properties, welding heat input, and three technological variables in the welding process were established herein. Analysis of variance (ANOVA) implied that the heat input relied on voltage, welding speed, wire feed rate, and the interaction effects among these factors. These models act as the basis to achieve the multi-objective optimization problem by the desirability function approach. Results suggest that the welding settings favoring a robust trade-off between minimum welding heat input and maximum mechanical properties involve an intermediate value of wire feed speed, a high value of voltage, and welding speed. This welding parameter combination not only can produce an optimum welding bead with robust mechanical performances but also guarantees the goal of optimum welding heat utilization and production efficiency, in which the high level of welding speed is strongly recommended.

In this investigation, the welding quality and the dynamic resistance signal in the welding process were correlated using different dimension reduction techniques and regression models. The 0.4-mm-thickness TC2 titanium alloy was used as the welding material, while the welding experiments were carried out by a small pneumatic high-frequency alternating current welding machine. The Rogowski coil and alligator type wire clips were respectively utilized to collect the welding current and voltage in the welding process. The mechanism of dynamic resistance signal changes was studied and explained. In order to extract the features related to the welding quality and reveal the efficiency of the automatic feature extraction method based on the dimension reduction techniques, several dynamic resistance signals with different welding process parameters were processed by the approaches of principal component analysis (PCA), isometric mapping (Isomap), and locally linear embedding (LLE). After that, the redundant information in the dynamic resistance signal which has little to do with the welding quality would be removed and the useful features could also be isolated. And then three regression models quantifying the extracted features and the nugget size were created and their performances were also compared with each other. The results implied that the regression model based on the LLE technique was more robust than those established on the basis of the features automatically extracted from the dynamic resistance signal using PCA and Isomap. Compared with the existing popular manual feature extraction methods in the previous research work, the method proposed in this investigation outperforms the other methods in terms of two aspects. It not only can minimize the prior assumptions about the certain shape of the dynamic resistance curve and remove the subjective factors caused by the manual extraction method, but can assess and monitor the welding quality with a good level of reliability.

Incorporating plasmonic nanostructures is a promising strategy to enhance both the optical and electrical characteristics of photovoltaic devices via more efficient harvesting of incident light. Herein, we report a facile fabrication scheme at low temperature for producing gold nanoparticles embedded in anatase TiO2 films, which can simultaneously improve the efficiency and stability of n-i-p planar heterojunction perovskite solar cells (PSCs). The PSCs based on rigid and flexible substrates with 0.2 wt % Au-TiO2/TiO2 dual electron transport layers (ETLs) achieved power conversion efficiencies up to 20.31 and 15.36%, superior to that of devices with TiO2 as a single ETL. Moreover, 0.2 wt % Au-TiO2/TiO2 devices demonstrated significant stability in light soaking, which is attributed to improved light absorption, low charge recombination loss, and enhanced carrier transport, and extraction with the plasmonic Au-TiO2/TiO2 dual ETL. The present work improves the practicability of high-performance and flexible PSCs by engineering the photogenerated carrier dynamics at the interface.

Organic-inorganic hybrid perovskite solar cells (PSCs) have achieved power conversion efficiency (PCE) from 3.8% to 25.2% in recent years. However, the charge transport ability of the transporting layers and the quality of crystalline films limit further development of PSCs. To fabricate highly efficient PSCs, effective charge transport to electrodes through transporting layers is a necessary requirement. Suitable interface engineering is very critical because it can not only benefit the charge extraction and transport, but also effectively passivate the traps on the surface and grain boundary of the perovskite. It has been shown that the passivation layer for the perovskite plays a vital role in the performance of PSCs. The close fit between the charge transport layer and the perovskite layer is required to reduce the interfacial recombination and accelerate the carrier extraction and collection. Besides, the appropriate passivation layer has a potential impact on the crystallization and the morphology of the perovskite film. To achieve high-performance devices, it is crucial to design an effective passivation layer with appropriate nanomaterials. In this work, we synthesized poly[(2-methoxy,5-octoxy)1,4-phenylenevinylene] (MOPPV) on few-layer graphene oxide (GO) by in situ polymerization at room temperature. MOPPV-GO can fully combine the advantages of the two materials. The novel nanocomposite MOPPV-GO is used as the ultra-thin passivation layer of PSCs, of which the structure is ITO/TiO2/(FAPbI3) x (MAPbCl3)1– x /MOPPV-GO/spiro-OMeTAD/Ag. Since the surface morphology of the perovskite layer would affect the performance of devices significantly, the perovskite films with and without the passivation layer by atomic force microscopy is found that the MOPPV-GO can facilitate the growth of perovskite crystal with larger grains and enhance the quality of perovskite films. The root mean square roughness values of the perovskite films with and without MOPPV-GO were evaluated to be 19.87 and 25.85 nm, justifying the improvement of the surface flatness of the perovskite film with the decoration of MOPPV-GO, which would enhance the contact and carrier transport between the hole transport layer and the perovskite layer. As a result, the PSCs with MOPPV-GO exhibited considerably low hysteresis indices (0.02) and showed a short circuit current density of 23.54 mA cm–1, an open circuit voltage of 1.09 V, and a fill factor of 76.46%, corresponding to a high power conversion efficiency of 19.73%. By contrast, the control PSCs without MOPPV-GO showed a high hysteresis index of 0.18, with a poor power conversion efficiency of 16.42%. Meanwhile, it is shown that the EQE curve of MOPPV-GO modified PSC is higher than that of unmodified devices, which is consistent with the experimental results of J-V curve. The steady-state power output of various devices in ambient conditions under continuous AM 1.5G illumination was tested, which shows excellent stability of the PSC with MOPPV-GO during the period of 1000 s, indicating the positive contribution of MOPPV-GO interlayer to the stability. This work could provide a new idea for the synthesis and application of graphene-based materials in solar cells.

In this study, a systematic research was conducted to compare the performances of the regression model and artificial neural network in predicting the nugget diameter of spot-welded joints by monitoring the dynamic power signature. The TC2 titanium alloy with a thickness of 0.4 mm was used as the welding material, and a high-frequency precision spot welder was used to join the titanium alloy sheets. The dynamic welding current curve was obtained using the Rogowski coil, while the voltage curve was detected via two leads clipped onto the upper and lower electrodes during the entire welding process. The variations in the welding power signal in the welding process were investigated, and the characteristics of the power signals for different welding currents and electrode forces were analyzed. The power signals of different types of welding joints varied significantly. Five characteristics were extracted from the power signal to describe the shape of the curve. The stepwise regression analysis and back propagation neural network were respectively used to classify the welding joints into three categories: bad welds, good welds, and welds with expulsion. The performances of the two established prediction models were compared, and their behavioral discrepancies were attributed to their own data-mapping capabilities. Keywords: Nugget size, Dynamic power, Quality assessment

Summary Design of polymeric networks with unique structural motifs can permit dynamic features, yet most existing material systems exhibit limited operational states or irreversible responsiveness. Here, we use a hydrogen-bond topological network as the design principle to construct an ionic gel material based on cellulose, ionic liquid, and H2O (designated as Cel-IL dynamic gel). The prepared Cel-IL dynamic gels exhibit tunable properties of mechanical strength, ionic conductivity, viscoelasticity, and self-healing. With limited H2O, the Cel-IL dynamic gel exhibits a bramble-like Turing-pattern microstructure with excellent adhesion, rapid self-healing, and moderate ionic conductivity features. By increasing the H2O content to 32 wt %, the microstructure switched to a dense and compact Turing pattern network, giving the gel good stretchability, robust toughness, and a high ionic conductivity. With this material, we demonstrate a flexible, transparent, designable, and biocompatible ion sensor device, which exhibits great potential for use in electronic skins and intelligent devices.

The separator is of great importance for regulating ion transmission, maintaining electrode stability, and device safety in lithium‐ion batteries. Despite their many advantages, glass microfiber separators have shortcomings that often give rise to poor cycle performance and fatal short‐circuit risk when used in flexible batteries. Here, we propose the use of a scalable non‐Newtonian fluidic cellulose permeation‐diffusion strategy to develop a cellulose/glass microfiber composite film with an hourglass‐gradient structure. Due to the unique gradient morphology resulting from the presence of cellulose macromolecules, the as‐prepared composite film showed an improved surface mass density, adjustable pore structure, controllable ion transport, ideal mechanical flexibility, and robustness. When used as the separator in an assembled lithium‐ion battery, the composite film exhibited rapid ion diffusion and Li dendrite inhibition, which endowed the battery with excellent cycle stability (specific capacity of 108.5 mAh g−1 after 1000 cycles) and good rate performance. This composite film shows great potential application in flexible lithium‐ion batteries including but not limited to pouch cells.

Five published Liquid Sublayer Dryout (LSD) models are assessed using the Groeneveld Look-up table 2006 (LUT-2006) and critical heat flux (CHF) experimental data in circular tube under both subcooled boiling conditions and saturated boiling conditions. The flow regime transition from inverted annular flow to dispersed flow at post-CHF is postulated as the upper limit of the LSD model application range in saturated boiling region. Lee and Mudawar’s LSD model modified by W.X. Liu shows good agreement when void fractions is lower than 0.7. The modified L&M’s LSD model is coupled into subchannel code, COBRA-TF, to predict DNB type CHF in rod bundles. In present study, the gap clearance or thermal equivalent diameter of rod bundles is adopted as characteristic length in the modified L&M’s LSD model. For rod bundles with simplified grid spacers, Karman velocity distribution equation is utilized to calculate the velocity distribution normal to pin wall. The rod bundle CHF predictions by COBRA-TF coupled with LUT-2006, Bowring’s CHF correlation and the modified L&M’s LSD model, are compared with the CHF experimental data in 2 × 2 rod bundles with non-uniform power profile. Based on reasonable predictability on both the input power and axial position at CHF, the deviations of CHF predictions by the modified L&M’s LSD model, which adopts gap clearance instead of thermal equivalent diameter as characteristic length, and Bowring’s CHF correlation are within ±20% as void fraction approaching to 0.7.

Amino acid as a green and non-toxic capping agent was used to regulate TiO2 crystal face exposure and morphology replaced common inorganic F− ions. In this paper, the hexagonal multi-walled tubular anatase TiO2 with hierarchical structure exposed to {010} and {101} planes were synthesized by solvothermal method via optimizing the amino acid (glutamine). The microstructure, crystal plane exposure and photocatalytic activity of TiO2 samples were tested comprehensively, and the formation mechanism of hexagonal multi-walled tubular anatase TiO2 was proposed. The {010} active plane exposure ratio was 70.76% thanks to the appropriate ratios of glutamine to SO42− and the band gap reduced to 2.95 eV for better visible region absorption. The degradation rate of the material for MO reached 94.6% within 80 min, which was 9.37 times than the sample without capping agent. Both high surface area and the synergy effect between the {010} and {101} facets contribute to the improvement of photocatalytic activity.

This paper numerically investigates bubble nucleation, growth, merger, and departure characteristics as well as the heat transfer distributions on the surface, and compared the simulation results with experimental results. Micro-heaters are utilized in experiments to provide constant temperature as well as measure the time-resolved heat flux variations. Bubble images and corresponding heat flux distributions under bubbles are obtained in experiments. A 3-dimensional computational domain with two symmetry planes is built and 5 heating elements are arranged at the bottom surface of the domain to simulate the real heaters used in experiments. The temperatures of these elements are set constant and the local heat fluxes were calculated. Liquid-vapor interface is captured with a volume of fluid (VOF) method in numerical simulations. Bubble growth and merger characteristics and heat flux distributions under bubbles calculated in numerical simulations are analyzed and compared to experimental observations. The heat transfer contributions of different heat transfer modes are calculated. The heat transfer mechanisms during nucleate boiling are better interpreted by the coupling of bubble dynamics and time- and space-resolved heat flux variations on the surface.

In this work, a systematic research was undertaken to predict the nugget size of the welding joints in real time through monitoring the dynamic power signature for TC2 titanium alloy. The welding current in the welding process was measured by a Rogowski coil and the welding voltage was obtained by means of clipping two leads onto the upper and lower electrodes during the welding process. The power signal and the corresponding dynamic resistance were compared with each other. As the constant high frequency alternating welding current was employed in the whole welding process, the power waveform indicated the similar characteristics of the dynamic resistance, besides; the power signal could better reveal an explicit physical meaning of the heat input applied to the welding zone. The disparities and differences of the power waveforms with different welding qualities were also investigated. Four features were extracted from the power waveform so as to indicate the variations of welding power profile in the welding process. A process quality prediction model based on Kriging method was set up to correlate the four extracted characteristics with nugget diameter of the welding joints. Verification test results proved that the method proposed in this paper effectively evaluated the welding qualities within the ranges of process parameters being studied, which could monitor the welding performances in the resistance spot welding process as feasibly and effectively as possible.

Herein, silver (Ag)-based urchin-like E-graphite carbon nitride/titanium dioxide (E-g-C3N4/TiO2) ternary composite was successfully synthesised via hydrothermal process and it showed excellent photocatalytic activity. The large interfacial contact between three-dimensional (3D) urchin-like TiO2 (UT) and g-C3N4 leads to high photocatalytic activity, compared with pure 3D UT. To enlarge the response of light and enhance the charge carriers’ transfer, the Ag nanoparticles with average sizes of 13 nm were loaded on the surface of g-C3N4/TiO2. Photodegradation test results of RhB shown that the 3% Ag-based urchin-like E-g-C3N4/TiO2 composite has the highest catalytic activity, which reaches 97.98%. Thus, the material has a promising application for the degradation of organics.

Silver-Silver direct bonding has been developed as an alternative interconnection technique for 3D power integration which can form high-strength and low-resistance Ag joints under solid-state conditions. However, the reliability and failure mechanisms of these direct bonded joints have not been characterized yet. In this study, four direct bonded structures were accelerated aged with two different temperature cycling tests (TCT) in the temperature range between -55 °C and 220 °C. The thermally induced stresses in the metallization during TCT can be relieved by elastic and plastic deformation of the Ag films and the debonding at the interface. At higher temperatures above 150 °C, plastic deformation mechanisms dominate the stress relaxation. Stress-driven void migration along grain boundaries may lead to cracking and interfacial failure. Metallization with a diffusion barrier and large grain size can restrict the void formation and diffusion, therefore, provide a higher temperature capability. The results indicate that both the adhesion of the Ag metallization and the Ag-Ag direct bonding remain stable after 1000 thermal cycles.

There is currently enormous and growing demand for flexible electronics for personalized mobile equipment, human-machine interface units, wearable medical-healthcare systems, and bionic intelligent robots. Cellulose is a well-known natural biopolymer that has multiple advantages including low cost, renewability, easy processability, and biodegradability, as well as appealing mechanical performance, dielectricity, piezoelectricity, and convertibility. Because of its multiple merits, cellulose is frequently used as a substrate, binder, dielectric layer, gel electrolyte, and derived carbon material for flexible electronic devices. Leveraging the advantages of cellulose to design advanced functional materials will have a significant impact on portable intelligent electronics. Herein, the unique molecular structure and nanostructures (nanocrystals, nanofibers, nanosheets, etc.) of cellulose are briefly introduced, the structure-property-application relationships of cellulosic materials summarized, and the processing technologies for fabricating cellulose-based flexible electronics considered. The focus then turns to the recent advances of cellulose-based functional materials toward emerging intelligent electronic devices including flexible sensors, optoelectronic devices, field-effect transistors, nanogenerators, electrochemical energy storage devices, biomimetic electronic skins, and biological detection devices. Finally, an outlook of the potential challenges and future prospects for developing cellulose-based wearable devices and bioelectronic systems is presented.

Designing and fabricating an efficient and reusable photocatalyst has become a pursuit, as photocatalyst plays a key role in solving the energy crisis and the environmental pollution. However, the major stumbling blocks such as low photo-efficiency, non-reusability and serious electron–hole recombination hinder practical application of photocatalyst. Herein, a novel self-growing ZnO with numerous nanosheets grown on the surface of dumbbell-shape have been successfully synthesized via a simple hydrothermal growth, meanwhile, the nanosheet was exposed high-energy (101) crystal plane. Electrochemical impedance spectroscopy measurements show that nanosheets with exposed (101) facet were dominantly promote charge generation, separation and transfer. In order to inhibit the photocorrosion of ZnO, the graphene was loaded on the surface of ZnO via secondary hydrothermal process. Moreover, in the measurements of degradation RhB, the rate constant of samples follow the sequence: RGO@ZnO-10 (0.0568 min−1) > ZnO-10 (0.0460 min−1) > ZnO-9 (0.0148 min−1), which is demonstrated that nanosheet enhances the photoelectrocatalytic properties. Therefore, the novel ZnO structure not only has a promising application in dealing with environmental and industrial pollutants, but also provides a new strategy to design and fabricate reusable and high efficiency photocatalysts.

The critical heat flux (CHF) is one of the main thermal-hydraulics safety limits in water-cooled reactors. At CHF, a film of vapor is formed on the heated wall and the wall temperature can sharply increase in a short period of time, which may lead to damage of the heater surface. In spite of many studies, the CHF mechanisms are still not well understood due to the complexity of this two-phase phenomenon and its dependence on local thermal-hydraulic conditions. Two-phase boiling experiments have been conducted to observe CHF and post-CHF behavior in prototypical conditions for small modular reactors (mass flux: 560–1570 kg/m2.s, pressure: 7.6–16.4 MPa, inlet subcooling: 160–440 kJ/kg) in a 2 × 2 square rod bundle geometry with a chopped-cosine power profile at the University of Wisconsin-Madison. The fuel rods temperature history during and following CHF were used in the solution of the two-dimension inverse heat transfer problem to estimate the wall temperatures and wall heat fluxes. This analysis showed different transient boiling curves for different flow regimes that differ qualitatively and quantitatively from the typical boiling curve considered in steady-state two-phase heat transfer analysis. The experiments suggest that the inverse heat transfer analysis approach can be used to estimate the post-CHF heat transfer and to better understand the CHF mechanisms at high pressure typical of water-cooled reactors.

A temperature controlled low field nuclear magnetic resonance (LF-NMR) T2 relaxometry technique based on the mobility changes of water trapped in hydrogels, was successfully used for on-line determination of the sol-gel transition temperature for chitosan/β-glycerophosphate (CS/GP) hydrogels in real time. The LF-NMR results indicated that the gelation temperature decreased gradually with increasing GP concentration, and the results were supported by both thermogravimetric differential scanning calorimetry (DSC) and rheological findings; however, LF-NMR allows non-destructive monitoring of samples during continuous heating. Moreover, as the mobility of water molecules varies greatly during the sol-gel phase transition, the LF-NMR measurement was more sensitive and accurate (RSD ≤ 0.1 %, n = 5) compared with DSC (RSD: 1.2 %–3.7 %, n = 5) and rheology (RSD: 1.1 %–2.3 %, n = 5).

To improve the ability of water to wet coal in the process of coal seam water injection, different ionic liquids and surfactant compound solutions were added to water. Analyses of surface tension, reverse spontaneous imbibition, and contact angle were used to optimize the different compound solutions. The results showed that when the mixture ratio of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) and sodium dodecyl sulfate (SDS) was 3:1, and the concentration of the composite solution reached 0.1 wt%, the liquid surface tension reached a minimum of 28.946 mN/m, and the contact angle between the solution and the coal sample was 41.3°, which was lower than that of any concentrations of the other composite solutions. This solution could effectively wet the coal. In addition, infrared spectroscopy showed that different concentrations of the [BMIm][BF4] and SDS composite solution had different effects on the content of functional groups in coal. Further, based on the relationship between the content of the functional groups and contact angle, the relationship between the content of ring hydroxyl and OH⋯O in the hydroxyl structure and the size of the contact angle was found to be the most significant. Based on the above findings, a new type of composite wetting agent was prepared, and the wetting mechanism between coal and the wetting agent was clarified from the perspective of functional groups. The research results have important guidance and practical significance for improving the effect of increasing moisture and reducing dust in the process of coal seam water injection.

The hollow flower-like Gd-TiO2 (FGT) photocatalytic materials have been synthesized through a facile hydrothermal process by using gadolinium nitrate hexahydrate as a Gd source. The FGT was characterized with scanning electron microscopy, transmission Electron Microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and UV–Vis diffuse reflectance spectroscopy. The results show that the crystal structure of the synthesized material is rutile, the morphology is three-dimensional hollow flower-like. Gd-TiO2 material with the doping amount of 0.125 mol% exhibit an enhanced phoocatalytic activities on the degradation of RhB under simulated sunlight irradiation, which reaching to 95%. Therefore, the FGT shows favorable photocatalytic performance toward organic pollutant degaradation field.

Welding defects are generally considered to be undesirable in resistance spot welding process because they suggest deterioration of weld quality. A systematic investigation was undertaken with regard to addressing the effects of the welding defects, which were expulsion, shrinkage void, and cracks, on the quality of the welding joints for dual-phase steel. Peak load, the maximum displacement, energy absorption, and failure modes of the welding joints in the tensile shear tests were utilized to characterize welds performances. On the other hand, the nugget diameter was measured to describe the physical spot weld attributes. The metallographic observations and Vickers microhardness tests of the welding joints with defects were also carried out to better comprehend the mechanism of the welding defect occurrence.

Recent improvements in flexible electronics have increased the need to develop flexible and lightweight power sources. However, current flexible electrodes are limited by low capacitance, poor mechanical properties, and lack of cycling stability. In this article, we describe an ionic liquid-processed supramolecular assembly of cellulose and 3,4-ethylenedioxythiophene for the formation of a flexible and conductive cellulose/poly(3,4-ethylenedioxythiophene) PEDOT:poly(styrene sulfonate) (PSS) composite matrix. On this base, multiwalled carbon nanotubes (MWCNTs) were incorporated into the matrix to fabricate an MWCNT-reinforced cellulose/PEDOT:PSS film (MCPP), which exhibited favorable flexibility and conductivity. The MCPP-based electrode displayed comprehensively excellent electrochemical properties, such as a low resistance of 0.45 Ω, a high specific capacitance of 485 F g–1 at 1 A g–1, and good cycling stability, with a capacity retention of 95% after 2000 cycles at 2 A g–1. An MCPP-based symmetric solid...

Dual-phase steel has been employed in the automotive industry as it has the advantages of high strength, satisfying ductility, low yield ratio, and so on. A novel framework for the weld nugget size prediction and control using finite element modeling and experimental research was proposed in this paper. The two-dimensional axisymmetric numerical analysis model was established and the phase transition on thermal expansion coefficient was taken into account. The whole welding process was simulated and discussed using thermal elastic-plastic theory. To validate the predictive methods of developed weld nugget size and confirmation experiments were implemented with the same input parameters in the ranges of process parameters. The simulated weld nugget sizes were in good agreement with the experimental results except for extreme welding conditions. The microstructure of the welding zone was also investigated based on metallographic experiments and temperature field analysis. The welding parameters were adjusted using the model proposed in this paper so as to obtain the nugget size with pull out failure mode.

Disaster prevention effect of hydraulic techniques in mines depends on the migration range of water and the wetting degree of coal body. Therefore, it is of great significance to study the interaction among accumulated coal grains and water during migration and flow. First, this paper simulates the migration and wetting process of water and coal grains with an inverse spontaneous imbibition experiment. Then, theoretical and experimental results are compared to determine the optimal determination method of grain diameter as a key parameter in model. The research shows that the lower the metamorphic grade is, the more obvious the imbibition, and the grain diameter of approximately 100–297 μm produces the greatest imbibition effect. At the same time, after realizing that large grains have a dominant influence on formation of imbibition channels, the traditional mathematical model of imbibition height is improved and thus provides a theoretical guiding significance for improving hydraulic techniques.

This study focuses on weld quality evaluation by electrode voltage in small-scale resistance spot welding of titanium alloy. Voltage curve could be divided into four stages based on the variation characteristic. The single voltage peak was detected as combined effects of increasing bulk material resistivity and nugget size. Variations of voltage curve shape, voltage peak and failure load were more sensitive to welding current than electrode force. A generalised regression neural network was proposed to evaluate weld quality using features extracted from voltage signal. A discrete Hopfield neural network was also applied for electrode voltage recognition. The recognised voltage patterns were found effective in identifying different quality levels. A real-time and on-line quality monitoring system could be developed.

Abstract In this work, a systematic investigation was undertaken to explore the effects of welding process parameters on the mechanical performances of the welding joints in the laser welding process for DP600. Welding experiments were arranged by a uniform experimental design method with four control factors (laser power, welding speed, focal point position, and side-blowing shield gas flow). The tensile strength of the welding joints was used to quantify the welding quality. A mathematical model based on stepwise regression analysis was employed to correlate the welding process parameters and the tensile strength. The effects of the welding process parameters on the welding quality were discussed. The genetic algorithm was then employed to select the optimum welding parameters. The verification test results proved that the method proposed in this paper could effectively evaluate and optimize the welding quality within the range of process parameters, which could enhance the welding performance in the laser welding process as feasibly and effectively as possible.

Improving the conductivity stability of flexible conductors has a positive impact on the working performance and service life of portable electronic devices. However, designing a conductor material with both conductivity-stable and flexible performance is still not an easy task because of the conductive network damage under large deformation or high humidity conditions. Here, we surmount this challenge by developing an interfacial assembly/encapsulation integration strategy for the construction of flexible, transparent, and conductivity-stable film. Under the synergistic effect of coordination complexation and hydrogen bonding, silver nanowires (AgNWs) are sandwiched encapsulated by regenerated cellulose film (as flexible substrate) and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) nanosheets (as sealing coat). The resulting hybrid film has a robust interfacial structure and prominently stable properties. Even when subjected to harsh condition such as a high-moisture environment of 90% relative humidity and 65 °C temperature for up to 60 days, repeated bending for 500 times, peeling over 400 times or soaking in water for 30 days, the film still exhibits a high and stable conductivity, better than most previously reported values for AgNWs-based films. With this strategy as base, we demonstrate a flexible, transparent and biocompatible strain-to-electricity sensor with high working stability and performance.

It is of great significance to quantitatively describe the change in the permeability of the water-injected coal to improve the effect of the coal seam water injection technology. However, the current permeability model often assumes the pores of the porous medium are smooth, which is a large difference from the coarse coal matrix-pore interface. Therefore, a rough capillary bundle is used as the physical model to characterize the coal structure in this paper. Combined with fractal theory, a permeability model including the tortuosity fractal dimension and the specific surface area of the pores is established based on the traditional Kozeny-Carman equation, and the degree of influence of each factor on the permeability was obtained. Then, liquid permeability and structural parameters of the coal samples from the Daliuta Coal Mine and the Qincheng Coal Mine in China were obtained by nuclear magnetic resonance experiments, which verified the accuracy of the model. The research show that the tortuosity fractal dimension has the greatest influence on the theoretical permeability, and the theoretical permeability decreases rapidly when the tortuosity fractal dimension is between 1.05 and 1.20. Increasing the specific surface area of the pores will lead to an increase in the tortuosity fractal dimension and a decrease in the theoretical permeability. Under the different nuclear magnetic resonance experimental conditions, the theoretical permeability of the coal samples is consistent with the change in the liquid permeability and is closer to the measured value compared with the permeability models of Xu and Liu.

Inorganic fiber shows good insulation performance in civil construction and industry insulation. In the present paper, tensile strength of slag fiber produced with molten blast furnace slag was investigated systematically with the Weibull distribution theory in comparison with glass and basalt fibers. It was found that the mean tensile strength reached 2578.60 MPa and the shape parameter m in Weibull distribution is 2.4494, which indicates a lower uniformity. Anti-corrosion performances were also studied by means of the mass and strength loss after acid and alkaline solution treatment. Furthermore, SEM and FTIR were used to analyze the structural characteristics of original and treated fibers. This work has proved that the H + and OH − can both break the Si–O bond and then lead to the movement to high wavenumber for the bands of the symmetric stretching vibrations of [SiO 4 ]-tetrahedra. The anti-corrosion results indicated that slag fibers could not be used in acid environment, while its anti-alkali performance is relatively excellent compared with glass and basalt fibers.

The current study developed a novel kinematic model describing the molten slag fiberization process with a purpose of understanding the slag wool preparation. A reasonable predictive model to describe the diameter and length of slag fiber in commercial fiber making process is necessary because the length-to-diameter ratio has a huge impact on the thermal insulation performance, which will contribute to energy conservation. The current model was established based on melt droplet kinematics under relevant hypotheses. Through this model, changes in fiber dimensions with slag viscosity and rotational speed of spinning wheel have been systematically investigated to determine the optimized technological parameters. To verify the model, experiments were carried out and the results were in good agreement with the predicted values. Thus, the current model can serve as a useful guide for the industrial production of slag wool.

The thermal properties of wood-plastic composites (WPCs) and typical heating floor substrates heated by an electrothermal film were studied. Their effects on human feelings and the human autonomic nerve system were also investigated. The temperature changes of the specimens during heating and cooling were analyzed with an infrared thermal imager. People's subjective feelings of touching different materials were analyzed with a semantic differential (SD) technique, and their electrocardiography was recorded with a multi-channel physiological signal acquisition system. The thermal conductivity, temperature variation, tactile impression, and heart rate variability of WPCs and other heating floor substrates were investigated. The WPCs presented a markedly lower thermal conductivity and superior tactile impression compared with ceramic tile, which has a similar density to WPCs. There was a negative correlation between the scores of the warm-cool feeling and the density of the heating floor substrates under room temperature (19 °C ± 1 °C), and a positive correlation when heated (33 °C ± 1 °C). The thermal conductivity and heat storage capacity of WPC were higher than those of solid wood. Electric heating composite floors with a high comfort level and good thermal properties could be manufactured by combining WPCs and solid wood.

Sol–gel transition properties play a key role in various applications of thermosensitive hydrogels, but conventional methods for studying the sol–gel transition have some limitations. For extensive characterization of the water–polymer interaction and microstructure change during sol–gel transition, we propose a rapid and nondestructive method based on monitoring water mobility through low field NMR (LF-NMR), and this was applied to chitosan/β-glycerophosphate (CS/GP) hydrogels. The spin–spin relaxation time (T2) that depicted water mobility was measured by LF-NMR within 90 s. The T2 component corresponding to water protons trapped in polymer networks (T21) was very sensitive to sol–gel transition. A remarkable decrease of T21 value indicated obvious variations of water mobility when CS/GP was heated, and a turning point was observed on the T21–time curve. The gel point associated with this turning point could be easily determined by fitting the T21–time curves to a bilinear regression model, and the results showed good accuracy and repeatability owing to the nondestructive nature of LF-NMR. Variations in water components and microstructure of CS/GP caused by water migration after solidification were also analyzed by monitoring dynamic changes of T2. This rapid, nondestructive method provides a powerful tool for studying the sol–gel transition of hydrogels.

The porous structure characteristics of twenty-one porous microspheres with agarose framework were investigated based on the low-field nuclear magnetic resonance (LF NMR) relaxation time (T 2) distribution measurements. The feasibility of the technique was confirmed by direct relationship between T 2 and the mean pore size of the polymer networks (Rh) of agarose hydrogel which was established using the “Fiber-Cell” model. The expected pore radius distribution curve was obtained and the reliability was validated by comparing them with the results obtained by inverse size-exclusion chromatography. Thereafter, the technique was applied to characterize the pore size distribution (PSD) of soft microspheres and the pore size transformation of microspheres with or without grafted polymers in the process of protein adsorption. All of these results strongly support LF NMR as a promising, rapid and nondestructive technique for the determination of PSDs in many kinds of soft porous microspheres.

Titanium and its alloys have been applied in many industrial fields because of their high specific strength, good corrosion resistance and high thermal stability. Whereas, there is limited valuable references for recommendations of welding parameter selection and specific standards of the small scale resistance spot welding (SSRSW) of titanium alloy though it has been applied in many industrial production fields. Seventeen tests were designed according to the three-level three-factor Box–Behnken experimental design and the mathematical model correlating the process parameters and the failure energy was established on the basis of response surface methodology (RSM) technique. And then this model was used to analyze the effects/interactions of the welding parameters on the failure energy. The verification test results which were conducted with completely new welding parameters verified that the model presented in this paper was effective and robust. Sensitivity analysis was also carried out to explore the impact of each process parameter on the quality of welding joint. The optimal combination of process parameters for maximum failure energy of the welded joint was obtained using the model based on artificial fish swarm algorithm (AFSA).

The present paper investigated the process of the slag wool fabrication using high temperature blast furnace (BF) slag modified by coal ash (CA). The liquidus temperature and viscosity of the slag system with different mass ratios of BF slag and CA were measured through an inner cylinder rotation method. The approximate mass ratio used to fabricate the slag wool was therefore determined and slag wool was then successfully prepared with a high-speed air injection method in the laboratory. The effect of mBF/m ratio, slag temperature for injection and air pressure on the preparation of slag wool was systematically investigated. The mechanical and thermal properties were also studied to confirm the long-term working conditions of the slag wool. An industry-scale slag wool production application was established. The energy consumption and the pollutant generation, were analyzed and compared with the traditional production method, which indicated a 70% reduction in energy consumption and a 90% pollution emission decrease.

Titanium and its alloys have been identified as one of the best engineering metals for application in industrial fields. Whereas, there is limited research work on monitoring and controlling the small scale resistance spot welding (SSRSW) of titanium alloy. This paper performed a systematic research on the voltage curve, which turned out to be an indication for weld quality of SSRSW. It was obtained through clipping two leads onto the electrodes during SSRSW process. As the common equipment in SSRSW, the high frequency (HF) power supply and constant current mode were employed in this study. First voltage curves at different welding parameters were analyzed and then a probabilistic neural network (PNN) model using three factors extracted from the voltage curve was employed in order to classify the weld quality, and satisfied experiment results were acquired. It was demonstrated that the dynamic voltage during a welding process could be identified as a good signature for weld quality monitoring purpose.

Little work on the void fraction behaviors along structural materials with poor-wettability for liquid metals has been performed. In the present study, void fraction behaviors around a single cylinder with non-wetting surface condition were quantitatively discussed by using a gas jet-cylinder system where the impinging jet flow, the boundary layer flow, the separation flow, and the wake flow appear. One cylinder with a non-wetting surface and two cylinders with a wetting surface were used to vary the wettability for liquid sodium, and void fraction distributions were measured around the cylinders. In the case of wetting condition, void fraction distributions around the cylinder decrease clearly in the backward region of the cylinder, and liquid-rich region is formed due to bubble separation from the cylinder surface. On the other hand, under non-wetting condition, because of two-phase flow without bubble separation on the cylinder surface, void fraction distributions show almost steady values around the cylinder compared to those with wetting surface. The void behaviors on a non-wetting surface were also confirmed by a visualization experiment conducted in water. The observed differences can be basically attributed to the work of adhesion required for liquid-solid interfacial separation.

A new method for studying swelling behavior of hydrogels was developed based on low field NMR (LF-NMR). This method is established on these facts: firstly, internal water (water trapped in hydrogel) and external water (water outside of hydrogel) correspond to different components of transverse relaxation time (T2); secondly, T2 component amplitude is proportional to relative water content; and finally, T2 value is closely related to mesh size of hydrogel network, the main effect being due to the overall concentration (degree of swelling). This method was successfully applied to swelling ratio determination of chitosan/glutaraldehyde (CS/GA) hydrogels in situ, and the results had better accuracy and repeatability compared with that of weighing method. Furthermore, swelling kinetics at different pH and microstructure of CS/GA hydrogels was well elucidated based on T2. It is clearly showed that LF-NMR provides a powerful tool for probing processes related to water transport and microstructure variation of hydrogels.

The diluted magnetic semiconductors (DMSs) were achieved by the ion implantation. Fe+ ions (250 keV) were implanted into n-type GaN at room temperature with doses ranging from 8 X 10(15) cm(-2) to 8 X 10(16) cm(-2) and subsequently rapidly annealed at 800 degrees C for 5 m in N-2 ambient. PIXE was employed to determine the Fe-implanted content. The magnetic property was measured by the Quantum Design MPMS SQUID magnetometer. No secondary phases or clusters are detected within the sensitivity of XRD. Apparent ferromagnetic hysteresis loops measured at 10 K were presented. The relationships between the Fe-implanted content and the ferromagnetic property are discussed. (c) 2006 Elsevier B.V. All rights reserved.

A flexible, transparent, and renewable mesoporous cellulose membrane (mCel-membrane) featuring uniform mesopores of ≈24.7 nm and high porosity of 71.78% is prepared via a facile and scalable solution-phase inversion process. KOH-saturated mCel-membrane as a polymer electrolyte demonstrates a high electrolyte retention of 451.2 wt%, a high ionic conductivity of 0.325 S cm−1, and excellent mechanical flexibility and robustness. A solid-state electric double layer capacitor (EDLC) using activated carbon as electrodes, the KOH-saturated mCel-membrane as a polymer electrolyte exhibits a high capacitance of 110 F g−1 at 1.0 A g−1, and long cycling life of 10 000 cycles with 84.7% capacitance retention. Moreover, a highly integrated planar-type micro-supercapacitor (MSC) can be facilely fabricated by directly depositing the electrode materials on the mCel-membrane-based polymer electrolyte without using complicated devices. The resulting MSC exhibits a high areal capacitance of 153.34 mF cm−2 and volumetric capacitance of 191.66 F cm−3 at 10 mV s−1, representing one of the highest values among all carbon-based MSC devices. These findings suggest that the developed renewable, flexible, mesoporous cellulose membrane holds great promise in the practical applications of flexible, solid-state, portable energy storage devices that are not limited to supercapacitors.