Concave Surface Research Articles

Improvement of Fatigue Life of Arc Welded T-joints by Local Shape Change Near the Joint Line

ABSTRACT: The objective of this study is to improve fatigue life of T-shape arc welded joint structures which are often used in automobiles. In conventional T-shape joint, ST-joint (Standard T-joint), a vertical part is welded to a flat surface in the horizontal part. In this paper, a new structure, CCT-joint (Concave shape T-joint), is proposed which can reduce stresses around a joint line in car driving. In a CCT-joint, a vertical part is welded to a concave surface in the horizontal part. Fatigue life of a CCT-joint was significantly longer than that of a conventional ST-joint. Results of this study suggest that the drastic improvement in fatigue life was due to stress reduction by the concave shape around the joint line. FEM stress analysis revealed that the maximum stress near the weld line of CCT-joint was reduced to less than half that of the ST-joint. Furthermore, it was found that the locations of the maximum stress were different between the CCT-joint and the ST-joint. This suggests that the crack origin positions of both joints are different, which was also confirmed experimentally. The geometry, hardness, and residual stresses after welding were investigated around the weld toe. The effects of geometry and hardness were small on the fatigue life. The residual stresses were decreased by CCT-joint. The evaluation of the advantage of residual stress reduction by CCT-joint compared with that of stress reduction in car driving will be investigated and discussed in the next step of this study.

Исследование влияния параметров режима сварки трением с перемешиванием меди на механические свойства и электропроводность сварных соединений

Copper is widely used when producing current-conducting parts, basically the electrotechnical power equipment buses. Traditional ways of welding copper become complicated because of high thermal conductivity, fluidity, significant oxidation at fusing temperature, and susceptibility. The application of the solid-phase welding methods, a prominent representative of which is friction stir welding (FSW), is one of the ways to solve problems when welding copper. The paper presents the experimental study of the influence of a tool working part shape and the welding mode parameters: welding rate, tool rotation frequency, and tool dip angle – on the possibility of the appearance of defects in welded joints of M1 copper plates of 5 mm in thickness produced by FSW. The paper contains the results of mechanical tests on static tension and bending of welded joints with a tunnel defect and without it. Welded joints with a tunnel defect showed a decrease in mechanical properties level: the value of ultimate tensile strength at stretching is lower by 33 %, and the specific elongation is lower by 8 % than ones of a joint without defects. The authors specify some factors influencing the appearance of defects at FSW: the welding rate, tool rotation frequency, tool working part construction, tool dip angle, strength and depth of immersion, pin displacement, blank thickness, and grip conditions. The study identified that the application of a tool with a concave surface taper shoulder allows producing welded joints without external and internal defects. Based on data obtained during the experimental research, the authors determined the welding modes, which makes it possible to produce welded joints with the electrical resistance value at the level of a parent metal: tool rotation frequency is 1250 rpm, welding rate is 25 mm/min, and tool immersion depth is no less than 0.41 mm.

Design and Performance Test of Rotary Grate Concave Threshing and Separating Unit of Head-Feeding Combine Harvester

HighlightsThis research was aimed at assessing the performance of a head-feeding combine harvester.The rotary grate concave threshing and separating unit were effective for improving and preventing the threshing cylinder from being jammed and improving working efficiency.More broken grains were obtained at a faster speed of concave grate.The speed of feeding chain was significant on the performance parameters that were evaluated.Abstract. It is easy for the threshing cylinder to get blocked in the head-feeding combine harvester with the fixed grate concave threshing and separating unit to affect the working efficiency when high yield rice is harvested. The rotary grate concave threshing and separating unit was designed to solve the above problem. The rotary grate concave surface revolved in the same direction along the cylinder arc of threshing drum. A test-bench of the rotary grate concave threshing and separating unit was developed. The rotational speeds of cylinder (RC), the speed of the concave grate (SG), and the speed of feeding chain (SF) were regarded as experimental factors, and the grain loss rate, broken grain rate, and impurities rate were selected as indices. Central composite design combined with response surface methodology and multi-objective optimization method were employed to conduct experiments and explore the interaction effects of factors on indices. The optimal operating parameters were nonlinearly optimized and determined to be RC of 547.6 rpm, SG of 0.93 m·s-1, and SF of 1.06 m·s-1. Under these conditions, the predicted values of the grain loss rate, broken grain rate, and impurities rate were 1.95%, 0.29%, and 0.58%, respectively. Verification experiments indicated that the observed values were in agreement with the predicted values. Results suggested that the rotary grate concave threshing and separating unit developed in this study were effective for preventing the threshing drum from being blocked, and there was a good potential for performance improvement of head-feeding combine harvester. Keywords: Central composite design, Cylinder speed, Feeding chain speed, Head-feeding combine harvester, Response surface methodology, Rotary grate concave, Threshing and separating unit.

ЧИСЛЕННОЕ РЕШЕНИЕ КРАЕВОЙ ЗАДАЧИ НА СОБСТВЕННЫЕ ЗНАЧЕНИЯ

In this article, when numerically calculating an equation with boundary conditions, the velocity distributions along the longitudinal coordinate were obtained for various values of the Mach number. Eigenvalues were also calculated. New variables and notation have been introduced to study the effect of various flow parameters. An equation with the same boundary conditions is obtained, which is an ordinary linear differential equation of the second order, which was solved by the sweep method. Solving the block diagram of an equation for determining the parameters of influence on the flow pattern near a concave surface, in the case of a compressible fluid, by examining, these parameters for the velocity distribution.

Designing Tetraoxa[8]circulenes To Serve as Hosts and Sensors.

In D4-symmetric tetraoxa[8]circulenes, alternating fused benzene and furan rings form an octagonal array. These compounds are little known despite their novel properties, which include extended planar π-conjugation and a formally antiaromatic cyclooctatetraene core. Tetraoxa[8]circulenes can be formed by acid-induced cyclocondensations of suitable quinones, but existing methods often give very low yields. In addition, π-stacking of simple tetraoxa[8]circulenes reduces solubility and limits opportunities to form homogeneous mixtures or cocrystals with other compounds. To help make tetraoxa[8]circulenes more useful, we have developed better ways to synthesize them, and we have used these methods to produce awkwardly shaped derivatives with large concave electron-rich aromatic surfaces. These compounds crystallize to form open structures that can accommodate various guests, including C60. Analysis of the structures shows that the cyclooctatetraene core of the hosts exhibits surprising variations in C-C bond lengths and conjugation, which appear to be related to the gain or loss of aromaticity. This allows tetraoxa[8]circulenes to serve as sensitive probes of local molecular environment and to be used as sensors of electron-deficient species such as nitroaromatic compounds.

Reshapable MXene/Graphene Oxide/Polyaniline Plastic Hybrids with Patternable Surfaces for Highly Efficient Solar‐Driven Water Purification

AbstractAlthough many solar‐driven water evaporators are developed for solar steam generation, most solarthermal energy conversion materials cannot be used repeatedly for constructing solarthermal water evaporators with variable shapes and patternable surfaces. Herein, reshapable Ti3C2Tx MXene/graphene oxide (GO)/polyaniline (PANI) (MGP) hybrids with variable shapes and patternable surfaces are fabricated by PANI‐assisted assembly of GO and MXene for efficient solar‐driven purifications of both seawater and wastewater. The variable shapes, patternable surfaces, and reusability of the plastic MGP hybrids are attributed to the strong interactions of PANI with both GO and MXene. Benefiting from the excellent solarthermal energy conversion of hydrophilic GO and MXene, the variable shapes and patternable surfaces of the MGP, and the reduced water vaporization enthalpy, the patternable MGP evaporators with flat and concave pyramid surfaces exhibit average water evaporation rates of as high as 2.89 and 3.30 kg m−2 h−1 under 1‐sun irradiation, respectively. When the plastic MGP is molded to a flower‐shaped evaporator, an outstanding evaporation rate of ≈3.94 kg m−2 h−1 with an exceptional evaporation efficiency of ≈135.6% is achieved under 1‐sun irradiation. The reusable MGP evaporators are highly efficient in generating clean water from both seawater and wastewater with satisfactory ion rejection rates of nearly 100%.

Atomically Dispersed Iron with Densely Exposed Active Sites as Bifunctional Oxygen Catalysts for Zinc-Air Flow Batteries.

Atomically dispersed iron embedded carbon is a promising bifunctional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), but its exposed iron sites must be increased. Herein, the authors propose a double steric hindrance strategy by using zeolitic imidazolate frameworks-8 as the first barrier skeleton and encapsulated phenylboronic acid as the second space obstruction to realize densely exposed atomic iron sites. Prepared PA@Z8-FeNC has the highest iron content (5.49 wt%) among reported transition-metal-based single-atom oxygen catalysts. Meanwhile, its concave surfaces, hollow structures, and hierarchical pores enable the high utilization rate of iron sites to 88.5 ± 4.5%and exposed active site density to 5.2±0.3×1020 sites g-1 . Resultantly, PA@Z8-FeNC exhibits superior activity and stability to commercial Pt/C and IrO2 for the ORR and OER in half-cells and zinc-air flow batteries. This provides insight for developing densely and accessibly active sites in single-atom catalysts.

Variable Stiffness Electroadhesion and Compliant Electroadhesive Grippers.

Soft adhesion is capable of attaching and bonding to rough surfaces and gripping nonplanar materials. It is preferable for material handling applications where safe interactions with external environments and enhanced adaptability to changing conditions are required. Soft electroadhesion (EA) is an emerging controllable adhesion technology that is especially suited to soft adhesion applications, but is prone to contact peeling that causes unwanted de-adhesion and cannot lift heavy objects unless the lifting force is applied parallel to the surface. Variable stiffness electroadhesion (VSEA) can be used to overcome these issues. Here a VSEA solution is developed by integrating electrostatic layer jamming and soft EA into a monolithic electrically controllable structure. The VSEA pad can achieve rapid response (within 1 s) and significant stiffness change (2200%), resist over four times the peeling force under a weight of 70 g, and generate 24.2%, 34.8%, and 49.3% greater adhesive forces on flat, convex, and concave surfaces, respectively. The promising gripping performance of the VSEA gripper was demonstrated by lifting and moving curved and flat objects. The VSEA concept and solution shown in this work may pave the way for the ready integration of EA into soft robotic systems and promote the broad application of EA technologies.

Silk fibroin-decorated with tunable Au/Ag nanodendrites: A plastic near-infrared SERS substrate with periodic microstructures for ultra-sensitive monitoring of lactic acid in human sweat

The flexible and plastic near-infrared surface-enhanced Raman spectroscopy (NIR-SERS) substrate, with efficient tunable surface microstructures for probe molecular detection on irregular targets, has great potential for ultra-sensitive monitoring in real-world scenarios. Herein, we propose an interesting 785 nm laser-excited plastic SERS substrate based on the silk fibroin fibers (SFF) decorated with multiple-branched Au/Ag nanodendrites (NDs). Compared with the original smooth flexible substrate, the further constructed plastic SFF-Au/Ag NDs with concave pyramid surface microstructures provides a relatively higher NIR-SERS activity at bottom of the inward concave region. Moreover, the enhanced NIR-SERS activity is also highly related to the content of Au/Ag NDs in the hybrid flexible substrate. The maximal NIR-SERS signal intensity can be realized at the content of 0.15 wt% Au/Ag NDs in the SFF-Au/Ag NDs, which is about 8-fold enhancement compared to that obtained at the content of 0.01 wt%. Then, the molecular detection limits of crystal violet (CV) and 4-mercaptobenzoic acid (4-MBA) are calculated about 10−15 and 10−13 M, respectively, reaching the ultra-sensitive requirements of NIR-SERS trace detection. Moreover, the substrate can detect lactic acid (LA) molecules with a concentration as low as 10−9 M, and can effectively reflect slight LA fluctuation in human sweat, providing a basis for the realization of ultra-sensitive NIR-SERS health monitoring.

Distinct dynamics of self-propelled bowl-shaped micromotors caused by shape effect: Concave vs convex

Although artificial micromotors with unconventional shapes are emerging as a powerful tool in various applications, little research has been undertaken to clarify their propulsion mechanism, especially how the shape effect alters the bubble dynamics and hydrodynamic flows. In this study, we fabricated two types of bowl-shaped micromotors to investigate the distinct dynamics due to the shape effect of concave and convex surfaces, by coating a platinum (Pt) layer on either the concave surface or the convex surface of the micromotor. In the single-bubble propulsion mode at low fuel concentration, the concave-surface-Pt-coated micromotor moved unexpectedly slower than the convex-surface-Pt-coated micromotor, and the bubble growth on the concave surface was also much slower than that on the convex surface. It was elucidated that the confinement effect of the concave surface hindered fuel replenishment and thus the catalytic reaction. We further introduced the Kelvin impulse to explain why the concave shape eventually weakened the propulsion from hydrodynamic jet flows caused by bubble collapse. In the multi-bubble propulsion mode at high fuel concentration, the interaction among bubbles rendered a “more is less” phenomenon—increase in the fuel concentration did not enhance the maximum instantaneous propulsion speed. These findings inspire the development of new manipulation strategies utilizing the unconventional shape effect in micromotors.

Evaporation kinetics of sessile droplets morphed by substrate curvature

In this article, we report the experimental evidence and an analytical model for the first time to predict the evaporation kinetics of sessile droplets seated on generic curved surfaces, either concave or convex. We appeal to the steady state, isothermal vapor diffusion theory, and incorporate conditions suitable to the geometry of curved substrates in a toroidal coordinate system, which is inherently different and more complicated than flat surfaces. We portray the mannerism in which the nature and magnitude of the curvature may dictate the evaporation behavior compared to a flat substrate. To validate the analytical model, we experimentally delineate the droplet evaporation phenomenon under the influence of substrate curvature. Convex cylinders and concave grooves of different radii have been employed for this purpose, and optical diagnostics of the droplet profile has been carried out to monitor evolution of the evaporation progress. Our model predicts that substrate convexity leads to substantial increase in evaporation rates due to augmented vapor diffusion domain over the liquid–vapor interface, whereas on a concave surface there is a decrease in evaporation rates due to droplet confinement phenomenon. The present model also addresses the fact that on the concave surface, the evaporation rate is not directly governed by substrate curvature, as discussed in the literature. The predictions from the model are found to be in good agreement with our detailed experimental observations.

The Polar Coordinate Transformation Numerical Steepest Descent Path Method for Calculating Physical Optical Scattering Field of Quadric Concave or Convex Surfaces

In this letter, the polar coordinate transformation numerical steepest descent path (PCT-NSDP) method is proposed to calculate the physical optics (PO) scattered field from concave or convex quadratic surfaces. In the proposed method, only three triangles integral domains are calculated, which avoids the complicated decomposition in the former NSDP methods. The PCT-NSDP method has a closed-form formula of the contribution of PO stationary phase point. Therefore, the calculation time can be much smaller. Moreover, the workload is frequency-independent. The numerical examples of the radar cross section of a quadratic convex surface demonstrate the high accuracy and efficiency of the PCT-NSDP method.

Whispering-gallery-mode sensors for biological and physical sensing

The term whispering gallery mode (WGM) was first introduced to describe the curvilinear propagation of sound waves under a cathedral dome. The physical concept has now been generalized to include light waves that are continuously reflected along the closed concave surface of an optical cavity such as a glass microsphere. The circular path of the internally reflected light results in constructive interference and optical resonance, a morphology-dependent resonance that is suitable for interferometric sensing. WGM resonators are miniature micro-interferometers that use the multiple-cavity passes of light for very sensitive measurements at the microscale and nanoscale, including single-molecule and ion measurements. This Primer introduces various WGM sensors based on glass microspheres, microtoroids, microcapillaries and silicon microrings. We describe the sensing mechanisms, including mode splitting and resonance shift, exceptional-point-enhanced sensing and optomechanical and optoplasmonic signal transductions. Applications and experimental results cover in vivo and single-molecule sensing, gyroscopes and microcavity quantum electrodynamics. We also discuss data analysis methods and the limitations of WGM techniques. Finally, we provide an outlook for molecule, in vivo and quantum sensing.

Film Cooling of a Concave Surface with Two-Row Coolant Supply in Trenches

Film Cooling of a Concave Surface with Two-Row Coolant Supply in Trenches

Spray-drying microencapsulation of polyphenols by polysaccharide from yeast cell walls

This study used polysaccharide (PS) from yeast cell walls to encapsulate polyphenols (PP) extracted from green tea (a good antioxidant substance) to avoid the effects of sensitive factors such as temperature, light and oxygen, and to preserve its stability and bioactivities. The objective of this study was to investigate the effects of four types of wall material (PS-MD (maltodextrin), PS-whey, whey, and MD). After selecting the most appropriate wall material, the study continued to investigate the effects of the ratios of the core to the wall material (1:1, 1:2, 1:3 and 1:4, w/w); the inlet air temperatures of spray-drying (130, 140, 150 and 160 °C); and the feed flow rates (04, 05, 06 and 07mL/min) on the microencapsulation yield (MEY) and the microencapsulation efficiency (MEE). The results showed the best settings as follows the wall material being PS-MD, the ratio of PP to the wall material as 1:3 (w/w), the inlet air temperatures at 140 °C, and the feed flow rate at 05mL/min. Under those conditions, the MEY and the MEE were found to be highest as 31.118mg/g and 86.73%, respectively. When examined by scanning electron microscopy (SEM), they had various sizes and spherical shapes and some of them had smooth or concave surfaces. As a result, it could be concluded that polyphenols were successfully encapsulated in the PS-MD matrix by spray-drying and the application to some food products could be further studied.

Study of Allowable Interlaminar Normal Stress Based on the Time-Temperature Equivalence Principle in Automated Fiber Placement Process.

Automatic fiber placement (AFP) is a type of labor-saving automatic technology for forming composite materials that are widely used in aviation and other fields. In this process, concave surface delamination is a common defect, as existing research on the conditions for this defect to occur is insufficient. To predict the occurrence of this defect, the concept of allowable interlaminar normal stress is proposed to define its occurrence conditions, and based on this concept, probe tests are carried out using the principle of time–temperature equivalence. Through the laying speed/allowable normal stress curve measured in the probe experiment, the physical meaning of allowable normal stress is discussed. At the same time, the measured curve is quantitatively analyzed, combined with viscoelastic theory and the molecular diffusion reptation model, and the dominating effect in the formation of a metal/prepreg layer and prepreg/prepreg layer is determined. Finally, the experimental data are used to guide the parameter selection in an automatic placement engineering case and prove its correctness.

Застосування метода регулярного режиму для визначення середніх коефіцієнтів тепловіддачі при струминному охолодженні поверхні складної форми

One of the most effective ways to intensify heat transfer when blowing surfaces with air is jet blowing. High intensity of transfer processes during jetting, relatively low energy costs for its implementation, simplicity and flexibility of control of this process have led to its widespread use in various fields. Mathematical modeling of heat transfer regularities in systems of impact jets is significantly complicated due to the three-dimensional nature of the flue-channel flow near the surfaces of complex shape. Therefore, it is advisable to use experimental research methods. The purpose of this study is to justify the use of the method of regular thermal regime to determine the average heat transfer coefficient during jet cooling of the surface. Regular mode of cooling (heating) of bodies is characterized by the fact that the relative rate of change of excess temperature for all points of the body remains constant. Since the thermal model was made of a highly thermally conductive duralumin alloy, the condition Bi <0.1 was met, when the average temperatures on the surface and volume will be the same. Therefore, the experiments recorded the readings of only one thermocouple. To compare the results of this experimental study with the results of other authors, cases of blowing a smooth concave surface with single - and three - row jet systems were chosen. The first case was studied in [3,4], the second - in [5]. The results of the performed test experiments agree satisfactorily with the data of these works, which were obtained both by the method of regular mode [5] and other methods of recording heat fluxes ([3] - passive heat flux sensor; [4] - electrocalorimetry). The difference between the average heat transfer coefficients and the known literature data does not exceed ±7..12%, which indicates a sufficient probability of the results obtained in this work, and the possibility of using the method of regular thermal regime in the study of jet cooling of complex bodies. Key words: heat exchange, jet system, cooling, concave surface

Temperature and Electric Field Distribution Characteristics of a DC-GIL Basin-Type Spacer with 3D Modelling and Simulation

The temperature properties of real-type direct-current gas-insulated transmission lines (DC-GIL) with a basin-type spacer were investigated by the finite element method in this paper. A horizontally installed model was established and the temperature distribution was obtained with a 3D model. The specific heat capacity and thermal conductivity of the spacer were measured and applied in the simulation. The results show that the temperature of the convex surface was slightly higher than that of the concave surface. With an increase in the SF6 pressure, the temperature of the spacer decreased, which can be attributed to the improvement of convection due to increases in the heat capacity per unit volume. With an increase in the ambient temperature, the temperature of the spacer increased linearly. The temperature difference between the inner and outer parts of the spacer increased with increases in the load current. Besides, an obvious increase in the surface electric field strength appeared under the influence of the thermal gradient compared to the results without the thermal gradient. Thus, special attention should be paid to the insulation properties of the spacer considering the influence of temperature distribution. This study evaluates both the thermal and insulation characteristics of the GIL along with the spacer under various conditions.

Triple Leidenfrost Effect: Preventing Coalescence of Drops on a Hot Plate.

We report on the collision-coalescence dynamics of drops in Leidenfrost state using liquids with different physicochemical properties. Drops of the same liquid deposited on a hot concave surface coalesce practically at contact, but when drops of different liquids collide, they can bounce several times before finally coalescing when the one that evaporates faster reaches a size similar to its capillary length. The bouncing dynamics is produced because the drops are not only in Leidenfrost state with the substrate, they also experience Leidenfrost effect between them at the moment of collision. This happens due to their different boiling temperatures, and therefore, the hotter drop works as a hot surface for the drop with lower boiling point, producing three contact zones of Leidenfrost state simultaneously. We called this scenario the triple Leidenfrost effect.

Effects of electrostatic spray drying on the sensory qualities, aroma profile and microstructural features of instant Pu-erh tea

The sensory qualities, aroma profile, and microstructural features of instant Pu-erh teas (IPTs) produced by electrostatic spray drying (ESD) were evaluated by sensory and instrumental analyses and compared with those produced by other drying methods (freeze-drying [FD], vacuum drying [VD], and conventional spray drying [CSD]). The sensory qualities of ESDIPT were similar to those of FDIPT, and better than those of VDIPT and CSDIPT. Eighty-eight volatiles were detected in all IPTs, and 45 odor-active compounds were captured. Most of their OAVs were higher in ESDIPT than in VDIPT and CSDIPT but were lower than those in FDIPT. Dihydro-β-ionone had the highest OAV. Aroma recombination experiments were performed to verify the identification results. ESDIPT was present in the shape of microspheres with many regular concave surfaces, which was different from those treated by other drying methods. In terms of sensory quality and productivity, ESD would be a potential method for IPT production.