Internal Bending Research Articles

Heterojunction nanoarchitectonics with SnS2/g-C3N4 S-scheme toward enhanced photooxidation and photoreduction

Novel g-C3N4/SnS2 van der Waals heterojunctions were fabricated via SnS2 crystals embedded superior thin g-C3N4 nanosheets for efficient photocatalytic oxidation and reduction activities simultaneously. S-scheme charge migration path was confirmed through test and density functional theory (DFT) calculation. Two dimensional (2D)/2D interfaces, powerful internal electric field (IEF) and band bending effect together expedited charge transfer. Photocatalytic removal of organic pollutants and hydrogen evolution were employed to evaluate photocatalytic performance. Particularly, the g-C3N4/SnS2 heterojunctions exhibited excellent 2,4-dichlorophenol (2,4-DCP) photooxidation and Cr(VI) photoreduction activities at the same time. 85% of Cr(VI) and 94% of 2,4-DCP were removed in the mixed solution after visible light irradiation for 2 h (λ > 420 nm). The hydrogen evolution rate enhanced to ∼6.58 times of g-C3N4. DFT simulation matched with test for narrowed band gap and enhanced IEF (accelerating photogenerated carrier transfer). This work provided new insights for constructing S-scheme multifunctional g-C3N4-based photocatalyst.

Shafts with U-shaped circumferential grooves: design charts for stress concentration factors, radial displacement and Poisson’s ratio influence

Shafts with U-shaped circumferential grooves subjected to internal normal force and bending moment are investigated on the basis of finite element analysis. The classical problem of the stress concentration factors (SCFs) identification is addressed. SCF charts are provided, adopting the maximum equivalent von Mises stress in the SCF definition. The discrepancy between the uniaxial SCFs extracted from the standard reference books and the multiaxial SCF obtained by finite element increases from 5% up to 20%. The intersections between the SCF curves are studied, which reveal a non-monotonic profile of the SCFs with respect to the outer and inner diameter ratio of the notched shaft. The radial displacement at the notch root is examined and design charts of ample validity and prompt access are compiled. It is found that the radial displacement sign and magnitude are largely dependent on the geometry of the notch. Furthermore, the strain and stress state of extremely shallow grooves are analysed, and a critical discussion on their SCFs using the von Mises criterion is presented. The influence of Poisson’s ratio is considered. A simplified method for the evaluation of a multiaxial SCF is proposed to account for the Poisson’s ratio effect. Thanks to the employment of few dedicated diagrams, and the present method allows an accurate evaluation of the SCF for U-grooved shafts, when Poisson’s ratio differs from the common 0.3 value.

On the cracking patterns of brittle rings with elastic radial support under hydrostatic pressure

The evolution of the cracking pattern of an internally pressurized, circular, brittle ring supported with radial elastic springs is investigated. The ill-posed Griffith-type energy functional is regularized via a sequence of boundary value problems (BVPs). We show, that internal bending in the fragments plays an essential role in the position of the new crack. We also find that the pattern formation is driven by a co-dimension one bifurcation, which leads to the conclusion that in the beginning of the cracking process the new crack emerges in the vicinity of the existing cracks. In the second phase of the evolution the cracking process obeys a halving rule. The critical value of the fragment-length is derived. The results obtained are readily applicable to describe the crack evolution of hemispherical domes.

DYNAMIC MODEL OF A RAILWAY LIFTING CRANE

Introduction: Currently, mobile boom cranes equipped with telescopic boom equipment are widely used in construction, loading and unloading, as well as installation. Purpose of the study: We aimed to develop a dynamic model for a railway lifting crane, taking into account the interaction of its structural elements with each other and the bearing soil surface in a three-dimensional formulation. Methods: In the course of the study, we used Simulation and Motion modules of the SolidWorks software package, Klepikov’s non-linearly deformable soil model, and Lagrange’s equation of the second kind. Results: As a result, we developed a numerical analytical 3D model describing dynamic loading and deformation of the “mobile boom crane – foundation” system in a three-dimensional formulation. The model takes into account the following: the internal bending deformation and the interaction of the mating structural elements of a crane (telescopic sections, telescoping hydraulic cylinders, and outriggers), hoist rope rigidity, grillage (framework of sleepers) influence, elastic and plastic properties of the base platform soil, and action of inertial loads on the structural elements of the lifting crane.

Energy/entropy partition of force at DNA stretching.

We compute by molecular simulation the energy/entropic partition of the force in a stretched double-stranded (ds)DNA molecule that is not yet available from the single-molecule measurements. Simulation using the coarse-grained wormlike chain (WLC) model predicts a gradual decrease in the internal (bending) energy of DNA at stretching. The ensuing negative energy contribution to force fU is outweighed by the positive entropy contribution fS . The ratio fU /f, used to assess the polymer elasticity, is about -1 at the moderate extension of DNA. At the high extension, the extra energy expenses due to the contour length elongation make the ratio fU /f less negative. The simulation findings of the hybrid energy/entropy nature of DNA elasticity at weak and moderate forces are supported by computations using the thermoelastic method mimicking the polymer experiments in bulk. It is contended that the observation of the negative energy elasticity in DNA can be generalized to other semiflexible polymers described by the WLC model.

Internal Rotor Actuation and Magnetic Bearings for the Active Control of Rotating Machines

Passive rotors are often limited in rotational speed due to bearing constraints, stability and excessive vibration levels. To address the vibration issue, Active Magnetic Bearings (AMBs) levitating the rotor with a magnetic field can be used. They offer a clearance and variable stiffness and damping to the rotor support, which help to mitigate greatly the vibration issue. However, they are also limited at large rotational speed because of the high frequency control force required to levitate the rotor safely. To overcome the frequency limitation, a dual AMBs/internal bending control concept is investigated with associated modelling and control algorithms. This approach is examined in simulation with a 19 kg rotor running up to 10,000 RPM, where three resonance frequencies are present at 2700, 5300, and 9300 RPM, with the first resonant frequency being the most strongly excited. Using internal rotor bending control, a maximum radial displacement of 15 μm for the rotor mid-point is achieved, which gives a reduction in vibration amplitude of 45% compared to the case of no control. Variations of the algorithm are presented and discussed, showing the potential of the proposed approach.

Limit Load Solution for Thin-Walled Cylinder with Circumferential Crack under Combined Internal Pressure, Axial Force, Bending Moment and Torsion Moment

T his research aims to establish the limit load solution for thin-walled cylinder with circumferential crack under combined internal pressure, axial force, bending moment and torsion moment. The solution is derived based on the net-section collapse principle and the von Mises yield criterion. The material considered in this work is assumed to be elastic-perfectly plastic. The solutions obtained from this work are compared with the results from the finite element models. The comparison shows that the equations established from NSC analysis provide acceptable results for the case of cracked cylinder under combined axial force and bending moment. For the case of cylinder subjected to internal pressure or torsional moment, however, these equations can be used to predict the limit load only if np ≤ 0.40 and nT ≤ 0.6 . This is because when the effects of internal pressure or torsional moment are included, the distribution of stresses on the crack plane at the yielding does not correspond to the NSC principal.

Directional dependence of critical axial strain in X65 pipeline steel subject to combined internal pressure and bending loading

In this exploratory study, a X65 seam weld pipeline steel is investigated by considering the effect of anisotropy on plasticity and fracture responses of biaxially (combined bending and internal hydrostatic pressure) loaded pipes having different crack lengths, diameter sizes and internal pressure levels. The results indicate that directional dependency is strong for pipes with relatively large diameters, deep cracks and loaded at high internal pressure. However, critical strain seems to be slightly influenced by anisotropy when the pipe diameter-to-thickness ratio decreases. That is, smaller pipes are quite insensitive to its effect irrespective of crack depth, crack length and internal pressure level.

Approximate field measures for ionic polymer-metal composite materials and a simplified order-of-magnitude actuator model

As the field of soft robotics grows and new applications for this technology are discovered, the use of simplified models for the soft actuators found in these devices will be critical. In this study we explore arguments based on the magnitude of field gradients that arise in the ionic polymer-metal composite (IPMC) under large applied voltages and their use for approximating measures of the fields inside the polymer. Using the order-of-magnitude based arguments provides exceptional results for quantifying the field measures of maximum ionic concentration and electric potential within the bulk of the polymer. These measures are leveraged to reconstruct the fields themselves in such a way that the internal bending moments generated inside the actuator may be approximated. With the internal moments, a simplified kinematic model may be used to formulate the steady-state actuator response of the IPMC. This actuator model shows a great deal of accuracy as compared to a full multiphysics model, and we discuss the prospects for future development of this model to account for dynamic actuation.

Stochastic Strength Analyses of Screws for Femoral Neck Fractures

This paper represents a multidisciplinary approach to biomechanics (medicine engineering and mathematics) in the field of collum femoris fractures, i.e., of osteosyntheses with femoral/cancellous screws with full or cannulated cross-sections. It presents our new numerical model of femoral screws together with their stochastic (probabilistic, statistical) assessment. In the first part of this article, the new simple numerical model is presented. The model, based on the theory of planar (2D) beams on an elastic foundation and on 2nd-order theory, is characterized by rapid solution. Bending and compression loadings were used for derivation of a set of three 4th-order differential equations. Two examples (i.e., a stainless-steel cannulated femoral screw and full cross-section made of Ti6Al4V material) are presented, explained, and evaluated. In the screws, the internal shearing forces, internal normal forces, internal bending moments, displacement (deflections), slopes, and mechanical stresses are calculated using deterministic and stochastic approaches. For the stochastic approach and a “fully” probabilistic reliability assessment (which is a current trend in science), the simulation-based reliability assessment method, namely, the application of the direct Monte Carlo Method, using Anthill software, is applied. The probabilities of plastic deformations in femoral screws are calculated. Future developments, which could be associated with different configurations of cancellous screws, nonlinearities, experiments, and applications, are also proposed.

Formulation of kinematics and gait locomotion for Hyper-Redundant robot

Robots with numerous excess degrees of freedom (DOF) are known as hyper-redundant. These robots resemble snakes or tentacles are suitable for use in extremely constrained situations as well as new modes of locomotion. This work discusses kinematic analysis of hyper-redundant (H-R) systems over solid terrain. The analysis is based on travelling wave gait which is used to model variety of locomotion for example: locomotion of flatworm or inchworm. The H-R locomotion describes displacement generated from internal bending or twisting of its mechanism. Kinematics of gait is formulated for both extensible and non-extensible H-R locomotion. Its kinematics is modelled using differential geometry of planar curves. Flatworm and inchworm locomotion has been idealized using travelling wave gait models. An H-R precise manipulation method of grasping wave is also introduced.

Theoretical and experimental studies for the evaluation of yarn transportation issues and suit thread stiffness in textile industry

Differential equations of thread motion must satisfy initial and boundary conditions as well as holonomic and nogolonomic bonding conditions. Holonomic and nogolonomic bonds lead to the nonlinearity of the differential equations of yarns where the law of deformation is linear. This, in turn, limits the ability to obtain analytical solutions to the differential equations of motion of yarns. Because of this, most studies consider yarns to be an environment that can only resist elongation. Methods of theoretical and experimental research and evaluation of the bending strength of the suit thread material are proposed in this article. Besides that, yarn transportation issues were also discussed according to the loss of yarn deformation. An algorithm for calculating and the results of numerical experimental studies of the dependence of bending deformation on the main deformation parameters of the filament material are presented. The developed methods of theoretical and experimental study of internal forces, bending deformation and bending stiffness coefficient can be used in designing new filament materials and assessing the strength of specified materials.

FEM analysis for the behaviour of two-dimensional CHS joints with asymmetrical Full-Overlapped top-connection

Circular hollow section steel profiles are often used for industrial purposes, like offshore structures or for aesthetical reasons. By welding two or more steel members with different inclination angles columns with a tree-shaped structure will be formed. Designers are using this column to get a natural optic for example in representative halls. Like in nature the connected members often have asymmetrical angles. To calculate the nodes of these structures is a complex part. Due to the geometrical and material heterogeneity, different stresses arise in the microstructure. Current standards have got limitations. These limitations are there for material, geometrical options or process in welding. The vertical column is defined as chord, the connected members as braces. The inclination angle is the horizontal imperfection between braces and chord. Standards have got limitations regrading this inclination angle. There is no definition for an angle smaller than 30°. Because of aesthetical reasons, there are steel joints with two or more braces, where the inclination angles are not equal. An example is the natural optic as the ideal of a tree. Columns with an on-top connection, together with a steel plate node is not included in the current standards. However, designing engineers often have to build their own models for complex structures or design it with the help of laboratory tests. In literature, it was figured out, that the inclination angle has got a large influence on the resistance of a steel joint. Due to the geometrical heterogeneity, internal bending moments can arise, which degrades the carrying capacity of the joint. This paper is about numerical case studies of tree-shaped columns with an asymmetrical shape. The full-overlapped node is made of circular hollow section profiles (CHS), which are welded in a three-dimensional way. The aim is to figure out the influence of the inclination angles on the stability of asymmetrical shaped columns in the ultimate limit state, when the angles are not equal.

Электронная микроскопия микроструктуры тонких пленок сурьмы переменной толщины

Thin Sb films with a thickness gradient deposited in vacuum were investigated by transmission electron microscopy. Microstructures in films with increasing thickness change from amorphous islands of increasing density and size to labyrinthine and continuous films with texturing, which also changes with increasing thickness. Based on the analysis of the patterns of bend extinction contours, a strong internal bending of the crystal lattice, up to 120 deg/μm, and the dependence of the crystallographic orientations in the structures of the film on the thickness were revealed.

Electron microscopy of the microstructure of antimony thin films of variable thickness

Thin Sb films with a thickness gradient deposited in vacuum were investigated by transmission electron microscopy. Microstructures in films with increasing thickness change from amorphous islands of increasing density and size to labyrinthine and continuous films with texturing, which also changes with increasing thickness. Based on the analysis of the patterns of bend extinction contours, a strong internal bending of the crystal lattice, up to 120 deg/μm, and the dependence of the crystallographic orientations in the structures of the film on the thickness were revealed. Keywords: Antimony, thin films, TEM, crystallography, extinction bend contours.

3D network-like rGO-MoSe2 modified g-C3N4 nanosheets with Z-scheme heterojunction: Morphology control, heterojunction construct, and boosted photocatalytic performances

The transition-metal dichalcogenides (TMDs) is a promising photocatalyst for degrading contaminant, while limited active sites and poor carrier mobility are the primary challenges for improving photocatalytic degrading efficiencies in both bare TMDs and TMDs-based photocatalysts. A rGO-MoSe2 composite with 3D network hierarchical structure was fabricated by the GO-assisted solvothermal method. And then rGO-MoSe2/g-C3N4 3D/2D hierarchical structures were constructed by combining rGO-MoSe2 with g-C3N4 nanosheets. The optimal rGO-MoSe2/g-C3N4 composite exhibited the highest photocatalytic degrading rate of 97.4% towards RhB under simulated solar light, and its pseudo-first-order apparent rate constant (k) was 0.0715 min−1, being 5.9 and 12.5-folds higher than that of MoSe2/g-C3N4 (0.0121 min−1) and bare g-C3N4 (0.00573 min−1), respectively. The 3D/2D hierarchical structure endow rGO-MoSe2/g-C3N4 composite with the improved light-harvesting and abundant active sites, supported by the DRS and BET analyses. And rGO nanosheets could act as efficient transfer and separation channels for electron-hole pairs between MoSe2 and g-C3N4, confirmed through the photocurrent response and EIS tests. According to the results of DRS spectra and Mott-Schottky plots, the spatial behavior of photo-induced carriers at interface of rGO-MoSe2/g-C3N4 would comply to a Z-scheme transfer pathway under the synergy effects of the internal electric field and band bending.

A New Stress Intensity Factor Solution Based on the Response Surface Method for Nozzle Corner Cracks in Nuclear Reactor for Thermal Energy Generation

As considered carbon-free, the use of nuclear energy for thermal energy generation may expand in the future, with the guarantee of safe operation of the nuclear reactor. In a nuclear reactor pressure vessel (RPV), the nozzle area is an important part of the safe operation. It bears internal pressure, axial force, and overall moment, and at the same time bears higher stress than the rest of the vessel. To assess the integrity of the nozzle structure with a crack under combined load, an accurate solution of stress intensity factors (SIF) along the crack front is necessary. To obtain the SIF, this paper proposes a solution method that uses the stress on the crack surface and the response surface method to fit the stress under the framework of the linear superposition technique. This method is the first choice to determine a series of influence coefficients under unit pressure load. Then, one can estimate the SIFs by superposition method for an arbitrary stress distribution resulted from combined loads. The proposed solution is verified for a typical RPV with cracks under internal pressure, axial force, and global bending moment. The results reveal that the proposed solution is in good agreement with the existing solutions under internal pressure. Therefore, it can be obtained that this solution can be effectively used for the structural integrity assessment of RPV with nozzle corner cracks.

Graphene and NTCDA adsorbed on Ag(111): Temperature-dependent binding distance and phonon coupling to the interface state

Flat lying physisorbates on surfaces can be expected to be lifted by heating. The details of this lattice expansion depend on the competition between two mechanisms. On the one hand, the interaction potential of each atom with the substrate is anharmonic and constitutes the reason for lifting. On the other hand, the internal bending stiffness of the planar adsorbate reduces its tendency to lift with temperature. Here we show that this competition can be investigated in a simplified molecular-dynamics simulation which considers only the vertical motion of the atoms of the adsorbate in respective model potentials. For two prototypical systems, i.e., graphene and 1,4,5,8-naphthalene-tetracarboxylic acid dianhydride (NTCDA) on Ag(111), we observe lifting by 0.04 \AA{} (graphene) and 0.06 \AA{} (NTCDA) between zero and room temperature. For the latter system, the impact of the temperature-dependent geometrical and vibrational properties on the occurring interface state (IS) is discussed. By introducing a local electron-phonon interaction model, we combine the indirect dependence of the IS on the average binding distance with direct coupling to the vibrational modes and obtain good agreement with the experimental results.

Estimation of blade forces in wind turbines using blade root strain measurements with OpenFAST verification

This paper introduces an inference method for computing the forces and bending moments on operating wind turbine blades using strain measurements and supervisory control and data acquisition (SCADA) data. Operational data from four months of a Clipper Liberty C96 2.5 MW turbine instrumented with interferometric strain sensors at the blade roots as well as SCADA data such as wind speed, rotor hub speed, and blade pitch angle allow for accurate calculation of blade forces and moments. To perform such calculations, certain structural properties of the turbine blades must be inferred in the absence of detailed, proprietary information. This is done by inferring missing information from the National Renewable Energy Laboratory (NREL) 3 MW WindPACT reference wind turbine specifications. The derived forces and moments computed on the blades of the Clipper turbine are compared with the behavior of the NREL 3 MW reference turbine according to OpenFAST simulation outputs. Comparison of blade root reaction forces to OpenFAST outputs match closely, demonstrating that this inference method can be used to successfully estimate the internal forces and bending moments acting on the blades. These methods are useful on turbines for which all the structural information is not available.

Evaluation of the Environmental Fatigue at a Long Radius Elbow of a Piping System under Transient Thermo Mechanical Stresses

Thermal fatigue widely takes place in light water reactor (LWR) piping systems. It is an important aging mechanism of a nuclear reactor. Thermal transient effects occur at the startup and shutdown of a nuclear power plant. During the thermal transients, local and global cyclic stresses are induced in the piping systems. They are exacerbated by local geometric imperfections and environmental factors, which may lead to crack initiation. The elbows of such piping systems are subject to various combinations of loads (internal pressure, bending, and torsion, as well as thermal fluctuations) during their service life. As can be seen, high-stress concentrations are developed in these piping elements. Therefore, it is important to make a failure evaluation. In this paper, a 12” pipe system segment, which was made with SA 106 Gr C steel, has been considered. It was composed by two straight sections joined by a long radius elbow. Typical start-up and shutdown transient effects of a BWR-5 were considered. A computer-aided thermo-mechanical analysis was carried out using the finite element method. The linearization of the stresses was considered, based on the ASME B & PVC Code Section III, subsection NB. Under these conditions, environmental fatigue was analyzed after 40-and 60-years operation.