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The second generation (2G) high-temperature superconducting (HTS) REBCO tape and the HTS cable made by the REBCO company are considered to be alternative materials for future superconducting magnet design due to their exceptional performance. The twisted stacked-tape slotted-core (TSSC) cable-in-conduit-conductor cable, which is one of the crucial layout structures in HTS cables, has been extensively studied by numerous research groups over the years. In this paper, a 3D finite element model of the TSSC HTS cable under bending and axial tensile loads is established using the bilinear isotropic hardening model in COMSOL commercial finite element software. The mechanical behavior of the TSSC cable under bending and axial tensile loads, as well as the evolution process of overall cable performance and critical current of individual tapes inside slots, are revealed by conducting mechanical analysis and using an empirical fitting formula between the critical current density of the 2G HTS tapes and axial strain. Furthermore, optimization engineering suggestions for its structure are provided, such as reducing the twist pitch, decreasing the tape width, increasing the number of tapes, reducing the slot width while avoiding direct contact between tapes and slot walls, increasing the number of slots, increasing diameter of diversion trench and inner diameter of helical core under predominant bending loads. In the case of axial tensile loads, the aforementioned suggestions are also applicable except for the inner and outer diameters of the helical core. The critical current performance can be enhanced by augmenting the outer diameter of the helical core in this case. However, it is almost unaffected by the inner diameter of the helical core. [ABSTRACT FROM AUTHOR]

Topological insulators (TIs) are a new type of quantum state materials. Due to their novel physical properties, such as topological protection defect immunity to edge states, TIs have become the focus of attention in condensed matter and material physics. At present, the research on TIs has been gradually extended to classical wave fields such as electromagnetic waves, acoustic waves, and elastic waves, and has aroused extensive research interest. However, for elastic wave systems, most TIs cannot actively control topological interface states due to the limitation of fixed structure, which hinders their application in practical situations. Here, we propose a kind of tunable three-dimensional (3D) valley Hall insulator composed of magnetoelastic materials. First, the topological phase transition can be induced by the asymmetric geometry. Then, the working frequency of topological interface states can be changed by using static magnetic fields. Second, topological phase transformation can also be induced by independently tuning the distribution of static magnetic fields or pre-stress in each unit. Based on this, reconfigurable propagation routes of interface states with arbitrary shapes can be realized by tuning the distribution of static magnetic fields or pre-stress in each unit. Finally, considering the sandwich structure composed of different magnetic fields or pre-stress distribution modes, the waveguide with tunable width and route is designed by coupling edge and bulk states, which is convenient for application and better energy transfer. This study provides a reference for the design of a tunable intelligent elastic waveguide. [ABSTRACT FROM AUTHOR]

Propagation characteristics of Love waves in a layered structure composed of a piezomagnetic layer attached to an elastic substrate exposed to a magnetic field and compressive stress are investigated theoretically in this article. The effective elastic, piezomagnetic and magnetic permeability constants of a piezomagnetic material can affect by a magnetic field and compressive stress. The effects of magnetic field and compressive stress on the phase velocity, group velocity, mode shape, and magnetic potential of the Love wave are discussed in detail. It is found that the number of modes increases as the intensity of magnetic field increases while this tendency is reverse when applying compressive stress. As the intensity of magnetic field increases, the group velocity decreases but the magnitude of surface displacement of a piezomagnetic layer increases. The findings presented in this article are useful for improving the performance of surface acoustic wave (SAW) devices. [ABSTRACT FROM AUTHOR]

Given the importance of large-scale engineering applications of the superconducting compound Nb3Sn, both its use and performance under certain operating conditions have attracted the interest of applied superconductivity researchers and material scientists for several years now. Huge efforts are directed toward understanding the response to applied loads and predicting fracture damage within their internal microstructure; this is fundamental in the design of superconducting coils and magnets which must meet stringent requirements in terms of maximum thermal and electromagnetic loads. In this paper, the fracture behaviors in polycrystalline Nb3Sn and Nb3Sn filaments with composite structures are investigated using the micromechanical finite element (FE) models with Voronoi tessellation. First, the 2D and 3D Voronoi FE models of the polycrystalline Nb3Sn tensile tests are developed and validated to provide insight into the cracking behavior in the intergranular brittle fracture of polycrystalline Nb3Sn. A cohesive zone model is used to simulate crack propagation at the grain level model including grain boundary zones. It is found that the pre-existing cracks of polycrystals and martensitic phase transformation of grains significantly impact the fracture properties in polycrystalline Nb3Sn. Second, detailed FE models of powder-in-tube (PIT) and bronze route filaments with Voronoi structures for fracture analysis are then developed on the basis of experimental observations of sectional morphologies. The mechanism of crack initiation and propagation under tensile load have been investigated by analyzing the mechanical properties of each component and the characteristics of multi-scale composite structures of filaments. Furthermore, the damage situation is investigated in PIT filaments undergoing transverse compressive load. The proposed simulation method in this paper can be extended to the fracture and damage analysis of Nb3Sn superconducting wires with different layouts and fabrication processes. [ABSTRACT FROM AUTHOR]

Considering the nonlinear coupling behavior of magnetostrictive material, the modulation of Lamb wave bandgaps in magneto-elastic phononic plates composed of Terfenol-D pillars on a silicon matrix is investigated by the finite element method. By the introduction of holes, two schemes, i.e., the pillars only case for scheme-I and the trampoline (pillars and holes) case for scheme-II, are considered for exploring the effect of magnetostriction and trampoline on band structures. Numerical results show that the edges of bandgaps shift toward higher frequencies and the relative bandwidth enlarges as the magnetic field increases. The greater the compressive pre-stress applied, the greater the magnetic field at the open or closed points of the bandgap required. Compared to scheme-I, we find that the existence of holes for scheme-II can cause the closing of the higher branches' bandgaps and the generation of a new bandgap, and larger relative bandwidth of the bandgap and wider range of the required magnetic field can be observed due to the trampoline effect. Meanwhile, the height of the pillar is a key parameter for generating or vanishing bandgaps. According to the displacement distribution of eigenmodes, it can be seen that the opening or closing of the bandgap is controlled by the coupling between Lamb modes of the plate and resonant modes of the pillars, which is induced by the combined effect of trampoline, magnetic field, and pre-stress as well as geometry parameters. These results give guidance for active controllability of Lamb wave propagation and intelligent regulation of phononic devices in complex environments. [ABSTRACT FROM AUTHOR]

Under time-varying loads, thermoelectric devices are prone to failure due to fatigue accumulation. The fatigue life of annular thermoelectric generators (ATEGs) has not yet been studied. The primary goal of this paper is to numerically investigate the fracture parameters and fatigue life of ATEG legs with central cracks. When there are central circumferential and radial cracks, the effects of temperature difference on the stress intensity factor (SIF) at the crack tip and fatigue life of the ATEG are investigated in the case of specific geometry. The results show that, in the temperature range 300–550 K, while the SIF at the fracture tip increases as the temperature difference increases, none of its values exceed the critical SIF, which prevents crack propagation. Nonetheless, the thermal cycling load can cause fatigue fracture and crack propagation in the legs, and a greater temperature difference shortens the service life of the ATEG. Furthermore, when the temperature difference is 50 K, the ATEG with a central radial crack have an 18.7% longer lifetime than the ATEG with a central circumferential crack. The findings will provide a theoretical foundation and recommendations for long-term reliable application of ATEGs in waste heat recovery. [ABSTRACT FROM AUTHOR]

In this paper, a novel type of cross‐like holes phononic crystal with excellent band gap characteristics, machinability and stability is optimized and designed based on genetic algorithm. The improved genetic algorithm is used to enlarge the band gap in the low frequency range, and the transmission spectrum of the structure is calculated by finite element method. In addition, the magnetorheological elastomer was introduced to optimize the spatial magnetic field distribution and study the influence of magnetic field on the band gap. This work provides useful guidance for the topological design of other types of intelligent phononic crystals. [ABSTRACT FROM AUTHOR]

Characteristics of trapped thickness-twist waves in an inhomogeneous plate consists of the piezomagnetic material and elastic material affected by the magnetic field and compressive stress are investigated theoretically in the article. Variations of the effective elastic, piezomagnetic and magnetic permeability constants in the piezomagnetic material with the magnetic field and compressive stress are analyzed. The active controls of trapping characteristics have been achieved. Bisection method is used to solve the frequency equation of trapped thickness-twist waves. It is found that the number of trapped modes increase as the central region length increase and the magnetic field can not only induce new trapped modes in the structure but also accelerate the energy trapping. The advantage of this method is that the trapping characteristics can be modulated easily and without physical contact. [ABSTRACT FROM AUTHOR]

This paper establishes a data-driven Neural Network (NN) framework. The contact resistance of T2 copper blocks with different roughnesses is predicted by deep learning at room temperature and cyclic loading. The contact resistance problem can be regarded as a regression problem of mapping the high-dimensional array space of multiple variables to the contact resistance. This paper measures the contact resistance of copper blocks with different surface roughnesses under loading and unloading states and obtains the original dataset required by the algorithm. The data characteristics include three surface topography parameters, number of cyclic loads, loading and unloading conditions, and load magnitude, with the data labeled contact resistance. This paper compares the results of the NN model and Holm model results to verify the NN model's effectiveness. The comparison results show that the prediction results of the NN are consistent with the predictions of the Holm model. After training and debugging, the root mean square error of the multiple hidden layers neural network test set is 6.81%, showing a good prediction effect. In conclusion, the deep learning algorithm provides a new way for fast and accurate prediction of the relationship between T2 copper blocks and contact resistance under cyclic loading times and unloading states. [ABSTRACT FROM AUTHOR]

Assessment of the pressure drop that occurs in cable-in-conduit conductors (CICCs) requires a reliable predictive model. In this paper, a fractal model to predict the pressure drop of helium flows in CICCs is proposed based on the porous media analogy and fractal theory. A fractal friction factor correlation is also derived using the proposed pressure drop model. The good agreement between the predictions and the experimental data for conductors with n 1 = 3 verifies the validity of both the fractal pressure drop model and the friction factor correlation for such configuration conductors. The fractal correlation indicates that the friction factor of the cable bundle in a CICC is related not only to the void fraction but also to the average hydraulic diameter, the tortuosity of the fluid flow paths, the maximum pore size and the fractal dimension of the cable cross-section. This theoretical correlation does not contain any fitting constants and each parameter has a clear physical meaning. [ABSTRACT FROM AUTHOR]

A novel phononic crystals (PnCs) structure that comprises periodically arranged hollow pillars filled with magnetorheological fluid (MRF) is fabricated by three-dimensional printing. The dispersion relations and transmission characteristics of the PnCs filled with MRF are numerically calculated using the finite element method and verified by experiment. Additionally, straight and bent type waveguides are fabricated. The results show that the MRF filling can control the frequency range at the bandgap and passband of the PnCs plate. The bandgap frequency range shifts to a lower frequency when an external magnetic field is applied. [ABSTRACT FROM AUTHOR]

Both the pancake coiling and conductor on round core (CORC) cabling processes consist of winding second-generation high-temperature superconducting tape (REBCO) in a core. The contact behavior between the tape and the core during the winding process directly affects the critical current, cable flexibility, mechanical support and electrical contact resistance. Therefore, the winding process needs to be optimized to produce pancake coils and CORC cables with the desired electrical and mechanical properties. This paper comprehensively considers the role of the relaxation and Poisson effects. The theoretical model and the finite element model (FEM) for calculating the contact stress during the winding process are established, and a formula for the estimation of the contact force is proposed. The suitable winding pre-tension force, winding curvature radius of SCS2030 (2 mm width and 30 m substrate thickness) and SCS4050 (4 mm width and 50 m substrate thickness) of REBCO tapes are obtained and discussed by accounting for the relaxation effect and the critical current degradation limit. With consideration of the Poisson effect, the nonlinear contact behavior is investigated. In addition, the relaxation effect, Poisson effect and plasticity of the REBCO tape are taken into account in the FEM model. The results show that the axial strain in the REBCO layer during the winding process is related to the contact behavior. The greater the winding pre-tension force, the smaller the helical curvature radius, and the greater the contact force. The distribution of contact stress for several winding factors (winding pre-tension force, winding angle and the core radius) is divided into three contact types: the single-line contact, the double-line contact and the surface contact. The FEM model results are consistent with the theoretical evaluation and are more suitable for practical winding cases. This research is the basis for designing and optimizing pancake coils and CORC cables. [ABSTRACT FROM AUTHOR]

The aim of this article is to present a three-dimensional (3D) simulation based on Voronoi tessellation, used to assess the strain dependence of the superconducting critical properties of inhomogeneous polycrystalline Nb3Sn at the microstructural level. To support this objective, we first present a polycrystalline model with equiaxed grains used to analyze the relationship between the polycrystalline structure and the strain response. We analyze the Young's moduli of Nb3Sn at different temperatures with random and preferential polycrystalline orientations, and the relation between the Young's modulus of polycrystalline Nb3Sn and spontaneous tetragonal transformation is discussed. The results indicate that the elastic properties (Young's modulus, stress/strain field) of polycrystalline Nb3Sn are mainly associated with ambient temperature and phase transition and are affected by the grain orientation. Meanwhile, an estimation-based model for the superconducting critical properties of single-crystal Nb3Sn is proposed. This model is based on changes in the electron density of states and phonon frequency induced by strain. The results calculated by the estimation-based model are consistent with the experimental data and the values calculated according to first principles. The change in the strain-induced superconducting properties of polycrystalline Nb3Sn is analyzed by combining the numerically simulated strain field of the polycrystal with the estimation-based model of single-crystal Nb3Sn. Compared to ideal single-crystal Nb3Sn, the superconducting critical temperature of the polycrystalline Nb3Sn superconductor has a higher strain sensitivity, which is related to the non-uniformity of the strain field of the polycrystal. [ABSTRACT FROM AUTHOR]

Superconducting Nb3Sn Rutherford cables can be used in the accelerator magnets above 10 T regions that cannot be reached with NbTi. These cables are composed of superconducting multifilamentary strands, interstitial epoxy, and insulation materials. To properly design the magnets made from these cables, it is essential to analyze their mechanical behavior. The prerequisite for this is the knowledge of the mechanical performance of Rutherford cables. In large magnets, these cables cannot be modeled with all details but effective properties and homogenization are typically required. In this work, an analytical model and numerical approach for predicting the effective mechanical properties of Rutherford cables are developed. The analytical model is established on a two-step homogenization and mechanical analysis for composite. The effective mechanical properties of the filament area and the transverse Young's modulus of the strand are first determined by means of utilizing the mechanical theory of the unit cell approach. The composite effective mechanical properties of the strand and interstitial epoxy are homogenized in the first step. The second step homogenization derives the effective mechanical properties of the strands epoxy composite and insulation layers. The numerical approach to determine the effective mechanical properties is based on the finite-element analysis. The developed methodologies are used to obtain the effective mechanical properties of two Nb3Sn Rutherford cables. The influence of the insulation thickness and modulus, the strand's modulus, is studied. [ABSTRACT FROM AUTHOR]

A thermo-mechanical-electromagnetic model is developed for estimating the delamination and current-carrying degradation of epoxy-impregnated pancake coils. The mixed-mode traction–separation law and the Weibull distribution of delamination strength are considered in simulating the onset and extension of the delamination caused by thermal stress. Because of the considerable differences in thermal shrinkage between the epoxy resin, insulation tape, and second-generation high temperature superconducting (2G HTS) tape, the accumulated radial thermal stress locally exceeds the electro-mechanical delamination strength and even the mechanical delamination strength. The electro-mechanical delamination strength of the 2G HTS tape is the transverse tensile or shear stress level corresponding to an abrupt irreversible critical current degradation. The mechanical delamination strength is the transverse tensile or shear stress limit corresponding to a structural failure. After injecting current into the coil, we obtained the E–I curve of the coil. The critical current and n-value of the superconducting coil indicate a strong degradation after epoxy-impregnation. The current-carrying degradation precedes delamination because the electro-mechanical delamination strength is smaller than the mechanical delamination strength. The degradation is more obvious in large than in small superconducting coils because the radial thermal stress is larger. The onset of degradation depends on the minimum delamination strength, suggesting that caution is required in screening the 2G HTS tape before winding the coil. The simulation results indicate that reducing the thickness of the insulation tape and the amount of epoxy resin effectively reduces the degradation of epoxy-impregnated pancake coils. [ABSTRACT FROM AUTHOR]

Pressure drop of cable-in-conduit conductors (CICCs) cooled by a flow of liquid or supercritical helium is one of the key parameters for the design of large superconducting magnet systems, which determines the heat removal capability and the thermal stability. In this article, an analytical model for predicting the pressure drop in CICCs is developed based on an analogy to porous media with the equivalent geometry configuration. This new prediction model indicates that the pressure drop in CICCs is affected by the geometry parameters of cable and the physical properties of the liquid helium, such as void fraction, tortuosity, pore–throat ratio, hydraulic diameter, density, and viscosity of the liquid helium. To verify the validity of the pressure drop model proposed in this article, the predictions are compared with the experimental data, the results show that the predictions are in good agreement with the experimental data. Then, an analytical expression for predicting the friction factor is derived, the obtained expression is in good agreement with experimental data and is superior to the Katheder correlation at large Reynolds number. In addition, the effects of the major geometric parameters on pressure drop are analyzed, the results explain why the Katheder correlation can be used to predict the pressure drop of CICCs. [ABSTRACT FROM AUTHOR]

In this work, we have proposed a general 3D analytical model for giant magnetostrictive composites based on the Mori-Tanaka theory. Taking into consideration both the interface effect and thermal residual stress (TRS) in the curing process, we have studied the relationship between the effective magnetostriction of giant magnetostrictive composites and different magnetic fields, and investigated the influence of TRS, inclusion shape, and direction of the magnetic field on the effective magnetostriction. The results show that TRS has significant influence on the effective magnetostrictive normal strains but little effect on the effective magnetostrictive shear strains. Both the magnetic field direction and the inclusion shape significantly affect the effective magnetostriction. Moreover, the Wiedemann effect is expected to occur on the giant magnetostrictive composites according to our theoretical calculations. [ABSTRACT FROM AUTHOR]

The heat removal capability and the coolant pumping costs in the design of cable-in-conduit conductors are depend on the thermo-hydraulics of the liquid helium flow. Therefore, the accurate knowledge of the thermo-hydraulics of the flow is significant for the design of the cables, especially for permeability. In this paper, the fractal method is proposed to describe the cable cross-section and an approximate expression is derived. Then, a fractal permeability model for helium flow in CICCs is presented based on a porous medium analogy. The feasibility and validity of this model is verified by the comparison of the predicted values and the experimental values. The fractal model indicates that permeability of cables is determined by the cable geometric parameters, such as the effective porosity, the average cabling angle, the average diameter of strands and the pore area fractal dimension of the cable cross-section. This model does not contain any empirical constants or fitting constants and can be used to explain the mechanism and to predict the permeability of the helium flow in CICCs. Furthermore, the effects of cable geometric characteristics on the presented fractal permeability model are also analyzed and simulated. The results imply that permeability of cables decreases with increasing the cabling angle, increases with the effective porosity, the pore fractal dimension and the average diameter of the strands increase. These results are consistent with the physical situations. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) effect in a Ni/PZT/Terfenol-D composite cantilever was tested under three different magnetic loading modes. The frequency-dependent ME effect and dual-peak phenomenon were observed in the experiment. The influence of orientations of magnetic fields on the dual-peak phenomenon of ME coupling was investigated. Magnetic field distribution inside the ME composite structure was simulated, which agrees well with experimental data. The experiment results indicate that ME coefficient versus bias magnetic field curve presents a novel dual-peak phenomenon near the resonant frequency, and the ME coefficient which depends upon the amplitude and orientation of magnetic field presents a nonlinear shift whether at the resonant frequency or not. In addition, the optimal angle corresponding to the largest ME coefficient for different bias fields were obtained. The proposed ME composites-based sensors can be used for detecting or harvesting magnetic signals of uncertain orientations and amplitudes in complex environments. [ABSTRACT FROM AUTHOR]

It is well known that the interaction between defect-induced strain field and vortex lattice (VL) gives rise to vortex pinning behaviors. Likewise, magneto-elastic (ME) interaction is caused by the difference between specific volumes of normal phase and superconducting (SC) phase. Acting as inhomogeneous strain sources, the normal-state vortex cores produce local deformation in the surrounding SC matter and thus affect VL energy. ME interaction belongs to the fundamental physics of interdependences between vortex matter and crystal lattice. The review starts with the effects of ME interaction on magnetization, vortex morphology and intervortex interaction. In Sect. 2, theoretical descriptions of ME interaction are classified in terms of different simplifications. The core ideas and outstanding results of these theories are given. It is followed by Sect. 3, where the correlation and difference between ME and pinning interaction are outlined. Although pinning differs from ME interaction in their formation mechanisms, the pinning interaction is established upon the vortex-induced strain field from Ginzburg-Landau (GL) viewpoint. Section 4 goes further with the GL treatment for solving ME and pinning problem; the general thoughts and steps can be found in this section. The last section gives some outlooks which involve pressure dependence of Tc and anisotropy. [ABSTRACT FROM AUTHOR]

Portable flexible electronic devices are receiving much attention for their flexible, portable, and wearable characteristics. The performance of such devices depends on the performance of the flexible battery to a great extent. The resistance of the battery is an important index of performance and a series of tests show that the resistance increases during deformation of the battery. In investigating how the mechanical behavior affects the resistance of the battery and optimizes the battery structure, a finite element model is developed to analyze the properties of the flexible-cable battery from a mechanical view. The model is used to analyze the mechanical behaviors of a wire-cable-type battery when the battery is solely subject to axial stretching, bending, or torsion. Effects of the cable lay angle and friction coefficient are considered. Effects of different loads on the resistance are presented considering the relationship between the strain and resistance. Simulation results show that the effect of the friction coefficient can be ignored. When the battery bears different loads, different lay angles are suggested for good flexibility and a small increase in resistance. [ABSTRACT FROM AUTHOR]

Future accelerator magnets are pushed to their limits in terms of magnetic field, mechanical strength and from the quench protection point of view. These forces the magnet designers to rethink the quench modelling. One issue that has not so far been largely explored is the mechanical behavior of the superconducting coils during a quench. This can cause limitations to the design of high-field accelerator magnets. This paper focuses on mechanical behavior in the event of a quench of an Nb3Sn 16 T dipole magnet currently developed in the framework of the EuroCirCol project in view of the future circular collider conceptual design study. The thermo-mechanical analysis is performed through the finite element modeling. The analysis takes into account the Lorentz force and the thermal stress due to the nonuniform temperature distribution in the winding during a quench. [ABSTRACT FROM PUBLISHER]

At present, conventional low-temperature superconductors such as NbSn strands have been extensively applied in high-energy and nuclear physics, as well as in magnetic resonance imaging systems. In this paper, a 3D finite element model considering sophisticated structure of superconducting filament bundles and metal matrix elements is built to deal with the electromagnetic behaviors of a NbSn strand exposed to tension and bending loads. The mechanical constitutive relations of filament bundles and metal matrix are described with elastic and elasto-plastic axial stress-strain curve, respectively. The voltage-current characteristic of the metal matrix elements is determined with the Ohmic law, and that of the superconducting filaments follows the n power relation. The stress-strain state is simulated and then implemented in the electromagnetic model, through the scaling law of ITER NbSn strand. We find that the plasticity of copper and the twist filaments cause the enhanced inhomogeneous strain profile in a strand composite, compared to the strain profile in a strand with untwisted filaments. We also discuss the current/field profile, critical current degradation, and AC loss in the strand composite under the tension and bending loads. [ABSTRACT FROM AUTHOR]

International Thermonuclear Experimental Reactor (ITER) Cable-in-conduit Conductor (CICC) presents a typical hierarchical twisted configuration. An unpredictable stress-strain distribution is generated in each-level subcable under experimental loading tests or realistic operating conditions. The mechanical response relates to the threshold of transport currents on CICC which indicates the performance and stability of ITER magnets. To quantitatively assess mechanical deformation we develop an analytical scheme based on the hierarchical approach in the classical wire rope theory, following a successive top-down algorithm from the highest cable level to the lowest. The determination and evaluation of complex contact occurrence among adjacent strands is a key aspect which is formulated via a friction-contact model. Finite element (FE) method is used to extend the analytical approach that treats only elastic and isotropic material to the anisotropy and plasticity. The results show that the interstrand friction acts as a moderation for the axial deformation, and the interaction among the conductors has a stronger impact on the cable deformation than that between the conductor and jacket. It is suggested that under tensile load, the displacement constraints at the end and the strand anisotropy help to reduce the cable longitudinal deformation. It is also recommended that increasing the subsequent pitch is beneficial to reducing the cable deformation level. [ABSTRACT FROM AUTHOR]

International Thermonuclear Experimental Reactor (ITER) Cable-in-conduit Conductor (CICC) presents a typical hierarchical twisted configuration. An unpredictable stress-strain distribution is generated in each-level subcable under experimental loading tests or realistic operating conditions. The mechanical response relates to the threshold of transport currents on CICC which indicates the performance and stability of ITER magnets. To quantitatively assess mechanical deformation we develop an analytical scheme based on the hierarchical approach in the classical wire rope theory, following a successive top-down algorithm from the highest cable level to the lowest. The determination and evaluation of complex contact occurrence among adjacent strands is a key aspect which is formulated via a friction-contact model. Finite element (FE) method is used to extend the analytical approach that treats only elastic and isotropic material to the anisotropy and plasticity. The results show that the interstrand friction acts as a moderation for the axial deformation, and the interaction among the conductors has a stronger impact on the cable deformation than that between the conductor and jacket. It is suggested that under tensile load, the displacement constraints at the end and the strand anisotropy help to reduce the cable longitudinal deformation. It is also recommended that increasing the subsequent pitch is beneficial to reducing the cable deformation level. [ABSTRACT FROM AUTHOR]

A theoretical model taking into consideration the interface effects is established to predict the Seebeck coefficient and the electrical conductivity for a polycrystalline thermoelectric (TE) thin film. The interface scattering mechanisms (including the film-surface scattering and grain-boundary scattering) of the transport electrons in the film materials are revealed. The relations between the Seebeck coefficient, the electrical conductivity and the interface parameters (the film-surface reflection coefficient and the grain-boundary transmission coefficient) are then discussed with respect to the proposed model. The differences in the TE properties between the films and bulk materials caused by size restriction are investigated. The results indicate that the higher grain number leads to stronger grain-boundary scattering and more distinct size effects of the TE properties. In contrast to the surface effect, the grain-boundary effect plays a main role in the TE properties of TE films with polycrystalline structures. [ABSTRACT FROM AUTHOR]

The deep well drilling in Gigante oil province in the mountainous area of Columbia is extraordinarily complex. There are problems such as severe inclination within the piedmont structure, downhole troubles caused by several sets of pressure systems, the wide range of brittle shale collapse caused by severe lost circulation and the collapse due to high density drilling fluid caused by micro cracks, wellbore collapse caused by the under-compacted thick mudstone, illite smectite mixed layer and the tectonic stress, and drill plpe sticking caused by soft-hard cross formations. There are also problems such as wellbore unstability caused by geostress and fracture belts and severe leakage, anomalous geothermal gradient(up to 42 °C/1000 m), Thus it is extremely difficult to perform drilling operatios because of severe lost circulation, collapse, stuckpipe and blowout. In view of the troubles encountered in deep well drilling in this oil province, this paper has analyzed the geologic origin and characteristics of this block, depicts the main factors which affect the drilling rate of deep wells and presents the solutions and suggestions, which have great significance in improving deep well drilling rates, reducing drilling costs and drilling cycle and accelerating the exploration & developing rate of the entire block. [ABSTRACT FROM AUTHOR]

The effect of electric charge on the mechanical properties of graphene under tensile loading is investigated by using molecular dynamics method. A modified atomistic moment method based on the classical electrostatics theory is proposed to obtain the distribution of extra charges induced by an external electric field and net electric charges stored in graphene. The electrostatic interactions between charged atoms are calculated using the coulomb law. The results show that the Young's modulus and the critical fracture stress under uniaxial tension decrease with the increase of electric potential and net charges on graphene. The failure of graphene induced by electric charges is found to be controlled by charge level. The results indicate that the carbon-carbon bonds at the edge of graphene will break first. [ABSTRACT FROM AUTHOR]

Based on the Boltzmann transport equation of electrons and taking the scattering effect of electrons in the grain boundary as the boundary conditions of electrons transport in the grain, we presented a theoretical model for the Seebeck coefficient of bulk polycrystalline thermoelectric materials, and applied it to studying the grain size effect on the Seebeck coefficient. Then we discussed the effects of transmissivity, temperature and the mean free path of electrons on the size effect. The results show that the proposed theoretical model is reasonable and effective and the predicted results for the Seebeck coefficient are in good agreement with the experimental data reported in literature. The bulk polycrystalline materials have notable (big) grain size effects on the Seebeck coefficient, and the influences of transmissivity, temperature and the mean free path of electrons on the Seebeck coefficient are also significant. [ABSTRACT FROM AUTHOR]

This paper presents an analysis on magnetic-elasto-plastic buckling and bending of a ferromagnetic rectangular plate with simple supports in applied magnetic fields. A numerical code is built to quantitatively simulate the characteristics of the magnetic-elasto-plastic nonlinear coupling problem by using a finite element method. The numerical results indicate that deformation of a ferromagnetic plate with elastic-plastic deformation is larger than that only with the elastic deformation. The incident angle of the applied magnetic field plays an important role in the deformation of the ferromagnetic rectangle plate: not only affects the magnitude of the deformation; but also the mode of the deformation. The configurations and plastic regions of ferromagnetic rectangular plates for different magnitude of the applied magnetic field are simulated and displayed as well. [ABSTRACT FROM AUTHOR]

Contact resistance is key for stable operation of electrical contact equipment, and can also be extensively applied. For Tokomak devices in fusion reactors, contact resistance of the superconductor magnet system strongly relates to the alternating current (AC) loss of the cable; the cable is assembled using a certain number of contacting superconducting tapes coated with copper layers on both sides. The contact resistance of a metal solid surface is affected by many factors. In this work, the contact resistance of copper surface samples was studied experimentally under variable normal cyclic load, temperature and number of contact surfaces. This is consistent with real-world working conditions, as the structure of superconducting cables can be changed, and such cables are used under cyclic electromagnetic forces in temperatures which range from room to working temperature. Experimental results showed that contact resistance decreased rapidly with an increase of load. Further, when temperature was varied from 77 to 373 K, the load–unload contact resistance lag decreased. When the number of contact surfaces was increased, contact resistance increased. Finally, a fitted formula describing the relationship between contact resistance and cyclic times, temperature and number of contact interfaces was determined. This formula can be used to predict variation trends of contact resistance in complex environments and provide more accurate contact resistance parameters for calculating the AC loss of superconducting cables. [ABSTRACT FROM AUTHOR]

In this work, an innovative vibration energy harvester is designed by using the point defect effect of two-dimensional (2D) magneto-elastic phononic crystals (PCs) and the piezoelectric effect of piezoelectric material. A point defect is formed by removing the central Tenfenol-D rod to confine and enhance vibration energy into a spot, after which the vibration energy is electromechanically converted into electrical energy by attaching a piezoelectric patch into the area of the point defect. Numerical analysis of the point defect can be carried out by the finite element method in combination with the supercell technique. A 3D Zheng-Liu (Z-L) model which accurately describes the magneto-mechanical coupling constitutive behavior of magnetostrictive material is adopted to obtain variable band structures by applied magnetic field and pre-stress along the z direction. The piezoelectric material is utilized to predict the output voltage and power based on the capacity to convert vibration energy into electrical energy. For the proposed tunable vibration energy harvesting system, numerical results illuminate that band gaps (BGs) and defect bands of the in-plane mixed wave modes (XY modes) can be adjusted to a great extent by applied magnetic field and pre-stress, and thus a much larger range of vibration frequency and more broad-distributed energy can be obtained. The defect bands in the anti-plane wave mode (Z mode), however, have a slight change with applied magnetic field, which leads to a certain frequency range of energy harvesting. These results can provide guidance for the intelligent control of vibration insulation and the active design of continuous power supply for low power devices in engineering. [ABSTRACT FROM AUTHOR]

In this paper, the magnetoelectric (ME) effect is investigated in two kinds of A-line shape Terfenol-D/PZT-5A structures by changing the position of the NdFeB permanent magnet. The experimental results show that both ME composite structures had multiple resonance peaks. For the ME structure with acrylonitrile-butadiene-styrene (ABS) trestles, the resonance peak was different for different places of the NdFeB permanent magnet. Besides, the maximum of the ME coefficient was 4.142 V/A at 32.2 kHz when the NdFeB permanent magnet was on top of the Terfenol-D layer. Compared with the ME coefficient with a DC magnetic field, the ME coefficient with NdFeB magnets still maintained high values in the frequency domain of 65~87 kHz in the ME structure with mica trestles. Through Fourier transform analysis of the transient signal, it is found that the phenomenon of multiple frequencies appeared at low field frequency but not at high field frequency. Moreover, the output ME voltages under different AC magnetic fields are shown. Changing the amplitude of AC magnetic field, the magnitude of the output voltage changed, but the resonant frequency did not change. Finally, a finite element analysis was performed to evaluate the resonant frequency and the magnetic flux distribution characteristics of the ME structure. The simulation results show that the magnetic field distribution on the surface of Terfenol-D is non-uniform due to the uneven distribution of the magnetic field around NdFeB. The resonant frequencies of ME structures can be changed by changing the location of the external permanent magnet. This study may provide a useful basis for the improvement of the ME coefficient and for the optimal design of ME devices. [ABSTRACT FROM AUTHOR]

The interaction between vortex and crystal lattice (periodic arrays of flux quantum and atoms) in type‐II superconductors is evaluated through Ginzburg–Landau theory. It is found that, in an isotropic crystal, the magneto‐elastic coupling energy counteracts the elasticity‐driven intervortex interaction energy. Thus, the elastic response is induced entirely by individual vortices taken separately. Furthermore, the strain in a vortex‐lattice cell decays quadratically with the distance from the vortex core, which allows a cutoff at the cell boundary. Finally, it could be concluded that if the jump in the elastic constant at Hc2 is comparable to unity, the elasticity energy dominates the competition between the vortex lattice and crystal elasticity. This effect likely results in the second magnetization peak in the reversible magnetization. The interaction between vortex lattice and crystal in type‐II superconductors is evaluated through Ginzburg–Landau theory. The vortex‐driven strain in a vortex‐lattice cell decays quadratically with the distance from the vortex core, which allows a cutoff at the cell boundary. This strain pattern is responsible for the second magnetization peak in reversible magnetization. [ABSTRACT FROM AUTHOR]

Although numerous studies have shown that contact resistance depends significantly on roughness and fractal dimension, it remains elusive how they affect contact resistance between rough surfaces. The interface similarity index is first proposed to describe the similarity of the contact surfaces, which gives a good indication of the actual contact area between surfaces. We reveal that the surfaces’ similarity be an origin of contact resistance variation. The cyclic loading can increase the contact stiffness, and the contact stiffness increases with the increase of the interface similarity index. These findings explain the mechanism of surface roughness and fractal dimension on contact resistance, and also provide reference for the reliability design of the electrical connection. [ABSTRACT FROM AUTHOR]