Electromagnetic Loadings Research Articles

The adjustable adhesion strength of multiferroic composite materials via electromagnetic loadings and shape effect of punch

Tunable and reversible dry adhesion possess great potential in a wide range of applications including transfer printing, climbing robots, wearable devices/electronics, and gripping in pick-and-place operations. Multiferroic composite materials offer new routines and approaches to achieve tunable adhesion due to their multi-field coupling effects. In this paper, the classical Johnson-Kendall-Roberts (JKR) adhesion model is extended to investigate the adhesive contact problem of a multiferroic composite half-space indented by an axisymmetric power-law shaped punch, whose shape index is denoted by n. The JKR-n adhesion models under the action of the power-law shaped punches with four different electromagnetic properties are set up by means of the total energy method. The explicit analytical expressions relating the indentation load and indentation depth to the contact radius are obtained, which can include the existing results in open literature as special cases. The generalized Tabor parameter and the interfacial adhesion strength applicable to multiferroic composite materials are defined. The effects of the shape index and the electromagnetic loadings on adhesion behaviors are revealed. It is found that both of them have prominent influences on the relationships among the indentation load, indentation depth and contact radius, the contact radius and indentation depth at self-equilibrium state, and the critical contact radius and indentation depth at pull-off moment. The pull-off force under the action of the conducting spherical punch subjected to non-zero electromagnetic loadings is dependent on material properties, which is different from the classical JKR result. More importantly, our analysis indicates that the pull-off force and the interfacial adhesion strength can be adjusted via altering the electromagnetic loadings and the shape index of the punch, which provides new approaches to achieve tunable adhesion.

The Irradiation Effects in Ferritic, Ferritic-Martensitic and Austenitic Oxide Dispersion Strengthened Alloys: A Review.

High-performance structural materials (HPSMs) are needed for the successful and safe design of fission and fusion reactors. Their operation is associated with unprecedented fluxes of high-energy neutrons and thermomechanical loadings. In fission reactors, HPSMs are used, e.g., for fuel claddings, core internal structural components and reactor pressure vessels. Even stronger requirements are expected for fourth-generation supercritical water fission reactors, with a particular focus on the HPSM's corrosion resistance. The first wall and blanket structural materials in fusion reactors are subjected not only to high energy neutron irradiation, but also to strong mechanical, heat and electromagnetic loadings. This paper presents a historical and state-of-the-art summary focused on the properties and application potential of irradiation-resistant alloys predominantly strengthened by an oxide dispersion. These alloys are categorized according to their matrix as ferritic, ferritic-martensitic and austenitic. Low void swelling, high-temperature He embrittlement, thermal and irradiation hardening and creep are typical phenomena most usually studied in ferritic and ferritic martensitic oxide dispersion strengthened (ODS) alloys. In contrast, austenitic ODS alloys exhibit an increased corrosion and oxidation resistance and a higher creep resistance at elevated temperatures. This is why the advantages and drawbacks of each matrix-type ODS are discussed in this paper.

Modelling of dynamic fracture in bulk superconductor during pulsed field magnetization using ordinary state-based peridynamics

Bulk superconductor is subjected to a combination of huge electromagnetic force and temperature rise owing to the rapid movement of magnetic flux during pulsed field magnetization (PFM). Meanwhile, the heat generated will decrease the shielding effect and limit the strength of trapped field in turn. In view of its intrinsic brittle property and existing defects in fabrication, the bulk is prone to fracture under the complicated electromagnetic and thermal loadings. In this paper, the fracture behavior and damage evolution of the bulk superconductor with two or more cracks during PFM are investigated. Based on the electromagnetic field and temperature obtained by solving governing equation of H-formulation and heat transfer equation, the mechanical behavior of bulk is simulated with ordinary state-based Peridynamic model. The dynamic stress intensity factors considering thermal stress at crack tips are studied for different external magnetic fields and crack angles. Then, the influences of thermal contact resistance and local heat source are discussed. Finally, crack propagation in the bulk samples without reinforcement is modelled during PFM.

Magnetization loss of CORC cables under axial tensile loading

As a highly flexible and fully isotropic cable structure, CORC (Conductor on Round Core) cable wound with high-temperature superconducting (HTS) tapes has promise for giant magnets, including fusion magnets, high-energy accelerator magnets, and nuclear magnetic resonance. CORC cables are subjected to mechanical, thermal, and electromagnetic loadings during preparation and operation. Axial tension is one of the basic deformation modes of CORC cables. To investigate the impact of axial tension loads on the electromagnetic performance of CORC cables, a mechanical-electromagnetic model is created in this study. A comparison of numerical simulations and experiments was first performed for single straight tape and single-layer CORC cables to verify the model's reliability, with particular attention to the critical current reduction and the variation of magnetization loss during axial tension. The model developed in this paper may evaluate electromagnetic performance under applied AC magnetic fields with small amplitudes and mechanical response to axial tension loads. On this basis, the strain distribution of CORC cables under axial tension and their magnetization loss characteristics under various strain states are presented. The effects of different cable design parameters on the critical current and magnetization loss are discussed. The results show that the strain affects the magnetization loss of CORC cable significantly, especially for ones with larger winding angles. The magnetization loss can be reduced by choosing a narrower tape, a smaller winding angle, or a cable core material with a higher Poisson ratio. This study can provide a theoretical basis for the structure optimization design and practical application of CORC cables.

Structural Modeling of REBCO VIPER Cable for High-Field Magnet Applications

A structural model has been developed for the REBCO-based VIPER cable [1], which is designed for high magnetic field applications. In this work, structural finite element analysis (FEA) is used to simulate the stresses incurred within the REBCO tape stacks under the following conditions: (1) bending to 1 m diameter (2) cooling down to 77 K and (3) repeated transverse electromagnetic Lorentz loadings up to 1600 kN/m. The effect of solder impregnation onto the stress state of the tapes was studied via a set of friction coefficients of 0.02 (perfect-slip), 0.2 (metal-to-metal contact), and 1 (no-slip). For bending, high friction between the tape-stack and solder results in high axial strain in the tape-stack which may lead to I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation. During thermal cooldown, the stress on the tape-stack is negligible. However, the differential in thermal contraction between the copper and stainless-steel jackets leads to the formation of a small gap that may cause mechanical instability. Under cyclic Lorentz loading, a higher friction coefficient reduces the deformation of the cable by restricting the relative sliding between the neighboring tapes, which results in a more uniform stress distribution and a lower peak stress. A lower friction coefficient results in larger deformation of the solder and stack and a higher peak stress. In addition, due to the accumulated plastic deformation and stress concentration in the solder, both the averaged von Mises stress and the peak stress of the outermost four tapes increase with each of the first three loading cycles. These results may explain the early-stage degradation observed in the experiments conducted on VIPER cables (Z. S. Hartwig <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2020).

Study of the ITER TF CICC Mechanical Behavior Under Cool-Down and Repetitive EM Loadings

High-current and high-field superconducting magnets sustain huge electromagnetic loads. On top of that, the high field constraint pushes towards the use of high-performing superconducting Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands, which are strain sensitive. In recent fusion magnets, the loads reach few hundreds of kN/m in static and sometimes cyclic regimes. These loads modify the strands local strain state and the overall mechanical properties of the cable. In this article, the finite element mechanical code MULTIFIL is applied to model an ITER Cable-In-Conduit Conductor (CICC) petal for the Toroidal Field (TF) coil under operating loadings. The local strain maps and the macroscopic mechanical behavior of the cable are analyzed for both thermal and electromagnetic loadings. A possible explanation for the initial drop of the current sharing temperature observed in some of the TF CICCs tested in the SULTAN facility (PSI, Villigen) is proposed. The impact of important model parameters, such as the void fraction and the friction coefficient between strands, on the mechanical behavior of the conductor is investigated.

Magneto-electro-elastic analysis for two mode-III semi-permeable collinear cracks in piezo-electro-magnetic strip

A mode-III crack problem for piezo-electro-magnetic strip weakened by two transversely oriented semi-permeable collinear cracks under out-of-plane shear stress and in-plane electric-displacement and magnetic induction is addressed. The problem is formulated and then solved using Fourier series method and integral equation technique. Closed-form analytic expressions are derived for various fracture parameters viz. crack sliding displacement, crack opening potential drop, crack opening induction drop, field intensity factors and energy release rates. Numerical case study is presented graphically for BaTiO3-CoFe2O4 piezo-electro-magnetic material to show the influence of inter-crack distance, volume fractions and electro-magnetic crack-face boundary conditions on crack sliding displacement, crack opening potential drop, crack opening induction drop and energy release rates. Moreover, the effect of prescribed mechanical loadings as well as electro-magnetic loadings on energy release rates are also presented graphically. Results obtained are presented graphically, analyzed and concluded.

Electromagnetic design and performance analysis of a two‐phase AFPM BLDC motor for the only‐pull drive technique

This study proposes a two-phase single-air-gap axial flux permanent magnet (AFPM) motor that offers a trapezoidal back-electromotive force (EMF) waveform to improve the performance of the only-pull drive technique compared with the radial flux PM (RFPM) motor. The only-pull drive technique provides the benefit of allowing the use of thin magnets in the motor without suffering from irreversible demagnetisation. In the proposed motor, the design geometry is primarily considered to achieve the desired trapezoidal shape of back-EMF. The effects of the geometry are explained with the help of air-gap flux density, flux linkage, and the leakage flux. Both the radial flux and the proposed motor adopt the same design concept and hold equal electromagnetic loadings. The profile of back-EMF and the electromagnetic torque driven by the only-pull drive technique are compared with that of RFPM motor with non-trapezoidal back-EMF. Furthermore, the split configuration is proposed for the AFPM motor to reduce torque ripples. The demagnetisation analysis is performed to confirm the operating point of the magnets in a split-AFPM motor. The results reveal that the AF motor is a good candidate for the only-pull drive technique.

Strengthening mechanism in laser-welded 2219 aluminium alloy under the cooperative effects of aging treatment and pulsed electromagnetic loadings

Electromagnetic (EM) forming is a high-speed forming technology which uses pulsed EM loadings to form metal sheet parts. A particular advantage of pulsed EM loadings is material strengthening. In the present work, a novel process is proposed to strengthen laser-welded 2219 aluminium alloy. EM uniaxial tension is performed to study the strengthening mechanism in laser-welded 2219 aluminium alloy under the cooperative effects of solid solution-double aging (SS-DA) treatment and pulsed EM loadings. The results indicate that the strength, hardness, and plasticity of the laser-welded joints after SS-DA treatment dramatically improved in comparison to that of as-welded joints. This is due to the elimination of brittle eutectic phases and precipitation of dispersive G.P.(Π) zones, as well as precipitation hardening which dominates the strengthening mechanism. However, under the cooperative effects of SS-DA treatment and pulsed EM loadings, the strength and hardness of the weld joints increase, but the plasticity decreases as the discharge energy increases. The strength and hardness of the laser-welded joints are improved not only because of the appearance of dislocations but also because of the substantial transformative growth of G.P.(Π) zones with a bilayer structure to a thick θ'' phase with a multilayer structure which is in close proximity to the dislocations. This demonstrates the combined strengthening mechanism of the strain and intensified precipitation hardening. The significant growth of the precipitates mainly results from the concentration of the solute Cu atoms and the internal energy rise under the effect of the pulsed EM loadings.

Fracture Analysis in an Imperfect FGM Orthotropic Strip Bonded Between Two Magneto-Electro-Elastic Layers

In this study, a functionally graded orthotropic layer sandwiched between two magneto-electro-elastic layers under anti-plane time-harmonic mechanic and in-plane electromagnetic loadings is studied. This paper examines the modeling of cracks by distribution of strain nuclei along crack lines. During this investigation, the Volterra-type screw dislocation is employed in the FGM orthotropic layer and the magneto-electro-elastic coating. The material properties of the strip are considered to obey exponential variations. To solve the dislocation problem, the complex Fourier transform is applied. One merit of this technique is the possibility of determination of the stress intensity factors for multiple smooth cracks. The system of equations is derived by considering the distribution of line dislocation on the crack. These equations are of Cauchy singular type in the location of dislocation, which can be solved numerically to obtain the dislocation density on the faces of the cracks. Various examples are solved, and the dynamic stress intensity factors are obtained. The effect of the cracks configuration, bonding constant, angular frequency and material properties on the mode III stress intensity factor is studied, and the validity of the analysis is checked.

Statistics of Test Results for the ITER Nb3Sn and NbTi Conductors in the SULTAN Facility

The series production of Nb3Sn and NbTi cable-inconduit conductors (CICC) for the winding of various coils in the International Thermonuclear Experimental Reactor (ITER) magnet system is being completed in 2015. The tests of the ITER conductor samples are running in the SULTAN test facility in Villigen, Switzerland, in the scope of a framework contract, flanked by six bilateral agreements between IO and the Domestic Agencies (DAs) of China, EU, Korea, Japan, Russian Federation, and USA. The key acceptance parameter of the tests for the conductor samples made from the series production ITER CICCs is the current sharing temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cs</sub> at the nominal operating field and current after applied electromagnetic cyclic loadings at the nominal field and sinusoidal swing of conductor current from zero to nominal one. The T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cs</sub> is defined as the maximum temperature at which the conductors operate (nominal current and field) before developing an electric field of 10 μV/m. This paper gathers the latest test results of the ITER series production CICC. The qualified conductor units will be used in the winding of the toroidal field and poloidal field coils, as well as the central solenoid. The test results for the series production conductors are compared with the results of the conductors tested at the early stages of their development. The performance variation among the suppliers and the performance evolution since the start of the conductor production are discussed as well.

Fracture behavior of filament in Nb3Sn strands with crack-bridging model

The Nb3Sn strands which have high critical field are used in cable-in-conduit conductors (CICCs). The superconducting strands are twisted multistage and experience complex thermal and electromagnetic loadings. Due to their brittleness, the cracking of the Nb3Sn filaments will occur under mechanical loading. In this paper, based on the linear elastic fracture theory, we study the effects of tension loading on the fracture behavior of central crack firstly. The strain energy release rates for different twist pitches and cabling stages are presented. As the triplet is subjected to the uniaxial strain, the cracking probability will increase with the twist pitch. The crack number increases with the applied strain, and wider filament or bronze can lead to smaller crack number under the same applied strain. In addition, multistage cabling has better mechanical stability. Next, the two collinear crack problem is considered. The variations of microcrack number show that the wider bronze can provide more resistance for the propagating of the large cracks. We can conclude that the bronze plays an important role in improving the stability and strength.

Dynamic analysis of an interface crack between magnetoelectroelastic and functionally graded elastic layers under anti-plane mechanical and in-plane electro-magnetic loadings

The dynamic response of an interface crack between magnetoelectroelastic and functionally graded elastic layers under anti-plane shear and in-plane electric and magnetic impacts is investigated by the integral transform method. Fourier and Laplace transforms are applied to reduce the mixed boundary value problem of the interface crack to dual integral equations, which are expressed in terms of a Fredholm integral equation of the second kind. The singular stress, electric displacement and magnetic induction fields near the crack tip are obtained asymptotically, and the stress intensity factors (SIFs), electric displacement intensity factors (EDIFs) and magnetic induction intensity factors (MIIFs) are determined accordingly. Laplace inverse transform is applied to get the field intensities in time domain. Numerical results show how the dynamic SIF is influenced by the magnetoelectric interactions, the material properties, the electric and magnetic loadings, and the geometric size ratios and the functionally graded parameter.

Magnetoelectroelastic analysis of an arbitrary shape inclusion undergoing eigenfields and remote loadings

Within the framework of the linear theory of magnetoelectroelasticity, the problem of an arbitrary shape inclusion in an entire plane under remotely uniform in-plane electromagnetic and anti-plane mechanical loadings is investigated in this paper. The inclusion is undergoing eigenfields and has different magnetoelectroelastic moduli as that of the matrix. Using complex variable and Faber series method, the complex potential for each component can be expressed in series form with unknown coefficients. The continuity conditions of the interfaces are used to build up a set of linear equations to determine the unknown coefficients. Through solving these linear equations, one can obtain the complex potentials both inside the inclusion and in the matrix. Numerical results are provided and shown that different combinations of piezoelectric/piezomagnetic exhibit significant magnetoelectromechanical coupling effect that is not present in single-phase piezoelectric or piezomagnetic material. Applying appropriate remote loadings and eigenfields can effectively reduce stress level and increase magnetoelectric response around the inclusion.

Approach to Heterogeneous Strain Distribution in Cable-In-Conduit Conductors Through Finite Element Simulation

The ITER Cable-In-Conduit Conductors are submitted to high thermal and electromagnetic cyclic loadings responsible for conductivity loss in the strain-sensitive Nb3Sn strands. The complex mechanical phenomena occurring at the local scale of the strands make the final performances of the CICC difficult to predict from single-strand properties. In order to assess the amplitudes of the local strains that drive the conductor electrical behavior, a nonlinear finite element simulation code is used. The successive stages of the conductors' service life, from the forming of the cable to its thermal cool down and Lorentz force loading, are simulated. Each strand is individually modeled along with the great number of contacts-friction interactions between the strands. This paper presents the simulation results obtained for 144 strand cables of two different designs. It is shown that the various loadings result in a heterogeneous distribution of strains along and across the strands with occurrence of extreme tensions and compressions. The use of simulation would eventually help to better characterize the influence of conductor design parameters.

Finite element modelling of cable-in-conduit conductors

The ITER (International Thermonuclear Experimental Reactor) cable-in-conduit conductors (CICCs) are subjected to high thermal and electromagnetic cyclic loadings, responsible for conductivity loss in the strain-sensitive Nb3Sn strands. The complex mechanical phenomena occurring at the local scale of the strands make the final performances of the CICC difficult to predict from single-strand properties. In order to assess the amplitudes of the local strains that drive the conductor electrical behaviour, a nonlinear finite element simulation code is used. The successive stages of the conductors’ service life, from the forming of the cable to its thermal cool-down and Lorentz force loading, are simulated. Each strand is individually modelled and contact–friction interactions between the strands are considered. After a description of the issues regarding the modelling of the mechanical behaviour of cables and the main features of the finite element code employed, this paper presents the simulation results for the testing of pure copper wire inclusion for the conductor strain state. The code was then used to model four different cable designs in terms of twist pitches and void fractions. The analysis of the axial strain distributions within the cable is presented here.

Structural Analysis of a Prototype Fast Shutter for ITER cCXRS Diagnostic

Optical lifetime of the first mirror is a critical issue for the ITER upper-port-plug core-charge-exchange-spectroscopy diagnostic. A fast shutter is engaged to protect the mirror from depositions between measurements. The prototype shutter will be examined in a test vacuum vessel that is now under development in Forschungszentrum Jülich, Germany. Being located near the plasma, the shutter operates under severe thermal and electromagnetic (EM) loads. The multifield analyses conducted for the shutter are presented in this paper. Since the fast shutter can operate within 0.7 s, its static structural analysis should be accompanied by dynamic studies. This paper gives details about the numerical strategy used for a multifield ANSYS modeling of a complex structure. The shutter structural performance under the service, thermal, and EM loadings is in line with the requirements. A solution for a problem of high local thermostresses revealed by the analysis is proposed. Problems connected with other possible port-plug–shutter layouts are discussed.

Damage model of bone under mechanical and electromagnetic loadings

Bone, as a living tissue, has an amazing property which is distinctly different from common engineering materials and up to now we have not been able to build into artificial materials: it can repair itself. This renewing process is performed by bone remodeling, but the functions of bone remodeling are far more than repairing the damaged bone tissue. Bone can also adapt its internal microstructure and, subsequently, mechanical properties to the varying mechanical and physiological environments. So the bone damage behavior can be easily influenced by many factors. In the present paper, we establish a mechanism-based damage model to rationalize the damage evolution law of bone under simultaneously applied mechanical and electromagnetic fields. Some crucial physical and biological mechanisms underlying the sophisticated damage, remodeling and healing process of bone tissues have been incorporated in the model. Especially, an evolutionary law of bone damage and the corresponding modeling methodology are presented to analyze the complicated damage/repair behavior of bone under multi-fields. Several representative examples are given to verify the application of the proposed theoretical model in modeling the effects of environmental loadings on bone damage and repair. The results demonstrate that this model can well describe how the bone resists the damage accumulation induced by overloading and how the extreme overloading causes stress fracture of bone. We also study the role which electromagnetic fields play in bone remodeling.

The damage and healing of bone in the disuse state under mechanical and electro-magnetic loadings

The damage behaviour of bone tissues has attracted many interests of scientists and engineers due to it can repair itself. This renewing process is performed by bone remodelling. In the present paper, we establish a mechanism-based damage model to rationalize the damage evolution law of bone under simultaneously applied mechanical and electromagnetic fields. An evolutionary law of bone damage and the corresponding modelling methodology are presented to analyze the complicated damage/repair behaviour of bone under multi-fields. The model for bone injury under disuse status is established. Then the numerical examples are considered to verify the present theoretical model and the influence of those mechanical and non-mechanical factors on the bone damage and healing are simulated based on the new damage model. It is shown by result that compared with mechanical stimulation, electromagnetic field is a kind of more reliable method for improving disuse osteoporosis with relatively small side effect.

Closed-form solutions for two collinear dielectric cracks in a magnetoelectroelastic solid

The problem of two collinear electromagnetically dielectric cracks in a magnetoelectroelastic material is investigated under in-plane electro-magneto-mechanical loadings. The semi-permeable crack-face boundary conditions are adopted to simulate the case of two collinear cracks full of a dielectric interior. Utilizing the Fourier transform technique, the boundary-value problem is reduced to solving singular integral equations with Cauchy kernel, which then are solved explicitly. The intensity factors of stress, electric displacement, magnetic induction, crack opening displacement (COD) and the energy release rates near the inner and outer crack tips are determined in closed forms for two cases of possible far-field electro-magneto-mechanical loadings respectively. Numerical results for a BaTiO 3–CoFe 2O 4 composite are carried out to show the effects of applied mechanical loadings on the crack-face electric displacement and magnetic induction, the stress intensity factor and the COD intensity factor, respectively. The obtained results reveal that when the applied mechanical loading is stress, applied electromagnetic loadings have no influences on the stress intensity factor. When the applied mechanical loadings is train, the applied positive electromagnetic loadings decrease the intensity factors of stress and COD, and the applied negative ones increase the intensity factors of stress and COD. The variations of energy release rates are also given to show the effects of the geometry of two collinear dielectric cracks.