Force Fp Research Articles

The influence of HIP on the homogeneity, Jc, Birr, Tc and Fp in MgB2 wires

Unreacted MgB2 wires were made at Hyper Tech Research, USA by a continuous tube forming and filling method using mixtures of Mg and B with and without SiC powder additions. All of the wires underwent hot isostatic pressure (HIP) treatment at the Institute of High Pressure. The first part of the wire was annealed at a pressure of 1 GPa, and the second part was annealed at 0.1 MPa. In this work, we show the influence of high pressure on critical current density (Jc), pinning force (Fp), critical temperature (Tc), irreversible magnetic fields (Birr) and the Fp scaling and microstructure of MgB2 wires. The results obtained indicate that after annealing at high pressure, the MgB2 wires show increases of Jc and Fp in high magnetic fields (8 T–12 T); in SiC doped MgB2 wires, Fpmax shifts to higher magnetic fields. We also compared the Jc of the doped and undoped MgB2 wires (without HIP and with HIP). The scanning electron microscope (SEM) results show that HIP increases the density of MgB2 material and improves its uniformity.

Anomalies in vortex lattice dynamics driven by induced ac currents in superconducting films with magnetic arrays of two-fold symmetry

We study the dynamics of the vortex lattice driven by ac induced currents in the critical state regime, for T > 0.70 TC. The samples are superconducting films grown on top of two-fold symmetry array of magnetic dots. In these heterostructures, the induced ac currents flow parallel to the short and to the long side of the pinning array in different areas of the samples simultaneously. This behavior produces remarkable effects in the vortex lattice dynamics. First of all, periodic features are observed in the ac susceptibility versus applied magnetic field measurements which are related to matching effects between the vortex lattices and the magnetic array. However, the vortex lattice reconfiguration observed in magnetotransport experiments is absent. Some of these features are revealed as maxima instead of being minima, indicating higher mobility at certain matching fields. Competing unstable vortex configurations could lead to increase vortex mobility precluding the reconfiguration transition. At high temperatures, where the matching effects show up, the magnetic permeability of the dots is the mechanism that governs the JC(T) behavior. Moreover, the temperature dependence of the pinning force FP(T) shows a temperature crossover related to an unexpected enhancement in vortex mobility. Vortex–vortex interaction and the interplay between trapped and interstitial vortices are a hint to explain these phenomena.

Influence of particle characteristics on impact event of dry granular flow

The process of a dry granular flow impacting a rigid retaining wall was systematically studied using three types of granular materials with different physical parameters. The experimental results show that the particle characteristics in terms of dynamic internal friction angle and particle diameter directly influence the flow velocity, flow thickness, critical time, and volume of the stagnant zone, and indirectly influence the proportion of the force components in the total normal force. The dissipated energy in a dry granular flow is linearly related to the product of the surface area, coefficient of internal friction, and sine of the slope angle. Impact tests of various granular materials indicate that the total normal force exerted on a retaining wall consists of a drag force (Fd), gravitational and frictional force (Fgf), and passive earth force (Fp). The existing empirical equations are suitable for the calculation of Fd for flows with Froude numbers between 6.0 and 12.4.

Influences of BaZrO3 particles on the microstructure and flux pinning of YBCO film prepared by using modified TFA-MOD approach

YBa2Cu3Oy (YBCO) films with BaZrO3 (BZO) particles were fabricated on LaAlO3 (00l) single crystal substrates by benzoate modified trifluoroacetate metal organic deposition (modified TFA-MOD). The influences of BZO particles on the texture, microstructure and the flux pinning properties of YBCO films were discussed. At high level of BZO doping, the BZO particles were considered to play an important role in the formation of a-axis oriented YBCO grains and the degradation of texture. When the optimal BZO content was 5%, the BZO particles as the flux pinning centers could significantly improve the critical current density (Jc) and flux pinning force (Fp) of BZO-doped YBCO film. Jc value of YBCO + 5%BZO film was about 4.9 MA/cm2 at 77 K and 0 T, and the highest Fp value (Fpmax) was about 4.3 GN/m3 at 77 K.

Enhanced flux pinning in YGdBCO film grown by sol–gel approach

Gd-doping YBCO films were fabricated on LaAlO3 (00l) substrates by sol–gel method using benzoic acid modified trifluoroacetates precursor solution. Effects of Gd doping on texture, microstructure and flux pinning properties of YBCO films were investigated. With optimal Gd-doping, the surface and texture of YGdxBa2Cu3Oy films have been improved. The introduction of ion defects can improve the critical current density (Jc) and flux pinning force (Fp) of the YGdBCO films. The Jc and Fp values of YGd0.1Ba2Cu3Oy film are almost two times higher than that of pure YBCO film in magnetic field. These results indicate that Gd-doping YBCO phase with sol–gel process is a perspective method for enhancement of current carrying capability of YBCO film.

Flux-pinning properties of nanocrystalline HfO2 added YBa2 Cu3 O7−δ superconductor

The effect of addition of different weight percentages of nanocrystalline HfO2, synthesized through a modified combustion method in bulk coarse-grained orthorhombic YBa2Cu3O7−δ powder was studied. The structure and microstructure of the samples examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed the formation of a secondary phase YBa2HfO5.5 in the superconductor without deteriorating the superconducting properties. The variation of sintering temperature, density, critical transition temperature (Tc), magnetic field dependence of critical current density (Jc), and flux-pinning force (Fp) of YBa2Cu3O7−δ having different proportions of YBa2HfO5.5 formed in the matrix were studied in detail. The samples showed a transition temperature (Tc) of ∼92 K and the self-field critical current density (Jc) increases significantly up to an optimum value of 5.42 × 104 A cm−2 for 2 wt% addition of nano HfO2. The enhancement of the critical current density in the YBa2Cu3O7−δ-HfO2 samples is attributed to the presence of the nonreacting YBa2HfO5.5 phase, formed due to the addition of HfO2 as artificial pinning center. The formation of YBa2HfO5.5 in YBa2Cu3O7−δ bulk superconductor also enhances the pinning force density from 3 × 106 to 30.4 × 106 N m−3 at 77 K.

Hard Cutting and Diamond Burnishing of 100Cr6 Steel Bearings

The paper deals with research concerning optimal technological parameters in diamond burnishing after hard turning by standard tool geometry and by wiper geometry. Burnishing is a less known method, by which the surface of workpiece is finished by a harder tool, without chip removal. Experiments focus on the surface roughness of workpiece, at combination of feed (f) and burnishing force (Fp). We measured also machining forces (Fc, Ff, Fp) at hard turning. Workpiece was made of 100Cr6-type bearing steel with hardness of HRC64.

Investigation of the Impact of Orthogonal Cutting Processes on Nanocrystalline Surface Layer Generation

The present work analyzes the influence of an orthogonal machining process on the generation of nanocrystalline surface layers. Thereby, AISI 4140 is used as work piece material. Metallic parts with a severe nanocrystalline grain refinement in the near-surface area show many beneficial properties. Such surface layers considerably influence the friction and wear characteristics of the work piece in a subsequent usage as design elements working under tribological loads. The focus of this paper is an experimental analysis of a finishing orthogonal cutting operation, carried out with a broaching machine, to generate nanocrystalline surface layers. The influence of process and geometry parameters on the generation of nanocrystalline surfaces is investigated with the aim to massively decrease the grain size in the work piece surface layer. Parameters that are studied and taken into account in the manufacturing process are cutting edge radius rβ, depth of cut h and cutting velocity vc. The cutting edge radius rβ is modified by a drag finishing process. The generation of nanocrystalline surface layers is especially influenced by the design of the uncoated carbide cutting tools. Additionally, cutting force Fc and passive force Fp are determined by a 3-component dynamometer to calculate the relationship between specific cutting force kc and specific passive force kp. The temperature beneath the clearance face is detected by a fiber optic pyrometer. These measurement methods and devices are applied to detect the impact of the most relevant measurement values occurring during machining and causing a drastic reduction of grain size in the surface layer. The evaluation of the manufacturing process is carried out by detailed analyses of the microstructural conditions in the surface layer after processing using a Focused Ion Beam (FIB) system. These material characterizations provide information about the surface engineering concerning the microstructural changes in the surface layer of the work piece due to finishing orthogonal cutting processes.

Jc improvement by double artificial pinning centers of BaSnO3 nanorods and Y2O3 nanoparticles in YBa2Cu3O7 coated conductors

Double artificial pinning centers of BaSnO3 nanorods and Y2O3 nanoparticles were investigated in YBa2Cu3O7 films on textured substrates prepared using ion beam assisted deposition. The BaSnO3 and Y2O3 content was varied in pulsed laser deposition. Transmission electron microscopy observation revealed the systematic change in density of the BaSnO3 nanorods and the Y2O3 nanoparticles in the films. In YBa2Cu3O7 + BaSnO3 films, maximum global pinning force (Fp,max) was improved at high magnetic fields, and Fp,max was shifted to high magnetic field by the Y2O3 incorporation due to an increase in density of the pinning centers. The angular dependences of critical current density (Jc) in the YBCO + BaSnO3 films were tuned by introducing Y2O3, and some of the YBa2Cu3O7 + BaSnO3 + Y2O3 films exhibited isotropic Jc behavior at low magnetic field. The double artificial pinning centers of BaSnO3 nanorods and Y2O3 nanoparticles are effective in improving Jc angular dependences, Jc values at high magnetic fields, and Fp,max.

Optimization of a fluorine-free metal-organic deposition to fabricate BaZrO3-doped YBa2Cu3O7−δ film on RABiTS substrates

In this study, we used a systematic route to optimize the fluorine-free MOD process to achieve a high critical current density (Jc) in BaZrO3 (BZO)-doped YBCO films on RABiTS substrates. The BZO content is given by 1 YBCO+x BZO films, where x is moles of BZO per 1 mole of YBCO. We found x = 0.10 to be the optimal BZO content and ∼795–805 °C to be the optimal growth temperature window with 60–90 min processing time. TEM studies show the BZO nanoparticles are ∼20 nm in size and spaced ∼50–100 nm apart. The in-field Jc and the peak pinning force (Fp) of the film grown at the optimal conditions were greatly increased at 77 K relative to pure YBCO films, achieving ∼6.7 GN m−3 at 77 K, H ‖ c in a ∼800 nm thick x = 0.10 film. The angular dependence of in-field Jc measurements also shows greatly reduced angular anisotropy at 1 and 4 T at 77 K due to isotropic pinning by BZO nanoparticles.

The flux pinning mechanism, and electrical and magnetic anisotropy in Fe1.04Te0.6Se0.4 superconducting single crystal

The temperature and magnetic field dependences of the magnetization and critical current density of Fe1.04Te0.6Se0.4 single crystals have been investigated, and the flux pinning mechanism has been analysed. The normalized pinning force (fp = Fp/Fp,max) vs. h(H/Hirr) curves, are scaled using the Dew-Hughes' theory, f(h) ≈ hp(1 − h)q with p = 1.35 and q = 3.06. The angular dependence of the resistivity under different magnetic fields shows a dip-like structure, below the superconducting transition temperature. The anisotropic value of 2 was obtained using Ginzburg-Landau theory.

Temperature- and field-dependent critical currents in [(Bi,Pb)2Sr2Ca2Cu3Ox]0.07(La0.7Sr0.3MnO3)0.03 thick films grown on LaAlO3 substrates

La0.7Sr0.3MnO3 (LSMO) nanoparticles were embedded in (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) thick films, which were grown by simple melting-quenching-annealing (MQA) method on (001)-oriented LaAlO3 (LAO) substrates. The nominal composition of the composite-like hybrid system was (Bi2223)1−x(LSMO)x with x = 0.03. The constituent elements, Bi2223 and LSMO, were prepared separately by standard solid state reaction and Pechini's method, respectively. The analysis of the X-ray diffraction patterns suggested a polycrystalline growth mode of the thick films on the LAO substrates. From electric transport measurements, the superconducting onset temperature and the superconducting critical temperature (ρ = 0) ended up being 105 and 62 K, respectively. The flux pinning energy U was determined using the Anderson-Kim model. The value of U was compared with those obtained for similar samples with concentrations x = 0.01 and x = 0.05. Current-voltage characteristics were recorded at different temperatures in order to analyze the behavior of the superconducting current (Ic) of the films. A dramatic drop of Ic was observed at ∼20 K. This seems to be linked to the presence of flux creep acting as dissipation factors attributed to LSMO nanoparticles. Isothermal magnetization loops recorded at T < Tc and T > Tc showed clear diamagnetic and ferromagnetic signals, which verify the multifunctional character of the system. Based on the isothermal M(H)-loops recorded at 5, 20, and 40 K and taking Kim's model into account, the dependence of superconducting current density (Jc), and the volume pinning force (Fp) on the magnetic field were calculated. The dependence Jc(B) at 5 K showed an exponential-type behavior, which is described by an empirical equation. This empirical equation considers the maximum value of Fp, which may be scaled with the Kramer's expression for Fp. From this scaling procedure, diverse exponents, associated with different pinning mechanisms, were determined. The drastic fall of Jc(B) at T > 20 K is discussed by considering the decreasing of the lower critical field (Hc1), penetration field (Hp), irreversible magnetic field (Hirr), and magnetization maximum (Mmax) with increasing in the LSMO particle content.

Enhanced critical current density in GdBa2Cu3O7 − δ thin films with substrate surface decoration using Gd2O3 nanoparticles

The effect of substrate surface decoration on the critical current density (Jc) of GdBa2Cu3O7−δ (GdBCO) thin films has been investigated. Prior to GdBCO deposition, uniformly-distributed Gd2O3 nanoparticles were applied to a substrate surface by using the pulsed laser deposition technique. GdBCO films deposited on Gd2O3-decorated SrTiO3 (STO) substrates showed an enhanced in-field Jc in comparison with that of GdBCO film on untreated STO. The Jc enhancement may be attributed to both the Gd2O3 nanoparticles located at the film/substrate interface and to induced linear defects that were nearly parallel to the c-axis of the film, as confirmed by the transmission electron microscope analysis. A significantly improved pinning force Fp in terms of a larger Fpmax values was obtained with Gd2O3 decoration.

Superconducting and Magnetic Properties of Polycrystalline [(Bi,Pb)2Sr2Ca2Cu3O x ]1−x (La0.7Sr0.3MnO3) x Thick Films Grown Using MQA Method

Polycrystalline thick films with the nominal composition [(Bi,Pb)2Sr2Ca2Cu3Ox]1−x(La0.7Sr0.3MnO3)x (x=0, 0.01, 0.03, 0.05) were prepared by the melting-quenching-annealing (MQA) method on (001)-oriented LaAlO3 (LAO) substrates. The XRD patterns show that the samples are composites consisting of (Bi,Pb)2Sr2Ca2Cu3Ox and La0.7Sr0.3MnO3 particles with average grain sizes of ∼60 and ∼30 nm, respectively. From electric transport measurements, the superconducting onset temperature, Tonset, and superconducting critical temperature, Tc, ended up being ∼80 and ∼60 K, respectively. The depression of Tc may be attributed to the proximity effect between ferromagnetism and superconductivity. The M–H hysteresis loops indicate the coexistence of ferromagnetism and superconductivity in the films. The magnetic field dependence of the superconducting current density and the volume pinning force Fp=Jc×B were obtained by applying Bean’s model to the isothermal M–H loops.

Experimental Study of Dry Granular Flow and Impact Behavior Against a Rigid Retaining Wall

Shallow slope failure in mountainous regions is a common and emergent hazard in terms of its damage to important traffic routes and local communities. The impact of dry granular flows consisting of rock fragments and other particles resulting from shallow slope failures on retaining structures has yet to be systematically researched and is not covered by current design codes. As a preliminary study of the impact caused by dry granular flows, a series of dry granular impact experiments were carried out for one model of a retaining wall. It was indirectly verified that the total normal force exerted on a retaining wall consists of a drag force (Fd), a gravitational and frictional force (Fgf), and a passive earth force (Fp), and that the calculation of Fd can be based on the empirical formula defined in NF EN Eurocode 1990 (Eurocode structuraux. Base de calcul des structures, AFNOR La plaine Saint Denis, 2003). It was also indirectly verified that, for flow with Froude number from 6 to 11, the drag coefficient (Cd) can be estimated using the previously proposed empirical parameters.

Experimental investigations into the application of direct tension indicators with preloaded structural bolting assemblies (HV system) to EN 1090‐2

AbstractEN 1090‐2 provides several tightening methods for the preloading of bolting assemblies. One of the prescribed procedures is the use of direct tension indicators, so‐called DTIs, with lubrication according to k‐class K0. According to the definition of k‐class K0, the lubrication should not have an influence on achieving the required preloading force Fp,C. For this reason, the main focus of the investigations presented here was how the lubrication influences the behaviour of preloaded HV bolting assemblies with and without DTIs. The experimental investigations were carried out on the institute’s own tightening torque testing machine.

Superconducting Properties Comparison of SiC Doped Multifilamentary ${\rm MgB}_{2}$ Wires of Various Sheaths (Cu, Monel, Glidcop) After High Pressure HIP Treatment

Wires with 6 filaments of cores surrounded by a Nb barrier, and Cu, Monel and Glidcop sheath, drawn by Hyper Tech Inc. to diameters of 0.83 mm, have been treated in a Hot Isostatic Pressure process under high Ar pressures. The pressure of the HIP varied in different processes in order to find the optimal sintering conditions to obtain the highest at high magnetic fields. Also a stainless steel sheathed MgB2 wire has been used for comparison. The effect of sintering under high pressures on transport properties of those wires was measured by means of critical current and pinning forces Fp. The samples of 70 and 20 mm length were measured in parallel and perpendicular magnetic fields, respectively. High magnetic fields, of up to 14 T, were obtained in a Bitter magnet. The microstructure of annealed samples was investigated by SEM analysis.

PINNING-FORCE SCALING AND ITS LIMITATION IN INTERMEDIATE AND HIGH TEMPERATURE SUPERCONDUCTORS

We present the scaling law of the pinning force FP in intermediate and high temperature superconductors, the factors which influence its field and temperature dependence, the limitations imposed by the enlarged anisotropy and high operating temperatures, giant creep included. The theoretical developments which incorporate the new features of these classes of superconductors, most of them based on the Anderson–Kim theory, prove to be a useful source of information relative to the nature of the pinning and the characteristic fields. The use of models based on thermal activation integrates into scaling the tail of pinning force and also substantiates the use of the irreversibility field H irr as scale field. Finally, the data on scaling law in the two class of superconductors are presented and discussed.

Flux pinning characteristics in cylindrical niobium samples used for superconducting radio frequency cavity fabrication

We present the results from DC magnetization and penetration depth measurements of cylindrical bulk large-grain (LG) and fine-grain (FG) niobium samples used for the fabrication of superconducting radio frequency (SRF) cavities. The surface treatment consisted of electropolishing and low-temperature baking as they are typically applied to SRF cavities. The magnetization data are analyzed using a modified critical state model. The critical current density Jc and pinning force Fp are calculated from the magnetization data and their temperature dependence and field dependence are presented. The LG samples have lower critical current density and pinning force density compared to FG samples, favorable to lower flux trapping efficiency. This effect may explain the lower values of residual resistance often observed in LG cavities than FG cavities.

Enhancement of Vortex Pinning in YBa2Cu3O7−δ -BaHfO3 Superconductor-Insulator System

A systematic study on phase evolution, bulk density, resistivity, critical transition temperature (T C), critical current density (J C) and in-field transport critical current density (J C–B) of pure and nano particles of BaHfO3 added YBa2Cu3O7−δ (YBCO) samples of different weight percentages has been carried out. The result shows a significant improvement in the electrical transport properties of the superconductor, namely the J C, J C–B characteristics and flux pinning force (F p) of the BaHfO3 added samples. The transition temperature also was found to increase marginally. A maximum transport J C of 742 A/cm2 at 77 K (for x=2 wt%) was observed for BaHfO3 added samples against 147 A/cm2 for pure YBCO sample. The enhancement of the critical current density in the YBCO–BaHfO3 sample is attributed to the formation of an insulating and non-reacting YBa2HfO5.5 phase, acting as artificial pinning centers in the matrix. The introduction of nano particles of BaHfO3 in bulk YBCO increases the pinning force density from 30×103 N/m3 to 424×103 N/m3 at 77 K. The improvement in sintering density due to an optimum value 2 wt% BaHfO3 addition in bulk YBCO indicates its potential use in electrical devices and technology. The enhancement in the superconducting properties, particularly in the J C–B characteristics due to BaHfO3 addition, seems to have great technological significance.