Resistivity Anisotropy Research Articles

Effect of texture evolution on corrosion resistance of AZ80 magnesium alloy subjected to applied force in simulated body fluid

The electrochemical corrosion behavior of a rolled AZ80 magnesium alloy after pre-compressive strain along different orientation in a simulated body fluid (SBF) was investigated by immersion test for 48 h. The results showed that the corrosion resistance is related to the crystal texture of the material. The texture evolution induced by plastic deformation changed the corrosion behavior of the magnesium alloy. Slip and twin associated with plastic deformation changed the orientation of crystallographic planes. The surface containing highly concentrated orientation of (0002) basal plane has higher corrosion resistance. The appearance of tension twinning could improve the corrosion resistance of magnesium alloy with specific orientation. However, the coexistence of tension twinning with high volume fraction and slip with high density dislocation reduced the corrosion resistance and corrosion anisotropy of the magnesium alloy.

Трансформация электрического тока анизотропными электропроводными средами

The authors consider the aspects of electric current distribution in electrically conductive anisotropic medium and establish how geometrical factors affect its longitudinal and transverse components. In the case of an a×b×с rectangular plate, its selected crystallographic axes are located on the plane of the side face a×b, whereas one of these axes is oriented at an angle α to the edge a. Applying a certain potential difference to the upper and lower end faces of the plate causes the appearance of longitudinal and transverse components of the internal electric current. The paper demonstrates the possibility of transforming the magnitude of the electric current and a way to optimize this magnitude. The transformation coefficient of such a device is determined by the anisotropy of the electrical conductivity of the plate and the coefficient of its shape k = a/b. The authors consider a few versions of anisotropic dielectric transformer design and offer their equivalent electric circuits. Another suggested transformer design is spiral in shape, compact and is characterized by high transformation coefficient value n. For example, at external radius r1 = 12,5 mm, internal radius r2 = 2 mm, height b = 2 mm and plate thickness c = 2,0 mm, its transformation coefficient n = 103. The information is given on existing monocrystalline and artificial anisotropic materials that can be used for the proposed device. High-temperature superconducting materials characterized by a high value of residual resistance anisotropy hold special promise in this case. Using the described transformation effect will significantly expand the possibilities of practical application of the considered electroohmic phenomenon. This will lead to the emergence of a new generation of devices for microwave technology, electronics and power engineering.

Room-temperature magnetoresistance of nanocrystalline Ni metal with various grain sizes

The room-temperature magnetoresistance (MR) characteristics of nanocrystalline (nc) Ni metal with various grain sizes (between 30 and 100 nm) are investigated in this work for the first time. The nc-Ni foils were produced by electrodeposition and the results are compared with data measured on coarse-grained (bulk) pure Ni metal samples prepared by cold-rolling and annealing. The MR(H) curves measured in magnetic fields up to H = 9 kOe are analyzed in detail to determine the anisotropic magnetoresistance (AMR) ratio. The magnitude of the AMR ratio was found to be around 2.5% for bulk Ni and in the range from about 2 to 2.5% for the nc-Ni samples, the latter data not exhibiting a systematic dependence on the grain size. On the other hand, the field-induced resistivity anisotropy splitting ∆ρAMR in the magnetically saturated state of the nc-Ni series was found to be proportional to the zero-field resistivity of the same samples with different grain sizes. The slope of this proportionality relation provided an AMR ratio of 2.4% for all nc-Ni samples, matching well the value for the bulk Ni samples. Thus, the AMR ratio for polycrystalline Ni metal seems to be fairly independent of the microstructural features. This also means that the AMR ratio is an inherent characteristic of the Ni metal matrix and it remains the same even if the matrix resistivity changes (e.g., by introducing grain boundaries) without noticeably modifying the electronic density of states at least in the vicinity of the Fermi level.

Electromagnetic Logging Response in Multilayered Formation With Arbitrary Uniaxially Electrical Anisotropy

Transversely isotropic (TI) formation is the most popular anisotropic electrical model for computing the electromagnetic (EM) field in multilayered media. However, the TI formation considers only electric parameters such as resistivity along the horizontal and vertical directions, which are not always available in real-life situations. The realistic electric parameter distribution mainly depends on the sedimentary formation environment and could be in arbitrary directions. This article developed a fast-forward algorithm used to calculate the EM field in multilayered media with arbitrary uniaxially electrical anisotropy. Formation resistivity, anisotropic dip, and anisotropic azimuth are adopted to characterize the arbitrary uniaxial anisotropic resistivity media. Half-space Fresnel coefficients are defined and used to analyze the EM reflection and transmission characteristics between different anisotropic media. Generalized reflection and transmission matrices are derived to express the EM field in arbitrary layers. To validate the proposed algorithm, we modeled the traditional logging while drilling (LWD) and triaxial induction tool responses under different conditions. The numerical results agree with the finite element results, demonstrating the feasibility, robustness, and stability of the algorithm.

Resistivity anisotropy of quantum Hall stripe phases

Quantum Hall stripe phases near half-integer filling factors $\nu \ge 9/2$ were predicted by Hartree-Fock (HF) theory and confirmed by discoveries of giant resistance anisotropies in high-mobility two-dimensional electron gases. A theory of such anisotropy was proposed by MacDonald and Fisher, although they used parameters whose dependencies on the filling factor, electron density, and mobility remained unspecified. Here, we fill this void by calculating the hard-to-easy resistivity ratio as a function of these three variables. Quantitative comparison with experiment yields very good agreement which we view as evidence for the "plain vanilla" smectic stripe HF phases.

Magnetotransport as a diagnostic of spin reorientation: Kagome ferromagnet as a case study

While in most ferro or antiferromagnetic materials there is a unique crystallographic direction, including crystallographically equivalent directions, in which the moments like to point due to spin-orbit coupling, in some, the direction of the spin reorients as a function of a certain physical parameter such as temperature, pressure etc. Fe3Sn2 is a kagome ferromagnet with an onset of ferromagnetism below 650 K, and undergoes a spin reorientation near 150 K. While it is known that the moments in Fe3Sn2 point perpendicular to the kagome plane at high temperatures and parallel to the kagome plane at low temperatures, how the distribution of the magnetic domains in the two different spin orientations evolve throughout the spin reorientation is not well known. Furthermore, while there have been various reports on the magnetotransport properties in the Hall configuration, the angular dependence of magnetoresistance has not been studied so far. In this paper, we have examined the spin reorientation by using anisotropic magnetoresistivity in detail, exploiting the dependence of the resistivity on the direction between magnetization and applied current. We are able to determine the distribution of the magnetic domains as a function of temperature between 360 K to 2 K and the reorientation transition to peak at 120 K. We discover that both out of plane and in plane phases coexist at temperatures around the spin reorientation, indicative of a first order transition. Although the volume of the magnetic domains in the different phases sharply changes at the spin reorientation transition, the electronic structure for a specific magnetization is not influenced by the spin reorientation. In contrast, we observe an electronic transition around 40 K, hitherto unreported, and reflected in both the zero-field resistivity and anisotropic resistivity.

Aim4res, an open-source 2.5D finite differences MATLAB library for anisotropic electrical resistivity modeling

Electrical Resistivity Tomography (ERT) is one of the oldest geophysical techniques, and due to the advances of numerical techniques along with computational resources, it is widely used for geophysical prospecting. It has found various domains of application as it is easy to implement and fast to image the ground resistivity heterogeneity. However, anisotropy, which is another key resistivity parameter, is seldom considered. Although being a well-known phenomenon, its consideration in the characterization process is only recent. Amongst the reasons behind this is the absence of available anisotropic resistivity modeling tools. We present aim4res (Anisotropic Inverse Modeling for RESisitivity) to that end. This open-source MATLAB library allows for 2.5D forward and inverse anisotropic resistivity modeling based on a finite differences scheme. The inverse problem is solved with a Gauss–Newton algorithm. The regularization coefficient, initial model and constraints can be adjusted from prior knowledge in order to avoid local minima during optimization. Analytical and synthetic studies have been carried out to prove the reliability of aim4res. The results demonstrate its ability to identify anisotropy, along with the correct geometry and resistivity amplitude. It is also able to correctly detect isotropy, as the inversion comparison with a previous toolbox already proven working showed. A real case study inversion is carried out to demonstrate that aim4res is a relevant tool to use on the field, able to reveal strong anisotropy fields even at short scales.

Growth and anisotropic transport properties of off-axis MgB2 thin films

Off-axis MgB2 thin films with c-axis tilted away from the film normal have been fabricated on MgO (211) substrate via a hybrid physical-chemical vapor deposition method. Microscopy images show that the film surface is characterized by terrace steps, which, in line with the x-ray diffraction experiment, demonstrates the tilted growth of the film. To probe the resistivity anisotropy resulted from this tilted growth, resistance measurements in Van der Pauw configuration have been performed. By refining an equivalent-circuit model proposed previously to simulate the measurement, the anisotropy ratio ρT/ρL is estimated, where ρT or ρL is the resistivity transverse or parallel to the terrace steps respectively. The validity of the estimation has been checked by direct measurements of ρT and ρL in standard linear-four probe configuration, which are performed by patterning microbridges from the film along or across the terrace steps. The patterned microbridges also enable us to measure the anisotropy of the superconducting critical current density Jc, which shows that Jc,L parallel to the terrace steps is higher than Jc,T transverse to the terrace steps and the anisotropy ratio Jc,L/Jc,T decreases as temperature increases, following a simple [1+(T/Tc)2]−1/2 dependence with Tc the superconducting transition temperature. The results are discussed under the framework of multiband transport of MgB2 which exhibits anisotropy between the crystallographic c-axis and ab-plane because of the anisotropic contribution of the σ bands.

Simulation of anisotropic crack growth behavior of nickel base alloys under thermomechanical fatigue

Allvac®718Plus is a nickel base superalloy possessing outstanding abilities to withstand both mechanical and thermal loads, which make this material ideal for turbine disks and blades in aero engines. The thermomechanical fatigue (TMF) crack growth behavior depends on temperature, in-service load cycles and material orientation. In particular, the crack growth at high temperature dwell time shows significant influence of material anisotropy due to platelet-like precipitations, which leads to crack deflection from the maximum principal stress direction. These specific properties must be taken into account properly to ensure a safe design and the desired lifetime of components. The focus of this paper is to develop an appropriate fracture criterion to describe crack deflection for such kind of anisotropic material resistance. This criterion and the associated crack growth laws for thermomechanical fatigue are implemented in the FEM software Procrack for fully automated three-dimensional crack propagation simulation. The numerical simulation of experiments on CT-specimens with various material orientations provided evidence that the software can capture the actual fracture behavior. Moreover, a suitable set of material parameters could be identified. The performance of the presented approach to predict realistic three-dimensional TMF crack propagation is demonstrated by an application to a typical turbine component made from Allvac® 718Plus.

On the Dwell-Fatigue Crack Propagation Behavior of a High-Strength Ni-Base Superalloy Manufactured by Selective Laser Melting

This study focuses on the dwell-fatigue crack propagation behavior of IN718 manufactured via selective laser melting (SLM). The dwell-fatigue test condition is 823 K (550 ^{circ }C) with a long 2160-s dwell-holding period. Effects of heat treatment and loading direction on dwell-fatigue crack propagation rates are studied. A grain boundary delta precipitate seems to be slightly beneficial to the dwell-fatigue cracking resistance of SLM IN718. A comparison has been made between SLM IN718 and forged counterparts at different temperatures, indicating that a creep damage mechanism is likely dominant for SLM IN718 under the present test condition. A general discussion of the inferior creep resistance of SLM IN718 is also included. The anisotropic dwell-fatigue cracking resistance has also been studied and rationalized with the effective stress intensity factor calculated from finite element modeling.

Magnetic field detwinning in FeTe

Iron-based superconductors (IBSs) possess nematic phases in which rotational symmetry of the electronic structure is spontaneously broken. This novel phase has attracted much attention as it is believed to be closely linked to the superconductivity. However, observation of the symmetry broken phase by using a macroscopic experimental tool is a hard task because of naturally formed twin domains. Here, we report on a novel detwinning method by using a magnetic field on FeTe single crystal. Detwinning effect was measured by resistivity anisotropy using the Montgomery method. Our results show that FeTe was detwinned at 2T, which is a relatively weak field compared to the previously reported result. Furthermore, detwinning effect is retained even when the field is turned off after field cooling, making it an external stimulation-free detwinning method.

On using the anisotropy in the thermal resistance of solid–fluid interfaces to more effectively cool nano-electronics

ABSTRACTAs power-intensive electronic components are further miniaturised into nanodevices, their heat dissipation is a serious operational and safety concern. While nanochannels and nanofins are often used for facilitating heat dissipation, the liquid-solid interfaces that form (Kapitza resistance), become significant barriers to heat transfer. We demonstrate that the thermal resistance of these interfaces is strongly anisotropic. The resistance of an interface to heat transfer parallel to the interface (solid surface) is significantly smaller than the more well-known Kapitza resistance (associated with heat transfer across the interface – perpendicular to the solid surface) and is even lower than that of the bulk fluid. As a result, if devices are designed to dissipate heat parallel to an interface, heat dissipation can be significantly enhanced. Our studies are also able to explain the molecular basis of this observed anisotropy in interfacial resistance, which has hitherto remained unreported for solid–liquid interfaces.

Crack deflection in short fiber reinforced composites: Theory and experiment

AbstractIn the past decades different crack growth and crack deflection criteria have been proposed, e.g. the maximum hoop stress criterion [1], the minimum strain energy density criterion [2] or the maximum energy release rate criterion [3]. These criteria were extended concerning phenomena such as crack path instability [4,5] and the anisotropy of fracture parameters [4]. Another approach for the prediction of crack growth and deflection angle is based on the Jk‐integral [6], assuming the crack to grow into the direction of the J‐vector [7]. The resulting deflection angles coincide well with those from other criteria in the case of small mixed‐mode ratios KII/KI or deflection angles, respectively. One challenge is the accurate calculation of the second coordinate J2 [8] and the appropriateness of this approach has been shown [9]. Nevertheless, in the cases of anisotropic crack resistance parameters, large mode‐II loading or unstable crack paths, the classical J‐vector criterion fails.In this paper, an extended J‐vector criterion is introduced providing the crack growth direction in the case of anisotropic fracture parameters and elastic constants [9,10]. The theory is validated by experimental results for different anisotropy ratios and orientations.

2D lateral imaging inversion for directional electromagnetic logging-while-drilling measurements

Deep-directional electromagnetic (EM) logging-while-drilling technology can map reservoir boundaries and fluid contacts for strategic geosteering, reservoir navigation, and more recently, for reservoir characterization. The inversion-based resistivity mapping is used to make real-time geosteering decisions and to refine and update the reservoir model during and after drilling. Traditional 1D and 2D inversion approaches ignore the lateral changes of the reservoir, which are contained in the azimuthally sensitive measurements and only provide a longitudinal 2D representation of the 3D reservoir structure around the well. A new 2D lateral imaging inversion uses the full azimuthal sensitivity of the measurements to map the vertical and lateral resistivity heterogeneities around the wellbore. A 2.5D EM solver is run in a Gauss-Newton optimization to reconstruct the measurements in complex scenarios and determine the 2D anisotropic resistivity distribution in an imaging plane along with the orientation of the formation invariant direction with respect to the wellbore. Continuous 2D imaging along the well path generates a 3D reservoir resistivity map in the proximity of the wellbore.

Magnetic and electrical anisotropy with correlation and orbital effects in dimerized honeycomb ruthenate Li2RuO3

Li2RuO3 undergoes a structural transition at a relatively high temperature of 550 K with a distinct dimerization of Ru-Ru bonds on the otherwise isotropic honeycomb lattice. It exhibits a unique herringbone dimerization pattern with a largest ever reported value of the bond shrinkage of about ~ 0.5 \r{A}. Despite extensive studies, both theoretical and experimental, however, its origin and its effect on physical properties still remain to be understood. In this work, using high quality single crystals we investigated the anisotropy of resistivity ($\rho$) and magnetic susceptibility ($\chi$) to find a very clear anisotropy: $\rho$$_c*$ > $\rho$$_b$ > $\rho$$_a$ and $\chi$$_b$ > $\chi$$_a$ > $\chi$$_c*$. For possible theoretical interpretations, we carried out density functional calculations to conclude that these anisotropic behavior is due to the correlation effects combined with the unique orbital structure and the dimerization of Ru 4d bands.

Structurally tailored 3D anisotropic controlled-source electromagnetic resistivity inversion with cross-gradient criterion and simultaneous model calibration

Geologic interpretation of 3D anisotropic resistivity models from conventional marine controlled-source electromagnetic (CSEM) data inversion faces difficulties in low-resistivity contrast sediments and structurally complex environments that typify the new frontiers for hydrocarbon exploration. Currently, the typically reconstructed horizontal resistivity [Formula: see text] and vertical resistivity [Formula: see text] models often have conflicting depth structures that are difficult to explain in terms of subsurface geology, and the resulting resistivities may not be close to the true formation resistivities required for estimating reservoir parameters. We have investigated the concept that an objective geologically oriented or structurally tailored inversion can be achieved by requiring that the cross-product of the gradient of horizontal resistivity and the gradient of the vertical resistivity is equal to zero at significant geologic boundaries. We incorporate this boundary-shape criterion in our 3D inverse problem formulations, implemented within nonlinear model-space and conjugate-gradient contexts, for cases in which a priori calibration data from wells and/or seismically derived subsurface boundaries are available and for cases in which these are lacking. The resulting fit-for-purpose solutions serve to better analyze the peculiarity of a given data set. We applied these algorithms to synthetic and field CSEM data sets representing a fold-thrust environment with low-resistivity and low-contrast sediments. The resulting [Formula: see text] and [Formula: see text] models from cross-gradient joint inversion of synthetic data of appropriate frequency bandwidth without a priori information are structurally similar and consistent with the test models, whereas those from the inversions of band-limited field data are consistent with the available seismic and resistivity well-log data. This particular approach will thus be useful for lithologic correlation in frontier regions with limited a priori information using broadband CSEM data. For these band-limited field data, we found that the anisotropic bulk resistivities of the low-contrast sediments are better determined by incorporating a priori calibration data from triaxial resistivity logs and seismic horizons.

Study of the relative growth rate, the anisotropy of electrical resistivity and anomalous photocurrent behavior of the unidirectional grown Rochelle salt crystals

This research article compares the growth rate along the directions [100], [010], and [001] of Rochelle salt crystals grown using the Sankaranarayanan–Ramasamy method, reports its electrical resistivity near its two Curie temperatures along the directions [100], [010], [001], [110], [011], and [101], presents the evaluated activation energy in the paraelectric and ferroelectric phases of the crystal, points out the change in the value of activation energy at Curie temperatures of the crystal, displays the anomalous behavior of the photocurrent along the polarization direction [100] of the crystal around the two Curie temperatures, and discusses the photo-stimulated shifts of the Curie temperatures.

Out-of-plane transport in ZrSiS and ZrSiSe microstructures

A recent class of topological nodal-line semimetals with the general formula MSiX (M = Zr, Hf and X = S, Se, Te) has attracted much experimental and theoretical interest due to their properties, particularly their large magnetoresistances and high carrier mobilities. The plateletlike nature of the MSiX crystals and their extremely low residual resistivities make measurements of the resistivity along the [001] direction extremely challenging. To accomplish such measurements, microstructures of single crystals were prepared using focused ion beam techniques. Microstructures prepared in this manner have very well-defined geometries and maintain their high crystal quality, verified by the observations of quantum oscillations. We present magnetoresistance and quantum oscillation data for currents applied along both [001] and [100] in ZrSiS and ZrSiSe, which are consistent with the nontrivial topology of the Dirac line-node, as determined by a measured π Berry phase. Surprisingly, we find that, despite the three dimensional nature of both the Fermi surfaces of ZrSiS and ZrSiSe, both the resistivity anisotropy under applied magnetic fields and the in-plane angular dependent magnetoresistance differ considerably between the two compounds. Finally, we discuss the role microstructuring can play in the study of these materials and our ability to make these microstructures free-standing.

Detection performance and inversion processing of logging-while-drilling extra-deep azimuthal resistivity measurements

We present systematic investigations on the physics, detection performance and inversion of logging-while-drilling extra-deep azimuthal resistivity measurements (EDARM). First, the definitions of EDRAM measurements are discussed, followed by the derivation of the attenuation and phase-shift geometrical factors to illustrate the relative contributions of formation units to the observed signals. Then, a new definition of detection depth, which considers the uncertainty of inversion results caused by the data noise, is proposed to quantify the detection capability of EDARM. Finally, the Bayesian theory associated with Markov chain Monte Carlo sampling is introduced for fast processing of EDARM data. Numerical results show that EDARM is capable of detecting the azimuth and distance of remote bed boundaries, and the detection capability increases with increasing spacing and resistivity contrast. The EDARM tool can accommodate a large range of formation resistivity and is able to provide the resistivity anisotropy at arbitrary relative dipping angles. In addition, multiple bed boundaries and reservoir images near the borehole are readily obtained by using the Bayesian inversion.

CONSTRUCTION OF DEFORMATION DIAGRAMS OF CONCRETE UNDER SHEAR BASED ON THE AUTHOR'S THEORY OF ANISOTROPIC MATERIALS POWER RESISTANCE TO COMPRESSION AND DEFORMATION THEORY OF PLASTICITY

The Aim of this work was the construction of a concrete deformation diagrams under shear on the basis of two approaches: the theory of anisotropic materials force resistance in compression and deformation theory of plasticity with the use of state diagrams of concrete under tension and compression, obtained by the authors jointly with Acad. N.I. Karpenko earlier. For this purpose, in the framework of the first approach, the main computational expression of the author's model was written in the current deformations, which ultimately allowed to establish a relationship between the diagrams σb-εb, σbt-εbt and τb-γb and reveal the mechanics of destruction of concrete elements under compression. The second approach additionally takes into account the change in the coefficient of transverse deformations, µb, and shear modulus of deformations, Gb as the load increases, but does not take into account the presence of normal stresses affecting the stress-strain state. This approach recreates the conditions of pure shear, which is possible only theoretically, and in real designs is applicable with a certain degree of error. Nevertheless, both approaches provide almost identical data in the construction of diagrams «τb-γb», which differ from the experiment by no more than 13-15%. In this regard, they are recommended for implementation: the first-to perform engineering calculations «manually», the second-to develop computer programs that allow you to automate the calculation.