Electrical Constriction Resistance Research Articles

An efficient method for solving electrical constriction resistance of rough surfaces

An efficient method is presented to solve the electrical constriction resistance (ECR) in electrical contact problem. For two contact parts under a specified total current, the conjugate gradient algorithm is proposed to determine the unknown current density in contact region. Two variations of discrete convolution-fast Fourier transform algorithm are used to solve the electrical potential for contact parts of finite and infinite size, then the ECR can be obtained. These algorithms lead to an efficient method, which is verified by finite element analysis and analytical formulas. Compared with widely used methods for estimating ECR, the present method shows broad applicability in diverse surfaces by considering both shapes and interactions of contact spots, and has capacity to capture the solution details.

A Prediction Model of Electrical Constriction Resistance (ECR) between Dry-Friction Rough Surfaces Based on Three-Dimensional (3-D) Fractal Theory

In this paper, firstly, based on the fractal theory, Hertz contact theory and fractal network, the prediction model of the ECR for rough interface is established in consideration of the modified hypothesis, 3-D interface topography and elastic-plastic deformation. Secondly, using the engineering data of material, the influences of fractal dimension D, fractal roughness G , dimensionless loading force F* and friction coefficient μ on the ECR are analyzed by numerical simulation. Finally, compared with the classical models, the tendency of established model is same as that of other models. During the design stage of electrical equipment, the present model of the ECR can provide a theoretical reference for the accurate ECR prediction of rough interface.

A 3D-FEM-based model to predict the electrical constriction resistance of compressed contacts

This work proposes a method to estimate the electrical constriction resistance of two mating metallic rough surfaces based on the finite element method (FEM). The FEM-based method generates a random array of three-dimensional orthogonal parallelepipeds to simulate the stochastic distribution of the asperities across the contact interface. The effect of the contact pressure is studied in detail, since once the contact materials and the topology of the contact area are settled, the contact pressure plays a critical role in determining the electrical constriction resistance. The proposed model is based on two critical variables, the contact pressure and the surface roughness of the mating surfaces, which must be measured in the laboratory to calibrate the model. Results provided by the FEM-based model are compared with experiments for three geometries, thus validating the accuracy of the proposed approach. Although the apparent contact areas of the analyzed specimens have a rectangular shape, the proposed method is also applicable to determine the electrical constriction resistance of other geometries. It is also proved that depending on the pressure applied to the contact interface, the electrical constriction resistance can be almost independent of the apparent area of contact. Although the aim of this work was to generate an electrical constriction resistance model for power connectors, it is also applicable to many other power devices.

Thermal Analysis of High-Power Prismatic LiFePO4 batteries: Modeling and Experiment

A 90Ah prismatic LiFePO4/graphite battery (Sinopoly Battery Ltd., China) is used for the experiments and thermal modeling [cf. Fig. 1]. In the experimental study, a power processing system is employed to cycle the experimental battery. Constant-current discharge tests at 1C-rate (90A), 2C-rate (180A), and 3C (270A) are performed to measure the battery voltage and surface temperatures.In the modelling study, a three-dimensional transient model has been developed to predict the thermal behaviour of the battery during galvanostatic processes. A transient heat conduction equation is sufficient to describe the thermal phenomenon of domain (1); while the heat transfer mechanism in domain (2) is modelled by the natural convection. A convective-radiation boundary condition is considered at the boundaries of the domain.The above-mentioned models are performed in a finite element solver (COMSOL Multiphysics, Version 4.4), and the accuracy of the model is validated through comparison with the experimental data. Some Results The rate of heat generation which is the main parameter calculation in the thermal model, is approximated from [1], g=I/ν[(V-V oc )+T dV oc/dT] (1)where I and V denote the battery operational voltage and current, respectively, ν represents the battery volume, V oc is the open circuit voltage of the battery and T is temperature. The heat generation terms can be determined by using experimental tests or electrochemical models, which the first approach is applied in this study. A constant value of -0.4337 mV/K adapted from Ref. [2], is considered for term dV oc/dT. The rate of heat generation caused by the polarization losses, V-Voc , is defined from the measured electrical performance of the battery.The heat generation rates inside the battery (domain (1)) during three different galvanostatic discharge processes (90 A, 180 A, and 270 A) are calculated based on Eq. (1) and the battery electrical performance, and then the obtained expressions are implemented into the thermal model.In Fig. 2, the modeling results for average surface temperature of the battery (shown by solid lines) are compared to the corresponding experimental data (symbols), during constant-current discharge processes with 90 A, 180 A, and 270 A. The comparison shows an excellent agreement between the predicted results and the data from the experiments.In future, an electrical model will be coupled to the presented model to describe the ohmic heating in the electrodes as a result of the electrical constriction resistance. [1] D. Bernardi, J. Electrochem. Soc., Vol. 132, pp. 5-12, (1985).[2] A. Samba et al. , J. Electrochimica Acta, Vol. 117, pp. 246–254, (2014).[3] P. Taheri et al., J. Electrochem. Soc., Vol. 160, pp. A1731–A1740, (2013).

Electrical Constriction Resistance in Current Collectors of Large-Scale Lithium-Ion Batteries

A new two-dimensional model is proposed to describe the electrical conduction in current collectors of prismatic lithium-ion batteries, and to investigate the effects of tab design on voltage drop. Polarization expression for a large-scale lithium-ion cell is determined experimentally and implemented in a numerical analysis to show that reaction current remains approximately uniform when depth-of-discharge is less than 85%. Based on this observation, a compact analytical model is developed to determine bulk and constriction/spreading resistances in current collectors. Moreover, the model predictions are successfully validated through comparisons with experimental data. It is demonstrated that constriction/spreading resistance in current collectors of the considered battery is fairly small; about 10% of the total cell resistance but it is larger than the contribution of bulk resistance which is about 3%. The model confirms that constriction/spreading increase with: decrease in the aspect ratio of the current collector, decrease in the tab width, and increase in the tab eccentricity.

Numerical computation of thermal and electrical constriction resistance in finite tube

This study presents an analysis of the coupled electrical and thermal constriction phenomena. The finite element method is used to calculate constriction resistance (thermal and electrical) of a conducting semi-infinite cylinder subjected to heat and current spot at the same time. Three fundamental cases are presented successively. The first case deals with the transient thermal constriction in a semi-infinite heat flux tube. The second one deals with the steady state electrical constriction in the same geometry. The third and most important case presents the numerical computation of constriction resistance when the semi-infinite tube is the site of volumetric heat generation resulting from Joule effect (electrical conduction). The preliminary studies are conducted to validate the numerical computation by their comparison to available analytical solutions in the literature. The transient thermal constriction resistance and the steady state electrical constriction resistance are presented and analyzed for different constriction ratio and coupling parameter. All presented examples use a uniform spatial distribution of the electrical density and the heat flux dissipated by the spot.

Minimization of thin film contact resistance

The geometry that minimizes the electrical constriction resistance of thin film contact is identified for both Cartesian and cylindrical geometries. Assuming uniform resistivity on an idealized model, simple scaling laws for the thin film contact resistance are constructed, for arbitrary ratio of constriction size to film thickness. Optimal conditions to minimize the thin film contact resistance are identified. The analytic calculations are confirmed with numerical code results.

Constriction Resistance of Thin Film Contacts

The electrical constriction resistance of a circular a-spot in a bulk interface stems from convergence of electrical current flow lines from a distance far from the constriction, and the subsequent spreading out of the current from the constriction. The spreading resistance of an a-spot located in a thin film cannot be identical to that generated in a bulk component of the same material since current spreading is constrained by the thin film boundaries. This paper addresses the effect of film thickness on spreading resistance, and hence on constriction resistance, in a thin conducting layer. If a and L are, respectively, the constriction radius and the film thickness, the spreading resistance is found to deviate significantly from that in a bulk solid only for relatively thin film and for values of a/L greater than 0.02. This paper also compares the dc spreading resistance in a thin film to the spreading resistance for high-frequency current in a bulk solid where current flow is limited to the electromagnetic skin depth. It turns out that spreading resistance at high-signal frequencies is comparable with the dc spreading resistance in a thin film if the thickness of the equivalent thin film is identified as the skin depth at the relevant frequency.

Health monitoring of bolted joints via electrical conductivity measurements

The use of electrical resistance as a diagnostic parameter in structural health monitoring of bolted joints is discussed in the paper. The proposed method is based on the phenomenon that the electrical constriction resistance of the rough contact interface between two conductive members clamped by a bolt is a sensitive indicator of bolted joint integrity. A simple formula for relationship between relative electrical conductance changes and relative tightening torque changes is analytically obtained. Based on this formula, a methodology is described for detecting a loosening failure of conductive bolted joints.

Acoustic scattering by a cluster of small sound-soft obstacles

The scattering problem of an incident plane sound wave by a finite number of small sound-soft arbitrarily shaped obstacles is considered. First, we study the case of multiple scattering in the long wave limit. By analogy with Greenwood's approximation for the electrical constriction resistance of a circular cluster of microcontacts, we obtain an approximation for the harmonic capacity of a system of a large number of small sound-soft obstacles grouped into a spherical cluster. We generalize Greenwood's approach for the case of an arbitrary convex cluster and, as a by-product of our analysis, we elicit an approximate formula for the harmonic capacity of a convex solid. The study of the general case of multiple scattering by a cluster of small soft-sound obstacles is based on the first order asymptotic model obtained in our previous paper. We use the method of artificial small parameter for constructing Padé approximants of the scattering amplitude. Explicit formulas are derived and illustrated on several examples.

The electrical/thermal conductance of rough surfaces––the Weierstrass–Archard multiscale model

Rough surfaces show a load-dependent electrical constriction resistance. Here, using a recent analogy due to Barber [Proc. R. Soc. London A 459 (2003) 53] between the incremental stiffness and the conductance in the elastic regime, and the Archard hypothesis to solve the multiscale contact problem, the conductance is found for the profile defined by the Weierstrass series. The analysis is also approximately valid, neglecting thermal effects on the contact area, for the thermal conductance.

Size-dependent electrical constriction resistance for contacts of arbitrary size: from Sharvin to Holm limits

A general analytical expression for the size-dependent constriction (contact) resistance is obtained for non-quantum contacts of arbitrary size as a solution of Laplace’s equation with appropriate boundary conditions. The new analytical expression contains both the Holm resistance and the Sharvin resistance as the asymptotic limits for the respective large and small contact sizes relative to the mean free path of electrons. This first general theoretical result is fully supported by available experimental data on the pressure dependence of contact resistance.

Electrical contact resistance: properties of stationary interfaces

The paper reviews the dependence of electrical constriction resistance on the shape and dimensions of /spl alpha/-spots and on the magnitude of the mechanical contact load. The range of validity of the classical voltage-temperature relation for electrical contacts is also examined. The paper describes experimental evidence of breakdown of the classical electrical contact theory when /spl alpha/-spots become too small. One of the interesting and useful properties of relatively small /spl alpha/-spots is that they are subject to large surface stresses. These stresses induce /spl alpha/-spot growth.