Some aspects of electrical conduction in granular systems of various dimensions

Abstract

Abstract. We report on measurements of the electrical conductivity in both a 2D triangular lattice of metallic beads and in a chain of beads. The voltage/current characteristics are qualitatively similar in both experiments. At low applied current, the voltage is found to increase logarithmically in a good agreement with a model of widely distributed resistances in series. At high enough current, the voltage saturates due to the local welding of microcontacts between beads. The frequency dependence of the saturation voltage gives an estimate of the size of these welded microcontacts. The DC value of the saturation voltage (≃ 0.4 V per contact) gives an indirect measure of the number of welded contact carrying the current within the 2D lattice. Also, a new measurement technique provides a map of the current paths within the 2D lattice of beads. For an isotropic compression of the 2D granular medium, the current paths are localized in few discrete linear paths. This quasi-onedimensional nature of the electrical conductivity thus explains the similarity between the characteristics in the 1D and 2D systems.

Scaling of ac electrical conductivity of powders under compression

“…ν (Hz) Indeed, in recent works, 15,16 we showed that the contact resistances between stainless steel beads are widely distributed, probably as a consequence of the inhomogeneity of the oxide layer. The distribution of resistance was well fitted by a lognormal distribution.…”

“…The amplitude of the voltage applied to the powder sample is fixed to a low value ͑U rms = 100 mV͒ in order to avoid any voltage-induced nonlinear effect. 14,15 The frequency ranges from 20 Hz to 1 MHz. Before each experimental run, the container is refilled with a new sample of powder.…”

Electromechanical modeling by DEM for assessing internal ball bearing loading

“…The forces applied to the bearing are sufficiently large to validate these approximations. However, some authors show that these approximations are questionable [27,8,7,28]. The contact is assumed perfect and the electrical transfer is described by linear Ohm law.…”

“…Previous work has shown that the voltage-current characteristics of a static bearing describe a hysteresis. This effect is attributed to Branly's effect [5] which is also manifested in a metallic granular medium [6][7][8]. This unconventional approach attempts to measure the electrical resistance of the ball bearing in operation.…”

Examination of Electrical Conduction of Carbonyl Iron Powder Compacts

“…Falcon et al 11,12) show that after compaction, a very broad distribution of contact resistance is expected in a conduction chain. At the beginning of current stressing, most of the potential drop may take place at the contacts along the conduction chain with the largest resistances.…”