Interfacial electro-mechanical behaviour at rough surfaces

Abstract

In a range of energy systems, interfacial characteristics at the finest length scales strongly impact overall system performance, including cycle life, electrical power loss, and storage capacity. In this letter, we experimentally investigate the influence of surface topology on interfacial electromechanical properties, including contact stiffness and electrical conductance at rough surfaces under varying compressive stresses. We consider different rough surfaces modified through polishing and/or sand blasting. The measured normal contact stiffness, obtained through nanoindentation employing a partial unloading method, is shown to exhibit power law scaling with normal pressure, with the exponent of this relationship closely correlated to the fractal dimension of the surfaces. The electrical contact resistance at interfaces, measured using a controlled current method, revealed that the measured resistance is affected by testing current, mechanical loading, and surface topology. At a constant applied current, the electrical resistance as a function of applied normal stress is found to follow a power law within a certain range, the exponent of which is closely linked to surface topology. The correlation between stress-dependent electrical contact and normal contact stiffness is discussed based on simple scaling arguments. This study provides a first-order investigation connecting interfacial mechanical and electrical behaviour, applicable to studies of multiple components in energy systems.

Stress-dependent electrical transport and its universal scaling in granular materials

“…For the considered loads in experiments, we observe a decreasing trend of the absolute exponent value, from 2 to 1/3 with increasing inter-particle force. This trend indicates the diminishing influence of surface roughness and the evolution of conduction mechanisms as discussed in previous research [33,45,48].…”

“…The latter exponent is comparable to that (1/3) of Hertzian contact with Holm conduction as the dominant transport mechanism. One can obtain relationships of ∝ 2/3 and ∝ −1/2 , respectively, based on Hertzian theory and Holm conduction, thus, having ∝ −1/3 [33,45,48], where, the subscript, , indicates the Holm conduction at Hertzian contact. The experimentally observed exponent, i.e., 0.32 ± 0.09, agrees well with the theoretical prediction, i.e., 1/3 , for a smooth sphere-to-sphere contact.…”

Electrical Contact Resistance of Contact Bodies With Cambered Surface

“…And the conductive mechanism is directly determined by the magnitude of contact radius. It has been experimentally validated that the conductive mechanism is Sharvin-type dominantly at low load, and transits to Holm-type with the load increasing [47], [48]. In this paper, only the Holm resistance is considered and investigated under different combinations of size parameters and contact load.…”

Characterization of the surface roughness of sand particles using an advanced fractal approach

“…[31]), triangulation or cube-counting (e.g. [26,32]). Another technique is to analyse the power spectrum of the surface, for example, as a Fourier power spectrum [33], by power spectral density (PSD) [34] or as a structure function [35].…”