Dimple Formation and Squeeze-Out of Resistive Powder in Hertzian ContactsPages 364-377
Marco Bruno Abstract:
Electrical contact resistance in powder-mediated interfaces is governed by the coupled evolution of roughness-induced contact area formation, particle rearrangement, compaction and current-path connectivity. This work investigates the normal indentation of a resistive Fe3O4 nanoparticle layer confined between a spherical steel indenter and a molybdenum-coated glass substrate. Contact resistance was measured under increasing normal force while the contact morphology was imaged from below using frustrated total internal reflection. The resistance decreased systematically with load, indicating progressive activation of conducting pathways through the granular interlayer. Optical images revealed an annular bright region surrounding a darker central zone, suggesting the formation of a dimple-like contact morphology. This observation is interpreted as the coexistence of a confined, solid-like granular core and an annular region that is rearranging during the indenter approach. A simplified contact-resistance model was introduced by combining Hertzian theory, multiscale rough contact mechanics and a first-order thickness contribution. The model captures the main resistance decrease for selected powder layers but cannot fully describe the strong sensitivity to layer thickness. The results suggest that dimple formation and contact-network evolution are key mechanisms in squeezed resistive powder contacts.
Keywords:
Dimple formation,
Electrical contact resistance Granular interlayer,
Fe₃O₄ nanoparticles,
Hertzian contact,
Powder compaction,
Contact area,
Frustrated total internal reflection
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