Material contacts under cyclic compression, studied in real time by electrical resistance measurement

Abstract

Contacts of similar materials under cyclic compression below the yield stress were studied in real time by measurement of the contact electrical resistance. For all materials studied (steel, aluminum, copper, polymer and cement mortar), the contact resistance decreased upon loading in every load cycle. The resistance at the minimum stress of a cycle decreased upon load cycling for steel (at a sufficiently high stress amplitude), polymer-matrix composite and mortar due to plastic deformation at asperities, but increased upon cycling for aluminum and copper, probably due to surface oxidation and/or strain hardening. For steel and aluminum, the resistance at the maximum stress of a cycle increased upon load cycling, probably due to oxidation and/or strain hardening, and it took more stress for the resistance to decrease in a cycle as cycling progressed, probably due to strain hardening. For the polymer (thermoplastic), it took less stress for the resistance to decrease in a cycle as cycling progressed, probably due to enhancement of the molecular orientation perpendicular to the stress. For the mortar, the minimum resistance at the maximum stress increased slightly as cycling progressed, probably due to debris generation.