Timewise increases in contact resistance due to surface roughness and corrosion

To understand failure and estimate connector reliability a connector model was made in which two mated rough copper surfaces were subjected to ingression and corrosive attack by atmospheric oxygen. The rough surface segments the connector contact area into many small discrete areas (a-spots) through which currents flow. The initial a-spot contact radii a_e (formed as metal-to-metal bridges by mating surface heights on the mating surfaces) was determined by the externally applied load, connector materials, geometry, and surface topography. Later, corrosive attack of the metallic surfaces cause the metallic contact radii to shrink and resistances to increase. Factors in the model that influence the corrosive process are environmental temperature, partial pressure of oxygen, and geometric factors associated with the contact. Resulting curves of contact resistance versus time are similar in trend and shape to experimentally measured curves by Takano and Mano. From time variations of contact resistance of the connector, methods for estimating the useful lifetime of electrical connectors are given