Utilization of Contact Resistance Measurements in the Investigation of the Metallic Adhesion of Iron

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Abstract
The utilization of contact resistance measurements in metallic systems in the presence of contaminant films has been under investigation in the electrical industry for many years. The purpose of this study was to show that the complete removal of such films could be detected by contact resistance measurements as well as the very deformation processes occurring between the asperity contact points in the interface as the contact area expands to receive the impressed load. A fully automatic apparatus was developed to record the variation of contact resistance with the applied load as an x-y plot under conditions of ultra clean or specifically contaminated metal surfaces. The samples of high purity iron (65 ppm carbon and 8 ppm carbon) were in the shape of 60 mil wires and loaded normally to 5 gms. The observed contact resistance values appeared to conform to a theoretical equation relating contact resistance and load. Room temperature creep of iron was also observed and the results agreed rather well with a proposed equation in which the contact resistance was inversely proportional to a fractional power of the applied load. A high concentration of contaminant was observed on the surface of the 65 ppm carbon iron samples which appears to be consistent with the predicted contact resistance of that system if iron carbides were in high concentration in the surface layers. Other investigators have confirmed that samples with 40 ppm carbon in iron do tend to concentrate carbon in the surficial layers.

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