Tribology of Material Contacts under Dynamic Loading, Studied by Electrical Resistance Measurement
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Tribology of Material Contacts under Dynamic Loading, Studied by Electrical Resistance Measurement Xiangcheng Luo and D.D.L. Chung Composite Materials Research Laboratory, University at Buffalo The State University of New York, Buffalo, NY 14260-4400, U.S.A. ABSTRACT The tribology of material contacts under cyclic compression in the direction perpendicular to the plane of the contact was studied by measurement of the contact electrical resistivity of the contact during the dynamic loading. The real-time monitoring allowed observation of both reversible and irreversible effects. The material contacts studied were those involving steel, carbon fiber polymer-matrix composite, cement mortar and graphite, due to their relevance to fastening, concrete structures, electric brushes and electrical pressure contacts. Correlation was made between the contact resistivity and the occurrence of elastic/plastic deformation at asperities. The interfacial structure was found to depend on the stress and the loading history. INTRODUCTION Tribology is related to the mechanical interaction of materials in contact. The consequence of the interaction can be deformation, loss of material, damage and change of the interfacial microstructure and composition, as conventionally indicated by weight loss, microscopy and mechanical testing. These methods typically involve observation after the interaction. Observation during the interaction is valuable for detecting the reversible and irreversible effects. A nondestructive method which is amenable to observation during the interaction is electrical measurement [1-3], in this case measurement of the contact electrical resistance. Wear or abrasion involves subjecting each point of a surface to dynamic shear. Studies of wear or abrasion are commonly conducted by monitoring the effect over an area rather than that at a fixed point. For example, in wear testing using the pin-on-disk configuration, the tip of the pin is continuously moved against the surface of the disk, so that different points on the disk are subjected to stress at different times and the effect of dynamic shear and the stress variation within a cycle of dynamic shear at a particular point of the surface are not monitored. Even if the effect of wear or abrasion is monitored in real time, say by measuring the contact electrical resistance at the sliding contact, the monitoring does not allow correlation of the effect (the resistance) at a point with the dynamic stress at the same point. This difficulty stems from the fact that wear or abrasion involves one element sliding against another, so that different points in a contact are not subjected to dynamic stress in an in-phase manner. In contrast, dynamic compression does not involve sliding, so that each point in a contact is subjected to dynamic compression in an in-phase manner. As a result, correlation is possible between the effect (say the resistance at the contact) and the dynamic stress during dynamic loading. This correlation allows identification of the point in a stress cycl
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