The Real Area of Contact in Polymeric Magnetic Media—II: Experimental Data and Analysis

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Abstract
Electrical-contact-resistance and two-beam optical-interference techniques were employed to measure the real area of contact of magnetic tapes. The former technique does not work well due to significant contributions from tunnel effect and multimolecular insulating films; the latter provides shape and size distribution of asperity-contact areas. Experiments were conducted at a pressure range of 13.8 kPa and 1.38 MPa. Normal pressure had strong dependence on both the real area of contact and the number of contact spots, and weak dependence on the mean asperity-contact diameter. This is in agreement with the theory. In the case of the two tapes tested in the pressure range, the real area of contact varied from 0.5 to 25 percent. The mean asperity-contact diameter and number of contact spots ranged from 6 to 13 μm and 200 to 2300 per mm2, respectively. The mean real pressure was in the range of 2 to 8 MPa. The real area of contact increased with an increase in the ambient temperature. Surface roughness had strong influence on the real area of contact, as expected. Tapes subjected to pressure and temperature for a period resulted in a growth of the real area of contact. When the tapes were unloaded, a significant portion of the deformation was not recovered.