The friction of a sliding tactile contact was measured in an apparatus which simulated a keyboard. Results were taken for several materials. The friction coefficient was found to decrease with increasing load and with increasing speed. Experiments at varying humidity and surface roughness helped to define the friction mechanisms. It is concluded that tactile friction is predominantly adhesive, but modified by liquid bridging between the ridges of the skin and the counterface. Increased bridging due to higher humidity causes increased friction from viscous shearing effects, while increased roughness allows fewer bridges to form, decreasing the friction.
The industrial applications of brush seals have been increasing due to their superior sealing performance. Advances in the understanding of seal behavior have been pushing the design limits to higher-pressure load, temperature, surface speed, and rotor excursion levels. The highest sealing performance can be achieved when the bristle pack maintains contact with the rotor surface. However, due to many design and operational constraints, most seals operate with some clearance. This operating clearance cannot be avoided due to rotor runouts, transient operating conditions, or excessive bristle wear. In some applications, a minimum initial clearance is required to ensure a certain amount of flow rate for component cooling or purge flow. Typically, brush seal failure occurs in the form of degraded sealing performance due to increasing seal clearance. The seal performance is mainly characterized by the flow field in close vicinity of the bristle pack, through the seal-rotor clearance, and within the bristle pack. This work investigates the flow field for a brush seal operating with some bristle-rotor clearance. A nonlinear form of the momentum transport equation for a porous medium of the bristle pack has been solved by employing the computational fluid dynamics analysis. The results are compared with prior experimental data. The flow field for the clearance seal is observed to have different characteristics compared to that for the contact seal. Outlined as well are the flow features influencing the bristle dynamics.
This paper describes the development and calibration of an original test apparatus to study the effect of frictional heating on lubricant effectiveness. The configuration used the Seebeck effect between a stainless steel ball and a disk of tool steel. Good agreement was found between the average temperature rise indicated by the thermoelectric voltage and Archard’s models. Surface temperature rises approaching 200°C were obtained in lubricated contact and an upper bound temperature of 830°C was found in dry contact. The likely effect of track heating was assessed by analysis and, for this configuration, was found to be negligible. A slight lag was found between a local increase of friction due to the passage of an asperity and the thermal response.
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