An Experimental Investigation on the Effect Operating Procedure Has on Tribometer Measurements

Abstract Tribological investigations are typically conducted on measurement devices coined tribometers. These simple yet complex measurement devices can be used to evaluate several distinct contact characteristics including friction, wear, heat induced failure modes, etc. The major benefit of using a tribometer is to simulate all the characteristics of a complicated contact mechanics problem with simple machine elements. Related to power transmission, tribometers are often used to produce heuristic traction curves covering operating conditions seen in real world applications of gears and bearings. This study provides insight into the effect operating procedure has on the results of traction (friction) tests using a twin-disk tribometer. Two sets of traction disks of different surface roughness amplitude are tested for their frictional performance behavior based on operating procedure. One set of disks paired two super-finished specimens against each other, simulating gear contacts typically seen in the aerospace industry. The second set of disks was a combination of a super-finished and as-ground disk, more representative of contact conditions seen in automotive powertrains. Measured deviations based on operating procedure clearly show an impact on frictional performance. For smoother surfaces, undesirable losses contribute more significantly to measured friction. Rough surfaces generate more heat and take much longer to reach steady-state. Misrepresentation of friction measurements can occur if test duration is not long enough. In either case, improper execution of traction tests will certainly alter the accuracy of the measurements. Since tribometer measurements can be used to develop regressed friction formulae or to directly compare elasto-hydrodynamic (EHL) model predictions, it is crucial that operating procedure does not influence contact characterization.