The ring test has previously been experimentally calibrated for friction studies on the assumption of constant coefficient of friction under metal-working conditions. This investigation has demonstrated that the same experimental results may be used to calibrate the ring test on the assumption of constant interface friction factor. Use of available mathematical solutions, based on the concept of a constant interface friction factor, provides a possible means for the calibration of different initial ring geometries by computer solution. Excellent correlation has been shown between the shape of calculated curves and experimental ring test results on a wide variety of materials. However, the actual values of m obtained by using the theory to analyze experimentally determined shape changes appear to be somewhat in error to a degree depending on the initial specimen geometry and the general friction level under which it is deformed. This is due essentially to the assumption used in the theoretical treatment, that the surface frictional stresses are transmitted uniformly throughout the specimen thickness, not being generally valid in the practical situation except with very thin specimens.

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