This note is concerned with the significance of a “hold period” on thermal fatigue endurances and on the use of a frequency exponent to correlate the results of mechanical fatigue tests at various temperatures.

In their note in the January 1965 Journal (pp. 53-55), Coles and Skinner quite rightly pointed out that residual stresses, set up as the result of plastic yielding in compression during an initial heating period, will undergo redistribution during a subsequent “hold period” at an elevated steady temperature. However, it is important to note that the redistributed stress pattern and the associated creep strains at the conclusion of the “hold period” will depend very much on the nature of the applied loading. For example, the compressive strain and the associated tensile stress set up in the rim of the disc will both fall in magnitude if the disc is not rotating and may reach infinitesimal values if the “hold period” is long enough.