This paper summarizes the results of rotating-bending fatigue tests on shafts 0.3- to 6-in. diameter from SAE plain carbon steels of 0.39 and 0.54 per cent carbon content in both the “as-forged” and normalized-and-tempered conditions. Shafts were tested with stress concentration, as represented by both fillets and press-fitted members, as well as plain specimens.

Shafts with stress concentration produced by fillets or press-fitted members from either untreated or normalized-and-tempered steels exhibited little or no size effect. An endurance limit ranging from 17,500 to 25,000 psi was found from tests on 101 plain specimens of 6-in. diameter untreated steel, while filleted shafts (r/d = 0.14 and 0.29) of the same material had endurance limit values within this range. A similar comparison exists on normalized-and-tempered steel, but here less extensive data are available.

Some effect of size was indicated on plain specimens 6 in. in diameter, which had a minimum endurance limit 35 per cent lower than that found for the conventional 0.3-in. diameter plain specimens from untreated steel. Data are reported on various groups of small specimens machined from large forgings and 22 in. bar stock.