Load- and stress-controlled fatigue tests were performed on smooth tubular specimens of carbon steel SGV410 and stainless steel SUS316NG under fully-reversed torsion with static tension. Majority of the life in both steels was spent for shear crack growth. For SGV410 steel, increase of crack growth rate and reduction of fatigue life were revealed with application of static tension. Conversely, the growth rate decreased and thus the life was lengthened with static tension for SUS316NG steel. Although cyclic stress-strain relation in SGV410 steel was unchanged with application of static tension. SUS316NG steel showed additional hardening. From the results of two kinds of steels, the effect of static tension appeared to be different depending on the cyclic hardening/softening characteristics of the materials. Therefore, a two-stage short crack growth model was modified incorporating the effect of the hardening in addition to the effect of mean tensile stress with application of static tension. The model can explain the influence of static tension on the torsional fatigue behavior of SGV410 and SUS316NG steels.
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