Affiliations: Department of Mechanical Engineering, Graduate School of Science and Engineering, Saga University, Honjo-machi 1, Saga, 840-8502, Japan | Department of Mechanical Engineering, Faculty of Science and Engineering, Saga University, Honjo-machi 1, Saga, 840-8502, Japan
Abstract: This study focused on the effects of tensile pre-strain on the torsional fatigue properties of four kinds of structural carbon steels (JIS S15C to S45C). The specimens were tensile pre-strained and aging processed before the torsional fatigue test. The fatigue properties investigated in this study included fatigue strength, crack initiation and propagation behaviors, surface hardness and characteristics of non-propagating crack behaviors. The results indicate that the torsional fatigue strength are improved after tensile pre-strain, the fatigue limits increase with the increasing of pre-strain ratio; tensile pre-strain does not affect the fatigue crack initiation and branch points, the cracks initiate in the weak part of the ferrite grains from the torsional slip lines in the surface and branch at the boundaries of grains, irrespective of ferrite or pearlite grains; for S25C, non-propagating crack is observed on the pre-strained specimens and the length becomes shorter with the increasing of tensile pre-strain ratio.
Keywords: Torsional fatigue, tensile pre-strain, crack initiation and propagation, non-propagating crack, aging process
