Abstract
The object of this study is to investigate the effect of roller-working on the torsional fatigue strength of machine structural steel. The material used in this test was carbon steel (JIS standards S25C). Three types of specimens were plastically deformed from plain specimen to notched one and their deformation values were 0mm, 0.5mm and 1.0mm, respectively. The main results obtained in this study are as follows: (1) When the plastic deformation value is 1.0mm, the torsional fatigue strength of roller-worked specimen increases more than twice of that of non-roller-worked specimens. (2) When observing the transverse section of roller-worked specimens, a compressed and elongated structure is formed at the notch bottom of the specimen. (3) The hardness number of notched specimen at the notch bottom is higher than that of the non-roller-worked one. (4) According to surface observation of roller-worked notch specimen, there exist many non-propagating micro-cracks just before the specimen fail. (5) Using FEM analysis, the residual stress at the notch bottom of specimen with roller-working is estimated.
