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SM40C 강재에서 미소부분노치가 피로강도에 미치는 영향
공기훈,김경모 동의공업대학 2001 論文集 Vol.27 No.1
This paper describes an experimental study of fatigue strength of SM40C carbon steel specimens, carried out by using rotating bending fatigue tests. The main purpose of the experimental investigation was to determine the influence of partial notch of fatigue strength of annealed and quenched-&-tempered SM40C carbon steel specimens with single or double partial notch. The present results was discussed based on the (area)^(1/2) parameter model and some of results for double partial notch specimens are compared with the analytical values obtained by the concept of linear notch mechanics.
공기훈 동의공업대학 1999 論文集 Vol.25 No.1
This fatigue testings by longitudinal loading with variable mean stresses were carried out on the specimens of SM20C and SM40C carbon annealed steels. The main results are summarized as follows : ① The S-N curves under various mean stresses are almost the same in the range of finite lives, Provided that the true stress amplitude is used by considering the constricted cross-sectional area. this is due to the fact that plastic deformation is easier to occur in the layer of specimen surface than in the inside of specimen. ② The constriction of specimen during fatigue tests occurs when the maximum stress during stress cycling is higher than a definite value close to the yield stress. ③ The range where the small crack growth law is applicable was clarified in these materials.
低사이클 反引張을 받는 鋼棒의 圓孔노치底 크랙發生에 관한 硏究
孔基勳,吳世旭 東亞大學校 大學院 1981 大學院論文集 Vol.5 No.-
Many studies on fatigue crack propagation have been presented but the behavior of fatigue and its mechanism is not clarified enough yet, especially low cycle fatigue. Some experiments in this study were carried out by the method of changing stress amplitude under constant mazimum stress and low cycle pulsating tension fatigue testing on fatigue crack propagation at room temperature. Propagating cracks were observed with potical microscope on crack initiation and growth. The obtained results are summarized as follows: ⑴ Fatigue strength was higher in S-N curve as stress amplitude was decreasing, mean stress inereasing, too. ⑵ The initiation of fatigue crack was occured at 28~32% through the total fatigue life. ⑶ The summarized relationship between crack propagation rate and stress intensity factor of structural steel (SM45C) is as follows. The value of exponent m was 1.41-1.85. ⑷ Propagating crack in fatigue generally passed along grain boundaries and ferrite matrix, it passed around and branched cause of hard inclusion. ⑸ In the case of higher stress amplitude the shpae of crack propagation and fracture surface was intricate.