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이금화,구경희,김재훈,윤서현,권영국,남기우,Lee, Gum-Hwa,Gu, Kyoung-Hee,Kim, Jae-Hoon,Yun, Seo-Hyun,Kwon, Yung-Kug,Nam, Ki-Woo 한국산업융합학회 2022 한국산업융합학회 논문집 Vol.25 No.5
Using the fatigue limit (△σ<sub>unsm</sub>) and residual stress (σ<sub>r</sub>) of the UNSM smooth specimen, the harmless maximum crack depth (α<sub>hml</sub>) according to the crack aspect ratio (As) was evaluated. α<sub>hml</sub> evaluated the reliability in the relationship between the minimum crack depth (α<sub>NDI1</sub>, α<sub>NDI2</sub>) detectable by nondestructive inspection(NDI) and the crack depth (α<sub>25</sub>, α<sub>50</sub>) that reduces the fatigue limit by 25% and 50%. All α<sub>hml</sub> was determined by the crack depth. The α<sub>hml</sub> of 80N UNSM with high σ<sub>r</sub> and high △σ<sub>unsm</sub> was found to be large. σ<sub>r</sub> in the depth direction had a much effect on α<sub>hml</sub>. Since α<sub>hml</sub>>α<sub>50</sub>(As=0.6-0.1) and α<sub>hml</sub>>α<sub>25</sub>, α<sub>25</sub> and α<sub>50</sub>(some range) can secure the safety and reliability. Since α<sub>hml</sub><α<sub>50</sub> (As=1. 0-0. 6), it cannot be made harmless by UNSM. So safety and reliability cannot be secured. α<sub>NDI1</sub> and α<sub>NDI2</sub> are larger than α<sub>25</sub>, α<sub>25</sub> cannot be detected by NDI. α<sub>NDI1</sub> and α<sub>NDI2</sub> are smaller than α<sub>50</sub>, α<sub>25</sub> can detected by NDI.
서브제로 온도 및 시간이 다른 STS316L의 탄성파 특성
이금화,구경희,탁영준,권영국,신기항,남기우,Lee, Gum-Hwa,Gu, Kyoung-Hee,Tak, Young-Joon,Kwon, Yung-Kug,Shin, Ki-Hang,Nam, Ki-Woo 한국산업융합학회 2022 한국산업융합학회 논문집 Vol.25 No.5
In this study, STS316L rolled at five rolling degrees were treated with two types of subzero temperatures for 10, 30, and 60 minutes, respectively, and the dominant frequencies of elastic waves was investigated. The dominant frequency was higher as the subzero temperature was lower and the subzero treatment time was longer at each rolling degree. On the other hand, the dominant frequency was higher as the elongation decreased. In the time-frequency analysis for subzero temperature and time of the specimen with a rolling degree of 33%, the dominant frequency was higher at a subzero temperature of -196℃ than -50℃ regardless of subzero treatment time.
이중 쇼트 피닝에 의한 SCM822H 강의 무해화 균열 크기 평가
최진우 ( Jin-woo Choi ),윤서현 ( Seo-hyun Yun ),권영국 ( Yung-kug Kwon ),이금화 ( Gum-hwa Lee ),남기우 ( Ki-woo Nam ) 한국산업융합학회 2023 한국산업융합학회 논문집 Vol.26 No.6
In this study, the harmless crack size (a<sub>hml</sub>) by double shot peening (DSP) using shot balls with different diameters was evaluated on carburized, quenched-tempered SCM822H steel. The minimum crack size (a<sub>NDI</sub>) detectable by non-destructive inspection was also evaluated. The relationship between the crack size (a<sub>25,50</sub>) that reduces the fatigue limit by 25% and 50% and a<sub>hml</sub> was evaluated. The residual stress of DSP was greater in SP(0.6+0.08) than SP(0.8+0.08) and appeared deeper in the depth direction. In addition, the hardness below the surface appeared larger. The fatigue limit of DSP increased 2.07 times and 1.95 times compared to non-SP. All a<sub>hml</sub> of the DSP specimen was determined at the depth (a). The compressive residual stress distribution affects a<sub>hml</sub>, and the a<sub>hml</sub> of SP(0.6+0.08), which has a large compressive residual stress and a high fatigue limit, appeared large. a<sub>hml</sub> of SP<sub>(0.6+0.08)</sub> introduced deeper than the residual stress of SP<sub>(0.8+0.08)</sub> is larger in the range of As=1.0-0.3. Since the residual stress in the thickness direction has a greater effect on a<sub>hml</sub> than the residual stress at the surface, it is necessary to introduce it more deeply. The relation of a<sub>hml</sub>, a<sub>25,50</sub>, and aNDI were evaluated in the point for safety and reliability.