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초음파 나노 결정 표면개질된 SCM435의 특이한 피로 파괴 특성
김재훈 ( Jae-hoon Kim ),윤서현 ( Seo-hyun Yun ),남기우 ( Ki-woo Nam ) 한국산업융합학회 2022 한국산업융합학회 논문집 Vol.25 No.2
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 (a<sub>hlm</sub>) according to the crack aspect ratio (As) was evaluated. In addition, the relationship between the minimum crack depth (a<sub>NDI1</sub>, a<sub>NDI2</sub>) detectable by non-destructive inspection(NDI), the crack depth (a<sub>25</sub>, a<sub>50</sub>) that reduces the fatigue limit by 25% and 50%, and a<sub>hlm</sub> were evaluated. The harmless crack condition was determined by the deepest crack point (point A). Since a<sub>hlm</sub> is larger than a<sub>25</sub> and a<sub>50</sub>, a<sub>25</sub> and a<sub>50</sub> can secure the safety and reliability of steel via UNSM. Because a<sub>NDI1</sub> and a<sub>NDI2</sub> are larger than a<sub>25</sub> and a<sub>50</sub>, cracks in a<sub>25</sub> and a<sub>50</sub> cannot be detected by non-destructive testing. Therefore it is necessary to apply more precise NDI.