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SCMH2 고속회전축재의 표면처리조건에 따른 VHCF 피로특성에 관한 연구
서창민,서창희,서민수,Suh, C.M.,Suh, C.H.,Suh, M.S. 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.4
SCMH2 steel is widely used in the industrial members of car and tractor. This study focused on material properties and evaluation technology of the SCMH2 steel regarding the surface treatment followed by carburizing and nitriding, by means of impact test, hardness test. and fatigue test including HCF (high cycle fatigue) and VHCF (very high cycle fatigue). Drop weight impact tester (Instron, 9250 Hv) and Cantilever type rotating-bending fatigue tester (YRB200, 3150 rpm) were used to characterize the SCMH2 standard specimen before and after carburizing/nitriding. In order to understand those effects on fatigue characteristics and material properties, the fractured surfaces were carefully observed and analyzed by SEM (scanning electron microscope) and EDS (energy-dispersive X-ray spectroscopy).
고온하 복수 표면균열의 성장 합체거동과 시뮬레이션에 관한 연구
서창민(C.M Suh),황남성(N.S Hwang),윤기봉(K.B Yoon) 한국해양공학회 1995 韓國海洋工學會誌 Vol.9 No.1
A simulation program concerned with multi-surface fatigue cracks which initiated at the semi-circular surface notches has been developed to predict their growth and coalescence behaviors at the elevated temperature. Three kinds of coalescence models such as SPC(surface point connection), ASME and BSI(British Standards Institution) conditions were applied, and the results of the simulation were compared with those of the experiment.<br/> This simulation is able to enhance the reliance and integrity of structures especially under the elevated temperature which have lots of difficulties in experiments and applications. This shows that the simulation result has utility for fatigue life prediction.<br/> Even though all the specimens were the same shape, the error rate was increased in accordance with the applied stress to the specimen. Among the material constants C and m in the narrow band, the results applied upper values of the band to the simulation has shown quite small error compared with the experiment results.
C.M. Suh(서창민),Y.D. An(안영동),Y.D. An(서창희),M.S. Suh(서민수),Y.S. Pyoun(편영식) 한국자동차공학회 2013 한국자동차공학회 지부 학술대회 논문집 Vol.2013 No.4
SUJ2(KS:STB2)는 베어링강의 재료로 지속적인 반복하중으로 인해 피로균열이 발생하고, 급격한 파괴에 이르는 경우가 발생한다. 따라서 부품에 사용되는 SUJ2 베어링강 재료는 피로강도와 피로수명의 향상 및 그 신뢰성, 무한수명으로의 요구가 증대되고 있다. 본 연구에서는 베어링강에 UNSM(ultrasonic nano crystal surface modification) 표면처리기술을 적용하였고 표면처리 전·후의 정량적인 데이터를 얻고 분석하였다. 즉, 미처리재와 UNSM인 표면처리기술에 의한 압축잔류응력을 형성시킨 시험편에 관한 피로시험을 실시하여 정량적인 자료 획득, 파면해석과 파괴역학적으로 분석하여 UNSM의 적용 가능성을 연구하는 것이다. 압축잔류응력 생성기법인 표면 나노 개질처리기술을 응용하여 처리재와 미처리재간의 정량적인 피로, 파괴역학적인 실험, 연구 및 해석으로 베어링의 피로균열에 관한 자료를 획득하였으며, 본 연구를 통해 VHCF(Very High Cycle Fatigue)연구 분야에 자료를 획득하였다.
초음파 나노 표면 개질(UNSM) 기술에 따른 베어링강의 VHCF 특성
서창민(C. M Suh),안영동(Y. D. An),서민수(M. S. Suh),편영식(Y. S. Pyun) 한국해양환경·에너지학회 2012 한국해양환경·에너지학회 학술대회논문집 Vol.2012 No.5
STB2 of bearing steel is used far roller bearing and ball bearing due to their high wear resistance and impact resistance. Among many useful surface strengthening technologies, ultrasonic nanocrystal surface modification (UNSM) technology is promising for increasing fatigue strength and wear resistance, and reducing friction as well The main idea to apply UNSM technology for improving both bending fatigue strength and rolling contact fatigue strength, of slim bearing rings is applying not only raceway but also the opposite side of the raceway - in other words, outer side of the outer ring and inner side of the inner ring. The test specimens for the rotary bending fatigue test were made of STB2 bearing steel and treated by the UNSM technology. In Ms study, fatigue result that was subjected to different loads of the UNSM treatment was investigated and compared with that of the untreated specimen. The microhardness of the UNSM-treated specimens increased by about 20%, higher than that of the untreated specimens. The X-ray diffraction analysis showed that a compressive residual stress of more than 1,000 MPa was induced after the UNSM treatment Also, electron backscatter diffraction analysis was used to study the surface structure and nanograin refinement. The results showed that the rotary bending fatigue life and fatigue strength of the UNSM-treated specimens increased by about 80% and 31%, respectively, compared to those of the untreated specimen. These results might be attributed to the increased micrchardness, the induced compressive residual stress, and the nanocrystal structure modification after the UNSM treatment In addition, the fracture surface analysis showed that the fish eye crack initiation phenomenon was observed after the UNSM treatment
초음파 나노 표면 개질(UNSM) 기술에 따른 베어링강의 VHCF 특성
서창민(C. M. Suh),안영동(Y. D. An),서민수(M. S. Suh),편영식(Y. S. Pyun) 대한조선학회 2012 대한조선학회 학술대회자료집 Vol.2012 No.5
STB2 of bearing steel is used for roller bearing and ball bearing due to their high wear resistance and impact resistance. Among many useful surface strengthening technologies, ultrasonic nanocrystal surface modification (UNSM) technology is promising for increasing fatigue strength and wear resistance, and reducing friction as well. The main idea to apply UNSM technology for improving both bending fatigue strength and rolling contact fatigue strength of slim bearing rings is applying not only raceway but also the opposite side of the raceway - in other words, outer side of the outer ring and inner side of the inner ring. The test specimens for the rotary bending fatigue test were made of STB2 bearing steel and treated by the UNSM technology. In this study, fatigue result that was subjected to different loads of the UNSM treatment was investigated and compared with that of the untreated specimen. The microhardness of the UNSM-treated specimens increased by about 20%, higher than that of the untreated specimens. The X-ray diffraction analysis showed that a compressive residual stress of more than 1,000 MPa was induced after the UNSM treatment. Also, electron backscatter diffraction analysis was used to study the surface structure and nanograin refinement. The results showed that the rotary bending fatigue life and fatigue strength of the UNSM-treated specimens increased by about 80% and 31%, respectively, compared to those of the untreated specimen. These results might be attributed to the increased microhardness, the induced compressive residual stress, and the nanocrystal structure modification after the UNSM treatment. In addition, the fracture surface analysis showed that the fish eye crack initiation phenomenon was observed after the UNSM treatment.
Effect of Inclusion Element on VHCF(Very High Cycle Fatigue) Strength of Bearing Steels
C.M. Suh(서창민),M.S. Suh,Y.S. Pyun 한국자동차공학회 2013 한국자동차공학회 지부 학술대회 논문집 Vol.2013 No.11
SU2 of bearing steel is used for roller bearing and ball bearing due to their high wear resistance and impact resistance. The test specimens for the rotary bending fatigue test were made of SUJ2 A-& B-bearing steels. In this study effect of inclusion element on VHCF strengthwas investigated and compared with that of the two kinds of bearing steel. The results showed that the rotary bending fatigue life and fatigue strength of the B-bearing steel’s specimen increased by about 10%, compared to those of the A-bearing steel. The fracture surface analysis showed that the fish eye crack initiation phenomenon was observed. These results might be attributed to the inclusion element difference of Ti and Cr at the fish eye crack initiation site.
高溫下 304 스테인리스鋼의 複數表面龜裂의 成長學動에 관한 實驗的 硏究
서창민(C. M. Suh),신형섭(H. S. Shin),황남성(N. S. Hwang),정대윤(D. Y. Jung) 한국해양공학회 1995 韓國海洋工學會誌 Vol.9 No.1
The crack which is discovered in various structures and machine elements is multi-cracks. Multi-cracks may cause serious problems because they grow individually, and coalesce into one and it leads to fracture.<br/> Fatigue tests have been carried out to study the growth and coalescence behavior of multi-surface-cracks initiated at the semicircular surface notch in type 304 stainless steel at elevated temperature.<br/> The results are as follows;<br/> When multi-surface-cracks are lying on the surface of material, the major surface crack has greater influence on the the fatigue life than the subcracks.<br/> The aspect ratio of multi-surface-cracks is lower than that of single crack because of the interaction and coalescence of surface cracks.<br/> Crack growth shape turns to semiellipse from the semicircle notch. After coalescence, the surface crack length increases rapidly, and it leads to fracture.<br/> Further, the slope transition of Paris law was found in the da/dN-ΔK₁ plots.