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오광근(Kwang Keun Oh),김재훈(Jae Hoon Kim),최훈석(Hoon Seok Choi) 대한기계학회 2015 大韓機械學會論文集A Vol.39 No.6
고장력 Cr-Mo강은 이온질화와 연질화 두가지 질화처리를 수행하였다. 각 질화처리의 특징을 비교하기 위해서 30분의 공정시간을 가지고 질화처리를 하였다. 표면강도의 변화를 비교하기 위해서 비커스 경도 시험이 수행되었으며 피로시험은 켄틸레버 회전굽힘 피로시험기(Yamamoto, YRB 200)를 이용하여 수행되었다. 초고주기영역(N > 10<SUP>7</SUP>cycle)의 특징을 알아보기 위해서 피로시험은 피로한도 이후까지 진행하였다. 피로 시험 후 주사전자현미경(SEM)을 이용해서 파단면을 분석하였으며 고주기영역과 초고주기 영역의 파괴기구를 관찰하였다. CrMo alloy steel was nitrided using two types of processing methods, ion-nitriding processing and nitrocarburizing. Both processes were conducted for a duration of 30 min. To compare the surface hardness of the alloys created by the different processes , microhardness tests were conducted, and fatigue tests of each material were performed by a cantilever rotary bending fatigue test machine (Yamamoto, YRB 200) in the very high cycle regime (N > 10<SUP>7</SUP>cycle). Fractography of the fractured surfaces was conducted by scanning electron microscopy - to observe the fracture mechanisms of very high cycle fatigue and the effect of the nitriding process on the fatigue characteristics.
김재우(Jae Woo Kim),조다희(Da Hee Cho),장광주(Gwang Ju Jang),박중철(Joong Cheul Park),이영철(Yeong Cheol Lee),구병춘(Byeong Choon Goo),조인식(In Sik Cho) 대한기계학회 2018 대한기계학회 논문집. Transactions of the KSME. C, 산업기술과 혁신 Vol.6 No.2
초음파 피로시험은 20㎑의 진동자를 이용한 가속피로시험기술로써 본 논문에서는 초음파피로시험선진기술의 동향을 분석하기 위하여 전문학술대회인 VHCF-6, 7(Very High Cycle Fatigue)에서 발표된 논문들을 위주로 새로운 아이디어의 장치 시스템 연구자료 소개와 각각의 기술적인 장점과 단점에 대하여 제시하고자 하였으며, 다양한 소재와 시편 형상들에 대한 방법으로 동탄성계수 측정관련 기술의 필요성을 설명하고자 하였다. 또한 국내에서 자체적으로 수행된 다양한 연구결과를 토대로 초음파 피로시험의 국내 신뢰성평가 기준 공고 소개와 추후 진행 중인, 응력비 변환과 저온 분위기등 다양한 조건과 요구에 대응할 수 있는 기반기술을 소개하고자 하였다. Ultrasonic fatigue test is an accelerated fatigue test technique using a 20㎑ oscillator. In this paper, in order to analyze the trend of the advanced technology of ultrasound fatigue tester (UFT), whose detailed information can be found in the conference papers published in VHCF-6 (2011), VHCF-7 (2014) (Very High Cycle Fatigue). dynamic young`s modulus, which can be obtained from acoustic test according to the ASTM E1875 standard. is required in order to obtain the maximum stress amplitude. The purpose of this paper is to present the research results of the UFT system and its technical advantages and disadvantages. Based on the experimental results of various studies performed at different stress ratio and cryogenic temperatures, the introduction of the reliability evaluation standard of the UFT system was presented.
오광근(Kwang Keun Oh),최훈석(Hoon Seok Choi),박해동,김재훈(Jae Hoon Kim) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
The Cr-Mo alloy steel was nitrided two kind of processing method. one is the ion-nitriding proessing and the other is nitrocarburizing. both conditions was proceeded during 30min. To compare the surface hardness, microhardness test were carried out and Fatigue tests of each material were carried out by cantilever-rotary bending fatigue test machine(YRB 200, Yamamoto) at very high cycle regime(10<SUP>7</SUP><). Fractograpic analysis was conducted by Scanning Electron Microscopy (SEM) to observe the fatigue characteristics of very high cycle fatigue and effect of niriding process at fatigue characteristics.
Ultrasonic Fatigue Test Method for Stress Ratio Control
Hyo-Ri Kim(김효리),Seung-Hyeon Song(송승현),Ji-U Ha(하지우),Jeong-Eun Lee(이정은),In-Sik Cho(조인식) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Ultrasonic Fatigue Testing (UFT) is an accelerated fatigue test, typically at 20 kHz, which significantly shortens the application period of newly developed processes and materials in various mechanical parts and materials fields. In this paper, the system technology for controlling the stress ratio in ultrasonic fatigue testing is to be explained. This fatigue stress ratio control test is important for fatigue testing of aviation and power plant turbine parts, and is also an important method for crack propagation testing. Basically, an ultrasonic fatigue tester designed by applying the resonance analysis results to a 20KN tensile tester was attached to set the average stress and then enabled it at various stress ratios. Also, as a method of setting the corrected fatigue stress, the method of measuring the strain gauge at the center of the specimen and the method of simultaneously measuring the amplitude of the end of the specimen are described. Therefore, the results of this paper are intended to explain the construction of an ultrasonic fatigue tester optimized to suit various fatigue conditions and environments.
한승욱(Seung-Wook Han),명노준(No-Jun Myung),최낙삼(Nak-Sam Choi) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
The paper presents an overview of the present state of study on fatigue strength at very high number of cycles (N<SUB>f</SUB> > 10?). A classification of materials with typical S? N curves and influencing factors like notches, residual stresses and environment are given. The microstructural inhomogeneities and statistical conditions play an important role. Some informations for fatigue design of components are recommended.
숏 피닝 처리에 의한 고강도 스프링강의 초고주기피로파괴 거동 분석
명노준(Nohjun Myung),최낙삼(Nak-Sam Choi) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
Shot-peening effects on the fatigue behavior of spring steel have been investigated under the high cyclic loading. The strength is en-hanced by the shot-peening treatment, which can be attributed to the effect of surface hardening and residual compressive stress. How-ever, the effect of shot-peening on fatigue behaviors over the very high cycle fatigue (VHCF, Nf < 10<SUP>7</SUP>) remains unclear. We studied whether those effects can be expected to the VHCF range. Hourglass shape specimens made of spring steel (SPS 8) were prepared for the VHCF test using a cantilever type rotary bending fatigue tester. Specimens were treated with a heat condition, and with a shot-peening after the heat. Subsurface crack initiation occurred in both kinds of specimens in the VHCF range. The compressive residual stress of the skin layer suppressed the growth of the fish-eye region. But it did not preclude a creation of the fish-eye micro fracturing zone during the subsurface fracture initiation. Shot-peening treatment has little effect on the VHCF life values for the subsurface initiation.
명노준(No-Jun Myung),한승욱(Seung-Wook Han),최낙삼(Nak-Sam Choi) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
Accelerated method of Ultrasonic fatigue test(UFT) has been used for analyzing very high cycle fatigue( VHCF, Nf > 10?). This paper reviews on how to determine the specimen. The UFT using a resonance of 20㎑ is focused. The specimen geometry is determined with the selection of test materials utilizing dynamic Young’s modulus and wavelength at 20 ㎑. Through a resonant vibration test method is calculated the length of the specimen at resonance of 20 ㎑. Dynamic Young’s modulus is calculated using the resonant frequency and the density. After designing the shape of the specimen, the stress can be calculated.