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백운봉(Baek Un Bong),이해무(Lee Hae Moo),이윤희(Lee Yun Hee),남승훈(Nahm Seung Hoon) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
In this study. Low cycle fatigue properties were experimentally measured for 9Cr-1Mo steel. This test data will using design and life assessment for fossile power plant boiler head and steam pipes. Low cycle fatigue test performed at room temperature and high temperature(design temperature). Temperature effect for low cycle fatigue is discussed in detail. Standardization performed that the temperature calibration method for high temperature low cycle fatigue. The measured Reversals to failure vs true strain amplitude curve for the 9Cr-lMo steel at room temperature as shown in Fig. 1.
응력상태의 비정질 표면에 형성된 압입흔적 회복인자를 이용한 잔류응력 분석
이윤희 ( Yun Hee Lee ),유하영 ( Ha Young Yu ),백운봉 ( Un Bong Baek ),남승훈 ( Seung Hoon Nahm ) 대한금속·재료학회 2010 대한금속·재료학회지 Vol.48 No.3
An application of the instrumented indentation technique has been expanded from the measurements of hardness and elastic modulus to the analysis of residual stress. A slope of the indentation loading curve increases (or decreases) according to compressive (or tensile) residual stress. A theoretical equation has been established for quantifying residual stress from the slope change. However, a precise observation of the remnant indents is indispensible because the theoretical approach needs actual contact information. In addition, the conventional hardness test is still used for predicting the residual stress distribution of welded joints. Thus, we observed the three-dimensional morphologies of the remnant indents formed on artificial stress states and analyzed stress effects on morphological recovery of the indents. First, a depth recovery ratio, which has been regarded as a sensitive stress indicator, did not show a clear dependency with the residual stress. Thus an analysis on volumetric recovery was tried in this study and yielded a inverse proportional behavior with the residual stress. In addition, an elastic to plastic volume recovery ratio showed more significant correlation with the residual stress.
미소 표면변형 관찰을 통한 가스배관 부재의 항복특성 평가
이윤희(Yun-Hee Lee),백운봉(Un-Bong Baek),정인현(In-Hyeon Cheong),남승훈(Seung-Hoon Nahm),이상혁(Sang-houck Lee) 한국가스학회 2008 한국가스학회지 Vol.12 No.2
가스배관 열화부재의 실시간 역학물성 측정기술로 계장화 압입과 압입흔적 입체측정의 융합이 시도되었다. 압입하중-변위곡선을 계장화 압입시험으로 획득한 후 반사식 레이저 스캔너를 이용하여 압입흔적을 3차원으로 관찰하였다. 압흔 단면프로파일로부터 소성역 크기와 실제 접촉경계를 분석할 수 있었고, 두 값을 이용하여 소재의 항복강도와 경도를 계산하였다. 항복강도는 단축 인장시험에서 얻어진 값과 유사한 경향을 나타내었고, 경도는 재료쌓임 영향으로 압입곡선에서 계산된 값에 비해 20~30% 낮은 값을 나타내었으나 최대 인장강도와 정량적인 관련성이 있음을 확인할 수 있었다. 덧붙여 압입하중 인가부의 형태를 수정하여 압입시험과 동시에 압흔주변 형상변화를 측정하기 위한 시스템도 고안되었다. A combination of the instrumented indentation and 3D morphology measurement has been tried in order to perform a real-time property measurement of degraded materials in gas pipelines; threedimensional indent morphologies were recorded using a reflective laser scanner after a series of insturmented indentations on three metallic specimens. Dimensions of the permanent deformation zone and contact boundary were analyzed from the cross-sectional profile over an remnant indent and used for estimating yield strength and hardness, respectively. Estimated yield strength was comparable with that from uniaxial tensile test and actual hardness implying material pile-up effects was lower than the calculated value from indentation curve by 20~30%. It means that this 3D image analysis can explain the material pile-up effects on the contact properties. Additionally, a combined system of indentation and laser sensor was newly designed by modifying a shape of the indentation loading fixture.
KIM, Hwan-Hee,KWAK, Dong-Hoon,YON, Jung-Min,BAEK, In-Jeoung,LEE, Se-Ra,LEE, Jeung-Eun,NAHM, Sang-Soep,JEONG, Jae-Hwang,LEE, Beom Jun,YUN, Young Won,NAM, Sang-Yoon Society for Reproduction and Development 2007 The Journal of reproduction and development Vol.53 No.3
<P>Expression of 3<I>β</I>-hydroxysteroid dehydrogenase (<I>3β-HSD</I>) is mainly found in the Leydig cells from which steroid hormones are biosynthesized in the testes. To investigate whether endocrine disruptors affect the microenvironment of the testes, the mRNA expression of <I>3β-HSD</I> as a molecular marker for androgen biosynthesis was analyzed in rat testes exposed to several endocrine disruptors using a reverse transcription-polymerase chain reaction technique. Testosterone [50, 200 and 1,000 <I>μ</I>g/kg body weight (BW)], flutamide (1, 5 and 25 mg/kg BW), ketoconazole (0.2, 1, 5 and 25 mg/kg BW), diethylhexyl phthalate (10, 50 and 250 mg/kg BW), nonylphenol (10, 50, 100 and 250 mg/kg BW), octylphenol (10, 50 and 250 mg/kg BW), and diethylstilbestrol (10, 20 and 40 <I>μ</I>g/kg BW) were orally administered to 4-week-old Sprague-Dawley rats for 3 weeks daily. Although testosterone at a low dose (50 <I>μ</I>g/kg/day) increased the expression of <I>3β-HSD</I> mRNA, it was significantly decreased in the rats treated with 200 or 1,000 <I>μ</I>g/kg/day testosterone compared with the control group (P<0.05). Furthermore, ketoconazole, diethylhexyl phthalate, nonylphenol, octylphenol and diethylstilbestrol caused significant downregulation of <I>3β-HSD</I> mRNA in the testes at all doses (P<0.05). However, flutamide remarkably increased the level of <I>3β-HSD</I> mRNA in the testes (P<0.05). These results suggest that endocrine disruptors may influence androgen biosynthesis in the testes by alteration of <I>3β-HSD</I> mRNA expression.</P>
남승훈(Seung Hoon Nahm),이윤희(Yun-Hee Lee),백운봉(Un Bong Baek),정인현(In Hyun Chung),이해무(Hae Moo Lee) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5
In order to guarantee the safety of the facility systems, one of the essential components is information on mechanical properties of materials used for the construction. Corresponding to the urgent needs and poor economical features, the MOCIE designated the Data Center of Mechanical Properties for Metallic Materials (DCMP). The DCMP plays roles of collection, edition and evaluation of the mechanical data and development of reference standards. In this study, several functions of the DCMP and standardization procedures of mechanical properties data will be introduced.