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Ti-50.1at.%Ni합금의 변태거동에 미치는 시효처리의 영향(Ⅰ)
우흥식,박성범,강봉수,김성진 한국안전학회 2004 한국안전학회지 Vol.19 No.4
This study investigated the effects of aging on the transformation behavior of Ti-50.lat.% Ni alloy by means of differential scanning calorimetry. It was found that aging in the temperature range of 350℃~550℃ induced complex transformation behavior, involving the R-phase and multiple-stage martensitic transformation. Usually aged Ni-rich NiTi alloys undergo martensitic transformation on cooling from high temperatures in two step : B2 to R and then R to B19' (normal behavior). But under certain ageing conditions, the transformation can also occur in three or more step(unusual multiple step behavior). In the present study we use differential scanning calorimetry(DSC) for a systematic investigation of the evolution of transformation behavior with ageing temperature and time.
우흥식,한지원 한국안전학회 2001 한국안전학회지 Vol.16 No.5
Fatigue crack growth behaviour of Ti-6A-4V alloy is investigated in air and salt solution environment at room temperature and $200^{\circ}C$. Fatigue crack growth rate is blown to be fast for the formation of corrosive product in hot salt environment. For the effect on corrosion fatigue crack growth behaviour of region II. fatigue crack growth rate in atmosphere had a little gap to both case, $200^{\circ}C$ and room temperature. However, it showed very fast tendency in salt corrosive atmosphere, and it was remarkably accelerated in $200^{\circ}C$ temperature salt environment. When $\Delta$K was approximately 30MPa(equation omitted), fatigue crack growth rate had a little difference between at room temperature and at $200^{\circ}C$ high temperature, however in case of salt corrosive environment the room temperature was 3.5 times Inter and $200^{\circ}C$ high temperature for 16 times than air environment respectively.
용접잔류응력장에서의 피로균열성장거동에 관한 연구(II)
우흥식 동국대학교 경주대학 1994 東國論集 Vol.13 No.-
Accidental failure of weld structures occurs frequently due to the growth of fatigue cracks propagated from such a weld defects as lack of penetration. In weld structures, residual stresses that were induced by welding operation are primary factors which influence the fatigue crack growth rate. Therefore, the objective of this paper is to investigate the effect of residual stresses on the ΔKth and fatigue crack growth behavior of butt weldments. For this purpose, transverse butt submerged arc welding was performed on SM50A steel plate and CT specimens which loading directions parallel to weld bead were selected. From the experimental results and discussion, the fatigue crack behavior of T specimens was different from that of P specimens in the region of low KK. The compressive residual stress in the base metal area among the T specimen was the largest therefor, the value of ΔKth of that area had the largest one.
Ti-6Al-4V의 저주기 고온염 피로균열성장거동에 관한 연구
우흥식,강봉수,김봉철 東國大學校 1999 東國論叢 Vol.38 No.-
Fatigue crack growth behaviour of Ti-alloy, Ti-6Al-4V were investigated in air and salt corrosive environments. The temperatures which was tested were room temperature and 200℃. Fatigue crack growth rate is known to be fast for formation of corrosive product by impregnation Ti-Alloy with salt solution in hot salt environment. For the effect on corrosion fatigue crack growth behabiour of sale corrosive transformation in air and high temperature of region Ⅱ, fatigue crack grwoth rate in air atmosphere had a little gap to both case, 200℃ and room temperature. However, it showed very fast tendency especially in salt corrosive atmosphere, and it was remarkably accelerated in 200℃ high temperature salt environment. When ΔK was approximately 30MPa√m, fatigue crack growth rate had a little difference between at room temperature and at 200℃ high temperature, however in case of salt corrosive environment, the former was 3.5 times faster and the latter for 16 times than air environment respectively. For salt corrosive environment of microstructure (Ⅲ), the fatigue life in 200℃ salt corrosive environment was shorter than that of in air, reached to only 32%.
고강도 알루미늄 합금의 부식피로균열 성장 거동에 관한 연구(Ⅱ) : 주기 하중 파형의 영향 The Effect of Load Cyclic Wave-Form
김봉철,우흥식 동국대학교 경주대학 1997 東國論集 Vol.16 No.2
Fatigue crack growth in commercial plate of high strength aluminum alloy 7075-T651 has been studied under corrosion environments. In this paper the effect of cyclic load wave-form(trapezoid and triangle) on fatigue crack growth in air, water and sea water environments were investigated using standard LEFM testing procedures. It was founded that the fatigue crack growth behaviors were not affected by cyclic load wave-forms. In regin Ⅱ(stable crack growth region), the fatigue crack growth behaviors were affected by corrosion environments but the values of m are not affected by corrosion environments.
광경화성 레진의 성분 변화에 대한 소수성 표면 제작을 위한 공정 조건
홍성호,우흥식 한국트라이볼로지학회 2020 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.36 No.5
This study experimentally investigates hydrophobic surfaces fabricated via additive manufacturing. Additive manufacturing, commonly known as 3D printing, is the process of joining materials to fabricate parts from 3D model data, usually in a layer-upon-layer manner. Digital light processing is used to fabricate hydrophobic surfaces in this study. This method uses photo-curable resins and ultraviolet (UV) sources. Moreover, this technique generally has faster shaping speeds and is advantageous for the fabrication of small components because it enables the fabrication of one layer at a time. Two photo-curable resins with different compositions are used to fabricate micro-patterns of hydrophobic surfaces. The resins are composed of a photo-initiator, monomer, and oligomer. Experiments are conducted to determine suitable process conditions for the fabrication of hydrophobic surfaces depending on the type of resin. The most important factors affecting the process conditions are the UV exposure time and slice thickness. The fabrication capability according to the process conditions is evaluated using the side and top views of the micro-patterns observed using a microscope. The micro-patterns are collapsed and intertwined when the exposure time is short because sufficient light (heat) is not applied to cure the photo-curable resin with a given slice thickness. On the other hand, the micro-patterns are attached to each other when the exposure time is prolonged because the over-curing time can cure the periphery of a given shape. When the slice is thicker, the additional curing area is enlarged in each slice owing to the straightness of UV light, and the slice surface becomes rough.