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複合組織鋼의 母相粒徑과 軸斷面形狀이 破壞擧動에 미치는 影響
吳世旭,姜鎬珉 東亞大學校 1985 東亞論叢 Vol.22 No.1
The weight reduction and reliability, stability of various steel materials used in industrial machinery have become a great importance as industry developes. For this reason a study on dual phase steel has been performed by the reporter with great interest. It was pointed out that fatigue fracture behaviours of MEF dual phase steel were dependent upon a unit of ferrite grain size when the plastic constraint effect and the internal stress were constant. However, when the plastic constraint effect and the internal stress were constant, fracture behaviours of MEF dual phase steel might be expected to depend upon the ferrite grain size and the shape of section. Specimens were prepared the combined microstructures having different size of ferrite grain which has approximatly the constant plastic constraint effect and the constant internal stress through careful heat treatments. Each of tensile specimens and fatigue specimens was conducted by universal testing machine and rotary bending fatigue test machine. They were prepared to be able to apply the stress intensity factor equations(K₁=σ? πℓ. F(?): solid shaft, K₁=k₁.k₂σ? πℓ:hollow shaft). The relationship between fatigue crack length, fatigue crack propagation velocity, stress intensity factor and scanning electron microscope investigation of tensile fracture surface and fatigue fracture surface was investigated during the test. The results of the experiment are as follows. 1. Fracture behaviours of MEF dual phase steel with the constant plastic constraint effect and the constant internal stress depend on great and small size of ferrite grain. It has been found that Hall-petch equation is applied dual phase-poly crystallization. 2. The crack propagation length and number of cycles of hollow specimen and solid specimen approaches nearly and makes a gentle slope in case of small ferrite grain size under low stress level. 3. The difference of fatigue crack propagation velocity is large about the influence of shape of specimen at the same △K value under high stress level and that is approached under low stress level. 4. It can be had for light weighted purpose as use of hollow shaft with MEF dual phase and MEF dual phase steel demands minute ferrite grain size under low stress level. 5. It has been found that the shape of striation changes according to shape difference of specimen. The space of striation is narrow as the ferrite grain size and the stress level are small.
SUH3-SUS303의 摩擦熔接部에 있어서의 크리이프 强度에 관한 硏究
吳世旭,李圭用 동아대학교 공과대학 부설 한국자원개발연구소 1981 硏究報告 Vol.5 No.2
Since it is very useful for production cost reduction and excellent bonding quality, etc., friction welded dissimilar materials have been widely used as engine components such as marine engine valves which are adapted under the conditions of high temperature oxidation/corrosion and high pressure combustion gas environment. Recently, these components have been asked to operate in the high temperature range of 700°-800℃ with combustion gas and high speed rotation for the increment of the engine performance. Therefore with the high temperature wear resistance, high temperature creep strength characteristics of friction welded heat/corrosion resisting materials on those conditions have come to important for stable operation of the engine. However, it seems difficult to find out any report concerning the high temperature creep strength of friction welded dissimilar materials. In this study high temperature creep testing was carried out under the condition of 700℃ high temperature for the purpose of to investigate of the aging effects on the high temperature creep strength characteristics of the friction welded dissimilar materials SUH3-SUS303 which were friction welded on optimum welding conditions and aging heat treated for 0 hr, 10 hr and 100 hr. The results obtained are as follows ; 1) The maximum creep strength life was demonstrated with 10 hr aged specimen by the average increasing rate of 87% compared with that of 0 hr aging but in the case of 100 hr aged specimen it was decreased by average 65% to the that of 10 hr aging. 2) The steady state creep rate to creep stress of 10 hr aging was expressed the lowest rate value and that of 100 hr had the highest one, so it was affirmed concerning between the steady state creep rate and aging time. 3) According to each aging time of 0 hr, 10 hr and 100 hr, the equations between creep stresses and steady state creep rates were obtained as follows ; ε'_(0)=1.4163×10^(-6)σ^(2.6258) ε'_(10)=4.2304×10^(-8)σ^(3.9635) ε'_(100)=2.2033×10^(-5)σ^(1.6969)
半無限平板의 楕円노치周邊에서 크랙先端의 應力擴大係數에 관한 光彈性 解析
吳世旭,姜吉洙 東亞大學校 大學院 1985 大學院論文集 Vol.10 No.-
This study is about stress intensity factors F?, F? and F? of the semi-infinite plane of 3mm epoxy resin plate under tensile load. The plate contains a central elliptical notch of h/c=2 or 0/5, with two cracks, one is perpendicular to the direction of σ and the other is inclined to the direction of σ. Experiments are performed by the photoelastic method, and the effects of notch ratio, crack ratio and crack angle on the stress intensity factors and dircussed. The results obtained by the experiments are as follows: 1. Stress intensity factor F? of the inclined crack showed wide variation with inclined crack angle but F? showed a slight variation. They increased with ratio of crack length. 2. Stress intensity factor F? decreased with increase of incline angle, and F? had the maximum vale at 45°. 3. Stress intensity factors F?, F? and F? for elliptical notch ratio h/c=0.5 were slightly greater than that of the case for h/c=2. 4. Stress intensity factor F? value of horizontal crack was little influenced by the variation for inclined crack angle. 5. As stress intensity factor F? of horizontal crack was greater than that of all the case for stress intensity factors F? and F? of inclined crack, designing on the basis of horizontal crack crisis would exclude that of inclined crack
回轉굽힘을 받는 複合組織網의 疲勞强度와 破壞擧動에 관한 硏究
吳世旭,金奉均 東亞大學校 1982 東亞論叢 Vol.19 No.1
The quality and reliability of various steel materials used in industrial machinery have become a great importance as industry developes. For this reason a study on dual phase steel have been performed by the reporter with great interest. The annealed steel and MEF steel. FEM steel of dual phase specimens were prepared on hollowed specimen. A rotated bending fatigue test was performed on these specimens. The relationship between fatigue crack propagation status, velocity and stress intensity factor was investigated during the test. The results of the test are as follows. 1. The fatigue limits of MEF and FEM showed 34% and 26% increases respectively compared to the annealed specimen. 2. The fatigue-life of MEF and FEM showed 15.6 and 10.5 times increase respectively over the annealed specimen. For initial crack occurance, MEF and FEM showed 40 and 15 times, increase over the annealed specimen. 3. The relationship between propagative speed of fatigue-crack and stress intensity factor is formulated as shown below : Annealed : ?? FEM : ?? MEF : ?? 4. The crack occurance in a ferrite particle of dual phase steel propagated thru the thinnist border of the martensite second phase for MEF specimen, and propagated alongside the border of the martensite second phase for FEM.
吳世旭,鄭海澤 東亞大學校 1967 東亞論叢 Vol.4 No.-
This report describes the investigation and study on the cupolas in pusan and Kyung-nam District, for which the antracitic-lump-coal has been used in Korea. Coke is used as the fuel for the cupola in every country of the world. In Korea, however, the coke has become very difficult to be produced since the end of the world was II, s) that the domestic anthractic-limp-coal only has been available, as this fuel has the low heating value and a great amount of the ash content and impurities, so the quality of casting has become more inferior. Thus it has cast a shadow over the future of the Korean machine industry. But nowadays it can be said that the quality of casting has been much developed and improved by the method of the trial and error proces for a long time, and yet the results being developed from an independent standhonint at each foundry have the various types of irrationality, so this report ead described for the purpose to investigate the special qualities of the cupola for the anthracitiv-limp-coal as a whole, to make some data for the cupola design from them and to find out some improvements of the cupola. The following are the summary about the special qualities of the cupola for th enthracitic-limp-coal comparing with te cupola for the coke. (1) The melting speed to the cupora inside diameter on tuyere plane is low as shown in Figure 2 and Figure 3. (2) The upper effectual height to the cupola inside diameter on tuyere plane is low and the lower effectual height is almost coinsident. (3) Tuyere ratio is very great, about 10 to 40. (4) Secondary tuyere or multiple step tuyere is more profitable. (5) The inclination of tuyere around 10 to 15 degrees is more profitable. (6) The calculation coefficient of the effectual inside diameter is very great as shown in Figure 11, Figure 12 and Table 5. (7) The tendency of the inferiority of casting quality being caused by the impurities of the anthracitic lump-coal should be developed by establishing front furnace. (8) Hot-blast should be established to increase the thermal efficiency and to get the high temperature melting carried out. Under the consideration of the above special qualities, the rational cupolas for the anthracitic lump-coal which are appiropriate the Korean situation should be designed.
계장화충격시험에 의한 복합조직강의 파괴인성에 관한 연구
오세욱,유재환,박원조,이경봉 동아대학교 공과대학 부설 한국자원개발연구소 1989 硏究報告 Vol.13 No.1
The dynamic fracture toughness (K_(Id)) is measured using the precracked standard Charpy specimen with an instrumented impact machine. The value of K_(Id) is determined as a function of yield strength and microstructure, and correlations are established between K_(Id) and both energy of initial fracture and total energy of fracture. Since the K_(Id) values of the precracted impact specimens are in accordance with their theoretical ones, this test method is sufficiently practical.
SUS 316L의 콘크리트强度 및 破壞擧動에 미치는 結晶粒度와 溫度의 影響
吳世旭,金晉坤 東亞大學校 1983 東亞論叢 Vol.20 No.3
SUS316L have been dealed with the solution treatment for 1hour, 5hour and 10 hour at 1100。C respectively, thus have been obtained grain size of ASTM number 6,5 and 4 and then conducted by creep test on the uniaxial state of strss. The effect of grain size on the creep strength and fracture behiviour of SUS316L have been investgated at the different temperatures(600。C) and the different stresses separately. Failure surface have been observed by scanning electric microscope. The main results obtained were as follows. 1. The optimum grain diameter for the maximum creep strength is hardly influnced by the change of stress but depends upon the temperature heavily. 2. The initial strain increase when the grain is coarsenned or the creep test temperature is raised. 3. The equation of rupture life, ?? was applied to the SUS316L well. 4. The SUS 316L of low carbon is only observed as the failure surface (thought of similar intergranular) but shown the behavior of ductile because of equiaxed and elongated dimple. 5. Under the various test temperature the optimum grain diameter is found with the fine and equiaxed dimple at perpendicular and flat fracture surface but is prevalently shown elongated dimple at the other grain diameter.
3.5% NaCl 水溶液의 溫度變化가 SS41鋼의 腐蝕疲勞破壞에 미치는 影響
吳世旭,姜鎬珉,金廣泳,都映旼 東亞大學校 海洋資源硏究所 1988 硏究論文集 Vol.1 No.1
Corrosion fatigue test was performed under rotary bending in 3.5% NaCl aqueous solution having a temperature from 278°K to 318°K in order to investigate the effects of aqueous solution temperature on the corrosion fatigue fracture of SS41 steel. Fatigue life was remarkebly decreased with an increase in aqueous solution temperature. Fatigue life reductions for high stress level were somewhat smaller than those for low stress level, but S-N curves were nearly become parallel lines. Corrosion fatigue crack propagations were accelerated with an increase in aqueous solution temperature. The corrosion fatigue result at aqueous solution temperature of 303°K was showed about the same behaviour as those at 318°K in both S-N curve and da/dN-ΔK curve, which was considered as consequence of limiting diffusion current density(??). As aqueous solution temperature was increased, corrosion was gradually activated in view of fractured surface.