• 한국해양공학회지
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• 제23권3호
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• pp.46-52
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• 2009

Nowadays, many components in automobile, aircraft, offshore structure and industry require lightness and high strength. However, since developments of advanced materials have limitations, it mainly is applying to method of surface hardening. This study offered research about camshaft that is one among engine important component. The material used in this study is 0.53% carbon steel as structure material of camshaft, splineshaft, coupling, pulley, driveshaft et cetera. Camshaft is processed using mainly carbon steel, and receives wear and fatigue by special quality high speed of parts. Therefore, camshaft need surface hardening to improve camshaft's fatigue life and increase durability of engine. This study compare to residual stress and martensite microstructure created by high frequency induction treatment, and these results lead to the conclusion of fatigue crack growth characteristics.

• Structural Engineering and Mechanics
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• 제60권3호
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• pp.471-488
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• 2016

This study predicts the strength of rotary brace damper by analyzing a new set of probabilistic models using the usual method of multiple linear regressions (MLR) and advanced machine-learning methods of multivariate adaptive regression splines (MARS), Rotary brace damper can be easily assembled with high energy-dissipation capability. To investigate the behavior of this damper in structures, a steel frame is modeled with this device subjected to monotonic and cyclic loading. Several response parameters are considered, and the performance of damper in reducing each response is evaluated. MLR and MARS methods were used to predict the strength of this damper. Displacement was determined to be the most effective parameter of damper strength, whereas the thickness did not exhibit any effect. Adding thickness parameter as inputs to MARS and MLR models did not increase the accuracies of the models in predicting the strength of this damper. The MARS model with a root mean square error (RMSE) of 0.127 and mean absolute error (MAE) of 0.090 performed better than the MLR model with an RMSE of 0.221 and MAE of 0.181.

• Journal of Welding and Joining
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• 제33권4호
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• pp.50-56
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• 2015

In general, discontinuity of metallurgical and structural points of weld zone could decline the fatigue strength. For the lightweight trend, the AHSS application in automotive chassis is in-progress. However, there are few research reports on AHSS welds fatigue strength in especially automotive chassis parts. Therefore, in this study, we evaluated the effects of the factors affecting the AHSS welding fatigue strength. As the result, the stress concentration of weld bead is the most important factor for welding fatigue strength. For the enhancement of welding fatigue strength, we focused on reducing the stress concentration of the welding beads. So, we applied and proved the plasma welding process and GTAW (Gas Tungsten Arc Welding) dressing method. It was verified by uniaxial fatigue specimen, fatigue performance increased from 40 to 60% by applying TIG dressing method compared to the conventional GMAW (Gas Metal Arc Welding). These results could be recommended the enhancement of fatigue performance of AHSS.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.744-751
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• 2017

The fatigue crack propagation behaviors of Z3CN20.09M duplex stainless steel (DSS) were investigated by studying oxide films of specimens tested in $290^{\circ}C$ water and air. The results indicate that a full oxide film that consisted of oxides and hydroxides was formed in $290^{\circ}C$ water. By contrast, only a half-baked oxide film consisting of oxides was formed in $290^{\circ}C$ air. Both environments are able to deteriorate the elastic modulus and hardness of the oxide films, especially the $290^{\circ}C$ water. The fatigue lives of the specimens tested in $290^{\circ}C$ air were about twice of those tested in $290^{\circ}C$ water at all strain amplitudes. Moreover, the crack propagation rates of the specimen tested in $290^{\circ}C$ water were confirmed to be faster than those tested in $290^{\circ}C$ air, which was thought to be due to the deteriorative strength of the oxide films induced by the mutual promotion of oxidation and crack propagation at the crack tip. It is noteworthy that the crack propagation can be postponed by the ferrite phase in the DSS, especially when the specimens were tested in $290^{\circ}C$ water.

• 한국강구조학회 논문집
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• 제16권6호통권73호
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• pp.737-745
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• 2004

최근 구조물의 정확한 해석을 위하여 접합부의 강성에 반강접 개념이 도입되고 있다. 우리나라의 경우 반강접 접합부의 실험과 이론해석에 대한 연구가 산발적으로 진행되고 있으며, 체계적인 강구조설계를 진행할 정도의 연구성과를 내지는 못 한 상태이다. 그래서 스플릿-티(Split-Tee)를 이용한 접합부의 설계는 국내의 강종과 하중특성을 고려되지 못한 선진국의 연구자료에 의존하고 있는 실정이다. 본 논문은 F10T 고력볼트를 사용한 스플릿-티 접합부의 반강접 특성을 파악하고자, 기둥-보 접합부에 대한 반강접 연구 이전 단계로서 스플릿-티 인장접합부의 구조성능과 변형특성에 대해 실험을 통하여 규명하고자 한다. 플랜지 두께, 도장, 초기도입축력 및 하중가력패턴을 실험변수로 하였으며, 총 20개의 실험체를 제작하여 300ton UTM으로 인장실험을 수행하였다. 각 변수에 따른 스플릿-티 인장 접합부의 구조성능과 거동을 평가하였다.

• Interaction and multiscale mechanics
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• 제1권4호
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• pp.437-448
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• 2008

This paper examined the stability of high-dense dislocation substructures (HDDSs) associated with martensite laths in High Cr steels supposed to be used for FBR, based on a series of dislocation dynamics (DD) simulations. The DD simulations considered interactions of dislocations with impurity atoms and precipitates which substantially stabilize the structure. For simulating the dissociation processes, a point defect model is developed and implemented into a discrete DD code. Wall structure composed of high dense dislocations with and without small precipitates were artificially constructed in a simulation cell, and the stability/instability conditions of the walls were systematically investigated in the light of experimentally observed coarsening behavior of the precipitates, i.e., stress dependency of the coarsening rate and the effect of external stress. The effect of stress-dependent coarsening of the precipitates together with application of external stress on the subsequent behavior of initially stabilized dislocation structures was examined.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.792-795
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• 2004

Despite is product that ship, vehicles, development equipment and Metal Bearing for plant equipment that is mass-produced by present domestic companies Cast White Metal Lining Bearing that is Bimetal Bearing standing 2 generation is accomplishing master and servant and this is foreseen to be used widely on industry whole in hereafter but Cast White Metal Bearing need minuteness processing, while price competitive power is depending on income from superior another thing area than itself manufacture already in advanced nation to lowdown that the technique is generalized widely, when take into account technology change aspect of industrial technology developing country, Go added value creation by deepening of price competition is judged to be difficult hereafter. Because domestic production and supply are wholly lacking almost in Metal Bearing Cladding that take advantage of these technology, Data-base about connection technology is weak with technique and Know-How for product. This research unites Back Steel and Aluminium Alloy different kind metal and make the Clad river studying technology about union of Gogangseong Dacheung metal bearing hereupon.

• Tribology and Lubricants
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• 제27권1호
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• pp.1-6
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• 2011

The possibility of Cu-Al-Ni intermetallic coating on the mild steel through the combustion synthesis has been investigated. In particular, the effect of the ball milling energy on the microstructure of the coating layer was examined to obtain the best coating condition. Experimental results show that Cu-Al-Ni powder compact was explosively synthesized and successfully coated with the steel matrix. It was revealed that the formation of $Cu_9Al_4$ intermetallic decreased with increase in the ball milling energy. This result supports that the high energy ball milling would be effective for obtaining the most suitable microstructure for Cu-Al-Ni coating layer. However, the excessive ball milling energy seems to decrease the bonding strength between the coating layer and the matrix.

• 한국분말재료학회지
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• 제24권2호
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• pp.128-132
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• 2017

Harmonic structure materials are materials with a core-shell structure having a shell with a small grain size and a core with a relatively large grain size. They are in the spotlight because their mechanical properties reportedly feature strength similar to that of a sintered powder with a fine grain size and elongation similar to that of a sintered powder with a coarse grain size at the same time. In this study, the tensile properties, microstructure, and stretch-flangeability of harmonic structure SUS304L made using powder metallurgy are investigated to check its suitability for automotive applications. The harmonic powders are made by mechanical milling and sintered using a spark plasma sintering method at 1173 K and a pressure of 50 MPa in a cylindrical die. The sintered powders of SUS304L having harmonic structure (harmonic SUS304L) exhibit excellent tensile properties compared with sintered powders of SUS304L having homogeneous microstructure. In addition, the harmonic SUS304L has excellent stretch-flangeability compared with commercial advanced high-strength steels (AHSSs) at a similar strength grade. Thus, the harmonic SUS304L is more suitable for automotive applications than conventional AHSSs because it exhibits both excellent tensile properties and stretch-flangeability.

• 열처리공학회지
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• 제13권5호
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• pp.346-354
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• 2000

Effect of Nb addition on the phase transformation behavior was studied through continuous cooling transformation tests after reheating(reheating CCT) and deforming(deforming CCT) the 0.07%C-1.3%Mn-0.015%Ti-(0~0.08)% Nb steels. Transformation temperatures for deforming CCT were lower than those for reheating CCT, and the critical cooling rate for bainite transformation during deforming CCT was lower than that during reheating CCT. These enhanced hardenability for deforming CCT was considered to come from the sufficient solid solution of Nb in austenite during high temperature reheating before deformation. With Nb addition, the phase transformation temperature decreased, the bainite formation was enhanced, and the hardness of steel increased. Furthermore, these phenomena were more remarkable for deforming CCT than for reheating CCT. From the results, Nb-Ti bearing low carbon steel was considered to be a very favorable alloy system with good strength/toughness balance by recrystallization control rolling process.