• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.551-554
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• 2002

As a general rule, the brazing process between cemented carbides and steel used by Silver (Ag) type brazing filler. The composition of Ag type filler were used Ag-Cu-Zn-Cd type filler mainly. But, the demand of Cadmium (Cd)-free in Ag type filler was raised recently. The reason why Cd-free in Ag brazing filler were occupied to vaporize as a CdO$_2$ when brazing process, because of Cd element was almost low boiling point of all Ag type filler elements. And, CdO$_2$ was a very harmful element for the human body. This experiment was developed Cd-freeing on Ag type filler that was used Indium (In) instead of Cd element. In this experiment, there were changed from 0 to 5% In addition in Ag brazing filler and investigated to most effective percentage of Indium. As a result, the change of In addition instead of Cd, there was a very useful element and obtained same property only 3% In added specimens compared to Cd 19% added specimens. These specimens were obtained same or more deflective strength. In this case, there were obtained 70 MPa over strength and wide brazing temperature range 650-800 C. A factor of deflective strength were influenced by composition and the shape of $\beta$ phase and between $\beta$ phase and cemented carbides interface. Indium element presented as $\alpha$ phase and non-effective factor directly, but it's occupied to solid solution hardening as a phase. $\beta$ phase were composed 84-94% Cu-Ni-Zn elements mainly. Especially, the presence of Ni element in interface was a very important factor. Influence of condensed Ni element in interface layer was increased the ductility and strength of brazing layer. Therefore, these 3% In added Ag type filler were caused to obtain a high brazing strength.

• 한국소음진동공학회논문집
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• 제15권3호
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• pp.251-258
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• 2005

The free vibration of a spinning flexible disk-spindle system supported by hydro dynamic bearings (HDB) in an HDD is analyzed by FEM. The spinning flexible disk is described using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. It is discretized by annular sector element. The rotating spindle which includes the clamp, hub, permanent magnet and yoke, is modeled by Timoshenko beam including the gyroscopic effect. The flexible supporting structure with a complex shape which includes stator core, housing, base plate, sleeve and thrust pad is modeled by using a 4-node tetrahedron element with rotational degrees of freedom to satisfy the geometric compatibility. The dynamic coefficients of HDB are calculated from the HDB analysis program, which solves the perturbed Reynolds equation using FEM. Introducing the virtual nodes and the rigid link constraints defined in the center of HDB, beam elements of the shaft are connected to the solid elements of the sleeve and thrust pad through the spring and damper element. The global matrix equation obtained by assembling the finite element equations of each substructure is transformed to the state-space matrix-vector equation, and the associated eigen value problem is solved by using the restarted Arnoldi iteration method. The validity of this research is verified by comparing the numerical results of the natural frequencies with the experimental ones. Also the effect of supporting structures to the natural modes of the total HDD system is rigorously analyzed.

• 자원리싸이클링
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• 제17권5호
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• pp.44-51
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• 2008

본 연구에서는 국산 99.7%순도의 수산화알루미늄을 대상으로 미량원소로 함유되어 있는 Na, Ca및 Fe의 제거실험을 수행하였다. 용출액으로는 유기산인 oxalic acid와 citric acid를 사용하였으며 수산화알루미늄은 초기 입도가 서로 다른 2종류의 시료를 사용하였다. 수산화알루미늄의 미립화를 위해 ball mill을 사용하여 미분쇄 실험을 수행하였으며, 용출조건에 따른 미량원소의 용출특성을 조사하였다. 실험결과 0.1$\sim$1.0mole/l 농도범위에서 oxalic acid에 의한 원소 용출율이 citric acid보다 높은 것으로 나타났으며, 유기산 농도가 증가할수록 또한 반응온도가 증가할수록 원소의 용출율은 증가하였다. 미분쇄 공정시 순수한 물에 의한 Na의 용출율은 약 45%에 달해 aluminum hydroxide에 함유된 Na성분의 상당 부분은 수용성 화합물인 것으로 확인되었다.

• 분석과학
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• 제8권2호
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• pp.195-203
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• 1995

Fe-5.7% Al 합금에 탄소 및 미량 합금원소를 첨가하고 그 제진특성 변화를 결정립 크기 및 자기적 특성과 관련하여 관찰하였으며, 탄소의 거동을 XRD 및 EDS로 조사하였다. 이 합금은 강자성형 제진 양상을 나타냈고, 제3원소 첨가는 그 SDC를 악화시키며 특히 탄소는 현저하였다. 제진 특성은 결정립 크기와는 직접적인 상관관계가 없었고, 자기이력곡선 면적은 상관관계가 있었다. 탄소가 이 합금의 제진특성을 악화시키는 원인은 고용탄소에 의한 $90^{\circ}$ 자구벽의 고착이 주원인이었으며, 탄화물도 자구벽의 이동을 방해할 것이므로 제진특성에 악영향을 미치는 것으로 해석되었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.572-578
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• 2003

The free vibration of a spinning flexible disk-spindle system supported by hydro dynamic bearings in a HDD is analyzed by FEM. The spinning flexible disk is described using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. It is discretized by annular sector element. The rotating spindle which includes the clamp, hub, permanent magnet and yoke, is modeled by Timoshenko beam including the gyroscopic effect. The flexible supporting structure with a complex shape which includes stator core, housing, base plate, sleeve and thrust pad is modeled by using a 4-node tetrahedron element with rotational degrees of freedom to satisfy the geometric compatibility. The dynamic coefficients of HDB are calculated from the HDB analysis program, which solves the perturbed Raynolds equation using FEM. Introducing the virtual nodes and the rigid link constraints defined in the center of HDB, beam elements of the shaft are connected to the solid elements of the sleeve and thrust pad through the spring and damper element. The global matrix equation obtained by assembling the finite element equations of each substructure is transformed to the state-space matrix-vector equation, and the associated eigenvalue problem is solved by using the restarted Arnoldi iteration method. The validity of this research is verified by comparing the numerical results of the natural frequencies with the experimental ones. Also the effect of supporting structures to the natural modes of the total HDD system is rigorously analyzed.

• 대한기계학회논문집A
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• 제35권7호
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• pp.821-826
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• 2011

CAE 기반 구조최적설계법인 위상최적설계와 형상최적설계를 크레인의 경량화에 적용하였다. 붐은 단면 형상을 설계 변수로 변화시키면서 질량의 최소화를 최적설계의 목적함수로 하고 붐의 정적강도와 동적강성이 초기 모델의 성능에 비해서 저하되지 않아야 한다는 제한조건을 설정하였다. 구조해석 및 최적설계는 상용소프트웨어인 Hyperworks를 이용하여 수행하였으며 붐의 단면 형상의 변형에 따르는 요소망의 변동은 모핑 기능을 사용하여 수치 안정성을 확보하였다. 붐의 지지부는 초기 모델을 단순화시킨 설계 영역을 설정하고 이를 삼차원 솔리드 요소로 이산화한 후 위상최적설계를 수행하였다. 최적설계 결과 시스템의 전체 동적, 정적 강성을 저하시키지 않은 채로 붐은 19%, 지지부는 17% 경량화시킬 수 있었다.

• Steel and Composite Structures
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• 제20권1호
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• pp.167-184
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• 2016

This paper presents the details of Finite Element (FE) analysis carried out to determine the limiting deformation capacity and failure mode of Laced Steel-Concrete Composite (LSCC) beam, which was proposed and experimentally studied by the authors earlier (Anandavalli et al. 2012). The present study attains significance due to the fact that LSCC beam is found to possess very high deformation capacity at which range, the conventional laboratory experiments are not capable to perform. FE model combining solid, shell and link elements is adopted for modeling the beam geometry and compatible nonlinear material models are employed in the analysis. Besides these, an interface model is also included to appropriately account for the interaction between concrete and steel elements. As the study aims to quantify the limiting deformation capacity and failure mode of the beam, a suitable damage model is made use of in the analysis. The FE model and results of nonlinear static analysis are validated by comparing with the load-deformation response available from experiment. After validation, the analysis is continued to establish the limiting deformation capacity of the beam, which is assumed to synchronise with tensile strain in bottom cover plate reaching the corresponding ultimate value. The results so found indicate about $20^{\circ}$ support rotation for LSCC beam with $45^{\circ}$ lacing. Results of parametric study indicate that the limiting capacity of the LSCC beam is more influenced by the lacing angle and thickness of the cover plate.

• 한국공간구조학회논문집
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• 제9권1호
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• pp.61-68
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• 2009

본 연구는 와플구조의 구조적 거동에 파악하고자 한다. 와플슬래브의 두께, 주요 보의 깊이와 기둥의 크기를 변수로 하여 와플구조의 모드형상과 고유진동수를 파악하고자 하였다. 또한 쉘요소와 입체요소를 사용한 유한요소모델의 해석결과를 비교하였다. i)레벨2에서 주요 보의 깊이가 증가함에 따라, ii)레벨3에서 와플슬래브 두께가 감소함에 따라 모드진동수는 증가하였다. 3차원 모델과 2차원 모델의 모드형상은 유사한 형상을 보였다. 또한, 3차원 모델과 2차원 모델사이의 모드진동수는 25%에서 36%의 차이를 보였다.

• 대한조선학회논문집
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• 제56권1호
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• pp.82-93
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• 2019

In this paper, the ductile fracture criteria for a marine structural steel (EH36) are presented and validated. The theoretical background of the recently developed Hosford-Coulomb (HC) fracture strain model and the DSSE fracture strain model which was developed to apply to the shell elements is described. In order to accurately estimate the flow stress in the large strain range up to the fracture, the material constants for the combined Swift-Voce constitutive equation were derived by the numerical analyses of the smooth and notched specimens made from the EH36 steel. As a result of applying the Swift-Voce flow stress to the other notched specimen model, a very accurate load - displacement curve could be derived. The material constants of the HC fracture strain and DSSE fracture strain models were independently calibrated based on the numerical analyses for the smooth and notch specimen tests. The user subroutine (VUMAT of Abaqus) was developed to verify the accuracy of the combined HC-DSSE fracture strain model. An asymmetric notch specimen was used as verification model. It was confirmed that the fracture of the asymmetric specimen can be accurately predicted when a very small solid elements are used together with the HC fracture strain model. On the other hand, the combined HC-DSSE fracture strain model can predict accurately the fracture of shell element model while the shell element size effect becomes less sensitive.

• Advances in materials Research
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• 제8권1호
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• pp.47-73
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• 2019

Joining of Mg/Ti hybrid structures by welding for automotive and aerospace applications has attracted great attention in recent years due mainly to its potential benefit of energy saving and emission reduction. However, joining them has been hampered with many difficulties due to their physical and metallurgical incompatibilities. Different joining processes have been employed to join Mg/Ti, and in most cases in order to get a metallurgical bonding between them was the use of an intermediate element at the interface or mutual diffusion of alloying elements from the base materials. The formation of a reaction product (in the form of solid solution or intermetallic compound) along the interface between the Mg and Ti is responsible for formation of a metallurgical bond. However, the interfacial bonding achieved and the joints performance depend significantly on the newly formed reaction product(s). Thus, a thorough understanding of the interaction between the selected intermediate elements with the base metals along with the influence of the associated welding parameters are essential. This review is timely as it presents on the current paradigm and progress in welding and joining of Mg/Ti alloys. The factors governing the welding of several important techniques are deliberated along with their joining mechanisms. Some opportunities to improve the welding of Mg/Ti for different welding techniques are also identified.