• 대한기계학회논문집A
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• 제24권1호
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• pp.69-78
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• 2000

The one-parameter singular expression for stresses and displacements near a crack tip has been widely thought to be sufficiently accurate over a reasonable re ion for any geometry and loading conditions. In many cases, however subsequent terms of the series expansion are quantitatively significant, and so we now consider the evaluation of such terms and their effect on the predicted crack growth direction. For this purpose the problem of a cracked orthotropic plate subjected to a biaxial load is analysed. It is assumed that the material is ideal homogeneous anisotropic. BY considering the effect of the load applied parallel to the plane of the crack, the distribution of stresses and displacements at the crack tip is reanalyzed. In order to determine values for the angle of initial crack extension we employ the normal stress ratio criterion.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.110-114
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• 2001

A numerical analysis has been perfonned to estimate the effect of turbulent penetration and thermal stratified flow in the branch lines piping. This phenomenon of thermal stratification are usually observed in the piping lines of the safety related systems and may be identified as the source of fatigue in the piping system due to the thermal stress loading which are associated with plant operating modes. The turbulent penetration length reaches to $1^{st}$ valve in safety injection piping from reactor coolant system (RCS) at normal operation for nuclear power plant when a coolant does not leak out through valve. At the time, therefore, the thermal stratification does not appear in the piping between RCS piping and $1^{st}$ valve of safety injection piping. When a coolant leak out through the $1^{st}$ valve by any damage, however, the thermal stratification can occur in the safety injection piping. At that time, the maximum temperature difference of fluid between top and bottom in the piping is estimated about $50^{\circ}C$.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.419-424
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• 2002

The HANARO, a multi-purpose research reactor of 30 MWth open-tank-in-pool type, has been under normal operation since its initial criticality In February, 1995. Many experiments should be safely performed to activate the utilization of the HANARO. A flow simulation facility is being developed for the endurance test of reactivity control units for extended life times and the verification of structural integrity of those experimental facilities prior to loading in the HANARO. This test facility is composed of three major parts; a half-core structure assembly, flow circulation system and support system. The flow circulation system is composed of a circulation pump, a core flow pipe, a core bypass flow pipe and instruments. The system is to be filled with de-mineralized water and the flow should be met the design flow to simulate similar flow characteristics in the core channel of the half-core test facility to the HANARO. This paper, therefore, describes an analytical analysis to study the flow behavior of the system. The computational flow analysis has been performed for the verification of system pressure variation through the three-dimensional analysis program with standard k-$\epsilon$ turbulence model and for the verification of the structural piping integrity through the finite element method. The results of the analysis are satisfied the design requirements and structural piping integrity of flow circulation system.

• 구강회복응용과학지
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• 제20권1호
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• pp.57-70
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• 2004

The significance of occlusion has regained its popularity in dentistry with the introduction of implant therapy. Literature has reported that the clinical success and longevity of dental implants can be achieved by biomechanically controlled occlusion. Occlusal overload is known to be one of the main causes for implant failure. Evidences have suggested that occlusal overload contribute to early implant bone loss as well as deosseointegration of successfully integrated implants. Unlike natural teeth, osseointegrated implants are ankylosed to surrounding bone without the periodontal ligament (PDL) which provides mechanoreceptors as well as shock-absorbing function. Moreover, the crestal bone around dental implants may act as a fulcrum point for lever action when a force (bending moment) is applied, indicating that implants/implant prosthesis could be more susceptible to crestal bone loss by applying force. Hence, it is essential for clinicians to understand inherent differences between teeth and implants and how force, either normal or excessive force, may influence on implants under occlusal loading. The purposes of this paper are to review the importance of implant occlusion, to establish the optimum implant occlusion with biomechanical rationale, to provide clinical guidelines of implant occlusion and to discuss how to manage complications related to implant occlusion.

• 대한기계학회논문집A
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• 제21권3호
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• pp.519-527
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• 1997

AISI 316 steel has been used extensively for heater and boiler tube of the structural plants such as power, chemical and petroleum plants under severe operating conditions. Usually, material degradation due to microcrack or precipitation of carbides and segregation of impurity elements, is occured by damage accumulated for long-term service at high temperature in this material. In this study, the effect of aging time on fracture toughness was investigated to evaluate the measurement of material degradation. The elastic-plastic fracture toughness behaviour of AISI 316 steel pipe aged at $550^{\circ}C$for 1h-10000h (the aged material) was characterized using the single specimen J-R curve technique and eletric potential drop method at normal loading rate(load-line displacement speed of 0.2mm/min) in room temperature and air environment. The fracture toughness data from above experiments is compared with the $J_{in}$ obtained from predicted values of crack initiation point using potential drop method.

• International Journal of Concrete Structures and Materials
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• 제10권sup3호
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• pp.33-41
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• 2016

Ultra-high performance concrete (UHPC) is one of the most promising construction materials because it exhibits high performance, such as through high strength, high durability, and proper rheological properties. However, it has low tensile ductility compared with other normal strength grade high ductile fiber-reinforced cementitious composites. This paper presents an experimental study on the tensile behavior, including tensile ductility and crack patterns, of UHPC reinforced by hybrid steel and polyethylene fibers and incorporating plastic beads which have a very weak bond with a cementitious matrix. These beads behave as an artificial flaw under tensile loading. A series of experiments including density, compressive strength, and uniaxial tension tests were performed. Test results showed that the tensile behavior including tensile strain capacity and cracking pattern of UHPC investigated in this study can be controlled by fiber hybridization and artificial flaws.

• Journal of Power Electronics
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• 제14권2호
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• pp.402-412
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• 2014

This paper proposes a novel electric propulsion system for naval ships, which consists of Active Front End (AFE) converters directly connected to battery Energy Storage Modules (ESMs). Employing the proposed AFE converters with ESMs in the power systems of naval ships can enhance the reliability and quality of the electric power. Furthermore, the fuel-efficiency of the generator can be improved by a higher loading factor of the generator and its prime movers. The proposed AFE configuration does not require an additional dedicated DC/AC converter for the ESMs. Instead of that, the AFE converter itself can control the DC link voltage and the discharging and/or charging of the ESMs. A control scheme to achieve these control objectives is also presented in this paper. The overall power system, including the generators and electrical loads of a naval ship, is implemented by a small scaled Power Hardware-In-the-Loop (PHIL) simulator. Through this experimental setup, the proposed system configuration and the power control strategies are verified. It is shown that the fuel-efficiency and transient dynamics can be improved in the normal and contingency operation modes.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1584-1592
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• 2000

Reversed plane bending fatigue tests were conducted on SiC whisker reinforced aluminum composite which were consolidated by squeeze casting process. Initiation and growth of small surface fatigue c racks were investigated by means of a plastic replica technique. The fatigue crack initiated in the vicinity of SiC whisker/matrix interface. It was found that a fatigue crack deflected along SiC whisker and grew in a zig-zag manner microscopically, although the crack propagated along the direction normal to the loading axis macroscopically. The coalescence of micro-cracks was observed in the tests conducted at high stress levels, but were not evident in tests in which lower levels of stress were applied. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn -ΔK realtionship.

• 한국압력기기공학회 논문집
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• 제12권2호
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• pp.50-57
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• 2016

The study presents structural integrity assessment of ductility degradation of a baffle former assembly by performing finite element analysis considering real loading conditions and stress triaxiality. Variations of fracture strain curves of type 304 austenitic stainless steel with stress triaxiality are derived based on the previous study results. Temperature distributions during normal operation such as heat-up, steady state, and cool-down are calculated via finite element temperature analysis considering gamma heating and heat convection with reactor coolant. Variations of stress and strain state during long operation period are also calculated by performing sequentially coupled temperature-stress analysis. Fracture strain is derived by using the fracture curve and the stress triaxility. Finally, variations of ductility degradation damage indicator with the fracture strain and the equivalent inelastic strain are investigated. It is found that maximum value of the ductility degradation damage index continuously increases and becomes 0.4877 at 40 EFPYs. Also, the maximum value occurs at top and middle inner parts of the baffle former assembly before and after 20 EFPYs, respectively.

• 한국항공우주학회지
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• 제34권10호
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• pp.24-31
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• 2006

본 논문에서는 유연수지 복합재료에 대하여 기하학적 비선형해석을 수행하였다. 실제 랜덤한 섬유배열을 사각배열과 육각배열로 가정하고 각각에 대해 단위구조를 정의하였다. 다양한 하중상태를 수치적으로 모사하여 단위구조해석을 통해 전체 구조물의 응력-변형률 선도를 예측하였고 이로부터 등가물성치를 계산하였다. 해석시 유연수지의 초탄성 성질을 정의하기 위해 Mooney-Rivlin모델을 사용하였다. 계산결과, 유연수지 복합재료 구조물은 변형률 증가에 따라 비선형의 응력-변형률 관계를 보였다. 비선형성은 횡방향 하중 상태에서 더욱 두드러지게 나타났으며, 이 경우 복합재 단면의 섬유배열 형태에 따라 상당한 차이를 보여주었다.