• Proceedings of the KAIS Fall Conference
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• 2011.05b
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• pp.989-992
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• 2011

삼원 촉매는 주로 코제라이트 세라믹으로 제작되는 다공성 부품이다. 그러나 코제라이트 세라믹은 열적충격온도가 낮아 엔진의 혼합기가 농후한 경우 삼원촉매의 열적 내구성이 급격히 떨어져 내구 수명을 제대로 만족시키지 못하는 차량이 급격히 증가하고 있다. 따라서 본 논문은 유한요소법으로 구한 SiC 세라믹 재료의 등가 물성치를 기초로 SiC 세라믹 촉매 담체의 기계적 물성치를 유한요소해석용시험편으로 구한 뒤 SiC 세라믹 촉매담체가 실차에 설치될 경우의 열피로 성능에 대하여 평가하였다.

• Journal of the korean Society of Automotive Engineers
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• v.9 no.2
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• pp.17-27
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• 1987

최근 자동차기술의 발달로 인한 차량의 경량화, 고급화 추세는 더욱 개선된 승차감을 요구하고 있다. 승차감에 영향을 미치는 주요인으로서는 엔진의 진동과 소음, 변속장치, 구동축 등의 구동 계통의 진동 및 소음, 그리고 노면으로부터의 진동, 외부 공기의 흐름에 의한 소음 등 여러가지가 있다. 엔진지지계는 이중 엔진의 진동 및 소음을 절연하는 기능을 맡고 있고 동시에 엔진하중의 지지, 변위제한, 충격흡수 등의 기능도 가지고 있다. 실제에 있어서 엔진지지계는 진동 및 소음 절연의 기능 외에 다른 기능도 갖고 있으나 이중 가장 어렵고 해석이 곤란한 것은 결국 진동절 연성능이라고 할 수 있다. 그러나 여러 가지 제약조건이 있으므로 최적의 진동절연특성의 실 현이 항상 가능한 것은 아니고 방진고무의 특성치난 지지각도 등의 어느 범위안에서만 선택이 가능하므로 실제 설계에 있어서는 적용상의 특정조건을 만족시키는 초기설계치를 정하여 그때의 진동절연특성을 평가하고 기준이하일때는 설계치를 재조정하여 다시 평가하는 접근방식이 실질 적이다. 따라서 이 설계과정에 필요한 엔진지지계의 진동절연특성해석 및 평가용 컴퓨터 프로 그램을 개발하였으며 그 해석치와 실험결과를 비교하여 타당성을 입증하였다.

• Korean Journal of Materials Research
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• v.7 no.7
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• pp.623-631
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• 1997

본 연구에서는 주조 2상 스테인리스강의열시효에 대한 시효온도, 시효시간 및 Nb함유량의 영향을 관찰하기 위해 기계적 성질 및 조직을 조사하였으며 Nb을 함유한 주조 2상 스테인리스강의 파괴기구를 규명하기 위해 SEM에 의한 파단면 관찰과 WDS성분분석을 통해 파괴기구의 특성을 고찰하였다. 시효온도와 시효시간이 증가함에 따라 페라니트으 미소경도가 증가하였으며 항복강도의 경우 시효온도와 시효시간에는 영향을 받지 않았으나 Nb을 함유한 재료들이 Nb을 함유치 않은 재료들에 비해 다소 낮은 항복강도 값을 보였다. 충격흡수에너지 값은 시효시간 및 시효온도의 증가에 따라 시험된 모든 재료에서 저하되었는데 0.4% Nb을 함유하는 경우 Nb을 약간 함유하거나 함유치 않은 재료들에 비해 시효시간에 따라 급격한 감소 경향을 보였다. 파단면 관찰결과 페라이트 기지 또는 페라이트/오스테나이트 상경계에서 석출된 VbC를 비롯한 탄화물들이 취성저항성을 낮추는데 크게 기여했음을 알 수 있었다.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.369-379
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• 2012

The collapse of concrete structures by extreme loads such as impact, explosion, and blast from terrorist attacks causes severe property damage and human casualties. Concrete has excellent impact resistance to such extreme loads in comparison with other construction materials. Nevertheless, existing concrete structures designed without consideration of the impact or blast load with high strain rate are endangered by those unexpected extreme loads. In this study, to improve the impact resistance, the static and impact behaviors of concrete beams caste with steel fiber reinforced concrete (SFRC) with 0~1.5% (by volume) of 30 mm long hooked steel fibers were assessed. Test results indicated that the static and impact resistances, flexural strength, ductility, etc., were significantly increased when higher steel fiber volume fraction was applied. In the case of the layered concrete (LC) beams including greater steel fiber volume fraction in the tensile zone, the higher static and impact resistances were achieved than those of the normal steel fiber reinforced concrete beam with an equivalent steel fiber volume fraction. The impact test results were also compared with the analysis results obtained from the single degree of freedom (SDOF) system anaysis considering non-linear material behaviors of steel fiber reinforced concrete. The analysis results from SDOF system showed good agreement with the experimental maximum deflections.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.525-538
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• 2014

Safety of reactive systems is one of the most important research areas in the field of weapon development. A NoGo response or at least a low-order explosion should be ensured to prevent unexpected accidents when the reactive system is impacted by high-velocity projectile. We investigated the shock-induced detonation of cased reactive systems subject to a normal projectile impact to the cylindrical surface based on two-dimensional hydrodynamic simulations using the I&G chemical rate law. Two types of energetic materials, namely LX-17 and AP-based solid propellant, were considered to compare the dynamic responses of the reactive system when subjected to the threshold impact velocity. It was found that shock-to-detonation transition phenomena occurred in the cased LX-17, whereas no full reaction occurred in the propellant.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.760-767
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• 2020

Sustainable growth of hydroelectric power plants is expected in consideration of climate change and energy security. However, hydroelectric power plants always have a risk of water hammer damage, and safety assurance is very important. The water hammer phenomenon commonly occurs during operations such as rapid opening and closing of the valves and pump/turbine shutdown in pipe systems, which is more common in cases of emergency shutdown. In this study, a computational numerical model was developed using the MOC-FDM scheme to reflect the mechanism of water hammer occurrence. The proposed model was implemented in boundary conditions such as reservoir, pipeline, valve, and pump/turbine conditions and then applied to simulate hypothetical case studies. The analysis results of the model were verified using the analysis results at the main points of the pipe systems. The model produced reasonably good performance and was validated by comparison with the results of the SIMSEN package model. The model could be used as an efficient tool for the safety assessment of hydroelectric power plants based on accurate prediction of transient behavior in the operation of hydropower facilities.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.67-74
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• 2019

In this paper the response factor is investigated for middle and small size-RC slab aged bridges. The response factor consists of static and dynamic response factors and is a main parameter in the frequency based-bridge load carrying capacity prediction model. Static and dynamic response factors are determined based on the frequency variation and the impact factor variation respectively between current and previous (or design) states of bridges. Here, the impact factor variation is figured out using the impact factor response spectrum which provides the impact factor according to the natural frequency of bridges. In this study, four actual RC slab bridges aged over 30 years after construction are considered and their span length is 12m. The dynamic loading test in field using a dump truck and eigenvalue analysis with FE models are conducted to identify the current and previous (or design) state-natural frequencies of the bridges, respectively. For more realistic considerations in the moving loading situation, the impact factor response spectrum is developed based on tri-axle moving loads representing the dump truck load distribution and various supporting conditions such as simply supported and both ends fixed conditions. From the results, the response factor is widely ranged from 0.21to 0.91, showing that the static response factor contributes significantly on the results while the dynamic response factor has a small effect on the result. Compared to the results obtained from the impact factor response spectrum based on the single axle-simply supported condition, the maximum percentage difference of the response factors is below 3.2% only.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.1
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• pp.37-44
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• 2016

This study is concerned with the numerical investigation of dynamic characteristics of 2.5MW-class wind turbine gearbox in which the misalignment improvement of plenary gear shafts by the flexible pins and the dynamic impact response are analyzed by the finite element method. The tooth contact between gears is modelled using the line element having the equivalent tooth stiffness and the contact ratio to accurately and effectively reflect the load transmission in the internal complex gear system. The equivalent tooth stiffness is calculated by utilizing the tooth deformation analysis and the impulse torque is applied to the input shaft for the dynamics response characteristic analysis. Through the numerical experiments, the equivalent tooth stiffness model was validated and the misalignment improvement of planetary gear shafts was confirmed from the comparison with the cases of fixed shafts at one and both ends.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.104-117
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• 1991

When a body starts to move, the flow near the intersection point between a body and a free surface changes violently and rapidly in a very short initial time interval. This flow phenomena must be investigated whenever one treats the interaction between a body and a fluid, such as the motion of a floating body, sloshing in a tank, wave maker problem, entry of a body into a fluid etc.. Until Roberts(1987), it was widely accepted that a singularity exists at the intersection point. However, he showed that the singularity does not exist if a body moves non-impulsively. In this paper, an analytical solution cosistent for the case of impulsive motion of a body is obtained by including the effect of surface tension. From the characteristics of the newly obtained solution, a critical value associated with an oscillating phenomenon is found, and further more, it is shown that the oscillating phenomenon does not appear in the region where the distance form the intersection point is less than this critical value.

• Journal of Dental Rehabilitation and Applied Science
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• v.27 no.3
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• pp.305-316
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• 2011

Cracked teeth are a common problem with incomplete fracture that typically shows pain on biting and temperature stimuli. The most common cause of crack is known to be the masticatory accident. Predisposing factors were aging, old restoration, and iatrogenic stress concentration, etc. Accurate diagnosis is needed for detecting the extent of crack and pulp vitality. There are many diagnostic tools like bite test, direct observation with transillumination, dye penetration, and radiographs. Immediate treatment for pain relief and occlusal adjustment would be needed. Composite resin and bonded amalgam showed favorable prognosis. Moreover, cusp protection is reliable permanent treatment for cracked teeth. The purpose of this article is to review the literature about the prevention, diagnosis, and treatment for cracked teeth.