• 대한기계학회논문집A
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• 제41권5호
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• pp.337-343
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• 2017

각종 기공과 같은 결함을 허용하는 다이캐스팅 부품의 강도를 현장 수준에서 평가할 수 있는 이론적 방법을 제안한다. 결함을 갖는 부재의 탄성시험을 통해 강성도를 구하고 이를 결함이 없는 이론적 강성도와 비교함으로써 등가 기공률을 산출한다. 등가 기공률 식은 Eshelby의 함유이론으로부터 유도하였다. 산출된 등가 기공률은 Mori-Tanaka 법을 이용하여 기공결함을 포함하는 재료의 응력-변형률 선도를 그리기 위하여 사용된다. 본 연구에서는 Hollomon 변형경화 모델을 사용하였다. 이 응력-변형률 선도를 이용하면 균일분포의 기공결함을 갖는 다이캐스팅 부재의 강도를 평가할 수 있게 된다. 등가 기공률을 고려한 하나의 이론해로서 직사각형 단면의 다이캐스팅 보에 대한 삼점 굽힘의 탄소성 강도를 소성힌지의 방법으로 유도하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제34권6호
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• pp.816-824
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• 2010

본 논문에서는 쓰레기 이송관로내의 물체에 작용하는 힘을 분석하고 그 물체의 운동방정식 확립하였다. 그 운동방정식은 1계 비선형 미분방정식이 되며 이것의 일반해를 이용하면 쓰레기 이송관로내 물체의 속도를 구할 수가 있다. 물체의 속도는 엘보우와 같은 쓰레기 이송관로의 곡선부에서 내벽의 충돌속도가 되므로 충돌시 물체의 운동에너지를 계산할 수 있고, 따라서 필요한 내벽의 충격강도를 알 수가 있다. 하나의 예로써 쓰레기 이송관로내 공기의 속도가 30m/sec일 때 물체의 속도를 계산하여 그래프로써 나타내었으며, 이것으로부터 물체가 내벽에 충돌할 때의 운동에너지를 계산할 수 있도록 하였다. 또한 용융주조 현무암 튜브를 철강파이프 내면에 보호벽으로 씌운 복합재료 파이프에 추를 자유낙하시켜 충격을 주는 방식으로 충격시험을 한 결과를 제시하였으며, 그 결과에 의하면 용융 주조 현무암 튜브는 쓰레기 이송관로의 내면 보호벽으로 충분한 충격강도를 가지는 것이 판명되었다.

• 소성∙가공
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• 제16권4호
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• pp.293-298
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• 2007

Recently, there is a need to produce a large forged part for the flight, shipping, some energies, and military industries, etc. Therefore, an open die forging technique of cast ingots is required to obtain higher quality of large size forged parts. Cogging process is one of the primary stages in many open die forging processes. In the cogging process prior to some open die forging processes, internal cavities have to be eliminated for defect-free. The present work is concerned with the elimination of the internal cavities in large ingots so as to obtain sound products. In this study, hot compression tests were carried out to obtain the flow stress of cast microstructure at different temperature and strain rates. The FEM analysis is performed to investigate the overlap defect of cast ingots during cogging stage. The measured flow stress data were used to simulate the cogging process of cast ingot using the practical material properties. Also the analysis of cavity closure is performed by using the $DEFORM^{TM}-3D$. The calculated results of cavity closure behavior are compared with the measured results before and after cogging, which are scanned by the X-ray scanner. From this result, the criteria for deformation amounts effect on the cavity closure can be investigated by the comparison between practical experiment and numerical analysis.

• Journal of information and communication convergence engineering
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• 제7권2호
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• pp.148-151
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• 2009

We consider the problem of optimizing the performance of a system with resources shared by non-cooperative users. The worst-cast ratio between the cost of a Nash equilibrium and the optimal cost, called Price of Anarchy, is investigated. It measures the performance degradation due to the users' selfish behavior. As the objective function of the optimization problem, we are concerned in a load balancing measure, which is different from that used in the previous works. Also we consider the Stackelberg scheduling which can assign a fraction of the users to resources while the remaining users are free to act in a selfish manner.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2006년도 학술발표회 논문집
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• pp.300-307
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• 2006

Integral pile shaft-column foundations are increasingly popular thanks to not only the comparative advantage of economy in constructing large cast-in-drilled-hole(CIDH) piles compared with driven piles with pile cap footings but also being free from problems associated with the critical column-footing connection. In this paper, the structural characteristics of integral pile shaft-column foundations as well as seismic analysis methodology and reinforcement details for seismic design are introduced.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1132-1143
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• 2008

A single Column/Shaft which extended the pile to the column of the bridge with same diameter has better safety and economical profit, but it usually has larger lateral displacement due to lateral loads such as wind, earthquake, wave, etc. A series of horizontal pile load testing were performed to study the lateral behavior of single column/shaft with varying different free lengths and embedded pile lengths. Eight instrumented test piles were cast-in-placed by bonding strain gauges at certain locations on both faces of the pile to measure bending moment, from two-way loadings. Linear variable differential transformers(LVDTs) were installed to measure the lateral pile displacement. Based on this, it is found that the test single column/shaft with different free lengths shows different failure modes. If the test pile has a longer free length, the failure occurs at the near the ground surface, but the shorter one's failure occurs at the below the ground surface.

• Journal of Mechanical Science and Technology
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• 제19권7호
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• pp.1488-1502
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• 2005

A three dimensional model was developed to analyze the mold filling and solidification in the casting processes. The model uses the VOF method for the calculation of the free surface and the modified Equivalent Specific Heat method for the treatment of the latent heat evolution. The solution procedure is based on the SIMPLER algorithm. The complete model has been validated using the exact solutions for phase change heat transfer and the experimental results of broken water column. The three-dimensional model has been applied to the benchmark test and the results were compared to those from experiment, a two-dimensional analysis, and another three dimensional numerical model.

• Tribology and Lubricants
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• 제36권2호
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• pp.88-95
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• 2020

In this study, we investigate the mechanical properties of high manganese steel, and the friction and wear characteristics of brake friction material containing this steel, for passenger car application, with the aim of replacing copper and copper alloys whose usage is expected to be restricted in the future. These steels are prepared using a vacuum induction melting furnace to produce binary and ternary alloys. The hardness and tensile strength of the high manganese steel decrease and the elongation increases with increase in manganese content. This material exhibits high values of hardness, tensile strength, and elongation; these properties are similar to those of 7-3 brass used in conventional friction materials. We fabricate high manganese steel fibers to prepare test pad specimens, and evaluate the friction and wear characteristics by simulating various braking conditions using a 1/5 scale dynamometer. The brake pad material is found to have excellent friction stability in comparison with conventional friction materials that use 7-3 brass fibers; particularly, the friction stability at high temperature is significantly improved. Additionally, we evaluate the wear using a wear test method that simulates the braking conditions in Europe. It is found that the amount of wear of the brake pad is the same as that in the case of the conventional friction material, and that the amount of wear of the cast iron disc is reduced by approximately 10. The high manganese steel is expected to be useful in the development of eco-friendly, copper-free friction material.

• Corrosion Science and Technology
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• 제8권3호
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• pp.110-115
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• 2009

At the onset of corrosion of steel in concrete, hydrogen ions usually evolve in the process of electrochemical reaction, thereby decreasing the pH of the pore solution, which can be buffered by cement hydration products, as being representatively illustrated by calcium hydroxide. Hence, a fall in the pH is dependent on properties of cement hydration (i.e. hydration products and degree of hydration). The present study tested acid neutralization capacity (ANC) of cementitious binders of OPC(Ordinary Portland Cement), 30% PFA(Pulverized Fuel Ash), 60% GGBS(Ground Granulated Blast Furnace Slag), 10% SF(Silica Fume) to quantify the resistance of cement matrix to a pH fall. Cement pastes were cast at 0.4 of a free W/C ratio with 1.5% chlorides by weight of binder in cast. Powder samples obtained crushed and ground specimen after 200 days of curing were diluted in still water combined with different levels of 1M nitric acid solution, ranging from 0.5 to 20 mol/kg. Then, the pH of diluted solution was monitored until any further change in the pH did not take place. It was seen that the pH of the diluted solution gradually decreased as the molar amount of nitric acid increased. At some particular values of the pH, however, a decrease in the pH was marginal, which can be expressed in the peak resistances to a pH fall in the ANC curve. The peaks occurred at the variations in the pH, depending on binder type, but commonly at about 12.5 in the pH, indicate a resistance of precipitated calcium hydroxide. The measurement of water soluble chloride at the end of test showed that the amount of free chloride was significantly increased at the pH corresponding to the peaks in the ANC curve, which may reflect the adsorption of hydration products to chlorides.

• 한국재료학회지
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• 제14권3호
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• pp.168-174
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• 2004

The aim of this study is to investigate the effect of process conditions on the microstructual changes and mechanical properties of large 7175 aluminum die forgings. The cast billets of 370 and 720 mm in diameter were homogenized and die forged after direct chill casting. The size and volume fraction of second phase particles in 720 mm billet were larger than those of 370 mm billet. The interdendritic sites containing the second phase particles was considered to be a crack initiation region in the process of cold upsetting. The tensile and yield strength of die forged specimens of 720 mm billet in the direction of Land L T were higher than those of 370 mm billet. However, the tensile strength of these specimens were 5 to 10% lower than that of American military specification. The plane strain fracture toughness of die forged specimens of 370 mm cast billet showed almost the same level of 720 mm billet, which was die forged after free forging.