• KCI Concrete Journal
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• 제13권2호
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• pp.42-48
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• 2001

The bend resistance of coated reinforcing bar is greatly influenced by both the adhesion strength between bar and coating materials, and the followed transformation of coating material as bars bend. Especially, tearing state or partial microscopic cracks are predicted on the inside and outside of bending angle, because tensile strength and elongation of polymer film are very different according to types of polymer dispersions in bar coating, and these damaged parts are rapidly corroded by penetration of corrosive factors. In this study, polymer cement slurry coated reinforcing bars with various polymer dispersions are prepared by following combined conditions, polymer-cement ratio of 50% and 100%, coating thickness of 250$\mu$m and 450$\mu$m, coating number, curing age of 3, 7, 14 and 28days. Then the specimens are tested for working life and bend resistance at bending angles $90^{\circ}$, $135^{\circ}$and $180^{\circ}$ to observe the microscopic damage effect as the bars bend. Also, epoxy-coated reinforcing bars for control experiment were used with 250$\mu$m of coating thickness. The tensile strength for polymer films is performed. From the test results, the working life of the polymer cement slurry is within 90 seconds. Among four types of polymer dispersion, polymer cement slurry coated reinforcing bar using St/BA-1 emulsion has the excellent bend resistance, which is remarkably improved than that of epoxy-coated reinforcing bar. And the bend resistance is more related to elongation than tensile strength of polymer film. Polymer cement slurry with a polymer-cement ratio of 100%, a coating thickness of $450\mu$m and one coating using St/BA emulsion is selected as a most suitable coating material for coated reinforcing bar.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.1017-1022
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• 2001

The bend resistance of coated reinforcing bar is greatly influenced by adhesion strength of bar and coating materials and transformation of coating materials to the bar. Expecially, tearing state or a limited microscopic cracks are predicted on the inside and outside of bending angle because of adhesion strength and elongation is very different with types of polymer materials using bar coating, and these parts are accelerated corrosion as penetration of bar corrosion effects factor. In this study, cement modified polymer are prepared four types and differ from polymer cement ratio of 50% and 100%, coating thickness of 250$\mu$m and 450$\mu$m, coating number, curing age of 3, 7, 14 and 280days, and then tested bend resistance as bending angle $90^{\circ}$, $135^{\circ}$ and $180^{\circ}$ for observe the microscopic demage effect according as bar bend. From the test results, when is used cement modified polymer as coating materials of bar, St/BA is showed excellent bend resistance than a polyacrylic emulsion and SBR because of softness. But it is to need attention because as coating parts are pressed down and tearing, also experimental study is proceeded to corrosion potential on the inside and outside of coated reinforcing bar.

• 한국세라믹학회지
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• 제43권7호
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• pp.439-444
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• 2006

Artificial graphite generally manufactured by carbonization sintering of shape-body of kneaded mixture using granular cokes as filler and pitch as binder, going through pitch impregnation process if necessary and finally applying graphitization heat treatment. Graphite materials are used for core internal structural components of the High-Temperature Gas-cooled Reactors (HTGR) because of their excellent heat resistibility and resistance of crack progress. The HTGR has a core consisting of an array of stacked graphite fuel blocks are machined from IG-110, a high-strength, fine-grained isotropic graphite. In this study, crack stabilization and micro-structures were measured by bend strength and fracture toughness of isotropic graphite grade IG-110. It is important to the reactor designer as they may govern the life of the graphite components and hence the life of the reactor. It was resulted crack propagation, bend strength, compressive strength and micro-structures of IG-110 graphite by scanning electron microscope and universal test machine.

• 콘크리트학회논문집
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• 제13권6호
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• pp.568-574
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• 2001

콘크리트 시험편에 대한 삼점휨실험을 실시하여 여러 실험에 대해 측정된 반응의 평균값을 계산하곤 계산된 평균거동으로부터 삼점휨 시험편이 완전히 파손될 때까지 연속적으로 성장하는 균열에 대한 파괴거동이 분석되었다. 이 연구에서 사용된 실험변수는 25.4mm와 6.4mm의 초기균열길이 그리고 2000sec와 20sec의 실험기간이며, 초기균열길이는 파괴진행대(FPZ) 크기의 영향과 시험편의 기하학적 특성 및 경계조건에 대한 영향을 분석하기 위한 것이다. 실험기간은 초기 크리프(creep)의 영향을 위해 설정되었으나, 이 연구의 하중점-변위 속도에서는 심각한 영향이 관측되지 않았다. 여러 실험의 평균 외부일로부터 평균하중이 계산되었으며, 변형률 게이지를 사용하여 평균 균열길이를 측정하였다. 최대하중 이전의 저항곡선은 파괴진행대의 크기에 대해 유사한 값을 보였다. 그러나 최대하중 직후에는 초기균열의 크기에 관계없이 0.088~0.154mm의 하중점-변위에서 88mm의 불안정 균열성장이 발생되었으며, 평균 파괴에너지율 $G_{F}$$^{ave}$ = 115N/m은 이 불안정 균열성장 동안에 발생되었다. 균열길이 111mm에서 완전한 파괴진행대가 형성되었고, 25.4mm와 6.4mm의 초기균열길이에 대해 파괴진행대의 크기는 각각 86mm와 105mm이었다. 완전한 파괴진행대의 형성이후 저항곡선의 평균 파괴에너지율은 25.4mm와 6.4mm의 초기균열길이에 대해 각각 229N/m로 284N/m로 $G_{F}$$^{ave}$의 두 배 이상이었다.이었다.이었다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1323-1324
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• 2006

Refractory materials, such as W and Mo, are very useful elements for use in high-temperature applications. But it is not easy to fabricat pure W and Mo with very high density and retaining very fine grain size because of their high melting point. In this paper, a newly developed method named as resistance sintering under ultra high pressure was use to fabricate pure fine-grained W and Mo. The microstructure was analysis by SEM. The sintering mechanism is primary analyzed. Basic physical property of these sintered pure W and Mo, such as hardness, bend strength, are tested.

• 대한치과기공학회지
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• 제30권1호
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• pp.65-71
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• 2008

The use of titanium in the field of dentistry has increased, due to their excellent biocompatibility, appropriate mechanical properties, corrosion-resistance and low price. However, many difficulties with the use of titanium for metal-ceramic crowns remain to be solved. The objective of this study was to evaluate the influence of surface modifications on the bonding characteristics of specific titanium porcelain bonded to cast titanium. The surfaces of Titanium were prepared with 4 test groups, i) sandblasted with particles of different size, ii) sandblasted after treated oxidization and oxidized after sandblast. We observed the bond strength and node aspect of titanium and ceramic, and respect to the methods of modifying surface of titanium by the test of mean roughness of surface, Scanning Electron Microscope, and 3-point flexural bend test. The results show that, 1. The specimens, which treated oxidization after process of sandblast with particles of 50um size, were the better for the bond strength in comparison with other specimen. 2. The specimen with process of sandblasting after oxidization treatment were the better for stability of the bond strength. 3. The wettability of titanium surface affect the bond strength.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1997년도 춘계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.35-35
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• 1997

High$\cdot$speed steels (HSS) with a combination of good wear resistance and toughness are finding new, non-cutting applications such as rolls and rollers. In this paper, the research interests are focused on the microstructural evolution of a SMo-6W series high speed steel during HIPping and the effect of HIPping process parameters on its microstructure and properties. HIPping process variables includes; temperature, pressure and hold time. The microstructures of the HIPped HSS were examined by SEM, OM and X-ray diffraction whereas the properties measured were the relative density, hardness, and bend strength at room temperature. In HIPped materials, MC and M6C were the major carbides formed in a matrix of martensite. The effect of powder size on the microstructure and mechanical properties of HIPped materials was insignificant. However, HIPping temperature and hold time strongly affected the carbide size and distribution. The results show that at proper HIPping temperature and pressure conditions, the final products approach the full density ( > 99% RD). The particle boundaries were completely eliminated without an eminent microstructural coarsening. The bend strength was about 2.3 Gpa, which is superior to cast HSS. At excessive HIPping temperatures, rapid carbide coarsening occurred, thus deteriorating the mechanical properties of the P/M steels.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
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• pp.237-244
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• 1995

Fracture properties for LEFM, S-FPZ and NS-FPZ models were determined using by finite element method and energy balance from the experimental results of three-point bend tests. For the LEFM model the stress intensity factor needed to increase continuously with crack extension, and for the S-FPZ model the fracture process zone characteristics need to change continuously if the critical stress intensity factor was to remain constant. The LEFM model showed the largest resistance and the slowest crack extension, while the NS-FPZ model showed the smallest resistance and the fastest crack extension. The responses for the S-FPZ model were intermediate between those for the LEFM and NS-FPZ models and the total fracture energy densities for the S-FPZ and NS-FPZ models and the total fracture energy densities for the S-FPZ and NS-FPZ models were equal.

• Structural Engineering and Mechanics
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• 제45권1호
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• pp.19-32
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• 2013

Cracking at low temperatures is one of the frequently observed modes of failure in asphalt concretes. In this investigation, fracture tests were performed on cracked asphalt concrete subjected to pure mode I and pure mode II loading at different subzero temperatures. An improved semi-circular bend (SCB) specimen containing a vertical crack was used to conduct the experiments. The SCB specimens produced from the gyratory compacted cylindrical samples were compressively loaded, and critical stress intensity factors, $K_{If}$ and $K_{IIf}$, were then calculated using peak loads obtained from the tests. The experimental results showed that with decreasing the temperature, mode I and mode II critical stress intensity factors increased first but below a certain temperature they both decreased. It was also found that at a fixed temperature, the mode II fracture resistance of the asphalt concrete was higher than its mode I fracture resistance.

• 한국금형공학회:학술대회논문집
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• 한국금형공학회 2008년도 하계 학술대회
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• pp.31-34
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• 2008

The L-bending of inner-structure bonded sandwich sheet metal is examined to reduce springback and defects of bent parts. The specimen is composed of top and bottom layers and a middle layer with dimple type-inner-structure and each layer is bonded by resistance welding. This specimen with hollow type-inner-structure shows different bending characteristics from the conventional sandwich sheet metals with solid type-inner-structure. The experiments were conducted for two kinds of working conditions, that is, clearance and movement of first bent specimen for second bending. The deformed profile, bend angle and springback were investigated and compared and then the proper working conditions for L-bending of sandwich sheet metal were prosed.