• 한국도로학회논문집
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• 제8권3호
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• pp.163-172
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• 2006

본 연구에서는 원유 정제과정에서 발생되는 산업부산물인 황을 주성분으로 폴리머 성분의 첨가제를 혼합하여 개발된 개질 첨가제인 SPC(Sulfur Polymer Cement;가칭)를 비율별 (0%, 10%, 30%, 50%)로 첨가하여 개질 아스팔트 바인더 및 혼합물의 실내 물성 평가를 수행하였다. 개질 아스팔트 바인더의 특성을 평가하기 위해 수퍼페이브 바인더 시험법을 이용하여 아스팔트 바인더의 PG(Performance Grade) 등급을 분류하고 온도에 따른 특성을 파악하였다. 또한 개질 아스팔트 혼합물의 피로균열 및 저온균열 특성을 평가하기 위해 $10^{\circ}C$ 및 $-10^{\circ}C$에서 간접인장실험(Indirect Tensile Test)을 수행하였으며, 소성변형에 대한 저항성을 평가하기 위해 휠트랙킹 실험을 수행하였다. 실험 결과, 개질 첨가제인 SPC의 첨가 비율이 증가할수록 소성 변형에 대한 저항성이 증가하는 것으로 나타났으며, 저온 균열 저항성을 증가시킬 수 있는 잠재성을 보여주었다. 그러나 피로균열 SPC는 피로균열 저항성 향상에는 큰 효과가 없는 것으로 나타났다.

• Corrosion Science and Technology
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• 제6권3호
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• pp.96-102
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• 2007

The resistance of the linepipe steel to hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC) is very important for steel to be used in sour oil/gas environments. Welding of steels is necessary to the construction of pipe-line transporting oil/gas. In this study, HIC and SSC resistance of an electric resistance welded (ERW) steel plate which belongs to API X70 grade was evaluated by using NACE TM0284-96A and NACE TM0177-96A methods. HIC and SSC fracturing behavior was investigated by observing fractured surfaces using optical microscopy (OM) and scanning electron microscopy (SEM). It was discussed in terms of metallurgical parameters such as the distribution of primary microstructure, second phases and inclusions. Results showed that the weld joint of ERW steel is more sensitive than base metal to HIC and SSC. This is due to difference in the contribution of metallurgical parameters to HIC and SSC nucleation and propagation.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2007년 추계학술발표대회 개요집
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• pp.73-75
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• 2007

The resistance spot weld is among the most common automotive weld method, now a constant current type is the most common used types. A constant current type have a weak point which can not deal with a defect occurrence by external factors, and recently the adaptive resistance spot weld have been applied around the advanced automotive company. This technology can maintain a stable weld quality through a suitable control the current and weld time with weld environment. In this research, the adaptive resistance spot weld is applied to high strength steels, and its application possibility and weld characteristics are presented.

• Advances in concrete construction
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• 제6권1호
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• pp.15-28
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• 2018

In the present investigation, influence of various material parameters on the cavitation erosion resistance of concrete was investigated on the basis of laboratory experiments. As there is no well-established laboratory test method for evaluating the cavitation resistance of concrete, a test set up called 'cavitation jet' was specially established in the present study in order to simulate the cavitation phenomenon experienced in the hydraulic structures. Various mixtures of concrete were designed by varying the grade of concrete, type and quantity of pozzolana, type of aggregates and cement type to develop good cavitation resistant concrete constructed using marginal aggregates. Three types of aggregates having three different Los Angeles abrasion values (less than 30%, between 30% and 50% and more than 50%) were employed in this study. To evaluate the cavitation resistance a total of 60 cylindrical specimens and 60 companion cubes were tested in the laboratory respectively. The results indicate that cavitation resistance of concrete degrades significantly as the L.A. abrasion value of aggregates goes beyond the 30% value. Incorporation of pozzolanic admixtures was seemed to be beneficial to enhance the cavitation resistance of concrete. Influence of other material parameters on the cavitation resistance of concrete was also noted and important observations have been made in the paper.

• 대한치과보철학회지
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• 제44권4호
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• pp.421-431
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• 2006

Statement of problem : Accurate impression is essential to success of implant prostheses. But there have been few studies about the accuracy of fixture-level impression technique in internal connection implant system. Purpose: This study evaluated the accuracy of splinted fixture-level impression technique using clinical methods and the effect of internal hex on fit of superstructure in internal connection implant system (Astra Tech). Material and method : Two metal master frameworks made from two abutments (Cast-to Abutment ST) each for parallel and divergent conditions and a corresponding. passively fitting, dental stone master cast with four future replicas (Fixture Replica ST) were fabricated. Ten dental stone casts were made with vinyl polysiloxane impressions from the master cast by acrylic resin splinted fixture-level impression technique. To evaluate the accuracy of impression technique, the fit of master frameworks for test models was evaluated using screw resistance test (SRT) and one-screw test. The results of SRT were recorded as SRT values from grade 1 to grade 5 by 1/4 turn. And to evaluate the effect of hex on fit of superstructure, the same tests were performed after removing hexes of master frameworks. Results: 1. There was only one case (2.5%) showing SRT value of test model below ade 2 in total before and after removing hexes of master frameworks. And, by removing hexes. SRT values decreased in only one test model (5%) and did not change in 17 test models (85%). 2. SRT values of the 1$^{st}$ screws were grade 2 in 80% of cases before, and grade 1 in 80% of cases after removing hexes. And, by removing hexes, SRT values decreased in 72.5% of cases. 3. SRT values of the 2$^{nd}$ screws were grade 3 in 85% of cases before, and grade 3 in 95% of cases after removing hexes. And, by removing hexes, SRT values did not change in 85% of cases. 4. There were only 2 cases regarded as acceptable fit by one-screw test, and SRT values of 2$^{nd}$ screws of both cases were grade 2. Conclusion. Within the limitations of this study, future-level impression of internal connection implant system is considered to obtain inaccurate working cast, even using acrylic resin splinted impression technique. And, it is considered to be unable improve the fit to remove the hexes of implant restoration.

• 한국재료학회지
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• 제13권11호
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• pp.761-768
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• 2003

The corrosion resistance and cytotoxicity behavior of Ti alloys were studied as a function of Nb contents(3wt.%Nb, 20wt.%Nb, 40wt.%Nb). Ti-Nb alloys were melted by vacuum arc furnace and then rolled to 50% reduction ratio after homogenized at 105$0^{\circ}C$ for 24hrs. The corrosion resistance of Ti-Nb alloys were investigated by potentiodynamic polarization test in the 0.9% NaCl and 5% HCI solution. Biocompatibility of Ti-Nb alloys was evaluated by cytotoxicity test. The results can be summarized as follows 1) The microstructure change from equiaxial to acicular and the increased $\beta$ phase in Ti-Nb alloys were obtained as the Nb content increased. 2) For the corrosion test in the solution of 0.9% NaCl and 5% HCI, the corrosion behavior of Ti-Nb alloys was similar to ASTM grade 2 CP Ti. 3) For the cytotoxicity test, Ti-Nb alloys showed excellent biocompatibility compared to ASTM grade 2 CP Ti, 316L STS and Co-Cr alloys.

• Corrosion Science and Technology
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• 제17권3호
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• pp.109-115
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• 2018

Electrical Resistance Welding (ERW) on a longitudinal seam-welded pipe has been extensively used in oil and gas pipelines. It is well known that the weld zone commonly suffers from grooving corrosion in ERW pipes. In this paper, the grooving corrosion performances of API X65 grade non-sour service (steel-A) and API X70 grade sour gas resistant (steel-B) steel electrical resistance welding pipelines were evaluated. The microstructure of the bondline is composed of coarse polygonal ferrite grains and several elongated pearlites. The elongated pattern is mainly concentrated in the center of the welded area. The grooving corrosion test and electrochemical polarization test were conducted to study the corrosion behavior of the given materials. A V-shaped corrosion groove was found at the center of the fusion zone in both the steel-A and steel-B ERW pipes, as the corrosion rate of the bondlines is higher than that of the base metal. Furthermore, the higher volume fraction of pearlite at the bondline was responsible for the higher corrosion rate at the bondline of both types of steel.

• 대한치과기공학회지
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• 제28권1호
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• pp.61-66
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• 2006

Titanium alloys have been used for dental materials due to it's very good biocompatibility. Ti-6Al-4V alloy instead of pure titanium is being widely used as biomaterials has some characteristics such as high fatigue strength, tensile strength and corrosion resistance. But it has been reported recently that the vanadium element expresses cytotoxicity and carcinogenicity and the aluminium element is related with dementia of Alzheimer type and neurotoxicity. The Ti-Nb alloys has designed and examined corrosion resistance. Ti-3wt.%Nb($\alpha$type), Ti-20wt.%Nb(${\alpha}+{\beta}$type) and Ti-40wt.%Nb($\beta$type) alloys were melted by vacuum arc furnace. The corrosion resistance of Ti alloys was evaluated by potentiodynamic polarization test in the solution of 0.9% NaCl and 5% HCl. The results can be summarized as follows: 1) For the corrosion test in the solution of 0.9% NaCl and 5% HCl, the corrosion behaviour of Ti-Nb alloys was similar to ASTM grade 2 CP Ti. 2) The corrosion resistance of Ti-20Nb alloy was better than that of CP-Ti, Ti-3Nb, Ti-40Nb alloy in 0.9% NaCl and 5% HCl, solutions.

• Journal of Advanced Marine Engineering and Technology
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• 제25권5호
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• pp.1108-1114
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• 2001

The fatigue crack propagation behavior of the SA516-Grade 70 steel which is used for pressure vessels was experimentally examined under the condition of at room temperature, $150^{\circ}C$, $250^{\circ}C$ and $370^{\circ}C$ with stress ration of R=0.1 and 0.3. The fatigue crack propagation rate , da/dN, related with the stress intensity factor range, $\vartriangle$N, was influenced by the stress ration within the stable growth of fatigue crack(Region II) with an increase in $\vartriangle$N. The resistance to the fatigue crack growth at high temperature is higher in comparison with that at room temperature, and the resistance attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations revels that the differences of the fatigue crack growth characteristics between room and high temperatures are mainly explained by the crack and oxide-induced by high temperature.

• 한국표면공학회지
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• 제37권2호
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• pp.110-118
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• 2004

The corrosion of pure titanium (CP- Ti Grade 2) and titanium alloy (Ti6Al4V ELI) were studied under various conditions of simulated body fluids. The static immersion test and the electrochemical test were performed in accordance with ISO 10271 : 2001. For the electrochemical test, the open circuit potential was monitored as a function of time, and the cyclic polarization curve was recorded. The corrosion resistance was evaluated from the values of corrosion potential, passivation current density, breakdown potential, and the shape of hysteresis etc. The effects of alloy type, surface condition, temperature, oxygen, and constituents in the fluids such as acid, chloride were estimated. Both specimens had extremely low dissolution rate in the static immersion test. They showed strong passivation characteristics in the electrochemical test. They maintained negligible current density throughout the wide anodic potential range. The passive layer was not broken up to 2.0 V (vs. SCE). The hysteresis and the shift of passivation potential toward the anodic direction was observed during the reversed scan. The passivation process appeared to be accelerated by oxygen in air or that dissolved in the fluids. The passivation also proceeded without oxygen by the reaction of constituents in the fluids. Acid or chloride in the fluids, specially later weakened the passive layer, and then induced higher passivation current density and less shift of passivation potential in the reversed scan. CP-Ti Grade 2 was more reactive than Ti6Al4V ELI in the fluids containing acid or chloride, but thicker layer produced on its surface provided higher corrosion resistance.