• Journal of Korean Society of Steel Construction
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• v.11 no.3 s.40
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• pp.319-327
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• 1999

This study makes mechanism of the fatigue strength improvement by the processing of weld toe clear for the vertical cross rib specimens which was made fillet weld joint, also it proposes to the appropriate later processing. As a result of tension fatigue test, the fatigue strength improvement could have been seen in later processed specimens than as-weld specimens. Especially fatigue crack initial life $N_c$ increased in specimens which processed grinder after hammer-peening. Also, fatigue crack propagation life $N_p$ improved more in hammer-peening specimens than as-weld or TIG specimens. It thinks that $N_c$ is because of the geometrical shape of weld toe, i.e. the relaxation of the stress concentration and also that $N_p$ is because the big compression residual stress which was introduced in the surface by hammer-peening is restraining the propagation of fatigue crack.

• Polymer(Korea)
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• v.38 no.2
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• pp.150-155
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• 2014

Polycaprolactone (PCL) is a synthetic biodegradable polymer with excellent mechanical properties. $TiO_2$ (titanium dioxide) has a hydrophilic, high density and excellent biocompatibility. In this work, we produced three-dimensional porous scaffolds with PCL and $TiO_2$ nanoparticles using a salt-leaching method. Physical properties of the scaffolds were analyzed by FE-SEM, FTIR, TGA and compressive strength. Interestingly, the addition of $TiO_2$ nanoparticles decreased the water absorption and swelling ratio of the porous scaffolds. However, the compressive strength was increased by $TiO_2$. CCK-8 assay, which is generally used for the analysis of cell growth, shows that $TiO_2$ nanoparticles have no cytotoxicity. Taken together, we suggest that the PLC/$TiO_2$-scaffold can be used for biomedical applications.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.110-115
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• 2017

This research was performed to investigate the mechanical performance of lightweight concrete including phase changing material(Low temperature PCM). Micro capsulised PCM consisted of wax type core and melamine based wall. Also, for PCM of one single kind, paraffin wax was inserted into Vermiculite and the surface was coated with melamine resin. Interfacial polymerization is based on the principle that macromolecule reaction takes place on the surfaces between 1-dodecanol(core material) and water (solvent) to form the wall material. Lightweight concrete has compressive strength of 10 MPa, tensile strength of 1.5 MPa, and oven dried density of 1.0kg/liter which included 10%, 20%, or 30% PCM by weight. To do so, this study fabricated light-weight foamed concrete ($1.0kg/m^3$) in pre-foaming method and mixed it with PCM micro capsule of 1-dodecanol and melamine to examine its physical properties.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.327-334
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• 2022

In this study, in order to evaluate the characteristics of mortar and concrete using wood chip cogeneration plant flooring as fine aggregate, mortar characteristics according to wood chip aggregate replacement rate and water-cement ratio as a substitute for crushed sand, and concrete characteristics according to wood chip aggregate replacement rate were compared and evaluated. The cement mortar flow according to the wood chip aggregate replacement rate showed a tendency to increase as the wood chip aggregate replacement rate increased, and the compressive strength and flexural strength increased as the wood chip aggregate replacement rate increased. The slump and air content of concrete increased as the aggregate replacement rate increased, and the compressive strength and tensile splitting strength of concrete tended to increase as the wood chip aggregate replacement rate increased. Accordingly, the possibility of using the flooring by the cogeneration plant as a fine aggregate for concrete was confirmed.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.299-306
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• 2015

In construction materials area, many research on polymer for cement-based materials have been conducted. In spite of these research, general research scope is limited to the normal strength range, and thus in this research, for both normal and high strength range mixtures, the strength and mechanical properties of high strength cement mortar incorporating Vinyle Acetate-Ethylene(VAE) type powder polymer are evaluated. As a result of experiment, in the case of high strength mixture, as the amount of VAE polymer addition was increased the compressive and flexural strengths were decreased while the tensile and bonding strengths were increased because of the formation of the polymer membrane inside of the mortar matrix.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.2
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• pp.133-144
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• 2006

In order to catch out such Bond Strength, the preceding researchers had ever examined the Bond Strength of FRP Plate through their experimentations by setting up of various fluent. However, since the experiment for research on such Bond Strength takes much of expenditure for equipment structure and time-consuming, also difficult to carry out, it is conducting limitedly. This Study purposes to develop the most suitable Artificial Neural Network Model by application of various Neural Network Model and Algorithm to the adhering experiment data of the preceding researchers. Output Layer of Artificial Neural Network Model, and Input Layer of Bond Strength were performed the learning by selection as the variable of the thickness, width, adhered length, the modulus of elasticity, tensile strength, and the compressive strength of concrete, tensile strength, width, respectively. The developed Artificial Neural Network Model has applied Back-Propagation, and its error was learnt to be converged within the range of 0.001. Besides, the process for generalization has dissolved the problem of Over-Fitting in the way of more generalized method by introduction of Bayesian Technique. The verification on the developed Model was executed by comparison with the resulted value of Bond Strength made by the other preceding researchers which was never been utilized to the learning as yet.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.162.2-162.2
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• 2015

플렉서블 디스플레이에 사용되는 투명전극은 벤딩에 의한 인장(tensile) 및 압축(compressive) 스트레스 하에서도 전극의 특성이 지속적으로 유지되어야 한다. 기존 OLED소자의 투명전극으로 사용되던 인듐산화물(ITO, Indium Tin Oxide)는 인듐(Indium)의 희소성 문제뿐만 아니라 벤딩에 대한 복원력이 나쁜 것으로 알려져 플렉서블 디스플레이에는 적합하지 않은 것으로 알려져 있다. 벤딩에 강하고 복원력이 우수한 투명전극 재료가 필요하게 되었다. 본 연구에서는 PEN (Polyethylene Naphthalate) 유연기판 상에 그래핀(Graphene)전극을 구현하여 벤딩에 대한 저항특성을 관찰하였고 일반적으로 많이 사용하는 Aluminum 전극과의 비교를 통해 광효율을 지속적으로 유지할 수 있는 플렉서블 OLED용 전극구현 가능성을 연구하였다. 일반적으로 Al금속은 인장 스트레스를 받음에 따라 저항이 증가하고 다시 복원되면 저항이 감소하는 특성을 갖고 있는데 인장 스트레스에 따라 저항과 늘어난 길이와의 관계는 다음과 같다. $R/R0=(L/L0)^2$ ----------------------------------------- (1) 그러나 반복된 스트레스가 가해질 경우 Al 금속 전극은 복원력을 잃고 저항이 원래대로 돌아가지 않는 문제가 발생하는데 반해 그래핀은 벌집모양의 구조를 갖고 있어 벤딩에 대한 강도가 셀 뿐만 아니라 고탄력으로 인해 복원력이 우수하여 여러 싸이클(cycle)의 벤딩 실험에 의해서도 복원력이 지속적으로 유지되었다. Al 금속 전극의 경우 벤딩 각도 또는 정도에 따라 복원력이 유지되는 구간이 있으나 반복적인 벤딩 싸이클에 의해 복원력이 감소하여 인장 스트레스에 의한 저항 증가 후 스트레스 제거 시 저항 감소가 되지 않는데 24시간 동안 전기 저항 변화를 관찰하면 수시간 후에나 저항이 어느 수준까지만 복원되는 것을 확인할 수 있었으나 복원에 오랜 시간이 소요된다는 점에서 그래핀과 비교가 된다. SEM(Scanning electron microscopy) 분석을 통해 인장 스트레스 인가/제거를 반복함에 따라 Al 금속표면이 표면에 열화되는 것을 확인하였으나 그래핀에서는 나타나지 않았다. 본 연구에서는 높은 투과도와 우수한 전기적 특성을 가지는 그래핀 투명 전도성 전극이 다양한벤딩 조건에서도 뛰어난 복원 특성을 보이는 것을 밝혀내어 차세대 투명 전극 물질로 개발하고자 하였다.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.407-413
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• 2017

The fundamental property of magnesia phosphate cement (MPC) for concrete repair material was investigated in this research. For mechanical properties, setting time, compressive strength and tensile/flexural bond strength were measured, and hydration products were detected by X-ray diffraction. The specimens were manufactured with dead burnt magnesia and potassium dihydrogen phosphate was admixed to activate the hydration of magnesia and a borax was used as a retarder. To observe the pore structure and ionic permeability of MPC mortar, mercury intrusion porosimetry was performed together with rapid chloride penetration test (RCPT). As a result, time to set of Fresh MPC mortar was in range of 16 to 21 min depend on the M/P ratio. Borax helped delaying setting time of MPC to 68 min. The compressive strength of MPC with M/P of 4 was sharply developed to 30 MPa within 12 hours. The compressive strength of MPC mortar was in range of 11.0 to 30.0 MPa depend on the M/P ratio at 12 hours of curing. Both tensile and flexural bond strength of MPC to old substrate (i.e. MPC; New substrate to OPC; Old substrate) were even higher than ordinary Portland cement mortar (i.e. [OPC; New substrate] to [OPC; Old substrate]) does, accounting 19 and 17 MPa, respectively. The total pore volume of MPC mortar was lower than that of OPC mortar. MPC mortar had the entrained air void rather than capillary pore. The RCPT showed that total charge passed of OPC mortar had more than that of MPC mortar, which can be explained by the pore volume and pore distribution.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.3
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• pp.160-170
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• 2010

Steel Fiber Reinforced Concrete (SFRC) beams has greater shear strength than typical reinforced concrete beams due to the high tensile strength of steel fibers. In this research, an experiment has been conducted to investigate the shear behavior of SFRC beams, and especially, the portion of shear resistance by uncracked compressive concrete section has been measured. Based on the test results in this study and 87 test data collected from literature, the accuracy of the existing equations for the estimation of shear strength has been evaluated. The shear strength of SFRC beams increased as more steel fibers were mixed. However, it is considered that the most efficient amount of steel fiber for enhancement of shear strength would be between 1% and 2% in that the specimen with 0.5% of steel fibers were abruptly failed after inclined cracking, and that the specimen with 2.0% of steel fibers showed a relatively low efficiency in increasing shear strength. The portion of shear resistance by the uncracked compressive concrete section was measured to be greater than 21%, and the equation proposed by Oh et al. provided the best accuracy on the estimation of shear strength of SFRC beams among the approaches evaluated in this study.

• Journal of Adhesion and Interface
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• v.6 no.2
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• pp.13-20
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• 2005

Interfacial shear strength (IFSS) of environmentally friendly natural fiber reinforced polymer composites plays a very important role in controlling the overall mechanical performance. The IFSS of various Ramie and Kenaf fibers/epoxy composites was evaluated using the combination of micromechanical test and nondestructive acoustic emission (AE) to find out optimal conditions for desirable final performance. Dynamic contact angle was measured for Ramie and Kenaf fibers and correlated the wettability properties with interfacial adhesion. Mechanical properties of Ramie and Kenaf fibers were investigated using single-fiber tensile test and analyzed statistically by both uni-and bimodal Weibull distributions. An influence of clamping effect on a real elongation for both Ramie and Kenaf fibers were evaluated as well. Two different microfailure modes, axial debonding and fibril fracture coming from fiber bundles and single fiber composites (SFC) were observed under tension and compression.