• Composites Research
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• v.26 no.3
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• pp.160-164
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• 2013

In this study, the effect of phosphoric acid (PA) as a fiber spinning aid on the strength increase of polyacrylonitrile (PAN) nano-fibers by using modified mechano-electrospinning technologies has been analyzed. The medium carbonization temperature of $800^{\circ}C$ has been selected for the future economic production of these new materials. The concentration of PAN in dimethyl sulfoxide (DMSO) was fixed as 5 wt%. The weight fraction of PA was selected as being 2%, 4%, 6%, and 8% in comparison to PAN. These solutions have been used to make the nanofibers. The mechano-electrospinning apparatus installed in KRICT was made by our own design. By using this apparatus the continous and highly aligned precursor nano-fibers have been obtained. The bundle of 50 well aligned nano diameter continuous fibers with the diametr of 10 microns with 6 wt% phosphoric acid for addition showed maximum mechanical properties of 1.6 GPa as tensile strength and 300 GPa as Young's modulus. The weight of final product can be increased 19%, which can improve the economical benefits for the application of these new materials.

• Journal of Ocean Engineering and Technology
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• v.2 no.2
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• pp.104-111
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• 1988

This paper deals with the micro-surface-cracks behavior on the unnotched smooth specimens of Type 304 stainless steel at $593^{\circ}C$ in air under creep and creep-fatigue conditions that have 10 mim and 1 min load holding times respectively. The behaviors of the micro-surface-cracks have been visualized by means of surface replica method and optical micro-photography. The quantitative characteristics of initiation, growth and coalescence of micro-surface-cracks have been investigated by observing and measuring the crack growth behaviors. some of the important results are as follows: Main crack initiates at grain boundary in the early stage(10 to 20%)of its life time and grows through coalescence and finally leads to fracture. The distribution of micro-surface-crack length, 2a, can be plotted against the composite Weibull distribution. The growth rate of the main crack can be plotted against the stress intensity factor, crack tip opering displacement and J integral.

• International Journal of Ocean System Engineering
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• v.1 no.3
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• pp.148-154
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• 2011

Generally, strength degradation is caused by the absorption of moisture in composites. For this reason, a fracture is generated in the composites and traces of glass fiber degrade human health and physical damage is generated. Therefore, in this research, we studied the mechanical properties change of composites by moistureabsorption. The composites were manufactured with and without the Gel-coating process and were immersed in a moisture absorption device at $80^{\circ}C$ for more than 100 days. The mechanical properties of the moistureabsorption composites and the composites which dry after moisture-absorption were compared. The mechanical properties degradation of basalt fiber composites according to the result of the measurement of moistureabsorption was smaller than that of glass fiber composites by about 20%. In addition, the coefficient of moisture absorption was lower for the case of Gel-coating processing than the composites without the Gel-coating process by about 2% and it was deduced that Gel-coating did not have a significant effect on the mechanical properties.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.454-460
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• 2001

장석, 석영, 점토와 17 wt% $Al_2$O$_3$를 함유한 알루미나질 자기 애자를 제조하였다. 분말을 ball milling으로 6시간 분쇄하였으며 성형체를 압출법으로 제조한 후 터널가마에서 130$0^{\circ}C$, 50분 동안 소결하였다. 터널가마에서 소결한 시편의 소결밀도는 이론밀도의 97%에 도달하였고, 3점 꺾임강도는 1658kgf/$ extrm{cm}^2$ 이었으며 ICL(indentation crack length) 방법으로 측정한 파괴인성은 2.3 MPa.m$^{1}$2/이었다. 기계적 성질을 향상시키기 위하여 ZrO$_2$를 첨가하여 15 wt% $Al_2$O$_3$-2 wt% ZrO$_2$와 12 wt% $Al_2$O$_3$-5 wt% ZrO$_2$를 복합체를 제조하였다. ZrO$_2$를 첨가한 시편의 꺾임강도는 1740kgf/$\textrm{cm}^2$이고 파괴인성은 2.4 MPa.m$^{1}$2/로 약 10% 기계적 성질이 향상되었다.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.539-544
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• 2013

A simple synthetic process is demonstrated for the preparation of MnS/carbon nanotube (CNT) composites for Li ion battery electrodes. CNTs were initially treated using a strong acid solution to generate carboxylate ions ($-COO^-$) on their surfaces. The MnS/CNT composites were synthesized by a polyvinyl-pyrrolidone-assisted hydrothermal method in the presence of as-functionalized CNTs. The phase and morphology of the MnS/CNT composites and pure MnS microspheres were characterized using X-ray diffraction and high-resolution transmission electron microscopy. Furthermore, the Li electroactivity levels of the MnS/CNT composites and MnS microspheres were investigated using cyclic voltammetry and galvanostatic cycling. The MnS/CNT composite electrodes showed higher specific capacities exceeding 365 $mA\;h\;g^{-1}$ at a C/10 current rate and enhanced cyclic performance compared to pure MnS microspheres.

• Journal of the Korean Society of Safety
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• v.24 no.6
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• pp.103-110
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• 2009

Since the mechanical properties of cement-based materials are time-dependent due to the prolonged cement hydration process, those of fiber reinforced concrete(FRC) may also be time-dependent. Toughness is one of important properties of FRC. Therefore, it should be investigated toughness development of FRCs with curing ages to fully understand the time-dependent characteristics of FRCs. To this end, the effect of curing ages on flexural toughness development of steel fiber reinforced concrete is studied. Three point bending test with notched beam specimen was adapted for this study. Hooked-end steel fiber(DRAMIX 40/30) was used as a fiber ingredient to investigate w/c ratio and fiber volume fraction effect on toughness development during curing. Three different water-cement ratios(0.44, 0.5 and 0.6) and fiber volume fractions(0%, 0.5% and 1%) were used as influence factors. Each mixture specimens were tested at five different ages, 0.5, 1, 3, 7 and 28 days. The study shows that flexure toughness development with age is quite different than other concrete material properties such as compressive strength. The study also shows that the toughness development trend correlates more closely to water/cement ratio than to fiber volume fraction.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.4
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• pp.165-170
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• 2005

A series of inorganic-organic hybrid membranes were prepared with a systematic variation of titanium dioxide nanoparticle content. Their water uptake, methanol permeability and proton conductivity as a function of temperature were investigated. The results obtained show that the inorganic oxide network decreases the proton conductivity and water swelling. It is also found that increase in inorganic oxide content leads to decrease of methanol permeability. In terms of the morphology, membranes are homogeneous and exhibit good adhesion between inorganic domains and the polymer matrix. The properties of the composite membranes are compared with the standard nafion membrane.

• Steel and Composite Structures
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• v.22 no.3
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• pp.589-611
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• 2016

The primary objectives of this research are to investigate the energy factor response of steel moment resisting frame (MRF) systems equipped with fuses subject to ground motions and to develop an energy-based evaluation approach for evaluating the damage-control behavior of the system. First, the energy factor of steel MRF systems with fuses below the resilience threshold is derived utilizing the energy balance equation considering bilinear oscillators with significant post-yielding stiffness ratio, and the effect of structural nonlinearity on the energy factor is investigated by conducting a parametric study covering a wide range of parameters. A practical transformation approach is also proposed to associate the energy factor of steel MRF systems with fuses with classic design spectra based on elasto-plastic systems. Then, the energy balance is extended to structural systems, and an energy-based procedure for damage-control evaluation is proposed and a damage-control index is also derived. The approach is then applied to two types of steel MRF systems with fuses to explore the applicability for quantifying the damage-control behavior. The rationality of the proposed approach and the accuracy for identifying the damage-control behavior are demonstrated by nonlinear static analyses and incremental dynamic analyses utilizing prototype structures.

• Structural Engineering and Mechanics
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• v.15 no.1
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• pp.115-134
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• 2003

The Ting Kau Bridge in Hong Kong is a cable-stayed bridge comprising two main spans and two side spans. The bridge deck is supported by three towers, an end pier and an abutment. Each of the three towers consists of a single reinforced concrete mast which reduces its section in steps, and it is strengthened by transverse cables and struts in the transverse vertical plane. The bridge deck is supported by four inclined planes of cables emanating from anchorages at the tower tops. In view of the threat from typhoons, the dynamic behaviour of long-span cable-supported bridges in the region is always an important consideration in their design. This paper is devoted to the ambient vibration measurements of the bridge for evaluation of dynamic characteristics including the natural frequencies and mode shapes. It also describes the modelling of the bridge. A few finite element models are developed and calibrated to match with the field data and the results of subsequent structural health monitoring of the bridge.

• Steel and Composite Structures
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• v.4 no.6
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• pp.419-435
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• 2004

The safety level of a structural system designed per code specifications can not be inferred directly from the reliability of members due to the load redistribution and nonlinear inelastic structural behavior. Comparison of the system and member reliability, which is scarce in the literature, is likely to indicate any possible inconsistency of design codes in providing safe and economical designs. Such a comparative study is presented in this study for moment resisting two-dimensional steel frames designed per AISC LRFD Specifications. The member reliability is evaluated using the resistance of the beam-column element and the elastic load effects that indirectly accounts for the second-order effects. The system reliability analysis is evaluated based on the collapse load factor obtained from a second-order inelastic analysis. Comparison of the system and member reliability is presented for several steel frames. Results suggest that the failure probability of the system is about one order of magnitude lower than that of the most critically loaded structural member, and that the difference between the system and member reliability depends on the structural configuration, degree of redundancy, and dead to live load ratio. Results also suggest that the system reliability is less sensitive to initial imperfections of the structure than the member reliability. Therefore, the system aspect should be incorporated in future design codes in order to achieve more reliability consistent designs.