• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.57-58
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• 2010

In this paper, direct tensile strength, $f_t$, and FR index, $F_i$, were considered, and factor ${\alpha}$ between and $f_t$ and $\sqrt{f'_c}$ was estimated through the results of preceding studies on the material properties of SHCCs in order to propose equation for evaluating shear strength of SHCC walls. Shear strength calculated by the proposed equation predicted shear strength of SHCC walls accurately, showing similar tendencies to experimental results.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.34 no.2
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• pp.61-66
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• 2002

This study was carried out to investigate sheet properties of Indian mallow hanji, made by different pulping methods such as alkali and sulfomethylated pulpings, and different stock compositions, various mixing ratios of bast fiber and woody core fibers. Effect of morphological properties of pulp stocks on the sheet formation and their optical properties were also evaluated using an image analyzer and confocal laser scanning microscope(CLSM). In addition, the effect of fiber distribution index(FDI), which was calculated based on the image in a z-direction of a sheet from CLSM, on the sheet properties of Indian mallow hanji was discussed. The proposed FDI had a good correlation with various properties of paper, such as apparent density, opacity, tear index, breaking length and zero-span tensile strength. Especially, sulfomethylated pulp sheets＇FDI was higher than alkali pulp sheets.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.3
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• pp.131-142
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• 2001

A wrinkling is the instability phenomenon influenced by material properties, shape geometry, forming conditions, stress state, etc. The wrinkling is considered as a critical defect in appearance of product. Many wrinkling prediction methods using thickness strain distribution and farming analysis have been proposed. The wrinkling, however, is not easily predicted precisely by these methods. In this study, the region in the biaxial plane stress state is modeled with a rectangular plate introducing the effective dimension, and critical stress values for the wrinkling are calculated. Prediction index for the wrinkling is then evaluated by normalizing the actual stress with respect to the critical stress. In order to show the validity and efficiency of the method proposed, the wrinkling prediction for a squared sheet in the uniaxial tensile stress and auto-body front finder panel is performed.

• Journal of the Korean Society of Safety
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• v.18 no.2
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• pp.56-63
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• 2003

Flame retardancy and mechanical properties of recycled polyolefinic plastics/inorganic filler composite systems were investigated by using several inorganic flame retardants such as magnesium hydroxide and slag powder generated electro arc furnace Compatibilizer user each maleic anhydride functionalized polyethylene (PE-g-MAH) and polypropylene(PP-g-MAH) or used mixture of these. The effect of polymeric compatibilizers on the properties of composites was studied by tensile and impact test, differential scanning calorimetry, in the changed fracture mechanism. The improved adhesion was particularly reflected in the mechanical properties. The flame retardancy of composites was examined by measuring limiting oxygen index(LOI, ASTM D2863), smoke density(ASTM D2843) and vertical burning test(UL94). Regarding the flame retardant effect, the EAF slag powder is behaving as synergists as they are only active in the presence of magnesium hydroxide.

• Advances in concrete construction
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• v.12 no.5
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• pp.439-450
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• 2021

In recent years, nano-reinforcing materials are widely utilized in cement composites due to their unique multifunctional properties. This study incorporated multi-walled carbon nanotubes (MWCNTs) into the cementitious composites at ratios of 0.1%, 0.3%, and 0.5%, and investigated their influence on the flowability, mechanical strength, and hydration heat properties. The addition of MWCNTs enhanced the compressive and split tensile strengths approximately by 18-51%. In the semi-adiabatic temperature rise test, the internal hydration heat of the composites reduced by 5%, 9%, and 12% with the increase of MWCNTs in 0.1%, 0.3%, and 0.5%. This study further performed hydration heat analysis and estimated the adiabatic temperature rise, thermal stress, and thermal crack index. The internal hydration heat of the concrete decreased by 5%, 10%, and 13% with the increase of MWCNTs. The thermal stress of the concrete decreased with increase in the addition of MWCNTs, and the obtained temperature crack index was effective in controlling the thermal cracks.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.651-658
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• 2010

Sixteen concrete mixes reinforced with hybrid steel-polybinyl alcohol (PVA) fibers and a control concrete mix with no fiber were tested in order to examine the effect of the micro and macro fibers on the slump and different mechanical properties of concrete. Main variables investigated were length and volume fraction of steel and PVA fibers. The measured mechanical properties of hybrid fiber reinforced concrete were analyzed using the fiber reinforcing index and compared with those recorded from monolithic steel or PVA fiber reinforced concrete. The initial slump of hybrid fiber reinforced concrete decreased with the increase of the aspect ratio and the volume fraction of fibers. In addition, splitting tensile strength, modui of rupture and elasticity, and flexural toughness index of concrete increased with the increase of the fiber reinforcement index. Modulus of rupture and flexural toughness index of hybrid fiber reinforced concrete were higher than those of monolithic fiber reinforced concrete, though the total volume fraction of hybrid fibers was lower than that of monolithic fiber. For enhancing the flexural toughness index of hybrid fiber reinforced concrete, using the steel fiber of 60 mm length was more effective than using the steel fibers combined with 60 mm and 30 mm lengths.

• Tunnel and Underground Space
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• v.24 no.4
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• pp.325-333
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• 2014

Hydraulic fracturing is the key technology for production of shale gas, which is one of the major unconventional resources. Brittleness index is one of the most important mechanical properties which determine the efficiency of hydraulic fracturing. It was required that the production of shale gas increases with more brittle behavior. Confusingly, there are numerous definitions available for brittleness of rock. This paper summarizes various definitions of brittleness index, and presents correlation analysis of the brittleness indices by using the laboratory experimental results of 48 shale specimens in Korea. Generally, it shows a very weak positive correlation between the brittleness index ($B_1$) which is the ratio of uniaxial compressive strength to tensile strength and the brittleness index ($B_3$) which is calculated by using the Youngs modulus and Poisson's ratio. In addition, the role of Poissons ratio is not clear in defining brittleness indices. In conclusion, standardization of definition for brittleness index is required to apply it to hydraulic fracturing as a parameter for predicting the efficiency.

• Journal of the Optical Society of Korea
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• v.19 no.4
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• pp.376-381
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• 2015

Transmission characteristics of long-period fiber gratings (LPFGs) fabricated by periodically etching a conventional single-mode fiber (SMF) are investigated. After coating the SMF with photoresist, the cladding of the SMF is symmetrically and periodically removed by using a wet etching technique resulting in the formation of the LPFG. Tensile strain reinforces the coupling strength between the core and the cladding mode based on the photoelastic effect. The extinction ratio of the SMF-based LPFG at a wavelength of 1550.8 nm is measured to be -15.1 dB when the applied strain is $600{\mu}{\varepsilon}$. The ascent of ambient index shifts the resonant wavelength to shorter wavelength because of the increase of the effective refractive index of the cladding mode. The extinction ratio is diminished by increase in the ambient index because of the induction of the optical attenuation of the cladding mode. The transmission characteristics of the proposed LPFG with variations in torsion are also measured. The photoelastic effect based on torsion changes the extinction ratio and the resonant wavelength of the proposed SMF-based LPFG. The polarization-dependent loss of the LPFG is also increased by torsion because of the torsion-induced birefringence. The polarization-dependent loss of the LPFG at torsion of 8.5 rad/m is measured to be 3.9 dB.

• Journal of the Korea Institute of Building Construction
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• v.8 no.1
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• pp.43-48
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• 2008

Fifteen concrete specimens were mixed and tested to explore the significance and limitation of appling the polyvinyl alcohol (PVA) fiber and steel fiber with end hook to concrete. Main parameters investigated were volume fraction and length of the fibers. The measured mechanical properties of fiber reinforced concrete are analyzed according to the equivalent fiber amount index explaining the adding amount and length of fibers. Test results showed that compressive strength of fiber reinforced concrete was higher than that of concrete with no fiber by $10{\sim}20%$. The normalized splitting tensile strength and flexural strength of PVA fiber reinforced concrete were similar to those of concrete with no fiber, whereas those of steel fiber reinforced concrete increased with the increase of the equivalent fiber amount index. In particular, much higher ductile behavior was observed in steel fiber reinforced concrete than in PVA reinforced concrete, indicating that the slope of descending branch of load-displacement relationship of steel fiber reinforced concrete decreased with the increase of the volume fraction and length of the fiber.

• Journal of Sericultural and Entomological Science
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• v.39 no.2
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• pp.186-196
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• 1997

The IR crystallinity index of Calcium nitrate treated silk fiber decreased proportionally to the concentration of calcium nitrate. A partial change of conformation was observed in the concentration of over 46.4-47.6% changing from $\beta$-sheet or to random coil in the crystalline region. This is in coincidence with the result of crystallinity index, which was started to be reduced in the concentration range of 46.4-47.6%. A same trend was observed for the X-ray order factor, birefringence, degree of orientation and surface structure. These structural parameters were remarkably changed on the treatment of silk fibers with concentration of 46.4-17, 6% calcium nitrate. Therefore, it seems that there exists a critical concentration of calcium nitrate in affection the structure and morphology of silk fibers. According to the examination of surface morphology, the fine stripe was observed in the direction of fiber axis at 46.4% concentration. However, the treated concentration was exceeded by 47.6%, the cracks were appeared severely on the fiber surface in the transverse direction as well as fiber axis direction. This result might be related to the tensile properties, specially a tenacity of silk fibers. As a result of quantitative analysis of a dilute acid hydrolysis, three different regions, which are known as a amorphous, semi-crystalline and crystalline region, could be obtained. The hydrolysis rate curves were different with various concentrations of treatment and the relative contents of each region could be calculated.