• Steel and Composite Structures
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• v.32 no.5
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• pp.559-569
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• 2019

The bond strength between composite laminates and concrete is a key factor that controls the behavior of concrete members strengthened with fiber reinforced polymer (FRP) sheets, which can be affected by several parameters such as thermal stresses and surface preparation. This article presents the result of an experimental study on the bond strength between FRP sheets and concrete at ambient temperature after specimens had been exposed to elevated temperatures of up to $200^{\circ}C$. For this purpose, 30 specimens of plain concrete with dimensions of $150{\times}150{\times}350mm$ were prepared. Three different conventional surface preparation methods (sandblasting, wire brushing and hole drilling) were considered and compared with a new efficient method (fiber implantation). Deformation field during each experiment was monitored using particle image velocimetry. The results showed that, the specimens which were prepared by conventional surface preparation methods, preserved their bond integrity when exposed to temperature below glass transition temperature of epoxy resin (about $60^{\circ}C$). Beyond this temperature, the bond strength and stiffness decreased significantly (about 50%) in comparison with control specimens. However, the specimens prepared by the proposed method displayed higher bond strengths of up to 32% and 90% at $25^{\circ}C$ and $200^{\circ}C$, respectively.

• Korean Journal of Metals and Materials
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• v.46 no.1
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• pp.1-5
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• 2008

This study has been investigated the deformation behavior of a hot-extruded Mg-Zn-RE (RE: rare earth elements) alloy containing $Mg_{12}$(RE) particles at the elevated temperatures. The particles are intrinsically produced by breaking the eutectic structure of the alloy during the hot-extrusion process. The grain size of the extruded Mg-Zn-RE alloy developed via dynamic recrystallization is around $10{\mu}m$. Under the heat treatment at 200o C up to 48 hr, no change has been observed on the microstructure and mechanical properties due to the pinning effect of the thermally stable particles. Under the tensile test condition in the initial strain-rate range of $1\times10^{-3}s^{-1}$ and the temperature range up to $200^{\circ}C$, the alloy shows yield strength of 270 MPa and elongation to failure around 9% at room temperature and yield strength of 135 MPa at $200^{\circ}C$. Furthermore, although the alloy contains large amount of the second phase particles around 15%, it shows excellent hot-workability possibly due to the presence of the thermally stable interface between the particles and the matrix.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.133-134
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• 2021

Limestone-calcined clay-Cement (LC3) concrete provides a solution for sustainability, durability, and profitability of concrete industry. This study shows experimental studies of the macro properties (residual compressive strength), the meso properties (mesoscopic images), and micro properties (thermogravimetric (TG) analysis, X-ray powder diffraction (XRD), FTIR spectra, Raman spectra, Mercury intrusion porosimetry, and SEM) of LC3 paste with various mixtures and at high elevated temperatures (20 ℃, 300 ℃, 550 ℃ and 900 ℃). We find (1) Regarding to macro properties, LC3 cementitious materials are at a disadvantage in compressive strength when the temperature is higher than 300 ℃. (2) Regarding to meso properties, when the temperature reached 550 ℃, all samples generated more meso cracks. (3) Regarding to micro properties, first, as the substitution amount increases, its CH content decreases significantly; second, at 900 ℃, for samples with calcined clay, a large amount of gehlenite crystalline phase was found; third, at elevated temperatures (20 ℃, 300 ℃, 550 ℃ and 900 ℃), there is a linear relationship between the residual compressive strength and the cumulative pore volume; fourth, at 900 ℃, a large amount of dicalcium silicate was generated, and damage cracks were more pronounced. The experimental results of this study are valuable of material design of fire resistance of LC3 concrete.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.03a
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• pp.139-148
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• 1994

An experimental study on material characterization and mechanical properties of SMC(Sheet Molding Compounds) compression molding parts was carried out. Simple compression test using grease oil as a lubricant was carried out to characterize flow stress of SMC at elevated temperatures. Two different mold temperatures, 130$^{\circ}C$ and 150$^{\circ}C$ and two different mold speeds, 15, 45mm/min were used for preparing the specimen of SMC compression molding parts. Surface roughness, tensile, and 3-point bending tests were used to determine the effects of molding temperatures and speeds on mechanical properties of compression molded SMC parts.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2396-2403
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• 1994

An experimental study on material characterization and mechanical properties of SMC(Sheet Molding Compounds) compression method parts was carried out. Simple compression test using grease oil as a lubricant was carried out to characterize flow stress of SMC at elevated temperatures. Two different mold temperatures, $130^{\circ}C{\;}and{\;}150^{\circ}C$ and two different mold speeds, 15, 45 mm/min were used for preparing the specimen of SMC compression molded parts. Surface roughness, tensile, and 3-point bending tests were used to determine the effects of molding temperatures and speeds on mechanical properties of compression molded SMC parts. Orientation and distribution of glass fiber in the compression molded SMC parts were also investigated by photographing the burnt flat specimen and taking SEM(Scanning Electron Microscope) of cross-sectional T-specimen.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.3
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• pp.177-181
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• 2016

Hot shearing is a method of producing various high-quality planar machine parts by using reduced punch load. In order to predict the results of this process, the deformation behavior of work material at elevated temperatures need to be studied. In this research, a tensile test was carried out for 5052 aluminum alloy at high temperatures of $240-540^{\circ}C$ and strain rates of 0.001-0.1/s. The results of the tensile tests were studied to predict the deformation of the alloy during the hot shearing process. The results showed that hot shearing within a temperature range of $340-440^{\circ}C$ and a strain rate rage of 0.001-01/s will be the most effective in reducing punch load and increasing the sheared edge in the case of 5052 aluminum alloy.

• Bulletin of the Korean Chemical Society
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• v.9 no.6
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• pp.388-393
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• 1988

The chemisorption of CO molecules on polycrystalline nickel surface has been studied by investigating the resulting chemisorbed species with the X-ray photoelectron spectroscopy at temperatures between 300K through 433K. It is found that the adsorbed CO molecules are dissociated by the simple C-O bond cleavage as well as by the disproportionation reaction at temperatures above 373K. The former type dissociation is more favored at low coverages and at elevated temperatures. The isotherms of CO chemisorption are obtained from the xps intensities of C 1s peaks, and then the activation energy of the dissociative adsorption is estimated as a function of the CO exposure. These activation energies are extrapolated to zero coverage to obtain the activation energy of chemisorption in which thermal C-O bond cleavage takes place. The value obtained is 38.1 kJ/mol.

• Korean Journal of Food Science and Technology
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• v.36 no.3
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• pp.393-397
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• 2004

Rice was steeped at elevated temperatures of $40,\;50,\;or\;60^{\circ}C$ for 2 hr, and physicochemical properties of starches isolated from wet-milled rice flour were investigated. Steeping at elevated temperatures slightly decreased lightness of rice starch, while increased yellowness and redness. Average granule size of rice starch was decreased by steeping treatment. Swelling power and solubility increased as temperature increased. Starch from rice steeped at $40^{\circ}C$ displayed highest swelling power and solubility. Differential scanning calorimetry data of starch obtained from steeped rice at $60^{\circ}C$ showed increased onset and peak temperatures, with narrower gelatinization temperature range, suggesting partial annealing effect. Pasting properties of starch measured by Rapid Visco-Analyzer indicated increased peak viscosity due to rice steeping at $40^{\circ}C$. Peak and breakdown viscosities decreased at $50\;and\;60^{\circ}C$, whereas setback and final viscosities increased.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.87-95
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• 1990

Rotating bending fatigue tests of an authentic steel 304 were performed at various temperatures such as room temperature, $538^{\circ}$ and $593^{\circ}C$. The plastic replica method was also applied in order to estimate the fatigue life on the basis of serial observation of small fatigue crack initiation and growth on the pit specimen surface. The fatigue crack growth behavior of 304 stainless steel was investigated within the frame work of elastic-plastic fracture mechanics within a narrow scatterband in spite of different stress levels at elevated temperature as at room temperature. The growth law of small surface crack is determined uniquely by the term. $\DELTA\sigma^{n}a$ where $\DELTA\sigma$ is the stress amplitude, a is the crack length, and n is a constant. It is found that the small crack growth behavior is basically equivalent to the S-$N_{f}$ relationship, where S and $N_{f}$ are stress and number of cycles to failure, and the fatigue life prediction is in good agreement with the experimental results.

• Journal of Korean Society of Steel Construction
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• v.18 no.3
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• pp.395-403
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• 2006

Recently constructed bridges often have long spans and simple structure details considering not only the function but other important factors such as aesthetics, maintenance, construction duration and life cycle cost. Therefore, bridges require high-performance steels like extra-thick plate steels and thermo-mechanical control process (TMCP) steels. TMCP stels are now gaining wide attention due to their weldability improved strength and toughness. Recently, SM570-TMC steel, which is a high-strength TMCP steel with a tensile strength of 600 MPa, has been developed and applied to steel structures. However, using this steel in building steel structures requires the elucidation of not only material characteristics but also the mechanical characteristic of welded joints. In this study, high-temperature tensile properties of SM570-TMC steel were investigated through the elevated temperature welded joints of SM570-TMC steel were studied through the three-dimensional thermal elasticplastic analyses on the basis of mechanical properties at high temperatures obtained from the experiment.