• Steel and Composite Structures
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• v.50 no.4
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• pp.475-487
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• 2024

The usage of fiber-reinforced polymer materials increases in the construction sector due to their advantages in terms of high mechanical strength, lightness, corrosion resistance, low density and high strength/density ratio, low maintenance and painting needs, and high workability. In this study, it is aimed to improve mechanical properties of GFRP box profiles, produced by pultrusion method, by filling the polymer concrete into them. Within the scope of study, hybrid use of polymer concrete produced with GFRP box profiles was investigated. Hybrid pressure and bending specimens were produced by filling polymer concrete (polyester resin manufactured with natural sand and stone chips) into GFRP box profiles having different cross-sections and dimensions. Behavior of the produced hybrid members was investigated under bending and compression tests. Hollow GFRP_xx profiles, polymer-filled hybrid members, and nominative polymeric concrete specimens were tested as well. The behavior of the specimens under pressure and bending tests, and their load bearing capacities, deformations and changes in toughness were observed. According to the test results; It was deduced that hybrid design has many advantages over its component materials as well as superior physical and mechanical properties.

• Land and Housing Review
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• v.2 no.1
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• pp.47-52
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• 2011

Recent advances of technology in materials science have made it easy to respond to user's needs on high performance steel in civil and building structures. The high-performance and high-strength steel are required for large scale structure and high-rise building to have high-strength, high fracture toughness and better weldability etc. Therefore development of 600MPa class steel for mega structure is necessary. high strength steels, however, may have mechanical properties that are significantly different from those of the conventional steels. The application of high-strength steels to building structures should be reviewed as to whether inelastic behavior equivalent to that of conventional steels can be attained or not. This study researched the structural behavior of high strength circular tubes compression and under flexure. Three column tests and three flexural tests were carried out. The suitability of existing design formulae(KBC 2009) and the structural behavior were investigated through these columns and beams with various types.

• Journal of Powder Materials
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• v.29 no.1
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• pp.34-40
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• 2022

Recently, high-entropy carbides have attracted considerable attention owing to their excellent physical and chemical properties such as high hardness, fracture toughness, and conductivity. However, as an emerging class of novel materials, the synthesis methods, performance, and applications of high-entropy carbides have ample scope for further development. In this study, equiatomic (Hf-Ti-Ta-Zr-Nb)C high-entropy carbide powders have been prepared by an ultrahigh-energy ball-milling (UHEBM) process with different milling times (1, 5, 15, 30, and 60 min). Further, their refinement behavior and high-entropy synthesis potential have been investigated. With an increase in the milling time, the particle size rapidly reduces (under sub-micrometer size) and homogeneous mixing of the prepared powder is observed. The distortions in the crystal lattice, which occur as a result of the refinement process and the multicomponent effect, are found to improve the sintering, thereby notably enhancing the formation of a single-phase solid solution (high-entropy). Herein, we present a procedure for the bulk synthesis of highly pure, dense, and uniform FCC single-phase (Fm3m crystal structure) (Hf-Ti-Ta-Zr-Nb)C high-entropy carbide using a milling time of 60 min and a sintering temperature of 1,600℃.

• Journal of the Korean Society of Food Culture
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• v.17 no.1
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• pp.70-77
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• 2002

Jangachi(salted and fermented vegetable) has been made by Korean traditionally using several kinds of vegetables, which is a good source of variety of nutrients and vitamins. There are many methods for making Jangachi. Generally soy sauce Jangachi is made through two steps. First, as a pretreatment, vegetables are soaked in salt water. Second, soaked vegetables are fermented in various ingredients like soy sauce, sugar, garlic, ginger and so on. This study was performed to observe changes in contents of chemical components and sensory evaluation of pretreated perilla leaf. Perilla leaf was soaked in water with different levels of salt concentration(2, 5 and 8 %) and soaking time(1, 3 and 5 days). The optimal level of salt and soaking time was determined with the results of sensory evaluation by response surface methodology and analysis of composition. The moisture contents decreased as the levels of salt and soaking time increased. The moisture content of untreated sample was 87.5 % and when soaked for 5 days in the water of 8 % salt concentration, it became 78.27 %. pH of Perilla leaf was high in high levels of salt concentration and short soaking time. Total acidity was so opposite to pH that was low in high levels of salt concentration and short soaking time. In the water of 8 % salt concentration, total acidity was 0.14 % when soaked for 1 day, 0.20 % for 3 days and 0.30 % for 5 days. Salt contents became greater as the soaking time increased. As the results of puncture test, soaked Perilla leaf's toughness increased as the levels of salt increased and soaking time decreased. Among the sensory attributes, greenness increased as the levels of salt concentration increased when soaked for more than 3 days. Saltiness and bitterness became greater as the levels of salt concentration increased. Perilla flavor decreased with the short soaking time. Off-flavor increased with the increased levels of soaking time and decreased salt concentration when soaked for more than 3 days. Toughness decreased as the levels of soaking time increased. Crispness increased with the increased levels of salt concentration. The condition of pretreated Perilla was optimum when it soaked for 42 hours in 4 % salt concentration.

• Journal of Korean Society of Steel Construction
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• v.26 no.4
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• pp.335-348
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• 2014

For high-strength steel, it is difficult to be applied to flexible structural member because it have high yield ratio and low basic material's toughness. One of the great problems when using high-strength steel connections is the brittle fracture at the end of the beam member in common with general mild steel connections. In the cases of mild steel connections, it has be developed that special moment frame connection details by reinforcing structural member or improvement of welding access hole. But, it is incomplete at yet about applicability estimation of high-strength steel connections. This study is the initial step research for the applicability estimation of beam-to-column connections being applied to developed high-strength steel, HSA800. And, it studied about structural performance of the high-strength steel connections according to the details of welding access hole through full-scale test and analytical method.

• Journal of Powder Materials
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• v.31 no.1
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• pp.30-36
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• 2024

The aerospace and power generation industries have an increasing demand for high-temperature, high-strength materials. However, conventional materials typically lack sufficient fracture toughness and oxidation resistance at high temperatures. This study aims to enhance the high-temperature properties of Nb-Si-Ti alloys through ball milling. To analyze the effects of milling time, the progression of alloying is evaluated on the basis of XRD patterns and the microstructure of alloy powders. Spark plasma sintering (SPS) is employed to produce compacts, with thermodynamic modeling assisting in predicting phase fractions and sintering temperature ranges. The changes in the microstructure and variation in the mechanical properties due to the adjustment of the sintering temperature provide insights into the influence of Nb solid solution, Nb5Si3, and crystallite size within the compacts. By investigating the changes in the mechanical properties through strengthening mechanisms, such as precipitation strengthening, solid solution strengthening, and crystallite refinement, this study aims to verify the applicability of Nb-Si-Ti alloys in advanced material systems.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.3
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• pp.17-23
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• 2005

In this study, the high strength and superior toughness spring steels as the suspension material, used for automobile and railroad industries were utilized to carry out the following investigations. Corrosion times were controlled in 7, 14,30 and 60days to examine the relation between corrosion pit and compressive residual stress in the static corrosion environment after shot peened. And then corrosion current and corrosion potential were measured for every 24 hours to investigate the corrosion mechanism. Shot peened material shows the low or rate of corrosion current as compared with unpeened material. In case of hot peened material which has the highest residual stress, it has a low corrosion current density.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.342-346
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• 2012

This work deals with the preparation of dense SiC based ceramics with high electrical conductivity without oxide sintering additives. SiC samples with different content of conductive Ti-NbC phase were hot pressed at $1850^{\circ}C$ for 1 h in Ar atmosphere under mechanical pressure of 30 MPa. The conductive phase is a mixture of Ti-NbC in weight ratio of Ti/NbC 1:4. Composite with 50% of conductive Ti-NbC phase showed the highest electrical conductivity of $30.6{\times}10^3\;S{\cdot}m^{-1}$, while the good mechanical properties of SiC matrix were preserved (fracture toughness 4.5 $MPa{\cdot}m^{1/2}$ and Vickers hardness 18.7 GPa). The obtained results show that use of NbC and Ti as sintering and also electrically conductive additives is appropriate for the preparation of SiC-based composite with sufficient electrical conductivity for electric discharge machining.

• Proceedings of the KWS Conference
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• 1993.05a
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• pp.120-124
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• 1993

The Charpy V impact test on subsize was performed on narrow laser welds of low carbon steel sheets, joined by using a continuous wave 3kW CO$_2$ laser. Under certain conditions, a bimodal fracture behaviour has been experienced in Charpy V impact test of narrow laser beam welds. Deviation of the fracture path from the fusion zone into the base metal was dominated at high test temperature. It can be seen that the deviation always occurred after ductile initiation. If the deviation occurs on a small testing specimen, the same trend would happen on the actual laser welded structure. Fracture will then propagate through the base material even if the weld metal has low toughness.

• The Korean Journal of Ceramics
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• v.1 no.1
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• pp.45-54
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• 1995

Four kinds of silicon nitride based ceramic materials have been hot pressed. Effect of the sintering additives on the phase transformation, microstructural development and mechanical properties was investigated. While sintering under the same condition a big difference among the microstructures of the specimens, they appeared alike if sintered to have a similiar $\alpha$-$\beta$ phase ratio. The specimen of the stoichiometric $\alpha$-$\beta$ sialon composition showed very limited amount of the intergranular glassy phase and a significant degree of the residual stress. It exhibited almost no strength degradation up to $1300^{\circ}C$, and the strength of the specimen degraded more as its composition deviated from the stoichiometry.