• Journal of the Korean Society for Precision Engineering
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• v.28 no.12
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• pp.1403-1410
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• 2011

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-elastic polymers, Polymethyl methacrylate(PMMA) which is used broadly for engineering polymer, as it has excellent mechanical and thermal properties compared to other polymers, was studied for creep characteristic at various level of stresses and temperatures. From the experimental results, the creep limit of PMMA at room temperature is 85 % of tensile strength. which is higher than that of PE (75%)at room temperature. Also the creep limits decreased to nil linearly as the temperatures increased, up to $120^{\circ}C$ of the melting point($267^{\circ}C$). Also the first and third stage among the three creep stages were non-existent nor were there any rupture failure which occurred for many metals at high temperatures.

• Journal of Ocean Engineering and Technology
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• v.35 no.6
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• pp.426-433
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• 2021

In this study, three types of synthetic fiber materials were evaluated, namely, DM20, SK78, and T147, to replace steel chains in shipbuilding and offshore fields with fiber chains as there is increasing demand for chains with lighter weights and improved usabilities. The strength and quasi-static stiffness were analyzed to select suitable yarns for the fiber chains. The durability of the yarn was evaluated by performing a 3-T (time to rupture) test as a specific tension level. The results of the experiment revealed excellent dynamic stiffness in DM20 and highest values of the windward and leeward stiffness in T147. 3-T linear design characteristic curves for a specific tension level were derived for the three types of fiber materials. The findings of this study can provide insights for improving strength and durability in fiber chain design.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.105-113
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• 2016

Most studies on mechanical properties of concrete with recycled aggregate was focused on the concrete with compressive strength of less than 40 MPa. Therefore, this paper concerns the compressive strength and mechanical properties of concrete with compressive strength of greater than 40 MPa containing recycled coarse aggregate (RCA). The experimental parameters were compressive strength level and replacement ratio of RCA. Compressive strength level was 45 and 60 MPa, and replacement ratio of RCA was 30, 50, 70 and 100%. The results of the test were discussed: compressive strength, elastic modulus, split tensile strength and modulus of rupture. Test results of elastic modulus were compared to the design code predictions. The design code predictions for elastic modulus overestimated the experimental results. However, the design code predictions for modulus of rupture were generally in agreement with the measured values.

• Journal of the Korean Wood Science and Technology
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• v.18 no.4
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• pp.86-101
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• 1990

The primary objective of this research was to investigate the strength properties of Comply, a composite panel. fabricated with particle board as core material and veneer or plywood as face and back. 20types of comply composites were manufactured according to the four specific gravity levels(0.5, 0.6, 0.7 or 0.8) of particleboard core and three veneer or two plywood thicknesses for face and back. They were tested and compared with matching particleboard (control) on moisture content. specific gravity, bending properties(MOE, MOR SPL). nail resistance and internal bond strength. The obtained results were summarized as follows: The increasing effect of modulus of elasticity was shown by the increase of face and back veneer or plywood thickness. The modulus of rupture and stress at proportional limit of the comply composites bonded with 3mm thick veneers or 3mm thick plywood face and back were higher than 2mm thick veneer or 2mm thick plywood as face and back. Both of modulus of rupture and stress at proportional limit on bending of Comply were higher than those of control board. Also the modulus of elasticity of Comply showed much higher than that of control board. The nail resistance of Comply, composed of plywood as face and back was higher than that of veneer. The nail resistance of control board was higher than that of Comply at Sp.Gr 0.7 and 0.8 core boards. Internal bond of Comply, composed of 1mm and 2mm thick veneer as face and back was higher than that of 3mm thick veneer. The increasing effect of modulus of elasticity was shown by the increase of shelling ratio in Comply composed of veneer and plywood as face and back. The modulus of rupture was increased by the increment of shellmg ratio in Compiy, composed of plywood as face and back. The modulus of elasticity and modulus of. rupture of comply were higher than those of particleboard(control) in effect of shelling ratio. Therefore it was concluded that the mechanical property values of Comply were clearly greater than those of particleboard(control).

• Journal of Biosystems Engineering
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• v.40 no.3
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• pp.201-211
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• 2015

Purpose: Designing equipment for processing, sorting, and other post-harvest operations of agricultural products requires information about their physical properties. This study was conducted to investigate some of the mechanical and physical properties of Moringa oleifera L. pods and seeds. Methods: Properties such as the length, width, thickness, bulk density, porosity, mass, static coefficient of friction, and angle of repose were determined as a function of moisture content. Statistical data and force-deformation curves obtained at each loading orientation and moisture level were analyzed for bioyield point, bioyield strength, yield force, rupture point, and rupture strength using a testrometric machine. Result: The basic dimensions (length, width, and thickness) of moringa pods and seeds were found to increase linearly from 311.15 to 371.45 mm, 22.79 to 31.22 mm, and 22.24 to 29.88 mm, respectively, in the moisture range of 12 to 49.5% d.b. The coefficient of friction for both pods and seeds increased linearly with an increase in moisture content on all the surfaces used. The highest value was recorded on mild steel, with 0.581 for pods and 0.3533 for seeds, and the lowest on glass for pods, with a value of 0.501, and of 0.2933 for seeds on galvanized steel. The bioyield and rupture forces, bioyield and rupture energies, and deformation of the pods decreased with an increase in moisture content to a minimum value, then increased with further decrease within the moisture content range, while the yield force increased to a maximum value and then decreased as the moisture content increased. Conclusion: These results will help to determine the most suitable conditions for processing, transporting, and storing moringa pods, and to provide relevant data useful in designing handling and processing equipment for the crop.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.248-253
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• 2003

Titanium alloy has widely been used as glasses rim material because it has high specific strength and also is light, harmless to men. But, we have little design data about the creep behaviors of the alloy. Therefore, in this study, an apparatus has been designed and built for conducting creep tests under constant load conditions. A series of creep tests on them have been performed to get the basic design data and life prediction of titanium products and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy is estimated about 13. And last, the fractographs at the creep rupture show both the ductile and the brittle fracture according to the creep conditions.

• Proceedings of the Materials Research Society of Korea Conference
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• 1993.11a
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• pp.48-48
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• 1993

• Architectural research
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• v.11 no.1
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• pp.25-33
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• 2009

This study presents the testing of 15 hwangtoh-based cementless concrete mixes to explore the significance and limitations of the development of eco-friendly concrete without carbon dioxide emissions while maintaining various beneficial effects. Hwangtoh, which is a kind of kaolin, was incorporated with inorganic materials, such as calcium hydroxide, to produce a cement-less binder. The main variables investigated were the water-to-binder ratio and fine aggregate-to-total aggregate ratio to ascertain the reliable mixing design of hwangtoh-based cementless concrete. The variation of slump with elapsed time was recorded in fresh concrete specimens. Mechanical properties of hardened concrete were also measured: including compressive strength gain, splitting tensile strength, moduli of rupture and elasticity, stress-strain relationship, and bond resistance. In addition, mechanical properties of hwangtoh-based cement-less concrete were compared with those of ordinary portland cement (OPC) concrete and predictions obtained from the design equations specified in ACI 318-05 and CEB-FIP for OPC concrete, wherever possible. Test results show that the mechanical properties of hwangtoh-based concrete were significantly influenced by the water-to-binder ratio and to less extend by fine aggregate-to-total aggregate ratio. The moduli of rupture and elasticity of hwangtoh-based concrete were generally lower than those of OPC concrete. In addition, the stress-strain and bond stress-slip relationships measured from hwangtoh-based concrete showed little agreement with the design model specified in CEB-FIP. However, the measured moduli of rupture and elasticity, and bond strength were higher than those given in ACI 318-05 and CEB-FIP. Overall, the test results suggest that the hwangtoh-based concrete shows highly effective performance and great potential as an environmental-friendly building material.

• Korean Journal of Materials Research
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• v.17 no.10
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• pp.560-566
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• 2007

AlN plates were fabricated by hot pressing at $1700-1900^{\circ}C$ using yttria and alumina (3 and $10\;{\mu}m$ particle size) powders as additives and characterized: density, thermal conductivity, transverse rupture strength, and grain size measurement by SEM and EDS. Density values of $3.31-3.34\;g/cm^3$ are largely attributed to hot pressing of powder mixtures in carbon mold under $N_2$ atmosphere which caused effective degree of oxygen removal from yttrium-aluminate phase expected to form at $1100^{\circ}C$. The grain size of hot pressed AlN was almost homogeneous, with size approximately from 3.2 to $4.0\;{\mu}m$ after hot pressing. $Al_2O_3$ powder of $3\;{\mu}m$ particle size resulted in better transverse rupture strength and finer grain size compared to $10\;{\mu}m$ $Al_2O_3$ powder. The thermal conductivity of AlN ranged between $83-92.7\;W/m{\cdot}K$ and decreased with $Al_2O_3$ addition. Fine grain size is preferred for better mechanical properties and thermal conductivity.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.373-378
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• 1996

This paper presents the characteristics of various strengths of underwater non-segregation concrete. Three types of cements including low-heat cements has been used to make the test specimens for compressive strength, modulus of rupture and bond strength. The test specimens have been made both in ambient and underwater conditions to take into account the variation according to the environmental condition.