• Steel and Composite Structures
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• v.19 no.4
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• pp.995-1009
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• 2015

This study presents design optimization of spot welded structures to attain maximum strength by using the Nelder-Mead (Simplex) method. It is the main idea of the algorithm that the simulation run is executed several times to satisfy predefined convergence criteria and every run uses the starting points of the previous configurations. The material and size of the sheet plates are the pre-assigned parameters which do not change in the optimization cycle. Locations of the spot welds, on the other hand, are chosen to be design variables. In order to calculate the objective function, which is the maximum equivalent stress, ANSYS, general purpose finite element analysis software, is used. To obtain global optimum locations of spot welds a methodology is proposed by modifying the Nelder-Mead (Simplex) method. The procedure is applied to a number of representative problems to demonstrate the validity and effectiveness of the proposed method. It is shown that it is possible to obtain the global optimum values without stacking local minimum ones by using proposed methodology.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.81-84
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• 2006

Currently, natural aggregates of good quality are hard to use because of continuous decrease of internal aggregate resource and regulation of gathering. So, use of crushed sand was being increased. On the other hand, skyscraper projects with 100 stories are being planned within the country and high strength concrete must be used to construct a skyscraper with 100 stories. High strength concrete is necessary to use crushed sand too because we are still unable to secure natural aggregates of good quality. So, This study indicated basic data necessary for mix design of high strength concrete through valuation of concrete property by quality variation of crushed sand.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.313-317
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• 2003

The study is the results of accelerated tests and the specimens, mortars, are submerged in a 5% sulfuric acid solution. The deterioration of specimens is followed up by investigating the change in weight and compressive strength of the specimens and techniques such as XRD and XRF are used to examine the chemical changes. Sulfuric acid is a very aggressive acid that reacts with the free lime [$Ca(OH)_2$] in the concrete forming gypsum($CaSO_{4}.2H_{2}O$). This reaction is associated with an increase in volume of the concrete, and the corroded surface becomes soft and white. The results showed that the OPC mortar caused an decrease in weight above 18% and strength loss about 57%. On the other hand, AASC(alkali-activated slag composites) did not cause any decrease in weight and in the case of strength caused an decrease below 10%. In addition, this mechanical results was verified to XRD and XRF.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.60-66
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• 2004

Hardness value decreased about 3% for annealed specimens and increased about 60% for one hour aged specimens. But the values of the other specimens aged two hours or more showed almost the same. The yield strength was the highest about 1,800㎫ in 0.06%Nb specimen having twice as much as the base meta1 specimen. Also, the elongation was the highest in 0.03%Nb specimen showing the same as base metal specimen. The higher aging temperature and the longer aging time, the higher fatigue life. On the other hand, the 0.03%Nb specimen showed the highest fatigue life which increased about 12% more than base metal specime. 0.06%Nb specimen aged at 482$^{\circ}C$ for 8 hours simultaneously satisfied the 250 grade strength and 200 grade elongation having the most superior mechanical properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.3
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• pp.287-291
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• 2006

This paper describes mechanical and electric properties of ACSR $410\;mm^2$ conductor from many of older overhead conductor. Samples of conductors itemized two division according to operation sector, green area, salt and pollution area. Samples of conductors operated various environment conditions have undergone laboratory metallurigical investigation and tensile strength torsional ductility and electrical performance. The steel core were found to have retained their original properties to a large degree in both tensile strength and the number of turns to failure. On the other hand the aluminum conductor showed reductions in tensile strength. To determine the remaining useful life of aged conductor, an unacceptable deterioration level has to established for each diagnostic procedure.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.29 no.4
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• pp.36-44
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• 1997

This experiment was mainly performed with a mechanical treatment using ultrasound. We got the following conclusions : At seven minutes-ultrasonic treatment using nonionic surfactant, yield, brightness and residual ink contents were superior to other treatment, but several strength properties were decreased. On the other hand anionic surfactant was considerably low ink removal efficiency. For ultrasonic treatment using nonionic surfactant, yield and brightness were dropped when temperature was over 4$0^{\circ}C$, but were observed to be insensitive to the pulp consistency and flotation time. In the case of nonionic surfactant, tensile and burst strength were improved when ultrasonic treatment was used comparing to non-treatment, and nonionic surfactant was generally better than anionic surfactant in terms of tensile and burst strength regardless of ultrasound conditions. Several properties were decreased when anionic surfactant was used in comparison with nonionic surfactant except yield, therefore, anionic surfactant. was not proper to be used in this condition.

• Journal of Surface Science and Engineering
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• v.27 no.3
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• pp.134-142
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• 1994

$Al_2O_3$coatings on mild steel substrate by plasma spray process were produced to evaluate microstructural characterization and mechanical properties. As-coated $Al_2O_3$coating samplessd were subjected to two heat treat-ment conditions : ⅰ) annealing under vacuum circumstance, ⅱ) hot press treated condition. The two heat treat-ed coatings were investigated in terms of microhardness, adhesion strength, wear resistance, porosity forma-tion, and microstructures. In the case of the coatings which were subject to preparation step ⅰ, the porosity in the coating was decreased with the increase of temperature ($700^{\circ}C$-$1100^{\circ}C$), and the wear resistance, microhardnesss and adhesion strength were increased with the increase of temperature. On the other hand, in the case of the coatings which were subject to preparation step ⅱ, wear resistance and adhesion strength were improved with the increase of temperature and pressure. Experimental measurements of coatings which were produced by both preparation conditions were enhanced compare to those of as-coated coatings.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1417-1423
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• 1995

α/β sialon based composites containing silicon nitride whisker and silicon carbide platelet were fabricated by hot pressing. Effect of the reinforcing agents on the α to β phase transformation of the sialon as well as on the mechanical properties was investigated. Silicon nitride whisker and silicon carbide platelet promoted the phse transformation. TEM/EDS analysis revealed that the grain containing the whisker had 'core-rim' structure; core being high purity Si3N4 whisker and rim being β-sialon. Flexural strength of the composite decreased with the reinforcement addition which, on the other hand, improved fracture toughness of it. High temperature strength was measured at 1300℃ to be about 130 MPa lower than that measured at RT for the whisker reinforced composites.

• Advanced Composite Materials
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• v.18 no.3
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• pp.287-295
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• 2009

$\beta$-Tricalcium phosphate ($\beta$-TCP) particles reinforced bioresorbable plastics poly-L-lactide (PLLA) composites were prepared by injection molding. The nominal weight ratio of $\beta$-TCP was selected as 5, 10 and 15%. In order to clarify effects of the PLLA crystallinity on the mechanical properties, the specimens were heat treated isothermally. Results of differential scanning calorimetry indicated that the PLLA crystallinity increased with increasing heat treatment temperature. Bending and compressive tests were conducted on the specimen with different $\beta$-TCP contents and crystallinities. The results show that the bending and compressive moduli increased with increasing $\beta$-TCP contents and crystallinity. On the other hand, bending strength decreased with increasing $\beta$-TCP contents. Maximum bending strength was obtained at the heat treatment of $70^{\circ}C$ for 24 h, whereas compressive 0.2% proof strength increased with increasing heat treatment temperature. This difference is attributed to the difference in the microscopic damages.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.141-142
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• 2019

As part of the recent low-energy policy, insulation standards for buildings are increasing every year. In addition, the conventional styrofoam heat insulation material has a problem in that the thickness of the heat insulation material to achieve the standard heat transmission rate is rapidly increased. Although the risk of spreading the structure vulnerable to fire due to insufficient spacing between buildings due to thickened insulation is increasing, the high cost of high efficiency insulation is difficult to solve. On the other hand, it is known that the method to be used as a formwork using insulation is excellent in cost reduction effect by reducing the amount of formwork used and simplifying the subsequent insulation work. The purpose of this study is to evaluate the strength characteristics of multi - layered insulation materials with appropriate strength by reducing the thickness of the insulation by appropriately combining high performance phenolic foam insulation and styrofoam insulation.