• Applied Chemistry for Engineering
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• v.25 no.2
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• pp.121-133
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• 2014

Block copolymers including ABA triblock architectures are useful as thermoplastic elastomers and toughened plastics depending on the relative glassy and rubbery content. These materials can be blended with other polymers and utilized as additives, toughening agents, and compatibilizers. Most of commercially available block copolymers are derived from petroleum. Renewable alternatives are attractive considering the finite supply of fossil resources on earth and the overall economic and environmental expenses involved in the recovery and use of oil. Furthermore, tomorrow's sustainable materials are demanding the design and implementation with programmed end-of-life. The present review focuses on the preparation and evaluation of new classes of renewable ABA triblock copolymers and also emphasizes on the use of carbohydrate-derived poly(lactide) or plant-based poly(olefins) having a high glass transition temperature and/or high melting temperature for the hard phase in addition to the use of bio-based amorphous hydrocarbon polymers with a low glass transition temperature for the soft components. The combination of multiple controlled polymerizations has proven to be a powerful approach. Precision-controlled synthesis of these hybrid macromolecules has led to the development of new elastomers and tough plastics offering renewability, biodegradability, and high performance.

• Journal of the Korean Wood Science and Technology
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• v.34 no.1
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• pp.23-31
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• 2006

X-ray transit materials with straight path and the its intensity is proportional to the density of materials. Therefore, X-ray has been extensively used as a nondestructive evaluation (NDE) method in various fields. This study was carried out for development of a portable X-ray CT (computed-tomography) system to detect deteriorations of wood members in buildings. Based on the results of our previous study, a procedure of CT image reconstruction was established In order to verify the applicability of developed system, CT images of three wood disks were reconstructed by newly developed procedure and compared with the prototypes. From the results of this study, it was shown that the newly developed system could be used not only to determine the shape, size, and position of defects, but also to find the density distribution in cross section of wood structure members. The density distribution may be utilized to clarify the reason of wood deterioration and to provide the preventive method on how to treat or repair wood buildings. Because it was initial stage of system development, there were some limitations concerned with measuring equipment and image reconstruction algorithm. Especially, measuring time including equipment setup time was longer and measuring accuracy was lower than we expected. Therefore, we planned some additional studies on improvement of equipment and algorithm to enhance the capability of X-ray CT system.

• Clean Technology
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• v.24 no.3
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• pp.190-197
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• 2018

Various waterborne polyurethanes (WPU) with three different types of polyol such as ester type polyol [adipic acid (A)/BD/3-methyl-1,5-pentandiol (MPD) and A/BD]//carbonate type polyol (C/HD/MPD, C/HD, C/BD)//ether type polyol (PTMG) were prepared in this study. This study focused on the effect of polyol type on the properties of WPU. Soft segment Tg (Tgs), 100% elastic modulus and tensile strength were highest when using carbonate polyol, followed by ester polyol and ether polyol, while those of elongation showed the opposite trend. The WPU synthesized with MPD - containing polyol showed lower Tgs, 100% elasticity and strength, and higher elongation than MPD - free WPU. The % transmittance and transparency of the WPU film containing the MPD component was superior to that of the WPU film containing no MPD component, and it was found that the film based on carbonate polyol was slightly better than the film based on ester polyol and ether polyol.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1438-1443
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• 2001

The significance of the casting/forging process for reducing the production cost of large components is being noted in these days. This casting/forging process is a method of forging a workpiece preformed by casting into the final shape. In this study, the casting/forging process has been applied in manufacturing a large aluminum flange in order to reduce press capacity and material cost. Firstly, a hot compression test was performed with cast cylindrical billets in order to determine the optimum forging condition of the aluminum flange. The optimum range of forging temperature of Al 5083 was from 420$\^{C}$ to 450$\^{C}$. The suitable strain rate was 1.5 sec(sup)-1. The deformation amount of a preform of a preform in a forging process is a key role in the mechanical properties of casting/forging products. In order to find the change of mechanical properties according to effective stain of cast aluminum billets, a hot upsetting test were performed with rectangular blocks and then a uniaxial tensile test was performed with specimens cut from the upsetted billets. The tensile strength and the elongation of cast/upsetted aluminum billets were increased largely until the effective strain was 0.7. FE analysis was performed to determine the configurations of case preform and die for an aluminum flange. In the FE analysis, the forging load-limit was fixed 1500ton for low equipment cost. The cast preform was designed so that the effective stain around the neck of a flange exceeded 0.7. From the result of FE analysis, optimal configurations of the cast preform and the die were designed for a large flange. The filling and solidification analysis for a sound cast-preform was carried out with MAGMA soft. In the forging experiment for an aluminum flange, it was confirmed that the optimal configuration of the cast preform predicted by FE analysis was very useful. The cast/forged products using designed preform were made perfectly without any defects.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.962-969
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• 1999

Elastic and elasto-plastic stress analyses of AlN/Cu and AlN/W pints produced by active-metal brazing method using Ag-Cu-Ti insert-metal were performed with use of Finite-Element-Method(FEM). The results of stress analyses were compared with those from the pint strength tests and the observations of fracture behaviors. It was shown that a remarkably larger maximum principal stress is built in the AlN/Cu pint compared to the A1N/ W joint. Especially, the stress concentration with tensile component was confirmed at the free surface close to the bonded interface of AlN/Cu. The elasto-plastic analysis under consideration of stress relaxation effect of Ag-Cu-Ti insert possessing a so-called 'soft-metal effect' showed that the insert leads to a lowering of maximum principal stress in AlNiCu pint, even though an increase of the insert thickness above 100$\mu\textrm{m}$ could not bring its further decrease. The maximum pint strengths measured by shear test were 52 and 108 MPa for AlNiCu and AlN/W pints. respectively. Typical fractures of AlN/Cu pints occurred in a form of 'dome' which initiated from the free surface of AlN close to the bonded interface and proceeded towards the AlN inside forming a large angle. AlN/W pints were usually fractured at AlN side along the interface of AlN/insert-metal.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.109-119
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• 2017

In this research, it was investigated that whether the upper sand deposited in Nakdong River Estuary Delta region has the role of horizontal drains like sand mat. The results from tests for particle size distribution and permeability of the upper sand deposit did not meet completely the criteria for the horizontal drain material. Thus, numerical analysis has been conducted additionally. Numerical analyses of consolidation of soft soils with upper layer of sand deposit are conducted in both the sand mat with a thickness of 1m and the upper sand deposit with 1, 2, 3, and 4 m of thickness and their results are compared. As the results of numerical analysis, the upper sand deposit with a thickness of 2m or more may play the role of horizontal drains similar to a sand mat. If a PVD is installed, the ability of upper sand deposit as horizontal drains is increased. Form this study, it was concluded that the upper sand deposited in Nakdong River Estuary Delta has the role of horizontal drain.

• Journal of Korea Water Resources Association
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• v.52 no.11
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• pp.905-916
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• 2019

This study explores the effect of mother wavelet in the bivariate wavelet analysis. A total of four mother wavelets (Bump, Mexican hat, Morlet, and Paul) which are frequently used in the related studies is selected. These mother wavelets are applied to several bivariate time series like white noise and sine curves with different periods, whose results are then compared and evaluated. Additionally, two real time series such as the arctic oscillation index (AOI) and the southern oscillation index (SOI) are analyzed to check if the results in the analysis of generated time series are consistent with those in the analysis of real time series. The results are summarized as follows. First, the Bump and Morlet mother wavelets are found to provide well-matched results with the theoretical predictions. On the other hand, the Mexican hat and Paul mother wavelets show rather short-periodic and long-periodic fluctuations, respectively. Second, the Mexican hat and Paul mother wavelets show rather high scale intervention, but rather small in the application of the Bump and Morlet mother wavelets. The so-called co-movement can be well detected in the application of Morlet and Paul mother wavelets. Especially, the Morlet mother wavelet clearly shows this characteristic. Based on these findings, it can be concluded that the Morlet mother wavelet can be a soft option in the bivariate wavelet analysis. Finally, the bivariate wavelet analysis of AOI and SOI data shows that their periodic components of about 2-4 years co-move regularly every about 20 years.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.6
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• pp.599-615
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• 2022

In order to excavate underground tunnel most safely such as Han river, the slurry shield TBM method is applied to cope with face of high water pressure for many metro projects. In downtown subway project most of excavated soil is discharged externally whereas in road construction excavated soil is used as filling materials so it becomes important factor for success of the project. After excavated soil, weathered rock and soft rock are discharged with bentonite through discharge pipe to slurry treatment plant then those soils are separated in separation plant according to those size. Fine grained soil has been discarded together with filter cake but it is not toxic and can be mixed with coarse aggregate in proper ratio so this study is performed to find use of qualified filling material to meet quality standard. Therefore, in this study, legal standards and quality standards for the utilization of excavated soil of the slurry shield TBM method were examined and test was conducted to derive recycling way for filter cake and aggregate. And a plan for using it as a filling material for road construction was derived. Because bentonite is a clay composed of montmorillonite, and the excavated soil in the tunnel is also non-toxic, disposal of this material can waste social cost so it is expected to be helpful in the underground space development project that carries out the TBM project by recycling it as a valuable resource.

• Clean Technology
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• v.25 no.1
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• pp.7-13
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• 2019

Recently, attention has been paid to obtaining bio-polyols from renewable resources. Successful use of these natural ingredients successfully produced in the industry for the synthesis of various polyurethanes is a very important task. In this study, a series of dimethylformamide (DMF) based polyurethanes were synthesized from methylene diphenyl diisocyanate (MDI)/1, 4-butanediol and bio-polyol (polytrimethylene ether glycol based on 1, 3-propanediol : B-POL)/polyester polyol (polyadipate diol based on 1,4-butandiol : H-PET). The effect of different ratio of bio-polyol (B-POL)/polyester polyol (H-PET) on the physical properties of polyurethane was investigated. As the B-POL content in B-POL/H-PET mixture increased, the glass transition of soft segment (Tgs) and tensile strength of polyurethane decreased, however, the elongation at break and tear strength increased. On the other hand, artificial leather was produced by wet process using synthesized DMF-based polyurethanes. It was found that there was almost no difference in the effect of the B-POL/H-PET composition on the average size and density (the number of cells per unit volume) of the porous cells formed in artificial leather. These results show that there is no problem in using bio-polyol (B-POL) based polyurethane for artificial leather produced by wet process.

• Fire Science and Engineering
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• v.33 no.2
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• pp.68-78
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• 2019

In modern society, the paradigm of terrorism is shifting to the form of soft targets focusing on an unspecified number of people, which is different from previous terrorist tendencies, and frequent attacks using chemicals. Therefore, this study analyzed the evacuation environment and characteristics, manual analysis of a terror response manual, and the domestic chemical management status of multi-use facilities, and proposed the following management measures for chemical terror prevention in multi-use facilities. First, a multi-use facility guideline for prompt onsite response is proposed. Second, an improvement plan is suggested through the analysis of the manual for counter terrorism. Third, integrated management is proposed through the selection of chemicals available for terrorism. Through this, it is expected that an additional improvement plan will be prepared for countermeasures against chemical terrorism in multi-use facilities. In the future, it will be necessary to analyze the problems through cases of foreign countries and take customized countermeasures.