• Composites Research
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• v.18 no.4
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• pp.14-20
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• 2005

To determine the effect of chemical structure of aromatic amino curing agents on thermal and mechanical properties, standard epoxy resin DGEBF (diglycidylether of bisphenol F) was cured with diaminodiphenyl methane (DDM) and diaminodiphenyl sulphone (DDS) in a stoichiometrically equivalent ratio. From this work the effect of aromatic amino curing agents on the thermal and mechanical properties is significantly influenced by the chemical structure of curing agents. In contrast, the results show that the DGEBF/DDS system having the sulfone structure between the benzene rings had higher values in the thermal stability, density, shrinkage ($\%$), thermal expansion coefficient, tensile modulus and strength, flexural modulus and strength than the DGEBF/DDM system having methylene structure between the benzene rings, whereas the DGEBF/DDS system presented low values in maximum exothermic temperature, conversion of epoxide, and grass transition temperature. These results are caused by the relative effects of sulfone group having strong electronegativity and methylene group having (+) repulsive property. The result of fractography shows that the grain distribution of DGEBF/DDS system is more irregular than that of the DGEBF/DDM system.

• Composites Research
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• v.33 no.4
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• pp.220-227
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• 2020

When curing the composite, the fibers have little thermal deformation, but the resin changes its properties with time and temperature, which leads to residual stress in the product. Residual stress is caused by the difference in the coefficient of thermal expansion of the fibers and resin during the curing process and the chemical shrinkage of the resin. This difference causes thermal deformation such as spring-in and warpage. Thermal deformation of composite structure is important issue on quality of product, and it should be considered in manufacturing process. In this study, a subroutine was developed to predict thermal deformation by applying 3-D viscoelastic model. The finite element analysis was verified by comparing the results of the plate analysis of the 2-D viscoelastic model. Spring-in of L-shaped structure was predicted and analyzed by applying the 3-D viscoelastic model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.4
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• pp.779-789
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• 2015

Because cable-supported bridges have long spans and large members, their movements and geometrical changes by temperatures tend to be bigger than those of small or medium-sized bridges. Therefore, it is important for maintenance engineers to monitor and assess the effect of temperature on the cable-supported bridges. To evaluate how much the superstructure expands or contracts when subjected to changes in temperature is the first step for the maintenance. Thermal movements of a cable-stayed bridge in service are evaluated by using long-term temperatures and displacements data. Displacements data are obtained from extensometers and newly installed GNSS (Global Navigation Satellite System) receivers on the bridge. Based on the statistical data such as air temperatures, each sensor's temperatures, average temperatures and effective temperatures, correlation analysis between temperatures and displacements has been performed. Average temperatures or effective temperatures are most suitable for the evaluation of thermal movements. From linear regression analysis between effective temperatures and displacements, the variation rate's of displacement to temperature have been calculated. From additional regression analysis between expansion length's and variation rate's of displacement to temperature, the thermal expansion coefficient and neutral point have been estimated. Comparing these parameters with theoretical and analytical results, a practical procedure for evaluating the real thermal behaviors of the cable-supported bridges is proposed.

• Journal of the Korean Geosynthetics Society
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• v.23 no.1
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• pp.39-47
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• 2024

In this study, physical property tests and standard consolidation tests were conducted on the marine clay of Busan New Port and North Port, the middle and lower reaches of the Nakdong River including Gimhae and Yangsan, and Ulsan regions. The moisture content, a property unrelated to sample disturbance with small individual test errors, was used for regression analysis with the compression index, virgin compression index, consolidation coefficient, expansion index, and secondary compression index, among others. Subsequently, the correlation and accuracy were evaluated. Upon analyzing the correlation between the moisture content, void ratio, and liquid limit commonly used physical properties for calculating compression indexes, it was confirmed that the liquid limit had the lowest correlation. Through a linear regression analysis of the consolidation constants using the current moisture content in the natural state, a high correlation was demonstrated. Relationship equations were then presented to determine settlement and settlement time. This study suggests that moisture content can be utilized as an alternative for evaluating and calculating consolidation constants when examining ground settlement in sedimentary clays distributed in the Busan and Gyeongnam regions.

• Applied Chemistry for Engineering
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• v.17 no.1
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• pp.73-81
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• 2006

Heat treatment condition for the stabilization of foamed glass block through the foaming process of the hydrolized waste glass was investigated and scale-up test for the manufacturing of foamed glass was also attempted for the actual foaming process. Proper heat treatment condition was quenching from the foaming temperature to $550{\sim}600^{\circ}C$ for stabilization, and then annealing from stabilization temperature to $200^{\circ}C$ and holding up at $200^{\circ}C$ for removal thermal stress, and then annealing to the room temperature with cooling speed of $0.3^{\circ}C/min$. Through this heat treatment conditions, foamed glass block with size of $250mm{\times}250mm{\times}90mm$ was produced successfully. The properties of this foamed glass block showed density of $0.28{\pm}0.06g/cm^3$, thermal conductivity of $0.048{\pm}0.005kcal/hm^{\circ}C$, moisture absorption of $0.5{\pm}0.09vol%$, linear expansion coefficient of $(8.6{\pm}0.2){\times}10^{-6}m/m^{\circ}C$($400^{\circ}C$), flexural strength of $15.0{\pm}0.6kg/cm^2$, and compression strength of $39.5{\pm}0.6kg/cm^2$.

• Journal of the Korean Chemical Society
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• v.12 no.2
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• pp.65-80
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• 1968

The physico-chemical properties of nine selected thallium borosilicate glasses and other 21 supplementary compositions were investigated. Their composition-property curves are found to be in many respects analogous to those of other borosilicate glasses containing lithia, soda, and lead oxide. It is indicated that certain minima found in the composition-property curves of thallium borosilicate glasses might be caused by a change in boron coordination as has been observed to occur in the $Na_2O-B_2O_3-SiO_2$ glasses. Typical effects of thallium ions on the borosilicate glass are summarized as follows: 1) Addition of thallium ions increased density, refractive index, water solubility, linear coefficient of thermal expansion, and dielectric constant. 2) Increased concentration of thallium decreased the softening point of the glasses, caused fluorescence under ultraviolet radiation and smeared out the absorption edges up to $15{\mu}$ in the infrared region. An extensive liquid immiscibility was found by replication electron microscope technique in the $Tl_2O-B_2O_3-SiO_2$ system. The immiscibility covers a composition range roughly from 55 wt. % Tl2O to the binary system $B_2O_3-SiO_2.$ By acid treatment, it was found that the immiscible glass consists of separate silica-rich and boron-rich phases.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.3
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• pp.139-148
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• 2000

In this paper, the interaction of oblique incident waves with a bottom-mounted and fluid-filled flexible membrane structure is investigated in the frame of linear hydro-elastic theory. The static shape of a membrane structure containing the fluid of a specific density is initially unknown and must be calculated before the hydrodynamic analysis. To solve hydrodynamic problem, the fluid domain is divided into the inner and outer region. The inner solution based on discrete membrane dynamic model and simple-source distribution over the entire fluid boundaries is matched to the outer solution ba~ed on an eigenfunction expansion method. The numerical results were compared to a series of Ohyama's experimental results. The measured reflection and tran¬smission coefficients reasonably follow the trend of predicted values. Using the computer program developed, the performance of a bottom-mounted and fluid-filled flexible membrane strocture is tested with various system parameters (membrane shape, internal pressure, density ratio) and wave characteristics (wave frequencies, incident wave angle). It is found that a bottom-mounted and fluid-filled flexible membrane structure can be an effel;tive wave barrier if properly designed.

• Korean Journal of Agricultural and Forest Meteorology
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• v.21 no.1
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• pp.29-41
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• 2019

Terrestrial Gross Primary Production (GPP) is the largest global carbon flux, and forest ecosystems are important because of the ability to store much more significant amounts of carbon than other terrestrial ecosystems. There have been several attempts to estimate GPP using mechanism-based models. However, mechanism-based models including biological, chemical, and physical processes are limited due to a lack of flexibility in predicting non-stationary ecological processes, which are caused by a local and global change. Instead mechanism-free methods are strongly recommended to estimate nonlinear dynamics that occur in nature like GPP. Therefore, we used the mechanism-free machine learning techniques to estimate the daily GPP. In this study, support vector machine (SVM), random forest (RF) and artificial neural network (ANN) were used and compared with the traditional multiple linear regression model (LM). MODIS products and meteorological parameters from eddy covariance data were employed to train the machine learning and LM models from 2006 to 2013. GPP prediction models were compared with daily GPP from eddy covariance measurement in a deciduous forest in South Korea in 2014 and 2015. Statistical analysis including correlation coefficient (R), root mean square error (RMSE) and mean squared error (MSE) were used to evaluate the performance of models. In general, the models from machine-learning algorithms (R = 0.85 - 0.93, MSE = 1.00 - 2.05, p < 0.001) showed better performance than linear regression model (R = 0.82 - 0.92, MSE = 1.24 - 2.45, p < 0.001). These results provide insight into high predictability and the possibility of expansion through the use of the mechanism-free machine-learning models and remote sensing for predicting non-stationary ecological processes such as seasonal GPP.

• Composites Research
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• v.12 no.4
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• pp.71-78
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• 1999

To determine the effect of chemical structure of linear amine curing agents on thermal and mechanical properties, standard epoxy resin DGEBA was cured with diaminodiphenyl methane (DDM), diaminodiphenyl sulphone (DDS) in a stoichiometrically equivalent ratio. From this work, the effect of aromatic amine curing agents. In contrast, the results show that the DGEBA/DDS cure system having the sulfone structure between the benzene rings had higher values in the conversion of epoxide, density, shrinkage (%), glass transition temperature, tensile modulus and strength, flexural modulus and strength than the DGEBA/DDM cure system having methylene structure between the benzene rings, whereas the DGEBA/DDM cure system presented higher values in the maximum exothermic temperature, thermal expansion coefficient, and thermal stability. These results are caused by the relative effects of sulfone group having strong electronegativity and methylene group having (+) repulsive property and stem from the effect of the conversion ratio of epoxide group. The result of fractography shows that the each grain size of the DDM/DGEBA system with feather-like structure is larger than that of the DDS/DGEBA system.