• Elastomers and Composites
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• v.41 no.1
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• pp.19-26
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• 2006

In this study, the effect of thermal aging temperature on the weight loss, glass transition temperature, and morphology of epoxy adhesives cured with amine (D-230), amide (G-5022), and anhydride (HN-2200) was investigated. As a result, the weight loss of three specimens was increased with increasing the thermal aging temperature. The result was attributed to the thermal aging which was occurred at the surface of adhesive specimens at high aging temperature, resulting in increasing the weight loss of the specimens. According to the DSC result, the glass transition temperature of DGEBA/D-230 and DGEBA/G-5022 samples war increased as the aging temperature increased, whereas the glass transition temperature of DGEBA/HN-2200 samples was constant above aging temperature of $150^{\circ}C$ and aging tine of 7 days. The SEM result indicated that the surface of DGEBA/G-5022 specimen showed more rough topography than that of DGEBA/D-230 or DGEBA/HN-2200 specimen after thermal aging. This could be correlated with the result of weight loss.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.5
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• pp.816-822
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• 2001

The thermoforming process is widely used in the plastics industry to produce articles for the packaging, automotive, domestic construction and leisure industries. The microcellular foaming process appeared at M.I.T. in 1980s to save a quantity of polymer materials and increase their mechanical properties. The glass transition temperature of polymer materials is one of many important process variables in appling the microcellular foaming process to the conventional thermoforming process. The goal of this research is to evaluate the relation between gas absorption and glass transition temperature in batch process using microcellular foaming process. The weight gain ratio of polymer materials has a conception of gas absorption. Polymers such as acrylonitrile-butadiene-styrene(ABS), polystyrene(PS) have been used in this experiment. According to conventional Chows model and Cha-Yoon model, it was estimated with real experimental result to predict a change of glass transition temperature as a function of the weight gain ratio of polymer materials in batch process to gain microcellular foamed plastic products.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.13-18
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• 2014

In order to clarify the effect of Nb addition on the ductile-brittle transition property of sintered TiC, TiC-10 mol% Nb composites were researched using a three-point bending test at temperatures from room temperature to 2020 K, and the fracture surface was observed by scanning electron microscopy. It was found that the Nb addition decreases the ductile-brittle transition temperature of sintered TiC by 300 K and increases the ductility. The room temperature bending strength was maintained at up to 1800 K, but drastically dropped at higher temperatures in pure TiC. The strength increased moderately to a value of 320MPa at 1600 K in TiC-10 mol% Nb composites, which is 40% of the room temperature strength. Pores were observed in both the grains and the grain boundaries. It can be seen that, as Nb was added, the size of the grain decreased. The ductile-brittle transition temperature in TiC-10 mol% Nb composites was determined to be 1550 K. Above 1970 K, yieldpoint behavior was observed. When the grain boundary and cleavage strengths exceed the yield strength, plastic deformation is observed at about the same stress level in bending as in compression. The effect of Nb addition is discussed from the viewpoint of ability for plastic deformation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.408-410
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• 2012

In this study, High temperature properties of carbon fiber reinforced composites is performed using strand specimens and resin specimens. As for the tensile test at the different temperature, the tensile modulus of resin specimens decreases slightly until the temperature reaches the glass transition temperature. but the tensile modulus of strand specimens maintains tensile modulus at the room temperature. The tensile strength of resin and strand specimens decreases rapidly until the temperature reaches the glass transition temperature.

• Progress in Superconductivity and Cryogenics
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• v.1 no.2
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• pp.37-42
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• 1999

The stability of high-temperature superconducting current leads for cryogenic devices are investigated. By assuming full transition from superconducting state to normal state at a transition temperature, the HTS current at a transition temperature, the HTS current lead shows bifurcation phenomenon. There is a bifurcation shape-factor, HTS leads have three steady state. Below the bifurcation shape-factor, the superconducting current lead is unconditionally stable, because there exists only one steady-factor HTS current lead is conditionally stable depending on the shape and intensity of disturbance.

• Polymer(Korea)
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• v.26 no.5
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• pp.653-660
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• 2002

The volume phase transition of poly(N-isopropylacrylamide) (PNIPAAm) and poly (N-isopropylacrylamide-co-sodium methacrylate) (P (NIPAAm-co-SMA)) hydrogels crosslinked with poly (ethylene glycol) diacrylate (PEGDA) was investigated in consideration of water content and surface area. The volume phase transition temperature of hydrogel was not affected by the concentration of crosslinking agent, which increased over 40$\^{C}$ by incorporating a small amount of SMA. Higher volume phase transition temperature was obtained when PEGAD was used as a crosslinking agent, suggesting that the chain length of crosslinking agent had a significant effect on the volume phase transition temperature. The surface area of PNIPAAm and P (NIPAAm-co-SMA) gels fell off around the volume phase transition temperature, resulting from the fact that the size of pores reduced remarkably in the course of the volume phase transition. Hence, the surface area and the pore size were considered to be important factors indicating the volume phase transition.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.8
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• pp.629-633
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• 2001

Electrical properties of the $\alpha$-In$_2$Se$_3$ single crystals grown by use of the Bridgman technique were examined in the transition temperature range between $\alpha$-phase and $\beta$-phase. $\alpha$-In$_2$Se$_3$ single crystal has ' the rhombohedral structure and lattice constants are a=4.025 $\AA$, c=28.771 $\AA$ in c-axis. The transition temperatures of the stoichiometric $\alpha$-In$_2$Se$_3$ single crystal is 198.8$^{\circ}C$ according to the specimens. The temperature of $\alpha$longrightarrow$\beta$ phase transition decreased but the temperature of $\beta$longrightarrow$\alpha$ phase transition increased as the number of heating-cooling cycle increased.

• Journal of the Korean Society for Heat Treatment
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• v.14 no.6
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• pp.345-349
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• 2001

This study has investigated the effect of thermal stability and mechanical property of $Fe_{80-X}P_{10}C_6B_4M_X$(X=2, 4, 6, M=transition metal) amorphous alloys fabricated by the melt-spun process. The glass transition temperature($T_g$), crystallization temperature($T_x$) and hardness increase with decreasing electron concentration (e/a) from about 7.38 to 7.18. The decrease of e/a implies the increase in the attractive bonding state between the M elements and other constituent element. The decrease in a/e leads to the enhancement of the attractive bonding state among the constituent elements which is favorable for the increase in $T_g$, $T_x$ and hardness.

• Composites Research
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• v.37 no.3
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• pp.215-218
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• 2024

Liquid crystalline thermosetting epoxy oligomer DD-A was synthesized with Diglycidyl ether of 4,4'-dihydroxy-α-methylstilbene (DGE-DHMS) and aniline in a ratio of 2:1 and cured with a catalytic curing agent, 1-Methyl Imidazole. The gelation times and vitrification times were measured to create Time-Temperature-Transition Diagrams with liquid crystalline phase changes. It was found that the gelation and vitrification times were decreased as the concentration of curing agent increased, and the vitrification curve showing a typical S-shape was confirmed.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.590-597
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• 2016

In this study, six kinds of low-carbon steel specimens with different ferrite-pearlite microstructures were fabricated by varying the Nb content and the transformation temperature. The microstructural factors of ferrite grain size, pearlite fraction, interlamellar spacing, and cementite thickness were quantitatively measured based on optical and scanning electron micrographs; then, Charpy impact tests were conducted in order to investigate the correlation of the microstructural factors with the impact toughness and the ductile-brittle transition temperature (DBTT). The microstructural analysis results showed that the Nb4 specimens had ferrite grain size smaller than that of the Nb0 specimens due to the pinning effect resulting from the formation of carbonitrides. The pearlite interlamellar spacing and the cementite thickness also decreased as the transformation temperature decreased. The Charpy impact test results indicated that the impact-absorbed energy increased and the ductile-brittle transition temperature decreased with addition of Nb content and decreasing transformation temperature, although all specimens showed ductile-brittle transition behaviour.