• Elastomers and Composites
• /
• v.51 no.2
• /
• pp.147-153
• /
• 2016

Polyvinyl chloride (PVC) has been used as a general-purpose polymer because of its lower cost, good durability and mechanical properties compared to other materials. However, PVC is vulnerable to heat deformation and generates a toxic gas like hydrogen chloride. Therefore, it is important to delay or prevent the flame retardancy and thermal degradation of the PVC during the processing. It was reported that aluminum trihydroxide (ATH) improved flame retardancy as well as smoke inhibition of the virgin polymer. In this study, PVC composites by addition of ATH were compounded in a modular intermeshing co-rotating twin screw extruder. The PVC composites with different concentrations of ATH (0~5 phr) were analyzed. Flame retardancy of the PVC composite significantly increased depending on the ATH concentration. LOI of the composite also increased with the concentration of ATH. There were no significant differences for the thermal properties of the PVC composites with ATH.

• Wind and Structures
• /
• v.28 no.4
• /
• pp.255-270
• /
• 2019

Aerodynamic configurations of bridge decks have significant effects on the aerostatic torsional divergence and flutter forsuper long-span bridges, which are onset for selection of suitable bridge decksfor those bridges. Based on a cable-stayed bridge with double main spans of 1500 m, considering typical twin-box, stiffening truss and closed-box section, which are the most commonly used form of bridge decks and assumed that the rigidity of those section is completely equivalent, are utilized to investigate the effects of aerodynamic configurations of bridge decks on aerodynamic instability performance comprised of the aerostatic torsional divergence and flutter, by means of wind tunnel tests and numerical calculations, including three-dimensional (3D) multimode flutter analysis and nonlinear aerostatic analysis. Regarding the aerostatic torsional divergence, the results obtained in this study show twin-box section is the best, closed-box section the second-best, and the stiffening truss section the worst. Regarding the flutter, the flutter stability of the twin-box section is far better than that of the stiffening truss and closed-box section. Furthermore, wind-resistance design depends on the torsional divergence for the twin-box and stiffening truss section. However, there are obvious competitive relationships between the aerostatic torsional divergence and flutter for the closed-box section. Flutter occur before aerostatic instability at initial attack angle of $+3^{\circ}$ and $0^{\circ}$, while the aerostatic torsional divergence occur before flutter at initial attack angle of $-3^{\circ}$. The twin-box section is the best in terms of both aerostatic and flutter stability among those bridge decks. Then mechanisms of aerostatic torsional divergence are revealed by tracking the cable forces synchronous with deformation of the bridge decksin the instability process. It was also found that the onset wind velocities of these bridge decks are very similar at attack angle of $-3^{\circ}$. This indicatesthat a stable triangular structure made up of the cable planes, the tower, and the bridge deck greatly improves the aerostatic stability of the structure, while the aerodynamic effects associated with the aerodynamic configurations of the bridge decks have little effects on the aerostatic stability at initial attack angle of $-3^{\circ}$. In addition, instability patterns of the bridge depend on both the initial attack angles and aerodynamic configurations of the bridge decks. This study is helpful in determining bridge decksfor super long-span bridges in future.

• Economic and Environmental Geology
• /
• v.40 no.4
• /
• pp.461-471
• /
• 2007

A temperature of deformation and the state and direction of paleostress at that time when twins in calcite grains had been produced were observed, using analysis of calcite twins as indicators of paleostress history. The study was performed with the target of carbonate rocks distributed randomly small size in the southern area of south Korea. Considering the appearance of twins (thin or thick straight twins with one or two twin sets), average twin strain (1.235-7.453%), thickness ($0.77-1.94{\mu}m$) and intensity (25.26-41.99 twins/mm) from the results of calculated calcite twins, it is estimated that calcite twins were produced under temperatures lower than approximately $150-200^{\circ}C$. In the magnitudes and directions of principal strains, the maximum shortening strain axis ($e_3\leftrightarrow{\sigma}_1$) is approximately N-S direction in the GS-1 area in the southern Gyeongsang Basin as well as in the BS-1 area in the southern Yongnam Massif, whereas E-W direction in the NR-1 area in the southwestern Ogcheon Fold Belt. In case of the maximum extension strain axis ($e_1\leftrightarrow{\sigma}_3$), it is oriented in NW-SE and NE-SW directions in the GS-1 and BS-1 area, respectively, and in N-S direction in the NR-1 area. That is, it is suggested that the paleostress which produced the calcite twins may be applied at least more than two times in the study area.

• Advances in materials Research
• /
• v.5 no.2
• /
• pp.121-130
• /
• 2016

In an attempt to reach a balance of performances in homo-polypropylene based system, the effects of single and hybrid reinforcements inclusions comprising calcium carbonate nanoparticles (2, 4 and 6 phc) and glass fibers (10 wt.%) on the mechanical and thermal properties were investigated. Different samples were prepared by employing twin-screw extruder and injection molding machine. In morphological studies, the uniform distribution of glass fibers in PP matrix, relative adhesion between glass fibers and polymer, and existence of nanoparticles in polymer matrix were observed. $PP/CaCO_3$ (6 phc) as compared to pure PP and PP/GF had superior tensile and flexural strengths, impact resistance and deformation temperature under load (DTUL). $PP/GF/CaCO_3$ (6 phc) composite displayed comparable tensile and flexural strengths and impact resistance to neat PP, while its tensile and flexural moduli and deformation temperature under load (DTUL) were 436%, 99% and $26^{\circ}C$greater respectively. The maximum impact resistance was observed in $PP/CaCO_3$(6 phc). The highest DTUL was perceived in PP hybrid nanocomposite containing 10 wt.% glass fiber and 4 phc $CaCO_3$ nanoparticle.

• Journal of the Korean Society for Precision Engineering
• /
• v.14 no.12
• /
• pp.73-85
• /
• 1997

The rolling force and roll deformation behavior in the twin roll type strip continuous casting process has been computed to estimate the thermal charcteristics of a caster roll. To calculation of rolling force, the relationship between flow stress and strain for a roll material and casting alloy are assumed as a function of strain-rate and temperature because mechanical properties of a casting materials depends on tempera- ture. The three dimensional thermal dlastic-plastic analysis of a cooling roll has also been carried out to obtain a roll stress and plastic strain distributions with the commercial finite element analysis package of ANSYS. Temperature fields data of caster roll which are provided by authors were used to estimated of roll deformation. Roll life considering thermal cycle is calculated by using thermal elastic-plastic analysis results. Roll life is proposed as a terms of a roll revolution in the caster roll with and without fine failure model on the roll surface. To obtain of plastic strain distributions of caster roll, thermomechan- ical properties of roll sleeve with a copper alloy is obtained by uniaxial tensile test for variation of temperature.

• Tunnel and Underground Space
• /
• v.23 no.2
• /
• pp.130-140
• /
• 2013

In this study, scaled model tests were performed to investigate the stability of twin tunnels with small clearance, where the pillar widths were 0.5D and 0.25D, respectively. The tunnels were supposed to be constructed in anisotropic weathered rocks with $30^{\circ}$ inclined bedding planes, and the model tests were conducted under the condition of lateral pressure ratio, 1. Six types of test models which had respectively different pillar widths and support conditions were experimented, where crack initiating pressures, maximum pressures, failure modes of pillar and deformation behaviors around tunnels were investigated. The models with wider pillar were cracked under higher pressure than the models with shallower pillar. The models with lining support were cracked under higher pressure and showed less tunnel convergence than the unsupported models. The models with both lining and pillar reinforcement were proved to be most stable among the tested models. In particular, as the model of 0.25D pillar width with only lining support showed shear failure of pillar according to the existing bedding planes, so both lining and pillar reinforcement were thought to be indispensable in that case of tunnel.

• The Journal of Natural Sciences
• /
• v.7
• /
• pp.83-90
• /
• 1995

The microstructural and textural development during rolling is compared in two Hadifield's steels (high Mn steel), one having low carbon content (0.65 wt.%) and the other high carbon (1.35 wt.%).In low carbon Hadfield's steel (LCHS) mixed microstructures are formed which contain intrinsic stacking faults, deformation twins, and brass type shear bands. The deformation twins are thought to be formed by the stacking of intrinsic stacking faults. The similar development to 70-30 brass texture is observed in early deformation. However the abnormal texture is developed after 40 % deformation, which is thought to be due to the martensite phase transformation. In high carbon Hadfield's steel (HCHS) mixed substructures of dislocation tangles, deformation twins, and shear bands (both copper and brass type) are found to develop. The texture development is similar to that of 70-30 brass. This is consistant with no carbon segregation and no martensitic phase transformation in HCHS. In spite of the difference of substructure and texture development during rolling in two steels, the difference in stacking fault energy is measured to be small ($2 mJm^-2$). The carbon segregation is only occurred in LCHS. Thus it is thought that the carbon segregation influence the microstructure and texture development during rolling. This is related with martensite phase transformation in LCHS.

• Journal of the Korean Society for Heat Treatment
• /
• v.7 no.1
• /
• pp.44-52
• /
• 1994

In order to investigate the effect of tempring treatment on the mechanical properties of ausformed martensite in Fe-30%Ni-0.35%C alloy, the hardness, yield strength and elongation were examined by tensile test. 1. The strength of deformed austenite in Fe-30%Ni-0.35%C alloy was increased due to the work hardening induced from the dislocation density increased during deformation. The strength of ausformed martensite was increased because of defects inherited from deformed austenite by martensitic transformation. 2. The ductility of ausformed martensite was shown a nearly constant values independent of deformation degrees because of the interaction of multiple factors such as increased retained austenite, formation of void and decrement of twin in ausformed martensite. 3. The strength of ausformed martensite by tempering treatment was shown a little decrement up to $340^{\circ}C$, especially showed remarkable softening resistance in higher deformation degrees. 4. Virgin martensite and ausformed martensite were shown a maximum yield strength by clustering in tempering at $100^{\circ}C$ and above $100^{\circ}C$, yield strength was very small decreased due to the decrement of solute carbon by the destruction of clustering. 5. The decomposition of retained austenite was not shown up to $450^{\circ}C$ in ausformed martensite with tempering treatment, and the matrix was rapidly softening because of the decomposition of martensite and the formation of reversed austenite with tempering above $400^{\circ}C$.

• Korean Journal of Metals and Materials
• /
• v.49 no.2
• /
• pp.112-120
• /
• 2011

The out-of-phase thermo-mechanical fatigue (OP TMF) in a <001> oriented single crystal nickel-based superalloy CMSX-4 has been studied. OP TMF life was less than a half of low cycle fatigue(LCF) life in spite of a small hysteresis loop area of OP TMF compared to that of LCF. The failure was caused by the initiation of a crack at the oxide-layered surface followed by its planar growth along the <100> ${\gamma}$ channel in both LCF and OP TMF. However, deformation twins appeared near the major crack of OP TMF. The multiple groups of parallel twin plates on {111} planes provided a preferential path for crack propagation, which caused a significant decrease in OP TMF life. Additionally, the analysis on the surface crack morphology revealed that the tensile strain at the minimum temperature of OP TMF was found to accelerate the crack propagation.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.12 no.5
• /
• pp.187-197
• /
• 2004

This paper presents the effects of cylinder shell elasticity on effective bulk modulus of oil $K_e$ in automotive hydraulic dampers. A theoretical model of cylinder shell bulk modulus $K_c$ based on the elasticity theory of thick-walled cylinder incorporating not only radial but longitudinal deformation is proposed. In a cylinder, values of $K_c$ by the new model and traditional models are computed and the discrepancies among them are discussed. In a twin-tube type automotive damper, the variation of $K_e$ under different pressure values in chambers of the damper cylinder, based on different theoretical models for $K_c$ is computed. Through these computations, it is shown that remarkable discrepancies in computed values of $K_e$ might occur according to the $K_e$ models in connection with $K_c$ models.