Jo Oct 13, 2025
Welding has been widely used in many fields of industry. Its advantages include high efficiency of joining, simple operation, good flexibility and low cost. However, uneven temperature distribution inevitably exists during welding. Such uneven temperature distribution causes rapid thermal expansion, which leads to heterogeneous plastic deformation by thermal constriction in and near the welding joint. Thus, residual stress appears in welding structure after cooling.
In order to accurately predict welding residual stress and deformation, welding temperature distribution should be simulated properly. What is important in welding simulation is to apply suitable heat source models according to the welding methods. The models include spot heat source model, line heat source model (HSM), surface heat source model and volume heat source model. As heat is transferred to workpieces in the form of volume in most welding methods, volume HSM is most widely used. Volume HSM is classified into semi-sphere HSM, elliptical heat source model and double-elliptical heat source model. At present, double-elliptical model is accepted as the most appropriate heat source model for gas metal arc welding (GMAW) with steep temperature slope at the front section of the welding pool and smooth slope at the rear section.
Cha Kwang Jin, a researcher at the Faculty of Materials Science and Technology, has performed a welding temperature simulation by FEM and predicted temperature distribution while varying welding parameters such as welding current.
For the simulation, he employed ANSYS software widely used for welding simulations across the world that offers the most approximate parameters to the desired result by varying several parameters of its own optimization module.
The FEM analysis results and experiment results of welding show that the analysis result is accurate when Gauss-distributed double-elliptical heat source for GMAW process simulation is used.
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Jo Oct 9, 2025
Recently, attempts have been made to use fiber-reinforced plastic composites as aircraft structural materials, but aluminum alloys still have 70% utilization as airborne fuselage materials. In particular, high-alloy duralumin Du16 has been used as the main material for manufacturing aircraft fuselage surfaces and blades.
The body material of an airplane varies in its nature with the speed of flight, so it is very important to determine whether a given alloy can be used as a body material for subsonic and supersonic aircrafts.
Previous studies show that the grain growth of duralumin alloy at annealing temperatures above 300 °C leads to poor mechanical properties, but they failed to deal with annealing at temperatures below that. What is more, they did not cover the changes in the texture and property with temperature when the body of an airplane is heated during the flight.
Therefore, Ri Hyon Song, a researcher at the Faculty of Materials Science and Technology, has measured the fuselage heating temperature range by means of simulation analysis and investigated the changes in the texture and property with annealing temperature.
First, he designed a model of a supersonic aircraft and conducted a simulation analysis of the temperature distribution of the body surface according to flight speed. Then, he performed hardness and microstructure observation experiments.
The results showed that Du16 alloy does not degrade its hardness at 100℃ for 8 hours of annealing, and above 300℃, the hardness is gradually degraded with time.
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Jo Oct 8, 2025
Hyonmu Gate is the north gate of the northern castle of the Walled City of Pyongyang of Koguryo on Moran Hill.
The gate was named after the mythological turtle symbolizing the God of the North, one of the four gods in charge of the four directions.
It was first built in the sixth century when the Walled City of Pyongyang was being built during the Koguryo dynasty and underwent repair and rebuilding several times during the Koryo dynasty. The present gate was rebuilt in 1714. After that, it underwent thorough repairs in 1855 and 1954.
The gate is made up of an embankment, the extension of the castle wall, and a tower on it.
Like the castle wall, the embankment is built with stones faced in the form of quadrangular pyramid that are placed one upon another to avoid longitudinally straight joint lines. There is an arched gate in the middle of it.
There are battlements on the embankment that is about 2.5 meters tall. The gatehouse is a single-eaves gabled house which is three kans (7.05m) in length and one kan in width.
Hyonmu Gate is a precious cultural legacy demonstrating the ardent patriotism and advanced castle gate architecture of the Korean ancestors.
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Jo Oct 6, 2025
Electrospinning is widely used as a versatile and convenient method for producing nanofibers. However, the drawback of this method is its low productivity. To overcome this drawback, various kinds of electrospinning methods have been developed. They are divided into two broad sorts. One is multi-needle electrospinning, which uses a spinneret consisting of many needles, and the other is needleless electrospinning. Multi-needle electrospinning finds its wide application in the field of advanced materials as it enables controlling the properties of nanofibers as well as producing special kinds of nanofibers such as core-shell nanofibers.
In multi-needle electrospinning, strong electrical interaction between the spinneret needles caused by the increased number of nozzles breaks the uniformity of electric field at the spinneret needle tip, which consequently destabilizes the flow of polymer jet and degrades the quality of fibers. Therefore, keeping the electric field uniform at the spinneret needle tip is a key factor for obtaining good-quality nanofibers.
There have been many studies so far to improve the uniformity of electric field. However, few of them dealt with optimal structure parameters to maximize the uniformity of electric field at the spinneret needle tip. In addition, there are almost no reports on the investigation of uniformity of electric field while varying the parameters of a dielectric medium such as the length, the diameter and the relative permittivity when it is inserted between spinneret needles.
Jang Kum Chol, a researcher at the Institute of Nano Science and Technology, has investigated the effects of geometric parameters of a dielectric medium around the spinneret needle on electric field uniformity in order to obtain uniform electric field distribution at the spinneret needle tip.
He simulated the electric field distribution using COMSOL Multiphysics 5.4 and optimized the dielectric medium parameters to improve the electric field uniformity by using Taguchi method.
As a result, he has confirmed that the electric field uniformity is the best when the diameter, length, arrangement distance and relative permittivity of a dielectric medium are 1.5mm, 5mm, 4mm and 2.3, respectively.
After optimization, the uniformity was over 1.27 times higher than before optimization.
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Jo Oct 5, 2025
Yut-game is a folk game in which players compete with each other moving pieces on the board as indicated by the faces of sticks.
It is one of the typical folk games enjoyed by the Korean people from olden times.
The terms used in the game “to”, “kae”, “kol”, “yut” (“shyung”) and “mo” are said to have originated from the job titles of the Puyo dynasty or from the purposes of breeding five kinds of domestic animals―pig, dog, sheep, cow and horse―distributed to five villages.
The yut-game is played with four sticks.
The sticks were usually made of wood, and chestnuts and beans were also used instead of wood sticks.
Round straight wood sticks 2 centimeters in diameter and 10-15 centimeters long were split in two semi-circle sticks for the game.
Who moved pieces round more on the board than opponents as indicated by the faces of sticks was the winner.
The yut-game, which has been enjoyed by the Korean people from olden times, is still being widely played on public holidays including the Lunar New Year’s Day.
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Jo Oct 2, 2025
Research on temperature field is of great importance for hot-pressing processes of ceramic materials. It affects both the uniformity of materials and the properties of ceramic products. Additionally, non-uniformity causes formation of thermal residual stresses during sintering.
Previous works mostly focused on the sintering of traditional ceramics and very few of them aimed at the hot pressing of modern ceramic materials.
Mun Hyok Chol, a researcher at the Faculty of Chemical Engineering, has proposed a heat transfer model for a system comprised of the mixture of Al2O3 and TiB2 and a graphite mould. Then, he has established a new method of determining the coefficient of heat transmission of ceramic composite by taking into account the change of porosity with sintering temperature, and simulated the temperature field using the COMSOL Multiphysics software.
He set the most suitable heating rate as 0.5K/s by analyzing both material properties and manufacturing efficiency.
The simulation result has shown increased initial relative density of blanks and more uniform temperature distribution of the system during hot pressing, which leads to further improvement of the physical and mechanical properties of ceramic composite materials.
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