Brilliant LeaderShip

Story of Mullet Soup Cooked with Cold Water

One morning in April several decades ago, President Kim Il Sung called an official to acquaint himself with the preparation for a consultant meeting which was due that morning. Calling upon him to ...

Exposed to Rain Bright and Early

Little rain in spring is one of the typical climate features of our country. One year some decades ago, very little rain fell throughout the country until the beginning of April. On April 14 ...

Chicken and Eggs Returned

One day in April, Juche 40(1951), in the midst of the Fatherland Liberation War, President Kim Il Sung learnt that the officials were doing some preparation for his birthday and called one ...

Brilliant Lineage

It happened on a day before the parade for marking the 35th anniversary of the Victorious Pochonbo Battle. Chairman Kim Jong Il visited a unit of the Korean People’s Army (KPA) and went ...

On Munsu Hill

It was April 6, Juche 36(1947). On the day President Kim Il Sung climbed Munsu Hill after attending a grand commemoration ceremony of tree-planting. The President was heartbroken at the sight of the ...

Spring Fragrance on International Women’s Day

On March 8 over a decade ago, there was a performance in the presence of Chairman Kim Jong Il. The women who were enjoying the performance together with him could ...

News

Jo Apr 23, 2024

300M steel is a typical ultra-high strength steel with very high strength, excellent fracture toughness, good fatigue strength and stress corrosion resistance, and thus it has found expansive applications in the manufacture of key components of military and civil aircrafts.

300M steel can be formed into complex-shaped parts such as landing gears which are one of the four core components of aircraft, as well as into sheet or rod. However, deformation of 300M steel should be performed at elevated temperatures because of its high strength and limited ductility.

In recent years, some scholars have established constitutive models to predict the hot deformation behavior in ultra-high strength steels. Unfortunately, few studies on phenomenological models for 300M steel have been conducted or reported, except for the AT model.

Sim Kyong Ho, a researcher at the Faculty of Materials Science and Technology, has developed and improved sc-AT, m-JC and KHL models to describe the hot deformation behavior of 300M ultra-high strength steel.

First, he conducted isothermal uniaxial compression tests under various thermo-mechanical processing conditions.

Second, by using the experimental data, he developed the AT, m-JC and KHL models for 300M steel, and evaluated the predictability of the models.

Based on the analysis of the cause of large deviation, he further improved the m-JC and KHL models, and verified the prediction accuracy of the five constitutive models by using standard statistical parameters.

He drew the following conclusions.

The m-JC and KHL models show relatively good predictability at the reference conditions. The sc-AT model exhibits the highest R2 value of 0.9971 and the lowest AARE value of 3.57 %. In view of the prediction accuracy and computation complexity, the improved versions of m-JC and KHL models are preferred models among the phenomenological constitutive models he studied.

The details are found in his paper “Development and Improvement of Several Phenomenological Constitutive Models for Thermo-mechanical Processing of 300M Ultra-high Strength Steel” in “Journal of Materials Engineering and Performance” (SCI).

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Jo Apr 22, 2024

Solid polymer electrolyte water electrolysis (SPEWE) is considered to be a promising way of producing “green” hydrogen at lower temperatures without use of fossil fuel or emission of greenhouse gas. In addition, electrolyser with proton exchange membrane (PEM) is expected to be used extensively due to its higher efficiency and current density, and use of distilled water as reactive agent.

Currently, the most widely used proton exchange membrane material is Nafion due to its moderate proton conductivity and chemical stability. But owing to the high cost of Nafion membrane, researches for alternative membranes based on hydrocarbon polymer and composite membrane have been prompted. Sulfonated polyether ether ketone (sPEEK) membranes are potential candidates to take the place of Nafion membranes as they are cheap while exhibiting good properties. Their conductivity and water uptake increase with increasing sulphonation degree are superior to Nafion. In addition, the dependence of conductivity with water content is stronger than in the case of Nafion. Especially, the conductivity of sPEEK at high levels of hydration is far superior to that of Nafion.

Jang Tae Il, a researcher at the Nano Physics Engineering Institute, has prepared ZrO2-sPEEK composite membrane with proper solvency by dimethyl formamide (DMF) and mechanical strength, and studied the factors for preparation of MEA. He chose ZrO2 based on the following motivations; firstly, chemical stability of ZrO2-sPEEK composite membrane can be enhanced by acid resistance of ZrO2 and secondly, good hydrophilicity of ZrO2 can improve or at least not worsen the proton conductivity of composite membrane.

He concluded from his study that the reasonable content of ZrO2 in the proposed composite membrane is 12wt%.

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Jo Apr 19, 2024

Taylor-Couette flow, the flow in the gap between two independently rotating coaxial cylinders, is one of the most discussed problems in fluid mechanics, due to its conception simplicity and applications in processing technology.

In the case of a circular Couette flow with superimposed axial throughput, the flow patterns are expected to be more complicated due to strong interactions between axial and rotating flows.

Recently, there have been some reports that Taylor-Couette flow could be used for production of nano materials. Due to the very strong shear rate of particles in the Taylor-Couette flow, the shaking particles in the fluid tend to split with time and so this is one of the main reasons that Taylor-Couette systems are used to produce nano materials.

Ju Jong Min, a section head at the Faculty of Materials Science and Technology, has developed a machine for producing nano materials by deciding the geometrical dimension of a system and the rotating speed of inner cylinder to form TC flow in Taylor-Couette system without axial flow.

Observing Taylor-Couette vortex at Reynolds number of 500~2 000, he chose rotating speed, viscosity of fluid and geometrical structure of system like the radii of inner and outer cylinders and its ratio and the aspect ratio of system suitable for obtaining steady Taylor-Couette flow. He concluded from the experiment that the rotating speed of 800r/min, the viscosity of fluid of 0.1Pa•s and the radius ratio of 0.88 are appropriate for steady Taylor-Couette flow.

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Students on “Risang” Local Network (1)

“Risang”, homepage for distance education of Kim Chaek University of Technology, has been making the part-time learners realize their ideal to the full.

Nov 11, 2022