• Journal of the Korean Geotechnical Society
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• v.37 no.10
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• pp.13-25
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• 2021

The most widely used method for determining the blast effects of explosives is the Trauzl test. This test is used to measure the explosive power (strength) of a substance by determining volume increase, which is produced by the detonation of a tested explosive charge in the cavity of a lead block with defined quality and size. In this paper, Trauzl lead block test and High speed 3D-DIC (Digital Image Correlation) system were conducted to evaluate the stemming effect of the blast hole. The effects of stemming materials can be expressed as the expansion of the cavity in a standard lead block through explosion of the explosives. The blasting experiment was conducted with emulsion explosives. The stemming material in the blast hole of lead block, which was adopted in this study, were using sand and stone chips. Results of blasting experiment and numerical analysis showed that the expansion rates of lead block were most affected by stone chips followed by sand. Also, as result of dynamic strain measurement on the lead block surface of High speed 3D-DIC system, the displacement and surface strain on the block were the highest in the experiment case of stone chips stemming.

• Explosives and Blasting
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• v.39 no.3
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• pp.15-23
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• 2021

Ventilation shafts are pathways in mines and tunnels for the removal of dust or smoke during underground space construction and operation. In mines, blasting with long blast holes is preferred for the excavation of a ventilation shaft in the 10~20m long crown pillar section. In this case, the bottom part of the blast hole is completely drilled in order to determine the drilling error, and this causes a problem of lowering the explosive charge and blasting efficiency. It is possible to solve the problem of explosive loading and to increase the blast efficiency by covering the curb of the blasthole by using stemming material. In this study, simulations for the blasting of a ventilation shaft were performed with various stemming lengths and the blasthole diameters(45, 76mm) using AUTODYN 2D SPH(Smooth particle hydrodynamics) analysis technique. Also the optimal bottom stemming column was derived by checking the size of the boulder and burden line according to blasting. Analysis result, blasting efficiency is lessened in case of stemming length less than 30cm and the optimal length of the stemming material should be 30cm or higher to achieve high efficiency of blasting.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.595-601
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• 2020

During the safety inspection of nitrocellulose-made explosive containers stored for more than 10 years, cracks were found in the containers. Therefore, a failure cause analysis test was performed. First, the cause of failure through the failure tree analysis was conducted to select the factors that influenced failure. The changes in the properties of the container caused by the acceleration of the reaction were found to be the cause of the failure by confirming the influence on the environment and internal/external factors that may occur during storage. To confirm this, environmental tests, such as thermal shock test and vacuum thermal stability test, were performed using a naturally aged container to analyze the cause of failure, and an accelerated aging test was performed to reproduce the failure. Through this, the chemical reaction was accelerated by heat and charge, as in the result of the fault tree analysis, and it was confirmed that the physical properties of the container were changed. In addition, the service life of the container was estimated using the Arrhenius model for the storage life due to thermal aging.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.9
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• pp.103-109
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• 2003

The development of a pulse gun used for the combustion stability rating test(SRT) has been domestically tried out since the SRT should be accompanied in the process of the development of LREs. At the beginning of the development, a rupture problem of the pulse gun body had been solved by changing its material and increasing its thickness. Also, the sealing test was undertaken for a pulse gun equipped with a membrane before conducting a explosion test and by using a specially designed jig after a explosion test. Since it is appropriate to reuse the holder of a pulse gun cavity for an actual SRT, a series of experiments for several variants has been taken to make it reusable. After all, the solution for a reusable holder of a pulse gun has been found and applied for complementing its specification.

• The Journal of Korean Medicine
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• v.30 no.4
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• pp.28-36
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• 2009

Objectives: Fatigue is a prevalent symptom encompassing both acute and chronic manifestations. Most fatigue symptoms can be cured by taking a rest or removing underlying causes. However, chronic fatigue is frequently problematic due to its duration and effect on quality of life. There are no particularly effective therapies for chronic fatigue of unknown causes, and patients in Korea usually visit an Oriental clinic. This study aimed to analyze the current status of treatments and patients with chronic fatigue, and then map out of a strategy for development of generalized-treatments for chronic fatigue in Oriental Medicine. Methods: Clinical information related to chronic fatigue was selected from various different databases such as PubMed, KoreaMed, KStudy, DBPIA, OIM, and KOMS. Also, to understand current tendency of medical examination and treatment related with chronic fatigue, we requested Health Insurance Review & Assessment Service for clinical datum from 2003 to 2007. Results: The medical fees of National Health Insurance related with fatigue show an explosive year-on-year increase. On the other hand, it has been decreasing annually in the western medical fields. To take charge of clinical fields related with chronic fatigue by Oriental Medicine, we should make a unified diagnostic system. Then, we should also make standard evaluation tools and develop herbal drugs according to this unified diagnostic system. Conclusions: Fatigue-related symptoms will be a main target of Oriental medicine in the future. We expect that various studies related with chronic fatigue will be undertaken hereafter.

• Journal of Sensor Science and Technology
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• v.12 no.4
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• pp.191-197
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• 2003

Due to explosive increase of internet usage, broadband data transmission using optical fibers is broadly used. In order to decrease distortion during long distance transmission, the optical signal need to be restored, typically, by converting the optical signal into the electrical signal. The optical signal is converted into the electrical signal using a photo-diode, and then a clock-and-recovery (CDR) circuit is used to recover the clock and retime the data. In this study, a clock-and-data recovery circuit has been designed using a standard 1.8 V $0.18\;{\mu}m$ CMOS process. With this CDR circuit, the improved phase detector and charge pump have been utilized. Also, by using a ring oscillator, the CDR circuit can recover clock and data from broadband multi-rate data ranging between 750 Mb/s and 2.85 Gb/s.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.75-85
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• 2016

A pyrotechnic system consisting of donor/acceptor pair separated by a gap relies on shock attenuation characteristics of the gap material and shock sensitivity of the donor and acceptor charges. Despite of its common use, numerical study of such pyrotechnic train configuration is seldom reported because proper modeling of the full process requires precise capturing of the shock wave attenuation in the gap prior to triggering a full detonation of high explosive and accurate description of the high strain rate dynamics of the explosively loaded inert confinements. We apply a Eulerian level-set based multimaterial hydrocode with reactive flow models for pentolite donor and heavily aluminized RDX as acceptor charge. The complex shock interaction, critical gap thickness, acoustic impedance, and go/no-go characteristics of the gap test are quantitatively investigated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.172-178
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• 2017

Thermal property is one of the important characteristic in the field of energetic materials. As the energy material is released during decomposition, DSC(Differential Scanning Calorimetry) is frequently used for the thermal analysis. In case of the dynamic DSC measurements, thermal dynamic change like melting is prevented from the thermal property measurements. And due to the predicting kg scale, the conditions of the heat exchange with the environment significantly is changed. In this study, As the method to resolve the problem, we predict the thermal aging property using the AKTS thermokinetic program from DSC measurements which performed isothermal method. Predicting the thermal aging properties from ARC(Accelerating Rate Calorimetry) measurement, we compare two results.

• Geomechanics and Engineering
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• v.2 no.1
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• pp.1-18
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• 2010

The analysis of structure response and design of buried structures subjected to dynamic destructive loads have been receiving increasing interest due to recent severe damage caused by strong earthquakes and terrorist attacks. For a comprehensive design of buried structures subjected to blast loads to be conducted, the whole system behaviour including simulation of the explosion, propagation of shock waves through the soil medium, the interaction of the soil with the buried structure and the structure response needs to be simulated in a single model. Such a model will enable more realistic simulation of the fundamental physical behaviour. This paper presents a complete model simulating the whole system using the finite element package ABAQUS/Explicit. The Arbitrary Lagrange Euler Coupling formulation is used to model the explosive charge and the soil region near the explosion to eliminate the distortion of the mesh under high deformation, while the conventional finite element method is used to model the rest of the system. The elasto-plastic Drucker-Prager Cap model is used to model the soil behaviour. The explosion process is simulated using the Jones-Wilkens-Lee equation of state. The Concrete Damage Plasticity model is used to simulate the behaviour of concrete with the reinforcement considered as an elasto-plastic material. The contact interface between soil and structure is simulated using the general Mohr-Coulomb friction concept, which allows for sliding, separation and rebound between the buried structure surface and the surrounding soil. The behaviour of the whole system is evaluated using a numerical example which shows that the proposed model is capable of producing a realistic simulation of the physical system behaviour in a smooth numerical process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.9
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• pp.617-628
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• 2019

The currently considered pyrotechnic separation nut is separated through the complicated process, because it has many internal moving parts and two variable-volume chambers connected by the vent hole. Therefore, it has many design parameters. Some of these are the contact angles between internal moving parts, the masses of the internal moving parts, the inner diameter of the push rod protrusion, the initial volumes of the chambers, the mass of the explosive charge, and the diameter of the vent hole. To improve the pyrotechnic separation nut, it is necessary to understand how the behavior of the separation nut is changed according to design parameters. In this point of view, parametric studies are carried out using the previously proposed prediction model for pyrotechnic separation nut behaviors. In each case, the parameter of the interest is changed while the others are kept unchanged. From the results, it is investigated how each design parameter influences the separation behavior.