• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.3
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• pp.17-25
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• 2014

The purpose of this paper is to present a method to estimate the storage life of propellant bag for degradation of breaking load with storage time by using gamma process model. The nitrogen compound generated by natural decomposition of propellants degrades the breaking load of propellant bag with time. The statistical distributions of condition and lifetime with time were shown from the results of accelerated life test of propellant bag cloth at $80^{\circ}C$. It was found that the use of median for life was highly appropriate and the $B_1$ or $B_5$ life should be selectively applied to the quality assurance policy.

• Journal of Convergence for Information Technology
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• v.10 no.7
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• pp.147-152
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• 2020

The research is carried out to analyze the cost-effectiveness of blasting patterns with regard to the diameters and design of blasting holes. Blasting patterns for single diameter array, and mixed diameter array were comparatively analyzed with regard to drilling and charging time, and materials required. The number of blasting holes required for single array pattern and mixed array pattern were 138 and 93 holes, respectively. From the drilling time analysis, reduction in time and its efficiency of mixed pattern were 139 minutes and 25%, respectively, in comparison with single pattern. Charging time reduction and its efficiency of mixed blasting pattern were evaluated as 22.5 minutes per worker and 33%, respectively, compare to single blasting pattern. The explosive quantities of G1 and G2 required for single array patterns were 270 and 30, while those were 222 and 20 for mixed array patterns for tunnelling 4m. And single pattern required 45 more detonators than the mixed pattern. The evaluation of material required can also be positive parameter for cost reduction of tunnel construction.

• Explosives and Blasting
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• v.18 no.3
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• pp.49-58
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• 2000

본 논문은 양면발파에 의한 채석기술에서 주로 양면발파 장약패턴 및 다이아몬드 와이어쏘절삭기술에 관한 내용을 중심으로, 현재 각 석재광산에서 시행하고 있는 채석기술과 연구소 에서 시행한 현장 시험발파 결과를 기술한 것이다. 첫째, DA석재광산에서는 제트버너를 이용하여 자유면을 형성하고, 일면발파법과 양면발파법의 작업시간을 비교한 결과 양면 발파할 때에 37%이상의 작업시간 절약효과가 있었으며, 인원은 36%이상의 감소효과가 있었다.둘째, DH석재광산에서는 다이아몬드 와이어쏘를 이용하여 자유면을 형성하고 양면발파 작 업시간과 타 광산에서 일반적으로 사용하고 있는 제트버너에 의한 양면발파 작업시간을 비교하였을 때에 21%이상의 절감효과가 있었고, 작업인원도 21%이상의 감소효과가 있었다. 다이아몬드 와이어쏘를 이용하여 양측면에 자유면을 형성하고 양면 발파하는 채석기술은 소음 및 분진에 의한 환경공해를 방지할 수 있었으며, 작업공정 및 경제성 면에서도 매우 유 리하나 실패시 다른 채석기술에 비해 모암의 손상으로 인한 경제적 손실이 커질 수 있다는 단점도 있으므로 정밀한 발파설계 및 기술이 필요하다.

• Industry Promotion Research
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• v.7 no.4
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• pp.9-15
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• 2022

This study evaluated the automated system of the roll bending process, which is one of the difficult processes. In the past, 20 cartridges were produced per hour. but Automation changed it to a process that produces 50 pieces per hour. The average value of production was 57.6 pieces per hour, error of repeatability was 0.03 mm, average roll diameter error value was 0.49 mm, average alignment error value was 0.09 mm and average process lead time was 43.21 seconds. This paper presented specific evaluation methods such as productivity, repeatability, defect rate, alignment defect rate, and process lead time. It is thought that the contents performed in this study will be helpful in the verification of other automation systems in the future.

• Explosives and Blasting
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• v.23 no.1
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• pp.1-8
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• 2005

Explosive blasting performance is composed of charging, tamping and connecting performance, which need lots of power and time. Thus, operator's inconvenience and muscle load are increased by their pose. Then it's unavoidable for one to make a human error. As a result, blasting accidents and disasters of explosives may happen. So we need to have systematic study. According to their pose's changing we have OWAS, RULA, REBA, OSHA, ISI, NLE, TVAV, BLUE-X. In this article, OWAS, RULA, REBA have been evaluated. As a result of this research, it is shown that work-related musciloskeletal disorders are related to the second accident's happening.

• Journal of Korean Society of Disaster and Security
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• v.16 no.1
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• pp.91-103
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• 2023

This study aims to investigate the dynamic fracture characteristics of rocks and rock-like materials subjected to the Nonex Rock Cracker (NRC), a vapor pressure crushing agent that produces vapor pressure by instantaneously vaporizing a liquid mixture crystallized through the thermite reaction. Furthermore, the study seeks to develop an analytical technique for predicting the fracture pattern. A dynamic fracture test was performed on a PMMA block, an artificial brittle material, using the NRC. High-speed cameras and dynamic pressure gauges were employed to capture the moment of vapor pressure generation and measure the vapor pressure-time history, respectively. The 2-dimensional Dynamic Fracture Process Analysis (2D DFPA) was used to simulate the fracture process caused by the vapor pressure, with the applied pressure determined based on the vapor pressure-time history. The proposed analytical method was used to examine various fracture patterns with respect to granite material and high-performance explosives.

• Tunnel and Underground Space
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• v.16 no.5 s.64
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• pp.413-421
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• 2006

In order to explain entirely dynamic fracture process induced by blasting in rock mass, it needs to consider detonation pressure and gas pressure acting on blasthole wall simultaneously. In this study, prior to simulating the coupling between gas flow and rock mass, we analyzed effects of gas pressure-time history, length of cracks and equation of state adopted to calculate the gas pressure on the gas flow within a radial fracture created by single-hole blasting. The effects were investigated on two assumptions: (a) the radial fracture was composed of 5 cracks which were 0.01 m in length and 0.001 m in asperity each and (b) the PETN explosive which diameter was 36 mm was charged in a blasthole of 45 mm diameter. It was concluded that the maximum gas pressure and its travel time were dependent on characteristics of charged explosives and geometrical properties of radial fracture.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.75-85
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• 2003

Laboratory model blast and in-situ rock blast tests were conducted to determine blast-induced stress wave propagation characteristics under different explosive types, different loading conditions and different mediums. Dynamic numerical approaches were conducted under the same conditions as experimental tests. Stress magnitudes at mid-point between two blast holes which were detonated simultaneously increased up to two times those of single hole detonation. The rise time of maximum stress in a decoupled charge condition was delayed two times that of a fully charged condition. Dynamic numerical analysis showed almost similar results to blast test results, which verifies the effectiveness of numerical approaches fur optimizing the tunnel blast design. Dynamic numerical analysis was executed to evaluate rock behavior and damage of the contour hole, the sloping hole adjacent to the contour hole in the road tunnel blasting pattern. The rock damage zone of the sloping hole from the numerical analysis was larger than that of the contour hole. Damage in the sloping hole can be reduced by using lower density explosive, by applying decoupled charge, or by increasing distance between the sloping hole and the contour hole.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.4
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• pp.561-571
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• 2019

Drilling and charging of the blast holes during NATM tunneling works take more than 30% of construction time among the whole tunneling work process. Prediction of ground condition ahead of tunnel face has been studied by several researchers by correlating percussion pressure and drilling speed during tunneling work with the ground condition and/or RMR values. However, most of the previous researches were conducted in the granite rock condition which is the most representative igneous rock in the Korean peninsula. In this study, drilling speeds in igneous rocks were analyzed and compared with those in sedimentary rocks (most dominantly composed of conglomerates, sandstones, and shales) under the similar RMR ranges; it was identified that the drilling speed is pretty much affected by rock types even in a similar RMR range. Under the similar RMR values, the drilling speed was faster in sedimentary rocks compared with that in igneous rock. Moreover, while the drilling speed was not much affected by change of the RMR values in igneous rocks, it became faster in sedimentary rocks as the RMR values got lower.

• Explosives and Blasting
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• v.30 no.2
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• pp.29-42
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• 2012

Variables influencing the free face movement due to rock blasting include the physical and mechanical properties, in particular the discontinuity characteristics, explosive type, charge weight, burden, blast-hole spacing, delay time between blast-holes or rows, stemming conditions. These variables also affects the blast vibration, air blast and size of fragmentation. For the design of surface blasting, the priority is given to the safety of nearby buildings. Therefore, blast vibration has to be controlled by analyzing the free face movement at the surface blasting sites and also blasting operation needs to be optimized to improve the fragmentation size. High-speed digital image analysis enables the analyses of the initial movement of free face of rock, stemming optimality, fragment trajectory, face movement direction and velocity as well as the optimal detonator initiation system. Even though The high-speed image analysis technique has been widely used in foreign countries, its applications can hardly be found in Korea. This thesis aims at carrying out a fundamental study for optimizing the blast design and evaluation using the high-speed digital image analysis. A series of experimentation were performed at two large surface blasting sites with the rock type of shale and granite, respectively. Emulsion and ANFO were the explosives used for the study. Based on the digital images analysis, displacement and velocity of the free face were scrutinized along with the analysis fragment size distribution. In addition, AUTODYN, 2-D FEM model, was applied to simulate detonation pressure, detonation velocity, response time for the initiation of the free face movement and face movement shape. The result show that regardless of the rock type, due to the displacement and the movement velocity have the maximum near the center of charged section the free face becomes curved like a bow. Compared with ANFO, the cases with Emulsion result in larger detonation pressure and velocity and faster reaction for the displacement initiation.