• Journal of Ocean Engineering and Technology
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• v.12 no.3 s.29
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• pp.42-48
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• 1998

구형 관입시험에 의한 얼음의 균열을 연구 하였다. $-10^{circ}C$에서 S2 기둥얼음의 시편(152mm X 152mm X 152mm)에 stainless 강으로 된 구(지름 25.4mm)로 하중을 가하였다. 구형indentor는 얼음 시편의 장축인 기둥방향에 수직으로 하중을 가하였으며 이때 변위율은 0.038mm/s로 하여 단조증가 하중 시험을 하였다. 하중을 가하기 시작하면 indentor 하부에서 crushing 이 발생하고, 하중이 증가함에 따라서 방사선 균열 또는 횡균열이 성장하여 splitting 또는 spallation이 발생하였다. 단조증가 하중 때와 동일한 indentor를 사용하여 하중 및 비하중율 0.5KN/s로 맥박하중을 가할 때 이들 방사선 균열 및 횡 균열이 발생 성장하였다. 첫 맥박 하중의 크기는 1KN으로 하고 그 뒤 계속 이어지는 시험은 맥박 하중의 크기를 증가시킨 뒤 행하였으며 균열 길이는 맥박과 맥박 사이에서 계측 하였다. 기타 취성고체에서 관찰 되었던 것과 같이 방사선 균열 및 측면균열의 길이는 impression 반지름과 하나의 지수법칙이 성립함을 보여주었다.

• Explosives and Blasting
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• v.23 no.2
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• pp.45-56
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• 2005

In this study, fracture formation and fracture volume by blasting demolition of model reinforced concrete pillars were compared with various vertical load and influence of reinforced steel bar. The more vertical load increased, the more tensile cracks and vertical direction cracks produced. In vertical load of 2.0ton, tensile cracks on vertical direction were predominantly produced. Generally, the more vertical load increased, the more bending deformation of concrete steel bar decreased. As a result, vertical load was influenced fracture formation of concrete and bending deformation of reinforced steel bar. Reinforced steel bar was influenced fracture volume of concrete. According to vertical load and influence of reinforce steel bar by blasting demolition of reinforced concrete pillars, drilling and blasting pattern may be modified.

• Nuclear Engineering and Technology
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• v.28 no.2
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• pp.185-196
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• 1996

The purpose of this paper is to modify the ASME Code Z-Factor, which is used in the evaluation of circumferential surface crack in nuclear ferritic pipings. The ASME Code Z-Factor is a load multiplier to compensate plastic load with elasto-plastic load. The current ASME Code Z-Factor underestimates pipe maximum load. In this study, the original SC. TNP method is modified first because the original SC. TNP method has a problem that the maximum allowable load predicted from the original SC. TNP method is slightly higher than that measured from the experiment. Then the new Z-Factor is developed using the modified SC. TNP method. The desirability of both the modified SC. TNP method and the new Z-Factor is examined using the experimental results for the circumferential surface crack in pipings. The results show that (1) the modified SC. TNP method is good for predicting the circumferential surface crack behavior in pipings, and (2) the Z-Factor obtained from the modified SC. TNP method well predicts the behavior of circumferential surface crack in ferritic pipings.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.3
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• pp.251-260
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• 2003

Tunnel blasting has been performed with V-cut to investigate the characteristics. Blasting vibrations were measured at two directions, the proceed direction and side direction. Propagation characteristics were determined by regression analysis; square root scaled distance and cube root scaled distance with maximum charge per delay of the blast. Testing result, The cross point was 62m in the allowable vibration velocity of 3mm/sec and 46m in 5mm/sec. Also, vibration level with measuring point was highest and decayed fastest, adapting to cube root scaled distance, for the proceed direction on ground.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1472-1478
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• 1991

본 연구에서는 Rectangular Computer Tension(CT) 시편을 수정하여 만든 표준 시편인 MRL-CLWL시편(material research laboratorycrack line wedge loaded specimen )으로 균열정지 인성치를 결정하였다. 그리고 CT시편과 같은 효과를 갖는 Newman등 이 제안한 round compact tension(RCT)시편을 수정한 Round-CLWL 시편으로 균열정지인 성치를 결정하여 상호 비교평가하였다. Round-CLWL 시편은 시편제작시 round-bar를 절단하여 시편으로 가공할 수 있으므로 가공성이 좋으며 따라서 가공비가 적게 든다. 특히 균열 위치 및 방향을 임의로 선택하여 가공하기가 용이하므로 방향성이 있는 소 재의 균열정지 인성치를 결정하는 데 매우 편리한 시편이라 생각된다. 본 논문에서 는 Round-CLWL 시편으로 $K_{1a}$ 값을 계산하는데 필요한 형상계수를 결정하였으며, Polymethylmethacrylate(PMMA)를 사용하여 Round-CLWL 시편 채택의 타당성 확인을 위 한 MRL-CLWL과 Round-CLWL 시편 채택의 타당성 확인을 위한 MRL-CLWL과 Round-CLWL시 편의 $K_{1a}$결정 실험을 하였다.하였다.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.129-137
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• 2000

This paper presents groundwater flow characteristics in discontinuous rock mass using fracture network program(NAPSAC) by statistical approach. Equivalent permeability coefficients are estimated from borehole data around Mabuk test tunnel site and fracture map on the arch of the tunnel. The reliability of fracture network model is obtained from determination of input data for statistical fracture network analysis from the real data(data of fracture network, data of hydraulic tests). The variation of permeability and mean anisotropic permeability coefficients are calculated from the realized model by increasing the size. As a result of analysis, a strong anisotropy of permeability is observed according to the direction of the fracture sets around the test tunnel.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.378-386
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• 2000

This paper presents groundwater flow characteristics in discontinuous rock mass using fracture network program(NAPSAC) by statistical approach. Equivalent permeability coefficients are estimated from borehole data around Mabuk test tunnel site and fracture map on the arch of the tunnel. The reliability of fracture network model is obtained from determination of input data for statistical fracture network analysis from the real data(data of fracture network, data of hydraulic tests). The variation of permeability and mean anisotropic permeability coefficients are calculated from the realized model by increasing the size. As a result of analysis, a strong anisotropy of permeability is observed according to the direction of the fracture sets around the test tunnel.

• Korean Journal of Food Science and Technology
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• v.31 no.1
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• pp.164-170
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• 1999

Cracking of rice caused by moisture migration during storage under different relative humidity conditions was investigated for the establishment of safe storage condition of rice. Rice was cracked when a large difference in equilibrium relative humidity $({\Delta}ERH)$ between the rice and the environment was present. External and internal cracks were generated as the results of moisture desorption and adsorption, respectively. The external cracks by moisture desorption generated in all directions and shaped irregularly, while the internal cracks by moisture adsorption did in radial direction and showed a typical shape. The cracking trend could be analyzed by the Weibull function, and the cracking constant increased with ${\Delta}ERH$. The frequency of cracked rice increased linearly with In $({\Delta}ERH)$. The critical crack-inducing ${\Delta}ERH$ was $11.3{\sim}16.4%$ during desorption and $10.8{\sim}17.1%$ during adsorption. A diagram for the safe storage of rice was developed with respect to the initial moisture content and the water activity of rice.

• Journal of the Korean Ceramic Society
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• v.39 no.5
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• pp.484-489
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• 2002

Hot-pressure sintered laminar composites with alumina/zirconia or mullite/zirconia as an outer layer and alumina/zircon (resulting in reaction-bonded mullite/zirconia during sintering) as an inner layer were fabricated by tape casting and lamination. Various forms of crack were observed in sintered laminar composites, these cracks included channel cracks in the outer layer, transverse cracks in the inner layer and interface cracks debonding interlayer. Based on detailed microscopic observations, the cracks were attributed to thermal expansion mismatch between the oxides consisting of the each layer. In particular, the interlayer and transverse cracks were confirmed in the laminates consisted of the mullite/zirconia system as the outer layers, however, those cracks were not observed in the alumina/zirconia system used. In addition, the crack propagation did not exhibit same behavior in the two kinds of outer layer when the indentation load was applied.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.353-356
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• 2007

Asphalt pavements of the airport in service were monitored to construct new runway and taxiway and longitudinal cracks were found on the pavements. The sources of the longitudinal cracks were the low density which was caused by the longitudinal cold joint with asphalt Pavement constructions and the excessive loads of aircraft. Therefore, the echelon paving method using a 12m-wide screed finisher was used to eliminate longitudinal cracks. When the echelon paving is used, construction of the longitudinal joint is changed so that the compaction of the unconfined edge of the first lane is delayed until the second lane is placed. In conclusion, the use of this construction method results in the density of the longitudinal joint being equal to that of the adjacent mat.