• Title/Summary/Keyword: fracture network

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The Effects of a Chain Extending Agent and Crosslinking Agent on the Toughness of Castor Oil based Polyurethane-Epoxy IPNs (Castor Oil형 폴리우레탄-에폭시 IPNs에서 사슬연장제와 가교제의 영향에 의한 강인성)

  • Kim, Jong-Seok;Yang, Yeong-Seok
    • Applied Chemistry for Engineering
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    • v.10 no.5
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    • pp.639-643
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    • 1999
  • Interpenetrating polymer networks(IPNs) composed of castor oil(CO) polyurethane(PU) and epoxy resin were prepared by the simultaneous polymerization technique. Two types of PU were prepared using 1,4-butanediol(BD) and BD/trimethylolpropane(TMP) as a chain extending agent and crosslinking agent. The PU/epoxy based on BD as a chain extending agent showed more shift in the damping peak than PU/epoxy based on BD/TMP as the PU content was increased. BDPU/epoxy simultaneous interpenetrating polymer networks(SINs) had a better compatibility than BD/TMP-PU/epoxy SINs. For both systems, it was postulated that unique network formation of PU/epoxy SINs as a chain extending agent and crosslinking agent had occurred to a significant extent of phase mixing. The types of chain extender in the PU were found to be an important factor in determining the phase mixing of the IPNs. When the BD/TMP-PU reaction was faster than epoxy network, the extent of phase mixing was retarded by decreasing entanglement of networks. It was found that both PU/epoxy SINs provided enhanced flexural properties and fracture toughness, fracture surfaces of BDPU/epoxy and BD/TMP-PU/epoxy SINs showed the localized shear deformation and generation of stress whitening associated with the cavitation.

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Hydrogeological Stability Study on the Underground Oil Storage Caverns by Numerical Modeling (수치모델링을 이용한 지하원유비축시설의 수리지질학적 안정성 연구)

  • 김경수;정지곤
    • The Journal of Engineering Geology
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    • v.12 no.1
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    • pp.35-51
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    • 2002
  • This study aims to establish the methodology for design of an optimum water curtain system of the unlined underground oil storage cavern satisfying the requirements of hydrodynamic performance in a volcanic terrain of the south coastal area. For the optimum water curtain system in the storage facility, the general characteristics of groundwater flow system in the site are quantitatively described, i.e. distribution of hydraulic gradients, groundwater inflow rate into the storage caverns, and hydrogeologic influence area of the cavern. In this study, numerical models such as MODFLOW, FracMan/MAFIC and CONNECTFLOW are used for calculating the hydrogeological stability parameters. The design of a horizontal water curtain system requires considering the distance between water curtain and storage cavern, spacing of the water curtain boreholes, and injection pressure. From the numerical simulations at different scales, the optimum water curtain systems satisfying the containment criteria are obtained. The inflow rates into storage caverns estimated by a continuum model ranged from about 120 m$^3$/day during the operation stage to 130~140m$^3$/day during the construction stage, whereas the inflow rates by a fracture network model are 80~175m$^3$/day. The excavation works in the site will generate the excessive decline of groundwater level in a main fracture zone adjacent to the cavern. Therefore, the vertical water curtain system is necessary for sustaining the safe groundwater level in the fracture zone.

Numerical simulation of groundwater flow in LILW Repository site:I. Groundwater flow modeling (중.저준위 방사성폐기물 처분 부지의 지하수 유동에 대한 수치 모사: 1. 지하수 유동 모델링)

  • Park, Kyung-Woo;Ji, Sung-Hoon;Kim, Chun-Soo;Kim, Kyung-Su;Kim, Ji-Yeon
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.6 no.4
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    • pp.265-282
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    • 2008
  • Based on the site characterization works in a low and intermediate level waste(LILW) repository site, the numerical simulations for groundwater flow were carried out in order to understand the groundwater flow system of repository site. To accomplish the groundwater flow modeling in the repository site, the discrete fracture network(DFN) model was constructed using the characteristics of fracture zones and background fractures. At result, the total 10 different hydraulic conductivity(K) fields were obtained from DFN model stochastically and K distributions of constructed mesh were inputted into the 10 cases of groundwater flow simulations in FEFLOW. From the total 10 numerical simulation results, the simulated groundwater levels were strongly governed by topography and the groundwater fluxes were governed by locally existed high permeable fracture zones in repository depth. Especially, the groundwater table was predicted to have several tens meters below the groundwater table compared with the undisturbed condition around disposal silo after construction of underground facilities. After closure of disposal facilities, the groundwater level would be almost recovered within 1 year and have a tendency to keep a steady state of groundwater level in 2 year.

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Cure Behaviors and Fracture Toughness of PEl/Difunctional Epoxy Blends (PEI/DGEBA 블랜드계의 열적특성 및 파괴인성)

  • Park, Soo-Jin;Jin, Sung-Yeol;Kaang, Shinyoung
    • Journal of Adhesion and Interface
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    • v.4 no.3
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    • pp.33-40
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    • 2003
  • In this work, diglycidyl ether of bisphenol A (DGEBA)/polyetherimide (PEI) blends were cured using 4,4-diaminodiphenyl methane (DDM). And the effects of addition of different PEI contents to neat DGEBA were investigated in the thermal properties and fracture toughness of the blends. The contents of contents of containing PEI were varied in 0, 2.5, 5, 7.5, and 10 phr. The cure activation energies ($E_a$) of the cured specimens were determined by Kissinger equation and the mechanical interfacial properties of the specimens were performed by critical stress intensity factor ($K_{IC}$). Also their surfaces were examined by using a scanning electron microscope (SEM) and the surface energetics of blends was determined by contact angles. As a result, $E_a$ and $K_{IC}$ showed maximum values in the 7.5 phr PEI. This result was interpreted in the increment of the network structure of DGEBA/PEI blends. Also, the surface energetics of the DGEBA/PEI blends showed a similar behavior with the results of $K_{IC}$. This was probably due to the improving of specific or polor component of the surface free energy of DGEBA/PEI blends, resulting in increasing the hydrogen bonding of the hydroxyl and imide groups of the blends.

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Rheological Models for Simulations of Concrete Under High-Speed Load (콘크리트 재료의 동적 물성 변화를 모사하기 위한 유변학적(Rheological)모델 개발 및 평가)

  • Hwang, Young Kwang;Lim, Yun Mook
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.4
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    • pp.769-777
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    • 2015
  • In this study, the rheological models were introduced and developed to reflect rate dependent tensile behaviour of concrete. In general, mechanical properties(e.g. strength, elasticity, and fracture energy) of concrete are increased under high loading rates. The strength of concrete shows high rate dependency among its mechanical properties, and the tensile strength has higher rate dependency than the compressional strength. To simulate the rate dependency of concrete, original spring set of RBSN(Rigid-Body- Spring-Network) model was adjusted with viscous and friction units(e.g. dashpot and Coulomb friction component). Three types of models( 1) visco-elastic, 2) visco-plastic, and 3) visco-elasto- plastic damage models) are considered, and the constitutive relationships for the models are derived. For validation purpose, direct tensile test were simulated, and characteristics of the three different rheological models were compared with experimental stress-strain responses. Simulation result of the developed visco-elasto-plastic damage(VEPD) model demonstrated well describing and fitting with experimental results.

Development of Intelligent System to Select Production Method in Coalbed Methane Reservoir (석탄층 메탄가스 저류층의 생산방법 선정을 위한 지능형 시스템 개발)

  • Kim, Chang-Jae;Kim, Jung-Gyun;Lee, Jeong-Hwan
    • Journal of the Korean Institute of Gas
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    • v.18 no.2
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    • pp.1-9
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    • 2014
  • To develop a coalbed methane(CBM) reservoir, it is important to apply production methods such as drilling, completion, and stimulation which coincide with coal properties. However, the reliability of the selected resulted in most of CBM field is not enough to accept because the selection of production method has been done by empirical decision. As the result, the empirical decision show inaccurate results and need to prove using simulation whether it was true exactly. In this study, the intelligent system has been developed to assist the selection of CBM production method using artificial neural network(ANN). Before the development of the system, technical screening guideline was analyzed by literature survey and the system to select drilling and completion method, and hydraulic fracture fluid was developed by utilizing the guideline. The result as a validation of the developed system showed a high accuracy. In conclusion, it has been confirmed that the developed system can be utilized as a effective tool to select production method in CBM reservoir.

Analysis of the mechanical properties and failure modes of rock masses with nonpersistent joint networks

  • Wu, Yongning;Zhao, Yang;Tang, Peng;Wang, Wenhai;Jiang, Lishuai
    • Geomechanics and Engineering
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    • v.30 no.3
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    • pp.281-291
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    • 2022
  • Complex rock masses include various joint planes, bedding planes and other weak structural planes. The existence of these structural planes affects the mechanical properties, deformation rules and failure modes of jointed rock masses. To study the influence of the parameters of a nonpersistent joint network on the mechanical properties and failure modes of jointed rock masses, synthetic rock mass (SRM) technology based on discrete elements is introduced. The results show that as the size of the joints in the rock mass increases, the compressive strength and the discreteness of the rock mass first increase and then decrease. Among them, the joints that are characterized by "small but many" joints and "large and clustered" joints have the most significant impact on the strength of the rock mass. With the increase in joint density in the rock mass, the compressive strength of rock mass decreases monotonically, but the rate of decrease gradually decreases. With the increase in the joint dip angle in rock mass, the strength of the rock mass first decreases and then increases, forming a U-shaped change rule. In the analysis of the failure mode and deformation of a jointed rock mass, the type of plastic zone formed after rock mass failure is closely related to the macroscopic displacement deformation of the rock mass and the parameters of the joints, which generally shows that the location and density of the joints greatly affect the failure mode and displacement degree of the jointed rock mass. The instability mechanism of jointed surrounding rock is revealed.

Evaluation of Residual Stress Effect about Fatigue Characteristic of U-shaped Structure (U자형 구조의 피로특성에 대한 잔류응력의 영향 평가)

  • Kim, Sang-Young;Koo, Jae-Mean;Seok, Chang-Sung;Mo, Jin-Yong
    • Journal of the Korean Society for Precision Engineering
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    • v.27 no.4
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    • pp.79-86
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    • 2010
  • Mechanical structures with power sources experience repeated force produced by motors. In result, the life of the pipes reduces and ultimately, the pipes collapse. Such pipes are formed into several shapes and particularly, the U-shape pipe is damaged frequently. In most cases, the U-shape pipe is made with a straight pipe by complicated bending work. During this work process, plastic deformation of the pipe produces residual stress in the pipe. This residual stress significantly affects the fracture behavior of the pipe and induces the change of the stress ratio (min. stress/Max. stress = R). For this reason, residual stress has to be evaluated. In this paper, the residual stress of a U-shaped pipe was evaluated by FEM analysis. In addition, fatigue tests of the U-shaped pipe were performed by using a uniaxial fatigue testing machine. The results of the fatigue test were modified with the results of FEM (Finite Element Method) analysis for residual stress. The modified fatigue test results of the U-shaped pipe were compared with those of a straight pipe.

The Utilization of Medical Care Benefits of School Personnel on Duty (교직원의 공무상 요양급여제도 이용 현황)

  • Lee, Hee-Woo;Shin, Sun-Mi;Kim, Joo-Ja;Kang, Se-Won
    • Journal of the Korean Society of School Health
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    • v.21 no.2
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    • pp.107-117
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    • 2008
  • Purpose: To investigate the utilization of medical care benefits of school personnel on duty in Seoul. Method: The subjects were 551 workers under Seoul Metropolitan Office of Education(male 301, female 250) who got medical care benefits from March 2000 to February 2005. To analyze the data, frequency, chi-square test, and t-test by SAS package 9.12 were used. Result: The results show that elementary school personnel got the highest ranking, 314(57.0%). Among subjects, 57.2% personnel got accident when they were working on their own duty, 21% during school events and 13.5% were during commutes. They got medical care from orthopedics 75.9%, neurosurgery 7.6%, dental 4%, and 8 male and 2 female died during these days. The most frequent diseases of males and female were fracture and joints related disease. The reason of most health problem was due to injury(92.3%). Conclusion: The results of this study suggest that the continuous health care services like regular health check for school personnel, or social safety network to prevent injury are needed.

Classification of Acoustic Emission Signals from Fatigue Crack Propagation in 2024 and 5052 Aluminum Alloys

  • Nam, Ki-Woo;Moon, Chang-Kwon
    • International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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    • v.4 no.1
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    • pp.51-55
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    • 2001
  • The characteristics of elastic waves emanating from crack initiation in 2024 and 5052 aluminum alloys subject to static and fatigue loading are investigated through laboratory experiments. The objective of the study is to determine difference in the properties of the signals generated from static and fatigue tests and also to examine if the sources of the waves could be identified from the temporal and spectral characteristics of the acoustic emission (AE) waveforms. The signals are recoded using non-resonant, flat, broadband transducers attached to the surface of the alloy specimens. The time dependence and power spectra of the signals recorded during the tests were examined and classified according to their special features. Three distinct types of signals were observed. The waveforms and their power spectra were found to be dependent on the material and the type of fracture associated with the signals. Analysis of the waveforms indicated that some signals could be attributed to plastic deformation associated with static tests. The potential application of the approach in health monitoring of aging aircraft structures using a network of surface mounted broadband sensors is discussed.

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