• Carbon letters
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• v.19
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• pp.47-56
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• 2016

In this study, the fracture behavior of a thermoplastic-modified epoxy resin reinforced with continuous carbon fibers for two levels of fiber-matrix adhesion was performed. A carbon fiber with commercial sizing was used and also treated with a known silane, (3-glycidoxy propyl trimethoxysilane) coupling agent. Toughness was determined using the double cantilever test, together with surface analysis after failure using scanning electron microscope. The presence of polysulfone particles improved the fracture behavior of the composite, but fiber-matrix adhesion seemed to play a very important role in the performance of the composite material. There appeared to be a synergy between the matrix modifier and the fiber-matrix adhesion coupling agent.

• Composites Research
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• v.17 no.5
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• pp.39-46
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• 2004

In this study, the strength of spatially reinforced composites (SRC) are predicted by using stiffness reduction for each structural element composed of a rod stiffness in each direction and a matrix stiffness proportional to its rod volume fraction. Maximum failure strain criteria is applied to rod failure, and modified Tsai-Wu failure criteria to matrix failure. The material properties composed of the tensile failure strain of a rod, the compressive failure strain of 3D SRC, the tensile and compressive strength of the 3D SRC in the $45^{\cir}$ rotated direction from a rod and the shear strength of the 3D SRC are measured to predict the SRC strength. The strength distributions of the 3D/4D SRC in rod and off-rod direction have the largest and the smallest values, respectively. A variable load step is selected to increase an efficiency of strength distribution calculation. Uniform load step is applied when a load history is needed. The results of compressive strength from analysis and experiment show the 18 % difference though the initial slop is coincident with each other.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.181-192
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• 1999

The progressive failure following strain localization in concrete can be analyzed effectively using finite element modeling of fracture process zone of concrete with a finite element embedded discontinuity. In this study, a finite element with embedded discontinuous line is utilized for the analysis of progressive failure in concrete. The finite element with embedded discontinuity is a kind of discrete crack element, but the difficulties in discrete crack approach such as remeshing or adding new nodes along with crack growth can be avoided. Using a discontinuous shape function for this element, the displacement discontinuity is embedded within an element and its constitutive equation is modeled from the modeling of fracture process zone. The element stiffness matrix is derived and its dual mapping technique for numerical integration is employed. Then, a finite element analysis program with employed algorithms is developed and failure analysis results using developed finite element program are verified through the comparison with experimental data and other analysis results.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.1
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• pp.35-43
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• 2006

Concerns related to protecting, identifying, and isolating of subsystems of a water distribution network have led to the realization of the increased importance of valves in the system. The most important purpose of valves in water distribution systems is to isolate a subsystem due to breakage, maintenance activities, or contamination. A subsystem called segment is isolated by the closure of adjacent valves. Minimizing the pipe failure impact, an efficient algorithm is required to identify adjacent valves quickly. In this paper, an algorithm to identify adjacent valves to be closed to isolate a subsystem from the remainder of a network when a pipe failure is presented. The algorithm is operated on a matrix called the valve location matrix containing the information of valve locations. An application to an existing water distribution system demonstrates the developed algorithm efficiently locates the adjacent valves for the isolation of a broken pipe.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.1
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• pp.78-84
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• 2005

The main goal of this work is to study the effects of temperature and volume fraction of fiber on the Charpy impact test with GF/PP composites. The critical fracture energy and failure mechanisms of GF/PP composites are investigated in the temperature range of 60^{\circ}C$ to -50^{\circ}C$ by impact test. The critical fracture energy increased as the fiber volume fraction ratio increased. The critical fracture energy shows a maximum at ambient temperature and it tends to decreases as temperature goes up or goes down. Major failure mechanisms can be classified such as fiber matrix debonding, fiber pull-out and/or delamination and matrix deformation.

• International Journal of Safety
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• v.2 no.1
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• pp.23-27
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• 2003

Recently, continuous fiber reinforced ceramic composite(CFCC) has attracted attention to a number of engineers because of its significant benefit for several industrial area. This work was conducted to provide a basic characteristic of CFCC for tensile loading condition. The numerical analysis by general purpose finite element program was accomplished and compared with an experimental tensile test. The stress strain curves were expressed well by the numerical analysis and the first matrix cracking stress was in accordance with that of the experimental result. Moreover, fracture pattern was shown by kill command graphically.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.131-136
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• 1998

The creep behavior and failure mechanism of the 30 vol% hot-pressed $SiC_t/Si_3N_4$ ceramic composite was experimentally investigated at $1200^{\circ}C$ and at various stress levels in air. The creep threshold stress for zero creep rate after 100 hr was found to be approximately 60 MPa. The stress exponent was estimated to be n~1, which suggests that fiber-reinforcement reduced the stress sensitivity of the HPSN matrix with the stress exponent of 2. The tertiary stage leading to creep rupture was found at 250 MPa but was very short. The microstructure of the crept specimen showed random fiber fracture and no matrix cracking. Interfacial debonding was absent.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.11a
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• pp.618-629
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• 2006

This Paper is about optimizing preventive maintenance period of connected (r,s) out of(m,n) : F lattice system that one of multi-component system, (m,n) matrix failure of whole system is occurrence when parts that belong in (r,s) matrix part procession of parts arranged with procession are breakdown all. The preventive maintenance about system is very important viewing from system reliability and operational expense viewpoint. Preventive maintenance that misses a time calls big loss by system failure and expense of frequent full equipment is paid excessively in preventive maintenance itself but expense is paid much in preventive maintenance itself and whole expense escalation can be achieved preferably. Through this research, reliability model is constructed that do expense by smallest under full equipment policy chosen through comparison of each full equipment policy and preventive maintenance expense full equipment cycle and r ,s value are made using simulated annealing algorithm and simulated annealing algorithm that converge fast in multi-component system certified most suitable to optimization decision

• International Journal of Control, Automation, and Systems
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• v.5 no.5
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• pp.492-500
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• 2007

This paper focuses on the problem of guaranteed cost control for a class of uncertain linear delay systems with actuator failures. When actuators suffer "serious failure" the never failed actuators can not stabilize the system, based on switching strategy of average dwell time method, under the condition that activation time ratio between the system without actuator failure and the system with actuator failures is not less than a specified constant, a sufficient condition for exponential stability and weighted guaranteed cost performance are developed in terms of linear matrix inequalities (LMIs). Finally, as an example, a river pollution control problem illustrates the effectiveness of the proposed approach.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.242-245
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• 2003

The purpose of this study is to investigate the shear modulus, the shear strength at failure and the failure process of QLS(quadruple-lap shear) Test specimen were made of two different fiber contents CFRR and HTPB based polyurethane matrix. The CFRR specimen were prepared with 6.16% chopped carbon fiber and 11.6% chopped carbon fiber. We carried out the shear tests for three types of specimen. The shear modulus and strength of the CFRR was inspected with the increasing contents of chopped carbon fiber. In the other hand the shear strain of the CFRR was inspected with the decreasing contents of chopped carbon fiber.