• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.425-428
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• 2006

In order to estimate the reduction of laodbearing capacity, followed by the attributive change of heat while high strength concrete structure is revealed on fire it is necessary to evaluate, it is necessary to evaluate the property of material under high temperature such as thermal conductivity, specific heat, compressive strength, modulus of rigidity and diminution figure. Therefore, this study is for the purpose of presenting evaluation data for the analysis of thermal behavior about the high strength concrete material under high temperature, through the experiment by manufacturing concrete(40, 50, 60, 80, 100 MPa) commonly used in the construction field. As a result of the study, in the case of physical attribute, it demonstrates a greater fluctuation of change than the one of 30 MPa concrete. In case of specific heat, the high strength concrete, shown the serious diminution between $500{\sim}600^{\circ}C$, presents the thermal change area corresponding to the change of high strength concrete. In compressive strength, regardless of intensity of concrete, all of them show the first intensity loss between normal temperature and $100^{\circ}C$, the dramatic loss beyond $400^{\circ}C$. The concrete weighing above 50 MPa shows a twice lower dramatic intensity loss than the one weighing $30{\sim}40MPa$. The concrete ranging from $60{\sim}80MPa$, shows the biggest diminution of modulus of elasticity under $400^{\circ}C$, which implies the structural unstability of temperature.

• Journal of Adhesion and Interface
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• v.10 no.4
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• pp.162-168
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• 2009

As a preliminary study of optimum composite properties under cryogenic temperature, the comparison of interfacial properties of carbon or glass fibers reinforced epoxy composites was evaluated at ambient and intermediate low temperature, i.e., 25 and $-10^{\circ}C$ by using micromechanical techniques. Under tensile and compressive loading conditions, their mechanical modulus at low temperature was higher than that atambient temperature. Interfacial shear strength (IFSS) at ambient and low temperatures was compared to each other, depending on epoxy matrix toughness and apparent modulus at the interface. The IFSS was much higher at low temperature than that at room temperature because of the increased epoxy matrix modulus. Statistical distributions of tensile strengths of glass and carbon fibers were evaluated for different temperature ranges, which is dependent upon fiber's inherent flaws and rigidity.

• Structural Engineering and Mechanics
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• v.53 no.4
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• pp.625-644
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• 2015

In this paper, a two-layer partial interaction composite beams model considering the higher order shear deformation of sub-elements is built. Then, the governing differential equations and boundary conditions for static analysis of linear elastic higher order composite beams are formulated by means of principle of minimum potential energy. Subsequently, analytical solutions for cantilever composite beams subjected to uniform load are presented by Laplace transform technique. As a comparison, FEM for this problem is also developed, and the results of the proposed FE program are in good agreement with the analytical ones which demonstrates the reliability of the presented exact and finite element methods. Finally, parametric studies are performed to investigate the influences of parameters including rigidity of shear connectors, ratio of shear modulus and slenderness ratio, on deflections of cantilever composite beams, internal forces and stresses. It is revealed that the interfacial slip has a major effect on the deflection, the distribution of internal forces and the stresses.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.234-238
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• 1999

This study suggests the design of the functionally gradient composite, [0/90/0/core]$_s$ cross-ply laminate, to prevent stress concentration induced from the difference of rigidity between the bone and the artificial hip joint and to reinforce the wear property of the surface and the expectation of their mechanical properties. First, the four-point bending test is done about wet bones and dry bones to know the mechanical properties of the cortical bones. In result, the wet bone shows the viscoelastic behavior and the dry bone shows the elastic behavior. Moreover, we expect the properties of the proposed gradient composites as a function of carbon fiber volume fraction in each layer to apply Halpin-Tsai equation, CLPT(classical laminate plate theory), and Bernoulli beam theory etc. and decide the thickness ratio of each lamina in order to match Young's modulus of the anisotropic cortical bone with the proposed gradient composites.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.12
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• pp.938-946
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• 2003

Length of an unconstrained viscoelastic damping layer on beams is determined to maximizeloss factor using a numerical search method. The fractional derivative model can describe damping characteristics of viscoelastic damping materials accurately, and is used to represent nonlinearity of complex modulus with frequencies and temperatures. Equivalent flexural rigidity of the unconstrained beam is obtained using Ross, Ungar, Kelvin[RUK] equation. The loss factors of partially covered unconstrained beam are calculated by a modal strain energy method. Optimal lengths of the unconstrained viscoelastic damping layer of beams are identified with ambient temperatures and thickness ratios of beam and damping layer by using a finite-difference-based steepest descent method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.665-671
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• 2003

Length of an unconstrained viscoelastic damping layer on beams is determined to maximize loss factor using a numerical search method. The fractional derivative model can describe damping characteristics of the viscoelastic damping material, and is used to represent nonlinearity of complex modulus with frequencies and temperatures. Equivalent flexural rigidity of the unconstrained beam is obtained using Ross, Ungar, Kerwin(RUK) equation. The loss factors of partially covered unconstrained beam are calculated by a modal strain energy method. Optimal lengths of the unconstrained viscoelastic damping layer of beams are obtained with respect to ambient temperatures and thickness ratios of beam and damping layer.

• Magazine of the Korean Society of Agricultural Engineers
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• v.45 no.2
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• pp.68-77
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• 2003

Shell structure are widely used in a variety of engineering application and mathematical solution of shell structures are available only for a few special cases. The solution of shell structure is more complicated when it has such condition as winker foundation, variable thickness and other problem. In this paper, a simple finite element method is presented for the analysis of axisymmetric several types of shell structure subjected to axisymmetric loads and having uniform and varying wall thickness on elastic foundation. The method is based on the analogy with a beam on elastic foundation (BEF), foundation stiffness matrix where the foundation modulus and beam flexural rigidity are replaced by appropriate parameters pertaining to the shell under considerations. The technique is attractive for implementation on a numerical solution by means of a computer program coded in FORTRAN language with a few elements. To demonstrate this fact, it gives good results which compare well with SAP2000.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.619-622
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• 2005

Purpose of this study is to investigate the size-dependent mechanical properties in micron scale medium. Theories such as the couple stress theory and strain gradient theory explain that the deformation in the micron scale is dependent upon the size of the medium. Specimens of the cantilever type, bridge type and paddle type beam that have thickness of 900, 1000 and 1200 nm and width of 10, 20, 30 and $50{\mu}m$ were fabricated by the MEMS technique. We carried out the bending and torsion test to measure the mechanical properties such as the young's modulus, yield strength and torsional rigidity using the AFM(Atomic Force Microscopy).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.114-121
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• 1998

This paper presents the model updating of an equipment panel by using modal test and sensitivity analysis. The equipment panel is one of the major structures of communication satellite, on which broadcasting and communication equipments are mounted. For high rigidity and light weight, the panel was designed as an aluminum honeycomb sandwich panel. In addition, heat pipes were embedded in the panel for thermal control. It is essential to improve the finite element model of a satellite by using modal test in order to verify the satellite is designed with adequate margin under launch environment. In this paper, Young's modulus of aluminum facesheet was selected as a modified parameter by sensitivity analysis. The effect of rotational springs of boundary points was also considered.

• Journal of Korea Foundry Society
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• v.2 no.2
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• pp.18-30
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• 1982

For the purpose of improving the casting yields of ductile iron castings, the casting conditions for riserlese design were investigated with 150mm cube. As the important casting conditions, chemical composition, pouring temperature, mold rigidity and cooling rate were confirmed. 1. We could obtain the sound castings with the hypereutectic ductile iron. 2. In order to reduce liquid contraction, the pouring temperature should be low as much as possible 3. We could obtain the sound castings through using the rigid mold without mold cavity deformation 4. The modulus of the castings should be 2.5cm one or larger.