• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.129-134
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• 2009

The dimension of forged part is different from that of die. Therefore, a more precise die dimension is necessarys to produce the precise part, considering the dimensional changes from forging die to final part. In this paper, both experimental and FEM analysis are performed to investigate the effect of several features including die dimension at each forging step and heat-treatment on final part accuracy in the closed-die upsetting. The dimension of forged part is checked at each stage as machined die, cold forged, and post-heat-treatment steps. The elastic characteristics and thermal influences on forging stage are analyzed numerically by the DEFORM-$2D^{TM}$. The effect of residual stress after heat-treatment on forged part could be considered successfully by using DEFOAM-$HT^{TM}$.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.394-400
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• 1996

Recently, the construction of infrastructures has been booming and acceleratin to keep up with rapid economic growth. Consturction activities and operation of transportation facilities caues unfavorable effects such as civil petitions associated with vibration-induced damages or nuisances. Vibration-controlled mixtures are latex, rubber powder and plastic resin, which have been deternimed to reduce vibration by and large reduce vibration. KS F2437 and travel time method have been used to figure out 1st natural frequency and dynamic elastic moduli. Dynamic damping ratios have been computed by adopting the polynomial curvefitting method and the geometric analysis method on the frequency spectrum curve, of which results have been compared and analyzed hereon.

• Advanced Composite Materials
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• v.17 no.2
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• pp.111-124
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• 2008

The effect of temperature on natural frequency and damping is investigated in two different composite materials, Kevlar 29 fiber woven and polyethylene cloth, used especially to design ballistic armor. A damping monitoring method is used experimentally to measure the frequency response curve and it is also modeled numerically using a finite element program. The natural frequencies of a material, or a system, are a function of its elastic properties, dimensions and mass. This concept is used to calculate theoretical vibration modes of the composites. The damping properties in terms of the damping factor are determined by the half-power bandwidth technique. Numerically analyzed and experimentally measured time response curves are compared. It is seen that polymer matrix composites have temperature dependent mechanical properties. This relationship is functional and they have different effects against temperature.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.05a
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• pp.32-38
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• 1999

Fatigue crack propagation behavior for block load in high strength aluminum alloys was investigated in this study. The materials used in this study are aluminum alloy 5052-H32. Initial crack was made by applying cyclic load to a through crack with chevron notch. Crack length was measured from calibration curve, which was plotted by known crack length and resistance of standard specimens. Load was obtained from linear regression formula. Unloading elastic compliance method was applied to check the crack closure and cracked area. The present study results can be usefully applied to predicting the change of crack propagation rate, the crack closure, and the delay of crack propagation.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.53-60
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• 2002

It has been recognized that damage control must become a more explicit design consideration. In an effort to develop design methods based on performance it is clear that the evaluation of the inelastic response is required. The methods available to the design engineer today are nonlinear time history analyses, or monotonic static nonlinear analyses, or equivalent static analyses with simulated inelastic influences. Some codes proposed the capacity spectrum method based on the nonlinear static(pushover) analysis to determine earthquake-induced demand given the structure pushover curve. This procedure is conceptually simple but iterative and time consuming with some errors. This paper presents a nonlinear direct spectrum method to evaluate seismic Performance of structure, without iterative computations, given the structural initial elastic period and yield strength from the pushover analysis, especially for multi degree of freedom structures. The purpose of this paper is to investigate accuracy and confidence of this method from a point of view of various earthquakes and unloading stiffness degradation parameters.

• Journal of Ocean Engineering and Technology
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• v.18 no.6 s.61
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• pp.51-57
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• 2004

In this study, the improved three-dimensional analysis model designed for a more accurate analysis of marine cable-supported structures, is presented. In this improved analysis model, the beam elements, of which the stability function is derived using Taylor's series expansions, are used to model space frame structures, and the truss elements. The equivalent elastic modulus of the truss elements is evaluated on the assumption that the deflection curve of a cable has a catenary function. By using the proposed three-dimensional analysis model, nonlinear static analysis is carried out for some cable-supported structures. The results are compared with previous studies and show good agreement with their findings.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.28-33
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• 2014

Recently, the actuator worked by the driving recovery-force of the thermo elastic martensitic transformation of shape memory alloys(SMA) has been studied. This paper presents a study on the fatigue life of shape memory alloy (SMA) actuators undergoing thermally induced martensitic phase transformation under various stress levels. shape memory recoverable stress and strain of Ti-44.5at.%Ni-8at.%Cu alloys were by means of constant temperature tensile tests. Differential scanning calorimetry (DSC) was employed in order to investigate the transformation characteristics of the alloy before the tests. the results were summarized as follows. The martensite inducing stress incerased with the increasing of the Cu-contents. The fatigue life decreased with the increasing of the test load and the Cu-content. The data acquired will be very useful during the design process of an SMA NiTiCu element as a functional part of an actuator.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3286-3288
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• 1999

The electrostatically actuated test structure was presented to measure the micro mechanical characteristics of micromaterials as thin films forming the microactuators. The test structure was fabricated by the surface micromachining processes and driven by the electrostatic force, In order to measure the fracture toughness, the sharp notch in the test structure was introduced by the etching process. On the basis of the beam bending theory, the elastic modulus was measured by using the microcantilevr beam and the mechanical displacement, curvature and deflection curve under the electrostatic force was evaluated by using the electrostatic structure.

• Tunnel and Underground Space
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• v.6 no.3
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• pp.239-244
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• 1996

Cracks have influence on the physical and mechanical and, more importantly, on the engineering properties of the rock. Physical properties including the volumetric deformation coefficient, electrical resistivity, seismic wave velocity, and the mechanical properties such as the elastic constants and strength of rock are affected significantly by the presence of cracks of various sizes. An experimental program was undertaken to investigate the effect of a finite line crack on the diffraction of the plane compressional wave. Horizontal and vertical components of displacement and acceleration curve were obtained using a single-source and multi-receivers system. A theoretical model from numerical analysis implementing the finite element method was compared with the measured data.

• Tribology and Lubricants
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• v.20 no.3
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• pp.132-139
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• 2004

Many researches about the contacts between cam and follower have investigated EHL film thickness either without dynamic loading effect or only with curve fitting formula such as Dowson-Hamrock's, because including squeeze film effect makes it hard to obtain convergence and stability of computation. Therefore, inaccurate information about minimum film thickness without dynamic loading condition causes inappropriate design of cam profiles and wrong selection of cam and follower materials. In this work, computation tools both for kinematics and dynamics of valve train system of push-rod type and for fluid film thickness with elastic deformation on the basis of dynamic loading condition with multigrid multi-level method is developed. The computational results of minimum film thickness with the respects of both static and dynamic loading conditions are compared for the contact of flat follower over the entire cycle.