• Applied Microscopy
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• v.43 no.2
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• pp.88-97
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• 2013

Technical investigation to figure out the problems arising during in-situ heating electron backscatter diffraction (EBSD) analysis inside scanning electron microscopy (SEM) was carried out. EBSD patterns were successfully acquired up to $830^{\circ}C$ without degradation of EBSD pattern quality in steels. Several technical problems such as image drift and surface microstructure pinning were taking place during in-situ experiments. Image drift problem was successfully prevented in constant current supplying mode. It was revealed that the surface pinning problem was resulted from the $TiO_2$ oxide particle formation during heating inside SEM chamber. Surface pinning phenomenon was fairly reduced by additional platinum and carbon multi-layer coating before in-situ heating experiment, furthermore was perfectly prevented by improvement of vacuum level of SEM chamber via leakage control. Plane view in-situ observation provides better understanding on the overall feature of recrystallization phenomena and cross sectional in-situ observation provides clearer understanding on the recrystallization mechanism.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.47-51
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• 2014

In this work, a possible mechanism for grain evolution in Al-Mg alloy films during thermal annealing is suggested on the basis of the phase transition and the related residual stress. Al-Mg alloy films with compositions of 14.0 and 18.0 wt% Mg content were deposited on cold-rolled steel substrates by the direct current co-sputtering method using Al and Mg targets. After the deposition, the samples were thermally annealed at $400^{\circ}C$ for 10 min. The featureless, dense cross-sectional microstructure of the as-deposited films turned into a grainy microstructure after the thermal annealing. According to the residual stress evaluated by using the $XRD-sin2{\psi}$ technique and the phase analysis by XRD, it is likely that grains were created in order to relieve the additional accumulation of residual stress originating from the phase transition from face-centered cubic Al (${\alpha}$) to Al3Mg2 (${\beta}$) and Mg (${\delta}$) phases, suggesting interplay between the microstructure and residual stress.

• Computational Structural Engineering
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• v.10 no.4
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• pp.267-280
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• 1997

This paper deals with the development of simplified methods to predict the creep deformation of reinforced concrete beams. The layer approach based on a degenerate kernel of compliance function in form of Dirichlet series is mentioned and a simplified analytical method derived from the equilibrium equations and compatibility conditions is proposed to overcome the sophisticated calculation procedures in the classical creep analysis. Correlation studies between analytical and experimental results and design codes are conducted with the objective to establish the validity of the proposed methods. Besides, various parameter studies are conducted with the objective to identify the effects of cracking, steel ratio and sectional shape in the creep deformation and the obtained results are discussed.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.18-21
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• 2004

A GFRP based composite blade was developed for a 750kW wind energy conversion system of type class I. The blade sectional geometry was designed to have a general shell-spar structure. The load cases specified in the IEC61400-1 international specification were considered. For withstanding all relevant extreme loads, the structural analysis for the complete blade was performed using a commercial FEM code. The static load carrying capacity, buckling stability, blade tip deflection and natural frequencies at various rotational speeds were evaluated to satisfy the strength requirements in accordance with the IEC61400-1 and GL Regulations. For designing a lightweight blade, the thickness and the lay-up pattern of the skin-foam sandwich structures were optimized iteratively using the DOT program T-bolts were used for joining the blade root and the hub, which were modeled using a 3D FE volume model. In order to confirm the safety of the root connection, the static stresses of the thick root laminate and the steel. bolts were predicted by taking account of the bolt pretension and the root bending moments. The calculated stresses were compared with the material strengths.

• Steel and Composite Structures
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• v.28 no.2
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• pp.179-194
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• 2018

Reliable and accurate method of computationally aided design processes of advanced thin walled structures in automotive industries are much essential for the efficient usage of smart materials, that possess higher energy absorption in dynamic compression loading. In this paper, most versatile components i.e., thin walled crash tubes with different geometrical profiles are introduced in view of mitigating the impact of varying cross section in crash behavior and energy absorption characteristics. Apart from the geometrical parameters such as length, diameter and thickness, the non-dimensionalized parameters of average forces which control the plastic bending moment for varying thickness has explored in view of quantifying its impact on the crashworthiness of the structure. The explicit finite element code ABAQUS is utilized to conduct the numerical studies to examine the effect of parametric modifications in crash behavior and energy absorption. Also the simulation results are experimentally validated. It is evident that the circular cross-sectional tubes are preferable as high collision impact shock absorbers due to their ability in withstanding axial and oblique impact loads effectively. Furthermore, the specific energy absorption (SEA), crash force efficiency (CFE), plastic bending moment, peak force responses and its impact for optimally tailoring a design to cater the crashworthiness requirements are investigated. The primary outcome of the study is to provide sufficient information on circular tubes for the use of energy absorbers where impact oblique loading is expected.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.2
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• pp.128-136
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• 2010

It has been verified that there is an effect of diminishing in section bringing in internal core section reinforcement and external prestressing rather than general plate-girder bridge as a consequence of analysis. In particular, positive effect was seen in the aspect of usability when external prestressing was in application as rises gained from it minimized the hanging down of a bridge. Based on the result of analysis, a sectional diagram applicable per number of girder has been illustrated which made it possible to estimate the intensity of internal stress in the futurewhere number of girder is limited to 4 and regression equation is presented after regression analysis has been carried out.

• Resources Recycling
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• v.7 no.4
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• pp.76-80
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• 1998

In order to establish the ICP composition analysis system of the compotes which have been producing and using the domestic iron oxides, the Sectional Committee of Iron Oxides had organized an analysis working team. which carried out the component analysis of several samples and den discussed about thou analysis results through 1 year. At the 1st meeting, the component deviation was reduced. At the 3rd meeting, the deviation range if each company was reduced below ${\pm}$20% and it means to be improved on an analysis level with Japaness steel companies.

• Structural Engineering and Mechanics
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• v.73 no.4
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• pp.397-405
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• 2020

In this study size optimization of large-scale dome structures with dynamic constraints is presented. In the optimal design of these structure, the Jaya algorithm is used to find minimal size of design variables. The design variables are the cross-sectional areas of the steel truss bar elements. To take into account the constraints which are the first five natural frequencies of the structures, the finite element analysis is coded in Matlab programs using eigen values of the stiffness matrix of the dome structures. The Jaya algorithm and the finite elements codes are combined by the help of the Matlab - GUI (Graphical User Interface) programming to carry out the optimization process for the dome structures. To show the efficiency and the advances of the Jaya algorithm, 1180 bar dome structure and the 1410 bar dome structure were tested by taking into the frequency constraints. The optimal results obtained by the proposed algorithm are compared with those given in the literature to demonstrate the performance of the Jaya algorithm. At the end of the study, it is concluded that the proposed algorithm can be effectively used in the optimal design of large-scale dome structures.

• Structural Engineering and Mechanics
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• v.6 no.3
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• pp.305-325
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• 1998

A method that determines the minimum stiffness of baracing to achieve non-sway buckling conditions at a given story level of a multi-column elastic frame is proposed. Condensed equations that evaluate the required minimum stiffness of the lateral and torsional bracing are derived using the classical stability functions. The proposed method is applicable to elastic framed structures with rigid, semirigid, and simple connections. It is shown that the minimum stiffness of the bracing required by a multi-column system depends on: 1) the plan layout of the columns; 2) the variation in height and cross sectional properties among the columns; 3) the applied axial load pattern on the columns; 4) the lack of symmetry in the loading pattern, column layout, column sizes and heights that cause torsion-sway and its effects on the flexural bucking capacity; and 5) the flexural and torsional end restrains of the columns. The proposed method is limited to elastic framed structures with columns of doubly symmetrical cross section with their principal axes parallel to the global axes. However, it can be applied to inelastic structures when the nonlinear behavior is concentrated at the end connections. The effects of axial deformations in beams and columns are neglected. Three examples are presented in detail to show the effectiveness of the proposed method.

• Steel and Composite Structures
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• v.39 no.5
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• pp.543-564
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• 2021

In this study free vibration analysis of a cracked Goland composite wing is investigated. The wing is modelled as a cantilevered beam based on Euler- Bernoulli equations. Also, composite material is modelled based on lamina fiber-reinforced. Edge crack is modelled by additional boundary conditions and local flexibility matrix in crack location, Castigliano's theorem and energy release rate formulation. Governing differential equations are extracted by Hamilton's principle. Using the separation of variables method, general solution in the normalized form for bending and torsion deflection is achieved then expressions for the cross-sectional rotation, the bending moment, the shear force and the torsional moment for the cantilevered beam are obtained. The cracked beam is modelled by separation of beam into two interconnected intact beams. Free vibration analysis of the beam is performed by applying boundary conditions at the fixed end, the free end, continuity conditions in the crack location of the beam and dynamic stiffness matrix determinant. Also, the effects of various parameters such as length and location of crack and fiber angle on natural frequencies and mode shapes are studied. Modal analysis results illustrate that natural frequencies and mode shapes are affected by depth and location of edge crack and coupling parameter.