• Tribology and Lubricants
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• v.18 no.3
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• pp.194-203
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• 2002

This paper is the first step fur thermo-mechanical stress analyses of part with coated layer under contact load. A lot of coated material is applied in many structures to endure severe situation, like thermal stresses, high temperature gradients, irradiation, impacts by microscopic meteorites, and so on. In this part we are going to apply the FEM to analyze space parts with a coated layer subjected to a contact load thermo-mechanically. Coating layer is very thin in comparision with the structure, therefore it should take more times and behaviors to analyze whole model. In these reason we develop the FEM method of analyzing part with coated layer under contact load using partial model. Steady state temperature distribution of the part is obtained first, and then we apply quasi-static external load on the part. To obtain the final stage of solution, we compute the total solution, and by subtracting the thermal strain from the total ones we get the mechanical strains to compute stresses of the parts. In using the FEM, one has to discretize the model into many sub-domain, finite elements. The method is consisited of two steps. First step is to analyze the whole model with rather coarse meshes. Second step we cut a small region near the loading point, and analyze with very fine meshes. This method is allowable by the Saint-Venant's principle. And then, we finally shall check the therma1 load on the stresses of the space part with coating layer with or without substrate cracks. Then, we predict the actual behaviors of the part used in space.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.7
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• pp.41-52
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• 2003

In this paper, three-dimensional thermo-mechanical properties of carbon-phenolic 8-hamess satin weave composites were predicted considering geometric parameters of microstructures. The effective properties were calculated by a series of numerical experiments based on unit cell analysis. The microstructural details were modeled through macro-elements, and the periodic boundary conditions were derived for corresponding un it cell types. The Monte Carlo method was employed to consider the random phase shift between the layers, and the results were investigated on the effect of the geometric parameters of shift, number of layers and waviness ratios. Experimental tests were also performed and the results were compared.

• Korean Journal of Metals and Materials
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• v.49 no.9
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• pp.692-698
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• 2011

The thermo-chemical treatment (TCT) process was applied to achieve surface hardening of CP titanium. The following three different surface modification conditions were tested so that the best surface hardening process could be selected:(a) PVD, (b) TCT+PVD, and (c) TCT+Aging+PVD. These specimens were tested and analyzed in terms of surface roughness, wear, friction coefficient, and the gradient of hardening from the surface of the matrix. The three test conditions were all beneficial to improve the surface hardness of CP titanium. Moreover, the TCT treated specimens, that is, (b) and (c), showed significantly improved surface hardness and low friction coefficients through the thickness up to $100{\mu}m$. This is due to the functionally gradient hardened surface improvement by the diffused interstitial elements. The hardened surface also showed improvement in bonding between the PVD and TCT surface, and this leads to improvement in wear resistance. However, TCT after aging treatment did not show much improvement in surface properties compared to TCT only. For the best surface hardening on CP titanium, TCT+PVD has advantages in surface durability and economics.

• Structural Engineering and Mechanics
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• v.53 no.4
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• pp.703-723
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• 2015

In this paper optimization of volume fraction distribution in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) and subjected to steady state thermal and mechanical loadings is considered. The finite element method with graded material properties within each element (graded finite elements) is used to model the structure. Volume fractions of constituent materials on a finite number of design points are taken as design variables and the volume fractions at any arbitrary point in the cylinder are obtained via cubic spline interpolation functions. The objective function selected as having the normalized effective stress equal to one at all points that leads to a uniform stress distribution in the structure. Genetic Algorithm jointed with interior penalty-function method for implementing constraints is effectively employed to find the global solution of the optimization problem. Obtained results indicates that by using the uniform distribution of normalized effective stress as objective function, considerably more efficient usage of materials can be achieved compared with the power law volume fraction distribution. Also considering uniform distribution of safety factor as design criteria instead of minimizing peak effective stress affects remarkably the optimum volume fractions.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.430-437
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• 2010

In this paper, we develop a shape design optimization method for thermo-elastoplasticity problems that is applicable to the welding or thermal deformation problems of ship structures. Shell elements and a programming language APDL in a commercial finite element analysis code, ANSYS, are employed in the shape optimization. The point of developed method is to determine the design parameters such that the deformed shape after welding fits very well to a desired design. The geometric parameters of surfaces are selected as the design parameters. The modified method of feasible direction (MMFD) and finite difference sensitivity are used for the optimization algorithm. Two numerical examples demonstrate that the developed shape design method is applicable to existing hull structures and effective for the structural design of ships.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.207-225
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• 1992

The study is concerned with the thermo-viscoplastic finite element analysis of axisymmetric forward hot extrusion through square dies. The problem is treated as a nonsteady state problem because the distribution of temperature and material properties are continuously changing with the punch travel. In square die extrusion, difficulties arise from the severe distortion and die interference of elements at the aperture rim of the die even with a small punch travel. And finite element computation is impossible without intermittent remeshing. Accordingly, an automatic remeshing technique is proposed by employing specially designed mesh structure near the aperture rim. The analysis of temperature distribution includes heat conduction through material interfaces, heat convection and radiation to the atmosphere and is carried out by decoupling the heat analysis from the analysis of the deformation. The extrusion load and the distributions of strain rate and temperature are computed for the given cases rendering reasonable results. Computed grid distortions are found to be in good agreement with the experimental results. It has been thus shown that the proposed method of analysis can be effectively applied to the axisymmetric hot extrusion through square dies.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1166-1180
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• 1990

The study is concerned with the two-dimensional thermo-viscoplastic finite element analysis for radial forging as an incremental forging process. The deformation and temperature distribution of the workpiece during radial forging are studied. The analysis of deformation and the analysis of heat transfer are carried out for simple upsetting of cylinder by decoupling the above two analyses. A method of treatment for heat transfer through the contact region between the die and the workpiece is suggested, in which remeshing of the die elements is not necessary. Radial forging of a mild steel cylinder at the elevated temperature is subjected to the decoupled finite element analysis as well as to the experiment. The computed results in deformation, load and temperature distribution are found to be in good agreement with the experimental observations. As an example of viscoplastic decoupled analysis of hot radial forging, forging of a square section into a circular section is treated. The stresses, strains, strain rates and temperature distribution are computed by superposing material properties as the workpiece is rotated and forged incrementally. It was been thus shown that proposed method of analysis can be effectively applied to the hot radial forging processes.

• Korean Journal of Metals and Materials
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• v.49 no.11
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• pp.882-892
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• 2011

The influence of rhenium (Re) and ruthenium (Ru) addition on the solidification and solute redistribution behaviors in advanced experimental Ni-base superalloys has been investigated. A series of model alloys with different levels of Re and Ru were designed based on the composition of Ni-6Al-8Ta and were prepared by vacuum arc melting of pure metallic elements. In order to identify the influence of Re and Ru addition on the thermo-physical properties, differential scanning calorimetry analyses were carried out. The results showed that Re addition marginally increases the liquidus temperature of the alloy. However, the ${\gamma}^{\prime}$ solvus was significantly increased at a rate of $8.2^{\circ}C/wt.%$ by the addition of Re. Ru addition, on the other hand, displayed a much weaker effect on the thermo-physical properties or even no effect at all. The microsegregation behavior of solute elements was also quantitatively estimated by an electron probe microanalysis on a sample quenched during directional solidification of primary ${\gamma}$ with the planar solid/liquid interface. It was found that increasing the Re content gradually increases the microsegregation tendency of Re into the dendritic core and ${\gamma}^{\prime}$ forming elements, such as Al and Ta, into the interdendritic area. The strongest effect of Ru addition was found to be Re segregation. Increasing the Ru content up to 6 wt.% significantly alleviated the microsegregation of Re, which resulted in a decrease of Re accumulation in the dendritic core. The influence of Ru on the microstructural stability toward the topologically close-packed phase formation was discussed based on Scheil type calculations with experimentally determined microsegregation results.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.10
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• pp.1137-1143
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• 2012

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-plastic polymers, Acrylonitrile Butadiene Styrene (ABS) which is used broadly for machine elements material, as it has excellent mechanical properties such as impact resistance, toughness and stiffness compared to other polymers, was studied for creep characteristic at different levels of stress and temperatures. From the experimental results, the creep limit of ABS at room temperature is 80 % of tensile strength which is higher than PE and lower than PC or PMMA. Also the creep limits decreased to linearly as the temperatures increased, up to $80^{\circ}C$ which is the softening temperature of Butadiene ($82^{\circ}C$). Also the secondary stage of creep among the three creep stages for different levels of stress and temperature was non-existent which occurred for many metals by strain hardening effect.

• Advances in Computational Design
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• v.1 no.1
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• pp.105-117
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• 2016

The objective of this work is to study the restraining effect in fire resistance of framed structures and to evaluate the global response of reinforced concrete frames when exposed to fire based on advanced finite element method. To study the response a single portal frame is analyzed. The effect of floor slab on this frame is studied by modeling a beam-column-slab assembly. The evolution of temperature distribution, internal stresses and deformations of the frame subjected to ISO 834 standard fire curve for both the frames are studied. The thermal and structural responses are evaluated and a comparison of results of individual members and entire structure is done. From the study it can be seen that restraining forces has significant influence on both stresses and deflection and overall response of the structure when compared to individual structural member. Among the various structural elements, columns are the critical members in fire and failure of column causes the failure of entire structure. The fire rating of various structural elements of the frame is determined by various failure criteria and is compared with IS456 2000 tabulated fire rating.