• Geomechanics and Engineering
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• v.12 no.3
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• pp.465-481
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• 2017

Thermal effect has great influence on wellbore stability in Dongfang 1-1 (DF 1-1) gas field, a reservoir with high-temperature and high-pressure. In order to analyze the wellbore stability in DF1-1 gas field, the variation of temperature field after drilling was analyzed. In addition, the effect of temperature changing on formation strength and the thermal expansion coefficients of formation were tested. On this basis, a wellbore stability model considering thermal effect was developed and the thermal effect on fracture pressure and collapse pressure was analyzed. One of the main challenges in this gas field is the decreasing temperature of the wellbore will reduce fracture pressure substantially, resulting in the drilling fluid leakage. If the drilling fluid density was reduced, kick or blowout may happen. Therefore, the key of safe drilling in DF1-1 gas field is to predict the fracture pressure accurately.

• Steel and Composite Structures
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• v.15 no.5
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• pp.481-505
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• 2013

This paper focuses on thermal post-buckling analysis of functionally graded beams with temperature dependent physical properties by using the total Lagrangian Timoshenko beam element approximation. Material properties of the beam change in the thickness direction according to a power-law function. The beam is clamped at both ends. In the case of beams with immovable ends, temperature rise causes compressible forces and therefore buckling and post-buckling phenomena occurs. It is known that post-buckling problems are geometrically nonlinear problems. Also, the material properties (Young's modulus, coefficient of thermal expansion, yield stress) are temperature dependent: That is the coefficients of the governing equations are not constant in this study. This situation suggests the physical nonlinearity of the problem. Hence, the considered problem is both geometrically and physically nonlinear. The considered highly non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. In this study, the differences between temperature dependent and independent physical properties are investigated for functionally graded beams in detail in post-buckling case. With the effects of material gradient property and thermal load, the relationships between deflections, critical buckling temperature and maximum stresses of the beams are illustrated in detail in post-buckling case.

• Journal of the Korean Ceramic Society
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• v.50 no.5
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• pp.326-332
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• 2013

In this study, we prepared yttria stabilized zirconia granules for thermal barrier coatings using a spray drying process. First, we characterized the properties of granules such as flow rate and packing density for utilizing the air plasma spray process. The flow rate and packing density data showed 0.732 g/sec and 2.14 $g/cm^3$, respectively, when we used larger and denser particles, which are better than hollow granules or smaller spherical granules. Second, we chose larger, spherical granules fabricated in alcohol solvent as starting powders and sprayed it on the bondcoat/nimonic alloy by an atmospheric plasma spray process varying the process parameters, the feeding rate, gun speed and spray distance. Finally, we evaluated representative thermal and mechanical characteristics. The thermal expansion coefficients of the coatings were $11{\sim}12.7{\times}10^{-6}/^{\circ}C$ and the indentation stress measured was 2.5 GPa at 0.15 of indentation strain.

• Restorative Dentistry and Endodontics
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• v.31 no.5
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• pp.344-351
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• 2006

The purpose of this study was to evaluate the thermal expansion characteristics of injectable ther-moplasticized gutta-perchas and a Resilon. The materials investigated are Obtura gutta-percha, Diadent gutta-percha, E&Q Gutta-percha Bar and Epiphany (Resilon). The temperature at the heating chamber orifice of an Obtura II syringe and the extruded gutta-percha from the tip of both 23- and 20-gauge needle was determined using a Digital thermometer. A cylindrical ceramic mold was fabricated for thermal expansion test, which was 27 mm long, with an internal bore diameter of 3 mm and an outer diameter of 10 mm. The mold was filled with each experimental material and barrel ends were closed with two ceramic plunger. The samples in ceramic molds were heated in a dilatometer over the temperature range from $25^{\circ}C$ to $75^{\circ}C$. From the change of specimen length as a function of temperature, the coefficients of thermal expansion were deter-mined. There was no statistical difference between four materials in the thermal expansion in the range from $35^{\circ}C$ to $55^{\circ}C$ (p > 0.05). However, Obtura Gutta-percha showed smaller thermal expansion than Diadent and Metadent ones from $35^{\circ}C$ to $75^{\circ}C$ (p < 0.05). The thermal expansion of Epiphany was similar to those of the other gutta-percha groups.

• Advances in materials Research
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• v.5 no.1
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• pp.35-53
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• 2016

Flexural bending analysis of perfect and imperfect functionally graded materials plates under hygro-thermo-mechanical loading are investigated in this present paper. Due to technical problems during FGM fabrication, porosities and micro-voids can be created inside FGM samples which may lead to the reduction in density and strength of materials. In this investigation, the FGM plates are assumed to have even and uneven distributions of porosities over the plate cross-section. The modified rule of mixture is used to approximate material properties of the FGM plates including the porosity volume fraction. In order the elastic coefficients, thermal coefficient and moisture expansion coefficient of the plate are assumed to be graded in the thickness direction. The elastic foundation is modeled as two-parameter Pasternak foundation. The equilibrium equations are given and a number of examples are solved to illustrate bending response of Metal-Ceramic plates subjected to hygro-thermo-mechanical effects and resting on elastic foundations. The influences played by many parameters are investigated.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.58-63
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• 1999

Almost all concrete structures have many inevitable cracks for various reasons such as drying shrinkage, heat liberation of cement, fatigues or repeating loads and movements. Conventionally, they are repaired with epoxy materials. The Epoxy resins used by repair materials are different from properties of the base concrete materials such as thermal and mechanical properties - thermal expansion coefficients, bending strength. And the epoxy resin cannot release the water inside the concrete structure and cause corrosion of the steel bars. In this study, before the experiment got launched, we had analyzed cement and slag. Then We blended the two grades of ultra fine cement using high blaine cement and slag. And the cement slurry was produced by water and suprplasticizer to each blended ultra fine cement in various conditions. The slurry produced by each conditions was evaluated with flow properties such as viscosity, dropping time, segregation and observation of dry surface after injection.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.10
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• pp.954-960
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• 2008

The effects of elastic modulus coefficient and linear expansion coefficient of overhead distribution power line(ACSR $58 mm^2$) on sag behavior in distribution line have been investigated to clarify the difference between specification and experimental level. The elastic modulus coefficients of Al wire and steel wire were $5,182.6 kgf/mm^2,\;18,348.8 kgf/mm^2$, respectively Therefore, the computational composition elastic modulus coefficient of the power line was $7,063.5 kgf/mm^2$, while that of experimentally measured was $7681.1 kgf/mm^2$. As a result, we found that elastic modulus coefficient which was experimentally measured was higher than that of computational by 8.7 %. However, when planner designs the sag of disoibution line, the elastic modulus coefficient of power line $8,400 kgf/mm^2$ should be generally adopted. These two different using values lead to the sag difference of 0.62 m. The other results will be discussed.

• Korean Journal of Materials Research
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• v.31 no.2
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• pp.97-100
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• 2021

We report the effect of Standard Clean-1 (SC-1) cleaning to remove residual Ti layers after silicidation to prevent Al diffusion into Si wafer for Ti Schottky barrier diodes (Ti-SBD). Regardless of SC-1 cleaning, the presence of oxygen atoms is confirmed by Auger electron spectroscopy (AES) depth profile analysis between Al and Ti-silicide layers. Al atoms at the interface of Ti-silicide and Si wafer are detected, when the SC-1 cleaning is not conducted after rapid thermal annealing. On the other hand, Al atoms are not found at the interface of Ti-SBD after executing SC-1 cleaning. Al diffusion into the interface between Ti-silicide and Si wafer may be caused by thermal stress at the Ti-silicide layer. The difference of the thermal expansion coefficients of Ti and Ti-silicide gives rise to thermal stress at the interface during the Al layer deposition and sintering processes. Although a longer sintering time is conducted for Ti-SBD, the Al atoms do not diffuse into the surface of the Si wafer. Therefore, the removal of the Ti layer by the SC-1 cleaning can prevent Al diffusion for Ti-SBD.

• Macromolecular Research
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• v.16 no.6
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• pp.503-509
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• 2008

A series of colorless polyimide (PI) nanocomposite films were synthesized from 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) with various organoclay contents by solution intercalation polymerization to poly(amic acid)s, followed by thermal imidization. The variation with the organoclay content of the thermomechanical properties, morphology, and optical transparency of the hybrids was examined at organoclay loadings ranging from 0 to 1.0 wt%. The hybrid films showed high optical transparency and almost no color, with cut-off wavelengths ranging from 352 and 356 nm and very low $b^*$ values of 1.19-1.77. The hybrid PI films showed good thermal properties with a glass transition temperature of $280-287^{\circ}C$. Most films did not show any significant thermal decomposition below $490^{\circ}C$. The addition of only a small amount of organoclay was sufficient to improve the tensile properties of the PI films with maximum enhancement being observed at 0.25 wt% organoclay. Moreover, these PI hybrids also had low coefficients of thermal expansion (CTE).

• Journal of Ocean Engineering and Technology
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• v.10 no.2
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• pp.106-119
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• 1996

The ceramic has various high mechanical properties such as heat, abrasion, corrosion resistance and high temperature strength compared with metal. It also has low speciffic weight, low thermal expansibillity, low thermal conductivity. However, it could not be used as structural material since it is brittle and difficult for the machining. Therefore, there have been many researches to attempt to join ceramic with metal which is full of ductillity in order to compensate the weakness of ceramic.The problem is that residual stress develops around the joint area while the ceramic/metal joint material is cooled from high joining temperature to room temperature due to remarkable difference of thermal expansion coefficients between ceramic and metal. Especially, the residual stress at both edges of the specimen reduces the strngth of joint to a large amount by forming a singular stress field. In this study, two dimensional finite element method is attempted for the thermal elastic analysis. The joint residual stress of ceramic/metal developed in the cooling process is investigated and the change of joint residual stress resulted from the repetitive heat cycle is also examined. In addition, it is attempted to clarify the joint stress distribution of the case of tensile load and of the case of superposition of residual stress and actual loading stress.