• Title, Summary, Keyword: Thermal Stress

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The Optimum Design of Casting Process through Prediction and control of Thermal Deformation (주조 공정 시 열변형 예측과 제어를 통한 금형의 최적 설계에 관한 연구)

  • Choi, Bong-Hak;Kwahk, Si-Young;Kim, Jeong-Tae;Choi, Jeong-Kil;Lee, Dong-Il
    • Journal of Korea Foundry Society
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    • v.25 no.5
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    • pp.209-215
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    • 2005
  • The design of the Metal mold casting should consider several variables such as the material properties and shape of the mold. In particular, the thermal stress generated by the thermal expansion and contraction depending on the thermal gradient of the mold causes partial plastic deformation on the mold, which causes damage or fracture of the cast. Consequently, the thermal deformation along with thermal stress leads to thermal deformation of the cast itself. In this study, the temperature analysis of the cast and mold is simulated by FDM to control the thermal deformation and stress as a result of the thermal gradient of mold. Using the results from FDM simulation, the thermal deformation and stress are analyzed by FEM and, the optimal mold design with minimum thermal deformation of the cast is suggested.

Study on Thermal Stability of Liquid Crystal Display for Projection TV Application (프로젝션 TV 적용을 위한 액정 디스플레이의 열적 안정성에 관한 연구)

  • Kang, Hee-Jin;Hwang, Jeoung-Yeon;Oh, Yong-Cheul;Seo, Dae-Shik
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.19 no.11
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    • pp.1033-1036
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    • 2006
  • We have investigated electro-optical characteristics in three kinds of twisted nematic (TN) cells on the polyimide surface. The threshold voltage and the response time of thermal stressed TN cells were same that of no thermal stressed TN cells. There were little change of value in these TN cells. On the other hand, transmittance of no thermal stressed TN cells were better than that of thermal stressed TN cells. Transmittances of TN cells on the polyimide surface decreased by increasing thermal stress time. Moreover, the residual DC of the thermal stressed TN cells increased as increasing thermal stress temperature and time. Therefore, thermal stability of TN cells were decreased gradually by giving high thermal stress for a long time.

Experimental investigation on the variation of thermal conductivity of soils with effective stress, porosity, and water saturation

  • Lee, So-Jung;Kim, Kyoung-Yul;Choi, Jung-Chan;Kwon, Tae-Hyuk
    • Geomechanics and Engineering
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    • v.11 no.6
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    • pp.771-785
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    • 2016
  • The thermal conductivity of soils is an important property in energy-related geotechnical structures, such as underground heat pumps and underground electric power cable tunnels. This study explores the effects of geotechnical engineering properties on the thermal conductivity of soils. The thermal conductivities of quartz sands and Korean weathered silty sands were documented via a series of laboratory experiments, and its variations with effective stress, porosity, and water saturation were examined. While thermal conductivity was found to increase with an increase in the effective stress and water saturation and with a decrease in porosity, replacing air by water in pores the most predominantly enhanced the thermal conductivity by almost one order of magnitude. In addition, we have suggested an improved model for thermal conductivity prediction, based on water saturation, dry thermal conductivity, saturated thermal conductivity, and a fitting parameter that represents the curvature of the thermal conductivity-water saturation relation.

Stress Evolution with Annealing Methods in SOI Wafer Pairs (열처리 방법에 따른 SOI 기판의 스트레스변화)

  • Seo, Tae-Yune;Lee, Sang-Hyun;Song, Oh-Sung
    • Korean Journal of Materials Research
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    • v.12 no.10
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    • pp.820-824
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    • 2002
  • It is of importance to know that the bonding strength and interfacial stress of SOI wafer pairs to meet with mechanical and thermal stresses during process. We fabricated Si/2000$\AA$-SiO$_2$ ∥ 2000$\AA$-SiO$_2$/Si SOI wafer pairs with electric furnace annealing, rapid thermal annealing (RTA), and fast linear annealing (FLA), respectively, by varying the annealing temperatures at a given annealing process. Bonding strength and interfacial stress were measured by a razor blade crack opening method and a laser curvature characterization method, respectively. All the annealing process induced the tensile thermal stresses. Electrical furnace annealing achieved the maximum bonding strength at $1000^{\circ}C$-2 hr anneal, while it produced constant thermal tensile stress by $1000^{\circ}C$. RTA showed very small bonding strength due to premating failure during annealing. FLA showed enough bonding strength at $500^{\circ}C$, however large thermal tensile stress were induced. We confirmed that premated wafer pairs should have appropriate compressive interfacial stress to compensate the thermal tensile stress during a given annealing process.

The Effects of Thermal Stress on Seal Dynamics (시일 동특성에 미치는 열응력의 영향에 관한 연구)

  • 양보석
    • Tribology and Lubricants
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    • v.7 no.2
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    • pp.36-40
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    • 1991
  • The dynamic characteristics of the annular pressure seal employed in pump have been theoretically deduced with consideration of the effects of elastic deformation due to the thermal stress. The thermal deformation is developed for the two-dimensional steady thermal stress distribution in a infinite circular cylinder subject to heating of the seal and shaft surface into the surrounding fluid. To demonstrate this analysis, the effects of thermal stress on rotordynamic coefficients and logarithmic decrement for annular plain seals was shown.

Thermal stresses in a non-homogeneous orthotropic infinite cylinder

  • Edfawy, E.
    • Structural Engineering and Mechanics
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    • v.59 no.5
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    • pp.841-852
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    • 2016
  • The present paper is concerned with the investigation of propagation of thermoelastic media, the finite difference technique is used to obtain the solution for the uncoupled dynamic thermoelastic stress problem in a non-homogeneous orthrotropc thick cylindrical shell. In implementing the method, the linear dynamic thermoelasticity equations are used with the appropriate boundary and initial conditions. Thermal shock stress becomes of significant magnitude due to stress wave propagation which is initiated at the boundaries by sudden thermal loading. Numerical results have been given and illustrated graphically in each case considered. The presented results indicate that the effect of inhomogeneity is very pronounced.

Treatment of Stainless Steel Cladding in Pressurized Thermal Shock Evaluation: Deterministic Analyses

  • Changheui Jang;Jeong, lll-Seok;Hong, Sung-Yull
    • Nuclear Engineering and Technology
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    • v.33 no.2
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    • pp.132-144
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    • 2001
  • Fracture mechanics is one of the major areas of the pressurized thermal shock (PTS) evaluation. To evaluate the reactor pressure vessel integrity associated with PTS, PFM methodology demands precise calculation of temperature, stress, and stress intensity factor for the variety of PTS transients. However, the existence of stainless steel cladding, with different thermal, physical, and mechanical property, at the inner surface of reactor pressure vessel complicates the fracture mechanics analysis. In this paper, treatment schemes to evaluate stress and resulting stress intensity factor for RPV with stainless steel clad are introduced. For a reference transient, the effects of clad thermal conductivity and thermal expansion coefficients on deterministic fracture mechanics analysis are examined.

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Determination of Thermal Dtress Intensity Factors for the Interface Crack under Vertical Uniform Heat Flow (수직 균일 열유동하에 있는 접합 경계면 균열의 열응력세기계수 결정)

  • 이강용;설창원
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.1
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    • pp.201-208
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    • 1991
  • In case that an interface crack exists in an infinite two-dimensional elastic bimaterial, the crack surface is insulated under traction free and the uniform heat flow vertical to the crack from infinite boundary is given. Temperature and stress potentials are obtained by using complex variable approach to solve Hilbert problems. The results are used to obtain thermal stress intensity factors. Only mode I thermal stress intensity factor occurs in case of the homogeneous material. Otherwise, mode I and II thermal stress intensity factor is much smaller than one of mode II.

Reasonable Evaluation of Thermal Stress in the Hydration Heat Analysis (범용구조해석 프로그램의 수화열응력 산정기법 연구)

  • 전세진
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.789-794
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    • 2002
  • The relationship is investigated between material modeling of concrete and the evaluation procedure of thermal stress by the hydration heat. In this respect, some important points are suggested to which special attention should be paid to reasonably evaluate the thermal stress using the widely-used structural analysis programs. This study indicates that proper material model should be used to draw incremental stress evaluation that takes into account the change of elastic modulus with time. Some correction techniques are also presented when using the program that don't have proper built-in procedure for the calculation of the thermal stress.

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A Study on the Effect of the Thickness of Bond Coating on the Thermal Stresses of a Sprayed Thermal Barrier Coating (접착층의 두께가 용사 열차폐 코팅의 열응력에 미치는 영향에 관한 연구)

  • 김형남
    • Journal of Welding and Joining
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    • v.19 no.2
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    • pp.221-227
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    • 2001
  • Based on the principle of complementary energy, an analytical method is developed which focuses on the end effects for determining thermal stress distributions in a three-layered beam. This method gives the stress distributions which completely satisfy the stress-free boundary conditions. A numerical example is given in order to verify this method. The results show that the present analytical solutions have the values of stress in excellent agreement with the solutions derived by other investigators. Using this method, the effects of the thickness of bond coat on the thermal stresses of a typical sprayed thermal barrier coating, which consists of IN738LC substrate, MCrAIY bond coat and ZrO$_2$-8wt%Y$_2$O$_3$top coat, were investigated.

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