• 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.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.9
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• pp.135-141
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• 2003

MEMS structures generally have been fabricated using surface-machining method, but the interface failure between silicon substrate and evaporated thin film frequently takes place due to the residual stress inducing by the applied the various loads. And the very important physical property in the heated environment is the linear coefficient of thermal expansion. Therefore this paper studied the residual stress caused the thermal loads in the thin film and introduced the simple method to measure the trend of the residual stress by the indentation. Specimens were made of materials such as Al, Au and Cu and thermal load was applied repeatedly. The residual stress was measured by nano-indentation using AFM and FEA. The existence of the residual stress due to thermal load was verified by the experimental results. The indentation length of the thermal loaded specimens increased minimum 11.8％ comparing with the virgin thin film caused by tensile residual stress. The finite element analysis results are similar to indentation test.

• 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.

• 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.

• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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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.

• 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.

• 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.

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.208-209
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• 2006

This study presents the thermal stress characteristics of TL porcelain insulators(healthy and ageing) by the accelerating thermal mechanical ageing test with forced temperature gradient. The test temperature gradient is $95^{\circ}C(-35{\sim}60^{\circ}C)$, it was focused to high temperature thermal stress as compared with IEC 60575 standard. There was no a discrimination in the case of healthy aluminous porcelain insulators, dissimilarly in crystoballite insulators according to this test method. It was indicated that the long tenn reliability by thermal stress was conformed reasonably through the conventional accelerating ageing test methods.