• Computers and Concrete
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• v.17 no.2
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• pp.173-188
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• 2016

Generally, thermal stress induced by hydration heat causes cracking in mass concrete structures, requiring a thorough control during the construction. The prediction of the thermal stress is currently undertaken by means of numerical analysis despite its lack of reliability due to the properties of concrete varying over time. In this paper, a method for the prediction of thermal stress in concrete structures by adjusting thermal stress measured by a thermal stress device according to the degree of restraint is proposed to improve the prediction accuracy. The ratio of stress in concrete structures to stress under complete restraint is used as the degree of restraint. To consider the history of the degree of restraint, incremental stress is predicted by comparing the degree of restraint and the incremental stress obtained by the thermal stress device. Furthermore, the thermal stresses of wall and foundation predicted by the proposed method are compared to those obtained by numerical analysis. The thermal stresses obtained by the proposed method are similar to those obtained by the analysis for structures with internally as well as externally strong restraint. It is therefore concluded that the prediction of thermal stress for concrete structures with various boundary conditions using the proposed method is suggested to be accurate.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.474-477
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• 2006

To predict thermal stress independent of uncertain material properties of early age concrete, such as elastic modulus and creep, thermal stress device is used. In order to verify the application of various degree of constraint in the thermal stress device, a series of experiments were performed on mass concrete followed by numerical simulation. The application of various degrees of constraint can be achieved by using constraint frame material with different thermal expansion coefficient, length, and cross sectional area. Temperature development in the real structure has been simulated using temperature and humidity control chamber. The results from experiments and numerical analysis show that the thermal stresses estimated from simulation agree well with the general stress variations in the real structure even though the properties of concrete are uncertain.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.129-130
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• 2005

The electrical stress has a major effect on the long-term reliability of the thyristor. Therefore, it is needed to analyze the relationship between reliability and stress. In this paper, we investigate the device failure mechanism which induced by the stress. And also investigate the effect of the thermal stress on the device failure and relationship between electrical and thermal stress. Two-dimensional process simulator ATHENA and device simulator ATLAS are used to analyze the failure mechanism of the device.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.39-47
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• 2002

Heat is always the root of stress acting upon the electronic package, regardless of the heat due to the device itself during operation or working under the adverse environment. Due to the significant mismatch in coefficient of thermal expansion (CTE) and the thermal conductivity (K) of the packaging components, on one hand intensive research has been conducted in order to enhance the device reliability by minimizing the mechanical stressing and deformation within the package. On the other hand the effectiveness of different thermal enhancements are pursued to dissipate the heat to avoid the overheating of the device. However, the interactions between the thermal-mechanical loading has not yet been address fully. in articular when the temperature gradient is considered within the package. To address the interactions between the thermal loading upon the mechanical stressing condition. coupled-field analysis is performed to account the interaction between the thermal and mechanical stress distribution. Furthermore, process induced defects are also incorporated into the analysis to determine the effects on thermal conducting path as well as the mechanical stress distribution. It is concluded that it feasible to consider the thermal gradient within the package accompanied with the mechanical analysis, and the subsequent effects of the inherent defects on the overall structural integrity of the package are discussed.

• Journal of the Korea Convergence Society
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• v.11 no.7
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• pp.361-368
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• 2020

This study aims to examine whether the use of a spinal column thermal massage device for patients with muscle pain is effective in improving muscle pain, and to verify whether it is also effective in improving affective depression and stress. To this end, 16 study participants (male 31.25%) were treated with a thermal massage device during 5 sessions a week for 4 weeks and 40 minutes per session. According to the study results, the subjective pain level changed by a rate of VAS -46.32% and PDI -44.86%; a significant decrease was observed in, both, VAS and PDI. The depression and stress levels changed by a rate of BDI -21.84% and SRI -11.48%; a significant decrease was observed in, both, BDI and SRI. Therefore, the use of a thermal massage device to treat patients with muscle pain is expected to have a positive effect in improving not only subjective muscle pain, but also depression and stress.

• Journal of Korea Foundry Society
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• v.40 no.1
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• pp.1-6
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• 2020

Many studies involving a thermal stress analysis using computational methods have been conducted, though there have been relatively few experimental attempts to investigate thermal stress phenomena. Casting products undergo thermal stress variations during the casting process as the temperature drops from the melting temperature to room temperature, with gradient cooling also occurring from the surface to the core. It is difficult to examine thermal stress states continuously during the casting process. Therefore, only the final states of thermal stress and deformations can be detemined. In this study, specimens sensitive to thermal stress, were made by a casting process. After which the residual stress levels in the specimens were measured by a hole drilling method with Electron Speckle-Interferometry technique. Subsequently, we examined the thermal stresses in terms of deformation during the casting process by means of a numerical analysis. Finally, we compared the experimental and numerical analysis results. It was found that the numerical thermal stress analysis is an effective means of understanding the stress generation mechanism in casting products during the casting process.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.4
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• pp.439-442
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• 2004

In this study, we investigated about electrooptics characteristic of three kinds of TN cell on the polyimide surface. Monodomain alignments of thermal stressed TN cell over temperature of liquid crystal isotropic phase were almost the same as that of no thermal stressed TN cells. However, the thermal stressed TN cells have many defects. Also, threshold voltage and response time of thermal stressed TN cells show the same performances as no thermal stressed TN cells. There were little changes of value in these TN cells. However, transmittances of TN cells on the polyimide surface decrease with increasing thermal stress time. Finally, the residual DC voltage of the thermal stressed TN cell on the polyimide surface shows decrease of characteristics as increasing thermal stress time. Therefore, the thermal stability of TN cell was decreased by high thermal stress for the long times.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.744-750
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• 1998

Unlike common device, MEMS(micro-electro-mechanical system) device consists of very small mechanical structures which determine the performance of the device. Because of its small mechanical structure inside. MEMS device is very sensitive to thermal stress caused by CTE(coefficient of thermal expansion) mismatch between its components. Therefore, its characteristics are affected by material properties. process temperature. and dimensions of each layer such as chip, adhesive and substrate. In this study. we investigated the change of the thermal stress in the chip attached to a substrate. With computer-aided finite element method (FEM), the computer simulation of the thermal stress was conducted on variables such as bonding material, process temperature, bonding layer thickness and die size. The commercial simulation program, ABAQUS ver5.6, was used. Subsequently 3-layer test samples were fabricated, and their degree of bending were measured by 3-D coordinate measuring machine. The experimental results were in good agreement with the simulation results. This study shows that the bonding layer could be the source of stress or act as the buffer layer for stress according to its elastic modulus and CTE. Solder adhesive layer was the source of stress due to its high elastic modulus, therefore high compressive stress was developed in the chip. And the maximum tensile stress was developed in the adhesive layer. On the other hand, polymer adhesive layer with low elastic modulus acted as buffer layer, and resulted in lower compressive stress. The maximum tensile stress was developed in the substrate.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.9
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• pp.58-66
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• 2010

This study examines thermal safety on three-way catalyst that dominates 70 % among whole exhaust gas purification device in 2003. Three-way catalyst durability in the Korea requires 5 years/80,000 km in 1988 but require 10 years/120,000 km after 2002. Three-way catalyst durability in the USA requires 7 years/120,000 km but require 10 years/160,000 km after 2004. Three-way catalyst maintains high temperature in interior domain but maintains low temperature on outside surface. Therefore this device shows tensile stress on outside surface. Temperature distribution of three-way catalyst was acquired by thermal flow analysis for predicted thermal flow parameter. Thermal stress analysis for three-way catalysis was performed based on this temperature distribution. Thermal safety of three-way catalyst was estimated by power law dynamic fatigue life estimation and strength reduction methods for thermal stress.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.228-236
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• 2001

Even though numerous researches have been performed for the prediction of thermal stresses in mass concrete structures by both analytical and experimental means, the limitations exist for both approaches. In analytical approach, the fundamental limitation is derived from the difficulty of predicting concrete properties such as modulus of elasticity, coefficient of thermal expansion, etc.. In experimental approach, there are many uncertainties related to in-situ conditions, because a majority of researches have focused on measuring thermal stresses in actual and simulated structures. In this research, an experimental device measuring thermal stresses directly in a laboratory setting is developed. The equipment is located in a temperature chamber that follows the temperature history previously obtained from temperature distribution analysis. Thermal strains are measured continuously by a strain gauge in the device and the corresponding thermal stresses are calculated simply by force equilibrium condition. For the verification of the developed device, a traditional experiment measuring thermal strains from embedded strain gauges is performed simultaneously. The results show that the thermal strain values measured by the newly developed device agree well with the results from the benchmark experiment.