• Corrosion Science and Technology
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• v.22 no.4
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• pp.265-272
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• 2023

The aim of this study was to develop a new in-situ observation method and instrument in micro-scale to investigate the mechanism of stress corrosion cracking (SCC) initiation of Ni-base alloys in a high temperature water environment of pressurized water reactors (PWRs). A laser confocal microscope (LCM), an autoclave with diamond window view port, and a slow strain-rate tester with primary water circulation loop system were components of the instrument. Diamond window, one of the core components of the instrument, was selected based on its optical, chemical, and mechanical properties. LCM was used to observe the specimen in micro-scale, considering the experimental condition of a high-temperature primary water environment. Using in-situ method and instrument, it is possible to observe oxidation and deformation of specimen surface in micro-scale through the diamond window in a high-temperature primary water in real-time. The in-situ method and instrument developed in this work can be utilized to investigate effects of various factors on SCC initiation in a high-temperature water environment.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.6
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• pp.938-946
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• 2008

Fe-base amorphous alloy and two crystalline phases composite were fabricated. The effect of temperature and strain rate on mechanical properties was evaluated utilizing compression test. Mixture of non-crystalline and crystalline phases were found using X-ray diffraction (XRD) and differential thermal analysis (DTA) tests. Based on glass transition temperature and crystallization temperature. compression tests were performed in the temperature ranging from $560^{\circ}C$ to $700^{\circ}C$ with $20^{\circ}C$ interval. Relationship between microstructure, including fracture surface morphology, and mechanical behavior was studied. The peak stress of Fe-base amorphous alloy was over 2GPa and expected to have a good wear resistance, but it is expected hard to deform because of low ductility. The peak stress and elongation of two crystalline phases composite was over 1GPa and about 20%, therefore it is possible to deform high strength wear resistant materials such as engine valve.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.206-209
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• 2004

Mechanical behavior of a fuel stack was studied using an orthotropic material model. The fuel stack is essentially composed of a bipolar plate (BP), a gasket, an end plate, a membrane electrolyte assembly (MEA), and a gas diffusion layer (GDL). Each component is fastened with a suitable pressure. It is important to maintain a suitable contact pressure distribution of BP, because it influences the power efficiency of the fuel cell stack. When it is exposed to high temperature, its behavior must be stable. Hence, we performed stress analysis at high temperature as well as at room temperature. At high temperature, the contact pressure distribution becomes poor. Many patents have shown that using an elastomer can overcome this phenomena. Its effect was also studied. By using an elastomer, we found a good contact pressure distribution at high temperature as well as at room temperature.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.2
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• pp.146-152
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• 2014

The temperature dependence of strain-enhanced electron mobility in nMOSFETs is investigated by using a self-consistent Schr$\ddot{o}$dinger-Poisson solver. The calculated results suggest that vertical compressive stress is more efficient to maintain the strain-enhanced electron mobility than longitudinal tensile stress in high temperature condition.

• Progress in Superconductivity and Cryogenics
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• v.15 no.3
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• pp.13-19
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• 2013

Superconducting field coils using a high-temperature superconducting (HTS) wires with high current density generate high magnetic field of 2 to 5 [T] and electromagnetic force (Lorentz force) acting on the superconducting field coils also become a very strong from the point of view of a mechanical characteristics. Because mechanical stress caused by these powerful electromagnetic force is one of the factors which worsens the critical current performance and structural characteristics of HTS wire, the mechanical stress analysis should be performed when designing the superconducting field coils. In this paper, as part of structural design of superconducting field coils for 17 MW class superconducting ship propulsion motor, mechanical stress acting on the superconducting field coils was analyzed and structural safety was also determined by the coupling analysis system that is consists of commercial electromagnetic field analysis program and structural analysis program.

• Korean Journal of Materials Research
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• v.24 no.4
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• pp.201-206
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• 2014

TiC-21 mol% Mo solid solution (${\delta}$-phase) and TiC-99 mol% Mo solid solution (${\beta}$-phase), and TiC-(80~90) mol% Mo hypo-eutectic composite were deformed by compression in a temperature range from room to 2300 K and in a strain rate range from $4.9{\times}10^{-5}$ to $6.9{\times}10^{-3}/s$. The deformation behaviors of the composites were analyzed from the strengths of the ${\delta}$- and ${\beta}$-phases. It was found that the high strength of the eutectic composite is due primarily to solution hardening of TiC by Mo, and that the ${\delta}$-phase undergoes an appreciable plastic deformation at and above 1420 K even at 0.2% plastic strain of the composite. The yield strength of the three kinds of phase up to 1420 K is quantitatively explained by the rule of mixture, where internal stresses introduced by plastic deformation are taken into account. Above 1420 K, however, the calculated yield strength was considerably larger than the measured strength. The yield stress of ${\beta}$-phase was much larger than that of pure TiC. A good linear relationship was held between the yield stress and the plastic strain rate in a double-logarithmic plot. The deformation behavior in ${\delta}$-phase was different among the three temperature ranges tested, i.e., low, intermediate and high. At an intermediate temperature, no yield drop occurred, and from the beginning the work hardening level was high. At the tested temperature, a good linear relationship was held in the double logarithmic plot of the yield stress against the plastic strain rate. The strain rate dependence of the yield stress was very weak up to 1273 K in the hypo-eutectic composite, but it became stronger as the temperature rose.

• International Journal of Industrial Entomology and Biomaterials
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• v.24 no.2
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• pp.69-74
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• 2012

Tropical tasar silkworm Antheraea mylitta Drury experiences extreme temperature stress conditions during its life cycle particularly during diapauses and first crop. The present study witnessed the impact of high temperature on some biochemical profiles and egg production (fecundity) of semi-domesticated Daba and Shorea robusta (Sal) based wild ecorace Laria during seed cocoon (pupa) preservation. Cocoons of Daba and Laria were treated with high temperature at $40^{\circ}C$ for 10 days in a BOD incubator. The protein profile and carbohydrate content in the hemolymph and fat body and total haemocyte count (THC) in the hemolymph of pupa were investigated. Further, the fecundity and fertility of egg was assessed. Significant increase in the protein concentration was observed in the hemolymph with reduction in the fat body (p<0.05). The difference in protein concentration was highly significant between the semidomesticated Daba and wild ecorace Laria (p<0.05). High pupal mortality (20%) and reduced fecundity (10-15%) in Daba was noticed compared to wild Laria. Also an increased THC (>28000) was recorded in Laria. The study infers the potentials of wild ecoraces in sustaining the extreme temperature conditions and need of adopting suitable package of practices for the preservation of diapause seed cocoons during extreme summer conditions. There is possibility to introgression thermal stress resistant traits in the semi-domesticated races of tasar silkworm by resorting to conventional breeding plans with wild races and keeping the thermal stress induced response as markers.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.709-713
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• 1996

The ceramic has such high qualities as light weight, abrasion resistance, heat resistance compared with metal, but since it is breakable, it can't be used as structural material and it is desirable to joining metal which is full of toughness, but, according as the ceramic/metal joint is executed at high temperature, the joint residual stress develops near the joint sides in the process of cooling the high temperature down to the suitable temperature due to difference of the thermal expansion coefficient between ceramic and metal, and the joint residualstress lowers the fracture strength. In this study, to ensure security and improvement of bending strength, 1 studies on see distribution shape of residual stress according to high thermal cycle, and the influnence of theraml cycle and distribution shape of residual stess on joint-strength.

• Journal of Environmental Science International
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• v.26 no.12
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• pp.1399-1405
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• 2017

We compared the spatial distribution of several heat stress indices (the Wet-Bulb Globe Temperature(WBGT) index, Environmental Stress Index (ESI), and Modified Discomfort Index(MDI)) for the heat wave of June 6~August 26, 2016, in Daegu. We calculated the heat stress indices using data from the high density urban climate observation network in Daegu. The observation system was established in February. 2013. We used data from a total of 38 air temperature observation points (23 thermometers and 18 automatic weather stations). The values of the heat stress indices indicated that the danger level was very high from 0900-2000h in downtown Daegu. The daily maximum value of the WBGT was greater than or equal to $35^{\circ}C$. The differences in the heat stress indices from downtown and rural areas were higher in the daytime than at nighttime. The maximum difference was about 4 before and after 1400h, and the time variations of the heat stress indices corresponded well. Thus, we were able to confirm that the ESI and MDI can be substituted with the WBGT index.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.1
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• pp.32-37
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• 2018

When designing high temperature piping system, creep phenomena must be considered. Since ASME code does not provide detailed methods of design by rule (DBR) for high temperature piping, Finite element analysis should be performed. However, In the case of piping system with frequent design changes, creep analysis of the entire piping system for every change is ineffective and practically impossible. Therefore, based on elastic and elastic-plastic analysis, which takes a relatively short time, the creep stress is predicted by using elastic follow-up factor method provided in R5 code and plastic-creep analogy presented by Hoff. The predicted creep stress for a virtual piping system was compared with the creep analysis result and the two results showed similar stress relaxation tendency in time.