• Journal of Welding and Joining
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• v.16 no.5
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• pp.67-75
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• 1998

This study aimed at he experimental and finite element analytic investigation of the effect of preheating on he residual stress of weldment. In this study, an autogenous arc welding was used on type 304 stainless steel and MARC as F.E.M. common code was utilized in analysis The analyses include transient and moving heat source and thermal properties as function of temperature. During welding, the thermal cycles of four locations in the weldment were recorded to investigate of the behavior of thermal stress and residual stress. The experimental and analytic results had good coincidence and show that there are two factors influencing the formation of welding residual stress in preheat process. One is the elevation of welding equilibrium temperature and the other is the increase of amount of heat input. The former decrease welding residual stress and the latter increase welding residual stress. Therefore, the cumulative effects result in the welding residual stress not being improved significantly with preheating in 304 stainless steel.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.7
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• pp.1705-1712
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• 1994

Hilbert problems are derived to evaluate thermal stress intensity factors for a partially insulated crack subjected to vertically uniform heat flow in infinite bonded dissimilar materials. In case of fully insulated crack surface, the present solutions of thermal stress intensity factors are reduced into the same as the previous results. For the homogeneous material, mode II thermal stress intensity factor only exists. However, in the bonded dissimilar materials, both mode I and II thermal stress intensity factors are obtained. Specially, in this case, mode II thermal stress intensity factor is dominent. Also, thermal stress intensity factors are strongly influenced by the material properties. Thermal stress intensity factors decrease when the degree of insulation decreases.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.8
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• pp.598-604
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• 1999

This paper describes the research to minimize the film stress and maximize the aspect ratio of photoresist structure, especially about SU-8 for electroplating mold. UV LIGA process using SU-8 allows fabricating high aspect ratio polymer structures. However, it is hard to get fine patterns in the high aspect ratio structures because of high internal stress and difficulty of removing SU-8. The purpose of this paper is to setup the process condition for the obtainment of both low film stress and high aspect ratio and to find design rules that make the pattern be less dependent on stress problem. Firstly, the process of heat treatment and exposure of SU-8 are proposed. These two conditions control the amount of cross-linkage in polymer structure, which is the most important parameter of both pattern generation and remaining stress. Heat treatment is dealed with soft bake and post-exposure-bake. Temperature and time duration of each step are varied with heat treatment condition. Some test patterns are fabricated to evaluate the proposed process. Nickel electroplating is performed with the mold fabricated through the proposed process to confirm the SU-8 as a good electroplating mold.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.119-129
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• 1990

In case that the body with a cusp crack is under uniform heat flow, thermal stress intensity factors are calculated by using boundary element method with linearized body force term. The crack surface is under insulated or fixed temperature condition and the types of crack are symmetric lip and airfoil cusps. Numerical values of thermal stress intensity factors for a Griffith crack and cusp cracks in infinite bodies are proved to be in good agreement within .+-.5% when compared with the previous numerical and exact solutions, respectively. The thermal stress intensity factors for symmetric lip and airfoil cusp cracks in finite bodies are calculated about various effective crack lengths, configuration parameters, and heat flow directions. With the same crack surface thermal boundary conditions, heat flow directions and crack lengths, there are no appreciable differences in variations of thermal stress intensity factors between symmetric lip and airfoil cusp cracks. The signs of thermal stress intensity factors for each cusp crack are changed with each crack surface thermal boundary condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.5
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• pp.1524-1533
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• 1996

Risidual stress of cylindrical glass rods are measured by photoelasticity to study the variation of stresses with respect to heat treatment temperatures. In order to measure the stresses accurately, fringe sharpening and multiplication techniques are applied to the determination of photoelastic fringe orders. Filon's separationmethod is used to resolve circumferential and redial stress ocmponents from isochromatic fringes which are the same as in-plane maximum shearing stresses. According to the photoelastic measurements, residual stress is increased as the heat treatment temperature of the rods is raised from $560^{\circ}C$ to $650^{\circ}C$ All the circumferential stress components are changed from tensile stresses to compressive ones at approximate $R_m$/$R_o$ = 0.6, where $R_o$/ is outer radius and $R_m$any measured radius. This analysis shows that residual stresses of the glass rods approach zero if the rods are heat-treated near the strain point.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.11
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• pp.68-73
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• 1999

In this paper, the residual stresses for the wide-band laser heat treatment using a polygon mirror have been analyzed. The results of FE analysis are compared with the experimental results. ANSYS Version 5.3, a commercial FE-code, is used for the FE stress analysis. The structural analysis was performed on after thermal analysis. The residual stress distribution across the hardened area was measured by the X-ray diffraction technique. The laser hardening conditions, 2kW laser power and 2mm/s travel speed, were used for the experiment and the FE analysis. Analysis results, which is maximum tensile residual stress is about 143MPa and maximum compressive residual stress is about -380MPa. Under same parameters with the analysis, experimental results indicate that MTRS is about 152MPa and MCRS is about -312MPa. The experimental results is about 6% higher than the FE analysis. As a result, residual stress data from the experiment close well with that of the FE analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1145-1153
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• 2011

The purpose of this study is to relieve the residual stress of Al6061 using cryogenic heat treatment. Experimental T6 and cryogenic heat treatments were carried out to define the convective heat-transfer coefficient, which was then applied in the finite-element method (FEM) to predict the residual stress. The predicted residual stress was compared with the residual stress measured by X-ray diffraction (XRD), and the results were in good agreement. The mechanical properties were estimated by measuring the electrical conductivity and hardness. In addition, the size and formation of the precipitations were observed by TEM and XRD analysis for both T6 and cryogenic heat treatments. The effects of the cryogenic heat treatment on the residual stress, mechanical properties, and precipitation of Al6061 alloys were thus confirmed.

• Food Science of Animal Resources
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• v.34 no.1
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• pp.20-25
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• 2014

This study evaluated the effects of frankfurter fat content on Listeria monocytogenes resistance to heat stress and gastric fluid, and the Caco-2 cell invasion efficiency of the pathogen. A 10-strain mixture of L. monocytogenes was inoculated on frankfurters formulated with 10%, 20%, and 30% fat content (10%: F10, 20%: F20, 30%: F30) and stored at $10^{\circ}C$ for 30 d. The samples were analyzed for L. monocytogenes resistance to heat stress and a simulated gastric fluid challenge. The total bacteria and L. monocytogenes survival rates were measured on tryptic soy agar plus 0.6% yeast extract and Palcam agar, respectively. L. monocytogenes colonies inoculated on F10, F20, and F30 samples were used for a Caco-2 cell invasion assay. In general, no obvious differences were observed between the survival rates of total bacteria and L. monocytogenes grown on different fat contents under heat stress and gastric fluid challenge. However, L. monocytogenes obtained from the F30 samples had a significantly higher Caco-2 cell invasion efficiency than those in the F10 and F20 samples (p<0.05). These results indicate that although high fat content in food may not be related to L. monocytogenes resistance to heat stress and gastric fluid, it may increase the Caco-2 cell invasion efficiency of the pathogen.

• KSBB Journal
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• v.18 no.4
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• pp.294-300
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• 2003

In the previous study, we have isolated several vaginal lactobacilli from Korean woman and selected one of them (KLB12) for further study, which was indentified as Lactobacillus fermentum by sequence analysis of 16S rRNA gene. Formulated L. fermentum KLB12 can be used for ecological treatment of bacterial vaginosis. For pharmaceutical formulation, the spray-drying process is required where stress such as high temperature is routinely applied. In this study, we found that heat stress at 60$^{\circ}C$ for 20∼30min reduced the viable cell population of KLB12 by 10$\sub$6/～10$\sub$9/. However, adaptation of KLB12 cells at 52$^{\circ}C$ made them more thermotolerant upon exposure to 60$^{\circ}C$. The level of thermal protection in RSM (reconstituted skim milk) by adaptation in acid (pH 5), cold (4$^{\circ}C$), ethanol (3％), NaCI (0.3M) was also examined. Although not as efficient as the homologous stress, adaptations in both cold and NaCI gave considerable cross protection against heat stress. When chloramphenicol was added during heat adaptation, adaptation effect was abolished. This suggests that de novo protein synthesis is necessary during the adaptation process. Important changes in proteome during heat adaptation was examined with two-dimensional gel electrophoresis.

• Journal of Animal Science and Technology
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• v.65 no.1
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• pp.197-208
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• 2023

The objective of this study was to investigate the effects of a traditional dry period (60 d) versus a no dry period (0 d) on the milk production, physiological response, and metabolic status of dairy cows exposed to heat stress during the transition period. Holstein dairy cows (n = 15) with similar expected calving dates were randomly assigned to two different dry period lengths: (1) no dry period (n = 7) and (2) a traditional dry period of 60 days (n = 8). All cows were studied from 8 weeks before expected calving to 10 weeks after calving and experienced heat stress during the transition period. The results showed that cows with no dry period decreased their milk yield in subsequent lactation, but compensated for the loss of milk yield accounted for by additional milk yield before calving. The energy balance at postpartum was improved in cows with no dry period compared to cows with a traditional dry period. There were no significant differences in the physiological response and blood metabolites at postpartum between the dry period lengths of dairy cows exposed to heat stress during the transition period. Taken together, our results showed that omitting the dry period improved the milk production and metabolic status of dairy cows exposed to heat stress during the transition period.