• Journal of Mechanical Science and Technology
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• v.17 no.2
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• pp.171-180
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• 2003

One of the most significant problems in the processing of composite materials is residual stress. The high residual stress may cause cracking in the matrix without external loads and degrade the integrity of composite structures. In this study, thermo-viscoelastic residual stresses occurred in an aluminum liner-inserted polymer composite cylinder are investigated. This type of the structure is used for rocket fuselage due to the convenience to attach payloads and equipment to the metal liner by machining. The time and degree of cure dependent thermo-viscoelastic constitutive equations are developed and coupled with a thermo-chemical process model. These equations are solved with the finite element method to predict the residual stresses in the composite cylinder and also in the interface between the liner and the composite during cure.

• International Journal of Automotive Technology
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• v.8 no.2
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• pp.219-224
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• 2007

Recently, atmospheric contaminations has become worse due to the increased number of automobile. The PCV (Positive Crankcase Ventilation) valve acts as a flow control to allow re-combustion of blow-by gas by having it flow from a crankcase to an inlet manifold suction tube. Also, during the fabrication of the PCV valve, micro cracks may occur in the valve body and be extended under operation. The excessive stress distribution and crack initiation on the PCV valve body would bring an unstable blow-by gas flow rate control and would cause valve failure. The purpose of this study is to examine the crack affects on the stress and strain variations on the PCV valve according to the inlet and outlet manifold under differential pressures. From the results, we can explain the behavior of the crack extension for a safe condition of PCV valve.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.3
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• pp.165-171
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• 2003

In a structure, many components are fastened together using bolts, nuts and rivets through drilled holes. Not only do these fastened joints enable easy assembly and dismantling, they are also able to transfer as well as to distribute loads applied onto the structures. The major drawback of such connections, however, is that the fatigue life of the components is reduced by the presence of the hole since the stress concentration around the hole is increased. In addition, the hole drilling process itself may introduce defects or roughness at the surfaces of the hole that may cause further decrease in fatigue performance of the components. For applications where fatigue loadings are important, one way to compensate the decrease in fatigue life of the components is by introduction of beneficial compressive residual stress around the hole using cold working. The material used for this research were A12024-T351 and A17050-T7451 using the primary member of aircraft. We present, In this paper, the characteristics of coldworking by evaluation of the hole expansion ratio, residual stress distribution, and fatigue properties.

• Proceedings of the SCSK Conference
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• 2003.09b
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• pp.456-457
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• 2003

The use of relaxing cosmetic products is more and more widespread on the self care market, since stress is considered as a major cause of discomfort in modem life. Cortisol, the stress hormone, helps the human body to regulate itself by acting on carbonhydrate, proteins and fat metabolisms. IgA are immune molecules involved in the stress response of the human body. The less the human body is stressed, the more the salivary IgA rate increases. Salivary cortisol and IgA have the advantage of being easily assessed with non invasive methods. Finally, conductance is the measurement of the modification in the electrical resistance of the skin. By this means, the measurement of the conductance enable the assessment of somebody's stress.(omitted)

• Journal of the Korean Society for Precision Engineering
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• v.15 no.12
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• pp.28-36
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• 1998

This investigation is the result of a structural analysis by the finite element method and static loading test for the optimal structural design of an electric railway vehicle made of stainless 301L materials. We analyzed the stress and displacement of the existing electric car-body structure for predicting the position of concentrated stress, the flow of stress, rigidity to be occurred in the car-body structure when it is subjected to the vertical load. It was exposed that the side sills and window corners around the bolsters are the weak parts of the electric car-body structure because the bolsters of the electric car-body structure were subjected to the vertical load and dynamic load to be occurred during running. The flow of stress and the cause of stress concentration in the weak zone were studied in order to prevent the concentration of stress and buckling. The rearrangement of the structure and the selection of the beam elements were also carried out for optimum design of the structure.

• Journal of Korean Public Health Nursing
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• v.26 no.1
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• pp.60-71
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• 2012

Objectives: The purpose of this study was to identify occupational stress and to determine level of depression of school nurses and to identify factors that influence depression. Methods: A cross-sectional design was employed in this study. Participants included 146 school nurses from D city. Data collection was conducted on January 17-21, 2011, using self-administered questionnaires. The SPSS/WIN 11.5 was used in performance of data analysis. Results: Significant differences in occupational stress were observed according to age, occupation and perceived mental health status, and in depression according to marital status, perceived mental health status and physical disease. Depression showed significant positive correlation with occupational stress (r=.35, p<.001). In regression analysis, occupational stress and physical health state were found to be the cause of depression in 17% of subject. Conclusion: Findings of this study allow for a comprehensive understanding of occupational stress and level of depression of school nurses in Korea. Further study using a larger random sample and various variables is needed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.167-171
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• 2001

High temperature deformation behavior of Fe-28Al-5Cr alloy has been investigated known to show anomalous temperature dependence of yield strength. Specifically, the effect of Cr addition has been examined. A series of tensile and load relaxation tests have been carried out to obtain the flow behavior of Fe-28Al-5Cr alloy at the elevated temperatures. The flow curves have then been analyzed using the inelastic deformation theory recently proposed. Firstly, high temperature flow stress of iron aluminides can be resolved into internal stress and frictional stress. Secondly, the temperature corresponding to peak strength gets higher level at faster strain rate, which presumably due to the increased contribution of internal stress in observed flow stress. And thirdly, the alloying of Cr seems to cause solid-solution strengthening of frictional stress level and the elevation of 2nd order transition temperature. In this analogy, Fe-28Al-5Cr exhibits better strength especially at relatively higher temperature and lower strain rate than Fe-28Al.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.378-385
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• 2000

Fracture resistance (J-R) curves, which are used for elastic-plastic fracture mechanics analyses, decreased under tension-compression loading condition. This phenomenon was proved by several former researches, but the causes have not been clear yet. The objective of this paper is to investigate the cause of this phenomenon. On the basis of fracture resistance curve test results, strain hardening hypothesis, stress redistribution hypothesis and crack opening hypothesis were built. In this study, hardness tests, Automated Ball Indentation(ABI) tests, theoretical stress field analyses, and crack opening analyses were performed to prove the hypotheses. From this study, strain-hardening of material, generation of tensile residual stress at crack tip, and crack opening effects are proved as the causes of the decrease hypothesis.

• BMB Reports
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• v.35 no.1
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• pp.67-86
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• 2002

Three routes have been identified triggering neuronal death under physiological and pathological conditions. Excess activation of ionotropic glutamate receptors cause influx and accumulation of $Ca^{2+}$ and $Na^+$ that result in rapid swelling and subsequent neuronal death within a few hours. The second route is caused by oxidative stress due to accumulation of reactive oxygen and nitrogen species. Apoptosis or programmed cell death that often occurs during developmental process has been coined as additional route to pathological neuronal death in the mature nervous system. Evidence is being accumulated that excitotoxicity, oxidative stress, and apoptosis propagate through distinctive and mutually exclusive signal transduction pathway and contribute to neuronal loss following hypoxic-ischemic brain injury. Thus, the therapeutic intervention of hypoxic-ischemic neuronal injury should be aimed to prevent excitotoxicity, oxidative stress, and apoptosis in a concerted way.

• Korean Journal of Occupational Health Nursing
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• v.19 no.2
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• pp.223-235
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• 2010

Purpose: This study was done to investigate the prevalence of job stress and musculoskeletal symptoms, and to identify the factors that affect work-related musculoskeletal symptoms of the 119 Emergency medical technicians (EMT). Method: From August 26 to September 10, 2010, the data were obtained from 456 EMT working in Daejeon city or Choongnam province. For data analysis, descriptive statistics and multiple logistic regression were performed using SAS version 9.1. Results: Physical environment, job demand, interpersonal conflict, and occupational climate were stressful to 119 EMT. The prevalence of musculoskeletal symptoms of female EMT was higher than those of the male EMT's. After gender and age were adjusted, there ware significant relationships between musculoskeletal symptoms and some risk factors including occupational class, hours of intensive musculoskeletal use, previous injury or work-related injury, physical burden, and job stress. Overall, a higher degree of job stress increased musculoskeletal symptoms. Conclusion: Job stress is a major cause of musculoskeletal symptoms. To prevent and manage musculoskeletal disease of 119 EMT, there is a need to develop a management program for musculoskeletal symptoms to reduce occupational stress, considering gender differences.