• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.34-41
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• 2014

The goal of this study is to investigate some crack behaviors which affect the crack propagation angle at the planar solid oxide fuel cell with cracks under the fabricating and operating temperature and analyze the stresses by 3 steps processing on the solid oxide fuel cell. Currently, there are lots of researches of the performance improvement for fuel cells, and also for the more powerful efficiency. However, the planar solid oxide fuel cell has demerits which the electrode materials have much brittle properties and the thermal condition during the operating process. It brings some problems which have lower reliability owing to the deformation and cracks from the thermal expansion differences between the electrolyte, cathode and anode electrodes. Especially the crack in the corner of the electrodes gives rise to the fracture and deterioration of the fuel cells. Thus it is important to evaluate the behavior of the cracks in the solid oxide fuel cell for the performance and safety operation. From the results, we showed the stress distributions from the cathode to the anode and the effects of the edge crack in the electrolyte and the slant crack in the anode. Futhermore the crack propagation angle was expected according to the crack length and slant angle and the variation of the stress intensity factors for the each fracture mode was shown.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.43.2-43.2
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• 2011

Wind turbine pitch/yaw bearings are relatively big and have different operating conditions like very heavy load to support compared with widely used industrial bearings. Once pitch/yaw bearings failed, according to their special surroundings, serious damages like higher repair costs and additional costs by stopped electricity generation are occur. Therefore, pitch/yaw bearings must be designed to have enough strength and fatigue life under actual operating conditions. In this study, with finite element analysis, it was investigated that stress distribution between rolling elements and raceway and comparatively analyzed using widely used guideline (NREL DG03). Design parameters of wind turbine pitch/yaw bearings are also analyzed, and it could be used as reference for the large bearing design field.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.5
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• pp.817-823
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• 2015

IPMSM for traction motor has high power density and wide operating range. But high power density causes internal temperature rise and it makes big armature reaction which causes irreversible demagnetization. And with wide operating range, rotor rotating fast gets stress from centrifugal force. For this reason, traction motor is designed to considerate stress of rotor and irreversible demagnetization for reliability. This paper explains shape design method of 120kW IPMSM accounting improvement of reliability. Finally, the validity of the analysis and the performance evaluation were verified through testing of the final model.

• Speech Sciences
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• v.11 no.3
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• pp.95-109
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• 2004

Metrical Phonology has asserted that stress shift does not occur in English compounds because it violates the Continuous Column Constraint. Noun phrases, on the other hand, freely allow for stress shift, whereby the preceding stress moves forward to the preceding heavy syllable. This paper hypothesizes that stress does not shift in compounds as opposed to noun phrases and compares their pitch accentual patterns in a phonetic experiment. More specifically, we examined two-word combinations, noun phrases and compounds, whose boundaries involve stress clash and assured that the preceding words involve a heavy syllable ahead of the stress to guarantee the place for a shifting stress. Depending on where the preceding pitch accent is aligned, stress shift is determined. Results show that stress shift occurs in approximately 47% of the noun phrases and 59% of the compounds; therefore, the hypothesis is not borne out. This suggests that the surface representations derived by phonological rules may not be implemented in real utterance but that phonetic forms may be determined by the phonetic constraints. directly operating on human speech.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.352-362
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• 2016

The purpose of this study was to examine the level of stress, healthcare accreditation related job stress, adaptation, and turnover intentions, as well as to identify influencing factors of turnover intentions for operating room nurses. This study employed a descriptive correlational design. The data were collected from 163 operating room nurses using a structural questionnaire. Stress was different by age (F=5.629, p=.004), marital status (t=-2.907, p=.004), and children (t=-2.623, p=.010). Healthcare accreditation related job stress was different by age (F=11.924, p<.001), marital status (t=-4.747, p<.001), children (t=-4.434, p<.001), work experience in the OR (F=6.000, p=.003), and work reasons in the OR (t=-2.543, p=.012). Turnover intention was different by age (F=21.472, p<.001), education level (F=4.997, p<.008), religion (t=3.235, p=.001), work experience in the OR (F=13.599, p<.001), position (t=3.222, p=.002), work reasons in the OR (t=-3.001, p=.003), and a shift pattern of duties (t=-2.797, p=.006). Turnover intention was significantly correlated with stress, healthcare accreditation related job stress, and adaptation. Factors affecting turnover intention were healthcare accreditation related job stress, adaptation, and age. These factors accounted for 36.2% of turnover intention. These results suggest that relief of stress and healthcare accreditation related job stress and interventions for improving stress management.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.05a
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• pp.171-176
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• 1999

Nondestructive inspection and accompanying life analysis based on fracture mechanics were the major conventional methods for evaluating remaining life of critical high temperature components in power plants. By using these conventional methods, it has been difficult to perform in-service inspection for life prediction. Also, quantitative damage evaluation due to unexpected abrupt changes in operating temperature was almost impossible. Thus, many efforts have been made for evaluating remaining life during operation of the plants and predicting real-time life usage values based on the shape of structures, operating history, and material properties. In this study, a core software for on-line life monitoring system which carries out real-time life evaluation of a critical component in power boiler(high temperature steam headers) is developed. The software is capable of evaluating creep and fatigue life usage from the real-time stress data calculated by using temperature/stress transfer Green functions derived for the specific headers and by counting transient cycles. The major benefits of the developed software lie in determining future operating schedule, inspection interval, and replacement plan by monitoring real-time life usage based on prior operating history.

• Nuclear Engineering and Technology
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• v.33 no.6
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• pp.566-584
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• 2001

In this paper, the progressive deformation and the creep-fatigue damage for the conceptually designed reactor internals of KALIMER(Korea Advanced Liquid MEtal Reactor) are carried out by using the elastic analysis method in the RCC-MR code for normal operating conditions including the thermal load, seismic load (OBE) and dead weight. The maximum operating temperature of this reactor is 53$0^{\circ}C$ and the total service lifetime is 30 years. Thus, the time- dependent creep and stress-rupture effects become quite important in the structural design. The effects of the thermal induced membrane stress on the creep-fatigue damage are investigated with the risk of the elastic follow-up. To calculate the thermal stress, detailed thermal analyses considering conduction, convection and radiation heat transfer mechanisms are carried out with the ANSYS program. Using the results of the elastic analysis, the progressive deformation and creep-fatigue damages are calculated step by step using the RCC-MR in detail. This paper ill be a very useful guide for an actual application of the high temperature structural design of the nuclear power plant accounting for the time-dependent creep and stress-rupture effects.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.918-927
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• 2018

Based on the actual operating environment of transformer, the aging tests of nitrile butadiene rubber (NBR) were conducted systematically under four conditions: in air, in transform oil, under compression in air and under compression in transform oil to studythe effect of high temperature, transform oil and compression stress simultaneously on the thermal aging behaviors of nitrile butadiene rubber and predict the lifetime. The effects of liquid media and compression stress simultaneously on the thermal aging behaviors of nitrile butadiene rubber were studied by using characterization methods such as IR spectrosc-opy, thermogravimetric measurements, Differential Scanning Calorimetry (DSC) measurements and mechanical property measurements. The changes in physical properties during the aging process were analyzed and compared. Different aging conditions yielded materials with different properties. Aging at $70^{\circ}C$ under compression stress in oil, the change in elongation at break was lower than that aging in oil, but larger than that aging under compression in air. The compression set or elongation at break as evaluation indexes, 50% as critical value, the lifetime of NBR at $25^{\circ}C$ was predicted and compared. When aging under compression in oil, the prediction lifetime was lower than in air and under compression in air, and in oil. It was clear that when predicting the service lifetime of NBR in oil sealing application, compression and media liquid should be involved simultaneously. Under compression in oil, compression set as the evaluation index, the prediction lifetime of NBR was shorter than that of elongation at break as the evaluation index. For the life prediction of NBR, we should take into account of the performance trends of NBR under actual operating conditions to select the appropriate evaluation index.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.193-203
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• 2014

Temperature-dependent stress analysis and heat transfer analysis of a rotating gas turbine blade made of functionally graded materials (FGMs) are presented considering turbine operating temperature and ceramic particle size. The material properties of functionally graded materials are assumed to vary continuously and smoothly across the thickness of the thin-walled blade. For obtaining system stiffness reflecting these characteristics, the one-dimensional heat transfer equation is applied along the thickness of the thin-walled blade for determining the temperature distribution. Using the results of the temperature analysis, the equations of motion of a rotating blade are derived with hybrid deformation variable modeling method along with the Rayleigh-Ritz assumed mode methods. The validity of the derived rotating blade model is evaluated by comparing its transient responses and temperature distribution with the results obtained using a commercial finite element code. The maximum tensile stress with operating speed and gradient index are obtained. Furthermore, the gradient index that minimizes blade temperature was investigated.

• Journal of the Korean Society for Railway
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• v.6 no.2
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• pp.142-148
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• 2003

A wheel and axle failure can cause a derailment with its attendant loss of life and property. The service conditions of railway vehicles have become severe in recent years due to a general increase in operating speeds. Damages of railway wheel are a spatting by wheel/rail contact and thermal crack by braking heat etc. One of the main source of damage is a residual stress. therefore it is important to evaluate exactly. A Residual stress of wheel is formed at the process of heat treatment when manufacturing. it is changed by contact stress developed by wheel/rail contact. Distributions of residual stress vary according to a magnitude of wheel load, a magnitude of friction when acceleration and deceleration. The objective of this paper is to estimate the influence of wheel motion on the residual stress distribution in the vicinity of the running surface.