• Journal of the Korean Society for Precision Engineering
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• v.24 no.5
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• pp.44-55
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• 2007

The method for fatigue life prediction of ball bearing is proposed applying the algorithm of contact fatigue prediction based on stress analysis. In order to do this, a series of simulation such as initial surface stress analysis, EHL analysis, subsurface stress analysis and fatigue analysis are conducted from the loading at each ball location calculated for a bearing subjected to external bearing load and contact shape function. And uniaxial fatigue tests are performed to obtain fatigue parameter of AISI 52100 steel. It was found that since stress is usually higher at the inner raceway contact than at the outer raceway contact, fatigue failure occurs on the inner raceway first. When the fatigue life calculated in the stress-based method are compared with L50 life of L-P model, Crossland criterion for the radial load increment is similar to L50 life and Dang Van criterion for the axial load increment is similar. In the case of EHL contact, there is no difference of fatigue life between dry contact and EHL contact, when maximum Hertz pressure exceeds 2.5GPa.

• Journal of Korean Society of Steel Construction
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• v.8 no.4 s.29
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• pp.19-29
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• 1996

In this paper, it is presumed that the stress time history was generated by simulation method and investigated compatibility in regard to the reappearance of stress time history. In this procedure, the identified frequency distribution of stress range of the steel railroad bridge varies with the rational values of cut off point and bar width. Thus, we show variable aspect of the equivalent stress range results from change of cut off point and bar width. In addition, we analyze the variable of RMC and RMS model due to the cut off point and bar width of the measured stress history which influencs the prediction of fatigue life in the steel railroad bridge. The simulated stress time history is carried out by the superposition method incorporating the vertical load with rotation moment obtained from the Hermition interpolation function, and compared with developing stress results from measured maxi mum stress. Through this study, we can estimate the remaining fatigue life from a safety point of view and comparative accuracy.

• International Journal of Reliability and Applications
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• v.15 no.1
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• pp.23-50
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• 2014

This paper deals with formulation of optimum multi-objective modified step-stress accelerated life test (ALT) plan for Burr type-XII distribution under type-I censoring. Since it is impractical to estimate only one objective parameter after conducting costly ALT tests; also, it is not desirable to assume instantaneous changes in stress levels because of limited capacity of test equipments and the presence of undesirable failure modes, therefore, an optimum multi-objective modified step-stress ALT plan has been designed. The optimal test plan consists in determining the optimum low stress level and optimal time at which stress starts linearly increasing from low stress by minimizing the weighted sum of the asymptotic variances of the maximum likelihood estimator of quantile lifetimes at design constant stress. The method developed has been illustrated using an example. Sensitivity analysis has been carried out. Comparative study has also been done to highlight the merits of the proposed model.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.7-12
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• 2004

A lifetime prediction of holddown spring screw in nuclear fuel assembly was performed using fracture mechanics approach. The spring screw was designed such that it was capable of sustaining the loads imposed by the initial tensile preload and operational loads. In order to investigate the cause of failure and to predict the stress corrosion cracking life of the screw, a stress analysis of the top nozzle spring assembly was done using finite element analysis. The elastic-plastic finite element analysis showed that the local stresses at the critical regions of head-shank fillet and thread root significantly exceeded than the yield strength of the screw material, resulting in local plastic deformation. Normalized stress intensity factors for PWSCC life prediction was proposed. Primary water stress corrosion cracking life of the Inconel 600 screw was predicted by using integration of the Scott model and resulted in 1.78 years, which was fairly close to the actual service life of the holddown spring screw.

• Composites Research
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• v.12 no.2
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• pp.62-69
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• 1999

During fatigue loading of composite materials, damage accumulation can be monitored by measuring their material properties. In this study, fatigue modulus is used as the damage index. Fatigue life of composite materials may be predicted analytically using damage models which are based on fatigue modulus and resultant strain. Damage models are propesed as funtions of applied stress level, number of fatigue cycle and fatigue life. The predicted life was comparable to the experimental result obtained using E-glass fiber reinforced epoxy resin materials and pultruded glass fiber reinforce polyester composites under two-stress level fatigue loading.

• Horticultural Science & Technology
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• v.33 no.5
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• pp.625-632
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• 2015

Drought is a severe abiotic stress that affects global crop production. A drought model was created for 'Toyonoka' Fragaria ${\times}$ ananassa, and the effects of drought stress on contents of proline, sugars, and antioxidant enzyme activities were investigated. Strawberry transplants with identical growth were chosen for the experiments and the randomized design included four replications (10 plants per block). The experimental sets differed in the moisture level of the culture medium relative to the range of moisture content as follows: control, 70-85%; mild drought stress, 50-60%; moderate drought stress, 40-50%; and severe drought stress, 30-40%. Drought stress was imposed by limiting irrigation. Plants were sampled and physiological parameters w ere measured on 0, 2, 4, 6, 8, and 10 days after the commencement of droughts tress. The water potential of strawberry leaves decreased in the plants under mild, moderate, and severe stress during the course of the water stress treatment and exhibited a significant difference from the control. Strawberry leaves subjected to drought stress had higher accumulation of proline, sugars, and malondialdehyde, and higher activities of superoxide dismutase, peroxidase, and catalase than leaves of control plants. Malondialdehyde levels increased in parallel with the severity and duration of drought stress. By contrast, antioxidant enzyme activity displayed dynamic responses to drought stress, first increasing and subsequently decreasing as the severity and duration of drought stress increased. These results suggest that strawberry plants respond to drought stress by altering the activities of antioxidant enzymes and the levels of osmotically active metabolites. These biochemical response changes may confer adaptation to drought stress and improve the capacity of plants to withstand water-deficit conditions.

• Journal of Korean Academy of Nursing
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• v.46 no.4
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• pp.583-597
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• 2016

Purpose: The study was done to evaluate the effects a Stress Management Program (SMP) on stress, problem solving skills, and quality of life for hospitalized patients with Schizophrenia. Methods: A mixed method design was used: a combination of a repeated-measure design with a non-equivalent control group and qualitative data collection. The participants were 40 patients with schizophrenia admitted in three psychiatric hospitals. The experimental group (n=20) received the SMP twice a week for a total of 8 weeks. Results: Study results revealed that the SMP was effective for stress (F=321.02, p<.001), problem solving ability (F=246.28, p<.001), and quality of life (F=63.35, p<.001) for hospitalized persons with schizophrenia. Conclusion: The results suggest that a SMP can be an effective strategy to reduce patients' hospitalization stress, and improve problem solving skills and quality of life. Therefore, it is recommended that mental health nurses use this stress management program in clinical practice to assist adaptation to hospitalization for persons with schizophrenia.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.977-985
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• 2004

An evaluation of fatigue life of welded components is complicated due to various geometrically complex welding details and stress raisers in vicinity of weld beads, ego under cuts, overlaps and blow holes. These factors have a considerable influence on the fatigue strength of welded joints, as well as the welding residual stress which is relaxed depending on the distribution of local stress at the front of the stress raisers. To reasonably evaluate fatigue life, the effect of geometries and welding residual stress should be taken into account. The several methods based on the notch strain approach have been proposed in order to accomplish this. These methods, however, result in differences between analytical and experimental results due to discrepancies in estimated amount of relaxed welding residual stress present. In this paper, an approach that involves the use of a modified notch strain approach considering geometrical effects and a residual stress relaxation model based on experimental results was proposed. The fatigue life for five types of representative welding details, ego cruciform, cover plate, longitudinal stiffener, gusset and side attachment joint, are evaluated using this method.

• Journal of Home Health Care Nursing
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• v.27 no.1
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• pp.29-41
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• 2020

Purpose: This study aimed to investigate the influence of post-traumatic stress on professional quality of life as mediated by cognitive emotion regulation among nurses working in small and medium hospitals who have experienced violence and to develop and test a structural equation model of that professional quality of life. Methods: Participants were 215 nurses who had experienced violence working in medium and small hospitals. They were surveyed using a structured questionnaire. Results: The final model was shown to have good fit with χ² (2.83), GFI (.90), TLI (.90), and CIF (.90). Therefore, the model was selected as the final model, supporting 7 of the 11 hypotheses. Post-traumatic stress, adaptive emotional regulation, and maladaptive emotional regulation had significant impacts on empathy satisfaction (professional quality of life subscale) and empathy fatigue (subscale of professional life quality) among nurses who had experienced violence, and the explanatory power of these variables was 28.7% and 38.6%, respectively. Conclusion: In the development of nursing intervention programs to improve the professional quality of life of nurses who have experienced violence, factors such as post-traumatic stress and cognitive emotion regulation (adaptive and maladaptive) should be considered as they were identified in this study as influencing the professional quality of life of such nurses in medium and small hospitals.

• Transactions of Materials Processing
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• v.16 no.6
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• pp.479-487
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• 2007

Die life is generally estimated taking failure life and wear amount into consideration. In this study, the forging die life was investigated considering both of these two factors. The fatigue life prediction for the die was performed using the stress-life method, i.e. Goodman's and Gerber's equations. The Archard's wear model was used in the wear life simulation. These die life prediction techniques were applied to the die used in the forging process of the socket ball joint of a transportation system. A rigid-plastic finite element analysis for the die forging process of the socket ball was carried out and also the elastic stress analysis for the die set was performed in order to get basic data for the die fatigue life prediction. The wear volume of the die was measured using a 3-dimensional measurement apparatus. The simulation results were relatively in good agreement with the experimental measurements.