• Journal of Welding and Joining
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• v.13 no.4
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• pp.155-162
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• 1995

Redistribution of residual stress and its effects during fatigue crack propagates from tensile residual stress region in weldment are investigated. Tests are performed by using welded CCT specimens of structual rolling steel (SS400) and it makes fatigue crack propagate from tensile residual stress region. For this study tension-tension loading type is selected by external loading condition and magnetizing stress indicator is used correctly to measure redistribution of residual stress according to fatigue crack growth and number of loading cycles. From this result, it is proved that redistribution of residual stress is mainly consist of residual stress released by fatigue crack growth. When fatigue crack propagates from tensile residual stress region residual stress are redistributed and it makes fatigue crack growth rate largely increase. Fatigue crack growth rate is low in case of redistributed residual stress compare with initial distributed residual stress.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.20 no.1
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• pp.76-85
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• 2012

Air traffic controllers often experience fatigue and stress on the job due to work-related factors. Performance impairment resulting from fatigue and stress is an important concern for aviation safety. The goal of this research was to investigate fatigue and stress factors for air traffic controllers. The research involved an extensive literature review of fatigue and stress in the air traffic control environment and surveyed fatigue and job stress level of Korean air traffic controllers compared to other occupation groups. Results of survey showed that fatigue and stress levels of air traffic controllers were significantly higher than other occupation groups. Specially air traffic controllers reported that night work created high level of fatigue and perceived that physical environment and job demand induced high level of stress. In addition, implications for fatigue and stress management were discussed.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.4
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• pp.253-257
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• 2016

The effects of re-peening on the compressive residual stress and fatigue life of Al7075-T6 were investigated. The compressive residual stress induced on the surface of components by shot peening is known to increase the fatigue life. However, the fatigue load relaxes the compressive residual stress of components. Re-peening is a technique to again induce the relaxed compressive residual stress and increase the total fatigue life of components. In this study, the re-peening process was applied to fatigue-loaded specimens. The compressive residual stress and fatigue life were examined for re-peened specimens with fatigue ratios of 30%, 50%, and 70%. The results showed that the compressive residual stress of the specimens was relaxed under the fatigue load. The re-peening process significantly increases the compressive residual stress and total fatigue life.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.9
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• pp.1498-1506
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• 1997

Procedures are presented for influence of shot peening on fatigue strength, fatigue life and effects of shot peening are discussed from experiments were taken between shot peened and unpeened SPS5, SM45C specimens. After the residual stress on shot peened specimens was measured by X-ray diffractometer, rotating bending fatigue tests were carried out. In addition, the compressive residual stress profile was obtained by the superposition method of three stresses which is based on Al-Obaid's equation. Predicted fatigue life considering residual stress profile which was obtained by the Al-Obaid's equation and another predicted fatigue life considering residual stress profile which was measured in test were compared. For the purpose of predicting fatigue life, Morrow's equation considering the residual stress and mean stress was used.

• Journal of the Korean Society of Safety
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• v.19 no.4 s.68
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• pp.20-24
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• 2004

Antifatigue failure technology take an important the part of current industries. Currently, the shot peening is used for removing the defect from the surface of steel and improving the fatigue strength on surface. Therefore in this paper the effect of compressive residual stress by shot peening on fatigue crack growth characteristics in stress ratio(R=0.1, 0.3, 0.6)was investigated with considering fracture mechanics. There is difference between shot peening specimen and unpeening specimen. Fatigue crack growth rate of shot peening specimen was lower than that of unpeening specimen. Fatigue lift shows more improvement in the shot peening material than in the unpeening material. And compressive residual stress of surface on the shot peening processed operate resistance force of fatigue crack propagation. That is the constrained force about plasticity deformation was strengthened by resultant stress, which resulted from plasticity deformation and compressive residual stress in the process of fatigue crack propagation.

• Structural Engineering and Mechanics
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• v.19 no.3
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• pp.261-279
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• 2005

The hot spot stress approach is usually adopted in the fatigue design and analysis of tubular welded joints. To apply the hot spot stress approach for fatigue evaluation of long span suspension bridges, the FEM is used to determine the hot spot stress of critical fatigue location. Using the local finite element models of the Tsing Ma Bridge, typical joints are developed and the stress concentration factors are determined. As a case for study, the calculated stress concentration factor is combined with the nominal representative stress block cycle to obtain the representative hot spot stress range cycle block under traffic loading from online health monitoring system. A comparison is made between the nominal stress approach and the hot spot stress approach for fatigue life evaluation of the Tsing Ma Bridge. The comparison result shows that the nominal stress approach cannot consider the most critical stress of the fatigue damage location and the hot spot stress approach is more appropriate for fatigue evaluation.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.4
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• pp.573-579
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• 2010

The notch effects on the fatigue strength of welded joints are both stress concentration and fatigue strength reduction. In the notch stress approach, the notch effects are usually approximated by introducing weld-bead parameters for the local detailed weld joints. In this paper, well-known notch stress approaches - critical distance method, area method and fictitious rounding method are presented for the fatigue strength of cruciform joints. The estimated results of the present methods are applied to the experiments performed in this study and reported in the references. The results of the application show that the fatigue-life scatterness of the experimental data expressed in the nominal stress is significantly reduced by introducing the effective fatigue stress of the present study.

• Laser Solutions
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• v.5 no.3
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• pp.1-8
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• 2002

Finite element analysis and experiment were peformed to estimate the fatigue strength for the lap joint of laser weld. To consider quantitatively residual stress which effects on the fatigue strength of the lap joint of laser weld, after three dimensional modeling for the longitudinal and transverse direction, residual stress fields in the weldment were calculated using thermo-elastic-plastic finite element analysis, then the equivalent fatigue stress considering the residual stress was obtained. To ensure reliability of calculated fatigue strength, fatigue tests were performed. The calculated and experimental results showed a good agreement. The fatigue strength considering a residual stress was lower than that of without considering a residual stress in the lap joint of laser welding. The fatigue strength in the transverse direction was higher than that of longitudinal direction.

• Journal of International Academy of Physical Therapy Research
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• v.8 no.2
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• pp.1135-1141
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• 2017

Stress and fatigue are general physical aspects of our daily lives. It has been shown that physical therapists have different levels of job stress and fatigue according to the type A/B behavior patterns. This study collected data from 212 physical therapists between October 28 and November 23, 2016 using an anonymous, self-administered questionnaire. The study results showed the proportion of physical therapists with the Type A behavior patterns(TABP) was 18% greater than that of physical therapists with the Type B behavior patterns(TBBP). In this study, physical therapists with TABP were compared with physical therapists with TBBP. The results indicated that physical therapists with TABP were more inclined to experience higher levels of overall job stress and fatigue from the following stress factors: physical environment, job requirement, and job autonomy. Therefore, the stronger the tendency toward TABP, the stronger the feeling of job stress and fatigue from physical environment, job requirement, and job autonomy. Those with a tendency toward TBBP showed positive correlations between job requirement and the total job stress score; thus, the stronger the tendency toward TBBP, the stronger the feeling of overall job stress and fatigue from job requirement. This study suggests that it is necessary to manage the job stress and fatigue of physical therapists with both TABP and TBBP and to manage the job stress and fatigue of physical therapists with the type A behavioral pattern.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.175-182
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• 2003

The fatigue life of welded joints is sensitive to welding residual stress and complexity of their geometric shapes. To predict the fatigue life more reasonably. the effects of welding residual stress and its relaxation on their fatigue strengths should be considered quantitatively, which are often regarded to be equivalent to the effects of mean stresses by external loads. The hot-spot stress concept should be also adopted which can reduce the dependence of fatigue strengths for various welding details. Considering the factors mentioned above, a fatigue life prediction model using the modified Goodman's diagram was proposed. In this model, an equivalent stress was introduced which is composed of the mean stress based on the hot-spot stress concept and the relaxed welding residual stress. From the verification of the proposed model to real welding details, it is proved that this model can be applied to predict reasonably their fatigue lives.