• 대한조선학회논문집
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• 제42권2호
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• pp.129-135
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• 2005

At present, fatigue design of welded structures is primarily based on a nominal stress or hot spot stress approach with a series of classified weld S-N curves. Although well accepted by major industries, the nominal stress based fatigue design approach is cumbersome in terms of securing a series of S-N curves corresponding to each class of joint types and loading modes. The hot spot stress based fatigue design has a difficulty of finding a proper stress through the global model, the midium size model, and the detail model of ship structure. Also, it is difficult to link proper displacements within three different mesh size models. Recently, the structural stress is proposed as a mesh-size insensitive structural stress definition that gives a stress state at weld toe with relatively large mesh size. However, this method requires an experimental validation in obtaining the fatigue strength of weldments. Therefore, in this study, a series of experiment is performed for various sizes of weldments.

• 대한기계학회논문집A
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• 제29권10호
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• pp.1384-1391
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• 2005

Damage often occurs on the surface of railway wheels due to wheel-rail contact fatigue. It should be removed before reaching wheel failure, because wheel failure can cause derailment with loss of life and property. The increase or decrease of the contact fatigue lift by the metal removal of the contact surface were investigated by many researchers, but they have not considered initial residual stress and traction force. The railway wheel has the initial residual stress formed during the manufacturing process, and the residual stress is changed by thermal stress induced by braking. The traction force and residual stress are operated on wheels of locomotive and electric motor vehicle. In this study, the effect of metal removal depth on the contact fatigue life for a railway wheel has been evaluated by applying lolling contact fatigue test. The effect of the traction force and metal removal on the contact fatigue life has been estimated by finite element analysis. It has been found that the initial residual stress determines the amount of metal removal depth if the traction coefficient is less than 0.15. If the traction coefficient is greater than 0.2, however, the amount of metal removal depth is independent on the intial residual stress.

• 산업기술연구
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• 제20권A호
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• pp.149-158
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• 2000

After measuring actual stress by two measurements(Dynamic Strain Meter, Histogram Recorder) on truss rail road bridge, we could perform time history analysis by 3-D beam element method on modelling bridge. And then, after analyzing bridge structure in static by 3-D modelling, we estimated degree of fatigue damage in main member, secondary member of tie zone, cutting area of base metal cross section for confirming the result. In case that the simulated stress is carried out on modeling bridge, most of those simulation mainly is performed by main members. But in real bridge fatigue damage problems generally caused by junctions, connections, joints in which especially local stress is activated. Therefore, in this paper actual stress on critical area was estimated through the analysis result by simulation. With this study, we can estimate the degree of fatigue damage from a safety point of view and comparative accuracy.

• 한국기계가공학회지
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• 제19권2호
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• pp.47-54
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• 2020

Themo-mechanical analysis was carried out using the finite element method for the steel shell of a cupola furnace. When the outer surface of the shell was cooled with water to within the temperature range of 35-80 ℃ during operation of the cupola, the inner surface of the shell was expected to exhibit a temperature of 65-248 ℃ based on heat transfer analysis. The shell was also expected to have an equivalent stress range of 100-280 MPa in the outer surface over the temperature range examined. Upon cooling the shell to obtain an outer surface temperature <80 ℃, the maximum equivalent stress of the shell did not exceed the yield strength. Although the temperature of the outer surface varied between 35 and 80 ℃ periodically due to the cooling control problem, the fatigue stress at the outer surface of the shell was calculated to be within the fatigue strength. During a non-operational period to examine the system between furnace operations, the thermal stress presented in the shell was sufficiently low to reach the desired yield strength and fatigue limit.

• Journal of Mechanical Science and Technology
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• 제14권4호
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• pp.401-407
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• 2000

An elastic-plastic finite element analysis is performed to investigate detailed closure behavior of fatigue cracks and the numerical results are compared with experimental results. The finite element analysis performed under plane stress using 4-node isoparametric elements can predict fatigue crack closure behavior. The mesh of constant element size along crack surface can not predict the opening level of fatigue crack. The crack opening level for the constant mesh size increases linearly from initial crack growth. The crack opening level for variable mesh size, is almost flat after crack tip has passed the monotonic plastic zone. The prediction of crack opening level using the variable mesh size proportioning the reversed plastic zone size with the opening stress intensity factors presents a good agreement with the experimental data regardless of stress ratios.

• 성인간호학회지
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• 제22권6호
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• pp.634-643
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• 2010

Purpose: The purpose of this study was to identify the reported factors influencing fatigue of middle aged women. Methods: Two hundred seven middle aged women between 40 and 59 years of age were recruited from five areas in Korea from March 1, 2010, to April 20, 2010. Data were collected by self-reported questionnaires. Data analysis was done using SPSS/WIN 15.0 program for descriptive statistics, Pearson correlation coefficients and stepwise multiple regression. Results: The average score of fatigue was $2.34{\pm}0.40$. There were significant differences in reported fatigue according to economic status and health status. The reported fatigue was significantly correlated with somatic attribution, psychological attribution, normalizing attribution, depression, marital adjustment, stress, and social support. The major factors that affect fatigue in middle aged women were stress, depression, and normalizing attribution, which explained 32.3% of fatigue. Conclusion: The findings can reduce the fatigue by controlling stress and depression. Additionally, this study can understand the attribution of fatigue in middle aged women. More studies are needed to identify other variables that influence on the fatigue of middle aged women.

• 대한조선학회논문집
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• 제40권1호
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• pp.28-35
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• 2003

Fatigue tests of transverse fillet weldment were performed under out-of-plane bending loads. Significant increase of the fatigue strength was observed under out-of-plane bending loads, compared to the one under in-plane loads (axial loads). Applicability of the crack propagation analysis using LEFM for the surface crack of fillet weldment were investigated as well, in parallel with the fatigue tests. For the rational assessment of the fatigue strength of welded ship structures where combined stresses of the in-plane axial stress and the out-of-plane bending stress are induced simultaneously due to complexity of applied load and structural geometry, further investigation is recommended for the effect of the out-of-plane bending stress on the fatigue strength of weldment.

• Journal of Ship and Ocean Technology
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• 제3권4호
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• pp.35-51
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• 1999

Fatigue strength assessment procedures have been implemented in the ship design rules by many classification societies. However, a large variation tin the details of the different approaches exists in practically all aspects influding load history assessment, stress evaluation and fatigue strength assessment. In order to assess the influences of thesd variations on the prediction of fatigue lives. a comparative study is organized by the ISSC Committee III.2 Fatigue and Fracture. A pad detail on the top of longitudinal hatch coaming of a panamax container vessel is selected for fatigue calculation. The work described in this paper is one set of results of this comparative study in which the ABS dynamics approach is applied. Through this analysis the following conclusions can be drawn. (1) With the original ABS approach, the fatigue life of this pad detail is very low, only 2.398 years. (2) The treatment of the stillwater bending moment in the ABS approach might be a source of conservatism. If the influence of stillwater bending moment is ignored, then the fatigue life for this pad detail is 7.036 years. (3) The difference between the nominal stress approach and the hot spot stress approach for this pad detail is about 26%.

• 산업기술연구
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• 제19권
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• pp.269-278
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• 1999

When a variety of repeated loads are given, most steel structures failed in much lower level of loads than static failure loads. In addition, bridge always includes the internal defects or discontinuities. from these, fatigue cracks initiates and can lead to sudden failure. Thus, in this study, tensile specimens by the cover plate shapes were used as the test specimens. The fatigue test was performed by constant amplitude fatigue loading and beach mark. From the results of this study, each specimen's fatigue section was observed. in addition, stress intensity factor at crack tip was calculated by using the Green's function which applied to discontinuous section where causing stress concentration. Therefore, the fatigue life of structural detail was investigated by adopting the theories of fracture mechanics. each specimen's crack shape is a semi-elliptical surface crack or center crack sheet, stress gradient correction factor, Fg is the most subjective of all stress intensity correction factors and fatigue life should be predicted by previous proposed function and finite element analysis.

• 한국안전학회지
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• 제20권4호
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• pp.1-8
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• 2005

Effects of Nb(Niobium) contents and solution annealing on the strength and fatigue life of 18%Ni maraging steel commonly using in aircraft, space field, nuclear energy, and vehicle etc. were investigated. Also the fatigue life stress intensity factor were compared experiment result and FEA(finite element analysis) result. The more Nb content, the higher or the lower fatigue life on base metal specimens or solution annealed specimens showing that the fatigue lift was almost the same. The maximum stresses of X, Y, and Z axis direction showed about $2.12{\times}10^2MPa,\;4.40{\times}10^2MPa\;and\;1.32{\times}10^2MPa$ respectively. The Y direction stress showed the highest because of the same direction as the loading direction. The fatigue lives showed about 7% lower FEA result than experiment result showing almost invariable error every analyzed cycle. Stress intensity factor of the FEA result was lower about $3.5{\sim}10%$ than that of the experiment result showing that the longer fatigue crack length the higher error. It considered that the cause for the difference was the modeled crack tip having always the same shape and condition regardless of the crack growth.