• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1997.10a
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• pp.140-145
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• 1997

In case of spot-welded joints, the fatigue cracks generally originate from the weld interfaces of the neighborhood nugget tips, and propagate toward the outer surfaces of the sheets. Generally, because fatigue crack was observed in nugget around, strain gage was attached at nugget zone. Accordingly, it was very difficult to detect the generation time of fatigue crack in spot-welded joints and to measure the propagation speed of fatigue crack. We developed the non-destructive method, according to which th fatigue crack propagation rate can be quantitatively estimated by utilizing information obtained from strain gages bonded on the electrode indentations of spot welds. The results measured by real crack were compared with the data which was measured by strain gauge method in fatigue testing. And so fatigue strength was evaluated by stress intensity factor. In this study behavior of fatigue crack propagation under repeated load were considered.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.239-245
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• 2005

Through the fatigue test of plastic gears using polyacetal polymer, this research aims at providing basic data for not only specifying operation conditions of plastic gears, but also designing dimensions of plastic gears with giving fatigue life and the estimated equation of fatigue life of plastic gears. That is, from the fatigue life curves, the estimated equation of fatigue life of plastic gears is taken out. For the estimated equation of fatigue life of plastic gears, this research provides two test methods; one is preserving non-limited temperature of tooth flank, the other is preserving limited temperature of tooth flank. As results, how the temperature of tooth flank affects the fatigue life is shown. In addition, based on the endurance limit, the essential factors of the unit load and K-factor are determined, which are needed in the design of gear by bending strength and surface durability.

• Journal of Korean Society of Steel Construction
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• v.12 no.5 s.48
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• pp.617-628
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• 2000

In this study, the 4-point bending test has been performed in order to estimate the effect of TIG-dressing on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strength of as-welded specimens has been satisfied the grade of fatigue strength prescribed in specifications of domestics and AASHTO & JSSC, and fatigue strength at $2{\times}106cycles$ of TIG-dressing specimens has been increased compared with as-welded specimens. As the result of beachmark tests, fatigue cracks have been occurred at several points, where the radius of curvature and flank angle in the weld bead toes are low, and grown as semi-elliptical cracks, then approached to fracture. As a result of finite element analysis, stress concentration factor in weld bead toes has been closely related to the flank angel and radius of curvature, and between these, the radius of curvature has more largely affected in stress concentration factor than flank angle. As a result of fracture mechanics approaches, the crack correction factor of test specimens has been largely affected on stress gradient correction factor in case a/t is below 0.4. From the relations between stress intensity factor range estimated from FEM analysis and fatigue crack growth rate, fatigue life has been correctly calculated.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.1
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• pp.187-194
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• 2002

It has been reported that cracks in mechanical joints is generally under mixed-mode and there is critical inclined angle at which mode I stress intensity factor becomes maximum. The crack propagates in arbitrary direction and thus the prediction of crack growth path is needed to provide against crack propagation or examine safety. In order to evaluate the fatigue life of cracks in mechanical joints, horizontal crack normal to the applied load and located on minimum cross section is major concern but critical inclined crack must also be considered. In this paper mixed-mode fatigue crack growth test is performed far horizontal crack and critical inclined crack in mechanical joints. Fatigue crack growth path is predicted by maximum tangential stress criterion using stress intensity factor obtained from weight function method, and fatigue crack growth rates of horizontal and inclined crack are compared.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.73-82
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• 1998

This paper is especially concerned with the weldment between support beam and square bar that plays important roles in control box of Expansion Joint as a brdige structure. Fatigue strength ({TEX}$$\sigma$_{ult}${/TEX}) of the weldment is dependent on notch factor ({TEX}$K_{f}${/TEX}) become important factors to predict fatigue life. The fatigue notch sensitivity (η) for metals can be divided into two types ; high and low notch sensitivity. In this work, the Expansion Joint weldment was found to have low notch sensitivity. The maximum strain distribution during static loading is similar to the FEM analysis. Fatigue test of real structure was performed up to {TEX}$10^{6}${/TEX} cycles to be compared with predicted endurance limit.

• Nuclear Engineering and Technology
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• v.44 no.6
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• pp.683-688
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• 2012

The structural integrity of mechanical components during several transients should be assured in the design stage. This requires a fatigue analysis including thermal and stress analyses. As an example, this study performs a fatigue analysis of the reactor pressure vessel of SMART during arbitrary transients. Using heat transfer coefficients determined based on the operating environments, a transient thermal analysis is performed and the results are applied to a finite element model along with the pressure to calculate the stresses. The total stress intensity range and cumulative fatigue usage factor are investigated to determine the adequacy of the design.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.136-142
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• 2004

Effects of Nb(Niobium) contents and solution annealing on the strength and fatigue lift 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 lift on base metal specimens or solution annealed specimens showing that the fatigue life was almost the same. The maximum stresses of X, Y, and Z axis direction showed about 2.12${\times}$10$^2$MPa, 4.40${\times}$10$^2$MPa and 1.32${\times}$10$^2$MPa 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∼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.

• Journal of Ocean Engineering and Technology
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• v.1 no.1
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• pp.104-110
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• 1987

Fatigue tests by axial loading (R = 0.05) were carried out to investigate fatigue crack growth characteristics of small surface cracks in 2 1/4 Cr-1 Mo steel at room temperature by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present test are determined as a function of the stress intensity factor range about a semi-elliptical crack, so that the application of linear fracture mechanics to the surface fatigue crack growth and to the fatigue crack growth into depth, and all the data obtained from tests were discussed in comparison with the data of Type 304 stainless steel and two type of mild steel under the same test conditions. The obtained results are as follows: 1)When the cycle ratios are same, surface fatigue crack length and its depth are almost same and fall within a narrow scatter band in spite of different stress levels. 2)Relations of the surface fatigue crack growth rate (da/dN) and fatigue crack growth rate into depth (db/dN) to its stress intensity factor range ($\Delta K_{Ia}, \Delta K_{Ib}$) can be plotted as a straight line at log-log diagram without dependence of stress level and coincide with the data of part-through crack in various steels.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.22
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• pp.9891-9898
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• 2014

Background: This study was planned in an attempt to develop scales for the assessment of fatigue in pediatric oncology patients aged 13-18 and also for their parents. Materials and Methods: In collecting the study data, we used the Child and Parent Information Form, Visual Fatigue Scale, Scale for the Assessment of Fatigue in Pediatric Oncology Patients Aged 13-18 and the Scale for the Assessment of Fatigue in Pediatric Oncology Patients Aged 13-18 for Parents. We also used Pearson correlation analysis, Cronbach alpha coefficient, factor analysis and ROC analysis for the study data. Results: In this study, the total Cronbach alpha value of the parent form was 0.99, the total factor load was 0.72-0.94 with 95% the total variance being explained. The cutoff point of the parent form is 73 points. The total Cronbach alpha value of the child form was 0.99, the total factor load was 0.82-0.95, with 89.4% of the total variance being explained. The cutoff point of the child form was 75.5 points. Conclusions: This study suggests that the Scale for the Assessment of Fatigue in Pediatric Oncology Patients Aged 13-18 and the Scale for the Assessment of Fatigue in Pediatric Oncology Patients Aged 13-18 for Parents are valid and reliable instruments in assessing the fatigue symptoms of children in Turkey.

• Journal of the Korean Society of Safety
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• v.6 no.4
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• pp.81-87
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• 1991

We propose the crack growth rate equation which will model fatigue crack growth rate behavior such that constant stress amplitude fatigue crack growth behavior can be predicted. Constant stress amplitude fatigue tests are conducted for four materials under three stress ratios of R＝0.2, R＝0.4 and R＝0.6. Materials which have different mechanical properties i.e. stainless steel, low carbon steel, medium carbon steel and aluminum alloy are used. Through constant stress amplitude fatigue test by using unloading elastic compliance method, it is confirmed that crack closure is a close relationship with fatigue crack propagation. We describe simply fatigue crack propagation behavior as a function of the effective stress intensity factor range ($\Delta$ $K_{eff}$＝U .$\Delta$K) for all three regions (threshold region, stable region). The fatigue crack growth rate equation is given by da / dN＝A($\Delta$ $K_{eff}$­$\Delta$ $K_{o}$ )$^{m}$ / ($\Delta$ $K_{eff}$­$\Delta$K) Where, A and m are material constants, and $\Delta$ $K_{o}$ is stress intensity factor range at low $\Delta$K region. $K_{cf}$ is critical fatigue stress intensity factor.actor.