• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.594-599
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• 2011

In this paper, the effect of the boundary conditions on the reliability and the cumulative distribution characteristics of the fatigue failure life is analyzed in a magnesium alloy AZ31. The boundary conditions are specimen thickness, stress ratio, and maximum fatigue load. The statistical data of the fatigue failure life are obtained by fatigue crack propagation tests under the detail conditions for each boundary condition. The 3-parameter Weibull distribution is used to analyze a statistical characteristics of the fatigue failure life in magnesium alloy AZ31. It is found that the statistical fatigue failure life is long in the case of a thicker specimen, a larger stress ratio, and a smaller maximum fatigue load. Under the opposite cases, the reliability on the fatigue failure life is rapidly dropped.

• Structural Engineering and Mechanics
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• v.49 no.2
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• pp.203-223
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• 2014

The extensive use of prestressed reinforced concrete (PSC) highway bridges in marine environment drastically increases the sensitivity to both fatigue-and corrosion-induced damage of their critical structural components during their service lives. Within this scenario, an integrated method that is capable of evaluating the fatigue reliability, identifying a condition-based maintenance, and predicting the remaining service life of its critical components is therefore needed. To accomplish this goal, a procedure for fatigue reliability prediction of PSC highway bridges is proposed in the present study. Vehicle-bridge coupling vibration analysis is performed for obtaining the equivalent moment ranges of critical section of bridges under typical fatigue truck models. Three-dimensional nonlinear mathematical models of fatigue trucks are simplified as an eleven-degree-of-freedom system. Road surface roughness is simulated as zero-mean stationary Gaussian random processes using the trigonometric series method. The time-dependent stress-concentration factors of reinforcing bars and prestressing tendons are accounted for more accurate stress ranges determination. The limit state functions are constructed according to the Miner's linear damage rule, the time-dependent S-N curves of prestressing tendons and the site-specific stress cycle prediction. The effectiveness of the methodology framework is demonstrated to a T-type simple supported multi-girder bridge for fatigue reliability evaluation.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.7
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• pp.3135-3141
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• 2012

This study was designed to adapt the Turkish versions of scales to evaluate fatigue in children with cancer from the perspectives of the children, parents and staff. The objective of this study was to validate "Child Fatigue Scale-24 hours" (CFS-24 hours), "Parent Fatigue Scale-24 hours" (PFS-24 hours) and "Staff Fatigue Scale-24 hours" (SFS-24 hours) for use in Turkish clinical research settings. Translation of the scales into Turkish and validity and reliability tests were performed. The validity of the translated scales was assessed with language validity and content validity. The reliability of the translated scales was assessed with internal consistency. The scales were evaluated by considering the following: calculation of the Cronbach alpha coefficient for parallel form reliability with 52 pediatric cancer patients, 86 parents and 43 nurses. The internal consistency was estimated as 0.88 for the Child Fatigue Scale-24 hours, 0.77 for the Parent Fatigue Scale-24 hours, and 0.72 for the Staff Fatigue Scale-24 hours (Cronbach's ${\alpha}$). The Turkish version of the Child Fatigue Scale -24 hours, the Parent Fatigue Scale -24 hours and the Staff Fatigue Scale -24 hours were judged reliable and valid instruments to assess fatigue in children and showed good psychometric properties. These scales should assist in understanding to what extent initiatives can minimize or eliminate fatigue. Our scales are recommended for further studies and use in pediatric oncology clinics as routine measurements and nursing initiatives should be planned accordingly.

• Journal of Applied Reliability
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• v.17 no.4
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• pp.280-288
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• 2017

Purpose: PBA buried in underwater requires high reliability because of its mission critical characteristic and harsh operational environment during its life cycle. Therefore, various reliability improvement activities are necessary. The defect on PBA manufacturing process have been studied, as a result, many activities and standards have been presented. However, there are less studies regarding failure pattern on physical features based on design. In this paper, we studied a possible failure patten based on physical features that is related with manufacturing process of PBA. And reliability improvement design based on PoF (Physical of Failure) were intruduced in this paper. Methods: A reliability prediction simulation were performed on the components A and B of the H system using Sherlock Software which is a PoF commercial tool from DFR solution. Solder fatigue and PTH fatigue analysis based on thermal cycling profiles and random vibration was analyzed on three earthquake response spectrum. Result: It was validated that life time and reliability improvement design through solder fatigue and PTH fatigue analysis in case of component. For compoenet B, random vibration fatigue was additionally analyzed and validated reliability for earthquakes profile. Conclusion: In design stage prior to manufacturing, PoF can be analyzed, and it is possible to make a reliability improvement/validated design using design data. This study can be applied in every design step and contribute to make more stable development product.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.11 no.2
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• pp.220-225
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• 2004

Purpose: The purpose of this study was to test the reliability and validity of FAI and to apply it in Korea. Method: Data were collected from 180 middle-age women. The questionnaire, which was originally developed by Schwartz, Jandorf & Krupp, was analyzed using Cronbach's a and factor analysis. Results: Cronbach's a for the FAI was .9198. As a result of item analysis, 27 items were selected from the total of 29 items, Items that showed low correlation with the total scale were excluded. Six factors were fixed from the data analysis performed using principle component analysis and varimax rotation. These six factors account for 65.3% of total variance. The first factor was global fatigue severity, and the second one was fatigue consequences. The other factors were method of fatigue reduction, fatigue caused by exercise, fatigue caused by routine activity, and fatigue caused by stress and depression, sequentially. Conclusion: The reliability and validity of FAI were verified.

• Smart Structures and Systems
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• v.33 no.3
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• pp.177-188
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• 2024

The fatigue-induced sequential failure of a structure having structural redundancy requires system-level analysis to account for stress redistribution. System reliability-based design optimization (SRBDO) for preventing fatigue-initiated structural failure is numerically costly owing to the inclusion of probabilistic constraints. This study incorporates the Branch-and-Bound method employing system reliability Bounds (termed the B³ method), a failure-path structural system reliability analysis approach, with a metaheuristic optimization algorithm, namely grey wolf optimization (GWO), to obtain the optimal design of structures under fatigue-induced system failure. To further improve the efficiency of this new optimization framework, an additional bounding rule is proposed in the context of SRBDO against fatigue using the B³ method. To demonstrate the proposed method, it is applied to complex problems, a multilayer Daniels system and a three-dimensional tripod jacket structure. The system failure probability of the optimal design is confirmed to be below the target threshold and verified using Monte Carlo simulation. At earlier stages of the optimization, a smaller number of limit-state function evaluation is required, which increases the efficiency. In addition, the proposed method can allocate limited materials throughout the structure optimally so that the optimally-designed structure has a relatively large number of failure paths with similar failure probability.

• Structural Engineering and Mechanics
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• v.44 no.1
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• pp.35-49
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• 2012

A series of fatigue test were carried out on scarfed lap joints (SLJ) using in airfoil siding to explore the effect of structural details, such as rows of rivets, lap angles, on its fatigue performance. Finite element (FE) analysis was employed to explore the effect of lap angle on load transfer and the stress evolution around the rivet hole. At last, the fatigue lives were predicted by nominal stress approach and critical plane approach. Both of the test results and predicted results showed that fatigue life of SLJ was remarkably increased after introducing lap angle into the faying surface. Specimen with the lap angle of $1.68^{\circ}$ exhibits the best fatigue performance in the present study.

• Proceedings of the Korea Concrete Institute Conference
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• 1991.04a
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• pp.129-132
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• 1991

The safe design against fatigue failure becomes more important criterion in highway bridges. The fatigue-safety evaluation is performed for the current bridge code. A reliability model incorporating fatigue damage is formulated and the satety indices are calculated. The present study indicates that the calculated safety indices vary greatly with traffic volumes and loadometer values. A method is proposed to maintain uniform reliability for vafious traffic conditions and loadings.

• Proceedings of the Korean Reliability Society Conference
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• 2000.04a
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• pp.213-222
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• 2000

In present study, a stochastic model is developed for the low cycle fatigue life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. In the proposed model, fatigue phenomenon is considered as a Markov process, and damage vector and reliability are defined on every plane. Any low cycle fatigue damage evaluating method can be included in the proposed model. The model enables calculation of statistical reliability and crack initiation direction under variable multiaxial loading, which are generally not available. In present study, a critical plane method proposed by Kandil et al., maximum tensile strain range, and von Mises equivalent strain range are used to calculate fatigue damage. When the critical plane method is chosen, the effect of multiple critical planes is also included in the proposed model. Maximum tensile strain and von Mises strain methods are used for the demonstration of the generality of the proposed model. The material properties and the stochastic model parameters are obtained from uniaxial tests only. The stochastic model made of the parameters obtained from the uniaxial tests is applied to the life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. The predicted results show good accordance with experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.751-757
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• 2016

The aim of this study is to estimate the reliability of fatigue limit of the material used for crank throw components according to the staircase method. The material used for crank throw components is forged S34MnV grade steel, which is heat treated by normalizing and tempering. In this work, to predict the reliability of the design fatigue strength, axially loaded constant amplitude fatigue testing was conducted. The test specimens were loaded with an axial push/pull load with a mean stress of 0 MPa, which corresponds to a stress ratio of R=-1. The fatigue test results were evaluated by Dixon-Mood formulas. The values of mean fatigue strength and standard deviation predicted by the staircase method were 296.3 MPa and 10.6 MPa, respectively. Finally, the reliability of the fatigue limit in some selected probability of failure is predicted. The proposed method can be applied for the determination of fatigue strength for design optimization of the forged steel.