• Journal of Applied Reliability
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• v.7 no.2
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• pp.45-55
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• 2007

In this study, two types of fatigue tests were conducted. Firs, cyclic bending tests were performed using the micro-bending tester. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. A three-dimensional finite element analysis model was constructed. A finite element analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. Creep deformation was dominant in thermal fatigue and plastic deformation was main parameter for bending failure. From the inelastic energy dissipation per cycle versus fatigue life curve, it can be found that the bending fatigue life is longer than the thermal fatigue life.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.241-246
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• 2003

In order to develop a method of corrosion fatigue design and estimate reliability of TMCP steel using as the material of heavy industries and plants, its corrosion susceptibilities, corrosion fatigue strength, and determination of fatigue design criterion considering corrosion degradation were investigated. From the results, the corrosion characteristic of TMCP steel is very susceptible in 3.5wt.% NaCl solution. Its susceptibility was linearly increased with the solution temperature increase. The corrosion fatigue strength in $25${\circ}$, 3.5wt.% NaCl solution is very lower than that of in air. And also, it was decreased with the frequency decrease in the same environment. It is expected that the developed corrosion fatigue design method for TMCP steel is useful. However, it is necessary to verify its reliability for actual application.

• Structural Engineering and Mechanics
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• v.27 no.1
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• pp.33-48
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• 2007

An Articulated tower is one of the compliant offshore structures connected to the sea-bed through a universal joint which is the most vulnerable location of the tower that sustains the randomly fluctuating shear stresses. The time history response of the bottom hinge shear is obtained and presented in the spectral form. The fatigue and fracture reliability assessment of the tower joint against randomly varying shear stresses have been carried out. Non-linear limit state functions are derived in terms of important random variables using S-N curve and fracture mechanics approaches. Advanced First Order Reliability Method is used for reliability assessment. Sensitivity analysis shows the influence of various variables on the hinge safety. Fatigue life estimation has been made using probabilistic approach.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.3
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• pp.131-140
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• 2015

The purpose of this study is to predict the fatigue life of a planet carrier of a slewing reducer for a tower crane. To predict the fatigue life of the carrier, the inertia endurance test was carried out, and then the input torque profile for the reducer was obtained. The load profile acting on the planet pins that assembled the carrier was calculated from the measured input torque profile using commercial gearbox analysis software. The stress profiles of the carrier weak points were analyzed from the calculated load profile and boundary conditions using commercial FE software, and the stress cycles were determined using the rainflow counting method. Finally, the fatigue life of the carrier was predicted using the equivalent stress range by considering the effect of mean stress, and an S-N curve was drawn up using the GL guideline and the cumulative damage law.

• Journal of Korean Society of Steel Construction
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• v.21 no.3
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• pp.331-342
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• 2009

A reliability analysis of the fatigue failure of highway steel bridges was performed by applying the Miner's fatigue damage rule for the fatigue design truck proposed for the LRFD code and for the current DB 24 truck. The limit state function for fatigue failure is expressed as a function of various random variables that affect fatigue damage. Among these variables, the statistical parameters for the equivalent moment, the impact factor, and the loadometer were obtained by analyzing recently measured domestic traffic data, and the parameters for the fatigue strength, the girder distribution factor, and the headway factor were obtained from the measured data reported in literature. Based on the reliability analysis, the fatigue truck model for the LRFD code was proposed. After applying the proposed fatigue truck to the LRFD code, 16 composite plate and box girder bridges were designed based on the LRFD method, and the LRFD design results for the fatigue limit state were compared with those by the current KHBDC.

• The Journal of the Korea Contents Association
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• v.14 no.11
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• pp.175-185
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• 2014

This study is to develop a fatigue scale for the private security guard for a private security guard to effectively manage fatigue were tested for validity and reliability. To achieve that, this study employed purposive sampling to draw 300 samples among private security guards working for the security firms registered in Seoul District Police Office as of 2014, and used 259 samples for final analysis. Fatigue scale was developed on the basis of the scale development methods and procedures in previous studies. For data processing, SPSSWIN 18.0 program was applied to conduct exploratory factor analysis, reliability analysis, and correlation analysis, and AMOS 18.0 program was employed to conduct confirmatory factory analysis. This study came to the following conclusion. First, the validity of the fatigue measurement tool was high. In other words, content validity was high, and construct validity was also high. The factor loading of exploratory factor analysis was .452, and the standard value of confirmatory factor analysis was .403. Therefore, the tool satisfied the basis value of fit index. The sub categories of fatigue, finally drawn from validity test, were mental fatigue, nervous system dysfunction, physical deformity, and exhaustion. Secondly, the reliability of the fatigue measurement tool was high. In other words, according to item analysis, the correlation between items and their sub categories, and between items and total score was more than .602, relatively high. And the reliability coefficient (Cronbach's ${\alpha}$) was high, or more than .658. Fatigue Scale tool will be developed by private security guards in the present study is to measure the validity and reliability verification is clearly tired of the private security guards than the tools that are used in other studies in the existing area.

• Structural Engineering and Mechanics
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• v.63 no.6
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• pp.703-712
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• 2017

The composite blades of offshore wind turbines accumulate structural damage such as fatigue cracking due to harsh operation environments during their service time, leading to premature structural failures. This paper investigates various fatigue crack models for reproducing crack development in composite blades and proposes a stochastic approach to predict fatigue crack evolution and to analyse failure probability for the composite blades. Three typical fatigue models for the propagation of fatigue cracks, i.e., Miner model, Paris model and Reifsnider model, are discussed to reproduce the fatigue crack evolution in composite blades subjected to cyclical loadings. The lifetime probability of fatigue failure of the composite blades is estimated by stochastic deterioration modelling such as gamma process. Based on time-dependent reliability analysis and lifecycle cost analysis, an optimised maintenance policy is determined to make the optimal decision for the composite blades during the service time. A numerical example is employed to investigate the effectiveness of predicting fatigue crack growth, estimating the probability of fatigue failure and evaluating an optimal maintenance policy. The results from the numerical study show that the stochastic gamma process together with the proper fatigue models can provide a useful tool for remaining useful life predictions and optimum maintenance strategies of the composite blades of offshore wind turbines.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.6
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• pp.1-8
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• 1994

To enhance the strength of gears for transmission, Generally caburizing heat treatment is applied. But there are some problems in this technology the distortion of gears during heat treatment process, and the discontinuity of manufacturing process. For these reasons, the high frequency induction hardening process is widely used. This method is one of the surface hardening process to improve the wear resistance and fatigue life of the machine components. In this study, to compare the bending fatigue strength of caburized gear with that of induction hardened gear, bending fatigue testing of gears with two different cases was performed by using an electrohydraulic servo-controlled fatigue testing machine and double tooth bending fatigue test fixture. Fatigue life distributions at constant stress levels were established directly from fatigue data. For gear design, the fatigue strength distribution at specified life is more important. This distribution is obtained by statical transformation from fatigue life distribution. Reliability of bending fatigue strength was estimated by P-S-N curves and Weibull distribution.

• Journal of the Korean Society for Railway
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• v.11 no.1
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• pp.107-113
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• 2008

As it recently appears that LCC (Life Cycle Cost) analysis may be considered as an essential method for economic evaluation of infrastructures. Many researches have been made to assess LCC of each facility based on reasonable methods. However, expected maintenance repair cost must be reasonably estimated to enhance the reliability of LCC analysis through systematic and rational methods. This study is intended to propose a rational approach to reliability-based LCC analysis of high-speed railway steel bridges considering lifetime corrosion and fatigue damage. However in Korea, since high speed railway steel bridges are only recently constructed, no direct statistical data are available for the account of the maintenance cost and thus their maintenance characteristics are not clear yet. In this paper, for the assessment of expected maintenance/repair cost, the fatigue system reliability analysis incorporating the corrosion effect is proposed by considering the corrosion and fatigue damage using measured data of high speed railway steel bridges. A model proposed by Rahgozar, of at for fatigue notch factor considering the corrosion effect is used in order to incorporate the corrosion effect into the fatigue strength reduction and S-N curve. Finally, the effectiveness of LCC model proposed for high-speed railway steel bridges is demonstrated by a numerical example.

• Proceedings of the KSR Conference
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• 2003.10a
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• pp.181-186
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• 2003

In order to develop a high speed train, various conditions have been considered. Fatigue strength assessment by the fluctuation of pressure is an important one. In this study, a numerical simulation has been performed to estimate the fluctuation and frequency of pressure when KHST(Korean High Speed Train)passes through tunnels in the Kyung-Bu high-speed railway. The simulation was based on KHST running the Kyung-Bu high-speed line with the speed of 350km/h and the interval of 10 minute headway. And the tunnel entrance speed was estimated by TPS program. Therefore, the fluctuation and frequency of pressure is expressed in Weibull distribution function in the above running situation. The result in this study would be good guidance to calculate the fatigue life and the index of reliability of body structure. We are going to conduct more study to measure the real value of the pressure of the carbody passing through tunnels, to assess the fatigue reliability and to develop method ＆ procedure for the fatigue reliability design.