• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1915-1926
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• 1995

The Fatigue characteristics of 8-harness satin woven CFRP composites with a circular hole are experimentally investigated under constant amplitude tension-tension loading. It is found in this study that the fatigue damage accumulation behavior is very random and history-independent, and the fatigue cumulative damage is linearly related with the mean number of cycles to a specified damage state. From these results, it is known that the fatigue characteristics of CFRP composites satisfy the basic assumptions of Markov chain theory and the parameter of Markov chain model can be determined only by mean and variance of fatigue lives. The predicted distribution of the fatigue cumulative damage using Markov chain model shows a good agreement with the test results. For the fatigue life distribution, Markov chain model makes similar accuracy to 2-parameter Weibull distribution function.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.955-962
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• 2015

The Vickers test can be used for all types of materials, and it has one of the widest scales among hardness tests. The hardness may be considered as a probability variable when evaluating the mechanical properties of materials. In this study, we investigate the statistical properties of the bending strength and Vickers hardness in $ZrO_2$ monolithic and $ZrO_2/SiC$ composites depending on the amount of $TiO_2$ additives. The bending strength and Vickers hardness were found to agree well with the Weibull probability distribution. We evaluate the scale parameter and shape parameter in as-received $ZrO_2$ and $ZrO_2/SiC/TiO_2$ ceramics, as well as their heat treated ceramics. We also evaluate the parameters in accordance with the increase in in the indentation load.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.1
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• pp.1-5
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• 2020

In this study, the objective is to improve the criteria used for statistical comparison of the VLF tanδ (TD) database and failure rate according to water-tree degradation in underground distribution power cables. The aging condition of the KEPCO criteria is divided into 6 levels using the Weibull distribution, and the "failure imminent" condition is quantified by using the statistical end-point of the lifetime parameter of the VLF big-data group obtained from KEPCO. Moreover, new criteria with a 2-dimensional combination of TD, DTD, and a statistical normalized factor are suggested. These criteria exhibit high reproducibility for the detection of cables in an imminent failure state. Consequently, it is expected that the adoption of the extended VLF-2019 criteria will reduce the asset management cost of cable replacement compared to the VLF-2012 criteria of KEPCO.

• Smart Structures and Systems
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• v.21 no.5
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• pp.591-600
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• 2018

The probabilistic characterization of wind field characteristics is a significant task for fatigue reliability assessment of long-span railway bridges in wind-prone regions. In consideration of the effect of wind direction, the stochastic properties of wind field should be represented by a bivariate statistical model of wind speed and direction. This paper presents the construction of the bivariate model of wind speed and direction at the site of a railway arch bridge by use of the long-term structural health monitoring (SHM) data. The wind characteristics are derived by analyzing the real-time wind monitoring data, such as the mean wind speed and direction, turbulence intensity, turbulence integral scale, and power spectral density. A sequential quadratic programming (SQP) algorithm-based finite mixture modeling method is proposed to formulate the joint distribution model of wind speed and direction. For the probability density function (PDF) of wind speed, a double-parameter Weibull distribution function is utilized, and a von Mises distribution function is applied to represent the PDF of wind direction. The SQP algorithm with multi-start points is used to estimate the parameters in the bivariate model, namely Weibull-von Mises mixture model. One-year wind monitoring data are selected to validate the effectiveness of the proposed modeling method. The optimal model is jointly evaluated by the Bayesian information criterion (BIC) and coefficient of determination, $R^2$. The obtained results indicate that the proposed SQP algorithm-based finite mixture modeling method can effectively establish the bivariate model of wind speed and direction. The established bivariate model of wind speed and direction will facilitate the wind-induced fatigue reliability assessment of long-span bridges.

• Asian Journal of Atmospheric Environment
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• v.9 no.4
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• pp.288-297
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• 2015

In this study, wind conditions and its energy potential have been assessed by conducting a Weibull analysis of the wind speed data (over the period of 2002-2011) measured from a port city (Mongla) and an isolated island (Sandwip) in Bangladesh. The monthly mean wind speed at Mongla ranged from 1.60 m/s (December) to 2.47 m/s (April). The monthly values of Weibull shape parameter (k) were from 1.27 to 2.53. In addition, the values of the scale parameter (c) and the monthly wind power density ranged from 1.76 to 2.79 m/s and 3.95 to $17.45W/m^2$, respectively. The seasonal mean wind speed data varied from 1.72 (fall) to 2.29 m/s (spring) with the wind power density from 5.33 (fall) to $14.26W/m^2$ (spring). In the case of Sandwip, the results were comparable to those of Mongla, but moderate reductions in all the comparable variables were observed. The wind data results of these two areas have been compared with those of eight other locations in the world with respect to wind power generation scale. According to this comparison, the wind power generation scale for Mongla and Sandwip was adequate for stand-alone small/micro-scale applications such as local household consumption, solar-wind hybrid irrigation pumps, and battery charging.

• Journal of Power System Engineering
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• v.10 no.1
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• pp.60-64
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• 2006

Alumina ceramic for textile machinery was sintered and subjected to three-point bending. A semicircular surface crack was made on each sample. Crack-healing behavior was systematically studied, as a function of crack-healing temperature and crack size. The bending strength and fracture toughness of the crack-healed sample from $1200^{\circ}C\;to\;1400^{\circ}C$ were investigated. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the fracture toughness. Alumina ceramic for textile machinery have the ability to heal after cracking, from over $1300^{\circ}C$. The material can completely heal a $65{\mu}m$ diameter semielliptical crack. The fracture toughness could be explained by 2-parameter Weibull distribution.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3148-3154
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• 2010

This paper presents the probabilistic analysis for fatigue life of Glass/Epoxy laminates with impact-induced damage. For this, a series of impact tests were perfomed on the Glass/Epoxy laminates using instrumented impact testing machine. Then, tensile and fatigue tests carried out so as to generate post-impact residual strength and fatigue life. Two Parameter Weibull distribution was used to fit the residual strength and fatigue life data of Glass/Epoxy composite laminates. The residual strength was affected by impact energy and their variance decreased with increasing of impact energy. The fatigue life of impacted laminates was greatly reduced by impact energy and this trend depended on applied stress amplitude. Additionally, the variation of fatigue life was gradually decreased with the applied stress amplitude.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1663-1672
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• 2018

In recent times, gas insulated medium voltage (MV) circuit breakers (CB) form a vital component in power system network, considering its advantages such as reduced size and safety margins. Gas insulation characteristics of circuit breakers are generally measured by lightning impulse (LI) test according to IEC standard 60060-1 as a factory routine test. Considering the environmental issues of $SF_6$ gas, many research works are being carried out towards the mixture of $SF_6$ gases for high voltage insulation applications. However, few reports are only available regarding the LI withstand and streamer propagation characteristics (at both positive and negative polarity of waveform) of $SF_6/N_2$ gas mixture insulated medium voltage circuit breakers. In this paper, positive and negative polarity LI tests are carried out on 22 kV medium voltage circuit breaker filled with $SF_6/N_2$ gas mixture at different gas pressures (1-5 bar) and at different gas mixture ratios. Important LI parameters such as breakdown voltage, streamer velocity, time to breakdown and acceleration voltage are evaluated with IEC standard LI ($1.2/50{\mu}s$) waveform. Weibull distribution analysis of LI breakdown voltage data is carried out and 50% probability breakdown voltage, scale parameter and shape parameter are evaluated. Results illustrate that the $25%SF_6+75%N_2$ gas filled insulation considerably enhances the LI withstand and breakdown strength of MV circuit breakers. LI breakdown voltage of circuit breaker under negative polarity shows higher value when compared with positive polarity. Results show that maintaining the gas pressure at 0.3 MPa (3 bar) with 10% $SF_6$ gas mixed with 90% $N_2$ will give optimum lighting impulse withstand performance of 22 kV MV circuit breaker.

• Journal of Wetlands Research
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• v.2 no.1
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• pp.49-58
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• 2000

The frequency analysis of annual maximum rainfall data and the derivation of probable rainfall intensity formula at Masan station are performed in this study. Based on the eight different rainfall duration data from 10 minutes to 24 hours, eight types of probability distribution (Gamma, Lognormal, Log-Pearson type III, GEV, Gumbel, Log-Gumbel, Weibull, and Wakeby distributions), three types of parameter estimation scheme (moment, maximum likelihood and probability weighted methods) and three types of goodness-of-fit test (${\chi}^2$, Kolmogorov-Smirnov and Cramer von Mises tests) were considered to find an appropriate probability distribution at Masan station. The Lognormal-2 distribution was selected and the probable rainfall intensity formula was derived by regression analysis. The derived formula can be used for estimating rainfall quantiles of the Masan vicinity areas with convenience and reliability in practice.

• Journal of Applied Reliability
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• v.11 no.4
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• pp.319-330
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• 2011

We consider the stress-strength model in which a unit of strength $T_2$ is subjected to environmental stress $T_1$. An important measure considered in stress-strength model is the reliability parameter R=P($T_2$ > $T_1$). The greater the value of R is, the more reliable is the unit to perform its specified task. In this article, we consider the situations in which $T_1$ and $T_2$ are both independent and dependent, and have certain bivariate distributions as their joint distributions. To study the effect of dependency on R, we investigate several bivariate distributions of $T_1$ and $T_2$ and compare the values of R for these distributions. Numerical comparisons are presented depending on the parameter values as well.