• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.8
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• pp.619-624
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• 2013

To predict the probabilistic service life, statistical factors should be included to consider the uncertainty of parameters. Generally the probabilistic analysis is one of the common methods to account the uncertainty of parameters on the structural failure. In order to apply probabilistic analysis on the deterministic life analysis, it would be necessary to introduce Probability of Failure(PoF) and conduct risk assessment. In this work, we have studied probabilistic risk assessment of aircraft structures by using PoF approach. To achieve this goal, the Bayesian method was utilized to model PoF estimation since this method is known as the proper method to express the uncertainty of parameters. A series of proof tests were also conducted in order to verify the result of PoF estimation. The results from this efforts showed that the PoF estimation model can calculate quantitatively the value of PoF. Furthermore effectiveness of risk assessment approach for the aircraft structures was also demonstrated.

• Journal of Korean Society of Disaster and Security
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• v.7 no.1
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• pp.43-50
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• 2014

Based on the reliability theory, the risk assessment of steel beams is performed by the determination of failure probability. In the calculation, bending, shearing and combined (bending + shearing) modes are examined. The resistance and the loads on the beam are assumed to be normal distribution. To investigate the failure probability changes, total load applied at the mid span of beam is divided into 1 to 1 and 1 to 2 ratio and then these divided loads are placed on the trisected points on beam. The change of boundary conditions at beam ends are also included in the investigation. It shows that failure is governed by the combined mode for the present beams and the second order bound analysis of failure probability is not crucial. On the whole failure probability decreases with increasing end restraints at the beam ends with some exception.

• Composites Research
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• v.13 no.1
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• pp.33-39
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• 2000

A numerical approach for predicting the ultimate strength of laminate composites has been studied using the Weibull distribution of the strengths of lamina plies. The probabilistic initial failure strengths of laminates were calculated using Tsai-Hill failure criterion. The ultimate strength of the laminate composites has been predicted using progressive failure analysis. The experimental results show that the strength prediction based on the Weibull distribution of ply strength reasonably agrees well with the experimentals better than equal strength assumption.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2037-2047
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• 1991

Strength is not simply a single given value but rather is a statistical one with certain distribution functions. This is because it is affected by many unknown factors such as size, shape, stress distribution, and combined stresses. In this study, a model of loss probability is proposed in view of the fact that one of the fundamental configuration of nature is hexagonal, for example, the shapes of lattice unit, grain, and so on. The model sues the concept of loss of certain element in place of Jayatilaka-Trustrum's length and angle of cracks. Using this model, the loss probability due to each loss of certain elements is obtained. Then, the maximum principal stress is calculated by the finite element method at the centroid of the elements under the tensile load for the 4,095 models of analysis. Finally, the failure probability of the brittle materials is obtained by multiplying the loss probability by the ratio of the maximum principal stress to theoretical tensile strength. Comparison of the result of the Jayatilaka-Trustrum's model and the proposed model shows that the failure probabilities by the two methods are in good agreement. Further, it is shown that the parametric relationship of semi-crack lengths for various degrees of birittleness can be determined. Therefore, the analysis of the failure probability suing the proposed model is shown to be promising as a new method for the study of the failure probability of birttle materials.

• Journal of the Korean GEO-environmental Society
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• v.22 no.11
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• pp.15-21
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• 2021

Losses of both life and property increased from damage to underground pipe such as heat transmission pipe buried underground in downtown because pipes are gradually aging. Considering the characteristics of the heat transmission pipe, which is not exposed to the outside and difficult to immediately identify problems such as damage, it is realistic to indirectly check the condition of the facility based on the historical information that is periodically collected through facility maintenance. In this study, a methodology for estimating the damage probability was developed by examining the history information of the heat transmission pipe, deriving an evaluation factor that is related to the damage probability. The contribution factor of the damage probability were reviewed by analyzing not only the guidelines for maintenance of heat transmission pipe of advanced European countries and domestic district heating companies, but also the cases of waterworks with similar characteristics. Evaluation factors were selected by considering not only the correlation with the damage probability but also the possibility of securing data. Based on 1999, when the construction technology and standards of heat transmission pipe changed, the damage probability estimation function according to the period of use was divided into the case of being buried before 1998 and the case of being buried after 1999, and presented. In addition, the damage probability was corrected by assigning weights according to the measured data for each evaluation factor such as the diameter, use, and management authority.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1651-1664
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• 2013

Precise analysis on deterioration processes of road pavements is not so simple matter due to severe uncertainty originated from a lot of explanatory variables engaged in. For those reasons, most analytical models for pavement deterioration prediction have often preferred to probabilistic approaches than deterministic models. However, the general probabilistic approaches that treat overall characteristics of population or entire sample would not be suitable for providing detail or localized information on their changing process. Considering the aspects, this paper aimed to suggest a stochastic disaggregation method to analyze the localized deterioration speeds and its variances changed by time and condition states. In addition, life expectancies and their uncertainty were estimated by probabilistic algorithm using the disaggregated stochastic process. For an empirical study, pavement inspection data (crack) accumulated from 2003 to 2010 from Korean national highway network was applied. This study can contribute to securing reliability of life cycle cost analysis, which is one of the primary analyses in road asset management, with much advanced deterioration forecasting functions. In addition, it would be meaningful trials as fundamental research for preventive maintenance strategy that demands essential understanding on changing process of the deterioration speed of pavement.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.12
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• pp.1186-1192
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• 2008

The reliability of gas turbine engine blades was studied. Yield strength, Young’s modulus, engine speed and gas temperature were considered as statistically independent random variables. The failure probability was calculated using five different methods. Advanced Mean Value Method was the most efficient without significant loss in accuracy. When random variables were assumed to have normal, lognormal and Weibull distributions with the same means and standard deviations, the CDF of limit state equation did not change significantly with the distribution functions of random variables. The normalized sensitivity of failure probability with respect to standard deviations of random variables was the largest with gas temperature. The effect of means and standard deviations of random variables was studied. The increase in the mean of gas temperature and the standard deviation of engine speed increased the failure probability the most significantly.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.49-49
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• 2004

고도화로 정밀해진 현대 과학기기에는 여러 가지 전자 팩키징 제품들이 쓰이고 있으나 이 제품들은 여러 가지 파손인자들의 영향 때문에 고유의 수명을 다하지 못하고 고장이 발생하게 된다. 전자부품 실장에 이용되는 솔더 조인트의 열화에 관련되는 열 피로와 이온 마이그레이션(Migration) 현상이 솔더 조인트의 신뢰성에 영향을 미치는 가장 중요한 인자로 알려져 있고 이러한 인자 이외에도 여러 가지 요인들이 복합적으로 작용하여 솔더의 접합부분에 피로파괴를 일으킨다.(중략)

• Composites Research
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• v.19 no.3
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• pp.7-14
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• 2006

In this paper, an integrated probabilistic strength analysis was conducted to predict the reliability of a composite pressure vessel under inner pressure loading condition. As a probabilistic strength analysis, the probabilistic progressive failure model consisting of progressive failure model and Monte Carlo simulation was incorporated with a commercial FEA code, ABAQUS Standard, to perform the probabilistic failure analysis of composite structure which has a complex shape and boundary conditions. As design random variables, the laminar strengths of each direction were considered. Finally, from probabilistic strength analysis, the scattering of burst pressure could be explained and the reliability of composite pressure vessel could be obtained for each component. In case of composite structures in mass production, the effects of uncertainties in material and manufacturing on the performance of composite structures would apparently become larger. So, the probabilistic strength analysis is essential for the structural design of composite structures in mass production.

• Journal of the Korean Institute of Gas
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• v.24 no.4
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• pp.10-17
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• 2020

The structural reliability assessment can be used to improve the reliability in the asset integrity management of the pipeline by using a geometric variation, mechanical characteristics, load change and operating condition as evaluation factors. When evaluating structural reliability, the failure probability of the natural gas pipe is evaluated by the relationship of the resistance of the pipe material to external loads. The failure probability of the natural gas pipe due to the combined stresses such as the internal pressure, thermal stress and bending stress was evaluated by using COMREL program. When evaluating the failure probability of the natural gas pipe, a buried depth of 1.5 to 30 m, a wheel load of 2.5 to 20 ton, a temperature difference of 45℃, an operating pressure of 6.86MPa, and a soil density of 1.8 kN/㎥ were used. The failure probabilities of the natural gas pipe were evaluated by the Von-Mises stress criterion as the maximum allowable stress criterion under the combined stresses.