• 융합보안논문지
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• 제6권3호
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• pp.145-153
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• 2006

본 논문에서는 기록값 통계량을 이용한 무한 고장 NHPP 모형들이 제안되었다. 이 모형들은 결함당 고장 발생률이 단조 증가하거나 단조 감소하는 패턴을 가진다. 그리고 수명 분포에서는 어랑 분포, 랄리 분포와 굼벨를 이용한 소프트웨어 신뢰성 모형을 적용하여 비교연구에 초점을 두었다. 고장 간격 시간 자료를 이용한 무한 고장 NHPP 모형들에 대한 모수 추정법은 최우 추정법을 사용하였고 적용 분포들의 적용을 용이하게 하기 위하여 특수한 형태를 제시하였다. 고장 자료의 분석을 위하여 산술 및 라플라스 추세 검정과 적합도 및 치우침 검정을 실시하여 그 결과를 나열하였다.

• Structural Engineering and Mechanics
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• 제49권1호
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• pp.111-128
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• 2014

The stochastic response surface method (SRSM) and the response surface method (RSM) are often used for structural reliability analysis, especially for reliability problems with implicit performance functions. This paper aims to compare these two methods in terms of fitting the performance function, accuracy and efficiency in estimating probability of failure as well as statistical moments of system output response. The computational procedures of two response surface methods are briefly introduced first. Then their capabilities are demonstrated and compared in detail through two examples. The results indicate that the probability of failure mainly reflects the accuracy of the response surface function (RSF) fitting the performance function in the vicinity of the design point, while the statistical moments of system output response reflect the accuracy of the RSF fitting the performance function in the entire space. In addition, the performance function can be well fitted by the SRSM with an optimal order polynomial chaos expansion both in the entire physical and in the independent standard normal spaces. However, it can be only well fitted by the RSM in the vicinity of the design point. For reliability problems involving random variables with approximate normal distributions, such as normal, lognormal, and Gumbel Max distributions, both the probability of failure and statistical moments of system output response can be accurately estimated by the SRSM, whereas the RSM can only produce the probability of failure with a reasonable accuracy.

• Smart Structures and Systems
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• 제16권2호
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• pp.367-382
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• 2015

This paper aims to conduct the reliability-based assessment of the welded joint in the orthotropic steel bridge deck by use of a mesh-insensitive structural stress (MISS) method, which is an effective numerical procedure to determine the reliable stress distribution adjacent to the weld toe. Both the solid element model and the shell element model are first established to investigate the sensitivity of the element size and the element type in calculating the structural stress under different loading scenarios. In order to achieve realistic condition assessment of the welded joint, the probabilistic approach based on the structural reliability theory is adopted to derive the reliability index and the failure probability by taking into account the uncertainties inherent in the material properties and load conditions. The limit state function is formulated in terms of the structural resistance of the material and the load effect which is described by the structural stress obtained by the MISS method. The reliability index is computed by use of the first-order reliability method (FORM), and compared with a target reliability index to facilitate the safety assessment. The results achieved from this study reveal that the calculation of the structural stress using the MISS method is insensitive to the element size and the element type, and the obtained structural stress results serve as a reliable basis for structural reliability analysis.

• Structural Engineering and Mechanics
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• 제82권3호
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• pp.271-282
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• 2022

The active learning surrogate model based on adaptive sampling strategy is increasingly popular in reliability analysis. However, most of the existing sampling strategies adopt the trial and error method to determine the size of the Monte Carlo (MC) candidate sample pool which satisfies the requirement of variation coefficient of failure probability. It will lead to a reduction in the calculation efficiency of reliability analysis. To avoid this defect, a new method for determining the optimal size of the MC candidate sample pool is proposed, and a new structural reliability analysis method combining polynomial chaos-based Kriging model (PC-Kriging) with adaptive sampling region is also proposed (PCK-ASR). Firstly, based on the lower limit of the confidence interval, a new method for estimating the optimal size of the MC candidate sample pool is proposed. Secondly, based on the upper limit of the confidence interval, an adaptive sampling region strategy similar to the radial centralized sampling method is developed. Then, the k-means++ clustering technique and the learning function LIF are used to complete the adaptive design of experiments (DoE). Finally, the effectiveness and accuracy of the PCK-ASR method are verified by three numerical examples and one practical engineering example.

• Journal of Welding and Joining
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• 제29권1호
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• pp.46-51
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• 2011

TSV technology raises several reliability concerns particularly caused by thermally induced stress. In traditional package, the thermo-mechanical failure mostly occurs as a result of the damage in the solder joint. In TSV technology, however, the driving failure may be TSV interconnects. In this study, the thermomechanical reliability of TSV technology is investigated using finite element method. Thermal stress and thermal fatigue phenomenon caused by repetitive temperature cycling are analyzed, and possible failure locations are discussed. In particular, the effects of via size, via pitch and bonding pad on thermo-mechanical reliability are investigated. The plastic strain generally increases with via size increases. Therefore, expected thermal fatigue life also increase as the via size decreases. However, the small via shows the higher von Mises stress. This means that smaller vias are not always safe despite their longer life expectancy. Therefore careful design consideration of via size and pitch is required for reliability improvement. Also the bonding pad design is important for enhancing the reliability of TSV structure.

• Structural Engineering and Mechanics
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• 제59권5호
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• pp.853-866
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• 2016

This paper examines a methodology for computing the probability of structural failure of reinforced concrete beams subjected to fire. The significant load variables considered are dead load, sustained live load and fire temperature. Resistance is expressed in terms of moment capacity with random variables taken as yield strength of steel, concrete class (or grade of concrete), beam width and depth. The flexural capacity is determined based on the design equations recommended in Indian standard IS456:2000. Simplified method named $500^{\circ}C$ isotherm method detailed in Eurocode 2 is incorporated for fire design. A transient thermal analysis is conducted using finite element software ANSYS$^{(R)}$ Release15. Reliability is evaluated from the initial state to 4h of fire exposure based on the first order reliability method (FORM). A procedure is coded in MATLAB for finding the reliability index. This procedure is validated with available literature. The effect of various parameters like effective cover, yield strength of steel, grade of concrete, distribution of reinforcement bars and aggregate type on reliability indices are studied. Parameters like effective cover of concrete, yield strength of steel has a significant effect on reliability of beams. Different failure modes like limit state of flexure and limit state of shear are checked.

• Nuclear Engineering and Technology
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• 제44권5호
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• pp.471-482
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• 2012

To assess the risk of nuclear power plant operation and to determine the risk impact of digital systems, there is a need to quantitatively assess the reliability of the digital systems in a justifiable manner. The Probabilistic Risk Analysis (PRA) is a tool which can reveal shortcomings of the NPP design in general and PRA analysts have not had sufficient guiding principles in modelling particular digital components malfunctions. Currently digital I&C systems are mostly analyzed simply and conventionally in PRA, based on failure mode and effects analysis and fault tree modelling. More dynamic approaches are still in the trial stage and can be difficult to apply in full scale PRA-models. As basic events CPU failures, application software failures and common cause failures (CCF) between identical components are modelled.The primary goal is to model dependencies. However, it is not clear which failure modes or system parts CCF:s should be postulated for. A clear distinction can be made between the treatment of protection and control systems. There is a general consensus that protection systems shall be included in PRA, while control systems can be treated in a limited manner. OECD/NEA CSNI Working Group on Risk Assessment (WGRisk) has set up a task group, called DIGREL, to develop taxonomy of failure modes of digital components for the purposes of PRA. The taxonomy is aimed to be the basis of future modelling and quantification efforts. It will also help to define a structure for data collection and to review PRA studies.

• 한국터널지하공간학회 논문집
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• 제25권6호
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• pp.447-458
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• 2023

본 연구에서는 쉴드터널 세그먼트 라이닝의 하중과 부재저항의 확률적 특성뿐만 아니라 경계조건의 변동성을 고려한 비교모델을 선정하고 신뢰성해석을 수행하였으며, 파괴확률 산정 및 구조안전성 검토를 통해 한계상태설계의 적정성에 대해 분석을 수행하였다. 이러한 지반 정수의 확률특성치를 고려한 해석을 위해 지반스프링계수는 Muirwood식을 적용하여 정량적 값을 산정하여 Mean값으로 고려하였고, 변동계수는 기존 연구자료를 토대로 지반 경계조건 변화에 따른 검토대상 모델들을 선정하였다. 이러한 모델들에 대한 구조해석과 MCS기법을 적용한 신뢰성분석을 통해 파괴확률과 신뢰성지수를 산정하여 지반경계조건 변화에 따른 파괴확률의 변화를 검토하였다.

• Journal of Welding and Joining
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• 제31권5호
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• pp.59-63
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• 2013

A bendable electronic module has been developed for a mobile application by using a low-cost roll-to-roll manufacturing process. In flexible embedded electronic module, a thin silicon chip was embedded in a polymer-based encapsulating adhesive between flexible copper clad polyimide layers. To confirm reliability and durability of prototype bendable module, the following tests were conducted: Moisture sensitivity level, thermal shock test, high temperature & high humidity storage test, and pressure cooker tester. Those experiments to induce failure of the module due to temperature variations and moisture are the experiment to verify the reliability. Failure criterion was 20% increase in bump resistance from the initial value. The mechanism of the increase of the bump resistance was analyzed by using non-destructive X-ray analysis and scanning acoustic microscopy. During the pressure cooker test (PCT), delamination occurred at the various interfaces of the bendable embedded modules. To investigate the failure mechanism, moisture diffusion analysis was conducted to the pressure cooker's test. The hygroscopic characteristics of the encapsulating polymeric materials were experimentally determined. Analysis results have shown moisture saturation process of flexible module under high temperature/high humidity and high atmosphere conditions. Based on these results, stress factor and failure mechanism/mode of bendable embedded electronic module were obtained.

• 대한토목학회논문집
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• 제11권3호
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• pp.59-65
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• 1991

본 연구에서는 국내 고속도로의 표준단면들을 포함한 포장구조 해석모델을 사용하여 아스팔트 콘크리트 포장체의 피로파괴 기준식을 개발하였다. 해석 대상 모델은 쇄석 및 아스팔트 안정처리 기층을 갖는 2430개의 4충 포장구조로 하였으며, 각 모델의 물성을 공용성 한계를 PSI=2.5로 한 AASHTO 설계식과 다층 탄성해석 프로그램인 SINELA에 적용, 포장체의 통과예상 교통량과 아스팔트 콘크리트층 하단에서의 최대 인장 변형률과의 관계를 회귀분석하였다. 분석 결과로부터, 신뢰도 50%와 95% 수준의 파괴기준식을 제안하였다. 타 연구결과와 비교한 결과 신뢰도 95% 수준의 파괴기준식은 균열의 발생을 공용성 한계로 보는 기존의 피로 파괴기준식과 같은 정도의 교통량을 추정하고 있음을 알 수 있었다. 또한 신뢰도 수준에 따른 파괴기준식을 신뢰도 50%, 수준의 파괴기준식으로부터 간접 추정할 수 있는 관계식을 제안하였다.