• 한국정밀공학회지
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• 제22권10호
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• pp.137-143
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• 2005

The integrity of steam generator tubes in nuclear power plant should be maintained sufficiently during operation. For sake of this, complicated assessment procedures are required such as fracture mechanics analysis, etc. The integrity assessment of tubes has been performed by using conventional deterministic approaches while there are many uncertainties to carry out a rational evaluation. In this respect, probabilistic integrity assessment is considered as an alternative method for integrity assessment. The objectives of this study are to develop an integrity assessment system based on probabilistic fracture mechanics and to predict the failure probability of steam generator tubes containing an axial through-wall crack. The developed integrity assessment system consists of three evaluation modules, which apply first order reliability method, second order reliability method and Monte Carlo simulation method, respectively. The system has been applied to predict failure probability of steam generator tubes and the estimation results showed a promising applicability of the probabilistic integrity assessment system.

• Journal of Welding and Joining
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• 제23권6호
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• pp.61-66
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• 2005

A probabilistic approach for evaluating failure risk is suggested in this paper. Probabilistic fracture analyses were performed for a pressurized pipe of a Cr-Mo steel reflecting variation of material properties at high temperature. A crack was assumed to be located along the weld fusion line. Probability density functions of major variables were determined by statistical analyses of material creep and creep crack growth data measured by the previous experimental studies by authors. Distributions of these variables were implemented in Monte Carlo simulation of this study. As a fracture parameter for characterizing growth of a fusion line crack between two materials with different creep properties, $C_t$ normalized with $C^*$ was employed. And the elapsed time was also normalized with tT, Resultingly, failure probability as a function of operating time was evaluated fur various cases. Conventional deterministic life assessment result was turned out to be conservative compared with that of probabilistic result. Sensitivity analysis for each input variable was conducted to understand the most influencing variable to the analysis results. Internal pressure, creep crack growth coefficient and creep coefficient were more sensitive to failure probability than other variables.

• Structural Engineering and Mechanics
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• 제19권3호
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• pp.347-359
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• 2005

This paper attempts to develop the analytical model of estimating the fatigue damage using a linear elastic fracture mechanics method. The stress history on a welding member, when a truck passed over a bridge, was defined as a block loading and the crack closure theory was used. These theories explain the influence of a load on a structure. This study undertook an analysis of the stress range frequency considering both dead load stress and crack opening stress. A probability method applied to stress range frequency distribution and the probability distribution parameters of it was obtained by Maximum likelihood Method and Determinant. Monte Carlo Simulation which generates a probability variants (stress range) output failure block loadings. The probability distribution of failure block loadings was acquired by Maximum likelihood Method and Determinant. This can calculate the fatigue reliability preventing the fatigue failure of a welding member. The failure block loading divided by the average daily truck traffic is a predictive remaining life by a day. Fatigue reliability analysis was carried out for the welding member of the bottom flange of a cross beam and the vertical stiffener of a steel box bridge by the proposed model. Results showed that the primary factor effecting failure time was crack opening stress. It was important to decide the crack opening stress for using the proposed model. Also according to the 50% reliability and 90%, 99.9% failure times were indicated.

• 한국세라믹학회지
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• 제26권1호
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• pp.116-122
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• 1989

MOR test and concentric ring test were performed to evaluate the failure probability of sin/hip Si3N4 under uniaxial and biaxial stress state, respectively. Their failure probabilities were analized with KARA program based on Weibull PIA model and Batdorf model with 5 criteria, and they were compared with experiments. PIA model is in best accordance with experiments in higher fracture strength regions, especially for Pf 0.3. But in lower fracture strength region, none of the models predicts the failure probabilities appropriately.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1146-1147
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• 2006

Diamond segments were fabricated by cold pressing and sintering under pressure at the temperature up to $750^{\circ}C$. Based on the results of this investigation, it can be concluded that the segments containing 39wt.% cobalt in the matrix material have the highest bending strength at a fracture probability of 50 % due to the weibull distribution method. According to the weibull statistics, it was also determined that the transverse rupture strength was the best for 39 wt.% cobalt ratio in the matrix material for the fracture probability when the other variables are the same.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2009년도 학술논문요약집
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• pp.186-186
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• 2009

The characterization strategy of fracture networks are classified into a deterministic or statistical characterization according to the type of required information. A deterministic characterization is most efficient for a sparsely fractured system, while the statistics are sufficient for densely fractured rock. In this study, the ensemble mean and variability of the effective connectivity is systematically analyzed with various density values for different network structures of a power law size distribution. The results of high resolution Monte Carlo analyses show that statistical characteristics can be a necessary information to determine the transport properties of a fracture system when fracture density is greater than a percolation threshold. When the percolation probability (II) approaches unity with increasing fracture density, the effective connectivity of the network can be safely estimated using statistics only (sufficient condition). It is inferred from conditional simulations that deterministic information for main pathways can reduce the uncertainty in estimation of system properties when the network becomes denser. Overall results imply that most pathways need to be identified when II < 0.5 statistics are sufficient when II $\rightarrow$ 1 and statistics are necessary and the identification of main pathways can significantly reduce the uncertainty in estimation of transport properties when 0.5$\ll$1. It is suggested that the proper estimation of the percolation probability of a fracture network is a prerequisite for an appropriate conceptualization and further characterization.

• 터널과지하공간
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• 제11권2호
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• pp.156-166
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• 2001

균열암반에서의 지하수유동 모사를 위한 추계적 연속테 모델링 기법이 개발되었다. 추계적연속체 모델은 균열수의 제한을 가지는 개별균열연결망 모델의 단점을 극복할 수 있다. 뿐만 아니라 개별균열연결망 모델에서 가능한 확률론적 해석과 전도성이 큰 균열을 통한 지하수 유동을 근접하게 모사할 수 있는 장점을 가진다. 추계적연속체 모델은 개별균열연결망 모델에 근거하여 생성된다. 개별균열연결망 모델은 일정크기의 소블록으로 나누어지며 각 소블록 투수계수의 확률밀도함수와 베리오그램 함수로부터 추계적연속체 모델에서의 투수계수의 공간적 분포를 정의할 수 있다. 이 연구에서 추계적연속체 모델과 개별균열연결망 모델의 적합성을 보여 주기 위하여 수치실험을 통하여 지하수 유동 이동시간을 계산하고 상호 비교하였다. 그리고 추계적연속체 모델은 방사성폐기물 처분장의 확률론적 안전성 펑가를 위해 필요한 지하수 유동속도의 확률분포를 제공할 수 있는 모델임을 제시할 수 있었다.

• 여성건강간호학회지
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• 제18권4호
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• pp.237-247
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• 2012

Purpose: The purpose of this study was to investigate the incidence of osteoporosis and falls and their consequences, and to identify predictors of fracture risk in the postmenopausal women. Methods: A total of 687 postmenopausal women were recruited through a stratified convenience sampling. A structured questionnaire was used to obtain osteoporosis and fall history and details of their most recent fall. To predict fracture risk factors, we collected demographic and physical health variables related osteoporosis and fall. Fracture risk was measured by FRAX$^{(R)}$ to calculate 10-year probability of major osteoporotic and hip fracture. Results: The prevalence of osteoporosis was 22.1%, and 66.4% of them had treatments for osteoporosis. The incidence of falls during the past year was 19.2% and 38.6% of those who fell suffered consequent fractures. Women with history of osteoporosis and falls were significant predictors of 10-year probability of major osteoporotic and hip fracture. Other significant predictors were history of fracture, chronic disease, surgical menopause, lower BMI, poorer perceived health and no job. Conclusion: It appears that history of osteoporosis and falls are main predictors of fracture risk. Nursing assessment should be performed by detail history taking for osteoporosis, fall, chronic disease, and fracture to screen fracture risk group among postmenopausal women.

• 핵의학기술
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• 제13권3호
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• pp.137-142
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• 2009

목적: WHO (world health organization)에서는 골밀도뿐만 아니라 대규모 역학연구에서 정리된 골절의 위험인자 분석을 통하여 10년 내 골절위험도(10-year fracture probability)를 실제적으로 임상에 적용시킬 수 있는 소프트웨어 프로그램인 FRAX Tool (fracture risk assessment)이 2008년에 공개되었다. 본 연구는 기존에 사용하고 있는 GE Prodigy사의 골절위험도평가와 $FRAX^{TM}$를 이용한 골절위험도평가를 비교분석하고자 한다. 검사방법: 본원에 골밀도 검사를 시행한 201명($55{\pm}3.5$세)의 여자를 대상으로 GE Prodigy를 이용하여 Femur를 측정하였다. 측정한 Femoral Neck의 BMD (bone mineral density)를 구하여 GE Prodigy의 T-값과 골절위험인자를 고려하지 않은 $FRAX^{TM}$의 T-값를 사용하여 10년 내 대퇴골 골절위험도와 주요한 골다공증성 골절 위험도를 계산하여 SPSS통계프로그램으로 GE Prodigy의 골절위험도 평가와 $FRAX^{TM}$의 골절위험도 평가를 비교분석하였다. 결과: GE Prodigy의 T-값($-0.52{\pm}0.97$)과 $FRAX^{TM}$의 T-값 ($-1.45{\pm}0.81$)은 통계적으로 유의한 차이가 있었으며(p=0.000), GE Prodigy의 주요한 골다공증성 골절위험도($9.15{\pm}3.71$)와 $FRAX^{TM}$의 주요한 골다공증성 골절위험도($4.87{\pm}1.51$)도 또한 통계적으로 유의한 차이가 있었다(p=0.000). 그리고 GE Prodigy의 10년내 대퇴골 골절위험도($1.56{\pm}1.48$)와 $FRAX^{TM}$의 10년 내 대퇴골골절위험도($0.53{\pm}0.61$)도 통계적으로 유의한 차이를 보였다(p=0.000). 결론: GE Prodigy와 $FRAX^{TM}$에서 측정한 골절의 절대위험도는 통계적으로 유의한 차이를 보였다. 특히 GE Prodigy의 T-값, 주요한 골다공증성 골절위험도, 10년 내 대퇴골 골절위험도가 높게 측정되었다. 향후 $FRAX^{TM}$에 대한 평가 및 적용에 관한 연구가 필요할 것으로 생각된다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1682-1685
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• 2005

System algorithms estimated by deterministic input may occur the error between predicted and actual output. Especially, actual system can't predict the exact outputs due to uncertainty and tolerance of input parameters. A single output to a set of inputs has a limited value without the variation. Hence, we should consider various scatters caused by the load assessment, material characteristics, stress analysis and manufacturing methods in order to perform the robust design or estimate the reliability of structure. The system design with uncertainty should perform the probabilistic structural optimization with the statistical response and the reliability. This method calculated the probability distributions of the characteristics such as stress by combining stress analysis, response surface methodology and Monte-Carlo Method and got the probabilistic sensitivity. The sensitivity of structural response with respect to inconstant design variables was estimated by fracture probability. Therefore, this paper proposed the probabilistic reliability design method for fracture of uncorved freight end beam and the design criteria by fracture probability.