Papers by Keyword: Probabilistic Fracture Mechanics

Abstract: This chapter describes the cracking of stainless steel piping under Inter-granular Stress Corrosion Cracking (IGSCC) conditions using probabilistic fracture mechanics that predict the impact of in-service inspection (ISI) programs on the reliability of specific nuclear piping systems that have failed in service. The IGSCC is characterized by a single damage parameter, which depends on residual stresses, environmental conditions, and the degree of sensitization. The Probability of Detection (POD) curves and the benefits of in-service inspection in order to reduce the probability of the leak for nuclear piping systems subjected to IGSCC were discussed. The results show that an effective ISI requires a suitable combination of crack detection and inspection schedule. An augmented inspection schedule is recurred for piping with fast-growing crack to ensure that the inspection is done before the cracks reach critical sizes and that the use of a better inspection procedure can be more effective than a tenfold increase in the number of inspections of inferior quality.

Abstract: One potential challenge to the integrity of the reactor pressure vessel (RPV) in a pressurized water reactor is posed by pressurized thermal shock (PTS). Therefore, the safety of the RPV with regard to neutron embrittlement has to be analyzed. In this paper, the procedure and method for the structural integrity analysis of RPV subjected to PTS is presented. The FAVOR code is applied to calculate the probabilities for crack initiation and failure by considering crack distributions based on cracks observed in the Shoreham and PVRUF RPVs in the U.S. A local approach to fracture, i.e. the σ*-A* model is used to predict the warm prestressing (WPS) effect on the RPV integrity. The results show that the remaining stress contributes to the WPS effect, whereas the increase of fracture toughness is not completely attributed to the remaining stress. The modeled load paths predict a material toughness increase of 30-100%.

Abstract: A statistical model is proposed for the analysis of fatigue crack propagation, based on the theory of fracture mechanics and stochastic process. The fatigue growth process is approximated as a diffusive Markov process. The associated backward Fokker-Plank equation and boundary conditions are written, and the distribution of crack propagation time under a given crack size is obtained by using an Eigenfunction method. The sought distribution is expressed in the form of a convergent infinite series. An examples is presented to illustrate the application of the method. The predicted results seem to agree with the experimental data.

Abstract: Based on the theory of probabilistic fracture mechanics and Monte Carlo simulation, reliability analysis method for fatigue life of autofrettaged thick-walled cylinder was given. The forms of fatigue cracks in bore of autofrettaged thick-walled cylinder were considered as semi-elliptical cracks. The autofrettage residual stress solution was suitable for the thick-walled cylinder made of steel with strain hardening and Bauschinger effect. The stress intensity factors of thick-walled cylinder were calculated according to weight function method. The analysis of the examples showed that lognormal distribution is the best fit for fatigue life. Finally, the fatigue life of autofrettaged thick-walled on the condition of different reliabilities and confidences were presented.

Abstract: The residual fatigue life of a submarine pressure structure is investigated, based on the combination between the methods of conventional Monte Carlo and classical probabilistic fracture mechanics. Firstly, Monte Carlo method is employed to obtain the reliability of given initial fatigue life. Secondly, the two induced factors M_A1 and M_A2 in the paper are estimated according to the initial fatigue life and the reliability. Thirdly, based on the two factors, the residual fatigue life based on other reliability is obtained by using classical probabilistic fracture mechanics method. Numerical examples show that the proposed method is more efficient without accuracy loss for residual fatigue life compared with Monte Carlo method. This method can also be employed to predict the residual fatigue life on other analogue structures.

Abstract: A new method is presented in the paper. The fatigue life reliability of submarine cone-cylinder shell is investigated, based on the combination between the methods of conventional Monte Carlo and classical probabilistic fracture mechanics. Firstly, Monte Carlo method is employed to obtain the reliability of given initial fatigue life. Secondly, the two induced factors M1 and M2 in the paper are estimated according to the initial fatigue life and the reliability. Thirdly, based on the two factors, the other fatigue life reliability is obtained by using classical probabilistic fracture mechanics method. Finally, numerical cases show that the proposed method is more efficient without accuracy loss for fatigue life reliability compared with Monte Carlo method. This method can also be applied to predict the fatigue life reliability of analogue structures.

Abstract: This paper demonstrates sensitive analyses of probabilistic fracture mechanics (PFM) for reactor pressure vessel (RPV) during pressurized thermal shock (PTS) loading, and comparison of our calculation with the results of the international round robin (RR) analyses in Asian countries (Korea, Taiwan and Japan). The international Round Robin activity was performed in PFM sub-committees in the Atomic Energy Research Committee of Japan Welding Engineering Society (JWES) in conjunction with Korea and Taiwan research groups. The purposes of this program are to establish reliable procedures to evaluate fracture probability of reactor pressure vessels during pressurized thermal shock and to maintain the continuous cooperation among Asian institutes in the probabilistic approach to nuclear safety. Some parameters to RPV failure probabilities are chosen to evaluate their significance quantatively. The differences caused by selection of analyzing programs and some input parameters will be discussed.

Abstract: According to the fatigue damage failure mechanism of riveted members, a riveted member probabilistic fatigue failure model (RMPFFM) was proposed, and a fracture finite element program is developed to calculate the geometry function of RMPFFM. Furthermore, a system fatigue damage reliability model of riveted bridges was proposed, and based on Monte-Carlo method, a large system fatigue damage reliability analysis program was developed to calculate the system fatigue failure probability. Then the system evaluation model was used to predicate the system fatigue damage reliability of Ganjiang Railway Bridge. According to assessment results, the probabilistic remaining fatigue life, safe inspection intervals and maintenance strategy are determined, which can control and avoid fatigue failure accident and reduce the contingent disaster in bridge service life.

Abstract: There are many old steel bridges on Chinese transportation lines, which keep their normal traffic service function. The old bridges are often required to carry an increasing volume of traffic and heavier vehicles than the original design, so bridge management departments pay more attention to the actual remaining fatigue life of such structures. Based on probabilistic fracture mechanics theory, the member and the system fatigue failure evaluation models for old steel bridges are all proposed, and the fatigue reliability analysis program is developed using Monte-Carlo. As a case study, the evaluation models are used to predicate the fatigue reliability of Zhejiang Street Bridge. According to evaluation results, the probabilistic remaining fatigue life, safe inspection intervals and maintenance strategy are determined.