Structural Reliability Assessment for Thermal Fatigue Phenomena in Fast Breeder Reactors Based upon Probabilistic Fracture Mechanics

1.基于概率断裂力学，建立了快堆热剥离现象的数学模型。利用它，从理论上导出了闭合形式的剩余寿命分布函数和裂纹长度分布函数。当组件的失效概率为10^.2时，通过导出的分布计算的剩余寿命为10^8次循环<-5>。对模型参数进行了敏感性分析。结果表明，当温度波动谱为窄带型时，热疲劳裂纹扩展的随机性主要受材料性能随机性的影响，而不受温度随机性的影响.提出了一种用应力松弛因子来表示裂纹间应力交互作用的近似方法。应用该方法分析了结构构件中含有多个热疲劳裂纹的情况。计算结果表明，裂纹间距越大，平均剩余寿命越短.从理论上阐明了无论温度谱的形状如何，我们的模型都是适用的。

1. A mathematical model to analyze thermal striping phenomena in fast breeder reactors is constructed based upon a probabilistic fracture mechanics. By the use of it, a residual life distribution function, as well as a crack length distribution function, is theoretically derived in a closed form. The residual life calculated by the derived distribution is of order of 10^8 cycles when the failure probability of the component is 10^<-5>.2. Sensitivity analysis with respect to model parameters is performed. The result indicates that, if the spectrum of temperature fluctuation is of narrow-band type, the random aspect of thermal fatigue crack growth is mainly affected by the randomness of material's property rather than by the randomness of temperature.3. An approximation method is proposed to express stress interaction effect between cracks by the use of a stress relaxation factor. The method is applied to analyze the case in which the structural component contains many thermal fatigue cracks. The numerical result shows that the mean residual life is shortened as the crack spacing becomes larger.4. It is theoretically clarified that our model is applicable regardless of the shape of the temperature spectrum.