设计S—N曲线的概率估计和ASME法的可靠性评价

基于ＬａｎｇｅｒＳ－Ｎ曲线,提出了设计Ｓ－Ｎ曲线的概率估计方法和ＡＳＭＥ法的可靠性评价方法。Ｐ－Ｓ－Ｎ曲线由文中提出的广义极大似然法估计。方法可应用于处理具有双随机性特征的Ｓ－Ｎ数据,并可推广应用于处理应力控制成组法疲劳试验和极大似然法试验得到的Ｓ－Ｎ数据。     

平均应变对0Cr18Ni10Ti管道钢随机应变-疲劳寿命关系的影响规律

试验研究了平均应变对0Cr18Ni10Ti管道钢随机应变-寿命关系的影响规律从节约试样和试验费用角度,采用改进的极大似然疲劳试验法,应变比分别为-1、-0．52、-0．22、0．029、0．18和0．48的条件下,完成了104个试样的应变控制疲劳试验在材料具有完全平均应力松弛特征、现有平均应变理论无法表征其影响情况下,首先基于Coffin—Manson方程,应用广义极大似然法有效地测定出各应变比下材料的随机应变-寿命关系．通过比较各应变比下疲劳寿命均值、对数疲劳寿命均方差和概率疲劳寿命,揭示出0Cr18Ni10Ti管道钢高可靠性时,应变比大于0有大约1．3-1．6的正面效应,小于0为负面效应现有平均应变效应研究仅考虑疲劳寿命均值可能给出错误评价;必须综合考虑均值、均方差和样本量3因素才能给出合理评价。     

平均应变对0Gr18Ni10Ti钢随机循环应力-应变关系的影响规律

试验研究了平均应变对0Cr18Ni10Ti管道钢随机循环应力-应变关系的影响规律.从节约试样和试验费用角度,提出了改进的极大似然疲劳试验法,以应变比分别为-1、-0.52、-0.22、0.029、0.18和0.48完成了104个试样的应变控制疲劳试验.揭示出材料具有Masing行为和完全平均应力松弛特征,现有平均应变理论无法表征其影响.因此,首先基于Ramberg-Osgood方程,应用广义极大似然法有效地测定出各应变比的材料随机循环应力-应变关系.通过比较各应变比的循环应力幅均值、循环应力幅均方差和概率循环应力幅,揭示出高可靠性管理时,平均应变具有降低循环应力幅作用,应变比接近0时最显著,偏离逐渐减弱.说明了研究平均应变效应,仅考虑均值,可能给出错误评价;必须综合考虑均值、均方差和样本量3因素才能给出合理评价.     

平均应变对0Cr18Ni10Ti钢随机循环应力-应变关系的影响规律

试验研究了平均应变对0Cr18Ni10Ti管道钢随机循环应力．应变关系的影响规律从节约试样和试验费用角度，提出了改进的极大似然疲劳试验法，以应变比分别为-1、-0．52、-0．22、0．029．0．18和0．48完成了104个试样的应变控制疲劳试验。揭示出材料具有Masing行为和完全平均应力松弛特征，现有平均应变理论无法表征其影响。因此．首先基于Ramberg-Osgood方程，应用广义极大似然法有效地测定出各应变比的材料随机循环应力-应变关系。通过比较各应变比的循环应力幅均值、循环应力幅均方差和概率循环应力幅，揭示出高可靠性管理时．平均应变具有降低循环应力幅作用，应变比接近0时最显著．偏离逐渐减弱，说明了研究平均应变效应．仅考虑均值．可能给出错误评价；必须综合考虑均值、均方差和样本量3因素才能给出合理评价。     

结构材料常规疲劳数据库开发

开发了反应堆结构材料常规疲劳数据库管理系统，库中包含了常规疲劳设计分析曲线参量，即应力－寿命、概率－应力－寿命、应变－寿命、概率－应变－寿命、循环应力－应变及概率－循环应力－应变曲线参量，以及相关材料和试验条件信息。可通过材料名称或机械性能区间指标查询。根据查询结果，可进行常规疲劳设计分析与评价或常规疲劳可靠性设计分析与评价。     

有限数据下结构疲劳可靠性设计曲线的统计模型

提出了有限数据下确定反应堆结构疲劳可靠性设计S－N曲线的统计模型，该模型置信度－存活率概率－强度－寿命（C－P－S－N）曲线来表示考虑了常规P－S－N曲线预测结果的可信性，应用线性回归统计分析原理，将置信度引入到常规P－S－N曲线中，从而得到C－P－S－N曲线。1Cr18Ni9Ti不锈钢管道焊接缝金属材料试验数据分析结果说明了模型的合理性和可用性，同时还说明了有限数据下常规P－S－N曲线偏于危险。     

确定不锈钢管道焊缝金属随机循环应力幅良好统计模型的方法

应变控制疲劳试验揭示了要核工程材料1Cr18Ni9Ti不锈钢焊缝金属的循环应力－应变响应存在较大的分散性,现有的定性分析可能给出偏于危险的结果。考察这一分散性和常7种统计分布对试验数据的总体拟合效果、与疲劳失效机制的一致性和设计分析结果的安全性,提出了确定循环应力幅良好统计模型效率概率试验值与理论值的相关系数来评价;与疲劳失效机制的一致性按照给定总应变下失效率随循环应力幅增加而增加的原则,根据各分布统计参量的失效率曲线来判断;设计分析结果的安全性通过识别统计分布尾部失效概率预测误差的变化趋势来进行。     

多轴疲劳模型对比研究及其在核电结构热疲劳寿命预测中的应用

压水堆核电站余热排出系统冷热水混合区管道发现的热疲劳问题影响核反应堆的安全。本文通过一种采用单轴疲劳试验数据拟合疲劳寿命曲线，进而用于预测多轴疲劳寿命的分析方法，基于文献中的疲劳试验数据，对Dang Van模型、Matake模型和Fatemi-Socie模型进行了余热排出系统冷热水混合区管道材料304L不锈钢疲劳寿命预测结果的对比研究。基于余热排出系统冷热水混合区管道的三维简化有限元模型，分别应用Dang Van模型、Matake模型和Fatemi-Socie模型对管道热疲劳寿命进行了预测，并与试验结果进行了对比验证。研究结果表明，基于应变（含平均应力修正）的Fatemi-Socie模型比较适用于304L不锈钢的疲劳分析，其热疲劳寿命预测结果相对Dang Van模型、Matake模型较合理。     

不锈钢管道焊缝金属240℃循环变形行为的试验研究

基于增量步和成组法低周疲劳试验,研究了1Cr18Ni9Ti不锈钢管道焊缝金属在240℃下的循环变形行为。结果表明,材料为循环软化材料,具有轻微Non-masing行为特征。相同总应变范围的循环应力、应变（CSS）行为存在很大分散性,意味着任何外载,即使恒幅载荷也将导入一个随机应变载荷史,现有确定性方法可能导致偏于危险的设计分析,有必要引入概率方法表征材料的循环变形行为。基于验证的应力幅统计分布－正态分布,建议了概率Ramberg-Osgood CSS曲线的描述方法。文中试验结果分析验证了方法的有效性。     

核电厂主管道材料低周疲劳寿命预测方法评价

采用总应变控制方法,对压水堆核电厂主管道国产材料Z3CN20.09M进行了室温与350℃温度下的低周疲劳试验研究,获得了材料的疲劳寿命演化规律。采用Manson-Coffin方程、单拉估算模型、拉伸滞后能寿命模型和三参数幂函数公式对该材料的低周疲劳数据进行了拟合。通过寿命预测结果比较发现,除单拉估算模型外,其他几种模型对350℃高温下疲劳寿命的预测结果分散性明显高于室温疲劳。在众多模型之中,单拉估算模型拟合效果较差且预测寿命偏于非保守,而室温下拉伸滞后能法预测精度相对较高,350℃下则采用三参数幂函数法获得的预测效果更好。     

Statistical model for the random cyclic strain–life relations of 1Cr18Ni9Ti pipe-weld metal under temperature of 240°C

Modeling of random cyclic strain–life (CSL) relations of engineering material should be a basis of strain-based fatigue reliability analysis. A statistical model for the relations of a nuclear engineering material, 1Cr18Ni9Ti stainless steel pipe-weld metal under temperature of 240°C, is presented. In the model, a verified distribution, i.e. lognormal distribution, is used as an appropriate assumed distribution of the material fatigue life data. Based on the Coffin–Manson law, the relations are modeled by mean value- and standard deviation-cyclic curves of the logarithm of fatigue life. Then, fatigue analysis at an arbitrarily given probability can be made conveniently according to the normal distribution function. An approach for estimating the curves and their confidence bounds is developed by a linear regression technique. Different from the existent reliability analysis methods that considered the material constants in the law as independently random variables, present work treats them as dependently random variables from the fit of test data. Availability of the model has been indicated by an analysis of the material test data.     

Deformation Behavior of Zircaloy-4 Cladding under Cyclic Pressurization

The deformation behavior of Zircaloy-4 cladding was investigated under cyclic pressurization. A cyclic pressurization test for a cladding tube was carried out and a stress-life diagram of the cladding tube was constructed. The result showed that the O'Donnell and Langer relationship can be fitted to the fatigue behavior of the Zircaloy-4 cladding under cyclic pressurization with the frequency of 1 Hz by assuming the fatigue limit of 344.7 MPa at 350°C. In terms of the effect of a loading frequency, the stress-life diagram deviated from the O'Donnell and Langer relationship when the applied frequency decreased to 0.1 Hz. Based on the change of the diametral differences and fractographic observations, it was found that a combined creep-fatigue interaction rather than pure fatigue had an influence on the failure of the Zircaloy-4 cladding under cyclic pressurization at 350°C.     

Random cyclic stress–strain responses of a stainless steel pipe-weld metal II — a modeling

This paper pays special attention to an issue that there is a significant scatter of the stress–strain responses of a nuclear engineering material, 1Cr18Ni9Ti stainless steel pipe-weld metal. Efforts are made to reveal the random fatigue damage character by fracture surface observations and to model the random responses by introducing probability-based stress–strain curves of Ramberg–Osgood relation and its modified form. Results reveal that the fatigue damage is subjected to, 3-D interacting and involved microcracks. The three stages, namely microstructural short cracks (MSC), physical short cracks (PSC) and long cracks (LC) subdivided by Miller and de los Rios, can give a good characterization of the damage process. Both micro- and macro-behaviour of the material have the character of three stages. The 3-D effects are strong in the MSC stage, tend to a gradual decrease in the PSC stage, and then show saturation after going to the LC stage. Intrinsic causes of the random behaviour are the difference and evolution of the microstructural conditions ahead of the dominant crack tips. The ‘effectively short fatigue crack criterion’ introduced by Zhao et al. in observing the material surface short crack behaviour could facilitate an understanding of the mechanism of interaction and evolution. Based on the previous obtained appropriate assumed distribution, normal model, for the cyclic stress amplitude, the probability-based curves are approximated by the mean value and standard deviation cyclic stress–strain curves. Then, fatigue analysis at arbitrarily given reliability can be conveniently made according to the normal distribution function. To estimate these curves, a maximum likelihood method is developed. The analysis reveals that the curves could give a good modeling of the random responses of material.     

122—1400keV能区同轴Ge(Li)和HpGe探测器效率曲线的函数拟合

在能量为122—1400keV范围内最优化方法用于四参数表达式ε=(a_1/E)~(a_2)+a_3Exp(-a_4E)和实验测定的同轴Ge(Li)和HpGe探测器效率的拟合。给出了初值计算方法。拟合结果是好的,实验和拟合值之间平均偏离小于2.0％。     

不锈钢管道焊缝金属随机循环应力幅的良好统计模型

与现有确定性分析方法不同，考虑材料循环变形的分散性，应用确定不锈钢管道焊缝金属随机循环应力幅统计模型的方法研究了1Cr18Ni9Ti不锈钢焊缝金属循环应力幅的良好统计模型。综合考虑了总体拟合效果、与疲劳失效机制的一致性和分析结果的安全性三要素，分析比较了三参数Weibull、两参数Weibull、极小值、极大值、正态、对数正态和指数分布对试验数据的拟合效果。结果表明，极小值、极大值、正态和对数正态分布可作为良好假设分布，以极小值和正态分布最好。其余分布因不符合三要素之二或三项，不适于表征循环应力幅数据。     

含凹坑缺陷结构疲劳寿命的快速估算方法

基于Miner线性累积损伤理论,探讨了含凹坑缺陷结构使用系数与相应的无缺陷结构使用系数之间的计算关系。在S-N曲线数据拟合的基础上,推导了许用循环次数的比值计算式,并以核压力容器常用材料为例,给出了计算式待定常数的取值及适用范围。形成的疲劳寿命估算方法,为含凹坑缺陷结构的快速疲劳分析及评定提供了一种参考方法。     

Fatigue behavior of pipes containing multiple flaws in inner surface

In this work was studied the growth behavior of multiple cracks in the inner surface of pipes. The fatigue tests were performed using two kinds of test pipes, i.e., the straight pipes and bend pipes of AISI Type 304L stainless steel, having 320 mm in outer diameter and 35 mm in thickness approximately.The crack growth curves obtained by the fatigue tests were compared with the analytical curves of two kinds of crack growth prediction methods. One method is based on the ASME Boiler and Pressure Vessel Code, Sec. XI. Another method is based on the procedure in which the crack growth formula is applied to both the surface and thickness directions. The analytical crack growth curves predicted by the ASME Code are conservative for the test results of the straight and bend pipes. However the results of bend pipe test suggest that the procedure of the ASME Code may give an unconservative fatigue life under the certain condition.On the other hand, the test results of the straight pipes can be evaluated reasonably and those of the bend pipes can be evaluated conservatively by the latter method.     

0Cr18Ni10Ti管道钢的概率机械性能

完成了反应堆管道新材料0Crl8Nil0Ti的概率机械性能试验研究。拓展赵等提出的确定有限疲劳可靠性数据良好假设分布的统一方法到本文机械性能数据分析。结果表明．数据具有明显正偏性，常见正态分布描述不适于该套数据。综合考虑各分布的拟合优度、与失效机制的一致性和尾部预测的安全性．数据的良好统计分布是对数正态分布和极大值分布。从统计分析的方便性角度。提出了给定可靠度和置信度下基于对数正态分布的机械性能参数估计方法。并有效地估计了材料的概率机械性能参数。