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。     

管道结构焊接头240℃低周疲劳试验裂纹萌生寿命的统计分布

从总体拟合效果,与疲劳物理的一致性和尾部预测的性角度,研究了可能的４种假设分布对管道结构焊接试样２４０℃低周疲劳裂纹萌生寿命数据的拟合效果。结果表明;三参数Ｗｅｉｂｕｌｌ分布总体拟合效果最好,但由于其３参量可能出现小于１的情况,不符合疲劳物理要求;其尾部大多数情况可能给出非保守估计,不是一种良好的假设分布。     

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。     

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。     

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。     

估计三种常用应力 -寿命模型概率设计 S-N曲线的统一方法

提出了适于三参数、Langer和Basquin三种常用应力－寿命模型称为广义极大似然法的估计概率设计S－N曲线及其置信限的统一方法。方法将概率设计S－N曲线表示为对数疲劳寿命均值和均方差曲线的广义形式。与现有常规和经典极大似然法方法不同,考虑所有试验数据的统计特征,应用最小二乘法先估计出均值曲线中的材料常数,然后利用极大似然原理和数学规划法估计出均方差曲线中的材料常数。有效性采用拟合相关系数、拟合误差均方差值和置信限综合评价。对反应堆不锈钢管道焊接头虚拟应力幅－裂纹萌生寿命数据及45＃碳钢成组法和极大似然法疲劳试验应力－寿命数据的分析说明了方法的有效性。一般来说,三参数模型的拟合效果最好,Langer模型次之,Basquin模型最差。本文方法的拟合效果好于现有方法,并尽量避免了现有方法受试验数据局部统计特征影响而可能给出偏于非安全估计的缺陷。     

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。     

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。     

疲劳寿命实验曲线拟合方法选择研究

疲劳寿命的分散性影响其实验曲线拟合方法的选择,通过引入极差离散系数CR,根据实验所取的不同应变水平或者应力水平下对应的CR最大值的大小,确定曲线拟合采用的最优拟合方式,并采用该原则对疲劳寿命实验数据进行曲线拟合.拟合结果表明,拟合方法选取原则有利于优化疲劳寿命实验曲线拟合.     

基于退化失效模型的旋转机械寿命预测方法

退化失效模型与传统可靠性预测的根本区别在于,不论在统计推断还是寿命分布拟合过程中,可以充分利用退化数据提供的更多过程和寿命信息,能较准确地进行具有耗损特性的机械产品的寿命预测.针对旋转机械运行过程中强度破损失效模式,本文利用正态随机过程模型描述其退化失效过程,进行了旋转机械的寿命预测方法研究.通过分析加速寿命方程与退化失效模型的关系,考虑到加速寿命试验方法以"应力换时间"的有效性,进行了旋转机械加速寿命试验.通过对试验结果进行最佳线性无偏估计,得到强度退化失效模型的退化轨迹;在解决了退化失效方程奇异性的基础上,进行了旋转机械的寿命预测,得到点估计与区间估计的可靠寿命预测结果.     

Random cyclic stress-strain responses of a stainless steel pipe-weld metal I — a statistical investigation

This paper pays a special attention to the issue that there is a significant scatter of the stress-strain responses of a nuclear engineering material, 1Cr18Ni9Ti stainless steel pipe-weld metal. Statistical investigation is made to the cyclic stress amplitudes of this material. Three considerations are given. They consist of the total fit, the consistency with fatigue physics and the safety in practice of the seven commonly used statistical distributions, namely Weibull (two- and three-parameter), normal, lognormal, extreme minimum value, extreme maximum value and exponential. Results reveal that the data follow meanwhile the seven distributions but the local effects of the distributions yield a significant difference. Any of the normal, lognormal, extreme minimum value and extreme maximum value distributions might be an appropriate assumed distribution for characterizing the data. The normal and extreme minimum models are excellent. Other distributions do not fit the data as they violate two or three of the mentioned considerations.     

余热排出系统管道热疲劳分析模型及寿命预测

余热排出系统管道发现的热疲劳裂纹问题关系到压水堆的安全。本文基于开源有限元软件Code_Aster,采用Lagoda-Macha-Sakane模型预测了余热排出系统管道材料304L不锈钢的疲劳寿命,并根据预测结果提出了改进的Lagoda-Macha-Sakane模型。采用改进的Lagoda-Macha-Sakane模型对余热排出系统管道的热疲劳寿命进行了预测,结果表明预测热疲劳寿命与试验热疲劳寿命吻合。     

CRDM承压壳体多故障模式下的动态可靠性分析

为研究控制棒驱动机构（CRDM）的结构可靠性规律,考虑CRDM承压壳体的多失效模式,根据应力强度干涉理论建立与CRDM步跃动作次数相关的结构动态可靠性模型。用顺序统计量描述强度失效模式下应力幅值的动态分布模型,基于Miner累积损伤理论和疲劳等效应力分布模型建立结构疲劳寿命和累积损伤分布与步跃冲击载荷作用次数的关系。研究结果表明,在步跃冲击载荷作用下,承压壳体前期的结构可靠度主要由强度失效模式的可靠度决定,当步跃动作达到一定次数时,疲劳失效模式的失效率开始显著增大;相对于疲劳失效模式,强度失效模式的可靠度对应力均值的变化更加敏感。该结果可对CRDM承压壳体的可靠性设计和维修管理提供参考。     

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.     

Low cycle fatigue properties of CLAM steel at room temperature

The low cycle fatigue (LCF) properties and the fracture behavior of China Low Activation Martensitic (CLAM) steel have been studied over a range of total strain amplitudes from 0.2 to 2.0%. The specimens were cycled using tension-compression loading under total strain amplitude control. The CLAM steel displayed initial hardening followed by continuous softening to failure at room temperature in air. The relationship between strain and fatigue life was predicted using the parameters obtained from fatigue test. The factors effecting on low cycle fatigue of CLAM steel consisted of initial state of matrix dislocation arrangement, magnitude of cyclic stress, magnitude of total strain amplitude and microstructure. The potential mechanisms controlling the stress response, cyclic strain resistance and low cycle fatigue life have been evaluated.     

Investigation on the Fatigue Characteristic in Support Structure of HL-2M Tokamak

In order to obtain enhanced plasma parameters a complete new tokamak HL-2M is now under construction in Southwestern Institute of Physics. To assure the structural safety of the device for the entire operation cycle, one of the most important issues is the lifetime-limiting effects due to the pulsed operation mode. Fatigue is one of the major failure modes to be considered in mechanical design, and pulsed operation imposes stress with significant alternating components on the support structure （SS）. Therefore, the reliability of the whole device is strongly affected by the stress and fatigue characteristic of the SS as the interface structure. This article introduces the SS design and details the fatigue life calculation methods based on the different characteristics of the sub-structures. The fatigue life in hazardous areas of the toroidal field coils anti-torque structure （TFCs-ATs） has been determined by non-linear analysis results. And with the stress- time history data of the vacuum vessel ＆ poloidal field coils support structure （VV＆PFCs SS）, the fatigue analysis of the hot spots has been completed based on rain-flow counting method and linear cumulative damage method. The calculated minimum fatigue life on TFCs-ATs and VVSzPFCs SS is 4.743E＋05 and 1.805E＋06 cycles, respectively. And the calculated fatigue life on sub-structures can meet the required life for HL-2M tokamak： 1.0E＋05 cycles.     

Uncertainties in fatigue life prediction and a rational definition of safety factors

To cope with uncerainties in mechanical and structural design, enigineers exercise their judgement through the use of safety factors based on service experience and laboratory data on relevant design parameters. Using the problem of fatigue life prediction as a vehicle, the relationship between the size of a safety factor and the associated risk and cost-benefit estimates of the engineering judgement based on new technical information, is demonstrated. The subtle influence of the choice of a distribution function for a given set of data is exhibited by comparing the gaussian with the three-parameter Weibull fits of a set of fatigue life data on 6061-T6 aluminum. A system of ranking the importance of different sources of uncertainties based on an analysis of service data is proposed along with an example to “refine” the system using up-to-date laboratory and field measurements. The concept of a rational definition of safety factors as a tool for engineers who design under uncertainty is discussed.