Zr-Sn-Nb薄片合金高温低周疲劳行为

采用Zr-Sn-Nb合金薄片漏斗试样,完成了室温和500℃高温下的低周疲劳试验,提出基于漏斗根部节点轴向应变的疲劳损伤等效假设。根据有限元分析,建立了Zr-Sn-Nb合金室温和高温下薄片漏斗试样测试应变到漏斗根部轴向应变的转换模型。结合低周疲劳试验结果,建立了在室温和500℃高温条件下用于估算Zr-Sn-Nb合金疲劳寿命的Manson-Conffin模型。结果表明:Zr-Sn-Nb合金具有循环稳定性;高温严重影响了Zr-Sn-Nb合金低应变幅下的疲劳寿命,随着应变幅的增加,温度影响趋弱。     

压水堆材料冷却剂环境疲劳修正因子研究

本文对考虑压水堆一回路冷却剂环境对材料疲劳影响的环境疲劳修正因子Fen进行研究，结合核电厂延寿需求，确立基于环境疲劳修正因子的疲劳分析流程。针对典型接管嘴结构，采用考虑瞬态应力时间历程的应变增量方法计算转换应变率和Fen，对比了环境修正对疲劳结果的影响。考虑环境影响后，奥氏体不锈钢的疲劳使用系数增大3.2倍，低合金钢的疲劳使用系数增大8.5倍，冷却剂环境对疲劳寿命的影响显著。将考虑环境影响后的疲劳使用系数与EPRI导则的计算结果进行对比，二者计算结果接近，验证了考虑瞬态组合的环境疲劳修正因子分析计算方法的正确性。     

Multiaxial fatigue analysis for IMIC of ITER upper ELM coil

Inconel Jacketed Mineral Insulated Conductor (IMIC) is a very important component of International Thermonuclear Experimental Reactor (ITER) Edge Localized Modes (ELM) coils, which are located between the vacuum vessel (VV) and blanket shield modules and subject to high radiation levels, high temperature and high magnetic field. These coils will experience thermal pulsed, cyclic electromagnetic (EM) load during operation. They are designed to sustain at 1.5e8 total stress cycles and shall have sufficient strength and excellent fatigue to transport and bear the high cyclic load. For IMIC, multiaxial fatigue analysis is used to evaluate failure. Two methods based on the alternating stress and mean stress in American Society of Mechanical Engineers (ASME) code provide the design codes for multiaxial fatigue evaluation: constant principal stress direction and variation of principal stress direction. Results show that using the two methods obtains basically the same equivalent alternating stress. Both of them can be recommended for the ELM coils and IMIC can meet the fatigue criteria.     

An experimental validation of the guideline for inelastic design analysis through structural model tests

In this paper, the inelastic analysis procedures recommended to use in the advanced elevated temperature structural design guide under development in Japan for the improved design of future fast breeder reactors were validated through the structural model tests and the evaluation of the experimental results by the inelastic analyses. First, a thermal fatigue test of a 316FR hollow cylinder with two longitudinal weldments was conducted under the condition of combined constant axial load and cyclic movement of axial temperature distribution, which simulated the loading condition near the free surface of coolant sodium in the main vessel of fast breeder reactors (FBRs). In the experiments, longitudinal and radial ratcheting deformation were measured and crack initiation life was also examined. Second, the inelastic analyses were carried out in accordance with the recommended procedure by using the measured results of oscillating temperature distribution. Finally, the results of inelastic analyses were compared with the experimental results and it was validated that the recommended practice gave a conservative result for the deformation and a good estimation of strain range for the fatigue life evaluation.     

Inelastic stress-strain response for notched specimen of Cr-1Mo steel at 600°C

Following a series of cooperative studies A-I and A-II (phase III) concerning the inelastic behaviour of high temperature materials under uniform state of stress, finite element analyses were carried out on circumferential notched cylinders subjected to plasticity-creep interaction conditions. Using an electric capacitance type extensometer “Strain-Pecker”, which is capable of measuring a local strain response with a gauge length of 0.5 mm under high temperature conditions, stress-strain responses for both global and local regions near the notch root were evaluated. Ten kinds of inelastic constitutive model were introduced into a finite element code, and the responses for four kinds of loading pattern were examined for two types of notch shape.     

基于格林函数的应力简化计算方法及试验验证研究

以格林函数为基础,开发了高温高压条件下管道应力影响函数,在实验室条件下选取管道壁面上的典型点,通过高温应变测量对该方法进行了验证。结果表明,基于格林函数的应力简化计算方法的计算结果与试验结果吻合较好,该方法可应用于核电厂关键设备和管道的强度及疲劳寿命的快速评价,亦可用于疲劳监测系统开发。     

Background to the elastic creep-fatigue rules of the ASME B&PV Code Case 1592

Recent modifications associated primarily with elastic analysis have been made to the creep-fatigue rules of the ASME B&PV Code for use in design of elevated temperature nuclear components. The changes involve: (1) a modified equation for predicting the total strain range per cycle based on a more accurate approximation to the Neuber equation; (2) a variable Poisson's ratio in calculating stresses and strain using elastic equations to account for local thermal strain concentrations; (3) a modified approach for determining the equivalent strain range and; (4) an adjusted design fatigue curve. The modified Neuber approach accounts for the beneficial effects of a residual stress related to the relaxation strength of the material and includes a strain concentration factor greater than the elastic stress concentration factor for geometrical notches for mechanical loads. Notch concentration factors are taken equal to the elastic stress concentration factors for peak thermal and creep strains. The background and intent for these rules are discussed. Correlations of the strain range predictions to those obtained using more rigorous detailed inelastic analysis and test data are presented.     

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.     

316LN不锈钢在高温高压水环境下的腐蚀疲劳行为研究

在室温纯水、高温纯水及高温硼锂水环境下开展了316LN不锈钢在不同应变幅加载下的腐蚀实验研究，并获得了3种条件下的腐蚀疲劳寿命曲线。结果表明，316LN不锈钢在加载过程中出现了先硬化后软化现象，且随循环周次增加，应力峰值逐渐下降；高温纯水及高温硼锂水环境下材料的腐蚀疲劳性能下降，加速了材料的腐蚀疲劳失效；在高应变幅条件下高温的软化作用占主要影响，低应变幅条件下腐蚀作用占主要影响；试验后的样品断面上均可观察到疲劳辉纹、滑移变形带及二次裂纹，高温水腐蚀环境会加速裂纹扩展，加速疲劳失效。      

一级设备的应力与应变分析研究

一级设备在核设备中非常重要,在该设备的设计和调试的过程中需要对其进行应力与应变分析,从而确保其安全性。对一级设备的应力与应变分析有两种方法,理论方法和实验方法。通过理论方法,可以得到一级设备在各种工况下的应力与应变状况,从而为设备的设计提供依据;通过实验方法,可以验证理论方法的准确性,并为设备的安全评定提供依据。中国实验快堆(CEFR)主容器属于一级设备,本文结合CEFR主容器的应力与应变分析研究,根据AMSE规范,描述了核安全一级设备的应力与应变分析的理论方法,同时也介绍了测量核安全一级设备的应力与应变的实验方法。     

应变幅对国产锻造奥氏体不锈钢环境疲劳寿命影响的试验研究

为验证模拟压水堆核电站冷却剂服役环境对国产锻造主管道用奥氏体不锈钢疲劳寿命的影响,采用高温高压循环水疲劳测试系统对从产品锻件取样加工后的标准试样进行了低周疲劳试验,分析了试验数据与美国机械工程师学会(American Society of Mechanical Engineers,ASME)规范平均/设计疲劳曲线的关系,获得了应变幅对奥氏体不锈钢环境疲劳寿命的影响规律,并初步评价了ASME规范设计疲劳曲线和环境疲劳修正系数的适合性。     

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.     

Inelastic evaluation of mechanical and structural components using the generalized local stress strain method of analysis

A simple and systematic method for carrying out inelastic evaluations of mechanical components and structures on the basis of two linear elastic finite element analyses is presented in this paper. The degree of interaction between the local and remainder regions is characterized by studying the relaxation response on the generalized local stress strain (GLOSS) diagram.GLOSS analysis is applied to several problems of practical interest involving multiaxial stress relaxation, follow-up, low cycle fatigue, plastic collpase and issues pertaining to the classification of stresses in pressure components. The results generated by the finite element method compare favourably with those obtained by GLOSS analysis.     

Weld metal creep–fatigue life prediction by modeling the microstructure degradation due to the exposure to high temperature and load

A new analytical method to evaluate creep–fatigue strength of stainless weld metals that were suffering from microstructure degradation was proposed. Based on the observation that creep–fatigue crack initiated adjacent to the interfaces of σ and δ-ferrite, an FE-model that consisted of matrix, σ and δ-ferrite was developed. The volume fraction of the σ in the model corresponded to the maximum amount of precipitation expected, which means that the model represents the degraded microstructure after long-term exposure to high temperature and load. Using the model, microscopic concentration of stress and strain adjacent to the interfaces were calculated. Fatigue and creep damage were consequently evaluated which allowed creep–fatigue life evaluation. The predicted results reproduced experimental results with sufficient accuracy in a relatively higher strain region. Validation in lower strain region is expected.     

N18锆合金的低周疲劳行为

在不同试验温度（室温～500℃）下，对N18合金进行了低周疲劳试验。试验结果表明：室温～300℃温区，合金表现为明显的循环软化；400、450℃时，合金逐渐呈现循环硬化，450℃时其硬化现象更为明显；500℃时则主要表现为循环饱和。随着温度的升高，疲劳寿命先增加后降低，300℃时疲劳寿命最高。低应变幅下，温度对疲劳寿命的影响更明显。通过疲劳断口SEM分析，室温下疲劳起源于单个裂纹源，疲劳裂纹扩展阶段的微观特征主要是疲劳条纹，局部区域出现轮胎状花样。在高温下为多裂纹源，大量二次裂纹的存在是高温疲劳断口的主要特征。     

示范快堆堆芯熔融物收集装置的安全分析

针对示范快堆堆芯熔融物收集装置的高温结构完整性问题，采用堆芯熔融物滞留在反应堆压力容器策略有效性评估方法（IVR-DOE10460），建立了316H本构模型、多轴修正以及具体的分析评价方法。通过搜集与分析ASME规范和R66材料数据手册中316H钢相关的材料数据，确定了输入数据。在此基础上，利用有限元分析软件ABAQUS开展堆芯熔融物堆积形态下堆芯熔融物收集装置的应力应变分析，并基于时间分数法与延性耗竭法（应变分数法）对堆芯熔融物收集装置进行蠕变强度校核。有限元分析结果表明：堆芯熔融物收集装置在设计时间内可满足时间分数和应变分数小于1的蠕变强度考核要求，且满足竖直位移小于设计指标的功能性要求。堆芯熔融物收集装置在堆芯熔化严重事故后能保持结构的完整性。     

Damage and fatigue crack growth of Eurofer steel first wall mock-up under cyclic heat flux loads. Part 2: Finite element analysis of damage evolution

In the preceding companion article (part 1), the experimental results of the high-heat-flux (3.5 MW/m²) fatigue tests of a Eurofer bare steel first wall mock-up was presented. The aim was to investigate the damage evolution and crack initiation feature. The mock-up used there was a simplified model having only basic and generic structural feature of an actively cooled steel FW component for DEMO reactor. In that study, it was found that microscopic damage was formed at the notch root already in the early stage of the fatigue loading. On the contrary, the heat-loaded smooth surface exhibited no damage up to 800 load cycles. In this paper, the high-heat-flux fatigue behavior is investigated with a finite element analysis to provide a theoretical interpretation. The thermal fatigue test was simulated using the coupled damage-viscoplastic constitutive model developed by Aktaa. The stresses, inelastic deformation and damage evolution at the notch groove and at the smooth surface are compared. The different damage behaviors at the notch and the surface are explained in terms of hydrostatic stress and inelastic strain fields. The effect of heating pulse length on inelastic deformation is also addressed. It is demonstrated that the predicted damage evolution feature agrees well with the experimental observation qualitatively.     

国产316LN不锈钢在模拟AP1000一回路水环境中的疲劳行为

一回路水环境下的疲劳性能是核电站主管道设计寿命评估的重要参数。针对国产主管道材料316LN开展了模拟AP1000一回路水环境的低周疲劳试验,分析了疲劳行为和失效机理。研究结果表明:国产316LN峰值应力随应变幅的增大而增大,大应变幅试样在疲劳过程中先后发生了循环硬化、循环软化和失稳,而小应变幅试样在失稳前未发生明显的循环硬化和循环软化;在应变幅由0.2%逐渐增加至1.2%的过程中,疲劳周次从105逐渐降低至102;疲劳断口具有典型的疲劳断口特征,裂纹萌生于试样表面,以穿晶方式垂直于主应力方向扩展,裂纹扩展区具有典型的疲劳辉纹,辉纹上有菱形颗粒状腐蚀产物,环境辅助开裂机制倾向于氢致开裂。     

反应堆压力容器疲劳时限老化分析研究

Based on two methods of evaluating the influence of the coolant environment on the fatigue life of equipment proposed by U.S.NRC in the management guideline RG1.207, the effects on different environmental fatigue correction factor（F_en） expressions and boundary conditions were compared between the NUREG/CR-6909 of USA and JNES of JAPAN. The difference of the environmental fatigue life assessment between environmental fatigue correction factor and environmental fatigue curve was also analyzed. Finally, the three methods were adopted in the analysis of the reactor pressure vessel inlet nozzle fatigue assessment. The methods are Fen method considering strain rate history, environmental fatigue curve method and the Fen method using conservative parameters. The results show that, compared with other two methods, the Fen method considering strain rate history can evaluate the environmental fatigue life of structures with higher accuracy.