12CrlMoV钢制部件蠕变—疲劳交互作用的特性曲线研制

本文在12CrlMoV钢母材和焊接接头两种材料的疲劳寿命。蠕变寿命和蠕变-疲劳交互作用行为试验研究工作的基础上，重点对12CrlMoV钢在蠕变-疲劳交互作用下的试验结时进行了整理、分析，在国内首次得出了可供工程应用的12CrlMoV钢蠕变-疲劳交互作用寿命评定曲线，并与ASME规范的相关曲线进行了比较。并应用该方法对一实例做了寿命评定。     

锅炉受压元件的高温蠕变-疲劳寿命设计计算方法

介绍了锅炉受压元件高温蠕变-疲劳寿命的设计计算方法.该方法建立在线弹性应力分析理论基础上,对我国锅炉制造业长期积累的锅炉受压元件寿命设计计算经验和方法进行了归纳总结,并参照了美国ASME等国际先进标准.它给出了电站锅炉高温受压元件蠕变、低周疲劳及交互作用条件下的寿命损伤计算方法和典型结构及材料的设计计算参数,可供水管锅炉高温受压元件寿命设计使用,在役元件的高温蠕变及高温蠕变-疲劳寿命计算也可借鉴.     

金属蠕变疲劳寿命预估模型研究进展

高温变载荷作用下的构件易发生蠕变疲劳损伤断裂,严重影响设备的安全运行.蠕变疲劳交互作用下的寿命预测是材料结构完整性的重要要素.综述了影响金属蠕变疲劳寿命的因素,并基于线性累积损伤法、延性耗损法、Manson-coffin方程、频率修正法与频率分离法、平均应变速率寿命预测模型、延性耗竭模型、能量守恒蠕变疲劳交互寿命模型、...     

电站锅炉用P91钢蠕变/疲劳交互作用的试验研究

对电站锅炉用P91的母材及焊接接头的蠕变/疲劳交互作用进行试验,使用改进的延性耗损法对试验结果进行分析和处理,得出了P91钢的蠕变/疲劳交互作用特性及交互作用状态下的寿命估算方法.结果表明,P91钢在蠕变/疲劳共同作用下呈负交互作用;在P91的电站锅炉构件寿命估算时,疲劳因素可忽略.     

304型不锈钢蠕变-疲劳损伤预测和剩余寿命评定

前言最近几年来,火力发电厂延长寿命的紧迫问题是对用于高温、长时的结构材料的损伤预测和剩余寿命评定。高温服役的材料,不仅承受纯蠕变或纯疲劳损伤,而且还承受机械应力和热应力造成的更复杂的蠕变—疲劳交互作用损伤。由于蠕变或疲劳作用下断裂和变形具有不旧样式,所以在蠕变—疲劳交互作用下的剩余寿命及损伤的精确评定相当复杂。为了精确评定蠕变—疲劳损伤,设法使用一些有损和无损试验方法,然而至     

基于材料老化和蠕变疲劳交互作用汽轮机转子寿命预测

根据材料老化和蠕变-疲劳交互作用对致裂寿命的影响，建立了汽轮机转子寿命预测模型和预测方法，以N75MW汽轮机转子为对象进行了寿命损耗分析和预测，指出基于材料老化和蠕变疲劳交互作用，可以有效提高汽轮机转子寿命预测的精度。     

高温环境下蠕变疲劳交互作用损伤力学研究

应力控制下的疲劳、蠕变及其交互作用损伤实际上是循环蠕变、静蠕变引起的材料延性不断耗竭的过程，本文在延性耗竭理论和损伤力学有效应力概念的基础上．对疲劳蠕变交互作用损伤演化进行了研究，提出了一个新的疲劳蠕变交互作用损伤模型．采用非弹性应变能密度变化作为损伤参量定义损伤变量。通过耐热钢1.25Cr0.5Mo光滑试样高温环境下应力控制的梯形波加载试验．验证上述疲劳蠕变交互作用模型，最终得到了1.25Cr0.5Mo钢540℃下不同最大应力、不同应力幅组合条件下的损伤演化统一表达式，试验损伤点与该模型的损伤演化规律符合较好．表明该模型和损伤变量适合于疲劳蠕变交互作用下的损伤描述．     

汽轮机转子钢疲劳—蠕变交互作用

本文对我国电站汽轮机常用的30Cr2MoV转子钢疲劳—蠕变交互作用进行了试验研究。根据火电厂转子运行工况,选择了不同保载时间,进行裂纹扩展试验。结果表明,这种材料在运行工况下存在疲劳—蠕变交互作用;随着保载时间的增加,裂纹扩展速率增加,寿命大大降低。断口分析发现,断面有沿晶断裂,且呈现“r”型空洞。运用线性累积损伤方法计算该转子钢疲劳—蠕变交互作用系数B=1.47～3.95,提出了交互作用下的裂纹扩展判据。     

汽轮机强度研究某些新进展的概述

介绍了汽轮机部件强度和寿命研究的某些新进展 ,综述了近几年来汽轮机部件的静强度和刚度、叶片和叶根的动强度、有限元分析、强度可靠性设计、低周疲劳寿命、蠕变寿命、疲劳和蠕变交互作用下的寿命、安全寿命等方面国内开发的一些新技术手段和取得的新成就。本文还提出了汽轮机部件强度和寿命计算技术的一些发展动向     

汽轮机关键部件总寿命计算方法的研究

提出了汽轮机关键部件在低周疲劳、高周疲劳与蠕变等多种损伤机理作用下总寿命的计算方法。介绍了汽轮机关键部件总寿命计算方法研究的技术背景,以及国际标准与电站业主对汽轮机寿命的要求。分析了汽轮机关键部件寿命计算所需的材料物理性能与力学性能试验数据、关键部件温度场与应力场计算结果和寿命计算的力学模型。给出了汽轮机关键部件在低周疲劳、高周疲劳与蠕变等单种损伤机理作用下裂纹萌生寿命和裂纹扩展寿命的计算方法。建立了汽轮机关键部件单种损伤机理作用下总寿命的计算方法和多种损伤机理作用下日历寿命的计算方法,以及汽轮机关键部件日历总寿命的计算与评定方法,给出了高压内缸日历总寿命计算的应用实例。汽轮机关键部件总寿命计算方法的研究,解决了在多种损伤机理作用下汽轮机关键部件日历总寿命计算的技术难题。     

A new high-temperature creep-fatigue damage rule based on the strain range partitioning concept

A new life prediction model based on the strain range partitioned crack growth rate equations is presented which can evaluate the material damage and the residual life under variable creep-fatigue strainings. Two-step sequential creep-fatigue straining tests such as High-Low and Low-High tests were conducted on Mod. 9Cr-1Mo steel and type 316LC stainless steel in order to examine the validity of the proposed model. It was found that the proposed model can be more successfully applied to the creep-fatigue life prediction under variable strainings than the conventional life prediction methods.     

Lifetime estimates of cracked high temperature components

Cracked high temperature components subjected to creep-fatigue loading can fail by crack growth, net-section rupture or some combination of both processes. Models for describing this behaviour are presented. The influence of build up of damage in a process zone at the crack tip, material deterioration in the uncracked ligament and the importance of tertiary creep on the mode of failure are each considered. It is shown how the models can be employed to predict crack growth and for making residual life assessments in high temperature equipment. Finally a simple cumulative damage law is outlined for describing creep-fatigue interaction.     

Study on creep-fatigue evaluation procedures for high chromium steels—Part II: Sensitivity to calculated deformation

High-chromium steels containing 9–12% chromium such as ASME SA-213 Grade 91 or Grade 122 are widely used in conventional and combined cycle fossil power plants and are also regarded as candidate structural materials for future nuclear power plants aiming at operation in the creep range. Evaluation of failure life under creep-fatigue conditions constitutes an important part of assessing the structural integrity of these plants. The author has been conducting a series of creep-fatigue tests for three types of high-chromium steels and the validity of life prediction methods has been evaluated using the measured deformation data. Here an additional exercise was carried out in order to evaluate the adequacy of the total life prediction procedure, including the process of predicting stress and strain. After making comparisons of the test data with various existing equations developed for describing deformation and failure behaviour of Grade 91 and Grade 122, prediction of creep-fatigue life was attempted using deformation behaviour analytically estimated by these equations. Many calculations revealed that failure lives predicted by the time fraction approach showed a strong dependency on stress relaxation behaviour, whereas those based on the modified ductility exhaustion method showed a much smaller sensitivity, and therefore some error or uncertainty in stress and strain would be tolerated.     

Evaluation of the creep–fatigue damage mechanism of Type 316L and Type 316LN stainless steel

Low-cycle fatigue tests with continuous cycling and creep–fatigue tests with 10 min hold times at tensile maximum strain were conducted at 600 °C in air for Type 316L and Type 316LN stainless steels containing nitrogen contents of 0.04% and 0.10%. The creep–fatigue life was less than the fatigue life for both alloys. The fatigue and creep–fatigue life and saturation stress were increased with the addition of nitrogen. The fracture mode was transgranular for fatigue and intergranular for creep-fatigue regardless of the nitrogen content. The dislocation structure was cellular for Type 316L and planar for Type 316LN after fatigue and creep-fatigue tests. Carbides were precipitated at grain boundaries after creep-fatigue tests and nitrogen decreased the precipitation. Creep–fatigue life was well predicted by a model based on cavity nucleation and growth at grain boundaries. The increase of creep–fatigue life with the addition of nitrogen was due to the decrease of precipitation and stress relaxation by the change in dislocation structure.     

A numerical investigation of creep-fatigue life prediction utilizing hysteresis energy as a damage parameter

This paper explores the hypothesis that there exists an intrinsic material property, hysteresis damage energy at failure, which could be used as a creep-fatigue life prediction parameter. The connection between hysteresis energy and fatigue damage was introduced in the 1920’s by Inglis, but the use of hysteresis energy as a measure of damage was first presented by Morrow and Halford. Hysteresis energy shows promise in bridging the gaps associated with life prediction when the combination of both creep and fatigue scenarios are present. Numerical simulations which replicate experimental test configurations with 9Cr–1Mo steel were performed from which the hysteresis energy failure density (HEFD) could be calculated for each experiment. Taking the average of the HEFD values calculated for all of the experimental data as the parameter for failure (E_Intrinsic), creep-fatigue life predictions were made using a simplistic hysteresis energy based method as well as the time fraction/cycle fraction method endorsed by ASME Code and compared to experimental results. A good correlation with experimental results was obtained for life predictions using hysteresis energy density as a damage parameter. An investigation of the interaction between creep damage and fatigue damage based on the hysteresis energy method was also performed and compared with the damage interaction diagram utilized by the ASME and RCC-MR design codes. The hysteresis energy based method proved easy to implement and gave improved accuracy over the time fraction/cycle fraction method for low cycle creep-fatigue loading.     

Predicted life of P91 steel for cyclic high temperature service

The P91 steel is widely used in high temperature components of power plants, and it is a candidate material for Gen-IV reactors. The P91 steel has relatively attractive mechanical and physical properties combined with resistance to stress corrosion cracking in water–steam environments. This study aimed to explore the combined cyclic, creep and relaxation behaviour of P91 material. Uniaxial specimens were subjected to cyclic loadings with periodic forward creep or relaxation at peak stress. The results indicate that prior creep or intermediate relaxation periods up to 72 h will influence the subsequent cyclic softening of P91, but do not significantly reduce the cyclic life. In contrast, prior cycling has a detrimental effect on the subsequent creep life. A simplified creep-fatigue model is shown to predict life better than usual code-based approaches. Improved verification of all models would benefit from the availability of more extensive long-term data on P91 steel.     

Creep-fatigue test of a SA 316SS structure and comparative damage evaluations based upon elastic and inelastic approaches

A creep-fatigue in the reactor structures of a liquid metal reactor needs to be dealt with from a structural integrity point of view. This paper deals with the creep-fatigue damage evaluation of a typical geometrical discontinuity structure made of 316SS based upon both an elastic approach and an inelastic approach. The creep-fatigue structural tests of a 7 mm thick cylindrical structure and a 5 mm thick cylindrical structure have been carried out with a 1MN actuator and a 50 kW induction heater with a 1 h hold time at 550 °C. The strain behaviors, by an analytical method, and the damage evaluations were compared with those by tests. For an inelastic analysis by using the developed code NONSTA-VP, by implementing Chaboche's unified viscoplasticity model into ABAQUS, the methods to determine the material parameters are presented. The current comparisons show satisfactory results, but more efforts are needed to verify them in full.