304不锈钢在单轴应变棘轮变形下的随动硬化实验研究

对304不锈钢在室温下进行了单轴应变控制下的应变棘轮变形与失效以及低周疲劳试验研究,对材料在循环过程中材料的硬化行为进行了系统的揭示。在对称应变循环下,研究了不同应变幅值下弹性区尺寸和背应力演化规律;在给定工程应变幅值和循环棘轮应变增量组合的应变棘轮变形下进行了弹性区尺寸和背应力演化研究。观察到了各向同性硬化和随动硬化演化对加载历史的依赖性。     

316L不锈钢室温和高温单轴循环塑性流动特性分析

在316L不锈钢室温、高温单轴应变控制和应力控制下的系统循环试验结果基础上，对两种控制模式下循环过程中的塑性流动特性进行了定量分析。揭示和分析了循环就变幅值、平均应变、温度及其历史与应变循环下以及应力幅值、平均应力、温度及其历史与应力循环下塑性模量演变规律之间的关系和影响。研究中着重讨论了循环棘轮行为与塑性模量和累积塑性应变之间关系。研究表明，应变循环中塑性模量的演变规律明显不同于非对称应力循环，室温和高温下非对称应力循环中的棘轮效应由塑性模量和积累塑性应变的演变规律共同决定。     

室温下304不锈钢的单轴循环棘轮行为实验研究

在室温下对固溶处理的304不锈钢进行了系统单轴应变与应力循环实验研究了具有平均应力的工程应力幅值历史以及相同工程应力幅值下平均应力历史、每一循环平均应力有一固定应力增量的应力幅值历史对单轴棘轮变形行为的影响：得到了一些有意义的结果．．     

316L不锈钢室温和高温单轴循环行为实验研究

对316L不锈钢分别进行了室温、高温单轴应变控制和应力控制下的系统循环试验,揭示和分析了循环应变幅值、为幅值历史以及温度历史对应变循环特性的影响以及应力幅值、平均应力和温度及其历史对循环棘轮行为的影响。研究表明,无论是单轴应变循环特性是还是非对称单轴应力下的棘轮效应不仅依赖于当前温度和加载状态,而且还于温度和加载的历史,并得到了关于316L不锈钢室温和高温单轴循环行为的若干有意义的结果。     

不锈钢316L单轴棘轮行为及其影响因素的研究

对不锈钢３１６Ｌ材料进行了多种平均应力以及多种应力幅值下的单轴循环加载棘轮效应试验，分析研究了平均应力大小及其历史对其棘轮效应的影响，以及应力值大小及其历史对其棘轮效应的影响，揭示了不锈钢３１６Ｌ的单轴棘轮效应演化的特征及导致这些特征的原因，得到一些有意义的结果，对建立能较为精确地估计结构的循环累积变形的本构模型具有一定的参考作用。     

基于一元应力参量的钛合金T225NG单轴棘轮演化模型研究

基于T225NG钛合金的单轴常温棘轮试验，本文研究了峰值棘轮应力对T225NG钛合金棘轮应变的影响。试验结果表明，常温单轴应力循环条件下材料棘轮应变随峰值棘轮应力的变化关系为一簇类线性的变化曲线，存在常值棘轮应力门槛值，峰值棘轮应力与该门槛值的关系可决定材料是否产生棘轮变形。由此，建立了一套一元应力能量控制的T225NG钛合金棘轮应变演化模型。该模型建模容易，适合棘轮应变预测的工程应用。     

应力循环下T225NG合金塑性累积行为研究

对应力循环下T225NG合金的塑性累积行为进行了试验研究,提出了预测棘轮饱和应变的本构关系及描述棘轮应变演化规律的指数型演化方程。讨论了蠕变效应对T225NG合金棘轮行为的影响．结果表明．应力幅越低,循环蠕变分量在塑性累积中的贡献越大。     

304不锈钢高温多轴非比例循环棘轮行为的粘塑性本构描述

对304不锈钢600℃下的非比例循环棘轮行为进行了系统的实验研究，在统一粘塑性循环本构模型的框架下对其进行本构描述，模型中，通过随动硬化背应力演化和各向同性变形阻力演化，对304不锈钢在非对称应力循环下的循环附加硬化流动特性进行模拟，在等温条件下，在各向同性变形阻力演化方程中引入温度项来考虑温度效应，在随动硬化应力演化方程中引入动态恢复项的衰减系数，反映材料在特定温度范围（500－600℃）下入最大应变幅值衰减记忆函数∧（q)和最大各向同性变形阻力衰减记忆系数ω反映加载历史对循环棘轮行为的影响，将模型应用于304不锈钢高温多轴循环棘轮行为及其对加载历史依赖性的描述中，预言结果与实验结果吻合较好。     

304不锈钢的非饱和循环硬化行为及其本构描述

针对循环硬化行为的应变幅值依赖性和相对大应变幅值下的非饱和特性．建立了新的粘塑性循环本构模型,在本构模型中．引入新的变量来表征材料的循环硬化特性,该变量的演变方程中引入一个临界状态来反映循环硬化对应变幅值的依赖性：同时,将该变量分解为2个具有不同演变规律的分量．以此来描述相对大应变幅值下的非饱和循环硬化特性．结果表明．新建模型能够很好地描述304不锈钢循环硬化行为的应变幅值依赖性和非饱和特性．     

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。     

Experimental study on uniaxial and nonproportionally multiaxial ratcheting of SS304 stainless steel at room and high temperatures

An experimental study was achieved for the cyclic properties of SS304 stainless steel subjected to uniaxial strain-controlled, uniaxial and nonproportionally multiaxial stress-controlled cyclic loading at room and high temperatures. The effects of cyclic strain amplitude, mean strain, temperature and their histories on the cyclic deformation behavior of the material were investigated under the uniaxial strain-controlled cyclic loading. The uniaxial and nonproportionally multiaxial ratcheting was researched under the asymmetrical stress-controlled cyclic loading with variable stress amplitudes, mean stresses, loading paths and their histories at room and high temperatures. It is shown that the uniaxial cyclic properties under strain-controlled cyclic loading and the ratcheting under asymmetric uniaxial and nonproportionally multiaxial stress-controlled cyclic loading depend not only on the current temperature and loading state, but also greatly on the previous loading history and the shape of loading path. The material presents much greater cyclic hardening and less ratcheting in the range of 400–600 °C than at room temperature, due to the strong dynamic strain aging taken place in this temperature range. Some significant results were obtained for the constitutive modeling of cyclic plastic deformation such as ratcheting.     

Thermal ratcheting under biaxial stress states

Thermal ratcheting, the phenomenon of net strain accumulation due to plastic straining of pressure vessels under cyclic thermal loading, is an important factor in the design of nuclear reactor pressure vessels. In this paper a cyclic thermal gradient loading idealized by means of a step distribution through the pressure vessel wall and biaxial thermoelastic-plastic stress-strain relations are used to calculate the strain accumulation under biaxial mechanical loads. It it shown that the uniaxial stress-strain models presently used in design calculations are adequate for spherical and cylindrical shells under internal pressure; however, for uniaxial loading and for torsional loading, the use of these models may underestimate the accumulated ratchet strain.     

Elastic–plastic analysis of the steel-to-tungsten transition joint for a high performance divertor

The use of tungsten as a plasma-facing material necessitates a transition joint to the oxide dispersion strengthened (ODS) steel or ferritic steel (FS) structural material of the primary coolant loop at the end of the divertor target plate where the surface heat flux is very low. A critical issue in the transition joints is the coefficient of thermal expansion (CTE) mismatch between the tungsten (or tungsten-alloy) and ODS steel, which can lead to unacceptably high thermal stresses during steady state and ratcheting during cyclic loads. Detailed 2D and 3D thermo-mechanical analyses were conducted to study the behavior of a transition from tungsten to FS with an intermediate layer of tantalum, located outside of the high heat flux region. The results include plastic strains under various loading conditions including fabrication processes, warm and cold shutdown, and allow for plastic behaviors leading to stress relaxation. The accumulation of plastic deformation may cause ratcheting. Modifications were proposed to the transition joint design in order to eliminate stress concentration and ratcheting under cyclic loading. The results of the modified design exhibited less plastic deformation in the joints as well as no ratcheting caused by warm and cold shutdown.     

Critical strains and necking phenomena for different steel sheet specimens under uniaxial loading

When defining ultimate loads or failure criteria for shells, vessels and containment liners, for instance, reference will be made to critical strains of the material under consideration.In general the critical strains are derived from uniaxial tensile test results obtained with rods.The actual deformation behaviour of sheets (plate and shell type structures), however, differs considerably from the uniaxial rod behaviour.From various tests - along with theoretical investigations - it was found that for membrane or even bending stressed sheets higher ultimate strains are reached.The typical strain behaviour caused by increasing load starts with uniform strain distribution over the specimen length and finally ends with localized necking.As “critical strains” the well known uniform elongation strain and the ultimate strain are defined.For sheets in addition the quasi uniform elongation strain has been introduced in this paper.Whereas for rods under tension localized necking is directly following the uniform straining, tests with sheets show a so-called diffuse necking behaviour before localized necking starts.As a consequence the deformation capacity of steel sheets turns out to be significantly higher than relying on the data from standard tension tests with rods.     

N18合金薄壁管高温应变循环与疲劳行为研究

应用新型自研夹具对N18合金薄壁短管进行400℃下的单轴拉伸和等幅低周应变疲劳试验。试验结果表明：N18短管高温循环应力应变滞回线有良好对称性；等幅循环下短管试样在较低应变幅下表现出循环硬化特性，而在较高应变幅下表现出循环软化；在多级应变循环加载下短管试样应力幅在循环中均保持稳定，循环本构关系不受多级应变循环工况差异的影响；材料循环特性不符合Manson律。获得了用于N18合金在400℃高温下的几个寿命估算式。