核电汽轮机末级长叶片材料的疲劳性能研究

为了掌握核电汽轮机末级长叶片材料1Cr12Ni3Mo2VN的疲劳性能,开展了低周疲劳试验研究,测试了材料的疲劳循环响应特性、循环应力-应变曲线和应变-寿命曲线,比较了不同疲劳寿命预测模型的预测结果.结果 表明:叶片材料在循环寿命的绝大部分期间都保持非常稳定的应力应变状态,仅在循环寿命初期表现出一定的循环软化特征;作为一...     

30Cr3MoV转子钢的常温低周疲劳的实验研究

在试验的基础上研究了30Cr2MoV钢在常温下的循环应力变特性，得到了该材料的低周疲劳特性参数，循环应力－应变曲线和具有95％置信度的不同存活率下的应变－寿命曲线。图9表3参4。     

30Cr2MoV转子钢常温低周疲劳软化规律的实验研究

针对国产200MW机组汽轮机转子上广泛使用的30Cr2MoV钢材料进行了常温下应变控制低周疲劳试验,在试验的基础上研究了30Cr2MoV钢在常温下的循环应力应变特性。得到了该材料的低周疲劳特性参数、循环应力－应变曲线和具有95％置信度,误差限为5％不同存活率下的应变－寿命曲线,并分析了与文献结果存在差异的原因。     

循环孔隙水压后的混凝土动态损伤特性研究

利用10MN大型多功能静动力三轴仪对经历不同循环孔隙水压(0、1、3、5、7 MPa)作用后的混凝土进行不同应变速率(10~(-5)、10~(-4)、10~(-3)s~(-1))下的压缩试验,分析其力学特性,并基于改进的能量法损伤表达式研究了不同应变速率对混凝土损伤发展的影响。结果表明,当应变速率较低时,混凝土的峰值应力、峰值应变随循环孔隙水压力值的增大呈减小趋势,损伤曲线比较分散,且增加循环孔隙水压力混凝土损伤将提前;当应变速率较高时,峰值应力、峰值应变呈现不同程度的上升,曲线较为集中,增加循环孔隙水压力使混凝土的损伤发生滞后。     

10Cr转子钢的低周疲劳特性试验研究

对国产转子钢14Cr10NiMoWVNbN和国外同种转子钢TOS107的拉伸性能及低周疲劳特性进行了试验研究,将国产和国外转子钢的循环特性、循环应力-应变特性及应变寿命特性进行了对比.结果表明:在室温及600℃下,国产和国外转子钢的拉伸强度无明显差异;国外转子钢的低周疲劳强度略优于国产转子钢.根据593℃下国产转子钢低周疲劳寿命的试验结果,通过虚拟应力转换并选取合适的安全系数,得到了10Cr转子的疲劳设计曲线,该曲线可用于估算10Cr钢制转子的疲劳寿命.     

应用等效应变法的30Cr1Mo1V钢疲劳-蠕变交互作用的试验分析

在540℃和565℃两种温度下进行了30Cr1Mo1V转子钢的疲劳-蠕变交互作用实验.采用Felltham公式建立了应变保持下应力与时间的关系;得到了应变循环幅保持不变、疲劳-蠕变交互作用下的循环应力-应变关系.根据等效应变概念建立了应变-寿命关系,并从分散度因子和标准偏差方面对等效应变法和线性累计损伤法的寿命预测有效性进行了比较;建立了等效应变的临界损伤公式和考虑硬度修正的等效应变寿命关系.试验结果表明,在预测寿命时等效应变法比线性累计损伤法具有更高的精度,等效应变的应力下临界损伤公式能够很好地预测实际损伤,考虑硬度修正的等效应变-寿命曲线和纯疲劳应变-寿命曲线基本一致.图5表2参9     

TA_5钛合金低循环疲劳特性试验研究

对特定规格ＴＡ５钛合金不件取样进行低循环疲劳试验研究,得到疲劳寿命曲线和应变寿命关系式,考虑适当的安全系数给出了ＴＡ５钛合金的设计疲劳曲线并分析了应力循环硬／软化特性。最后通过有限元应力分析,论述 主要承压部件采用单金属ＴＡ５钛合金代替以往双金属结构后钭大大提高使用寿命。     

周期性荷载作用下岩石力学特性数值模拟研究

为研究周期性荷载作用下岩石的力学特性,开展了基于离散单元法(DEM)的岩石疲劳数值模拟试验,通过模拟单轴压缩试验研究了数值模型中微观参数对试样宏观参数的影响,再通过数值疲劳试验研究了砂岩的疲劳变形特性。结果表明,砂岩的疲劳应力—应变曲线受控于单轴应力—应变过程曲线,疲劳破坏时的轴向应变即为周期性荷载最大应力在单轴应力—应变曲线中所对应的峰后部分应变。通过分析砂岩的疲劳渐进破坏过程发现,最大应力和平均应力是影响砂岩疲劳寿命的两个重要因素。研究成果对于了解岩体疲劳破坏机理、合理评价工程稳定性有重要意义。     

先进超超临界机组用Inconel 617与C-HRA-2合金高温低周疲劳性能试验研究

针对先进超超临界(A-USC)机组用进口和国产候选镍基合金Inconel 617和C-HRA-2,进行了700℃下应变幅为0.25%～0.75%的轴向应变控制低周疲劳(LCF)试验研究。通过循环应力响应、循环应力-应变特性、疲劳寿命预测及断口形貌分析,研究了2种合金的LCF性能。结果表明：材料的循环应力响应和疲劳寿命与应变幅有关;C-HRA-2合金的循环硬化程度明显高于Inconel 617合金,但循环硬化后2种合金的峰值应力幅相近;2种合金的稳定迟滞回线均表现出non-Masing行为;Manson-Coffin模型和能量法均能有效预测疲劳寿命;不同应变幅下2种合金的疲劳源均萌生于试样表面,Inconel 617合金的疲劳裂纹以穿晶方式扩展,而C-HRA-2合金以穿晶和沿晶混合的方式扩展。     

金沙江向家坝水电站坝基砂岩蠕变特性研究

选取了金沙江向家坝水电站坝基的典型砂岩试样,采用三轴压缩试验对砂岩蠕变特性进行研究,分析了流变失稳破坏时的特征及砂岩的轴向、侧向和体积应变的全过程蠕变曲线异同点,对砂岩的长期强度进行预测分析。试验结果表明,砂岩存在一个起始蠕变应力阈值,每级荷载下的蠕变曲线之前都存在一个瞬时应变且随着围压的增大和偏应力的增大幅度越来越小,轴向瞬时应变与偏应力具有很好的线性关系;侧向和体积变形则存在明显的蠕变三阶段,加速阶段要比轴向快且两者的蠕变曲线形状相似,在同一围压和同一级偏应力下侧向蠕变量比轴向及体积的大,其蠕变发展最快;砂岩的长期强度可用等时偏应力应变曲线簇来进行确定,采用体积偏应力应变曲线簇更适宜,在已有的流变模型中伯格斯模型能较好的反映砂岩蠕变特性。     

不同EPS粒径下轻量土变形强度特性三轴试验研究

为确定新型土工合成材料轻量土在不同发泡颗粒(EPS)粒径下的变形机理,通过三轴固结不排水试验系统研究其变形强度特性的影响规律。试验结果表明,轻量土应力-应变关系具有非线性、多阶段性、应变软化和应变硬化特性;抗剪强度破坏包络线有折线型与直线型两种,取决于自身结构强度与围压;粘聚力与内摩擦角均随EPS粒径的增大而递减。     

EDGE CRACK PROBLEMS IN HOMOGENOUS AND FUNCTIONALLY GRADED MATERIAL THERMAL BARRIER COATINGS UNDER UNIFORM THERMAL LOADING

In this study the axisymmetric crack problem for thermal barrier coatings under a uniform temperature change is considered. Modes I and II stress intensity factors and the strain energy release rate are calculated for various sizes and locations of the crack. The main variables in the problem are the material inhomogeneity parameter of the functionally graded material coating, the size and the location of the crack, and the relative dimensions of the specimen. The effect of the temperature dependence of the material properties on the stress intensity factors and the strain energy release rate is also investigated. The finite element method is used to solve the problem. The material property grading is accounted for by developing special inhomogeneous elements and the stress intensity factors are calculated by using enriched crack tip elements.     

Residual stress and plastic strain analysis in the brazed joint of bonded compliant seal design in planar solid oxide fuel cell

This paper uses finite element method (FEM) to predict the residual stress and plastic strain in the brazed joint of sealing foil-to-window frame in bonded compliant seal (BCS) design in a planar solid oxide fuel cell (PSOFC). The effects of window frame material type, sealing foil thickness, filler metal thickness and window frame thickness on residual stress and plastic strain are discussed. Large residual stress is generated in the joint, and the stress and strain are concentrated around the fillet. It is proved that the BCS design can mitigate and trap some residual stress by plastic deformation within the sealing foil. The residual stress and the ability of trapping stress of sealing foil are affected by window frame material and structure thickness. Based on the comprehensive considerations of the impact of residual stress and plastic strain, Alloy 625 as a window frame material is found to be better than Haynes 214, Hastelloy X and SUS 316L. The optimum thickness of sealing foil and filler metal BNi2 are found to be 150 μm and 75 μm, respectively. The residual stress and plastic strain are increased with the increase of window frame thickness.     

基于单剪试验邓肯E B模型参数的确定

土石坝应力应变有限元计算中常采用邓肯E-B模型,模型参数大多通过三轴试验确定,但操作相对比较复杂,为此提出一种通过单剪试验确定邓肯E-B模型参数的方法,即对某一级配粗粒料进行单剪试验,将试验得到的单剪条件下的应力应变关系通过转换公式得到三轴条件下的应力应变关系,据此整理得到的邓肯E-B模型参数与三轴试验结果基本一致,并用该参数对单剪试验进行有限元数值模拟,得到的应力应变关系与试验结果较为吻合。     

Service life estimation of liquid silicone rubber seals in polymer electrolyte membrane fuel cell environment

Polymer electrolyte membrane fuel cell (PEMFC) is a promising power source for many applications such as automobiles. Sealing around the perimeter of the cell is required to prevent the gases/liquids inside the cell from leaking and polymers are usually used for the seal or gasket materials. They in general possess the viscoelastic property which induces stress relaxation of the material under constant strain. The stress relaxation behavior of liquid silicone rubber, a type of polymer used as seals in PEMFCs, is studied in this work. A Prony series is used to predict the compression stress relaxation curve at different strain levels. Applying the time-temperature superposition, master curves are generated and used for predicting the service life of this material as seals in PEMFCs. The estimated lives in water and in air are compared.     

掺软岩粗粒料的湿化试验研究

堆石料填筑完成后,初次蓄水可造成不可忽略的湿化变形。采用GDS土动三轴仪对软岩含量为20%的粗粒料进行单线法和双线法湿化试验,获得了不同围压、应力水平下试样的湿化应力应变关系及其轴向变形,并对比研究了单线法和双线法的湿化变形经验公式的差异。结果表明,掺软岩粗粒料三轴剪切应力应变曲线均为应变软化型,湿化应变随围压和应力水平的增大而增大,且与应力水平呈指数型关系;在应力水平较小时,单线法和双线法湿化应变计算的经验公式计算值差距较小,在应力水平较大时,双线法经验公式计算值比单线法大。     

Stress relaxation behavior of EPDM seals in polymer electrolyte membrane fuel cell environment

Polymer electrolyte membrane fuel cell (PEMFC) is a promising power source. Sealing around the perimeter of the cell is required to prevent the gases/liquids inside the cell from leaking. Polymers are usually used as the seal or gasket materials. The viscoelastic property of polymers can induce stress relaxation of the seal under constant strain. The stress relaxation behavior of ethylene propylene diene monomer (EPDM) rubber, a potential candidate seal in PEMFC, is studied in this paper. The effect of temperature, applied strain, and environmental exposure on stress relaxation behavior of EPDM is investigated. Using time–temperature superposition, master curves are constructed to estimate the service life of this material used as seals in PEMFC.     

Thermal environment effects on wave dispersion behavior of inhomogeneous strain gradient nanobeams based on higher order refined beam theory

In this article, an analytical model for the wave propagation analysis of inhomogeneous functionally graded (FG) nanobeam in thermal environment is developed based on nonlocal strain gradient theory, in which the stress accounts for not only the nonlocal elastic stress field but also the strain gradients stress field. The nanobeam is modeled through a higher order shear deformable refined beam theory which has a trigonometric shear stress function. The temperature field supposed to have a nonlinear distribution across the nanobeam thickness. Temperature-dependent material properties of nanobeams are spatially graded based on Mori–Tanaka model. The governing equations of the temperature-dependent functionally graded (FG) nanobeam are derived using the Hamilton’s principle. Numerical examples show that the characteristics of the wave propagation of FG nanobeam are influenced by various parameters such as nonlocality parameter, length scale parameter, gradient index, and temperature changes.     

基于流固耦合作用下泵送混凝土管破损的力学特性分析

为明确混凝土泵送过程中弯管处的冲蚀破损机理,寻求合理的改善方法,利用ANSYS双向流固耦合流动模型,采用颗粒多相流和管道壁面相互作用传递数据的方式,模拟龙开口#1隧洞的泵送过程,得到应力、应变、应变能的变化曲线和云图。结果表明,泵送混凝土管道内部的应力、应变、应变能随时间呈现波动变化,持续的应力波动导致管材疲劳,增加了材料老化和破损几率,这是导致弯管处材料硬化开裂的主要原因,且弯管上半部分的应力峰值更高更易破裂。研究成果对于改进弯管处设计有重要意义。