Effects of Strain Rate on Low Cycle Fatigue Behaviors of High-Strength Structural Steel

 The low cycle fatigue (LCF) behavior of a high-strength structural steel was investigated in the strain rate range of 4×10-5-0. 12 s-1 (0. 001-3 Hz) under constant total strain (±1%) control. The cyclic stress response at all strain rates exhibited behavior of rapid softening in the early stage of fatigue life and subsequent saturation up to failure. It was found that the stress amplitude, the plastic strain amplitude, the plastic strain energy density and the fatigue life depend mainly on the strain rate. The strain rate of 0. 012 s-1 was found as a transition point where the LCF of the steel showed different behavior from low strain rate to high strain rate. The relationship between the time to failure and strain rate was expressed well by a power law relation. The fracture surfaces of the fatigue samples were characterized by using a scanning electron microscope (SEM) and the fracture mechanisms were discussed in terms of time-dependent deformation of the steel.     

极低屈服点钢低周疲劳特性

对100 MPa级的极低屈服点钢BLY100进行了包括模拟地震载荷的系列高应变低周疲劳试验。试验结果表明,BLY100钢板具有良好的低周疲劳性能,完全满足抗震设计用钢的需要。     

低周疲劳中结构钢的宏观与细观变形行为

应用显微硬度法研究了低周疲劳过程中退火１６Ｍｎ钢和正火４５钢的表面细观循环塑性状态变化及其硬化、软化行为，并在统计意义上与材料的宏观循环塑件变形规律进行了比较。结果表明，宏观材料的循环塑性响应与细观尺度上材料的循环硬化、软化行为两者在统计意义上是一致的，而后者在空间分布与时间序列上均表现出显著的不均匀性和非同时性特征。     

Low Cycle Fatigue Behavior and Deformation Mecha-nism of TWIP Steel

Low cycle fatigue behavior of TWIP （twinning induced plasticity） steel was investigated in axial symmetric tension-compression cyclic loading pattern. Fracture surfaces and microstructures were examined by optical, scanning electron and transmission electron microscopes. It was found that the fatigue life at the strain amplitude of 0.4 % is up to 15 000 cycles, which is much longer than TRIP780 and HSLAS00 steels. The strain hardening and softening features are significant until the strain amplitude comes to 1.25 ~. Persistent slip bands and tiny mechanical twinning layers were observed after fatigue deformation. Deformation mechanism of TWIP steel at low cycle fatigue process is not only twinning, but a complex of both twinning and persistent slip bands.     

Biaxial Low Cycle Fatigue Behavior and Martensite Formation of a Metastable Austenitic Cast TRIP Steel Under Proportional Loading

In this paper the biaxial low cycle fatigue behavior under proportional loading of a recently developed metastable austenitic stainless cast steel is presented. Total strain controlled tests were carried out on a 250 kN biaxial servohydraulic tension‐compression testing machine equipped with a biaxial orthogonal extensometer to measure the principal strains in the gauge area of the used cruciform specimens. The principal stresses were determined based on the compliance after the load reversals. The low cycle fatigue behavior under biaxial synchronous loading is compared to the uniaxial behavior. Therefore, biaxial single step tests and a biaxial multiple step load increase test were carried out. The dependence of the stress state on the cyclic deformation curves, cyclic stress‐strain curves and the formation of martensite are described. Finally, the fatigue life relationship according to Basquin and Manson‐Coffin was determined and compared to the Smith, Watson and Topper damage parameter, which provides a satisfactory fatigue life prediction.     

热轧H型钢的高应变低周疲劳性能研究

 对热轧H型钢的高应变低周疲劳性能进行了研究。采用轴向应变控制的方法，在Instron-1342型电液伺服疲劳试验机上测定了热轧H型钢的低周疲劳性能数据，研究了在循环载荷下材料的循环应力响应特征、循环应力与应变关系，并用Coffin-Manson公式拟合得到热轧H型钢的疲劳寿命计算公式，据此计算了 =100时的 值。通过断口扫描发现，裂纹不仅在试样表面处形核，同时也在试样内部杂质处形核，然后通过不断的扩展形成微裂纹，许多微裂纹通过扩展连接形成宏观裂纹，最终导致材料断裂。     

Microstructure Variation and Hardness Diminution During Low Cycle Fatigue of 55NiCrMoV7 Steel

 The influence of temperature and hardness level on the cyclic behavior of 55NiCrMoV7 steel, and the microstructure variation and hardness diminution during low cycle fatigue behavior were investigated. By means of SEM and XRD, the modality of carbides and the full width half maximum (FWHM) of martensite (211) [M(211)] of X ray diffraction spectrum in fatigue specimen were studied. The results showed that the cyclic stress response behavior generally showed an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. The fatigue behavior of the steel is closely related to the hardness level. The hardness diminution and the variation of half width M(211) are remarkably influenced by the interaction between the cyclic plastic deformation and the thermal loading when the fatigue temperature exceeds the tempering temperature of the steel.     

H13钢制分流模低周疲劳寿命的预测方法及应用

 利用Gleeble1500热模拟试验机对H13模具钢在650-800℃温度范围,0.1-20s-1应变速率下的热压缩变形行为进行了研究,并得到了该材料在20-650℃范围内的弹性模量,建立了H13钢的有限元模型;通过高温拉伸实验和通用斜率法建立了H13钢的应变-低周疲劳寿命关系;结合有限元方法提出了一种预测H13钢制铝型材挤压模具低周疲劳寿命的方法,并在此基础上得到了工艺和结构参数对模具疲劳行为的影响规律。结果表明：疲劳应变损伤值随着挤压速度的增加以及模桥根部圆角半径的减小而增大,其中结构参数为关键影响因素。最后通过生产实际验证了该方法的可靠性。     

双轴等拉低周疲劳实验装置

本文给出能在一般单向加载液压疲劳试验机上做双轴等拉低周疲劳实验研究的双向拉伸装置,并对有关影响因素进行了讨论。
本试验是在百吨液压低周疲劳试验机上进行的。双向拉体装置已经受近百万次疲劳载荷,其中交变载荷幅围5.5,t亦经受近20万次。在使用过程,各构件完好合手使用要求,将十字试样进行低周疲劳断裂试验,成功地开出合格裂纹,用它进行超速条件下叶轮材料性能研究亦取得初步结果。可以认为它适用于平而应力集中问题低周疲劳性能的研究。若使用液压高、中周疲劳试验机,它还可用于双轴载荷下裂纹试样裂纹扩展的研究。
本文指出了双向拉伸装置有待改进的方面。     

夹杂对高强钢超高周疲劳行为的影响

概述了夹杂对高强钢超高周疲劳行为影响研究的进展,探讨了临界夹杂尺寸和零夹杂钢的疲劳特性,得出夹杂尺寸对S-N曲线特性的影响.建议采用新的统计方法评估钢中夹杂尺寸、分布及其对疲劳强度的影响.     

GH586合金的高温低周疲劳特征

研究了GH586合金750℃的低周疲劳性能，并对疲劳机制进行了分析讨论。结果表明GH586合金具有很高的抗高温低周疲劳性能，疲劳裂纹产生于合金表面。     

M5合金的高温低周疲劳性能研究

M5合金是一种适用于高燃耗组件的新型锆合金,主要用作燃料棒包壳、端塞、导向管和定位格架材料。采用棒材试样,对M5合金在375℃温度下进行了5个应变水平的低周疲劳实验,应变比R=-1。对合金的循环响应特征进行了分析,并根据实验数据拟合出了疲劳寿命曲线和方程。用扫描电镜分析了低周疲劳样品的断口,讨论了合金的低周疲劳断裂特征。结果表明,在循环变形过程中,M5合金表现出了明显的硬化、饱和、软化阶段,其中饱和阶段所占比例较大,而硬化和软化阶段所占比例较小;其循环应变寿命特性遵循Coffin-manson关系;疲劳裂纹均起源于试样表面,且存在有多个裂纹源,断裂区布满发达的韧窝,属于明显的韧性断裂。     

莱钢齿轮钢生命周期及产品策略分析

介绍了莱钢20CrM nTi齿轮钢近几年生产发展、市场占有率及利润变化的情况,并运用生命周期理论判定该产品已处于生命周期成熟期。从提高现有产品质量、细分产品市场、完善营销管理体系、加强联系合作、采取直销方式等方面,提出稳固现有产品市场、延长该产品成熟期的相关措施;从积极开发性能更优越的新型齿轮钢,并慎重选择分销商、调整营销渠道、尽快树立新产品品牌形象等方面,提出开发新产品和拓展市场的相关策略。     

电镀锌产品的生命周期清单研究

宝钢电镀锌的生命周期清单的研究范围包括铁矿石和煤矿等原材料的开采、铁矿石和煤的运输、宝钢产品生产、副产品回用等阶段,即包含了从原材料开采到产品出厂的生命周期过程。清单分析的环境负荷有资源消耗、能源消耗、大气污染物排放、水体污染物排放和固体废弃物等50多种类型的环境负荷。在国际标准化组织的生命周期清单分析国际标准ISO14041的指导下,本研究建立了宝钢电镀锌产品生命周期清单模型和开发了计算软件,完成了焦化、烧结、高炉、转炉、热轧、冷轧和电镀锌等主生产工序的产品,以及电厂、制水、制氧、蒸汽锅炉等能源系统的产品生命周期清单。本研究为宝钢电镀锌产品的环境交流提供了生命周期清单数据;为宝钢其它产品的生命周期清单研究积累了经验;为宝钢倡导循环经济,生产资源节约型、环境友好型的产品提供了决策依据;也为宝钢产品的全生命周期评价打下了基础。     

微合金化和余热处理热轧带肋钢筋高低周疲劳性能对比研究

通过试验研究,对比分析了微合金化和余热处理带肋钢筋的高周疲劳和低周疲劳性能。研究表明,微合金化钢筋比余热处理钢筋具有更好的疲劳性能。在微合金化和余热处理带肋钢筋的高低周疲劳试验中,观察到在横肋根部裂纹萌生并沿该区域扩展。有限元模拟结果显示在横肋根部出现应力集中,应力三轴度变大。模拟过程中也发现在横肋根部拉应变累积。有限元模拟结果有助于解释试验观察结果,即疲劳裂纹沿热轧带肋钢筋的横肋根部萌生及扩展。     

枝晶间一次相对熔铸GH136合金低周疲劳性能的影响

本文对熔铸GH136合金的研究结果表明:存在于枝晶间的大的未溶一次相粒子能降低材料的低周疲劳性能。粒子的作用机构有两个,其一是激发主裂纹的早期萌生,其二是自身形成内疲劳源,通过内源的生长及与主裂纹的联结加速材料的破坏。
这两种作用机构均与裂纹扩展速率有关。在高裂纹扩展速率下(或高应力幅值),粒子的有害作用被减弱,反之,其有害作用加强。采用提高固溶温度的方法可以有效地去除这些一次相粒子,使材料在低交变应力范围的性能得以改善。     

提高轴承钢疲劳寿命工艺优化

本文分析了轴承钢的接触疲劳寿命影响要素,对钢中氮化物、氧化物、硫化物、残余奥氏体对轴承钢接触疲劳寿命的影响进行了研究,提出了工艺优化措施。     

斜轧零件应力应变特征与内部低周疲劳损伤机制

采用ANSYS/LS-DYNA软件,建立了斜轧零件基本变形过程的三维有限元分析模型,对不同工况下的斜轧过程进行了计算机数值模拟分析。仿真结果揭示了斜轧过程中轧件内部应力应变场的分布规律;导致Mannesmann缺陷的主要原因是在发生大塑性应变变形情况下,金属内部在承受交变应力作用下产生低周疲劳损伤和破坏。