16MnR 钢的高应变超低周疲劳性能

从压力容器的实际工况和抗震安全性设计出发,研究了压力容器用钢16MnR 钢的高应变超低周疲劳性能。采用横向应变控制方法,在 MTS809拉扭复合疲劳试验机上测定了试验钢应变疲劳过程中的循环应力响应特征及循环应力与应变的关系等超低周疲劳行为;通过拟合 Basquin 公式和 Coffin-Manson 公式,获得了试验钢的高应变超低周疲劳寿命预测公式。断口扫描发现,超低周疲劳下,多处裂纹萌生于试件表面,然后裂纹共同向内扩展,直到最后快速断裂。     

HRB400 Ⅲ级抗震钢筋的低周疲劳性能

对HRB400 Ⅲ级抗震钢筋的低周疲劳性能进行了研究。采用轴向应变控制方法,在岛津电液伺服疲劳试验机上测定了试验钢低周疲劳过程中的循环应力响应特征及循环应力与应变的关系;通过拟合Basquin公式和Coffin-Manson公式,获得了试验钢的低周疲劳寿命预测公式。断口扫描发现,试验钢裂纹起源于试样表面,通过不断扩展形成微裂纹,再连接成宏观裂纹,最终导致材料断裂。     

Q345R钢湿硫化氢预腐蚀低周疲劳行为

对Q345R钢在湿硫化氢环境中预腐蚀低周疲劳性能进行了研究,以硫化氢溶液的浓度和预腐蚀时间为环境因素.低周疲劳试验在MTS-809疲劳试验机上进行,对各试验组的结果数据进行回归分析,得到各试验组环境下Q345R钢的循环应力-应变曲线、应变-寿命曲线等低周疲劳特性.不同试验环境下的预腐蚀低周疲劳结果表明,材料循环应力应变响应特性不受环境因素影响,为循环硬化特性;预腐蚀时间因素对材料低周疲劳寿命的影响比硫化氢溶液的浓度因素显著.试样断口为典型的低周疲劳断裂形貌,裂纹扩展阶段为脆性准解理断裂特征.     

阻尼器用低屈服点钢BLY160的低周疲劳性能

对BLY160低屈服点钢低周疲劳性能进行了研究。采用轴向应变控制方法,在MTS809电液伺服疲劳试验机上开展低周疲劳试验,分别研究了在循环载荷作用下试验材料的循环应力响应特征、循环应力与应变的关系以及应变幅和应变速率对材料低周疲劳性能的影响。试验结果表明,BLY160钢具有良好的低周疲劳性能,完全满足耗能阻尼器用钢的需要。     

高强度热轧双相钢的低周疲劳性能

从热轧双相钢的实际应用需求出发,研究了高强度热轧双相钢DP600的低周疲劳性能。采用轴向应变控制方法对DP600钢进行了低周疲劳试验,并对试验数据进行拟合计算,得到DP600钢的循环应力-应变曲线、应变-寿命曲线和过渡疲劳寿命。通过扫描电镜观察疲劳断口,结果显示低周疲劳条件下,DP600钢断裂裂纹起源于试样表面,裂纹扩展前期呈现部分脆性断裂特征,后期则以明显的韧性断裂为主。     

4Cr5MoSiV1热作模具钢700 ℃的低周疲劳行为

采用轴向应变幅控制的低周疲劳试验研究了总应变幅对4Cr5MoSiV1热作模具钢700 ℃低周疲劳行为的影响,包括循环应力响应行为、循环应力应变行为、循环迟滞回线和应变疲劳寿命行为等。结果表明:随着总应变幅从0.2%增大到0.6%,4Cr5MoSiV1钢在700 ℃时循环应力响应均表现为先循环硬化再循环软化的特性,并且应力幅最大值从220 MPa增大到308 MPa。同时,随着总应变幅的增大,4Cr5MoSiV1钢在700 ℃下的低周疲劳寿命由6750循环周次降低到210循环周次,且其过渡寿命约为1313循环周次。疲劳断口形貌分析结果显示,高温低周疲劳过程中裂纹主要萌生于试样表面处,且随着应变幅增大,裂纹源逐渐增多,疲劳条纹间距变宽,其断裂方式由韧性断裂转变为脆性断裂。透射电镜分析结果显示,循环软化可能与板条结构转变为胞状结构、基体发生位错湮灭、碳化物的析出和粗化有关。      

TC4ELI钛合金低周疲劳性能研究

研究了具有网篮组织的TC4ELI钛合金材料在不同应变幅值下的低周疲劳性能,给出了TC4ELI钛合金在低周疲劳下的循环应力-应变曲线,拟合出循环应变硬化指数、循环强度系数以及应变-寿命特征系数,并通过光学显微镜进行金相分析,通过扫描电镜进行断口形貌分析。结果表明,TC4ELI钛合金呈现出循环软化的特性;距离疲劳断口1.5 mm处的组织形态与断口处无明显变化,疲劳裂纹以穿晶方式扩展直至断裂;随着应变幅值增大,韧窝变大变深,韧性断裂特征变得更加显著。     

连续油管用钢CT80低周疲劳性能研究

对CT80连续油管用钢进行了低周疲劳性能试验,通过应变幅为0．4％-1．5％,7个级别的恒应变控制实验,研究了CT80的循环特性、疲劳特性,确定了疲劳寿命与应变幅之间的关系式,并使用扫描电镜对疲劳断口形貌进行了观察和分析。结果表明：该材料为循环软化,疲劳裂纹起始于试样表面,呈多源性特征。     

汽车板QStE550TM应变疲劳性能研究

以3 mm厚汽车板用结构钢QStE550TM为研究对象,对其光滑试件进行了静态拉伸试验和不同应变水平控制下的应变疲劳性能测试,绘制了E-N曲线,并观察了疲劳断口形貌。试验结果表明,该汽车板屈强比和断层伸长率较高,具有良好的抗变形能力与加工成型性能。当应变幅小于0.8%时,循环寿命可达到104次以上,在低周应变循环中,该材料出现循环软化现象。疲劳断裂源于表面微裂纹的产生,疲劳源附近断口较为光滑,断口存在典型的疲劳辉纹。     

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。     

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。     

HRB400 �󼶿���ֽ�ĵ���ƣ������

Low cycle fatigue properties of anti-seismic HRB400 grade III reinforcing steel bar were investigated. The fatigue tests were conducted on Shimadzu servo-hydraulic testing machine. The tests were run under uniaxial tension-compression loading with total strain control. The cyclic stress response characteristics and relationship between cyclic stress and strain of the steel were measured. The strain-life data from the axial tests were used to derive suitable Coffin-Manson parameters for the test material. The scanning electron microscope (SEM) micrographs reveal that the fatigue cracks initiate from the surfaces of samples. Due to the propagation and connection of the micro-cracks, macro-cracks form and fracture occurs eventually.     

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.     

Energy-Based Prediction of Low Cycle Fatigue Life of High-Strength Structural Steel

 Energy-based models for predicting the low-cycle fatigue life of high-strength structural steels are presented. The models are based on energy dissipation during average of cycles, cycles to crack propagation and total cycles to failure. Plastic strain energy per cycle was determined and found as an important characteristic for initiation and propagation of fatigue cracks for high-strength structural steels. Fatigue strain-life curves were generated using plastic energy dissipation per cycle (loop area) and compared with the Coffin-Manson relation. Low cycle fatigue life was found similar from both methods. The material showed Masing-type behavior. The cyclic hysterisis energy per cycle was calculated from cyclic stress-strain parameters. The fracture surfaces of the fatigue samples were characterized by scanning electron microscope and the fracture mechanisms were discussed.     

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.     

奥氏体耐热钢低周疲劳性能研究进展

 为了进一步深入研究奥氏体耐热钢,介绍了奥氏体耐热钢低周疲劳性能方面的研究进展,对比了室温和高温下奥氏体耐热钢疲劳断裂特征。其中,间隙原子、应变、温度、层错能对奥氏体耐热钢疲劳性能影响较大;在高温疲劳-蠕变过程中,影响材料裂纹扩展和疲劳断裂的关键因素是温度和应力;在疲劳寿命预测方面,已建立了众多模型,但对一些新型材料会有一定偏差,需要建立适合的寿命预测模型。