扭转预应变对Q345R钢超低周疲劳性能影响研究

中文摘要: 采用横向应变控制方法，研究了扭转预应变对压力容器用钢Q345R超低周疲劳性能的影响。获得了预扭转前后材料的循环应力-应变关系、疲劳寿命等实验数据，据此，利用双参数威布尔分布数概率函数对疲劳寿命数据进行处理，结果表明其疲劳寿命以及置信度在双对数坐标系中的线性关系良好。通过Hollomon公式和Manson-Coffin公式拟合疲劳实验数据，建立了疲劳寿命预测公式。计算并拟合了材料塑性应变能和循环周次的关系，并对比研究了预扭转前后材料的循环韧度。试样疲劳断口观察表明预扭转的材料比未预扭转的材料断口形貌中有较多的孔洞、空穴和二次裂纹。
Abstract:Extremely low cycle fatigue (ELCF) properties of pressure vessel steel Q345R steel with torsional pre-strain were investigated. The fatigue tests were conducted on a MTS 809 servo-hydraulic material testing machine. The tests were run under uniaxial tension-compression loading with total lateral strain control. The ELCF behaviors, such as cyclic stress response characteristics, cyclic stress-strain relationships, and the fatigue life were investigated. The fatigue lives were processed by Weibull double parameters probability function, and the results revealed good linear correlations between the fatigue lives and the confidence level in the double logarithmic coordinate. The strain-life data from the axial tests were used to derive suitable Hollomon and Coffin-Manson parameters for the test material. And the fatigue life prediction models were obtained. Moreover, the relationship between the plastic strain energy and the cycles was calculated and the cyclic toughness was analyzed. The scanning electron microscope (SEM) micrographs revealed that compared to the material without pre-strain, the fracture of the torsional pre-strained material has more cavities, voids and secondary cracks.