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为了研究钢材的超低周疲劳性能及循环荷载作用下的本构关系,对50组Q235-B和Q345-B钢材进行超低周疲劳试验。研究了Q235-B和Q345-B钢材的力学性能,如:单调加载性能、滞回性能及滞回准则。通过对钢材全过程滞回性能的研究,建立了循环荷载作用下钢材的简化单轴本构模型。基于有限元软件ABAQUS的用户子程序接口UMAT,用户可自定义钢材的单轴本构属性。通过引入纤维梁单元,可利用单轴本构模型进行结构分析。通过对比各种荷载作用下Q235-B和Q345-B钢材的试验数据,验证了本模型的正确性,利用本模型可进行钢框架的非线性时程分析。试验和数值分析结果均表明:Q235-B和Q345-B钢材在循环荷载和单调荷载作用下的性能有很大不同,钢材屈服后,循环荷载作用下的骨架曲线比单调荷载作用下更高;循环次数和振幅大小对材料韧性的影响很大。当受循环荷载作用时,钢材提前发生颈缩和断裂,这表明累积损伤降低了钢材的韧性。
In order to study the ultra-low cycle fatigue behavior of steel and the constitutive relationship under cyclic loading, ultra low cycle fatigue tests were carried out on 50 steel Q235-B and Q345-B steel. The mechanical properties of Q235-B and Q345-B steel were studied, such as monotonic loading, hysteretic behavior and hysteresis. Through the study of the whole process of steel hysteretic behavior, a simplified uniaxial constitutive model of steel under cyclic loading was established. Based on the user subroutine interface UMAT of the finite element software ABAQUS, users can customize the uniaxial constitutive properties of steel. By introducing fiber beam elements, the uniaxial constitutive model can be used for structural analysis. By comparing the test data of Q235-B and Q345-B under various loads, the correctness of this model is verified. The nonlinear time-history analysis of steel frame can be carried out by using this model. The results of the test and numerical analysis show that the properties of Q235-B and Q345-B steel under cyclic loading and monotonic loading are quite different. The skeleton curve under cyclic loading is higher than that under monotonic loading after yielding. The number of cycles and amplitude have a great influence on the material toughness. When subjected to cyclic loading, the steel necked and fractured prematurely, indicating that cumulative damage reduced the toughness of the steel.