钢材的低周疲劳特性及双曲面本构模型的改进

Low-cycle fatigue behaviors of structural steel and modification of the two-surface constitutive model

摘要:

为合理评估钢结构的地震损伤，研究结构钢的塑性变形与低周疲劳之间的耦合关系以及循环软化特性.通过对Q345qC钢材进行高应变反复加载试验，获得了相应的低周疲劳破坏和循环软化特性.通过研究承载力下降与塑性耗能密度之间的关系及对边界面进行缩放和移动，将循环软化特征引入材料的本构关系模型.在此基础上，采用改进后的本构关系模型对钢桥墩进行了反复荷载作用下的力学行为分析，讨论了循环软化对构件承载能力的影响.结果表明：Q345钢材具有较好的延性和较强的抗低周疲劳性能，试验未发现钢材塑性变形与低周疲劳之间存在明显的相关性；循环软化特征在较大的塑性应变状态下表现得更明显，修正后的双曲面本构关系模型可以较好地模拟钢材循环软化行为；考虑材料循环软化效应后，钢桥墩在反复荷载或地震作用下的承载力略有降低.

Abstract:

In order to evaluate the damage of steel structures induced by earthquake, this research investigated the coupling relation between the ultimate plastic deformation and low-cycle fatigue life as well as the cyclic softening behavior of structural steel. The repeated high strain loading experiments were carried out on low carbon steel Q345qC, and the low-cycle fatigue life and cyclic softening behavior were studied. By analyzing the relationships between the bearing capacity deterioration and the dissipating energy density, the modification of the bounding surface radius and center and cyclic softening were introduced to the two-surface constitutive model. On this basis, the mechanical behaviors of a steel bridge pier under cyclic loading were investigated by employing the modified two-surface constitutive model, and the effects of material cyclic softening on the bearing capacity of the steel bridge pier were analyzed and discussed. Results show that the structural steel Q345 has good ductility and anti-low-cycle fatigue property. No evident coupling relation between ultimate plastic deformation and low cycle fatigue life of the steel was observed in the experiments. Cyclic softening is more apparent at a larger plastic strain state. The modified two-surface constitutive model is capable of simulating the cyclic softening behavior of the steel in a very satisfactory manner. The bearing capacity of the steel bridge pier under cyclic loading or in earthquake decreases slightly when material cyclic softening is considered.