管桁结构直接焊接节点焊材损伤累积演化规律试验研究

Experimental study on damage cumulative evolution law of damage of welding material of joints in steel tube truss structures

管桁结构直接焊接节点焊缝容易发生损伤累积,造成节点局部失效。为此,针对管桁结构直接焊接相贯节点的连接焊缝,制作标准试件进行低周疲劳试验,得到其应力-应变滞回曲线、循环应力幅退化曲线和累积耗能变化曲线,研究节点焊材的损伤累积演化规律。结果表明:循环荷载下焊材表现出循环软化现象,与其母材循环特性存在差别,节点抗震分析中应区别考虑二者本构关系;焊材的损伤累积演化规律主要表现为随着循环周数的增加,其循环应力幅值、卸载刚度和耗能能力逐渐减小;焊材损伤累积破坏分三阶段,其中裂纹萌生和破坏阶段应力幅退化较快,裂纹扩展阶段变化较慢;加载应变幅对损伤累积速率的影响表现为加载应变幅值越大,其损伤退化越快,在母材为Q235的焊材中影响更明显;焊缝形式的影响较小,表现为角焊缝的损伤累积稍大于全熔透焊缝。有限元分析中考虑损伤累积影响,得到的焊材损伤累积演化规律与试验结果较为吻合。

The weld bead of steel tube truss structures is prone to damage accumulation,which may cause local failure of the joint.The standard coupons of welding material in the joints of steel tube truss structures were made for low cycle fatigue tests,from which the stress-strain hysteresis curves,stress amplitude degradation curves and energy consumption curves were obtained,and the cumulative damage evolution law of the welding material were studied.The results show that the welding material exhibits cyclic softening under cyclic loading,which is different from the base metal.So the difference in constitutive relations between welding material and the base metal should be taken into consideration in the seismic analysis of the joints.The cumulative evolution law of damage of the welding material can be described as follows:the stress amplitude,unloading stiffness and energy dissipation gradually decrease with the loading cycles.The cumulative damage of welding materials can be divided into three stages.The stress amplitude degenerates fast in the crack initiation and failure stages,while slowly during the crack propagating stage.The rate of damage-induced degradation increases with the loading strain amplitude,and such effect is obvious for the welding material with base metal of Q235.The influence of the weld form is smaller,and the damage accumulation of the fillet weld is slightly greater than that of the butt weld.The cumulative evolution law of the welding material obtained from finite element analysis is consistent with the test results.