动力荷载作用下杆系钢结构节点疲劳裂纹扩展断裂破坏的分析方法

Analysis method of fatigue crack propagation and fracture at joints of steel lattice structures under dynamic loads

基于ANSYS有限元计算软件,提出杆系钢结构节点疲劳裂纹扩展断裂破坏的分析方法。首先介绍杆系钢结构节点子结构的多尺度有限元计算方法的原理和含三维裂纹节点子结构的有限元建模方法。其次提出疲劳裂纹扩展实时应力强度因子的计算方法及通过对节点子结构荷载边界条件采用分组的方式计算出多轴非比例加载情况下的应力强度因子幅的方法。再次通过Paris裂纹扩展公式完成裂纹扩展的疲劳寿命计算。最后通过一个铁路钢桁架桥工程实例的详细分析,得到其节点区疲劳裂纹扩展的全过程,并对此桥的疲劳寿命进行预测。

Steel lattice structures are popular in the construction engineering.It is known that under the long-term dynamic loads,fatigue cracks may occur in the welded joints,in particular in the joints with welding defects,which may cause brittle fracture of the joints and even lead to the collapse of the structures.Hence,in order to prevent the fatigue failure of a steel lattice structure,it is important to predict the fatigue crack propagation at its critical joints accurately.This paper presents a computational method for the fatigue crack propagation and fracture at the joints of the steel lattice structures.A multi-scale method for analyzing the stress of steel lattice structures is established and a solid element model of the commercial finite element software package ANSYS is used in this paper to model three dimensional cracked structures at first.Secondly,a real-time method for computing the stress intensity factor of the fatigue crack propagation is proposed.Based on this method,the grouped stress intensity factor ranges of the critical joints with fatigue cracks under the multi-axial non-proportional loading are calculated and the crack propagation life of the joints is estimated by the Paris law.Finally,a simulating analysis for a steel truss railway bridge,is carried out to show the fatigue crack propagation process of the joints and to predict the fatigue life of the railway bridge.