N型相贯节点考虑材料损伤累积效应的破坏机理

基于有限元软件ABAQUS平台,编制考虑材料损伤累积效应、Bauschinger效应、混合硬化、裂纹萌生等因素的材料子程序,建立N型相贯节点实体模型,对其在低周往复加载全过程中的破坏机理进行模拟分析。研究表明：主支管相贯部位材料屈服后,随着塑性变形的不断发展,材料内部空洞的增长合并达到一定门槛值时便萌生裂纹,随荷载及循环次数增加,裂纹的不断扩展与合并导致材料在很多晶粒周围形成滑移带并沿着相贯线向冠点处逐渐发展,最后产生沿主管轴向的横向裂缝,与试验结果基本一致。节点刚度在首次屈服至裂纹萌生的阶段退化较快,裂纹发展至破坏阶段退化缓慢。节点耗能主要源于主支管相贯线附近的支管根部及主管壁的滞回耗能。

Research on Failure Mechanism of N-joints ConsideringMaterial Damage Accumulation

The user material subroutine considering the effect of material damage accumulation, Bauschinger effect, mixed hardening, crack initiation and other factors was compiled on the platform of the finite element program ABAQUS. Solid model of N-joints was built to simulate and analysis the failure mechanism of the whole process under low cycle reciprocating loading. The results show that with the continuous development of plastic deformation after the material yielding at the intersecting part of the chord and brace member, cracks were generated when the interior cavity of material reached a certain threshold value, and that with load and cycle times increasing, the material forms slip bands around many grains because of the growing and merging of cracks, then gradually extend along the intersecting line to the crown point, and finally produce transverse cracks along the axial direction of the chord member. The simulation results are basically consistent with the experimental results. The stiffness of the joints deteriorates rapidly in the stage of first yield to crack initiation, and slowly while cracks develop to failure stage. The energy dissipation of the joints mainly comes from the hysteretic energy dissipation of the brace root and the chord wall near the intersecting line between the brace and the chord member.