基于微观机理的梁柱节点焊接细节断裂分析

FRACTURE ANALYSES OF WELDED DETAILS IN BEAM-TO-COLUMN CONNECTIONS USING MICROMECHANICS-BASED MODELS

为预测钢结构焊接节点在地震作用下的延性断裂,开展了微观机理断裂模型的标定和验证工作。空穴扩张模型VGM和应力修正临界应变模型SMCS,将延性断裂的微观机理(空穴形核、扩张和聚合)与宏观的应力-应变场结合了起来。利用已有的缺口圆棒拉伸试验,辅以有限元分析,标定了Q345钢材母材、焊缝和热影响区3种材料的VGM和SMCS模型参数。进行了7个梁柱节点局部焊接试件的拉伸试验,测得了试件的断裂伸长量。建立了试件的精细实体有限元模型,分别采用断裂力学J积分方法和VGM、SMCS模型预测试件的断裂伸长量,并与试验结果进行比较。结果表明,VGM和SMCS模型预测焊接节点延性启裂的准确性较好,而J积分方法过于保守。该文为钢结构焊接节点的延性断裂预测提供了一种仅依赖于材料属性的普适性方法。

In order to predict the ductile fracture of welded connections in steel structures due to earthquakes, the investigations were carried out on the calibrations and validations of micromechanics-based fracture models. The void growth model(VGM) and the stress modified critical strain(SMCS) model relate the micromechanism of ductile fracture(void nucleation, growth and coalescence) to macroscopic stress and strain fields. The VGM and SMCS model parameters for Q345 structural steel, the corresponding weld and heat-affected zone were calibrated by using the available tensile tests of notched round bars and the complementary finite element analyses(FEA). Seven local welded assemblies of beam-to-column connections were tested at monotonic tensile loading, and the fracture critical elongations were measured. The J-integral based fracture mechanics approach and micromechanics-based model VGM and SMCS were adopted to predict the fracture critical elongation of each specimen using the refined finite element model(FEM). The comparisons between FEA predictions and experimental measurements in fracture critical elongation indicate that the VGM and SMCS models could predict the ductile fracture of welded connections with reasonable accuracy, while the J-integral approach obtains quite conservative results. A general method that is only material dependant is proposed for the ductile fracture prediction of welded connections in steel structures.