Ductile fracture prediction for welded steel connections under monotonic loading based on micromechanical fracture criteria

Abstract

Micromechanics-based fracture criteria for structural steels can be used to predict ductile fracture initiation with large-scale yielding and no initial flaws. High-fidelity finite-element analyses were carried out on ten welded connection specimens between the square steel tube column and H-beam flange under monotonic tensile loading. The calibrated micromechanics-based fracture criteria, including the Stress Modified Critical Strain (SMCS) model and the Void Growth Model (VGM), were used to predict fracture initiation for each specimen. The predicted results demonstrated high accuracy compared to test results. Sensitivity analyses of fracture toughness parameters in the SMCS model and VGM to the predicted fracture results were conducted. The results show that, when the fracture toughness parameters were increased or reduced by twenty percent, fluctuations in the predicted fracture results were within the acceptable range. Therefore, calibrated micromechanics-based fracture criteria can be used to predict ductile fracture initiation of connections under monotonic loading. Subsequently, the user subroutine VUMAT, from ABAQUS software edited by the authors, was employed. Using the SMCS model and VGM as fracture criteria, the post-fracture load–displacement curves of eighteen notched round bar specimens and two welded connection specimens (between the square steel tube column and H-beam flange) that fractured at different locations were traced by deleting the failure elements one by one. The predicted results agree well with the test results. Consequently, these calibrated micromechanics-based fracture criteria and associated simulating techniques can be used for collapse analysis of steel structures during extreme events.