Micromechanical fracture model parameter influencing factor study of structural steels and welding materials

Micromechanical fracture models can be used to predict ductile fracture initiation for welded steel connections under strong earthquake. The parameter influencing factors of four such models including the void growth model (VGM), the stress modified critical strain model (SMCS), the Degraded Significant Plastic Strain (DSPS) model and Cyclic Void Growth model (CVGM) were analyzed in this paper. Firstly, the micromechanical fracture model parameters of three kinds of Chinese structural steels Q235, Q345, Q460 with nominal yield strength of 235 MPa, 345 MPa, 460 MPa respectively, and two kinds of welding materials ER 50, ER55-G were calibrated through the smooth notched tensile (SNT) tests, smooth notched cyclic (SNC) tests, their corresponding finite element analyses (FEA) and scanning electron microscope tests. Six kinds of loading histories were adopted in the SNC tests to study the influence of loading history on parameter calibration of Q460 steel. In order to investigate the influence of loading direction on the parameters of welding materials, two different loading directions including along and vertical to welding length direction were adopted in the tests on ER55-G welding material specimens. Subsequently, the parameter calibration results of different structural steels and welding materials were compared with that of previous studies to study the influence of material properties. The parameter calibration results of two batches of Q345 steel were compared to study the discreteness of the parameters between different batches of structural steels. Finally, the energy spectrum tests were carried out to obtain the chemical composition of each material, and the impacts of chemical composition on the parameters were analyzed. This paper is expected to contribute for the ductile fracture analysis of welded steel connections using micromechanical fracture models. (C) 2019 Elsevier Ltd. All rights reserved.