Fracture Research Of Q235B Circular Steel Based On Micromechanical Damage Models

Steel structures are widely used in the civil engineering. With the development of steel diversity and improvement of process property, steel structures will have a bright future, especially in the large-span structures. But steel structure failure occasionally happens. Ductile fracture is a common form of failure in steel structure. The research of steel behavior should be carried on to protect people’s lives.Based on the development of growth and coalescence of microvoids, Void Growth Model and Stress Modified Critical Strain were formed under the condition of monotonic loadings. Cyclic Void Growth Model and Degraded Significant Plastic Model were formed under the condition of cyclic loadings. They have been confirmed to predict members and joints well. However, research on fracture based on micromechanical damage models was barely applied on the steel Q235B, which is widely used in China.In this paper, the codes of micromechanical models VGM and SMCS were built by Fortran and linked to ABAQUS/EXPLICIT as subroutine VUMAT. Parameters of micromechanical models under the condition of monotonic loadings were calibrated through a serious of specimens including eight smooth bars and twenty-four notched bars extracted from hot-rolled and cold-formed tubes (base metal, heat affected zone and welding zone), characteristic length were calibrated by electron microscope experiment. Fracture predictions of notched tubes matched well with experiment results.Similarly, the codes of micromechanical models CVGM and DSPS were built by Fortran and linked to ABAQUS/STANDARD as subroutine UVARM. Coefficient of damage variable micromechanical models under the condition of cyclic loadings were calibrated through eight smooth bars and eight notched bars extracted from hot-rolled tubes and cold-formed tubes (base metal, heat affected zone and welding zone).Finally, in order to probe the wide adaptation of the method, cross baffle welded joints static test and a serious of circular steel pipe under cyclic loadings were simulated. The results of the experiment and finite element model were in accordance to some extent.