ICF100563OR DUCTILE FRACTURE ANALYSIS OF STRUCTURAL STEEL USING MICROMECHANICAL MODELLING M. Rakin1, A. Sedmak2, S. Sedmak1, M. Zrilic1, S. Putic1 1Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Yugoslavia 2Faculty of Mechanical Engineering, University of Belgrade, 27 Marta 80, 11000 Belgrade, Yugoslavia ABSTRACT Modelling of ductile fracture initiation on a precracked geometry, based on knowledge of the behaviour at tension of simple uncracked material, has been done within the scope of micromechanical analysis. Finite element calculation has been applied in two steps: first, on a tensile round smooth specimen and then, on the standard CT specimen. Analysis was performed on low-alloy structural steel as a part of Round Robin on Micromechanical Models, organised by European Structural Integrity Society (ESIS) - Technical Committee for numerical methods (TC8) [1]. Micromechanical model based on a particular criterion of flow in a porous solid has been applied. The model was initially established by Gurson, and later on modified by Tvergaard and Needleman (the GTN model). The value of critical void volume fraction, fc, was first determined on a smooth specimen, and then used for modelling of crack growth initiation in standard CT25 specimen. Four-node and eight-node isoparametric finite elements (FE) with reduced integration were used. Crack tip singularity of CT specimen has been modelled only using a rather fine mesh. The large strain analysis with updated Lagrangian formulation has been used in both calculations. Probably the most difficult part of ductile fracture analysis, to present physically void nucleation as accurately as possible, was carried out by quantitative metallographic analysis of size and number of non-metallic inclusions in steel. The results obtained suggest that the critical values of micromechanical parameters according to GTN model may be used for approximate prediction of ductile fracture initiation on CT specimen for tested steel. KEYWORDS ductile fracture of steel, micromechanical modeling, finite element calculation, crack initiation, non-metallic inclusions, void volume fraction INTRODUCTION Micromechanism of ductile fracture of most metals and alloys includes void nucleation, growth and coalescence. Application of so-called global criteria of fracture mechanics such as COD and J-integral in characterisation of ductile fracture initiation does not provide satisfactory results for all cases of external
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