KOSSAKOWSKI Paweł Kielce University of Technology

The paper is concerned with the strength of S235JR steel at stress triaxiality. Failure processes of steel and other metallic materials are closely linked with microstructural changes in the form of voids, which are initiated at inclusions and precipitates present in the material. These phenomena can be modelled using advanced material models that define the stage of material failure. This study deals with numerical modelling of the ductile fracture and failure of elements subjected to static tension in the spatial stress state. The analysis was conducted for notched specimens made of S235JR steel in the high stress triaxiality condition. The Gurson-based approach was used to study the microstructural processes contributing to the ductile fracture of S235JR steel. The Gurson-Tvergaard-Needleman (GTN) material model, able to calculate the relationships between the material microstructure and its strength and between the microstructural changes and plastic fracture, was applied to locally model the initiation of damage processes in the material structure. The analysis focuses on the effect of two of the most crucial GTN model parameters – the critical void volume fraction, fc and mean strain for void nucleation, εN – on the material response. Two different values of the fc and εN parameters were considered: those obtained experimentally and those assumed on the basis of the literature data. The simulation results were compared with the data obtained through the modelling of notched specimens under tensile loading, assuming that the GTN model of a porous material is used for the whole element.