Advances in Computational Design, Vol. 3, No. 2 (2018) 133-146 DOI: https://doi.org/10.12989/acd.2018.3.2.133 133 Copyright © 2018 Techno-Press, Ltd. http://www.techno-press.org/?journal=acd&subpage=7 ISSN: 2283-8477 (Print), 2466-0523 (Online) Numerical simulation of material damage for structural steels S235JR and S355J2G3 Paweł G. Kossakowski * and Wiktor Wciślik a Department of Strength of Materials and Concrete Structures, Kielce University of Technology, Al. Tysiąclecia Państwa Polskiego 7, 25-314 Kielce, Poland (Received December 12, 2017, Revised January 30, 2018, Accepted February 3, 2018) Abstract. The paper discusses numerical analysis of tensile notched specimens with the use of Gurson – Tvergaard – Needleman (GTN) material model. The analysis concerned S235JR and S355J2G3 steel grades, subjected to medium stress state triaxiality ratio, amounting 0.739. A complete procedure for FEM model preparation was described, paying special attention to the issue of determining material constants in the GTN model. An example of critical void volume fraction (f c ) experimental determination procedure was presented. Finally, the results of numerical analyses were discussed, indicating the differences between steel grades under investigation. Keywords: steel; static tensile tests; Gurson–Tvergaard–Needleman model; determination of model parameters; numerical simulation 1. Introduction Failure processes in structural materials occur in steps and are dependent on the rate of load applied. The failure of brittle materials including concrete or glass is different from that observed in elastic-plastic materials, e.g., structural steels and members (Mahmoud et al. 2007, Brnic et al. 2013, Brnic and Vukelic 2015, Vukelic and Brnic 2016, Vukelic and Brnic 2017). When steel is used in construction for structural purposes, it is essential to prevent brittle fracture (Boyd 2016), as specified in the European standard EN 1991-1-10: Design of steel structures - Part 1-10: Material toughness and through-thickness properties. Brittle fracture is an extremely dangerous phenomenon mainly because it occurs suddenly and rapidly. It is difficult to predict as there are no macroscale defects to be detected during routine visual inspections required, for instance, for bridges. Recent studies concerning steel bridges have focused on a phenomenon called Constraint Induced Fracture (CIF). This rapid brittle fracture is caused by excessive constraints occurring in structural elements mainly due to the overlapping of welded joints (Connor et al. 2007, Hesse et al. 2014). It is thus necessary that modern structural steels (grades S235JR and S355J2G3) have high fracture toughness under normal use conditions. Fatigue is another fundamental problem, which is especially important for old structures, i.e., bridges (Kossakowski 2013). Corresponding author, Ph.D., D.Sc., E-mail: kossak@tu.kielce.pl a Ph.D., Design Engineer, E-mail: wwcislik@tu.kielce.pl