ICF100393 DUCTILE FRACTURE IN HIGH STRENGTH STEEL WELDMENTS V. Olden 1, Z. Zhang 1, C. Thaulow 2 1SINTEF Materials Technology, Trondheim, Norway 2Norwegian University of Science and Technology (NTNU), Trondheim, Norway ABSTRACT By using the modified Gurson model recently developed at SINTEF, the ductility behavior of high strength steel weldments, including base metal (BM), weld-metal (WM) and heat affected zone (HAZ) in longitudinal and transversal directions has been studied. A fitting procedure based on smooth and notched cross weld tensile specimens which compares the strain predicted by finite element analyses to the actual strain at coalescence in the experiments, has been applied to determine the initial void nucleation parameter. Two simple models for void nucleation are used in the fitting procedure. Ductility behavior for the weldment has been described as a function of specimen geometry (stress triaxiality) and initial void volume fraction. Increased stress triaxiality by decreasing notch radius generally results in higher tensile stress and lower ductility. The HAZ ductility level both in longitudinal and transversal direction was slightly lower than for base metal but clearly higher than the WM ductility level. The modified Gurson model, with a void nucleation model describing a sudden initiation of all voids at the early stage of plastic strain (cluster model), gave satisfying description of the ductility behavior for medium sharp notched specimens. The obtained void nucleation parameter f0 (initial void volume fraction) was 0.0001 for BM and HAZ, and 0.001 for WM. KEYWORDS High Strength Steel, weld, ductile fracture, FE-Analysis, Gurson model, notch tensile INTRODUCTION Thermo-mechanical production methods have resulted in a new class of high strength construction steels, so called TMCP-steels, low in carbon content with excellent weldability and fracture toughness. Classical fracture mechanics theory based on brittle fracture will not give a satisfying description of fracture behavior of these steels and welded joints. Failure acceptance criteria based on linear elastic or elastic-plastic relationships are conservative because they fail to include that stress also will be needed for plastic deformation of the material. Hence, there is a need to include a description of ductile fracture in the evaluation of the fracture behavior of TMCP steels.
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