13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Numerical study of the fracture behavior of an electron beam welded steel joint by cohesive zone modeling Haoyun Tu*, Siegfried Schmauder, Ulrich Weber Institute for Materials Testing, Materials Science and Strength of Materials (IMWF) University of Stuttgart, Pfaffenwaldring 32, D-70569 Stuttgart, Germany * Corresponding author: haoyun.tu@imwf.uni-stuttgart.de Abstract The cohesive model has been used studying the ductile and brittle fracture mechanisms of homogenous and inhomogeneous structures in recent years. The traction-separation law which is described by the cohesive strength T0, critical separation δ0 and cohesive energy Γ0 is used to study the damage of materials. In this paper, the cohesive model is adopted to study the fracture behavior of an electron beam welded steel joint. The dimensions of different weld regions can be obtained from hardness tests across the welded joint. Local stress-strain curves are derived from the tensile test results of flat specimens which are obtained from the respective weld regions. Based on the axial stress versus diameter reduction curve of notched round specimens, the cohesive strength can be fixed. For pure mode I loading, the Γ0 value is set equal to the Ji value which is the J-integral value at fracture initiation. The cohesive parameters obtained from the base material (BM), the fusion zone (FZ) and the heat affected zone (HAZ), respectively, are used to predict the fracture behavior of compact tension (C(T)) specimens with the initial crack located at different positions in the weld region. Good comparison is obtained between the numerical and the experimental results in terms of force vs. Crack Opening Displacement (COD) curves as well as fracture resistance (JR) curves. Keywords Cohesive zone model, electron beam welded joints, crack propagation, finite element modeling 1. Introduction Compared to the traditional arc welding technique, advanced welding technique, such as electron beam welding (EBW) has found wide applications in industry fields as a narrow heat affected zone and small residual stresses are obtained after the welding process. The failure of the weldments always draws attentions as the fracture behavior of the welded joints influences the crack growth of structures, which affects the lifetime and safety of components. With the development of the finite element method, attention has been focused on the fracture behavior of welded joints in a numerical way. The Gurson-Tvergaard-Needlemann (GTN) model [1-3] has been used in studies of the fracture behavior of conventional fusion welded joints [4-6] and laser welded joints [7-9]. Later, the GTN model and the Rousselier model [10] were used successfully to study the ductile fracture of electron beam welded steel joints at IMWF [11-13]. Compared to the previous two damage models, the cohesive model possesses less model parameters, which make the model easy to use. The material separation is usually described by interface elements - the cohesive element, continuous elements remain undamaged in the cohesive model. The damage of the cohesive zone is depicted by a traction-separation law which is described by cohesive strength T0, critical separation δ0 and cohesive energy Γ0. The concept of a cohesive model was first introduced by Dugdale [14] and Barenblatt [15]. They assume that the crack consists of two parts: the stress-free part and the parts loaded by cohesive stresses. Following this assumption, different traction-separation laws were proposed in the past to investigate the ductile or brittle
RkJQdWJsaXNoZXIy MjM0NDE=