Numerical Simulation and Experimental Investigation of the Fracture Behaviour of an Electron Beam Welded Steel Joint

In this thesis, the author investigates experimentally and numerically

the fracture behavior of an electron beam welded joint made from

two butt S355 plates. The 2D Rousselier model, the Gurson-Tvergaard-

Needleman (GTN) model and the cohesive zone model (CZM) were

adopted to predict the crack propagation of thick compact tension (CT)

specimens. Advantages and disadvantages of the three mentioned models

are discussed. The cohesive zone model is suggested as it is easy to use

for scientists & engineers because the CZM has less model parameters

and can be used to simulate arbitrary crack propagation. The results

shown in this thesis help to evaluate the fracture behavior of a metallic

material. A 3D optical deformation measurement system (ARAMIS) and

the synchrotron radiation-computed laminography (SRCL) technique

reveal for the first time the damage evolution on the surface of the sample

and inside a thin sheet specimen obtained from steel S355. Damage

evolution by void initiation, growth and coalescence are visualized in

2D and 3D laminographic images. Two fracture types, i.e., a flat crack

propagation originated from void initiation, growth and coalescence

and a shear coalescence mechanism are visualized in 2D and 3D images

of laminographic data, showing the complexity of real fracture. In

the dissertation, the 3D Rousselier model is applied for the first time

successfully to predict different microcrack shapes before shear cracks

arise by defining the finite elements in front of the initial notch with

inhomogeneous f0-values. The influence of the distribution of inclusions

on the fracture shape is also discussed. For the analyzed material, a

homogeneous distribution of particles in the material provides the

highest resistance to fracture.