Heterogeneous butt welding of copper and AISI type 304L stainless steel was carried out using the electron beam process. Examination by scanning and transmission electron microscopy has indicated the possibility of obtaining joints free of cracks and porosity. Energy dispersive microanalysis of the weld bead cross-section has demonstrated the presence of non-equilibrium phases. The results show that the binary Cu -Fe equilibrium diagram is unable to predict the weld microstructure even at the moderate cooling and solidi cation rates expected under the present welding conditions. The feasibility of the Cu -304L electron beam welding process is therefore hindered by the problem of microstructural stability of the joint because of possible phase transitions during the service life of welded components.
MST/5303Dr Tosto (tosto@casaccia.enea.it), Mr Nenci and Mr Pierdominici are with ENEA
By means of a single void growth model, finite element simulations of incipient spallation experiments of high-purity aluminum under different plate impact velocities are carried out. The relationship between the influence of void growth in the sample on wave propagation and the feature of free surface velocity profile is discussed. By analyzing the change of stress field around the void, the occurrence of pullback signal in free surface velocity profiles is attributed to the local unloading wave effect caused by void growth in the sample, which cannot indicate the whole spallation of materials. Free surface velocity profiles and relative void volumes are simulated for different impact velocities and the simulation results are in good agreement with experimental results, which indicates that the stochastic damage evolution in incipiently spalled sample can be described by a single void growth in cell model.
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