Coupled numerical investigation of centerline crack formation in high power laser beam welding

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In this project, a multiphysical coupled numerical model for the solidification cracking in laser beam welding will be developed. In particular, the formation mechanisms of centerline cracking in presence of low-melting phases are under consideration. A contribution to the coupled approach of process simulation and structural mechanics simulation for the formation of centerline cracking in high power laser beam welding will be supplied. The physical problem consists of the sequential solution of various sub-problems: (a) the coupled problem of heat transfer and fluid dynamics in the melt, (b) the macroscopic structural mechanical load of the workpiece due to the heat input of the laser beam, and (c) the instability of the solidification front, which contains the diffusion problem of low melting phases taking into account melt convection and its influence on the structural mechanics.The main objective of the project is to evaluate the influence of process effects such as the Marangoni convection and the natural convection on the bulging effect, and its impact on the development of centerline cracking, which is due to the distribution of low-melting phases, and the resulting transient solidification characteristics.In this project local mechanisms for the formation of centerline cracking will be identified based on computer simulations. A numerical model containing a process contribution to the development of stresses and strains in the solidification zone during high power laser beam welding of low-alloyed steels while considering a realistic weld pool geometry will be provided. Both process simulation and structural mechanics simulations will be carried out. Finally, a numerical model being able to be adapted in terms of process optimization to avoid the investigated centerline cracking phenomena will be available.