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

在本项目中，将建立激光焊接凝固裂纹的多物理耦合数值模型。特别是，在低熔点相存在的情况下，中心线裂纹的形成机制正在考虑之中。为采用过程模拟和结构力学模拟相结合的方法研究高功率激光焊接中心裂纹的形成提供了有益的参考。该物理问题包括以下各个子问题的顺序解：(A)熔体内的热传递和流体动力学的耦合问题，(B)由于激光的热输入而引起的工件的宏观结构机械载荷，以及(C)凝固前沿的不稳定性，其中包含考虑熔体对流及其对结构力学的影响的低熔点相的扩散问题。该项目的主要目标是评估诸如Marangoni对流和自然对流等工艺效应对鼓包效应的影响及其对中心线裂纹发展的影响。这是由于低熔点相的分布和由此产生的瞬时凝固特征所致。在这个项目中，将基于计算机模拟来识别形成中心线裂纹的局部机制。在考虑实际熔池几何形状的情况下，提供了一个数值模型，该模型包含了在高功率激光焊接低合金钢过程中凝固区域应力和应变发展的工艺贡献。将进行工艺模拟和结构力学模拟。最后，将得到一个能够在工艺优化方面适应的数值模型，以避免所研究的中心线开裂现象。

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.