A two-dimensional computational fluid dynamics model is established to verify the correlation between periodic material flow and tool eccentricity during friction stir welding (FSW) process. In the model, the marker material is tracked by employing the Volume of Fluid technique. Besides, a novel boundary condition is proposed, which is not only non-uniformly distributed around the pin but is also connected with the real-time orientation of tool eccentricity. Finally, the dynamic evolution of marker material with the pin rotating is analysed, and the comparison between calculated and measured distribution of deposited marker material is carried out. The result demonstrates that tool eccentricity can be considered as the original mechanism for the formation of periodic material flow behaviour in FSW.

建立了二维计算流体动力学模型，以验证搅拌摩擦焊（FSW）过程中周期性材料流动与工具偏心率之间的相关性。在模型中，通过使用“流体体积”技术跟踪标记材料。此外，提出了一种新颖的边界条件，该边界条件不仅在销钉周围不均匀分布，而且与刀具偏心距的实时定向有关。最后，分析了标记材料随销旋转的动态演变，并对沉积的标记材料的计算分布与测量分布进行了比较。结果表明，工具偏心率可以被认为是FSW中周期性材料流动行为形成的原始机制。