This paper presents a novel pressure-dependent velocity boundary condition based on wear theory according to our former work, which provides an explainable perspective in understanding the physics of periodic time scale sliding-to-sticking transition condition and shear layer formation, as well as quality weld/void defects formation, during friction stir welding/self-reacting friction stir welding using computational fluid dynamics model. With this newly developed boundary condition, effects of welding speed and rotation speed on the weld cross-section geometry can be robustly captured. Furthermore, different cases of quality weld and void defects formation are validated with shear localization model. In both shear localization model and computational fluid dynamics model with pressure-dependent velocity boundary condition, the rationale and physical explanation of quality weld/void defects formation, as well as tool-workpiece sliding-to-sticking transition behavior, are investigated and compared: The pressure-dependent velocity boundary condition describes the relationship between weld pitch and applied velocity boundary from geometrical restrictions, and shear localization model captures transient shear layer formation within one pin revolution from one-dimensional standpoint; the pressure-dependent velocity boundary condition accounts for the time-averaged transitioning from pure sliding to full sticking during each shear layer generation and deposition cycle, whereas the shear localization model directly describes the transition from sliding to full sticking at pin/workpiece interface during each tool revolution. It is worth noting that the shear layer itself is not explicitly captured in computational fluid dynamics model due to continuity, instead the equivalent effects and movement of periodic shear layer are described and modeled. The importance of shear layer that forms during each tool revolution in periodic weld formation mechanism is emphasized in both pressure-dependent velocity boundary condition of computational fluid dynamics model and shear localization model.

本文根据我们以前的工作提出了一种基于磨损理论的新型压力相关速度边界条件，它为理解周期性时间尺度滑动-粘着过渡条件和剪切层形成以及质量的物理学提供了一个可解释的视角。在使用计算流体动力学模型的搅拌摩擦焊/自反应搅拌摩擦焊期间形成焊缝/空隙缺陷。通过这种新开发的边界条件，可以可靠地捕捉焊接速度和旋转速度对焊缝横截面几何形状的影响。此外，使用剪切定位模型验证了不同质量焊缝和空洞缺陷形成的情况。在具有压力相关速度边界条件的剪切局部化模型和计算流体动力学模型中，研究和比较了优质焊缝/空洞缺陷形成的原理和物理解释，以及工具-工件从滑动到粘着的过渡行为：几何限制，剪切定位模型从一维的角度捕获一针旋转内的瞬态剪切层形成；压力相关的速度边界条件解释了在每个剪切层生成和沉积循环期间从纯滑动到完全粘附的时间平均转变，而剪切定位模型直接描述了在每个剪切层/工件界面从滑动到完全粘附的转变工具革命。值得注意的是，由于连续性，计算流体动力学模型中并未明确捕获剪切层本身，而是描述和建模了周期性剪切层的等效效应和运动。在计算流体动力学模型的压力相关速度边界条件和剪切局部化模型中都强调了在每次工具旋转期间形成的剪切层在周期性焊缝形成机制中的重要性。