SGER: Investigating Recursive Plastic Heating in Third Body Regions during Friction Stir Welding

在搅拌摩擦焊接（FSW）过程中，第三体区域内的条件对于解决不对称和最小化工具前进侧形成空隙的固有趋势至关重要。尽管被认为是FSW过程的重要组成部分，但很少有人对第三体进行建模，以解释它是如何从系统变量中出现的，或者它在FSW过程中产生热量的作用。在这项探索性研究（SGER）的小额资助中，提出了递归塑性加热（RPH）理论，表明第三体区域内的塑性工作通过源于切屑形成机制的重要惯性效应来维持FSW，并产生所需热量的很大一部分。新的框架表明，摩擦主要是递归塑料加热的催化剂，可以通过混合FSW策略来增强。研究的目标是在第三个体中制定和验证RPH理论，并研究热腔方法，以增加FSW，创造条件，使第三个体比摩擦作为唯一的热量输入方式更快地出现和移动。本研究包括实验验证，将RPH理论与正交切削框架相结合，利用RPH理论建立并求解了预测加工条件下第三体发展的数学模型。RPH理论表明，体积加热和热机械热通道可以影响第三体条件，并最大限度地减少对工具材料的要求。随着FSW应用范围的不断扩大，RPH理论为生产更高硬度的刀具提供了另一种选择，以满足日益苛刻的工件材料的要求。在FSW过程中，递归塑料加热作为减少流动应力的主要机制的概念代表了一种范式的转变，即FSW工具的摩擦加热是中心机制。在RPH理论中，摩擦能被重塑为塑性流动的催化剂；因此，验证提供了将混合搅拌焊接技术扩展到热腔方法（如激光辅助搅拌焊接和等离子辅助搅拌焊接）的潜力。此外，与造船业的密切互动将导致快速的技术转移。

Conditions within the third body region during Friction Stir Welding (FSW) are crucial for resolving asymmetries and minimizing the inherent tendency to form voids on the advancing side of the tool. Despite being recognized as an important part of the FSW process, very little work has been done on modeling the third body to explain how it emerges from system variables or its role in generating heat during the FSW process. In this Small Grant for Exploratory Research (SGER), a theory of recursive plastic heating (RPH) is proposed to show that plastic work within the third body region sustains FSW through important inertial effects which originate from a chip forming mechanism and produces a significant portion of the heat required. The new framework suggest that friction is mainly a catalyst for recursive plastic heating which may be enhanced by hybrid FSW strategies. The goal of the investigation is to formulate and verify RPH theory within the third body and investigate hot cavity approaches for augmenting FSW to create conditions which allow the third body to appear sooner and move faster than possible with friction as the sole means of heat input. This research includes experimental verification, combining RPH theory with a framework for orthogonal cutting, and formulation and solution of a mathematical model using RPH theory to predict how the third body develops under processing conditions. RPH theory suggests that volumetric heating and thermo-mechanical hot channels can influence third body conditions and minimize demands on tool materials. As efforts continue to extend FSW to a wider range of materials, RPH theory provides an alternative to producing tools with increasing hardness to meet the demands of increasingly tough workpiece materials. The notion of recursive plastic heating as the dominant mechanism for reducing flow stresses during FSW represents a paradigm shift away from a framework where frictional heating from the FSW tool is the central mechanism. Within RPH theory, frictional energy is recast as a catalyst for plastic flow; therefore, verification offers the potential to broaden the interpretation of hybrid FSW technology to hot cavity methods like Laser Assisted Stir Welding and Plasma Assisted Stir Welding. In addition, strong interaction with the shipbuilding industry should lead to rapid technology transfer.