Abstract In friction stir welding (FSW), the real contact conditions between the tool and the workpiece and the range of strain rates experienced remain quite unclear. In this work, a coupled 3D thermo-mechanical numerical model was used to simulate the FSW process. A Parametric finite element analysis of the evolution of the contact conditions, strain rates and temperatures with the processing parameters, tool dimensions and base material plastic properties was conducted. The numerical model was able to capture the evolution of the mixed slipping/sticking contact conditions with the welding time and welding parameters. The temperature and strain rate gradients obtained in the numerical simulations were validated with experimental data, by calculating the grain size distribution, in the stirred volume, using the Zener-Hollomon parameter. Full sticking, full slipping and mixed slipping-sticking contact domains were identified in a process parameters chart. It was found that, meanwhile the temperature and the sticking fraction evolve in the same way with the processing parameters, the strain rate is mainly determined by the tool rotation speed, varying from an average of 68 to 324 s−1, when the tool rotation speed is increased from 300 to 1200 rpm. The contact conditions and the base material plastic properties were also found to mutually influence the material flow. In full sticking contact, high strength materials, with high strain rate sensitivity, may display a similar flow pattern to that of low strength materials. However, coarser and more uniform grain structures may result from the welding of high strength materials, as a result of the narrower range of strain rates experienced during welding combined with high heat input.

中文翻译：

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搅拌摩擦焊接触条件及其对应变速率和温度的影响分析

摘要 在搅拌摩擦焊 (FSW) 中，工具和工件之间的真实接触条件以及所经历的应变率范围仍不清楚。在这项工作中，耦合的 3D 热机械数值模型用于模拟 FSW 过程。对接触条件、应变率和温度随加工参数、工具尺寸和基材塑性特性的演变进行了参数化有限元分析。数值模型能够捕捉混合滑动/粘连接触条件随焊接时间和焊接参数的演变。通过使用 Zener-Hollomon 参数计算搅拌体积中的晶粒尺寸分布，数值模拟中获得的温度和应变速率梯度通过实验数据进行验证。在工艺参数表中确定了全粘、全滑和混合滑-粘接触域。发现，在温度和粘着率随加工参数变化的同时，应变率主要由刀具转速决定，平均为 68 至 324 s-1，当刀具旋转时转速从 300 rpm 增加到 1200 rpm。还发现接触条件和基材塑性性能相互影响材料流动。在完全粘附接触中，具有高应变率敏感性的高强度材料可能会显示出与低强度材料相似的流动模式。然而，高强度材料的焊接可能会导致更粗和更均匀的晶粒结构，