力学失配FSW焊接接头多区域力学行为及寿命预测

The macro-mechanical properties of FSW joints are strongly affected by the microstructures with respect to the special characteristics of the weld, such as ununiformity of microstructure and deformation, uneven performance and geometric discontinuity. The nominal stress method has been used to evaluate the fatigue property of FSW joint in engineering, but the influence of detailed microscopic features on the fatigue fracture behavior are neglected. The effect of heterogeneous welding microstructure distribution on the inhomogeneous mechanical response in two different types of mismatched FSW aluminum alloy joints will be studied from macro to micro scale by experiment, theoretical calculation and numerical simulation. DIC technology and optical in-situ fatigue test method will be utilized to observe multi region microstructures, mechanical properties and the inhomogeneous deformation behavior. Moreover, fatigue properties and fracture mechanisms, asymmetric crack tip plastic zones and cross regional crack propagation behaviors of different type of mismatched FSW joints will be analyzed, and the equivalent stress intensity factor model will be built to describe the compound crack propagation path. Finally, an accurate life prediction model will be proposed to simulate and calculate the fatigue growth lives of FSWed structures.

FSW焊接接头的组织不均匀、形变不均匀、性能不均匀与几何不连续等特点，导致其具有很强的微观结构依赖的宏观力学性能。工程上对其疲劳性能的评价基本上基于名义应力方法，往往忽略了细部微观特征对其疲劳破坏行为的影响。针对两种不同强度匹配的铝合金FSW焊接接头，采用实验、理论计算与数值仿真并行，宏-微观多尺度分析有机融合的研究方案，深入研究非均质焊接组织分布导致的接头非均匀力学响应。在借助DIC技术与光学原位疲劳试验等手段的基础上，测量FSW接头多区域微观组织、力学性能与非均匀变形行为，探讨不同强度匹配下FSW接头疲劳性能及破坏机制，深入研究力学失配对FSW接头非对称裂尖塑性区及跨区域裂纹扩展行为的影响，建立描述力学失配下FSW接头复合型裂纹扩展路径的焊缝局部等效应力强度因子模型，在此基础上建立FSW焊接结构的精确寿命预测模型，对其疲劳裂纹扩展和寿命进行数值模拟与计算。

FSW焊接接头的组织不均匀、形变不均匀、性能不均匀与几何不连续等特点，导致其具有很强的微观结构依赖的宏观力学性能。工程上对其疲劳性能的评价基本上基于名义应力方法，往往忽略了细部微观特征对其疲劳破坏行为的影响。针对不同强度匹配的铝合金FSW焊接接头，采用实验、理论计算与数值仿真并行，宏-微观多尺度分析有机融合的研究方案，深入研究了非均质焊接组织分布导致的接头非均匀力学响应。在借助DIC技术与光学原位疲劳试验等手段的基础上，测量了FSW接头多区域微观组织、力学性能与非均匀变形行为，探讨了不同强度匹配下FSW接头疲劳性能及破坏机制，深入研究了力学失配对FSW接头非对称裂尖塑性区及跨区域裂纹扩展行为的影响，在此基础上借助FRANC 3D软件建立了FSW焊接结构的寿命预测模型，计算了不同匹配焊缝的疲劳裂纹扩展和寿命。