钛合金飞机唇口蒙皮复杂轨迹激光深熔焊及其非线性疲劳损伤行为研究

Through the welding robot trajectory subsection precise planning, collaborative design of atomic ash tire jig and protective gas devic, and based on the strategy of reducing the welding deformation and the overlay of welding weak areas for improving the fatigue damage behavior of welded joint, an integrated manufacturing technology of shape and performance control will be developed by multi-source synergy superposition of electromagnetic stirring, heat sources and dynamic constraint technology in order to implement the titanium alloy aircraft lip skin component with complex trajectory by laser deep penetration welding.Facing the complex phenomenon of microstructure properties and welding residual stress with directional and nonlinear gradient characteristics in the welded joint of titanium alloy, the fatigue behaviors of the welded joint are proposed to depend on the gradient coupling effects of both the microstructure gradient and residual stress gradient, and the gradient coupling effects and their synergistic control strategies are investigated on the damage evolution and crack propagation of the fatigue. The microstructure gradient of the laser welded joint is finely characterized by the multi-scale from macro and micro. Using the micro-compression-shear and finite element inverse method to determine the micro constitutive relation in the welded joint, and based on the micro-blind-hole method and the FEM with considering the mechanical property of the welded region to characterize finely the welding residual stress gradient, and then the dual-gradient distribution and its vector characterization methods would be explored. Both the local temperature difference method and microscopic analysis one are used to build the fatigue damage evolution and crack growth model of the welded joint, and developing the efficient computing technology of fatigue process by taking the welding mechanical properties and residual stress into account, then the differences and gradient coupling effect of fatigue behavior could be explored.

通过焊接机器人的运动轨迹分段精细规划、原子灰胎夹具及保护气体装置协同设计，基于减小焊接变形和焊接接头薄弱区叠加从而改善焊接接头微区疲劳损伤行为的策略，开发集成电磁搅拌、热源叠加和动态拘束技术的多源协同控形控性一体化制造技术，实现钛合金飞机唇口蒙皮构件复杂轨迹激光深熔焊。提出钛合金焊接接头微区非线性疲劳损伤行为依赖于焊接接头组织和残余应力及其梯度耦合效应的科学问题，从宏观与微观多尺度精细表征飞机唇口蒙皮复杂轨迹焊接接头微区显微组织分布，利用微压剪试验结合有限元逆向法确定焊接接头微区应力应变本构关系，将微孔法与考虑焊接接头微区性能的有限元法结合精细表征焊接残余应力分布规律，利用局部温差法与细观组织分析法建立焊接接头微区疲劳损伤与裂纹扩展模型，开发考虑焊接接头组织与残余应力的疲劳损伤高效计算技术，研究非线性疲劳损伤演变与裂纹扩展的差异性，探索焊接接头显微组织与残余应力梯度耦合效应的矢量表征方法。

研究首次实现了复杂构件的一次性激光焊成形研究和变形控制，针对复杂轨迹的航空航天飞行器的复杂唇口蒙皮构件进行焊接研究，对钛合金脉冲激光焊进行焊接工艺优化，通过焊接机器人运动轨迹的分段精细规划、原子灰胎夹具及保护气体装置的协同设计、体壳耦合的有限元计算等，实现了复杂薄壁构件的一次性焊接成型和焊接变形控制。发明了施加外拘束的方法改善钛合金激光焊断面形貌和凹陷缺陷，并从减小焊接变形和避免焊接接头薄弱区叠加的角度出发改善了焊接接头性能。. 研究表明钛合金激光焊焊缝窄，使得焊缝微区产生极大的应力、组织、性能不均匀性，导致焊缝及其附近区域容易成为结构中失效发生的策源地。研究发现钛合金激光焊接头的组织、硬度和应力梯度，晶粒尺寸梯度峰值在熔合线上，显微硬度梯度在热影响区和母材界面处，应力梯度峰值主要在热影响区与母材交界处，靠近热影响区的母材处。. 研究分析了焊接接头厚度方向的梯度、焊接缺陷带来的几何非线性梯度、晶粒尺寸梯度、硬度梯度和应力梯度对接头力学性能的影响。当焊接接头为V型接头时，接头厚度方向存在组织性能梯度，使得V型接头的拉伸性能比H型接头差。熔合线附近的大组织梯度特征以及咬边型凹陷使得熔合线附近成为薄弱区域。对不同焊接速度的中心在熔合线上的漏斗形试样进行低周疲劳试验，结果表明对于承受小疲劳载荷的构件，应选择小热输入，防止生成晶粒过粗的焊缝；对于承受大疲劳载荷的构件，应避免生成梯度过大的焊接接头，防止焊缝和母材之间变形不协调导致构件过早失效。对于长期在120~300°C下的服役构件，为了防止焊缝晶粒过粗导致的疲劳性能恶化，应采用焊接速度较大的焊接接头。对添加微区性能和焊接残余应力的接头疲劳性能用疲劳分析软件Fe-safe进行计算，发现由于残余应力的影响，在热影响区与母材交界处的疲劳性能最差。. 研究已发表论文10余篇，国内外会议交流5次，授权发明专利1件，参加研究的博士7名，硕士5名。

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