钛合金铆钉超声振动铆接变形机理及接头性能研究

Titanium alloy rivet is a crucial element for assembling of titanium alloy and composite structures in aircraft. However, the current riveting technologies for titanium alloy rivet always accompanies several problems, like the inefficient forming force, cracks in rivet head and inhomogeneous interference. Therefore, an ultrasonic vibration assisted riveting technique for titanium alloy rivet will be established, based on the potential of ultrasonic vibration for reducing the metal deformation resistance and improving the formability. Numerical modeling of the ultrasonic riveting process for TB2 countersunk rivet are constructed after obtaining its constitutive equation under ultrasonic vibration. Combing with the ultrasonic riveting experiment, the material flow behaviors and microstructure evolution during the process will be studied, aiming to reveal the forming and failure mechanisms. The effect of the ultrasonic vibration on the riveting quality, mechanical properties and fatigue life of the riveted joint is also investigated. The relationships between residual stress, microstructure and mechanical properties, failure behaviors are concluded. The optimal process parameters will be provided to get a riveted part of good quality and performance. This research will promotes the development and industrial application of the ultrasonic riveting technology for titanium alloy rivet, and have great theoretical significance and engineering application value for the lifetime extension of the riveted parts on aircraft.

钛合金铆钉是钛合金和复合材料飞机结构铆接装配的关键零件，而现有铆接技术容易出现铆钉变形困难、镦头开裂和铆接干涉量不均匀等现象，影响铆接质量和连接件力学性能。针对该问题，本项目拟利用超声振动塑性成形技术在降低金属变形抗力和改善成形性能方面的积极作用，建立钛合金铆钉超声振动辅助铆接成形工艺。以TB2沉头铆钉为研究对象，建立超声振动下的材料本构模型，实现超声振动铆接成形过程的数值模拟，结合超声铆接实验，研究超声振动下钛合金铆钉材料流动行为和微观组织演变，探明超声铆接下钛合金铆钉变形机理和失效机制；研究超声振动对铆接质量、接头连接强度和疲劳寿命的影响规律，揭示残余应力和微观组织结构对接头力学性能及失效行为的影响机理，探索微观组织和力学性能的调控机制，获得铆接质量和组织性能优良的铆接件。这对于促进钛合金铆钉超声振动铆接工艺的发展和工程应用，提高飞机铆接件服役性能，具有重要的理论意义和工程应用价值。

钛合金铆钉是实现钛合金和复合材料飞机结构铆接装配的关键零件，而现有铆接技术容易出现成形困难、镦头开裂和铆接干涉量不均匀等现象，影响铆接质量和连接件力学性能。为此，本项目利用超声振动塑性成形技术在降低金属变形抗力、改善成形性能方面的积极作用，将超声振动引入了传统压铆工艺中，建立了钛合金超声振动辅助铆接成形工艺。（1）进行了钛合金超声振动辅助压缩实验，分析了钛合金在超声振动辅助塑性成形中的材料变形机理和表面减摩机理，结果表明超声振动可以降低钛合金流动应力和表面摩擦系数，导致晶粒的细化和孪晶的减少，超声振动降低流动应力的主要机制为超声软化和应力叠加效应；（2）改进了Johnson-Cook模型，建立了超声振动下钛合金本构关系，能够在实验应变范围内准确计算变形应力；（3）建立了超声振动辅助铆接成形过程的有限元仿真模型，分析了材料流动、应力应变分布及铆接后的残余应力和铆接干涉量分布，结果表明超声振动可以减小铆接力，降低了镦头处最大剪应力和铆接件残余拉应力，其分布也更为均匀；（4）搭建了超声振动铆接成形实验平台，研究了钛合金铆钉超声振动铆接成形过程中材料流动行为、塑性成形性能和微观组织结构演行为，结果表明超声振动能够提高铆接干涉量，提高了铆接构件连接强度。（5）本项目为钛合金铆钉的铆接成形提供了一种新的成形方法，提高了铆接构件的连接强度合服役性能，为改工艺的发展和工程应用提供了理论支持。