钛合金薄板自冲铆接头微动疲劳机理研究

Titanium alloy sheets have been applied emphatically in aeronautical and space engineering fields. There is an increasing need to develop new techniques for joining titanium alloy sheets that are hard to weld. Self-piercing riveting (SPR) is one of potential joining techniques. As a result of the specific characteristic of SPR process, high stress areas often occur around riveted point. The fretting wear will initiate from these areas under complicated unsteady load condition and lead to final fretting fatigue failure. This project deals with critical fretting fatigue characteristics of titanium alloy sheets SPR joints. Influences on the fretting fatigue life properties of the titanium alloy sheets SPR joints caused by variations in the geometry parameters, materials parameters and processing parameters of the joints will be investigated based on riveting process tests, static tests, full fatigue life tests and staged fatigue life tests. The micro-structure of typical cross-section of the titanium alloy sheets SPR joints will be studied qualitatively by infrared thermal imaging system and ultrasonic flaw detector. The composition of the fretting debris will be analyses quantitatively using scanning electron microscopy and photo-electric spectrometer to understand the position and seriousness of fretting wear and further to study the fretting fatigue mechanism of the joints. Fretting fatigue crack initiation and propagation processes will also be numerical simulated using non-linear finite element methods. Finally a numerical model will be established based on the theoretical and experimental results for predicting the fretting fatigue life of the titanium sheet materials SPR joints.

钛合金薄板广泛用于航空航天领域，但因其焊接性能不好，故急需开发连接新技术，自冲铆接技术是最有应用前景的新技术之一。自冲铆接工艺的特点决定了在铆接点附近易出现高应力区域，在复杂变载条件下易产生微动磨损最终导致微动疲劳失效。本课题针对钛合金薄板自冲铆接技术急需解决的关键问题进行研究，用钛合金薄板进行自冲铆接实验、静力学实验、全寿命疲劳实验及阶段寿命疲劳实验，研究几何参数、材料参数、过程参数对接头微动疲劳寿命的影响；采用红外热像仪和超声波扫描显微镜对试件铆接截面进行显微组织结构定性分析；采用SEM和光电子能谱仪进行材料微区成分的定量分析，弄清微动磨损产生的具体位置及程度，进而探索钛合金薄板自冲铆接头微动疲劳机理；采用有限元方法对自冲铆接头微动疲劳裂纹萌生及扩展过程进行数值仿真，最终在理论分析、实验和仿真的基础上建立钛合金薄板自冲铆接头微动疲劳寿命预测模型。

钛及钛合金因其具有诸多独有优势，在航空航天等领域应用广泛，但其焊接性能相对较差，尤其是与异种薄板连接时，因而急需开发钛合金薄板材料连接新技术。自冲铆接技术为此提供了全新的解决思路，能够有效地解决钛合金薄板同种或异种薄板材料组合的连接问题。自冲铆接工艺的特点及其接头受载特点决定了在铆钉与板材连接点附近易出现高应力区域，在复杂变载条件下易产生微动磨损，并最终导致疲劳失效。本课题针对钛合金自冲铆接技术急需解决的关键问题进行系统研究，以钛合金同种板材及其与其他板材组合进行自冲铆接工艺试验、静力学试验、全寿命疲劳试验及阶段疲劳试验，研究铆接工艺参数与板材参数对自冲铆接头疲劳性能的影响；采用SEM对失效接头进行微观断口分析，探究疲劳失效机理，并对微动磨屑层厚度进行定量分析；采用EDX对失效接头的微动磨屑进行定性与定量分析；采用白光干涉仪探究自冲铆接头在不同疲劳载荷下及不同疲劳寿命阶段的微动磨损情况，弄清微动演化机制；基于有限元方法对自冲铆接头的成形过程、疲劳失效及微动区域进行数值模拟，建立自冲铆接头疲劳寿命预测模型。