钛合金薄板自冲铆接工艺及失效行为研究

Process and Failure Behaviors of Self-piercing Riveting in Titanium Alloy Sheets

基于自冲铆接(SPR)技术,从降低板材硬度和提高铆钉硬度两个角度,实现了对TA1钛合金薄板的有效连接,并制备了TH(降低板材硬度)和TR(提高铆钉硬度)两组钛合金自冲铆接头。通过力学试验研究了两组接头的静力学和疲劳性能,并且基于三参数经验公式采用S-N曲线拟合法绘制出接头S-N曲线。最后,从宏观角度分析两组接头的失效行为,并利用高真空扫描电镜(SEM)进行TR接头的微观断口分析。结果表明:从自冲铆接技术优势和工程实际角度考虑,TR接头的铆接方式比TH接头更具实际操作意义。TH接头的静失效载荷和能量吸收性能均优于TR接头;且两组接头的静力学失效形式均为铆钉断裂。而TR接头疲劳性能更优,且两组接头均出现了下板断裂和铆钉断裂的多种疲劳失效形式。此外,依据SEM观测结果推断出因下板断裂而失效的TR接头,其疲劳裂纹源于铆钉脚应力集中点,且首先沿板宽方向扩展,后沿板厚方向延伸,直至接头完全断裂失效。而因铆钉断裂而失效的TR接头,其断口呈现出典型的疲劳脆性断裂特征。

Based on self-piercing riveting(SPR) technology, the effective connection for TA1 titanium alloy sheets is realized. And TH and TR joints are fabricated with reducing the sheet hardness and raising the rivet hardness, respectively. The static and fatigue performances are studied, and the S-N curves are fitted using the S-N curve fitting method. Finally, the failure behaviors of the joints are analyzed in a macro perspective, and the micro fracture analysis for TR joints is conducted with a scanning electron microscope(SEM). The results showed that: TR joints are more practical than TH joints. The peak load and energy absorption value of TH joints are superior to those of TR joints, and their static failure modes are all rivet fracture. TR joints had a better fatigue performance than TH joints, they both failed because of locked sheet fracture or rivet fracture. Furthermore, it can be referred that the fatigue cracks of TR joints, which failed due to locked sheet fracture, initiated at the stress concentration point of the rivet feet, and extended along the sheet width direction first, and then along the thickness direction of the plate until the joints are completely broken. And the rivet fracture surfaces of TR joints are the typical fatigue brittle fracture characteristics.