钛铝异质自冲铆接头疲劳性能及失效机理

对纯钛(TA1)和铝锂合金(AL1420)异质单搭自冲铆接头进行静力学实验和疲劳实验研究,通过三参数经验公式采用S-N曲线拟合法绘制接头的S-N曲线,分析接头的疲劳性能;采用扫描电子显微镜对接头疲劳断口进行观测,研究接头的微观疲劳失效机理.结果表明:接头的静力学性能与疲劳性能不具有一致性,TA1-AL1420(TA)接头静力学性能更优,但其疲劳性能比AL1420-TA1(AT)接头差;TA接头疲劳失效形式为下板断裂,疲劳裂纹萌生于靠近铆钉脚处的板材区域,随后沿着板宽方向扩展,最终导致下板完全断裂.AT接头在短寿命区因铆钉断裂失效,铆钉的断口属于脆性疲劳断裂;在中长寿命区出现铆钉断裂和下板断裂的混合失效形式,疲劳裂纹从下板一端萌生,沿着板宽向另一端方向扩展,导致下板断裂失效.

Fatigue properties and failure mechanisms of self-piercing riveted joints in titanium and aluminum alloy dissimilar sheets

A static test and fatigue test of dissimilar single-lap self-piercing riveted joints were conducted for pure titanium (TA1) and aluminum-lithium alloy (AL1420). The fatigue performance of the joints was analyzed on the basis of the S-N curves; specifically, a fitting method was used to construct the S-N curves of the joints using three empirical parameters. Scanning electron microscopy was used to study the fatigue fracture surfaces of the joints and the microfatigue failure mechanism of the joints. The results indicate that the static performance and fatigue characteristics of the joints are inconsistent:the TA1-AL1420(TA) joint exhibits better static performance, whereas its fatigue characteristics are worse than those of the AL1420-TA1(AT) joint. The fatigue failure mode of the TA joint for the lower sheet is fracture; the fatigue crack appears in the sheet area around the rivet tail and extends along the width of the sheet, leading to complete fracture of the lower sheet. The loss of efficacy of the AT joint in the short-life region is related to fracture failure of the rivet, which exhibits brittle fatigue fracture. A mixed failure mode of rivet fracture and lower sheet fracture occurs in the middle-long life region, and a fatigue crack appears from one side of the lower sheet, extends along the width of the sheet to the other direction, and eventually lead to the failure of the lower sheet.