缺口应力集中对5083-H111铝合金超高周疲劳性能的影响

为正确评价超高周范围内带缺口的5083-H111铝合金疲劳强度的降低程度和疲劳强度对缺口的敏感程度，用20kHz的超声疲劳实验技术分别对漏斗形光滑试件、缺口（2种）试件进行了105~1010周次的对称拉压超声疲劳实验，并用扫描电镜分析了疲劳断口形貌。结果表明:在1010周次内，光滑和缺口试件疲劳曲线分别表现出极限平台型和连续下降型特征，缺口显著降低了5083-H111铝合金的疲劳性能；绝大部分试件疲劳裂纹萌生于表面，断口上没有观察到鱼眼形貌特征。理论应力集中系数为1.94的试件疲劳弧线成凹形，理论应力集中系数为2.90的试件裂纹源分布在断口四周；不同的疲劳裂纹萌生机制使得缺口应力集中对疲劳性能的影响规律不同，对于只有一种表面裂纹萌生机制的5083-H111铝合金，超高周范围内疲劳缺口系数和疲劳缺口敏感系数均随着疲劳寿命的增加而增加。 

Influence of Notch Stress Concentration on Fatigue Properties of 5083-H111 Aluminum Alloy in Very High Cycle Regime

In order to correctly evaluate the reduction and sensitivity of fatigue strength to a notch of 5083-H111 aluminum alloy specimen in very high cycle regime, very high cycle fatigue tests were carried out by ultrasonic fatigue technique at a frequency of 20 kHz, using symmetric tension-compression loading within 105-1010 cycles for hourglass-type smooth specimens and two types of notched specimens. The scanning electron microscope (SEM) was used for analysis of the fracture morphology. The experimental results show that the S-N curves exhibited an extreme platform type for the smooth specimens and a continuous decline type for the notched specimens. The fatigue performances of the 5083-H111 aluminum alloy decreased significantly because of the notch stress concentration. Most of the cracks initiated in the surface, but the fish-eye morphology was not found. The macro fatigue striation was concave for the specimen with a theoretical stress concentration factor of 1.94, and the fatigue crack sources were distributed around the fracture surface in specimens with a theoretical stress concentration factor of 2.90. The influence of notch stress concentration on fatigue properties was dependent upon the mechanism of crack initiation. Since only one kind of surface crack initiation mechanism exists in 5083-H111 aluminum alloy, the fatigue notch coefficient and notch sensitivity coefficient increase with increasing number of cycles within the range of 109.