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.