SHORT FATIGUE CRACK-GROWTH IN AL-2024-T3 AND AL-7075-T6

Short fatigue crack growth behavior was investigated. The crack growth was monitored using a replica technique for cracks propagating on the specimen notch from an initial length of 40-50 mum to the specimen thickness of 2.3 mm. As part of the AGARD round robin test program Al 2024-T3 and Al 7075-T6 specimens with semi-circular notches on one edge were tested under R-ratios of 0.5, 0, -1 and -2. For each R -ratio several stress levels were used. In order to compare the behavior of short and long cracks, their crack growth rate data were drawn on the same graph. The general conclusion for both aluminum alloys is that the growth rates of short cracks were faster than the rates of long cracks for R-ratios of -1 and -2, no significant differences were observed for R = 0, and the short cracks actually grew more slowly at R = 0.5.