Variability of fatigue crack growth properties for 2024-T3 aluminium alloy

Abstract

Discussions between D-BAA and the NLR have shown that significant variability in fatigue crack growth properties is possible for the industry standard damage tolerant aluminium alloy, 2024-T3 sheet. This is important for two reasons: (1) design assumptions and (2) comparisons of different candidate materials, such as 6013-T6, with 2024-T3. Another important topic is the possibility of changes in damage tolerance properties owing to long term natural ageing. In this report a comparison was made between 2024-T3 aluminium alloy sheet crack growth obtained from two NASA reports (from 1958 and 1959) and an NLR report (from 1966) to examine batch to batch variability of fatigue crack growth rates. Two other NASA reports (from 1969 and 1988), which refer to test specimens from the same batch of material, were used to determine if there is any long term natural ageing effect on fatigue crack growth properties. From the results it can be concluded that: 1. There is a significant effect of long term natural ageing on crack growth properties of 2024-T3. 2. Significant variability in fatigue crack growth properties is possible for different batches of 2024-T3. 3. The effect of long term ageing is less than or similar to the effect of batch-to-batch variation. 4. The effect of cycle frequency has to be considered even when tests are done in laboratory air.