The Fatigue Crack Propagation Delay Behavior in 2024-T3Aluminum Alloy Due to Single Overload/Underload Sequences.

摘要

The fatigue crack delay behavior due to single overload/underload sequences was studied in center crack panel specimens of 2024-T3 aluminum alloy. The applied loading consisted of constant amplitude loading, an applied overload immediately followed by an underload and then constant amplitude loading at the pre-overload level. The loading parameters investigated are the stress intensity ratios, overload level to maximum fatigue level, underload level to overload level, and minimum fatigue level to overload level. The results show that increasing the amount of underload decreases the number of delay cycles. Also, it is shown that the number of delay cycles is directly related to the minimum growth rate following the overload. The concept of crack closure is extended to include the effects of the overload/underload sequence. From this the maximum value of the opening stress intensity level and the minimum growth rate are determined. This is used to predict the number of delay cycles.