CRACK-GROWTH RETARDATION DUE TO INTERMITTENT OVERLOADS

Fatigue crack propagation in the presence of isolated tensile overloads is known to lead to retardation which is a strong function of the overload severity. As overloads are applied closer to each other they start to interact. Based on the open literature, it is not possible yet to predict the growth rate under intermittent overloads from a knowledge of single-overload behaviour. Experiments on 7075 Al alloy revealed that retardation is a maximum when overloads are applied at 1 2NrrD* cycles where ND* is the number of cycles of retarded growth in a single-peak overload test. For other periodic applications the retardation can be predicted based on the information supplied. The analysis is limited to cases where ductile tearing during overloads is negligible compared to crack growt between overloads. © 1990.