Fundamental Investigation of Fatigue Crack Growth Retardation in Aluminum Alloys

摘要: Abstract : A fundamental investigation was performed to determine the important metallurgical and environmental factors that influence retardation behavior in aluminum alloys. The phenomenon found be very complex dependent on loading variables as well material parameters. results suggest a phenomenological model for prediction of fatigue-crack growth under variable amplitude can developed by taking various parameters into account. Of four alloys investigated (2024-T3, 2024-T8, 7075-T6 7075-T73), alloy with lowest yield strength, 2024- T3, give maximum delay. were cyclic-hardening exponent, microstructure. Overload ratio (OLR) most test-parameter. An increase OLR always produced an increased retardation. Crack-arrest occurred at either 2.5 or 3.0 depending baseline stress-intensity (Kmax). For SEN specimens, no significant changes crack-closure detected cycling progressed after overload cycle. cycle manifests itself stretch band fracture surfaces specimens. width zone increases Kmax decrease thickness. specimens discernible striations, correlation between measured da/dN striation spacing good. optical interference technique good agreement plastic-zone calculated plane-stress conditions.