Behavior of plasticity-induced crack closure and roughness-induced crack closure in aluminum alloy

Abstract

For center-cracked tension specimens subjected to constant amplitude loading, fatigue crack closure and crack growth behavior in an aluminum alloy 7050-T7451 were investigated. The specimens were tested with stress ratios of −1.0, 0.0, 0.1 and 0.3 under constant amplitude loading. Plasticity-induced crack closure and roughness-induced crack closure were found to be the main tools for explaining the crack growth behavior under plane strain and plane stress conditions. From a measurement of roughness height distribution of fractured surfaces using a surface profiler, the roughness-induced crack closure was evaluated as the main factor at low stress intensity factor range Δ K. This closure phenomenon was qualitatively predicted using a single asperity model. On the other hand, the plasticity-induced crack closure was the decisive factor at high Δ K and could be predicted by the modified strip-yield model based on a Dugdale model. In the case of concurrence of two crack closures, therefore, the total crack closure behavior with Δ K level for four stress ratios could be described effectively by two closure models, a single asperity model and a strip-yield model.