The effects of pre-cyclic stress on fracture properties and fatigue crack propagation life of 7N01 aluminum alloy

Material properties are of great significance for structural safety. In this paper, the mechanical property tests are described and fatigue crack propagation (FCP) behavior for material that had experienced a certain number (10e7) of pre-cyclic stress (PCS) cycles are analyzed. The results illustrate that the material properties increase with the increase of PCS level for relatively lower PCS, and decrease with further increase of PCS. The FCP experiment shows that the FCP rates of the specimens subjected to PCS become lower than that of the specimen without PCS. 'Turning' points are clearly shown in the FCP rate curves, indicating that the FCP rate in the range of small ΔK is more sensitive to PCS. This paper presents a bi-linear approximation to describe the FCP behavior and predict the FCP life. It is found that the PCS has 'coaxing' effect on material FCP behavior. The fracture morphologies of the material with and without PCS are analyzed to discuss the 'coaxing' effect on microstructures. The PCS decreases the void number and void size in fatigue crack initiation zone, decreases the striation width in FCP zone, and increases the dimple size in final rupture zone.