Effect of Microstructure on Fatigue Damage Accumulation in 7075 Aluminum Alloy Subjected to a Single Compressive Overload

Abstract

7075 aluminum alloy has been widely used because of its excellent mechanical properties. The fatigue crack acceleration induced by compressive overloading is detrimental to 7075 aluminum alloy in service, and the corresponding mechanisms are complex. To further reveal these mechanisms, the effect of microstructure on fatigue damage response ahead of the crack tip is simulated based on the damage-coupled crystal plasticity model for 7075 aluminum alloy. Results show that the ratchetting strain ahead of the crack tip at the compressive overload ratio of −3 is greater than that at the compressive overload ratio of −2, which is attributed to the fact that higher compressive overloading induces greater tensile residual stress ahead of the crack tip. The proportion of material points with no less than four activated slip systems increases after compressive overloading, indicating the number of activated slip systems ahead of the crack tip increases because of the compressive overload effect. This causes the dislocation multiplication rate to be faster, thereby accelerating the fatigue damage accumulation after compressive overloading. Furthermore, the effect of compressive overload changes the slip system activity, and this change in slip system activity depends on grain orientation. It is also found that for a grain ahead of the crack tip, the acceleration of fatigue damage accumulation caused by the effect of compressive overload is influenced by the orientation of its nearest neighbor grains. The findings provide further insight into the acceleration mechanisms induced by the compressive overload effect from a microscopic perspective.

Keywords

• 7075 aluminum alloy
• fatigue crack-acceleration mechanisms
• compressive overload effect
• crystal plasticity
• low-cycle fatigue damage