Micro-nanoscale strain fields around the crack tip of 2024 aluminum alloy

Aluminum alloy 2024 is widely used in aerospace and automobile manufacturing due to its high specific strength, plasticity and good welding performance. The quantitative characterization of the micro-nanoscale deformation fields near the crack tip during the crack propagation is crucial for understanding the fracture mechanical behaviors. In this study, cross-gratings with a frequency of 10,000 lines/mm were prepared on the surface of the 2024 aluminum alloy using scanning electron microscopy (SEM). The strain distribution in the range beyond 100 nm from the crack tip under load was investigated using geometric phase analysis (GPA) method and compared with the theoretical and simulated predictions. The results indicate that at a stress of 0.01 (the lowest load), the experiment converge with the linear elastic fracture mechanics (LEFM) and simulated results in the range beyond 770 nm from the crack tip. At stress levels of 0.04 and 0.14 (the higher loads), the errors of plastic zone at the crack tip between Irwin plasticity model predictions and experimental results are within 5.5%. The strain distribution observed experimentally is consistent with the predictions of LEFM outside the theoretical plastic zone at the crack tip, thereby confirming the applicability of both EPFM and LEFM for characterizing deformation fields at the crack tip of aluminum alloy at the micro-nanoscale.