Navigating Near-Threshold crack growth rate data for aluminium alloy 2024

Understanding and measuring the growth rates of small fatigue cracks is important for the ability to predict fatigue cracks in aircraft structures growing from small naturally occurring discontinuities. RMIT University, in collaboration with the Defence Science and Technology Group, have researched small fatigue cracks in common aerospace aluminium alloys for many years. Near-threshold crack growth rates have been collected for a range of materials, including aluminium alloys 7050-T7451, 7075-T7351 and 7085-T7452. In this paper, near-threshold crack growth rates are examined for aluminium alloy 2024-T351. Specially designed loading sequences were applied to coupons to create distinguishable markings on the fracture surface. Scanning electron microscopes and optical microscopes were utilised to determine crack growth rates. The findings were then compared to the extensive amount of experimental data and analytical methods available in the literature for near-threshold crack growth rates in AA2024 to highlight the differences in results between approaches. This paper presents new experimental data that further enhances the existing experimental data for near-threshold crack growth rate data for AA2024. Additionally, the paper aims to aid the aircraft engineer to navigate the vast amount of experimental data and analytical methods that can be utilised to predict small fatigue crack growth in AA2024 and other commonly used aerospace aluminium alloys.