Multiscale experimentation & modeling of fatigue crack development in aluminium alloy 2024.

The objective of this research project is to be able to understand the role of various microstructural features on Fatigue Crack Initiation (FCI) of metallic alloys. By employing a novel experimental set-up, mechanical testing was performed in situ within an SEM chamber, and the deformation of the individual grains was observed real time. A physically-based Crystal Plasticity (CP) model was then developed that accurately predicts the macro and micro mechanical behaviour for Al2024 T3. An experimentally informed FCI criterion was developed that accounts for the effect of local slip bands and the applied local strains. While ‘precious’ insights were given on the small crack growth regime observing the occurring microscale phenomena.
FCI is a multiscale process and thus evaluating the microscale does not cover fully the understanding of local deformation and damage. Thus a multiscale DIC process was employed to better understand the macro and mesoscale as well. 3D Digital Image Correlation (DIC) was employed and the strain distributions (at the sample scale) were obtained for various loading conditions. High magnification camera based 2D DIC was then used and the strain measurements were also extracted at clusters of grains. Useful observations were given for the different strain components (εxx, εyy, εxy). Finally the total fatigue lifetime of the component was compared to the modeled FCI for various loading conditions.