Integrated Computational-Experimental Study of Microstructurally Short Crack Propagation in AA7xxx alloys

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New generation 7xxx series Al alloys are commonly used material in aircraft structural applications due to their high specific strength and low production costs. However, these alloys exhibit an increased susceptibility environmentally assisted cracking (EAC) which needs to be better understood. The EAC performance of these alloys is thus an area of growing concern for the aerospace industry.The critical early stages of EAC is currently poorly understood with little published data. This project will thus aim to improve understanding of the initiation of cracks and specifically how microstructurally-short cracks grow, and their transition to a viable long crack which may go on to cause failure. During the short-crack phase, growth is dominated by the specific crack-front geometry and microstructural interactions, such as neighbouring cracks and grain boundaries. However, existing models for short-crack driving forces neglect these details and are thus limited in their predictive capability.The aim of this project is to refine the existing crack growth models, by considering the spatially-resolved crack-front geometry and microstructural interactions. Temporally and spatially resolved 3D X-ray computed tomography (CT) data of crack propagation from state-of-the-art in-situ testing will be directly imported into FE simulations to obtain the crack tip stress field and a local description of crack-front driving forces. The objective is to complement existing global crack-propagation models with local microstructural detail. This will provide insight into why some cracks propagate to form long cracks whilst other cracks arrest whilst they are still small, and why in some cases the growth of arrested cracks restarts.