In-situ characterisation and data-driven crystal plasticity analysis of short-to-long crack transition in a ductile aluminium alloy

Abstract: Crack arrest in ductile alloys plays a critical role in damage-tolerant design for aerospace and structural applications, yet the transition from microstructure-sensitive short cracks to load-controlled long cracks remains poorly understood. Here, we present an in-situ, high-resolution experimental study of crack propagation in cold-worked 5052 aluminium alloy using scanning electron microscopy digital image correlation (SEM-DIC), electron backscatter diffraction (EBSD), and novel data-driven crystal plasticity modelling that uses the SEM-DIC and EBSD directly to calculate the stress. The local (elastic) mode I and II stress intensity factors (SIFs) and the (elastic and elastoplastic) energy release rate were extracted from the DIC-measured displacement field and correlated with the crack interaction with microstructural features. We find that the microstructure-sensitive crack grows in a quasi-brittle manner at low energy release rate until reaching a critical energy release rate, where the crack's process zone becomes large enough to invoke plastic deformation that blunts the crack, marking a transition from elastically driven microstructure-sensitive crack propagation to plasticity-dominated crack arrest. Our findings establish that the short-to-long crack transition is process-zone governed, rather than being length-scale governed.