CRACKAR · Off-axis crack arrest by harnessing micro- and mesostructural design

Off-axis cracks are the first and most crucial design-limiting damage in composites, but studying their initiation and propagation is very challenging, causing a lack of understanding. Bio-inspiration is a powerful strategy to design new materials by circumventing the intricate interactions between structure and damage development. However, this strategy often fails to recreate the complex, multiscale nature of natural materials, does not fully consider the very different constituent properties, and, most importantly, limits the design space.CRACKAR thus takes a different path: it aims to (1) develop a fundamental understanding of off-axis crack initiation and propagation and (2) exploit this new understanding to arrest off-axis cracks by designing and manufacturing patterned laminates. We will first characterise off-axis crack development in situ by combining multiprojection imaging at MHz rates with a slower 3D technique down to 150 nm voxel size. These techniques, never or rarely applied to composites, can deliver unique, currently inaccessible insights. Applying them to crack initiation and propagation in conventional laminates will set the foundations to unravel the root causes. This is supported by the development and experimental validation of an efficient 3D numerical model that bridges the micro- and mesoscale via deep learning. Once validated, genetic algorithms will mimic evolutionary trial-and-error to optimise the established working principles and maximise crack arrest. The designed patterns will then be manufactured using a novel, scalable imprinting process or established processes such as tailored fibre placement and laser cutting.CRACKAR will showcase that careful experimental validation of a multiscale model can revolutionise mechanistic understanding. This achievement would yield profound gains for composites and materials research as a whole, enabling us to tailor the material to the loading scenario.