EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Unlike synthetic ceramics which are brittle and thus prone to catastrophic failures, biological materials have found ways to combine both stiffness and toughness. Nacre, for example, is composed of 95 vol.% brittle calcium carbonate, yet exhibits a fracture energy 3 orders of magnitude higher than its principal component. This toughness amplification finds its root in nacre’s brick-and-mortar architecture as it provides multiple toughening mechanisms acting at different length scales. For this reason, nacre has become a well-studied blueprint for composite manufacturing to improve the toughness of synthetic ceramics. We are now able to accurately reproduce at similar length-scale the brick-and-mortar architecture of nacre with processes such as magnetically assisted slip casting (MASC). MASC combines the controlled alignment of anisotropic platelets decorated with superparamagnetic nanoparticles under low intensity magnetic field with the consolidation offered by slip casting. Using this process and others, nacre-like composites (NLCs) of various compositions have been successfully developed recently. However, if the reinforcing mechanisms acting in biological nacre have been intensely studied, they are still not well understood in NLCs, especially in fully ceramic-based NLCs. In fully ceramic-based NLCs, the complexity of the highly deflected crack paths makes it difficult to evaluate fracture properties using the standard tools of fracture mechanics. In order to better describe the stable propagation of multiple deflected cracks observed in ceramic NLCs, we are investigating different fracture characterization formulations based on mixed-mode stress intensity factors. Our findings are compared with finite element analysis as well as experimental data obtained from in situ mechanical testing on an alumina/aluminium borate NLC. This new tool gives way to a clearer understanding of crack propagation in NLCs and will help us find even more effective tuning of their mechanical properties.