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Superior material properties have been recently exhibited under the concept of biomimetic designs, where the material architectures are inspired by nature. In this study, a computational framework is developed to present novel architectured bi-material structures with tunable stiffness, strength, and toughness to be used for additive manufacturing (AM). The structure of natural nacre is mimicked to design robust multilayered structures constructed from hexagonal brittle and hard building blocks bonded with soft materials and supports. A set of computational models consisting of fully bonded zones, while allowing for interlayer interactions are created to accurately mimic the interplay between the hard and soft organic phases. As required for such complex designs, the numerical constraints are properly set to run quasi-static non-linear explicit analysis, which allow for a 3× faster analysis with higher efficiency and 2× lower computational cost, when compared to static analysis. The models are used to assess the stiffness, strength and toughness of bi-material beams when subjected to a flexural three-point bending load. The influence of structural features like the soft-to-hard volume ratio (i.e. the distance between each building block, its aspect ratio, and overlap length), material features (e.g. the stiffness ratio of the hard-to-soft phases), the plastic strain failure of soft phase, and AM features (e.g. different types of within-layer/sandwiched supports) are systematically investigated. The results revealed that the toughness of the architectured beams was enhanced by up to 25% when compared to a monolithic structure. This improvement is due to the frictional tile sliding in the brittle phase and the extensive shear plastic deformation of the soft interfaces. This work provides compatible designs to facilitate the AM of nacre-based bi-martial structures with balanced/tailored mechanical performance and to understand the influence of the architectural parameters., (© 2022 IOP Publishing Ltd.)

Brittleness is a major limitation of polymer-derived ceramics (PDCs). Different concentrations of three nanofillers (carbon nanotubes, Si 3 N 4 and Al 2 O 3 nanoparticles) were evaluated to improve both toughness and modulus of a commercial polysilazane (PSZ) PDC. The PSZs were thermally cross-linked and pyrolyzed under isostatic pressure in nitrogen. A combination of mechanical, chemical, density, and microscopy characterizations was used to determine the effects of these fillers. Si 3 N 4 and Al 2 O 3 nanoparticles (that were found to be active fillers) were more effective than nanotubes and improved the elastic modulus, hardness, and fracture toughness (J IC ) of the PDC by ~ 1.5 ×, ~ 3 ×, and ~ 2.5 ×, respectively. Nanotubes were also effective in maintaining the integrity of the samples during pyrolysis. The modulus and hardness of PDCs correlated positively with their apparent density; this can provide a fast way to assess future PDCs. The improvement in fracture toughness was attributed to crack deflection and bridging observed in the micro-indentation cracks in the modified PDCs. The specific toughness of the modified PDCs was 4 × higher than that of high-purity alumina, and its specific modulus reached that of commercially available technical ceramics. These PDCs can also easily take different shapes and therefore are of interest in protective armor, propulsion, thermal protection, device packaging and biomaterial systems.