Reply to the correspondence: "On the fracture toughness of bioinspired ceramic materials"

This is a reply to the correspondence of Prof. Robert Ritchie: "On the fracture toughness of bioinspired ceramic materials", submitted to Nature Materials, which discusses the fracture toughness values of the following papers: Bouville, F., Maire, E., Meille, S., Van de Moort\`ele, B., Stevenson, A. J., & Deville, S. (2014). Strong, tough and stiff bioinspired ceramics from brittle constituents. Nature Materials, 13(5), 508-514 and Le Ferrand, H., Bouville, F., Niebel, T. P., & Studart, A. R. (2015). Magnetically assisted slip casting of bioinspired heterogeneous composites. Nature Materials, 14(11), 1172-1172.Comment: 5 pages, 2 figure

Magnetically assisted assembly of bioinspired composites

Heterogeneous composites with intricate microstructures can be found widely in nature fulfilling the functional demands imposed by their environment. Reaching this level of intricacy in synthetic composites remains a challenge due to the lack of suitable and easily available processing tools. We present a new method to produce bioinspired composites with a broad variety of locally controlled composition, texture and shape using low magnetic fields. Nacre-like all-ceramic, polymer-ceramic and metal-ceramic composites with volume fractions of ceramic phase spanning from 40 to values as high as 95 vol% are achieved. By mixing magnetically responsive alumina microplatelets with ceramic nanoparticles, we can also control the amount and the density of contact points between adjacent aligned platelets in scaffold structures. Depending on the choice of the secondary phase for these scaffolds we can create composites with remarkable fracture resistance combined with interesting additional functionalities, such as electrical conductivity and temperature resistance. This technique expands the current set of processing tools for the fabrication of bioinspired composites with an unprecedented architectural control

Inorganic/inorganic composites through emulsion templating

Inorganic/inorganic composites are found in multiple applications crucial for the energy transition, from nuclear reactor to energy storage devices. Their microstructures dictate a number of properties, such as mass transport or fracture resistance. There has been a multitude of process developed to control the microstructure of inorganic/inorganic composites, from powder mixing and the use of short or long fibre, to tape casting for laminates up to recently 3D printing. Here, we combined emulsions and slip casting into a simpler, broadly available, inexpensive processing platform that allow for in situ control of a composite's microstructure that also enables complex shaping. Emulsions are used to form droplets of controllable size of one inorganic phase into another, while slip casting enable 3D shaping of the final part. Our study shows that slip casting emulsions trigger a two-steps solvent removal that opens the possibility for conformal coating of porosity. By making magnetically responsive droplets, we form inorganic fibre inside an inorganic matrix during slip casting, demonstrating a simple fabrication for long-fibre reinforced composites. We exemplify the potential of this processing platform by making strong and lightweight alumina scaffolds reinforced by a confirmed zirconia coating and alumina with metallic iron fibres that displays work of fracture an order of magnitude higher than alumina

Collaborative Virtual Training with Physical and Communicative Autonomous Agents

International audienceVirtual agents are a real asset in collaborative virtual environment for training (CVET) as they can replace missing team members. Collaboration between such agents and users, however, is generally limited. We present here a whole integrated model of CVET focusing on the abstraction of the real or virtual nature of the actor to define a homogenous collaboration model. First, we define a new collaborative model of interaction. This model notably allows to abstract the real or virtual nature of a teammate. Moreover, we propose a new role exchange approach so that actors can swap their roles during training. The model also permits the use of physically based objects and characters animation to increase the realism of the world. Second, we design a new communicative agent model, which aims at improving collaboration with other actors using dialog to coordinate their actions and to share their knowledge. Finally, we evaluated the proposed model to estimate the resulting benefits for the users and we show that this is integrated in existing CVET applications

Templated Grain Growth in Macroporous Materials

We demonstrate a facile method to produce crystallographically textured, macroporous materials using a combination of modified ice templating and templated grain growth (TGG). The process is demonstrated on alumina and the lead-free piezoelectric material sodium potassium niobate. The method provides macroporous materials with aligned, lamellar ceramic walls which are made up of crystallographically aligned grains. Each method showed that the ceramic walls present a long-range order over the entire sample dimensions and have crystallographic texture as a result of the TGG process. We also present a modification of the March-Dollase equation to better characterize the overall texture of materials with textured but slightly misaligned walls. The controlled crystallographic and morphologic orientation at two different length scales demonstrated here can be the basis of multifunctional materials.Comment: 14 pages, 7 figures, 19 reference