In this work, we sought to provide a deeper understanding of the energy-absorbing capabilities of cast lattice structures. These structures absorb large amounts of energy via plastic deformation, but their most attractive characteristic from a structural standpoint is the favorable energy absorption-to-weight ratio. Conventional machining techniques are not well suited for manufacturing such complex features; therefore, we combined additive manufacturing (AM) with a well-known understanding of the metalcasting process. We used AM to produce sand molds in different sizes and with additional features for various applications — these molds were then filled with molten metal. Current literature suggests that this when appropriately applied, this methodology results in complex geometries castings comparable properties to parts made with traditionally produced sand molds. We chose to study periodic lattice structures for their repeatability and subsequent ease of making predictions via computer simulations. We first produced lightweight cast metal-ceramic composite panels of 225 x 225 x 60 mm. Our AM molds included provisions to install ceramic or hard metal tiles before pouring the molten metal. The tiles were encapsulated in the final casting to yield a composite structure. The initial material selection consisted of an aluminum A356-T6 alloy matrix with silicon carbide tiles. The composite lattice structures were tested against high-velocity projectiles — 0.30 caliber armor-piercing (AP M2) and NATO 7.62 mm ball rounds. We anticipated that the metal matrix alone would not be able to defeat these threats. However, the panels did reduce the striking velocity by approximately 20%. The thickness of the ceramic tiles varied from 4 mm to 8 mm at 2 mm increments. As expected, the hard ceramic tiles proved effective at improving the penetration resistance of the composite lattice structures — the impacts on regions with 4 mm thick tiles resulted in the reduction of striking velocity up to 49%; moreover, as the thickness was increased to 8 mm, the panels defeated the projectiles. We used these results to produce and validate a finite element (FE) model capable of replicating the experimental data within 5%. This model was later used to study how the ceramic material interacts with the lattice to absorb large amounts of kinetic energy from incident projectiles. Following, we manufactured smaller versions of these panels—50 x 50 x 90 mm test specimens for uniaxial compression testing for this instance. Once again, we relied on the capabilities of the FE method to replicate the test results within 10% for peak load and maximum displacement. We utilized computer simulations to optimize the design of the lattice structure. Its energy-absorbing capabilities were improved significantly — in this case, a 30% increase in the specific internal energy (internal energy per unit mass) as the evaluating criteria. The FE model was also used to study the performance of several other truss topologies. Lastly, we used computer simulations to evaluate the feasibility of making these cast lattice structures with ferrous alloys. We chose to work with Fe30Mn4Al0.9C due to its lower density and higher toughness than other steel grades. The first challenge was the lack of thermophysical property data in the literature for this alloy system. Hence, we used the CALPHAD method to calculate all the datasets needed to perform the mold filling and solidification simulation. Several of these calculations were validated experimentally. The location and severity of porosity between the model and the casting were in good agreement. / Doctor of Philosophy / The advent of additive manufacturing (AM), commonly known as 3D printing is a group of different digital-era technologies that has facilitated the production of complex designs that are not feasible to manufacture using conventional techniques. In the realm of metallic components one such technique involves the use of a laser beam to consolidate metallic powders via a layer-by-layer deposition process. Despite its advantages, this process has unique challenges, such as limited material selection and relatively small part volume. In this work, we have employed a hybrid approach that combines the use of AM with expertise in metalcasting to produce lightweight components with complex geometries. We used 3D printed sand molds that are then filled with molten metal of different alloy systems such as aluminum and steel. At first, we incorporate hard ceramic materials to increase the performance of the final parts under ballistics testing. Our aim is to upscale the size of current designs such that these devices can be used in various applications that require high absorption of kinetic energy, and that are lightweight and easy to replace.

L'objectif de cette thèse était de développer et de caractériser la microstructure et les propriétés mécaniques des céramiques bio-inspirées. L'alumine inspirée par la nacre fabriquée par texturation à la glace (freeze-casting), précédemment développée dans le cadre de la thèse de F. Bouville, a été choisie comme matériau de référence. La simplification et le changement d’échelle du procédé d’élaboration des matériaux ont été étudiés. Le procédé sophistiqué de freeze-casting a été remplacé par le pressage uniaxial à cru. Les mesures de diffraction des électrons rétrodiffusés ont confirmé le bon alignement après frittage des plaquettes d'alumine utilisées pour préparation du matériau. Le cycle de frittage assisté par effet de champs a été adapté à de plus grandes quantités de poudre céramique et d'additifs organiques. La deuxième partie du projet a été consacrée à la modification de l'interphase entre les plaquettes d'alumine, afin d’améliorer les propriétés mécaniques du matériau. Diverses possibilités ont été explorées: ajout de poudre de zircone, dépôt de zircone sur les plaquettes par réaction sol-gel ou substitution de la phase vitreuse par du graphène. Tous les matériaux obtenus ont été caractérisés par flexion quatre points sur des barrettes entaillées. La troisième partie de cette étude a porté sur le développement de composites multicouches métal/céramique, par frittage simultané d'alumine et de titane. L'épaisseur et la composition de la feuille de titane ont été modifiées pour étudier leur influence sur les phénomènes de diffusion lors du frittage. Les composites ont été caractérisés par MEB, EBSD, spectroscopie à rayons X à dispersion d'énergie et tomographie à rayons X au synchrotron. La fabrication simplifiée des matériaux permet de préparer des échantillons de plus grandes dimensions de céramiques inspirées par la nacre, sans passer par une étape de freeze-casting. Cependant, la croissance des grains doit être limitée pour maintenir de bonnes propriétés mécaniques. La modification de l'interphase entre les plaquettes d'alumine n'a pas amélioré les propriétés mécaniques des matériaux par rapport au matériau de référence. D'autre part, le dépôt de nano-zircone sur la surface des plaquettes semble prometteur et devrait faire l'objet d'études plus poussées. Dans le cas des composites alumine/titane, les composites architecturées multiéchelles ont été fabriqués de manière assez simple. Cependant, il est crucial d'éviter la fissuration des feuilles de métal afin d’améliorer les propriétés mécaniques. / The goal of this thesis was to develop and characterize the microstructure and the mechanical properties of bioinspired ceramic composites. Nacre-like alumina fabricated by freeze-casting previously developed in Bouville thesis was chosen as a reference material. Simplifying and up-scaling material fabrication was intended. Architectural levels were added to the microstructure to further improve mechanical properties of the material. Sophisticated processing by freeze-casting was substituted by uniaxial pressing. Electron backscatter diffraction observations confirmed the good alignment of alumina platelets used to prepare the material. The field assisted sintering cycle was adapted to greater quantities of ceramic powder and organic additives. The second part of the project was dedicated to the modification of the interphase between alumina platelets. Various possibilities were explored: adding fine zirconia powder, depositing zirconia on the platelets by sol-gel reaction, or substituting the glassy phase by graphene. All obtained materials were characterized by four point bending on notched bars. The third part of this study was focused on the development of multilayered metal/ceramic composites, by simultaneous sintering of alumina and titanium. The titanium foil thickness and composition were varied. The composites were characterized by SEM, EBSD, energy dispersive X-ray spectroscopy and synchrotron X-ray tomography. Detailed microstructural and chemical characterization was performed to understand mechanisms of titanium diffusion into ceramic matrix. Simplified material fabrication allows to prepare larger samples of nacre-like ceramics. However grain growth should be limited to maintain good mechanical properties. Modification of the interphase between alumina platelets did not improve mechanical properties of the materials as compared to the reference material. On the other hand, depositing nano-zirconia on platelets surface seems promising and should be further investigated. In case of alumina/titanium composites, a multiscale architecture composites were process in a rather simple way. However, avoiding metal foil cracking is crucial to improve mechanical properties.