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The main aim of this thesis is to investigate the manufacturability of different gyroid designs using Selective laser melting (SLM) process . This study paves the way for a better understanding of design aspects, process optimization, and characterization of titanium alloy (Ti6Al4V) gyroid lattice structures for bone implant applications. First, A MATLAB® code was developed to create various gyroid designs and understand the relationship between the implicit equation parameters and the measurable outputs of gyroid unit cells. A novel gyroid lattice structure is proposed, where the porosity is graded in a radial direction. Second, gyroid designs were investigated by developing a permissible design map to help choose the right gyroid parameters for bone implants. Third, response surface methodology was used to study the process-structure-property relationship and understand the effect of SLM process parameters on the manufacturability of Ti6Al4V gyroid lattice structures. Laser power was found to be the most significant factor affecting the errors in relative density and strut size of gyroid structures. A volumetric energy density between 85 and 103 J/mm3 induces the least errors in the gyroid’s relative density. Fourth, the quasi-static properties of the novel designs were compared to uniform gyroids. The proposed novel gyroids had the highest compressive strength reaching 160 MPa. Numerical simulations were studied to give insight into how manufacturing irregularities can affect the mechanical properties of gyroids. Last, an in-depth defect analysis was conducted to understand how SLM defects may influence the fatigue properties of different Ti6Al4V gyroids. Thin struts have less internal defects than thick ones; thus, they show less crack propagation rate and higher normalized fatigue life. These favorable findings contributed to scientific knowledge of manufacturability of Ti6Al4V porosity graded gyroids and determined the influence of SLM defects on the mechanical properties of gyroid designs for bone implants. / Thesis / Doctor of Philosophy (PhD) / This thesis studies the integration of design aspects, SLM manufacturability, and mechanical characterization of Ti6Al4V gyroid lattice structures used for bone implants. A MATLAB® code was developed to design novel porosity graded gyroids, and develop permissible design map to aid the choice of different gyroid designs for bone implants.. Process maps were also developed to investigate the relationship among laser power, scan speed, and the errors in the relative density of lattice structures. Moreover, the normalized fatigue strength of thin struts gyoid was found to be higher than that of thicker struts.Analytical models and finite element analysis (FEA) models were compared to experimental results. The variation of the results gives a better understanding of the effect of manufacturing defects. An improved insight of gyroids manufacturability has been obtained by integrating the permissible design space with the process-structure-property relationship, and the defect analysis of porosity graded gyroids.

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.

<p dir="ltr">The natural honeycomb made from beeswax is an engineering marvel. Modern-day engineering has taken several inspirations from it in the form of hexagonal panels and cells made of various materials such as polymers, ceramics, and metals for light-weighting without compromising on its mechanical properties. Previously, characterizing this structure has relied on two-dimensional (2D) surface observations on the macroscale which have an inherently limited scope in understanding complex three-dimensional (3D) structures. As a result, several seminal features of the honeycomb that would have shed light on how it is constructed and what makes it so mechanically robust are left out of reach and overlooked. X-ray microscopy (XRM) is a powerful tool to characterize these complex structures non-destructively, yielding insights that are not possible without three-dimensional (3D) datasets. Further, when a time-resolved approach is adopted, where an external stimulus is interrupted for an XRM scan, one can obtain four-dimensional (4D) datasets. This provides unrivaled information on how complex 3D structures evolve over time when a stimulus is applied.</p><p dir="ltr">In this work, a time-resolved approach towards understanding how bees build out their hexagonal cells, both under normal and abnormal conditions was developed. Several previously unreported, but seminal features of the honeycomb such as the “coping” and porosity at well-defined locations yielded insights into how the comb is constructed. The corrugated spine is seen to be the foundation on which all hexagonal cells are built on. Additionally, this work also explores how bees accommodate distortions within the ordered lattice during the merger of two combs. Behaviorally they are seen to reduce the distortion within cells to minimize the wastage of wax and to keep the cells usable. A 3D parameter using automated image processing was developed to quantify how distortions are accommodated in an ordered lattice.</p><p dir="ltr">This work will further shed light on the mechanical behavior of the natural honeycomb arising from the corrugated nature of the spine and the gradient in its wall thickness which plays a role in crack deflection when the honeycomb is loaded under tension. When loaded under compression, the honeycomb lattice crumples in a manner to limit the damage to very local regions thereby forming a damage-tolerant crumple zone.</p>

Additive manufacturing (AM), also known as 3D-printing, has gained widespread adoption across various industries owing to advancements in manufacturing methods and printers. This technology offers users creative freedom, diverse manufacturing methods, and a wide range of material options. Consequently, many industries, including defense, are keen on integrating AM into their production processes. In the defense sector, AM facilitates rapid prototyping and the efficient blending of different materials, unlocking new possibilities that conventional methods cannot achieve. The ability to fabricate intricate geometries is another pivotal aspect driving the preference for AM. Thus, this study aims to explore the potential of lattice structures to impart unique material properties applicable in defense applications. Specifically, the investigation focuses on understanding the impact of discharge directions and lattice structures on radar properties for Material X. Analysis revealed that while discharge direction exhibited minimal influence on radar properties, different lattice structures could modify these properties by altering parameters such as unit cell size and panel thickness. Keywords: Additive manufacturing, 3D printing, lattice structures, discharge direction, radar properties, defense industry

Laser Powder Bed Fusion (LPBF) is a metal additive manufacturing (AM) technique that creates objects layer by layer from a bed of loose powder, using a laser beam as the heat source. This layer-wise approach allows for the fabrication of highly complex structures and intricate geometries with high accuracy, including solid, porous, and lattice structures. LPBF offers significant potential for use in industries such as aerospace, biomedical, and automotive due to its ability to fabricate unique and sophisticated designs. This technology has recently attracted significant attention for the fabrication of multimaterial parts with improved properties and applicability in different fields. However, challenges persist in understanding the relationship between process parameters and the properties of resulting multimaterial parts and interfaces. Additionally, limitations exist in design and interface selection for multimaterial fabrication using this technique. Negative thermal expansion (NTE) metamaterials, discussed in this research, are mechanical structures that show negative expansion properties by contracting with increase in temperature, while expanding with a decrease in temperature. These metamaterials are typically multimaterial systems where constituents with positive coefficients of thermal expansion (CTE) are strategically integrated, resulting in an overall NTE effect in one or more directions This research focuses on the design, simulation, and fabrication of negative thermal expansion (NTE) metamaterials using Laser Powder Bed Fusion (LPBF) with Grade 304L Stainless Steel (SS304L), Grade 300 Maraging Steel (MS300), and Invar 36 (Invar) alloys. Bimaterial combinations of SS304L-MS300 and SS304L-Invar were explored. After determining the optimal processing parameters, results showed that a robust, defect-free interface could be achieved in both combinations. Various lattice structures were designed based on these alloy pairs and analyzed using finite element analysis. The designs with the high NTE potential were successfully fabricated through LPBF, using optimal interface parameters. Thermal expansion testing of the fabricated structures demonstrated NTE behavior in line with FEA analysis predictions. / Thesis / Master of Applied Science (MASc)

Les procédés de fabrication additive ont connus un fort essor dans les dernières décennies et entament aujourd'hui leur phase d'industrialisation pérenne. L'industrie, dans un souci d'améliorer sans cesse le ratio masse/rigidité des systèmes qu'elle produit (notamment l'industrie aéronautique), a pris conscience du potentiel de ces technologies à produire des structures plus complexes que les procédés classiques. Elle cherche aujourd'hui à tirer profit de ce potentiel pour alléger encore plus les pièces produites en utilisant notamment des géométries de type réseaux ou alvéolaires (Lattice en anglais). Les travaux présentés dans ce manuscrit ont pour but de proposer une méthodologie, des modèles et des outils permettant la conception, le dimensionnement et l'optimisation de telles structures en vue de leur fabrication par procédés additifs. Le framework proposé peut être résumé par les huit étapes ci-dessous:- Importation de l'espace de conception, comprenant également les cas de chargement.- Optimisation topologique sur l'espace de conception.- Reconstruction de la géométrie, appelée primitive, qui servira de support à l'insertion du réseau.- Calcul par éléments finis qui peut être réalisé pour s'assurer de la bonne tenue mécanique.- Définition de la topologie du réseau, par l'intermédiaire d'un graphe 3D.- Déformation du réseau et optimisation mécanique du réseau.- Reconstruction des volumes.- Préparation des fichiers de données et impression 3D. / Additive manufacturing processes have been quickly growing those past decades and are now getting to their sustainable industrial. Industry has been caring about the mass to rigidity ratio of the structures it produces (especially in aeronautics), and is now acknowledging the potential of additive processes to produce more complex shapes than classical processes. Industry is now trying to take advantage of this potential by designing highly complex structures like lattices or metal foams. The work that is presented in this document propose a methodology, models and numerical tools allowing the conception, dimensioning and optimization of such structures through additive manufacturing. The proposed framework can be describe through the height following steps:- Importing the design space and the technical requirement (load cases).- Topology optimization of the design space- Geometry reconstruction to create a primitive which will be the lattice insertion area.- Finite elements computation to ensure that the structure meets the requirements.- Lattice topology definition using 3D graphs.- Lattice deformation and optimization.- Creation of the volumes around the lattice.- Printing file creation and 3D printing.