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Strength and toughness are mutually exclusive mechanical properties; an increase in one result in the decline in the other. Accordingly, ceramics with superior strength have a very low toughness; likewise, metals with similar density have relatively lower strength but higher toughness. However, biological systems design lightweight materials, circumventing this limitation of conventional materials, by aggregating various multiscale toughening mechanisms. In challenging habitats, organisms evolve to produce remarkable multifunctional material systems that improve their "fit" and "survivability". Unlike traditional materials, natural materials employ special arrangements of structural elements into cellular, gradient, fibrous, layered, or overlapped "architected composites". These natural material systems are "architected" to delocalize damage and prevent defect coalescence, to avoid catastrophic failure, even though they are mainly composed of brittle building blocks (>90 vol% mineral content). Consequently, the study of natural materials has attracted the attention of scientists as the benchmark for the development of new synthetic materials. With the advent of additive manufacturing technology, the design and assessment of architected composites with bio-inspired motifs have become increasingly feasible. In this dissertation, I use multi-step fabrication methods with additive manufacturing as a key step to produce and study different biologically inspired architectures. With control over the design parameters of the architectural features, an in-depth understanding of the organization is accomplished. The case studies are primarily focused on bulk composite material systems with multiple phases and motifs inspired by various biological material systems. This dissertation aims to reveal the structure-property relationships of these structural motifs and the trade-offs to the mechanical robustness due growth-related constraints. With the help of stereolithographic additive manufacturing technique and centrifugal infiltration, we propose a bio-inspired method for preparing ceramic-metal composites. The approach allowed for flexible design, scalability, and dimensional control of individual phases. The ceramic-metal composites were fabricated with structures simplified from the mollusk shell architectures, exhibiting specific strength up to 169% higher than the base metal. The crack growth toughness of up to 12.9 MPa m1/2 was recorded, with crack deflection at ceramic-metal interfaces. Additionally, using tomographic analysis we show that the high porosities of 9% and 15% for green and sintered 3D printed parts, if improved, could further enhance the strength and fracture toughness of these composites. The outer protective layer of a bivalve mollusk exoskeleton, called the prismatic layer, is composed of normally oriented prismatic building blocks separated by soft organic matrix. The growth of the prismatic layer is regulated by the thermodynamic boundary conditions of the habitat and is directed from the exterior to the interior of the shell. A consequence of growth is a graded structure with a fine side (higher grain count with smaller grain size) and a coarse side (higher grain count with smaller grain size), however, the presence of grading results in asymmetry. Using mechanical testing we reveal that the organisms' selection of fine side as the loading face is "not the most optimized arrangement for templating". In fact, opting for the coarse side over the fine side as the loading side simultaneously enhances mutually exclusive properties such as stiffness, strength, and energy absorption. We further show that the curved prism motifs in the proximal parts of the Ostrea edulis shells result in a significant reduction in mechanical robustness due to the growth-related restrictions arising from the simultaneous normal and lateral growth of shells. Moreover, we show that although the addition of a nacre-like backing layer reduces the effects of axial directional asymmetry, the resistance of the prismatic layer to initiate damage in a coarse side-loaded hybrid composite is superior to the fine side-loaded counterpart. This part of the research highlights the need for caution when directly mimicking structural designs found in biological systems. Biological material systems are typically multifunctional, tailored to specific habitats and organism-specific needs, and often constrained by growth requirements and economic limitations. The shells of the pteropods – pelagic gastropod species, are comprised of helical or as posited by certain researchers "S-shaped" aragonite mineral motifs. These helical motifs are remarkably close packed in an organic matrix without noticeable spaces. We develop a biological process mimicking image processing technique called the "Bottom-up Sectional Morphing" to model perfectly closed packed structures with control over the radius and pitch of the helical motifs. With the developed composites we attempt to characterize the effect of the helix radius of individual motifs on the global mechanical properties. With the help of compressive tests, we characterize the delocalization of load as the radius of the helical motifs is increased. With the help of slab-shaped samples, we study the puncture resistance and interlocking behaviors due to increased helical radius. Using standardized fracture toughness tests, the toughness of the composites is determined. Additionally, the R-curve behaviors as a function of helical radiuses is characterized. On average, the fracture strength of the composite doubled as the radius of the helical motifs increased from 0 mm to 3.9 mm. Remarkably, the fracture toughness of helical composites was as high as 12-times the rule-of-mixtures estimated values. We summarize the extrinsic toughening mechanisms within the composites compared them to the mechanisms reported for helicoidal (twisted plywood) composites. Additional interlocking due to the uneven orientation of major axes in double basket weave pattern helical system are reported. Using explicit finite element simulations, we show that the curved motifs in comparison to normally oriented prisms, can help in developing localized high stress pockets, thus delocalization of damage that can help in increasing energy absorption during the progression of damage. Also, taking cues from fish scale ultrastructures, we design three-phase ceramic-epoxy-fiber composites. The fish scales feature gradient architectures with varying biomineralization extents from the distal to proximal regions (with respect to the fish body). From exterior to interior the mineralization content reduces, however, the collagen fiber count subsequently increases. To mimic the design approach, we use a 3D printed gradient ceramic lattice embedded in an epoxy matrix and backed using Kevlar fibers. With high-speed impact tests (73.5 ± 2.5 ms-1) we show that, although functionally graded composites (without Kevlar backing) show larger impact signatures compared to the similar density uniform density composites (without Kevlar backing) but absorb 35.7% higher energy during the process. High rebound velocity (22 ± 2.46 m/s) was observed for variable density composites with Kevlar backing. Additionally, using micro computed tomographic analysis of variable density composites with Kevlar backing we demonstrate that pre-stretching of fibers helps in the suppression crack. The results from this study were used in the design of polymer-elastomer composites with functionally graded material and fiber distribution. Interweaving fibers with hard solid lattices becomes challenging when one of the planar surfaces of the lattice is closed because of the functional grading. To overcome this challenge, I propose a new lattice interweaving method called "Warp-Assisted Binder-Tugging (WABT)", that can interweave the lattice using only one of the planar faces. Using WABT we refine the 3-phase composites design by incorporating strategically placed internal reinforcements. Cured photopolymer thermoset plastics are intrinsically brittle materials with mechanical properties like that of epoxy. Therefore, we choose this material along with urethane elastomer to prepare polymer-elastomer (hard-soft) composites, with and without reinforcements. We demonstrate the efficacy of strategic material distributions using dynamic puncture tests and projectile impact tests. The results show that concentrating brittle plastics towards the loading side improves energy absorption ability by 30.29% and puncture strength by 21.47%. A further 61.76% and 35.12% improvement in the energy absorption and puncture strength is recorded for slabs with backing and reinforcements. We show the response of the as-prepared composites under high speed projectile impact tests with incident projectile speeds of 151.5 ± 2.5 ms-1. The μ-CT characterization of damaged samples revealed the load delocalization and crack suppression behaviors due to the material distributions and reinforcements. / Doctor of Philosophy / It is challenging to develop materials that are strong and tough at the same time. Ceramics, for example, are very strong, but are highly sensitive to the inherent defects and subsequently, upon initiation of damage, fail catastrophically. Metals on the other hand are not as strong as ceramics but require high energy for failure. Biological materials, using ingeniously designed and organized brittle elements can combine strength and toughness into a single system. In this dissertation, I investigated various bioinspired material systems to characterize their structure-property relationships. The analysis of structures inspired by the biological materials provides valuable insights that will potentially benefit the design of new protective systems. In this dissertation, I fabricate, and study biological designs found in the bivalve mollusk shells, pteropod shells, and fish scales. Using experimental and computational methods the I studied the effects of design parameters on the mechanical robustness of the composites. Contrary to the common belief that biological systems are highly optimized, I show that the biological materials could feature "less-than-perfect" design arrangements. The case studies aim to highlight the mechanisms that help organisms to resist damage and survive in their challenging environments. These case studies allowed us to understand the design strategies as well as limitations that can help us develop mechanically robust materials based on biological materials.

The Whole Skin Locomotion robot propels itself using a motion similar to the cytoplasmic streaming exhibited by an amoeba. In the robot there are embedded ring actuators which evert the material of the robot to produce forward motion. The robot benefits from a highly flexible exterior allowing it to squeeze into constricted passageways or collapsed structures. The development of actuators for such a motion is performed by a shape memory alloy composite actuator. Unlike a typical composite model which utilizes a homogenization of fiber and matrix properties our model is developed for line loads produced in individual shape memory alloy wires onto the rod structure. The load vectors are determined in the deformed configuration of the actuator to account for the highly deformed actuator profiles that would be seen in operation. Also the load requirements for such actuators are developed in terms of the constriction forces and functional design limits are established. In addition, a helical spring backbone design is considered and stiffness properties for general helical springs are determined. The contact of spring coils is included in the analysis and a coupled constitutive model is developed for the spring when coils are in contact. The static design of helical springs for use in the actuators is performed and deformation and load restrictions are determined for subsequent design efforts. / Ph. D.

Background and Objectives: Intramedullary nailing of trochanteric fractures can be challenging and sometimes the clinical situation does not allow perfect implant positioning. The aim of this study was (1) to compare in human cadaveric femoral heads the biomechanical competence of two recently launched cephalic implants inserted in either an ideal (centre–centre) or less-ideal anterior off-centre position, and (2) to investigate the effect of bone cement augmentation on their fixation strength in the less-ideal position. Materials and Methods: Fourty-two paired human cadaveric femoral heads were assigned for pairwise implantation using either a TFNA helical blade or a TFNA screw as head element, implanted in either centre–centre or 7 mm anterior off-centre position. Next, seven paired specimens implanted in the off-centre position were augmented with bone cement. As a result, six study groups were created as follows: group 1 with a centre–centre positioned helical blade, paired with group 2 featuring a centre–centre screw, group 3 with an off-centre positioned helical blade, paired with group 4 featuring an off-centre screw, and group 5 with an off-centre positioned augmented helical blade, paired with group 6 featuring an off-centre augmented screw. All specimens were tested until failure under progressively increasing cyclic loading. Results: Stiffness was not significantly different among the study groups (p = 0.388). Varus deformation was significantly higher in group 4 versus group 6 (p = 0.026). Femoral head rotation was significantly higher in group 4 versus group 3 (p = 0.034), significantly lower in group 2 versus group 4 (p = 0.005), and significantly higher in group 4 versus group 6 (p = 0.007). Cycles to clinically relevant failure were 14,919 4763 in group 1, 10,824 5396 in group 2, 10,900 3285 in group 3, 1382 2701 in group 4, 25,811 19,107 in group 5 and 17,817 11,924 in group 6. Significantly higher number of cycles to failure were indicated for group 1 versus group 2 (p = 0.021), group 3 versus group 4 (p = 0.007), and in group 6 versus group 4 (p = 0.010). Conclusions: From a biomechanical perspective, proper centre–centre implant positioning in the femoral head is of utmost importance. In cases when this is not achievable in a clinical setting, a helical blade is more forgiving in the less ideal (anterior) malposition when compared to a screw, the latter revealing unacceptable low resistance to femoral head rotation and early failure. Cement augmentation of both off-centre implanted helical blade and screw head elements increases their resistance against failure; however, this effect might be redundant for helical blades and is highly unpredictable for screws.

O uso de fundações por estacas helicoidais tem aumentado consideravelmente nos últimos anos, devido às suas vantagens comparadas a outros tipos de fundação, como a sua rápida instalação e sua capacidade de resistir simultaneamente a esforços de tração e de compressão. No entanto, os métodos de previsão do comportamento deste tipo de fundação submetida a esforços de tração (denominadas ancoragens helicoidais neste caso), ainda são insatisfatórios, e normalmente são observadas discrepâncias entre os resultados estimados por métodos teóricos e medidos em provas de carga. Entre outras razões, estas diferenças ocorrem principalmente pelo fato dos efeitos da instalação destas ancoragens no solo não serem considerados nos métodos de previsão disponíveis. No momento da instalação, os parâmetros do solo atravessado são modificados, e como é o volume de solo alterado que deve resistir ao carregamento da ancoragem sob tração, é essencial entender e quantificar este efeito de instalação para uma previsão adequada da capacidade de carga deste tipo de ancoragem. Para contribuir com o entendimento deste efeito, no presente trabalho foram realizadas simulações numéricas com o software FLAC3D, para se conhecer as modificações ocorridas no solo devido à instalação de uma ancoragem helicoidal em areia compacta. Para este fim, na simulação do solo penetrado pela hélice, foram reduzidos os valores de ângulo de atrito e do módulo de elasticidade da areia. O modelo foi validado por meio da comparação com a curva carga-deslocamento obtida experimentalmente em ensaios realizados em centrifuga. Após o ajuste do modelo numérico, foi realizada uma análise paramétrica com o objetivo de investigar o efeito da instalação no fator de capacidade de carga (Nq). Por meio da análise paramétrica também foram avaliados o deslocamento da ancoragem sob carga máxima e as tensões horizontais atuantes na superfície de ruptura. Os resultados estimados de Nq foram comparados com estudos anteriores, e mostraram um bom ajuste com resultados de provas de carga in situ e em centrifuga. Além disso, o estudo paramétrico indicou que as tensões horizontais atuantes na zona de ruptura são distribuídas em forma de tronco de cone, e variam de acordo com o diâmetro da hélice. / The use of helical foundations has increased considerably in recent years due to its advantages compared to other types of foundations, such as rapid installation and the capacity of resisting tensile and compressive loads. However, the methods normally used to predict the behavior of this type of foundation under tensile loads (called helical anchors in this case), are still unsatisfactory, and discrepancies are usually observed between the results estimated by theoretical methods and measured in load tests. Among other reasons, these differences occur mainly because the effects of helical anchor installation in the soil are not considered in the available predicting methods. During installation, the parameters of the soil penetrated are modified, and since it is this disturbed soil volume that must support the loading of the anchor under tension, it is essential to understand and quantify this installation effect for an adequate prediction of the uplift capacity of this type anchor. In order to contribute to the understanding of this effect, in the present work numerical simulations with the software FLAC3D were performed to evaluate the modifications occurred in the soil due to the installation of a helical anchor in dense sand. For this purpose, in the simulation of the soil penetrated by the helices, the values of friction angle and modulus of elasticity of the sand were reduced. The model was validated by means of the comparison with a load-displacement curve obtained experimentally in centrifuge model tests. After adjusting the numerical model, a parametric analysis was carried out to investigate the effect of the installation on the breakout factor (Nq). The parametric analyses were also used to investigate the anchor displacement at the peak load and the horizontal stresses acting on the failure surface. The estimated Nq values were compared with previous studies, and showed a good agreement with experimental results obtained by field and centrifuge tests. Additionally, the parametric study indicated that the horizontal stresses acting on the failure zone are distributed in the shape of a truncated cone, and vary with the helix diameter.

O uso de fundações por estacas helicoidais tem aumentado consideravelmente nos últimos anos, devido às suas vantagens comparadas a outros tipos de fundação, como a sua rápida instalação e sua capacidade de resistir simultaneamente a esforços de tração e de compressão. No entanto, os métodos de previsão do comportamento deste tipo de fundação submetida a esforços de tração (denominadas ancoragens helicoidais neste caso), ainda são insatisfatórios, e normalmente são observadas discrepâncias entre os resultados estimados por métodos teóricos e medidos em provas de carga. Entre outras razões, estas diferenças ocorrem principalmente pelo fato dos efeitos da instalação destas ancoragens no solo não serem considerados nos métodos de previsão disponíveis. No momento da instalação, os parâmetros do solo atravessado são modificados, e como é o volume de solo alterado que deve resistir ao carregamento da ancoragem sob tração, é essencial entender e quantificar este efeito de instalação para uma previsão adequada da capacidade de carga deste tipo de ancoragem. Para contribuir com o entendimento deste efeito, no presente trabalho foram realizadas simulações numéricas com o software FLAC3D, para se conhecer as modificações ocorridas no solo devido à instalação de uma ancoragem helicoidal em areia compacta. Para este fim, na simulação do solo penetrado pela hélice, foram reduzidos os valores de ângulo de atrito e do módulo de elasticidade da areia. O modelo foi validado por meio da comparação com a curva carga-deslocamento obtida experimentalmente em ensaios realizados em centrifuga. Após o ajuste do modelo numérico, foi realizada uma análise paramétrica com o objetivo de investigar o efeito da instalação no fator de capacidade de carga (Nq). Por meio da análise paramétrica também foram avaliados o deslocamento da ancoragem sob carga máxima e as tensões horizontais atuantes na superfície de ruptura. Os resultados estimados de Nq foram comparados com estudos anteriores, e mostraram um bom ajuste com resultados de provas de carga in situ e em centrifuga. Além disso, o estudo paramétrico indicou que as tensões horizontais atuantes na zona de ruptura são distribuídas em forma de tronco de cone, e variam de acordo com o diâmetro da hélice. / The use of helical foundations has increased considerably in recent years due to its advantages compared to other types of foundations, such as rapid installation and the capacity of resisting tensile and compressive loads. However, the methods normally used to predict the behavior of this type of foundation under tensile loads (called helical anchors in this case), are still unsatisfactory, and discrepancies are usually observed between the results estimated by theoretical methods and measured in load tests. Among other reasons, these differences occur mainly because the effects of helical anchor installation in the soil are not considered in the available predicting methods. During installation, the parameters of the soil penetrated are modified, and since it is this disturbed soil volume that must support the loading of the anchor under tension, it is essential to understand and quantify this installation effect for an adequate prediction of the uplift capacity of this type anchor. In order to contribute to the understanding of this effect, in the present work numerical simulations with the software FLAC3D were performed to evaluate the modifications occurred in the soil due to the installation of a helical anchor in dense sand. For this purpose, in the simulation of the soil penetrated by the helices, the values of friction angle and modulus of elasticity of the sand were reduced. The model was validated by means of the comparison with a load-displacement curve obtained experimentally in centrifuge model tests. After adjusting the numerical model, a parametric analysis was carried out to investigate the effect of the installation on the breakout factor (Nq). The parametric analyses were also used to investigate the anchor displacement at the peak load and the horizontal stresses acting on the failure surface. The estimated Nq values were compared with previous studies, and showed a good agreement with experimental results obtained by field and centrifuge tests. Additionally, the parametric study indicated that the horizontal stresses acting on the failure zone are distributed in the shape of a truncated cone, and vary with the helix diameter.