The objective of this research is to determine how the sandwich's physical characteristics have an impact on the mechanical properties, determine under what conditions the specimens will be lighter and mechanically stronger, and determine if the use of an aluminum honeycomb sandwich as a construction material is feasible. The research has aimed at the use of aluminum sandwiches as light and strong material. The study of the structural layers' damage resistance and tolerance demonstrated that the top and bottom layers play a crucial role. The thesis presents three test results from aluminum honeycomb sandwich compression horizontal, compressive vertical, and bending tests. Also, each group was displayed mechanically and simulated in Abaqus. The study determines the mechanical properties such as maximum elastic stress-strain, ultimate stress-strain, fracture point, density, poison ration, young modulus, and maximum deflection was determined. The energy absorbed by the FEA, such modulus of elasticity, resilience, and toughness, the crack propagation, the test's view shows aluminum honeycomb behaved like a brittle material with both compression test. And the maximum deflection, crack propagation, shear forces, bending moment, and images illustrated that the layers play a crucial role in the 3-point bend test.

Thesis advisor: Fazel Tafti / The search for an ideal quantum spin-liquid (QSL) material which can host a QSL ground state as well as exotic excitations has been one of the leading research topics in condensed matter physics over the past few decades. Out of all the proposals to realize the physics of a QSL, the Kitaev model is the most promising proposal with a QSL ground state. The Kitaev Hamiltonian is exactly solvable via fractionalization of its spin degrees of freedom into Majorana excitations, and it can be engineered in real materials. Among all the proposed Kitaev candidates, α-Li2IrO3, Na2IrO3, Li2RhO3, and α-RuCl3 are the most promising candidates. During my Ph.D. research I explored new physics related to Kitaev materials via modification of the symmetry and structural properties of these known Kitaev candidates. First, I studied how modification of the inter-layer chemistry can alter the thermodynamic properties of Kitaev candidate α-Li2IrO3 via an enhancement of the spin-orbit coupling (SOC) effect. The light, octahedrally-coordinated inter-layer Li atoms are replaced with heavier, linearly-coordinated Ag atoms to synthesize Ag3LiIr2O6. In addition to these structural modifications to the parent compound α-Li2IrO3, having heavier elements between the honeycomb layers in the Ag compound increased the effect of SOC in the honeycomb layers and led to a decrease in the long-range ordering temperature in Ag3LiIr2O6 compared to its parent compound. Second, I studied the effect of local crystal distortion in the presence of a weak SOC effect to explore a new spin-orbital state different from the Jeff=1/2 state. Based on theoretical predictions, the ground states of Kitaev materials can be tuned to other exotic spin-orbital states such as an Ising spin-1/2 state. To provide the proper conditions for a competition between the trigonal crystal distortion and the SOC effect, I modified the crystal environment around the magnetic elements in the parent compound Li2RhO3 via a topo-chemical method and synthesized Ag3LiRh2O6. An increase in the strength of trigonal distortion in Ag3LiRh2O6, in the presence of weak SOC, led to a transition from the Jeff=1/2 ground state (Kitaev limit) in the parent compound to an Ising spin-1/2 ground state (Ising limit) in the product. This change in spin-orbital state resulted in a dramatic change in magnetic behavior. Whereas Li2RhO3 shows a spin-freezing transition at 6 K, Ag3LiRh2O6 reveals a robust long-range antiferromagnetic transition at 94 K. This is the first realization of a change of ground state between the Kitaev and Ising limits in the same structural family. Lastly, I studied how the crystal symmetry can be an important factor in the physics of Kitaev materials. Honeycomb layered materials can be crystallized in space groups C2/m, C2/c, and P6_322. However, the crystal symmetry of most Kitaev candidates is described by the C2/m space group. We successfully synthesized a polymorph of a 3d Kitaev candidate, hexagonal Na2Co2TeO6 (P6_322 space group) in space group C2/m. The change in crystal symmetry of this cobalt tellurate replaced three anti-ferromagnetic (AFM) orders at 27, 15, 7 K in the hexagonal polymorph by a single AFM peak at 9.6 K in the monoclinic Na2Co2TeO6. / Thesis (PhD) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

The mite ectoparasite Varroa destructor, poses a serious threat for the survival of the Apis mellifera colonies. The intensive use of acaricidal products is one of the most common methods for defending bees from Varroa that can cause the contamination of the wax foundation used in beekeeping. The natural honeycomb management could provide a solution for this problem, because it involves the use of frames without wax foundation which allows the bees to build a complete comb ex novo. On the other hand, colonies which are free to build cells of their choice, usually build a number of drone cells higher than colonies managed with the wax foundation. This could potentially lead to several negative consequences because the V. destructor reproductive success is greater on drone broods than on worker broods. The aim of the present study was to examine the colony development, to evaluate the honey production and to monitor the growth of V. destructor infestations and associated virus infections in Apis mellifera colonies managed by using natural honeycombs compared with the conventional management. Several colony parameters were measured in spring and summer. The strength of the colony was used to estimate the worker and drone populations. In order to measure the V. destructor infestations were used several methods, such as the natural mite fall, the powdered sugar roll, the soapy water and the brood cell uncapping. Molecular analysis was performed in order to measure the viral load of five Apis mellifera viruses. The honey produced was measured by collecting the honey stored in the supers, which are boxes placed on a beehive for bees to store. The results showed that the higher presence of drone brood in the colonies managed using the natural honeycomb did not negatively affect the colony development nor the mite V. destructor population compared to control colonies. The molecular analysis showed that the DWV was the most common virus found in bee samples, and its viral load was more influenced from the mite infestation rate than from the treatment. The analysis carried out in this study showed that the natural honeycomb management can represent a valid alternative to the wax foundation. This kind of colony management thus appears to contradict our primary hypothesis which was that letting the bees build their own honeycomb would have led to a significant increase in the V. destructor infestation. Productivity data did not provide reliable results about the difference between the natural honeycomb and the conventional colony management due to climatic adversities. Further studies will be performed to better investigate this aspect. Data about the natural mite fall and the estimation of the mite population in the phoretic/reproductive phases provided a useful starting point for further studies on the correct timing to carry out acaricide treatments both in conventional and natural honeycomb managed colonies.

<p> </p> <p>ndoor air quality (IAQ) due to the presence of airborne microorganisms or bioaerosols (0.01-10 μm) in indoor spaces has been a concern for many years; however, it gained significant attention during the COVID-19 pandemic. Photocatalytic oxidation (PCO) has shown promising potential to kill microorganisms (removal/disinfection) and has already been in use within HVAC systems to treat volatile organic compounds (VOCs) (treatment). The main motivation of this work is to understand whether PCO devices can be used for bioaerosol removal in indoor spaces by integrating them with HVAC systems. Among the various factors that influence the adoption of PCO for large-scale bioaerosol removal, this work specifically tries to investigate two factors 1) whether the commercially available PCO reactors for treatment can be used for removal/disinfection or not, and 2) how to setup a standardized experimental setup for evaluating the removal efficiency of these systems. Generally, most of the commercial PCO devices use UV- based photocatalysis, so the removal efficiency is a combination of inactivation by UV and the reactive oxygen species produced by photocatalytic reactions (pure photocatalytic effect).</p> <p>In this work, the bioaerosol transport and the photon transport in a reactor is hypothesized as central to using the photocatalytic effect to inactivate microorganisms. This study uses analytical models to estimate the collection efficiency of the bioaerosols inside the honeycomb channels as a function of non-dimensional aspect ratios and velocity typical of HVAC systems. Subsequently, the collection efficiency results are overlaid with the prior literature results on photon transport inside such channels to present a limiting case for the removal efficiency of these systems. Another crucial factor for the performance of PCO systems is to investigate about the bioaerosol remediation on a photocatalyst substrate. Since there are many challenges associated with the numerical modeling of this phenomenon, this work developed a standardized experimental setup at the Herrick Laboratories, Purdue to investigate these interactions and further validate the previous hypothesis .The setup is constructed to systematically characterize the bioaerosol flowing through the airstream and measure data crucial to the PCO reactor performance, such as fluence rate field, number concentration (#/cm3), and viable concentration (CFU or PFU/m3) of the microorganisms upstream and downstream of the treatment sections. </p> <p>The collection efficiency (CE) of bioaerosols in honeycomb channels with velocities typical to HVAC systems were estimated using analytical models, and the results were presented in dimensionless aspect ratios (AR= Lch/ Dch). Based on the CE modeling results, the highest CE for aspect ratio 25 was less than 20% for the entire bioaerosol size range. From the prior literature results on photon transport, it was found that the intensity of the light reduced significantly for aspect ratios less than or equal to 6. Based on these results, it was found that the existing honeycomb geometries weren’t effective for PCO disinfection in operating conditions typical of HVAC systems. Since there aren’t any existing well-established methods to experimentally investigate these kinds of systems, this work will present the details about the development of the proposed methods inspired from prior literature for general air cleaning devices and small-scale PCO experiments. Furthermore, a detailed discussion about the important subsystems such as aerosol generation subsystem, sampling subsystem, and reactor subsystem which is crucial to investigating the hypotheses is presented in this thesis. Finally, some preliminary results on each of these characterization experiments to test the hypotheses has been presented in this thesis.</p>

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A better understanding of the effect of impact damage on composite structures is necessary to give the engineer an ability to design safe, efficient structures. Current composite structures suffer severe strength reduction under compressive loading conditions, due to even light damage, such as from low velocity impact. A review is undertaken to access the current state-of-development in the areas of experimental testing, and analysis methods. A set of experiments on Nomex honeycomb core sandwich panels, with thin woven fiberglass cloth facesheets, is described, which includes detailed instrumentation and unique observation techniques. These techniques include high speed video photography of compression after impact (CAI) failure, as well as, digital image correlation (DIC) for full-field deformation measurements. The effect of nominal core density on the observed failure mode is described. A finite element model (FEM) is developed to simulate the experiments performed in the current study. The purpose of this simulation is to predict the experimental test results, and to conrm the experimental test conclusions. A newly-developed, commercial implementation of the Multicontinuum Failure Theory (MCT) for progressive failure analysis (PFA) in composite laminates, Helius:MCT, is included in this model. The inclusion of PFA in the present model gives it the new, unique ability to account for multiple failure modes. In addition, significant impact damage detail is included in the model as a result of a large amount of easily available experimental test data. A sensitivity study is used to assess the effect of each damage detail on overall analysis results. Mesh convergence of the new FEM is also discussed. Analysis results are compared to the experimental results for each of the 32 CAI sandwich panel specimens tested to failure. The failure of each specimen is accurately predicted in a high-fidelity, physics-based simulation and the results highlight key improvements in the understanding of honeycomb core sandwich panel CAI failure. Finally, a parametric study highlights the strength benefits compared to mass penalty for various core densities. / Ph. D.

The 2D honeycomb lattice started as a theoretical construct, until its realization in a crystalline system enabled the study of a host novel exotic phenomena arising from its unique electronic structure. Since the isolation of graphene, the search for crystalline materials hosting interesting electronic structures has only increased with the excitement of correlated phenomena that can arise in the two-dimensional limit. This dissertation details the characterization of a van der Waals (vdW) material that realizes a novel flat band lattice model via frustrated hopping. Chapter 1 starts with an introduction into vdW materials and the electronic structure of frustrated lattices. Chapter 2 goes through some of the characterization methods that will be mentioned in this dissertation. Chapter 3 introduces the material that will be the subject of investigation in this thesis and establishes its as arising from a novel flat band lattice model via frustrated hopping. Chapter 4 discusses the electronic properties of newly synthesized analogs of this material. Chapter 5 introduces potential applications of this material in plasmonics. Chapter 6 covers a research story that is independent of the rest of this dissertation. It goes through the optical properties that arise from in-plane structural anisotropy in a superatomic vdW material.

Sandwich Panels with cellular cores are widely used in the aerospace industry for their higher stiffness to mass, strength to mass ratio, and excellent energy absorption capability. Even though, sandwich panels are considered state of the art for lightweight aerospace structures, the requirement to further reduce the mass exists due to the direct impact of mass on mission costs. Traditional manufacturing techniques have limited the shape of the cores to be either hexagonal or rectangular, but, with rapid advancements in additive manufacturing, other core shapes can now be explored. This research aims to identify and evaluate the mechanical performance of two-dimensional cores having standard wall geometry, which provide higher specific stiffness than honeycomb cores. Triangular cores were identified to have higher specific in-plane moduli and equivalent specific out-of-plane and transverse shear moduli. To consider practical use of the triangular cores, elastic and elastic-plastic structural analysis was performed to evaluate the stiffness, strength, failure, and energy absorption characteristics of both the core and sandwich panels. The comparison made between triangular cores and hexagonal cores having the same cell size and relative density showed that triangular cores outperform hexagonal cores in elastic range and for applications where in-plane loading is dominant. Triangular cores also have excellent in-plane energy absorption capabilities at higher densities. / Master of Science / Sandwich panels with cellular cores are widely used in aerospace structures to reduce weight, which helps increase payload and improve fuel efficiency. They also have the ability to absorb energy during accidental impacts. Sandwich construction typically consists of two thin facesheets separated by a lightweight core and, is analogous to I-beams used in civil structures. Most commonly used core is the hexagonal honeycomb core inspired by beehives. While sandwich panels constructed using honeycomb cores are considered the state-of-the-art for lightweight aerospace structures, there is a need to further reduce the mass due to the direct impact on mission costs. This research aims to explore other core shapes that provide better stiffness to mass ratio than the hexagonal core. Among the two-dimensional cores explored, the triangular shaped core was identified to have higher stiffness than the hexagonal core of the same size and weight. To consider practical use of triangular cores, mechanical performance and failure behavior of sandwich panels constructed using triangular core sandwich panels was compared to hexagonal core sandwich panels. It was concluded that the triangular panels provided higher stiffness for the same mass and was more resistant to failure when axially loaded. Triangular cores also have excellent in-plane energy absorption capabilities at higher densities.

Wind tunnels are important tools used in physics and engineering, with a wide range of usability and applications in industrial, research, and educational settings. A wind tunnel holds an object steady while generating airflow over it, often to study the interaction between the object and the airflow. The design of wind tunnels can be very costly, extensive, and difficult to implement. This paper analyzes literature on wind tunnels to compile a method for designing a portable wind tunnel suitable for educational and demonstrative purposes. The method includes design guidelines for each component, including the test section, contraction, settling chamber, honeycomb, diffuser, and fan section. A blueprint for a wind tunnel with specified dimensions is presented. The blueprint is designed to fit a Boeing 747-200 model, scaled at 1:390, and therefore have a 40 cm long test section with a 20x20 cm square cross-section. The designed wind tunnel achieves a velocity of 5 m/s in the test section. Emphasizing portability, simplicity, and functionality, this wind tunnel design enhances educational experiences, making complex fluid dynamics concepts accessible and engaging for students.

Wind tunnels are important tools used in physics and engineering, with a wide range of usability and applications in industrial, research, and educational settings. A wind tunnel holds an object steady while generating airflow over it, often to study the interaction between the object and the airflow. The design of wind tunnels can be very costly, extensive, and difficult to implement. This paper analyzes literature on wind tunnels to compile a method for designing a portable wind tunnel suitable for educational and demonstrative purposes. The method includes design guidelines for each component, including the test section, contraction, settling chamber, honeycomb, diffuser, and fan section. A blueprint for a wind tunnel with specified dimensions is presented. The blueprint is designed to fit a Boeing 747-200 model, scaled at 1:390, and therefore have a 40 cm long test section with a 20x20 cm square cross-section. The designed wind tunnel achieves a velocity of 5 m/s in the test section. Emphasizing portability, simplicity, and functionality, this wind tunnel design enhances educational experiences, making complex fluid dynamics concepts accessible and engaging for students.