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The honeycomb sandwich structures are consisted of two thin facesheets and a thick honeycomb core. The commercially available sandwich structures used in aircraft interiors are based on synthetic fiber composite facesheet but have limitations like recycling, non-biodegradability and disposal problems. These factors push the need for environmentally friendly materials. From the literature review, it has been identified that the studies reported on the natural fiber-based composite facesheet with a honeycomb core are minimal. In this research, a new class of sandwich structures with glass fiber and natural fiber like flax and kenaf composite facesheet has been fabricated using the pre-cure fabrication technique. Two layers of the epoxy adhesive film sheet were used each to bond the top and bottom pre-cured facesheets with an aluminium honeycomb core. The mechanical properties of the sandwich structure specimens under various loads (Tensile, edgewise compression, and flexural) with respect to the fiber stacking sequence and natural fiber treatment were studied. The peel strength was measured through the climbing drum peel test to analyze the facesheet and core bonding strength. The lowvelocity impact behavior was analyzed by the drop weight impact test, and the residual strength of the impacted specimen was characterized through the bending test. Among the studied configurations, the glass composite facesheet revealed the highest mechanical performance than the natural composite facesheet. However, the compression strength and flexural stiffness of the natural fiber were improved when they were combined with synthetic material by around 38% and 66 % in flax/glass hybrid and 52% and 83% in kenaf/glass hybrid facesheet, respectively, compared to their non-hybrid composite. The mechanical performance of the sandwich structure was further enhanced by around 7% to 15 % when alkali-treated natural fibers were used in a hybrid combination. Overall, the hybrid combination, whi

The honeycomb sandwich structures are consisted of two thin facesheets and a thick honeycomb core. The commercially available sandwich structures used in aircraft interiors are based on synthetic fiber composite facesheet but have limitations like recycling, non-biodegradability and disposal problems. These factors push the need for environmentally friendly materials. From the literature review, it has been identified that the studies reported on the natural fiber-based composite facesheet with a honeycomb core are minimal. In this research, a new class of sandwich structures with glass fiber and natural fiber like flax and kenaf composite facesheet has been fabricated using the pre-cure fabrication technique. Two layers of the epoxy adhesive film sheet were used each to bond the top and bottom pre-cured facesheets with an aluminium honeycomb core. The mechanical properties of the sandwich structure specimens under various loads (Tensile, edgewise compression, and flexural) with respect to the fiber stacking sequence and natural fiber treatment were studied. The peel strength was measured through the climbing drum peel test to analyze the facesheet and core bonding strength. The lowvelocity impact behavior was analyzed by the drop weight impact test, and the residual strength of the impacted specimen was characterized through the bending test. Among the studied configurations, the glass composite facesheet revealed the highest mechanical performance than the natural composite facesheet. However, the compression strength and flexural stiffness of the natural fiber were improved when they were combined with synthetic material by around 38% and 66 % in flax/glass hybrid and 52% and 83% in kenaf/glass hybrid facesheet, respectively, compared to their non-hybrid composite. The mechanical performance of the sandwich structure was further enhanced by around 7% to 15 % when alkali-treated natural fibers were used in a hybrid combination. Overall, the hybrid combination, whi

We report the crystal structure and magnetic behavior of the spin- silicophosphate studied by high-resolution synchrotron x-ray diffraction, neutron diffraction, thermodynamic measurements, and ab initio band-structure calculations. Our data revise the crystallographic symmetry of this compound and establish its rhombohedral space group () along with the geometrically perfect honeycomb lattice of the ions residing in disconnected octahedra. Long-range antiferromagnetic order with the propagation vector observed below K is a combined effect of the nearest-neighbor in-plane exchange coupling K, easy-plane single-ion anisotropy K, and a weak interlayer coupling K. The 12% reduction in the ordered magnetic moment of the ions and the magnon gap of K induced by the single-ion anisotropy further illustrate the impact of spin-orbit coupling on the magnetism. Our analysis puts forward single-ion anisotropy as an important ingredient of honeycomb antiferromagnets despite their nominally quenched orbital moment. ©2021 American Physical Society

A design method is proposed for curved sandwich panels in order to improved their sound transmission loss in certain frequency regions. The ring frequency and coincidence effects may be suppressed simultaneously based on such method, resulting improved sound transmission loss properties of the curved sandwich panel in the low frequency range. The proposed method is based on an impedance approach that is developed for the estimation of the sound transmission loss of curved sandwich panels. Physical insights are drawn for the observed sound transmission behaviour of the panel based on the impedance approach over the frequency range of interest. The results are validated against the finite element simulations., Part of proceedings: ISBN 978-83-7880-799-5QC 20220517

The silver ruthenium oxide AgRuO3 consists of honeycomb Ru25+O62- layers and can be considered an analogue of SrRu2O6 with a different intercalation. We present measurements of magnetic susceptibility and specific heat on AgRuO3 single crystals, which reveal a sharp antiferromagnetic transition at 342(3) K. The electrical transport in single crystals of AgRuO3 is determined by a combination of activated conduction over an intrinsic semiconducting gap of ≈100 meV and carriers trapped and thermally released from defects. From powder neutron diffraction data a Néel-type antiferromagnetic structure with the Ru moments along the c axis is derived. Raman spectroscopy on AgRuO3 single crystals and muon spin rotation spectroscopy on powder samples indicate a further weak phase transition or a crossover in the temperature range 125-200 K. The transition does not show up in the magnetic susceptibility, and its origin is argued to be related to defects but cannot be fully clarified. The experimental findings are complemented by density-functional-theory-based electronic structure calculations. It is found that the magnetism in AgRuO3 is similar to that in SrRu2O6, however, with stronger intralayer and weaker interlayer magnetic exchange interactions. © 2021 authors. Published by the American Physical Society.

High-pressure chemistry is known to inspire the creation of unexpected new classes of compounds with exceptional properties. Here, we employ the laser-heated diamond anvil cell technique for synthesis of a Dirac material BeN4. A triclinic phase of beryllium tetranitride tr-BeN4 was synthesized from elements at ∼85 GPa. Upon decompression to ambient conditions, it transforms into a compound with atomic-thick BeN4 layers interconnected via weak van der Waals bonds and consisting of polyacetylene-like nitrogen chains with conjugated π systems and Be atoms in square-planar coordination. Theoretical calculations for a single BeN4 layer show that its electronic lattice is described by a slightly distorted honeycomb structure reminiscent of the graphene lattice and the presence of Dirac points in the electronic band structure at the Fermi level. The BeN4 layer, i.e., beryllonitrene, represents a qualitatively new class of 2D materials that can be built of a metal atom and polymeric nitrogen chains and host anisotropic Dirac fermions. © 2021 American Physical Society.

We measured the temperature dependence of low-frequency Raman spectra in Li2RuO3 and observed multipeak quasielastic scattering in the Ru honeycomb polarizations below and above the magnetostructural transition temperature. We attribute this scattering to the fluctuations of the energy density in the spin system. High-frequency electronic light scattering was observed at 2150cm-1. Its intensity increased significantly below the transition temperature, confirming substantial modification of the electronic structure due to removal of degeneracy in the t2g manifold of Ru4+ ions. © 2020 American Physical Society.

The objective of the research presented in this thesis is to develop analysis and test procedures for the characterization of disbonding crack growth in a honeycomb (HC) core sandwich structure. Face sheet-to-core disbonding are of particular interest to aircraft certification authorities due to several in-service occurrences. Experimental investigation was initially focused on the mode I dominated Single Cantilever Beam (SCB) test method. Various data reduction methodologies were employed to determine the fracture toughness. The MBT method produced the most consistent and conservative results. Finite element analysis (FEA) a double periodic array of hexagonal cells was conducted to determine the effective in-plane extensional modulus and Poisson ratio of the HC core. It was shown that deformation constraints on the core, due to attachment of the core to rigid face sheets, will drastically change the behavior of the HC core. The response changes from being governed by bending to stretching which substantially elevates the effective in-plane modulus. Fracture mechanics analysis of a face/core interface crack in a HC core SCB specimen was performed using FEA. The influence of in-plane properties of the constrained core on energy release rate and mode mixity phase angle was examined. Use of plane strain conditions and an elevated modulus of the constrained core in the analysis is recommended. The approach is substantiated by testing of HC core SCB sandwich. Test results showed good agreement with FEA prediction of compliance and kink angle., 2019, Includes bibliography., Degree granted: Dissertation (Ph.D.)--Florida Atlantic University, 2019., Collection: FAU Electronic Theses and Dissertations Collection

A self-supporting sandwich panel facade system under fire is studied. First, a thermomechanical FE model, which comprises the complete facade system, and incorporates material degradation and geometrical nonlinear behaviour except for the insulation material and connections, is loaded by a fire temperature curve. Eurocode design rules then predict the screw connections of a sandwich panel will fail in shear. Secondly, an existing programme, FDS-2-Abaqus, is extended to allow its two-way coupled analyses, in which CFD fire simulations are updated for changes in the thermomechanical FE model, to be applicable to the facade system. Again, these simulations show the shear failure of the screws. Parameter studies show differences in system behaviour for improved screw properties; a fuel-controlled vs. ventilation-controlled fire; and different panel thicknesses. Interestingly, as thermal bowing of the panel retards screw failure, and thicker sandwich panels bow less than thinner panels, thicker facade panels will decrease failure time. This and other insights obtained, and the predicted failure of two tiny but critical screws within 80 s, as compared to 150 min lasting sandwich panels in standard fire tests, stresses the need to study complete systems under realistic fires, rather than to study individual components in standard fire tests. Future research will focus on detailed FE models of the connections; full-scale fire experiments; CFD temperature measurement points at the facade outside; detailed modelling of the insulation; and the effects of high temperature creep. © 2019 Elsevier Ltd

Fractionalized excitations are of considerable interest in recent condensed-matter physics. Fractionalization of the spin degrees of freedom into localized and itinerant Majorana fermions is predicted for the Kitaev spin liquid, an exactly solvable model with bond-dependent interactions on a two-dimensional honeycomb lattice. As a function of temperature, theory predicts a characteristic two-peak structure of the heat capacity as a fingerprint of these excitations. Here we report on detailed heat-capacity experiments as a function of temperature and magnetic field in high-quality single crystals of α-RuCl3. We undertook considerable efforts to determine the exact phonon background. We measured single-crystalline RhCl3 as a nonmagnetic reference and performed ab initio calculations of the phonon density of states for both compounds. These ab initio calculations document that the intrinsic phonon contribution to the heat capacity cannot be obtained by a simple rescaling of the nonmagnetic reference using differences in the atomic masses. Sizable renormalization is required even for nonmagnetic RhCl3 with its minute difference from the title compound. In α-RuCl3 in zero magnetic field, excess heat capacity exists at temperatures well above the onset of magnetic order. In external magnetic fields far beyond quantum criticality, when long-range magnetic order is fully suppressed, the excess heat capacity exhibits the characteristic two-peak structure. In zero field, the lower peak just appears at temperatures around the onset of magnetic order and seems to be connected with canonical spin degrees of freedom. At higher fields, beyond the critical field, this peak is shifted to 10 K. The high-temperature peak located around 70 K is hardly influenced by external magnetic fields, carries the predicted amount of entropy R/2ln2, and may resemble remnants of Kitaev physics. © 2019 American Physical Society.

Nanoscale TiO2 (nTiO2) is manufactured in high volumes and is of potential concern in occupational health. Here, we measured workers exposure levels while ceramic honeycombs were dip coated with liquid photoactive nanoparticle suspension and dried with an air blade. The measured nTiO2 concentration levels were used to assess process specific emission rates using a convolution theorem and to calculate inhalation dose rates of deposited nTiO2 particles. Dip coating did not result in detectable release of particles but air blade drying released fine-sized TiO2 and nTiO2 particles. nTiO2 was found in pure nTiO2 agglomerates and as individual particles deposited onto background particles. Total particle emission rates were 420 × 109 min−1, 1.33 × 109 μm2 min−1, and 3.5 mg min−1 respirable mass. During a continued repeated process, the average exposure level was 2.5 × 104 cm−3, 30.3 μm2 cm−3, <116 μg m−3 for particulate matter. The TiO2 average exposure level was 4.2 μg m−3, which is well below the maximum recommended exposure limit of 300 μg m−3 for nTiO2 proposed by the US National Institute for Occupational Safety and Health. During an 8-hour exposure, the observed concentrations would result in a lung deposited surface area of 4.3 × 10−3 cm2 g−1 of lung tissue and 13 μg of TiO2 to the trachea-bronchi, and alveolar regions. The dose levels were well below the one hundredth of the no observed effect level (NOEL1/100) of 0.11 cm2 g−1 for granular biodurable particles and a daily no significant risk dose level of 44 μg day−1. These emission rates can be used in a mass flow model to predict the impact of process emissions on personal and environmental exposure levels

This paper applies to the design and simulation of a shipping container made of sandwich panels. The amount of stresses acting on the body of the container is calculated and is optimized to reduce stresses for the better design output of the structure. The design aims to produce an application to reduce the tare weight of the container in order to increase the payload. Finite Element Analysis (FEA) is performed to evaluate the strength of structures of both old and new models helps us to compare which model is better and more efficient. Complete design and analysis is performed using Autodesk Inventor., no

A sixth-order differential equation governing the flexural vibration of sandwich plates is derived. The sandwich plates considered consist of laminates bonded to honeycomb or foam cores. The structures are assumed to be symmetric. Shear and rotation in core are included in the model. The effect on the bending stiffness of rotation and shear in the core is discussed. Shear effects are of great importance, whereas rotation of the core has only a marginal effect on the bending stiffness of lightweight sandwich plates. The bending stiffness of a sandwich plate is found to strongly depend on frequency. The bending stiffness of a structure determines its acoustical coupling to any surrounding fluid and thus its sound transmission loss and sound radiation ratio. Loss factors of sandwich plates are discussed. Boundary conditions are formulated for rectangular plates having simply supported, clamped, or free edges. There are five boundary conditions to be satisfied at each edge of the plate. The bending stiffness of simply supported and infinite plates is presented as a function of frequency. Expressions for the point mobility for infinite or simply supported finite panels are given., QC 20190222

This paper applies to the design and simulation of a shipping container made of sandwich panels. The amount of stresses acting on the body of the container is calculated and is optimized to reduce stresses for the better design output of the structure. The design aims to produce an application to reduce the tare weight of the container in order to increase the payload. Finite Element Analysis (FEA) is performed to evaluate the strength of structures of both old and new models helps us to compare which model is better and more efficient. Complete design and analysis is performed using Autodesk Inventor., no

This paper applies to the design and simulation of a shipping container made of sandwich panels. The amount of stresses acting on the body of the container is calculated and is optimized to reduce stresses for the better design output of the structure. The design aims to produce an application to reduce the tare weight of the container in order to increase the payload. Finite Element Analysis (FEA) is performed to evaluate the strength of structures of both old and new models helps us to compare which model is better and more efficient. Complete design and analysis is performed using Autodesk Inventor., no

This paper applies to the design and simulation of a shipping container made of sandwich panels. The amount of stresses acting on the body of the container is calculated and is optimized to reduce stresses for the better design output of the structure. The design aims to produce an application to reduce the tare weight of the container in order to increase the payload. Finite Element Analysis (FEA) is performed to evaluate the strength of structures of both old and new models helps us to compare which model is better and more efficient. Complete design and analysis is performed using Autodesk Inventor., no

This paper applies to the design and simulation of a shipping container made of sandwich panels. The amount of stresses acting on the body of the container is calculated and is optimized to reduce stresses for the better design output of the structure. The design aims to produce an application to reduce the tare weight of the container in order to increase the payload. Finite Element Analysis (FEA) is performed to evaluate the strength of structures of both old and new models helps us to compare which model is better and more efficient. Complete design and analysis is performed using Autodesk Inventor., no

This paper applies to the design and simulation of a shipping container made of sandwich panels. The amount of stresses acting on the body of the container is calculated and is optimized to reduce stresses for the better design output of the structure. The design aims to produce an application to reduce the tare weight of the container in order to increase the payload. Finite Element Analysis (FEA) is performed to evaluate the strength of structures of both old and new models helps us to compare which model is better and more efficient. Complete design and analysis is performed using Autodesk Inventor., no

Peer Reviewed, Postprint (author's final draft)

Two single-bonded 2D nitrogen allotropes of the honeycomb (A7) and zigzag sheet (ZS) topology have been calculated using density functional theory (DFT). The optical (vibrational, absorption, nuclear magnetic resonance), thermodynamic and elastic properties of the A7 and ZS sheets have been calculated for the first time. The band structure calculation have revealed a semiconducting nature of the ZS sheet with a direct gap of 1.246 eV, while the A7 monolayer behaves as an insulator with an indirect gap of 3.842 eV. Phonon dispersion calculations have justified these structures as vibrationally stable 2D materials. The IR spectroscopy completely failed in the characterization of the studied materials, while the Raman spectroscopy can be effectively applied for the experimental spectral identification. The absorption spectra demonstrate complete opacity of the A7 and ZS monolayers to the UV irradiation only above ca. 9 and 6 eV, respectively. Thus, the studied materials are expected to be transparent to the visible light. The electron arrangement of the nitrogen nuclei in the studied polynitrogen sheets is denser compared to the N2 molecule which follows from the calculation of the values of magnetic shielding tensors. The elastic constants reveal a robust mechanical stability of the studied 2D nitrogen allotropes. The Young moduli values are only twice as lower than that of the graphene molecule., QC 20170613

Hexagonal boron nitride is a model lamellar compound where weak, non-local van der Waals interactions ensure the vertical stacking of two-dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes (10B and 11B) compared to those with the natural distribution of boron (20 at% 10B and 80 at% 11B). On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero-point renormalization. On the other hand, temperature-dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in 10BN than in 11BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

We report the revised crystal structure, static and dynamic magnetic properties of quasi-two dimensional honeycomb-lattice silver delafossite Ag3Co2SbO6. The magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long range order at low temperatures with Néel temperature TN ∼ 21.2 K. In addition, the magnetization curves revealed a field-induced (spin-flop type) transition below TN in moderate magnetic fields. The GGA+U calculations show the importance of the orbital degrees of freedom, which maintain a hierarchy of exchange interaction in the system. The strongest antiferromagnetic exchange coupling was found in the shortest Co-Co pairs and is due to direct and superexchange interaction between the half-filled xz + yz orbitals pointing directly to each other. The other four out of six nearest neighbor exchanges within the cobalt hexagon are suppressed, since for these bonds the active half-filled orbitals turned out to be parallel and do not overlap. The electron spin resonance (ESR) spectra reveal a broad absorption line attributed to the Co2+ ion in an octahedral coordination with an average effective g-factor g = 2.40 ± 0.05 at room temperature and show strong divergence of the ESR parameters below ∼150 K, which implies an extended region of short-range correlations. Based on the results of magnetic and thermodynamic studies in applied fields, we propose a magnetic phase diagram for the new honeycomb-lattice delafossite. © The Royal Society of Chemistry 2016.

In this paper, the post-critical behavior and buckling modes of single-walled carbon nanotubes are analyzed via a Molecular Mechanics model. The main target is to develop a general formulation for the model, which has been simplified under small strains assumption, and to implement a versatile tool for the structural analysis of carbon nanotubes in the framework of geometrical nonlinearity. For this purpose, a mechanical formulation able to reproduce any load configuration and supporting conditions has been derived by using an energy approach. Then, an incremental-iterative solution procedure has been implemented in order to trace several nonlinear equilibrium paths and to obtain the corresponding critical strains of clamped-clamped nanotubes under compressive, flexural and torsional loading distributions. The model shows a good numerical performance and results in agreement with previous atomistic works. Two interatomic potentials have been adopted in order to find out the influence of different constitutive relationships on the final nonlinear response. We have concluded that the choice of the potential function has no significant effect on the final buckling strains. Our results confirm that the final buckling response is strongly determined by geometrical imperfections in the nanotube, which can be well reproduced in the proposed model, but are much more difficult to handle in continuum models. (C) 2015 Published by Elsevier Ltd.

In this paper, the post-critical behavior and buckling modes of single-walled carbon nanotubes are analyzed via a Molecular Mechanics model. The main target is to develop a general formulation for the model, which has been simplified under small strains assumption, and to implement a versatile tool for the structural analysis of carbon nanotubes in the framework of geometrical nonlinearity. For this purpose, a mechanical formulation able to reproduce any load configuration and supporting conditions has been derived by using an energy approach. Then, an incremental-iterative solution procedure has been implemented in order to trace several nonlinear equilibrium paths and to obtain the corresponding critical strains of clamped-clamped nanotubes under compressive, flexural and torsional loading distributions. The model shows a good numerical performance and results in agreement with previous atomistic works. Two interatomic potentials have been adopted in order to find out the influence of different constitutive relationships on the final nonlinear response. We have concluded that the choice of the potential function has no significant effect on the final buckling strains. Our results confirm that the final buckling response is strongly determined by geometrical imperfections in the nanotube, which can be well reproduced in the proposed model, but are much more difficult to handle in continuum models. (C) 2015 Published by Elsevier Ltd.

The Principal Investigators research program in nonlinear wave propagation with emphasis in nonlinear optics is very active and covers a number of research areas. During the period 15 April, 2012 -- 14 April, 2015, fourteen papers were published in refereed journals. In addition, two refereed conference proceeding were published, and twenty one invited lectures were given. The key results and research directions are described in the associated Final Report. Full details can be found in the Principal Investigators research papers which are listed at the end of the Report. Key research investigations and areas studied include the following. A detailed theory describing the dynamics of nonlinear waves in photonic honeycomb lattices both in bulk regions and with boundaries was developed., The original document contains color images.

A 3-chamber in-line olfactometer designed for use with sand flies is described and tested as a high-throughput method to screen honeys for attractiveness to Phlebotomus papatasi (four geographic isolates), P. duboscqi (two geographic isolates), and Lutzomyia longipalpis maintained in colonies at the Walter Reed Army Institute of Research. A diversity of unifloral honey odors were evaluated as a proxy for the natural floral odors that sand flies may use in orientation to floral sugar sources in the field. In the 3-chamber in-line olfactometer, the choice modules come directly off both sides of the release area instead of angling away as in the Y-tube olfactometer. Of the 25 honeys tested, five had a significant attraction for one or more of the sand fly isolates tested. This olfactometer and high-throughput method has utility for evaluating a diversity of natural materials with unknown complex odor blends that can then be down-selected for further evaluation in wind tunnels and/or field scenarios., Pub. in Journal of Vector Ecology, v39 n1, p94-102, 2014. Sponsored in part by Department of the Army.

The objective of the project is to investigate the thermo-mechanical behavior of engineered shape memory polymer (SMP) materials for use as composite reconfigurable skin systems in morphing aircraft applications. An anisotropic, reconfigurable skin based on selective heating of a cellular SMP material was designed and investigated to understand its material characteristics. The engineered skin material is made of a cellular structure filled with a variable stiffness material, such as honeycomb filled with SMP and it was characterized by finite element analysis and MTS testing. The research provides a comprehensive initial feasibility study into the proposed filled honeycomb skin system, and thermal problems such as diffusion between cells, cooling the skin, the power required for operation, and cycle time are topics of further research., Prepared in collaboration with University of Dayton Research Institute, Dayton, OH.

A microfluidic approach to a honeycomb-structure material based on the synergistic effects of polymer rapid precipitation, double emulsion templating, and internal effervescent salt decomposition is reported. The delicate honeycomb structure exhibits unique characteristics with an external nanopore membrane and internal multiple cavities. The biological functionality of the artificial structure is explored to serve as microcarriers for cell culture and drug release, indicating their attractive properties for potential biomedical applications. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A microfluidic approach to a honeycomb-structure material based on the synergistic effects of polymer rapid precipitation, double emulsion templating, and internal effervescent salt decomposition is reported. The delicate honeycomb structure exhibits unique characteristics with an external nanopore membrane and internal multiple cavities. The biological functionality of the artificial structure is explored to serve as microcarriers for cell culture and drug release, indicating their attractive properties for potential biomedical applications. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report on the preparation of functional polymer surfaces with controlled topography by using the breath figures approach. The resulting surfaces prepared from a mixture of a PS-b-PAA diblock copolymer and a homopolymer (PS) exhibit pores that are mainly composed of diblock copolymer whereas the rest of the surface is formed by homopolymer. The formation of a hexagonal assembly of pores was achieved by controlling several parameters during the casting process including relative humidity, composition of the blend and polymer concentration. A selective modification of the pore inner part by using appropriate polypeptide sequences permitted the use of these surfaces as scaffolds for pattern and display of active biomolecules, as ordered templates for specific recognition processes and finally for the micropatterning of bacterial cells.

We design, fabricate and characterize a plasmonic honeycomb lattice absorber with almost perfect absorption at 1140 nm over a wide incident angle range. This absorber also possesses a narrow-band, angle-and polarization-dependent high-order resonance in the short-wavelength range, with a bandwidth of 19 nm and angle sensitivity of 3 nm per degree. The nature of this high-order absorption band is analyzed through finite-element simulations. We believe it is due to Bragg coupling of the incident light to the backward-propagating surface plasmon polariton through the periodic modulation of the structure. Such fine absorption bands can find applications in plasmonic sensors and spectrally selective thermal emitters., QC 20131024

Recent investigations of cyanate ester resins as high temperature resin materials for space and propulsion applications have brought attention to the need for high temperature composite materials with improved stiffness, strength, hot/wet performance and high maximum use temperatures. The addition of nanocomposite filler materials has been shown to provide property improvement to cyanate ester resins, but often only at high loading levels and with improvement in only one property. Graphene, an allotrope of carbon, is the strongest material yet measured and displays exceptionally high thermal conductivity, electrical conductivity and gas impermeability. Since graphene is an atomically thick monolayer of carbon atoms arranged in a honey-comb lattice, its high surface to volume ratio allows property improvements at lower weight fractions than other composite fillers. The morphology, surface chemical functionality and thermal properties of graphene vary depending on the method of isolation from graphite and subsequent chemical and thermal treatments. Two forms of graphene, graphene oxide and thermally reduced graphene oxide, were dispersed in a commercial cyanate ester resin. The methods of graphene synthesis, isolation and incorporation of graphene into cyanate resin networks will be presented, as will preliminary property investigations of graphene-polycyanurate composites., The original document contains color images. Presented at the 2013 International SAMPE Meeting held in Long Beach, CA on 6-9 May 2013.

The adhesion of bacteria to medical implants forming biofilms might lead to healthcare-associated infections. Initial bacterial adhesion is mediated by material surface properties. Therefore, control of bacterial adhesion to material surfaces is important for reducing infection. Numerous researches have been devoted to the chemical and physical modification of biomaterial surfaces to control initial bacterial adhesion. However, the successful design of biomaterials for the treatment of infections remains a challenge. Surface topographic patterns of micro- or nano-scale have been effective to manipulate behavior of different types of cells. Previously, the bacterial behavior on the micro-pillar patterned surfaces has been studied in our group and confirmed that the micro-pillar pattern do have effects on the bacterial behavior. Now in this study we further fabricated a honeycomb pattern which provided a reduced continuous surface area compared with micro-pillar pattern. The honeycomb patterns on silicon substrate with characteristic dimensions varied from 0.5 μm to 10 μm were fabricated. Two typical bacteria with distinctive shapes (E.coli and S.aureus) were used as study models. After culturing the samples with bacteria, the effects of honeycomb patterns on the bacterial adhesion, growth, proliferation and viability were investigated. Experimental results show that the honeycomb topography with specific feature size around 1 μm can significantly reduce bacterial adhesion. Furthermore, the honeycomb patterns can inhibit bacterial growth and change the direction of growth when the bacterial is confined into a well. These influences may result from the physical confinement effect on bacteria. By comparing Sample_UP vs. Sample_DOWN, the adherent bacterial is much less on Sample_DOWN, but the trends of bacterial adhesion are the same and irrespective of the gravity of bacteria. In comparison with bacterial responses to pillar patterns, we found that topographic patterns

A microfluidic approach to a honeycomb-structure material based on the synergistic effects of polymer rapid precipitation, double emulsion templating, and internal effervescent salt decomposition is reported. The delicate honeycomb structure exhibits unique characteristics with an external nanopore membrane and internal multiple cavities. The biological functionality of the artificial structure is explored to serve as microcarriers for cell culture and drug release, indicating their attractive properties for potential biomedical applications. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

It is estimated that over 5,000 adhesively bonded repairs (ABRs) have been applied to the Royal Australian Air Force (RAAF) F-111 aircraft over the last twenty five years, mainly to honeycomb sandwich panels. Retirement of the fleet in December 2010 presented a unique opportunity to evaluate the integrity of a large number of airworthy ABRs. Consequently, DSTO in partnership with the RAAF, through ASI at DGTA and with the assistance of Boeing Australia developed a program to assess the condition of the F-111 ABRs. The F-111 Adhesive Bonded Repair Assessment Program (FABRAP) was established in mid 2010 and initial field testing was carried out from October 2010. The current report provides an update on the analysis of the results from the field level testing undertaken between October 2010 and May 2011 on repairs to honeycomb structure which used FM300 adhesive and RAAF approved surface treatments and application procedures.

The density of currently produced polyacrylonitrile based carbon fibers is around 1.8 g/cm3. It will be of great benefit to reduce this density so that the high-performance structures made from such fibers can be lighter than those made from the solid carbon fibers. With the goal to produce high-strength and high-modulus carbon fibers with densities in the range of 0.9-1.3 g/cm3, polyacrylonitrile (PAN) based precursor fibers were produced with a honeycomb structure. Using dry jet wet spinning method, honeycomb precursor fibers were manufactured that consisted of PAN as the sea component and poly(methyl methacrylate) as the islands component. Subsequently, the precursor fibers were stabilized and carbonized to produce hollow carbon fibers. Resulting carbon fibers possessed the estimated density in the range of 1.1 to 1.2 g/cm3 with tensile modulus in number of trials in the range of 300 to 368 GPa. By comparison, modulus of IM7 fiber with a density of about 1.78 g/cm3 is 276 GPa. Thus the specific modulus of the hollow carbon fiber can be more than 50% higher than that of state of the art PAN based carbon fiber such as IM7. In addition, a number of other studies on structure, processing, and properties of polymer/CNT composite films and fibers were also conducted. Results of these studies are well documented in the many archival publications and two completed Ph.D. theses. These publications and thesis are listed below. Amongst the key additional findings include nanocomposite fibers with thermal conductivity in the range of 2 15 W/m/k. Details of the unpublished work of the honey-comb fiber are included with this report., The original document contains color images.

The objective of this project was to determine whether drag caused by turbulence in boundary layer flow can be reduced through the use of modified surfaces. This study encompassed the testing of four different surfaces: 1) Teflon SLIP, 2) Aluminum SLIP, 3) Honeycomb Superhydrophobic and 4) Polydimethylsiloxane elastomer (PDMSe) Superhydrophobic. Each of these surfaces uses specific geometrical surface features to modify the original water-surface interface. Due to the influence of the Green Fleet Initiative and the Navy's goal to increase the fleet efficiency, the Office of Naval Research is interested in determining the effectiveness of these surfaces in boundary layer flow under operating conditions similar to those in which Navy ships operate. The goal of this study was to provide data and analysis detailing the effect of these surfaces on boundary layer turbulence and drag reduction. The performance of each surface was compared with that of a smooth wall under similar operating conditions to characterize the effectiveness of each modified surface., The original document contains color images.

Presented at the AFOSR Spring Review 2013, 4-8 March, Arlington, VA.

“© © 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.”, [EN] We report experimental evidence of light guiding at telecommunication wavelengths along line-defect honeycomb-lattice photonic crystal waveguides created in suspended silicon slabs. Numerical results show that the guided bands correspond to modes below the cladding light line so they are inherently lossless, although the measurements show quite high losses owing to fabrication imperfections. Honeycomb photonic crystals are a suitable platform for confining light and sound in nanoscale waveguides. © 1989-2012 IEEE.

“© © 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.”, [EN] We report experimental evidence of light guiding at telecommunication wavelengths along line-defect honeycomb-lattice photonic crystal waveguides created in suspended silicon slabs. Numerical results show that the guided bands correspond to modes below the cladding light line so they are inherently lossless, although the measurements show quite high losses owing to fabrication imperfections. Honeycomb photonic crystals are a suitable platform for confining light and sound in nanoscale waveguides. © 1989-2012 IEEE.

“© © 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.”, [EN] We report experimental evidence of light guiding at telecommunication wavelengths along line-defect honeycomb-lattice photonic crystal waveguides created in suspended silicon slabs. Numerical results show that the guided bands correspond to modes below the cladding light line so they are inherently lossless, although the measurements show quite high losses owing to fabrication imperfections. Honeycomb photonic crystals are a suitable platform for confining light and sound in nanoscale waveguides. © 1989-2012 IEEE.

This project is concerned with a new class of light-weight, hierarchical engineered material systems designed to mitigate effects due to high intensity short duration loads, such as blast. A fundamental research program that combines elements of experiments, analysis and the conception of novel numerical tools to tackle several challenging issues are described. The proposed work will be focused on engineered materials and structures that are exposed to loads of high intensity and short duration. As a result, the design of the material will occur simultaneously with the design of the structure. The overarching issues this research addresses are the lack of fundamental understanding of the response of a structure made of a combination of materials and structural concepts (multi-material structures) at high strain rates. Towards achieving this goal, the static and dynamic response of honeycombs and filled honeycombs ave been studied. The filler material chosen is a elastomer. Several new results have been obtained as shown in the contents of this final report and these results shed new light on the utility of filled honeycombs as efficient energy absorbers under dynamic crush conditions.

Presented at the 2nd Multifunctional Materials for Defense Workshop in conjunction with the 2012 Annual Grantees'/Contractors' Meeting for AFOSR Program on Mechanics of Multifunctional Materials & Microsystems held 30 July - 3 August 2012 in Arlington, VA. Sponsored by AFRL, AFOSR, ARO, NRL, ONR, and ARL. U.S. Government or Federal Rights License See also ADA567141, ADA567143.

Presented at the 2nd Multifunctional Materials for Defense Workshop in conjunction with the 2012 Annual Grantees'/Contractors' Meeting for AFOSR Program on Mechanics of Multifunctional Materials & Microsystems held 30 July - 3 August 2012 in Arlington, VA. Sponsored by AFRL, AFOSR, ARO, NRL, ONR, and ARL. U.S. Government or Federal Rights License See also ADA567141, ADA567142.

Presented at the 2nd Multifunctional Materials for Defense Workshop in conjunction with the 2012 Annual Grantees'/Contractors' Meeting for AFOSR Program on Mechanics of Multifunctional Materials & Microsystems held 30 July - 3 August 2012 in Arlington, VA. Sponsored by AFRL, AFOSR, ARO, NRL, ONR, and ARL. U.S. Government or Federal Rights License See also ADA567142, ADA567143.

Graphene, 10 or fewer atomic layers of carbon atoms, has attracted much attention during recent years due to its unique structure and exceptional physical properties. While there exist a wide range of potential applications, as with many nanomaterials, new synthesis techniques are required that allow for a production of graphene on an industrial scale. In this study, in situ Raman spectroscopy was used to study the formation and doping of graphene during urea-assisted thermal exfoliation of graphite oxide (GO), a promising new synthesis method that can be scaled to industrial levels. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectroscopy were used complementary to Raman spectroscopy to assist with the interpretation of the obtained data. Raman spectroscopy is a powerful characterization tool for the analysis of carbon nanomaterials, such as graphene. While several researchers have reported on the reaction of urea and GO, none of the studies found in literature has provided deeper insights on the evolution of the graphene structure and the simultaneous incorporation of nitrogen into the honeycomb lattice during synthesis. The knowledge gained from this work allows for a better understanding of the graphene production process and provides further evidence for the potential nitrogen-doping of graphene via deposition of urea.

Presented at the 2nd Multifunctional Materials for Defense Workshop in conjunction with the 2012 Annual Grantees'/Contractors' Meeting for AFOSR Program on Mechanics of Multifunctional Materials & Microsystems Held 30 July - 3 August 2012 in Arlington, VA. Sponsored by AFRL, AFOSR, ARO, NRL, ONR, and ARL.

Conical refraction phenomena, i.e., the spreading into a hollow cone of an unpolarized light beam entering a biaxial crystal along its optic axis, are fundamental in classical optics and in mathematical physics [1 4]. Originally predicted by Hamilton in 1837 [3] and experimentally observed by Lloyd [4], these phenomena have been intensively studied in recent years by a large community of theorists and experimentalists [1 8]. The physical origin of the phenomenon is associated with the existence of the legendary diabolical points, which emerge along the axis of intersection of the two shells associated with the wave surface. Around a diabolical point the energy dispersion relation is linear while the direction of the group velocity is not uniquely defined., Published in Physical Review A, v85 p013818-1/013818-6, 2012.