Zherebtsov S.V.,Belgorod State University |
Dyakonov G.S.,Belgorod State University |
Salem A.A.,Air Force Research Lab |
Salem A.A.,Universal Technology Corporation |
And 3 more authors.
Acta Materialia | Year: 2013
Microstructure evolution in commercial-purity titanium during plane-strain multipass rolling to a true thickness strain of 2.66 at 77 and 293 K was quantified. Deformation at both temperatures was accompanied by twinning. At 77 K, twinning was more extensive in terms of the fraction of twinned grains and the duration of the twinning stage. Rolling to a true thickness strain of 2.66 resulted in the formation of a microstructure with a grain/subgrain size of ∼80 nm at 77 K or ∼200 nm at 293 K. The contribution of various mechanisms to the strength of titanium following rolling at 77 and 293 K was analyzed quantitatively. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Minteer S.D.,University of Utah |
Atanassov P.,University of New Mexico |
Luckarift H.R.,Universal Technology Corporation |
Luckarift H.R.,Air Force Research Lab |
Johnson G.R.,Air Force Research Lab
Materials Today | Year: 2012
Major improvements in biological fuel cells over the last ten years have been the result of the development and application of new materials. These new materials include: nanomaterials, such as nanotubes and graphene, that improve the electron transfer between the biocatalyst and electrode surface; materials that provide improved stability and immobilization of biocatalysts; materials that increase the conductivity and surface area of the electrodes; and materials that aid facile mass transport. With a focus on enzymatic biological fuel cell technology, this brief review gives an overview of the latest developments in each of these material science areas and describes how this progress has improved the performance of biological fuel cells to yield a feasible technology. © 2012 Elsevier Ltd.
OHara P.J.,Universal Technology Corporation |
Hollkamp J.J.,Air Force Research Lab
Journal of Sound and Vibration | Year: 2014
This paper investigates a coupled computational analysis framework that uses reduced-order models and the generalized finite element method to model vibratory induced stress near local defects. The application area of interest is the life prediction of thin gauge structural components exhibiting nonlinear, path-dependent dynamic response. Full-order finite element models of these structural components can require prohibitively large amounts of processor time. Recent developments in nonlinear reduced-order models have demonstrated efficient computation of the dynamic response. These models are relatively insensitive to small imperfections. Conversely, the generalized finite element method provides the ability to model local defects without geometric dependency on the mesh. A more robust version of the method, with numerically built enrichment functions, provides a multiple-scale modeling capability through direct coupling of global and local finite element models. Replacing the component finite element model with a reduced-order model allows for efficient computation of dynamic response while providing the necessary information to drive local, solid analyses which can zoom in on regions containing stress risers or cracks. This paper describes the coupling of these approaches to enable fatigue and crack propagation predictions. Numerical/experimental examples are provided. © 2014 Elsevier Ltd.
Bazzan G.,Air Force Research Lab |
Deneault J.R.,Universal Technology Corporation |
Kang T.-S.,Universal Technology Corporation |
Taylor B.E.,Universal Technology Corporation |
Durstock M.F.,Air Force Research Lab
Advanced Functional Materials | Year: 2011
A critical component in the development of highly efficient dye-sensitized solar cells is the interface between the ruthenium bipyridyl complex dye and the surface of the mesoporous titanium dioxide film. In spite of many studies aimed at examining the detailed anchoring mechanism of the dye on the titania surface, there is as yet no commonly accepted understanding. Furthermore, it is generally believed that a single monolayer of strongly attached molecules is required in order to maximize the efficiency of electron injection into the semiconductor. In this study, the amount of adsorbed dye on the mesoporous film is maximised, which in turn increases the light absorption and decreases carrier recombination, resulting in improved device performance. A process that increases the surface concentration of the dye molecules adsorbed on the TiO 2 surface by up to 20% is developed. This process is based on partial desorption of the dye after the initial adsorption, followed by readsorption. This desorption/adsorption cycling process can be repeated multiple times and yields a continual increase in dye uptake, up to a saturation limit. The effect on device performance is directly related and a 23% increase in power conversion efficiency is observed. Surface enhanced Raman spectroscopy, infrared spectroscopy, and electrochemical impedance analysis were used to elucidate the fundamental mechanisms behind this observation. The surface concentration of N719 dye molecules on mesoporous TiO 2 films is increased by up to 20% using an adsorption/desorption cycling process. After the initial adsorption of dye, a partial desorption is accomplished by immersing the sample in water. Cycling this process results in a continual overall increase in dye uptake. Ultimately, a 23% increase in dye-sensitized solar cell performance is observed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Varshney V.,Air Force Research Lab |
Varshney V.,Universal Technology Corporation |
Patnaik S.S.,Air Force Research Lab |
Roy A.K.,Air Force Research Lab |
And 2 more authors.
ACS Nano | Year: 2010
Carbon nanotubes (CNT) and graphene are considered as potential future candidates for many nano/microscale integrated devices due to their superior thermal properties. Both systems, however, exhibit significant anisotropy in their thermal conduction, limiting their performance as three-dimensional thermal transport materials. From thermal management perspective, one way to tailor this anisotropy is to consider designing alternative carbon-based architectures. This paper investigates the thermal transport in one such novel architectureOa pillared-graphene (PG) network nanostructure which combines graphene sheets and carbon nanotubes to create a three-dimensional network. Nonequilibrium molecular dynamics simulations have been carried out using the AIREBO potential to calculate the thermal conductivity of pillared-graphene structures along parallel (in-plane) as well as perpendicular (out-of-plane) directions with respect to the graphene plane. The resulting thermal conductivity values for PG systems are discussed and compared with simulated values for pure CNT and graphite. Our results show that in these PG structures, the thermal transport is governed by the minimum interpillar distance and the CNT-pillar length. This is primarily attributed to scattering of phonons occurring at the CNT-graphene junctions in these nanostructures. We foresee that such architecture could potentially be used as a template for designing future structurally stable microscale systems with tailorable in-plane and out-ofplane thermal transport. © 2010 American Chemical Society.
Betancor L.,ORT Uruguay University |
Johnson G.R.,Air Force Research Lab |
Luckarift H.R.,Air Force Research Lab |
Luckarift H.R.,Universal Technology Corporation
ChemCatChem | Year: 2013
Typically, the use of heterogeneous enzyme catalysis is aimed at sustainability, reusability, or enhanced functionality of the biocatalyst and is achieved by immobilizing enzymes onto a support matrix or at a defined interface. Controlled enzyme immobilization is particularly important in bioelectrocatalysis because the catalyst must be effectively connected to a transducer to exploit its activity. This Review discusses what must be addressed for coupling biocatalysts to an electrode and the toolbox of methods that are available for achieving this outcome. As an illustration, we focus on the immobilization and stabilization of laccases at electronic interfaces. Historically, laccases have been used for the decolorization of dyes and for the synthesis of bio-organic compounds; however, more recently, they have been applied to the fields of sensing and energy harvesting.1-3 There is an ever-increasing focus on the development of new energy technologies, in which laccases find application (e.g., as cathodic catalysts in enzymatic fuel cells). Herein, we discuss the heterogeneous laccase biocatalysts that have been reported over the past 10-15years and discuss why laccases continue to be biotechnologically relevant enzymes. Various methods for the immobilization of laccases are described, including the use of nanoscale supports and a range of encapsulation and cross-linking chemistries. We consider the application of immobilized laccases to the food industry, in the synthesis of pharmaceuticals, and in environmental applications, specifically in cases in which stabilization through heterogenization of the enzyme is critical to the application. We also include a consideration of electrochemical biosensors and the specific incorporation of laccases on the surfaces of transducers. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Haag J.M.,Air Force Research Lab |
Haag J.M.,Universal Technology Corporation |
Pattanaik G.,Air Force Research Lab |
Durstock M.F.,Air Force Research Lab
Advanced Materials | Year: 2013
By initially depositing a sub-10 nm-thick SnO2 film, the microstructural evolution that is often considered problematic can be utilized to form Sn nanoparticles on the surface of a 3D current collector for enhanced cycling stability. The work described here highlights a novel approach for the uniform deposition of Sn nanoparticles, which can be used to design electrodes with high capacities and high-rate capabilities. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Caton M.J.,Air Force Research Lab |
Jha S.K.,Universal Technology Corporation
International Journal of Fatigue | Year: 2010
A study of the long and small fatigue crack growth behavior in IN100 tested at 650 °C both with and without dwell periods is summarized. A significant small crack effect is evident in this alloy, and it is observed that the influence of loading variables on small crack behavior is profoundly different from that on long cracks. While a 6 s dwell has negligible effect on long crack growth rates, it results in more than an order of magnitude faster growth for small cracks (∼30 μm to 1 mm). Long crack growth is dominated by intergranular cracking both with and without 6 s dwell. Small crack growth mode depends on numerous factors including crack size, dwell time, exposure to environment, and character of initiation site. Transitions in small crack growth modes and the operative crack growth mechanisms are discussed. © 2010 Elsevier Ltd. All rights reserved.
Culler A.J.,U.S. Air force |
Culler A.J.,Universal Technology Corporation |
McNamara J.J.,Ohio State University
AIAA Journal | Year: 2011
The goal of the United States Air Force to field durable platforms capable of sustained hypersonic flight and responsive access to space depends on the ability to predict the response and the life of structures under combined aerothermal and aeropressure loading. However, current predictive capabilities are limited for these conditions due in part to the inability to seamlessly address fluid-thermal-structural interactions. This study aims to quantify the significance of a frequently neglected interaction, namely: the mutual coupling of structural deformation and aerodynamic heating, on response prediction. The quasi-static response of a carbon-carbon skin panel is investigated. It is found that the significance of this coupling depends largely on the in-plane boundary conditions, since increasing resistance to thermal expansion results in buckling and increasing deflections into the flow. Including these deformations in aerodynamic heating results in (1%) increase in peak temperature and (100%) increase in surface ply failure index for deflections (1%) of panel length. In these cases, the locations of peak temperatures and stresses are significantly altered. Finally, neglecting deformations in the aeroheating analysis results in the prediction of snap-through for a gradual heating trajectory, whereas, inclusion leads to a higher mode dominated, dynamically stable response. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Stange B.,Universal Technology Corporation
Joint Conference: MFPT 2015 and ISA's 61st International Instrumentation Symposium - Technology Evolution: Sensors to Systems for Failure Prevention | Year: 2015
PIWG and EVI-GTI have both enabled numerous advances in Instrumentation Technology for Turbine Engines PIWG/ISA Standard Committee participation is open to anyone willing to contribute.