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Dayton, OH, United States

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. Source

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. Source

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. Source

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. Source

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. Source

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